U.S. patent application number 13/339814 was filed with the patent office on 2012-04-26 for regioselectively substituted cellulose esters produced in a carboxylated ionic liquid process and products produced therefrom.
This patent application is currently assigned to EASTMAN CHEMICAL COMPANY. Invention is credited to Charles Michael Buchanan, Norma Lindsey Buchanan, Michael Eugene Donelson, Maryna Grigorievna Gorbunova, Robert Thomas Hembre, Thauming Kuo, Juanelle Little Lambert, Bin Wang.
Application Number | 20120101269 13/339814 |
Document ID | / |
Family ID | 41059941 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120101269 |
Kind Code |
A1 |
Buchanan; Charles Michael ;
et al. |
April 26, 2012 |
REGIOSELECTIVELY SUBSTITUTED CELLULOSE ESTERS PRODUCED IN A
CARBOXYLATED IONIC LIQUID PROCESS AND PRODUCTS PRODUCED
THEREFROM
Abstract
This invention relates to novel compositions comprising
regioselectively substituted cellulose esters. One aspect of the
invention relates to processes for preparing regioselectively
substituted cellulose esters from cellulose dissolved in ionic
liquids. Another aspect of the invention relates to the utility of
regioselectively substituted cellulose esters in applications such
as protective and compensation films for liquid crystalline
displays.
Inventors: |
Buchanan; Charles Michael;
(Bluff City, TN) ; Buchanan; Norma Lindsey; (Bluff
City, TN) ; Hembre; Robert Thomas; (Johnson City,
TN) ; Lambert; Juanelle Little; (Gray, TN) ;
Donelson; Michael Eugene; (Kingsport, TN) ;
Gorbunova; Maryna Grigorievna; (Kingsport, TN) ; Kuo;
Thauming; (Kingsport, TN) ; Wang; Bin;
(Kingsport, TN) |
Assignee: |
EASTMAN CHEMICAL COMPANY
Kingsport
TN
|
Family ID: |
41059941 |
Appl. No.: |
13/339814 |
Filed: |
December 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12539800 |
Aug 12, 2009 |
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13339814 |
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12030387 |
Feb 13, 2008 |
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12539800 |
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60901615 |
Feb 14, 2007 |
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Current U.S.
Class: |
536/65 ; 536/67;
536/68; 536/76 |
Current CPC
Class: |
C08J 2301/14 20130101;
G02B 1/105 20130101; C08B 3/16 20130101; G02B 5/3083 20130101; C08J
5/18 20130101; G02B 1/14 20150115; C08B 3/28 20130101; C08B 1/003
20130101; C07D 233/54 20130101; C08B 3/06 20130101 |
Class at
Publication: |
536/65 ; 536/76;
536/68; 536/67 |
International
Class: |
C08B 3/06 20060101
C08B003/06; C08B 3/04 20060101 C08B003/04; C08B 3/16 20060101
C08B003/16; C08B 3/08 20060101 C08B003/08 |
Claims
1. A process of making a regioselectively substituted cellulose
ester said process comprising: (a) dissolving cellulose in a
carboxylated ionic liquid to thereby form a cellulose solution; (b)
contacting said cellulose solution with at least two acylating
reagents to thereby provide an acylated cellulose solution
comprising a cellulose ester, wherein said cellulose ester
comprises at least one acyl group donated by said carboxylated
ionic liquid; wherein said acylating reagents are contacted
consecutively in stages with said cellulose solution; (c)
contacting said acylated cellulose solution with a non-solvent to
cause at least a portion of said cellulose ester to precipitate and
thereby provide a slurry comprising precipitated cellulose ester
and said carboxylated ionic liquid; (d) separating at least a
portion of said precipitated cellulose ester from said carboxylated
ionic liquid to thereby provide said regioselectively substituted
cellulose ester and a separated carboxylated ionic liquid; and (e)
optionally, recycling at least a portion of said separated
carboxylated ionic liquid for use in dissolving additional
cellulose.
2. A process according to claim 1 wherein about 80 mole percent of
a first acylating reagent is allowed to react prior to adding the
next acylating agent.
3. A process of making a regioselectively substituted cellulose
ester said process comprising: (a) dissolving cellulose in a
carboxylated ionic liquid to thereby form a cellulose solution; (b)
contacting said cellulose solution with at least two acylating
reagents to thereby provide an acylated cellulose solution
comprising a cellulose ester, wherein said cellulose ester
comprises at least one acyl group donated by said carboxylated
ionic liquid; wherein said acylating reagents are added
simultaneously to said cellulose solution; (c) contacting said
acylated cellulose solution with a non-solvent to cause at least a
portion of said cellulose ester to precipitate and thereby provide
a slurry comprising precipitated cellulose ester and said
carboxylated ionic liquid; (d) separating at least a portion of
said precipitated cellulose ester from said carboxylated ionic
liquid to thereby provide said regioselectively substituted
cellulose ester and a separated carboxylated ionic liquid; and (e)
optionally, recycling at least a portion of said separated
carboxylated ionic liquid for use in dissolving additional
cellulose.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
Non-Provisional application Ser. No. 12/539,800 filed on Aug. 12,
2009, which is a continuation in part application which claims
priority to U.S. Non-Provisional application Ser. No. 12/030,387,
filed Feb. 13, 2008, which claims priority to U.S. Provisional
Application Ser. No. 60/901,615; it also claims priority to U.S.
Provisional Application 61/088,423 filed Aug. 13, 2008, the
disclosures of which are herein incorporated by reference in their
entirety to the extent they do not contradict the statements
herein.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates generally to cellulose esters
and/or ionic liquids. One aspect of the invention concerns
processes for producing cellulose esters in ionic liquids.
[0004] 2. Description of the Related Art
[0005] Cellulose is a .beta.-1,4-linked polymer of anhydroglucose.
Cellulose is typically a high molecular weight, polydisperse
polymer that is insoluble in water and virtually all common organic
solvents. The use of unmodified cellulose in wood or cotton
products, such as in the housing or fabric industries, is well
known. Unmodified cellulose is also utilized in a variety of other
applications usually as a film (e.g., cellophane), as a fiber
(e.g., viscose rayon), or as a powder (e.g., microcrystalline
cellulose) used in pharmaceutical applications. Modified cellulose,
including cellulose esters, are also utilized in a wide variety of
commercial applications. Cellulose esters can generally be prepared
by first converting cellulose to a cellulose triester, then
hydrolyzing the cellulose triester in an acidic aqueous media to
the desired degree of substitution ("DS"), which is the average
number of ester substituents per anhydroglucose monomer. Hydrolysis
of cellulose triesters containing a single type of acyl substituent
under these conditions can yield a random copolymer that can
consist of up to 8 different monomers depending upon the final
DS.
[0006] Ionic liquids ("ILs") are liquids containing substantially
only anions and cations. Room temperature ionic liquids ("RTILs")
are ionic liquids that are in liquid form at standard temperature
and pressure. The cations associated with ILs are structurally
diverse, but generally contain one or more nitrogens that are part
of a ring structure and can be converted to a quaternary ammonium.
Examples of these cations include pyridinum, pyridazinium,
pyrimidinium, pyrazinium, imidazolium, pyrazolium, oxazolium,
triazolium, thiazolium, piperidinium, pyrrolidinium, quinolinium,
and isoquinolinium. The anions associated with ILs can also be
structurally diverse and can have a significant impact on the
solubility of the ILs in different media. For example, ILs
containing hydrophobic anions such as hexafluorophosphates or
triflimides have very low solubilities in water while ILs
containing hydrophilic anions such chloride or acetate are
completely miscible in water.
[0007] The names of ionic liquids can generally be abbreviated.
Alkyl cations are often named by the letters of the alkyl
substituents and the cation, which are given within a set of
brackets, followed by the abbreviation for the anion. Although not
expressively written, it should be understood that the cation has a
positive charge and the anion has a negative charge. For example,
[BMIm]OAc indicates 1-butyl-3-methylimidazolium acetate, [AMIm]Cl
indicates 1-allyl-3-methylimidazolium chloride, and [EMIm]OF
indicates 1-ethyl-3-methylimidazolium formate.
[0008] Ionic liquids can be costly; thus, their use as solvents in
many processes may not be feasible. Despite this, methods and
apparatus for reforming and/or recycling ionic liquids have
heretofore been insufficient. Furthermore, many processes for
producing ionic liquids involve the use of halide and/or sulfur
intermediates, or the use of metal oxide catalysts. Such processes
can produce ionic liquids having high levels of residual metals,
sulfur, and/or halides.
SUMMARY OF THE INVENTION
[0009] In one embodiment of the invention, a regioselectively
substituted cellulose ester is provided having a C.sub.6/C.sub.3
relative degree of substitution (RDS) ratio greater than one or a
C.sub.6/C.sub.2 RDS ratio greater than 1.
[0010] In another embodiment of the invention, a regioselectively
substituted cellulose ester is provided wherein the RDS is
C.sub.6>C.sub.2>C.sub.3.
[0011] In another embodiment of the invention, a process for making
a regioselectively substituted cellulose ester is provided. The
process comprises: [0012] (a) dissolving cellulose in a
carboxylated ionic liquid to thereby form a cellulose solution;
[0013] (b) contacting the cellulose solution with at least two
acylating reagents to thereby provide an acylated cellulose
solution comprising a cellulose ester, wherein the cellulose ester
comprises at least one acyl group donated by the carboxylated ionic
liquid; wherein the acylating reagents are contacted consecutively
in stages with the cellulose solution; [0014] (c) contacting the
acylated cellulose solution with a non-solvent to cause at least a
portion of the cellulose ester to precipitate and thereby provide a
slurry comprising precipitated cellulose ester and the carboxylated
ionic liquid; [0015] (d) separating at least a portion of the
precipitated cellulose ester from the carboxylated ionic liquid to
thereby provide a recovered cellulose ester and a separated
carboxylated ionic liquid; and [0016] (e) optionally, recycling at
least a portion of the separated carboxylated ionic liquid for use
in dissolving additional cellulose.
[0017] In another embodiment of the invention, a process of making
a regioselectively substituted cellulose ester is provided. The
process comprises: [0018] (a) dissolving cellulose in a
carboxylated ionic liquid to thereby form a cellulose solution;
[0019] (b) contacting the cellulose solution with at least two
acylating reagents to thereby provide an acylated cellulose
solution comprising a cellulose ester, wherein the cellulose ester
comprises at least one acyl group donated by the carboxylated ionic
liquid; wherein the acylating reagents are added simultaneously to
cellulose solution; [0020] (c) contacting the acylated cellulose
solution with a non-solvent to cause at least a portion of the
cellulose ester to precipitate and thereby provide a slurry
comprising precipitated cellulose ester and the carboxylated ionic
liquid; [0021] (d) separating at least a portion of the
precipitated cellulose ester from the carboxylated ionic liquid to
thereby provide a recovered cellulose ester and a separated
carboxylated ionic liquid; and [0022] (e) optionally, recycling at
least a portion of the separated carboxylated ionic liquid for use
in dissolving additional cellulose.
[0023] In another embodiment of the invention, photographic film,
protective film, or compensation film is provided.
[0024] In yet another embodiment of the invention, a compensation
film is provided comprising at least one regioselectively
substituted cellulose ester wherein the compensation film has an
R.sub.th range from about -400 to about +100 nm.
[0025] In yet another embodiment, articles are provided comprising
the regioselectively substituted cellulose ester, such articles
include, but are not limited to, thermoplastic molded products,
coatings, personal care products, and drug delivery products.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a simplified diagram depicting the majors steps
involved in a process for producing cellulose esters in ionic
liquids;
[0027] FIG. 2 is a more detailed diagram of a process for producing
cellulose esters, depicting a number of additional/optional steps
for enhancing to overall efficacy and/or efficiency of the
process;
[0028] FIG. 3 is a plot of absorbance versus time showing the
dissolution of 5 weight percent cellulose in
1-butyl-3-methylimidazolium chloride;
[0029] FIG. 4 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
chloride with 5 molar equivalents of acetic anhydride;
[0030] FIG. 5 is a plot of absorbance versus time showing the
dissolution of 5 weight percent cellulose in
1-butyl-3-methylimidazolium chloride;
[0031] FIG. 6 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
chloride with 3 molar equivalents of acetic anhydride at 80.degree.
C.;
[0032] FIG. 7 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
chloride with 3 molar equivalents of acetic anhydride and 0.2 molar
equivalents of methane sulfonic acid at 80.degree. C.;
[0033] FIG. 8 is a plot of absorbance versus time showing the
dissolution of 5 weight percent cellulose in
1-butyl-3-methylimidazolium chloride;
[0034] FIG. 9 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
chloride with 3 molar equivalents of acetic anhydride and 0.2 molar
equivalents of methane sulfonic acid at 80.degree. C.;
[0035] FIG. 10 is a plot of absorbance versus time showing the
dissolution of 10 weight percent cellulose in
1-butyl-3-methylimidazolium chloride;
[0036] FIG. 11 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
chloride with 3 molar equivalents of acetic anhydride and 0.2 molar
equivalents of methane sulfonic acid at 80.degree. C.;
[0037] FIG. 12 is a plot of absorbance versus time showing the
dissolution of 15 weight percent cellulose in
1-butyl-3-methylimidazolium chloride;
[0038] FIG. 13 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
chloride with 3 molar equivalents of acetic anhydride and 0.2 molar
equivalents of methane sulfonic acid at 100.degree. C.;
[0039] FIG. 14 is a plot of absorbance versus time showing the
dissolution of 15 weight percent cellulose in
1-butyl-3-methylimidazolium chloride;
[0040] FIG. 15 is an NMR spectra showing the proton NMR spectra of
a cellulose acetate prepared by direct acetylation;
[0041] FIG. 16 is plot of weight percent acetic acid versus time as
determined by infrared spectroscopy;
[0042] FIG. 17 is a plot of absorbance versus time showing the
removal of water from 1-butyl-3-methylimidazolium acetate prior to
dissolution of cellulose;
[0043] FIG. 18 is a plot of absorbance versus time showing the
dissolution of 10 weight percent cellulose in
1-butyl-3-methylimidazolium acetate at room temperature;
[0044] FIG. 19 is a plot of absorbance versus time showing the
acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium
acetate with 5 molar equivalents of acetic anhydride and 0.1 molar
equivalents of zinc acetate;
[0045] FIG. 20 is a spectral analysis showing infrared spectra of
1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium
acetate, a spectrum after 0.5 molar equivalents of acetic anhydride
has been added to the 1-butyl-3-methylimidazolium formate, and a
spectrum after another 0.5 molar equivalents of acetic anhydride
has been added to the 1-butyl-3-methylimidazolium formate;
[0046] FIG. 21 is a plot of relative concentration versus time for
1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium
acetate upon first and second additions of 0.5 molar equivalents of
acetic anhydride;
[0047] FIG. 22 is spectral analysis showing infrared spectra of
1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium
formate, and a spectrum after 1 equivalent of acetic anhydride has
been added to the 1-butyl-3-methylimidazolium formate in the
presence of 2 molar equivalents of methanol;
[0048] FIG. 23 is a plot of relative concentration versus time for
1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium
acetate upon addition of 2 molar equivalents of methanol and then
upon addition of 1 equivalent of acetic anhydride;
[0049] FIG. 24 is a plot of absorbance versus time showing the
dissolution of cellulose in 1-butyl-3-methylimidazolium acetate at
80.degree. C.;
[0050] FIG. 25 is a plot of absorbance versus time showing the
esterification of cellulose dissolved in
1-butyl-3-methylimidazolium acetate;
[0051] FIG. 26 is a spectral analysis showing the ring proton
resonances for cellulose acetates prepared from cellulose dissolved
in 1-butyl-3-methylimidazolium acetate (top spectrum), and the ring
proton resonances for cellulose acetates prepared from cellulose
dissolved in 1-butyl-3-methylimidazolium chloride (bottom
spectrum); and
[0052] FIG. 27 is a spectral analysis showing the ring proton
resonances for cellulose acetates prepared from cellulose dissolved
in 1-butyl-3-methylimidazolium acetate after water addition (top
spectrum) and before water addition (bottom spectrum).
[0053] FIG. 28 compares the viscosities of solutions of cellulose
(5 wt %) dissolved in [BMIm]Cl, [BMIm]Cl+5 wt % acetic acid, and
[BMIm]Cl+10 wt % acetic acid.
[0054] FIG. 29 compares the viscosities of solutions of cellulose
contact mixtures without a cosolvent and with methyl ethyl ketone
as a cosolvent.
[0055] FIG. 30 shows a plot of absorbance for an infrared band at
1212 cm.sup.-1 (propionate ester and propionic acid) versus contact
time during esterification (3.7 eq propionic anhydride) of
cellulose dissolved either in [BMIm]OPr or [BMIm]OPr+11.9 wt %
propionic acid.
[0056] FIG. 31 shows a plot of absorbance versus time for a staged
addition of Pr.sub.2O (1.sup.st) and Ac.sub.2O (2.sup.nd)
illustrating the esterification cellulose (1756, 1233, 1212
cm.sup.-1), the consumption of anhydride (1815 cm.sup.-1), and the
coproduction of carboxylic acid (1706 cm.sup.-1) during the
experiment.
[0057] FIG. 32 shows the proton NMR spectra for the samples removed
during the contact period following the staged addition of
Pr.sub.2O (1.sup.st) and Ac.sub.2O (2.sup.nd).
[0058] FIG. 33 shows the carbonyl region in the .sup.13C NMR
spectra of a sample following the staged addition of Pr.sub.2O
(1.sup.st) and Ac.sub.2O (2.sup.nd) [series 1], following the
staged addition of Ac.sub.2O (1.sup.st) and Pr.sub.2O (2.sup.nd)
[series 2], and following the mixed addition of Pr.sub.2O and
Ac.sub.2O [series 3].
[0059] FIG. 34 shows a plot of DS versus glass transition
temperature (Tg) for the cellulose acetate propionates prepared by
staged addition of Pr.sub.2O (1.sup.st) and Ac.sub.2O (2.sup.nd)
[series 1], by staged addition of Ac.sub.2O (1.sup.st) and
Pr.sub.2O (2.sup.nd) [series 2], and by mixed addition of Pr.sub.2O
and Ac.sub.2O [series 3].
[0060] FIG. 35 shows a plot of DS propionate versus glass
transition temperature (Tg) for the cellulose acetate propionates
prepared by staged addition of Pr.sub.2O (1.sup.st) and Ac.sub.2O
(2.sup.nd) [series 1], by staged addition of Ac.sub.2O (1.sup.st)
and Pr.sub.2O (2.sup.nd) [series 2], and by mixed addition of
Pr.sub.2O and Ac.sub.2O [series 3].
DETAILED DESCRIPTION
[0061] FIG. 1 depicts a simplified system for producing cellulose
esters. The system of FIG. 1 generally includes a dissolution zone
20, an esterification zone 40, a cellulose ester recovery/treatment
zone 50, and an ionic liquid recovery/treatment zone 60.
[0062] As shown in FIG. 1, cellulose and an ionic liquid ("IL") can
be fed to dissolution zone 20 via lines 62 and 64, respectively. In
dissolution zone 20, the cellulose can be dissolved to form an
initial cellulose solution comprising the cellulose and the ionic
liquid. The initial cellulose solution can then be transported to
esterification zone 40. In esterification zone 40, a reaction
medium comprising the dissolved cellulose can be subjected to
reaction conditions sufficient to at least partially esterify the
cellulose, thereby producing an initial cellulose ester. An
acylating reagent can be added to esterification zone 40 and/or
dissolution zone 20 to help facilitate esterification of the
dissolved cellulose in esterification zone 40.
[0063] As illustrated in FIG. 1, an esterified medium can be
withdrawn from esterification zone 40 via line 80 and thereafter
transported to cellulose ester recovery/treatment zone 50 where the
initial cellulose ester can be recovered and treated to thereby
produce a final cellulose ester that exits recovery/treatment zone
50 via line 90. A recycle stream is produced from cellulose ester
recovery/treatment zone 50 via line 86. This recycle stream can
comprise an altered ionic liquid derived from the ionic liquid
originally introduced into dissolution zone 20. The recycle stream
in line 86 can also include various other compounds including
byproducts of reactions occurring in upstream zones 20,40,50 or
additives employed in upstream zones 20,40,50. The recycle stream
in line 86 can be introduced into ionic liquid recovery/treatment
zone 60 where it can be subjected to separation and/or reformation
processes. A recycled ionic liquid can be produced from ionic
liquid recovery/treatment zone 60 and can be routed back to
dissolution zone 20 via line 70. Additional details of the streams,
reactions, and steps involved in the cellulose ester production
system of FIG. 1 are provided immediately below.
[0064] The cellulose fed to dissolution zone 20 via line 62 can be
any cellulose known in the art that is suitable for use in the
production of cellulose esters. In one embodiment, the cellulose
suitable for use in the present invention can be obtained from soft
or hard woods in the form of wood pulps, or from annual plants such
as cotton or corn. The cellulose can be a .beta.-1,4-linked polymer
comprising a plurality of anhydroglucose monomer units. The
cellulose suitable for use in the present invention can generally
comprise the following structure:
##STR00001##
Additionally, the cellulose employed in the present invention can
have an .alpha.-cellulose content of at least about 90 percent by
weight, at least about 95 percent by weight, or at least 98 percent
by weight.
[0065] The cellulose fed to dissolution zone 20 via line 62 can
have a degree of polymerization ("DP") of at least about 10, at
least about 250, at least about 1,000, or at least 5,000. As used
herein, the term "degree of polymerization," when referring to
cellulose and/or cellulose esters, shall denote the average number
of anhydroglucose monomer units per cellulose polymer chain.
Furthermore, the cellulose can have a weight average molecular
weight in the range of from about 1,500 to about 850,000, in the
range of from about 40,000 to about 200,000, or in the range of
from 55,000 to about 160,000. Additionally, the cellulose suitable
for use in the present invention can be in the form of a sheet, a
hammer milled sheet, fiber, or powder. In one embodiment, the
cellulose can be a powder having an average particle size of less
than about 500 micrometers (".mu.m"), less than about 400 .mu.m, or
less than 300 .mu.m.
[0066] The ionic liquid fed to dissolution zone 20 via line 64 can
be any ionic liquid capable of at least partially dissolving
cellulose. As used herein, the term "ionic liquid" shall denote any
substance containing substantially only ions, and which has a
melting point at a temperature of 200.degree. C. or less. In one
embodiment, the ionic liquid suitable for use in the present
invention can be a cellulose dissolving ionic liquid. As used
herein, the term "cellulose dissolving ionic liquid" shall denote
any ionic liquid capable of dissolving cellulose in an amount
sufficient to create an at least 0.1 weight percent cellulose
solution. In one embodiment, the ionic liquid fed to dissolution
zone 20 via line 64 can have a temperature at least 10.degree. C.
above the melting point of the ionic liquid. In another embodiment,
the ionic liquid can have a temperature in the range of from about
0 to about 100.degree. C., in the range of from about 20 to about
80.degree. C., or in the range of from 25 to 50.degree. C.
[0067] In one embodiment, the ionic liquid fed to dissolution zone
20 via line 64 can comprise water, nitrogen-containing bases,
alcohol, or carboxylic acid. The ionic liquid in line 64 can
comprise less than about 15 weight percent of each of water,
nitrogen-containing bases, alcohol, and carboxylic acid; less than
about 5 weight percent of each of water, nitrogen-containing bases,
alcohol, and carboxylic acid; or less than 2 weight percent of each
of water, nitrogen-containing bases, alcohol, and carboxylic
acid.
[0068] As mentioned above, an ionic liquid comprises ions. These
ions include both cations (i.e., positively charged ions) and
anions (i.e., negatively charged ions). In one embodiment, the
cations of the ionic liquid suitable for use in the present
invention can include, but are not limited to, imidazolium,
pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or
thiazolium cations, which correspond to the following
structures:
##STR00002##
In the above structures, R.sub.1 and R.sub.2 can independently be a
C.sub.1 to C.sub.8 alkyl group, a C.sub.2 to C.sub.8 alkenyl group,
or a C.sub.1 to C.sub.8 alkoxyalkyl group. R.sub.3, R.sub.4, and
R.sub.5 can independently be a hydrido, a C.sub.1 to C.sub.8 alkyl
group, a C.sub.2 to C.sub.8 alkenyl group, a C.sub.1 to C.sub.8
alkoxyalkyl group, or a C.sub.1 to C.sub.8 alkoxy group. In one
embodiment, the cation of the ionic liquid used in the present
invention can comprise an alkyl substituted imidazolium cation,
where R.sub.1 is a C.sub.1 to C.sub.4 alkyl group, and R.sub.2 is a
different C.sub.1 to C.sub.4 alkyl group.
[0069] In one embodiment of the present invention, the cellulose
dissolving ionic liquid can be a carboxylated ionic liquid. As used
herein, the term "carboxylated ionic liquid" shall denote any ionic
liquid comprising one or more carboxylate anions. Carboxylate
anions suitable for use in the carboxylated ionic liquids of the
present invention include, but are not limited to, C.sub.1 to
C.sub.20 straight- or branched-chain carboxylate or substituted
carboxylate anions. Examples of suitable carboxylate anions for use
in the carboxylated ionic liquid include, but are not limited to,
formate, acetate, propionate, butyrate, valerate, hexanoate,
lactate, oxalate, or chloro-, bromo-, fluoro-substituted acetate,
propionate, or butyrate and the like. In one embodiment, the anion
of the carboxylated ionic liquid can be a C.sub.2 to C.sub.6
straight-chain carboxylate. Furthermore, the anion can be acetate,
propionate, butyrate, or a mixture of acetate, propionate, and/or
butyrate.
[0070] Examples of carboxylated ionic liquids suitable for use in
the present invention include, but are not limited to,
1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium
propionate, 1-ethyl-3-methylimidazolium butyrate,
1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium
propionate, 1-butyl-3-methylimidazolium butyrate, or mixtures
thereof.
[0071] In one embodiment of the present invention, the carboxylated
ionic liquid can contain sulfur in an amount less than 200 parts
per million by weight ("ppmw"), less than 100 ppmw, less than 50
ppmw, or less than 10 ppmw based on the total ion content of the
carboxylated ionic liquid. Additionally, the carboxylated ionic
liquid can contain a total halide content of less than 200 ppmw,
less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based
on the total ion content of the carboxylated ionic liquid.
Furthermore, the carboxylated ionic liquid can contain a total
metal content of less than 200 ppmw, less than 100 ppmw, less than
50 ppmw, or less than 10 ppmw based on the total ion content of the
carboxylated ionic liquid. In one embodiment, carboxylated ionic
liquid can contain transition metals in an amount less than 200
ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw.
Sulfur, halide, and metal content of the carboxylated ionic liquid
can be determined by x-ray fluorescence ("XRF") spectroscopy.
[0072] The carboxylated ionic liquid of the present invention can
be formed by any process known in the art for making ionic liquids
having at least one carboxylate anion. In one embodiment, the
carboxylated ionic liquid of the present invention can be formed by
first forming an intermediate ionic liquid. The intermediate ionic
liquid can be any known ionic liquid that can participate in an
anion exchange reaction.
[0073] In one embodiment, the intermediate ionic liquid can
comprise a plurality of cations such as, for example, imidazolium,
pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or
thiazolium cations, which correspond to the following
structures:
##STR00003##
In the above structures, R.sub.1 and R.sub.2 can independently be a
C.sub.1 to C.sub.8 alkyl group, a C.sub.2 to C.sub.8 alkenyl group,
or a C.sub.1 to C.sub.8 alkoxyalkyl group. R.sub.3, R.sub.4, and
R.sub.5 can independently be a hydrido, a C.sub.1 to C.sub.8 alkyl
group, a C.sub.2 to C.sub.8 alkenyl group, a C.sub.1 to C.sub.8
alkoxyalkyl group, or a C.sub.1 to C.sub.8 alkoxy group. In one
embodiment, the cation of the intermediate ionic liquid used in the
present invention can comprise an alkyl substituted imidazolium
cation, where R.sub.1 is a C.sub.1 to C.sub.4 alkyl group, and
R.sub.2 is a different C.sub.1 to C.sub.4 alkyl group. In one
embodiment, the cation of the intermediate ionic liquid can
comprise 1-ethyl-3-methylimidazolium or
1-butyl-3-methylimidazolium.
[0074] Additionally, the intermediate ionic liquid can comprise a
plurality of anions. In one embodiment, the intermediate ionic
liquid can comprise a plurality of carboxylate anions, such as, for
example, formate, acetate, and/or propionate anions.
[0075] In one embodiment, the intermediate ionic liquid can
comprise an alkyl amine formate. The amine cation of the alkyl
amine formate can comprise any of the above-described substituted
or unsubstituted imidazolium, pyrazolium, oxazolium,
1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations. In
one embodiment, the amine of the alkyl amine formate can be an
alkyl substituted imidazolium, alkyl substituted pyrazolium, alkyl
substituted oxazolium, alkyl substituted triazolium, alkyl
substituted thiazolium, and mixtures thereof. In one embodiment,
the amine of the alkyl amine formate can be an alkyl substituted
imidazolium. Examples of alkyl amine formates suitable for use in
the present invention include, but are not limited to,
1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium
formate, 1-propyl-3-methylimidazolium formate,
1-butyl-3-methylimidazolium formate, 1-pentyl-3-methylimidazolium
formate, and/or 1-octyl-3-methylimidazolium formate.
[0076] The intermediate ionic liquid useful in the present
invention can be formed by contacting at least one amine with at
least one alkyl formate. Amines suitable for use in the present
invention include, but are not limited to, substituted or
unsubstituted imidazoles, pyrazoles, oxazoles, triazoles, and/or
thiazoles. In one embodiment, the alkyl amine formate can be formed
by contacting at least one alkyl substituted imidazole with at
least one alkyl formate. Examples of alkyl substituted imidazoles
suitable for use in forming the intermediate ionic liquid include,
but are not limited to, 1-methylimidazole, 1-ethylimidazole,
1-propylimidazole, 1-butylimidazole, 1-hexylimidazole, and/or
1-octylimidazole. Examples of alkyl formates suitable for use in
forming the intermediate ionic liquid include, but are not limited
to, methyl formate, ethyl formate, propyl formate, isopropyl
formate, butyl formate, isobutyl formate, tert-butyl formate, hexyl
formate, octyl formate, and the like. In one embodiment, the alkyl
formate used in forming the intermediate ionic liquid can comprise
methyl formate.
[0077] Once the intermediate ionic liquid has been formed, the
intermediate ionic liquid can be contacted with one or more
carboxylate anion donors at a contact time, pressure, and
temperature sufficient to cause the at least partial conversion of
the intermediate ionic liquid to at least one of the
above-mentioned carboxylated ionic liquids. Such interconversion
can be accomplished via anion exchange between the carboxylate
anion donor and the intermediate ionic liquid. In one embodiment,
at least a portion of the formate of the alkyl amine formate can be
replaced via anion exchange with a carboxylate anion originating
from one or more carboxylate anion donors.
[0078] Carboxylate anion donors useful in the present invention can
include any substance capable of donating at least one carboxylate
anion. Examples of carboxylate anion donors suitable for use in the
present invention include, but are not limited to, carboxylic
acids, anhydrides, and/or alkyl carboxylates. In one embodiment,
the carboxylate anion donor can comprise one or more C.sub.2 to
C.sub.20 straight- or branched-chain alkyl or aryl carboxylic
acids, anhydrides, or methyl esters. Additionally, the carboxylate
anion donor can comprise one or more C.sub.2 to C.sub.12
straight-chain alkyl carboxylic acids, anhydrides, or methyl
esters. Furthermore, the carboxylate anion donor can comprise one
or more C.sub.2 to C.sub.4 straight-chain alkyl carboxylic acids,
anhydrides, or methyl esters. In one embodiment, the carboxylate
anion donor can comprise at least one anhydride, which can comprise
acetic anhydride, propionic anhydride, butyric anhydride,
isobutyric anhydride, valeric anhydride, hexanoic anhydride,
2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride,
palmitic anhydride, stearic anhydride, benzoic anhydride,
substituted benzoic anhydrides, phthalic anhydride, isophthalic
anhydride, and mixtures thereof.
[0079] The amount of carboxylate anion donor useful in the present
invention can be any amount suitable to convert at least a portion
of the intermediate ionic liquid to a carboxylated ionic liquid. In
one embodiment, the carboxylate anion donor can be present in a
molar ratio with the intermediate ionic liquid in the range of from
about 1:1 to about 20:1 carboxylate anion donor-to-intermediate
ionic liquid anion content, or in the range of from 1:1 to 6:1
carboxylate anion donor-to-intermediate ionic liquid anion content.
In one embodiment, when alkyl amine formate is present as the
intermediate ionic liquids, the carboxylate anion donor can be
present in an amount in the range of from 1 to 20 molar equivalents
per alkyl amine formate, or in the range of from 1 to 6 molar
equivalents per alkyl amine formate.
[0080] The anion exchange between the intermediate ionic liquid and
the carboxylate anion donor can be accomplished in the presence of
at least one alcohol. Alcohols useful in the present invention
include, but are not limited to, alkyl or aryl alcohols such as
methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol,
t-butanol, phenol, and the like. In one embodiment, the alcohol can
be methanol. The amount of alcohol present in the contact mixture
during interconversion of the intermediate ionic liquid can be in
the range of from about 0.01 to about 20 molar equivalents of the
ionic liquid, or in the range of from 1 to 10 molar equivalents of
the ionic liquid.
[0081] In one embodiment, water can be present in the contact
mixture during the anion exchange between the intermediate ionic
liquid and the carboxylate anion donor. The amount of water present
in the contact mixture during interconversion of the intermediate
ionic liquid can be in the range of from about 0.01 to about 20
molar equivalents of the ionic liquid, or in the range of from 1 to
10 molar equivalents of the ionic liquid.
[0082] As mentioned above, the interconversion of the intermediate
ionic liquid to the carboxylated ionic liquid can be performed at a
contact time, pressure, and temperature sufficient to cause the at
least partial conversion of the intermediate ionic liquid to the
carboxylated ionic liquid. In one embodiment, the interconversion
can be performed for a time in the range of from about 1 minute to
about 24 hours, or in the range of from 30 minutes to 18 hours.
Additionally, the interconversion can be performed at a pressure up
to 21,000 kPa, or up to 10,000 kPa. In one embodiment, the
interconversion can be performed at a pressure in the range of from
about 100 to about 21,000 kPa, or in the range of from 100 to
10,000 kPa. Furthermore, the interconversion can be performed at a
temperature in the range of from about 0 to about 200.degree. C.,
or in the range of from 25 to 170.degree. C.
[0083] In one embodiment, the resulting carboxylated ionic liquid
can comprise carboxylate anions comprising substituted or
non-substituted C.sub.1 to C.sub.20 straight- or branched-chain
carboxylate anions. In one embodiment, the carboxylate anion can
comprise a C.sub.2 to C.sub.6 straight-chain carboxylate anion.
Additionally, the carboxylated ionic liquid can comprise
carboxylate anions such as, for example, formate, acetate,
propionate, butyrate, valerate, hexanoate, lactate, and/or oxalate.
In one embodiment, the carboxylated ionic liquid can comprise at
least 50 percent carboxylate anions, at least 70 percent
carboxylate anions, or at least 90 percent carboxylate anions. In
another embodiment, the carboxylated ionic liquid can comprise at
least 50 percent acetate anions, at least 70 percent acetate
anions, or at least 90 percent acetate anions.
[0084] In an alternative embodiment of the present invention, the
above-mentioned cellulose dissolving ionic liquid can be a halide
ionic liquid. As used herein, the term "halide ionic liquid" shall
denote any ionic liquid that contains at least one halide anion. In
one embodiment, the halide anion of the halide ionic liquid can be
fluoride, chloride, bromide, and/or iodide. In another embodiment,
the halide anion can be chloride and/or bromide. Additionally, as
mentioned above, the cation of the cellulose dissolving ionic
liquid can comprise, but is not limited to, imidazolium,
pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or
thiazolium cations. Any method known in the art suitable for making
a halide ionic liquid can be employed in the present invention.
[0085] Examples of halide ionic liquids suitable for use in the
present invention include, but are not limited to,
1-butyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium
chloride, 1-ethyl-3-methylimidazolium chloride,
1-allyl-3-methylimidazolium chloride, or mixtures thereof.
[0086] Referring again to FIG. 1, the weight percent of the amount
of cellulose fed to dissolution zone 20 to the cumulative amount of
ionic liquid (including recycled ionic liquid) fed to dissolution
zone 20 can be in the range of from about 1 to about 40 weight
percent, in the range of from about 5 to about 25 weight percent,
or in the range of from 10 to 20 weight percent based on the
combined weight of cellulose and ionic liquid. In one embodiment,
the resulting medium formed in dissolution zone 20 can comprise
other components, such as, for example, water, alcohol, acylating
reagent, and/or carboxylic acids. In one embodiment, the medium
formed in dissolution zone 20 can comprise water in an amount in
the range of from about 0.001 to about 200 weight percent, in the
range of from about 1 to about 100 weight percent, or in the range
of from 5 to 15 weight percent based on the entire weight of the
medium. Additionally, the medium formed in dissolution zone 20 can
comprise a combined concentration of alcohol in an amount in the
range of from about 0.001 to about 200 weight percent, in the range
of from about 1 to about 100 weight percent, or in the range of
from 5 to 15 weight percent based on the entire weight of the
medium.
[0087] The medium formed in dissolution zone 20 can optionally
comprise one or more carboxylic acids. The medium formed in
dissolution zone 20 can comprise a total concentration of
carboxylic acids in the range of from about 0.01 to about 25 weight
percent, in the range of from about 0.05 to about 15 weight
percent, or in the range of from 0.1 to 5 weight percent based on
the total concentration of ionic liquid in the medium formed in
dissolution zone 20. Examples of suitable carboxylic acids useful
in this embodiment include, but are not limited to, acetic acid,
propionic acid, butyric acid, isobutyric acid, valeric acid,
hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid,
palmitic acid, stearic acid, benzoic acid, substituted benzoic
acids, phthalic acid, and isophthalic acid. In one embodiment, the
carboxylic acid in the medium formed in dissolution zone 20 can
comprise acetic acid, propionic acid, and/or butyric acid.
[0088] As is described in more detail below with reference to FIG.
2, at least a portion of the carboxylic acids present in the medium
formed in dissolution zone 20 can originate from a recycled
carboxylated ionic liquid introduced via line 70. Though not
wishing to be bound by theory, the inventors have unexpectedly
found that the use of carboxylic acid in the medium formed in
dissolution zone 20 can reduce the viscosity of the cellulose/ionic
liquid solution, thereby enabling easier processing of the
solution. Additionally, the presence of carboxylic acid in the
medium in dissolution zone 20 appears to reduce the melting points
of the ionic liquids employed, thereby allowing processing of the
ionic liquids at lower temperatures than predicted.
[0089] The medium formed in dissolution zone 20 can optionally
comprise an acylating reagent, as is discussed in more detail
below. The optional acylating reagent can be introduced into
dissolution zone 20 via line 78. In one embodiment, the medium
formed in dissolution zone 20 can comprise acylating reagent in an
amount in the range of from about 0.01 molar equivalents to about
20 molar equivalents, in the range of from about 0.5 molar
equivalents to about 10 molar equivalents, or in the range of from
1.8 molar equivalents to about 4 molar equivalents based on the
total amount of cellulose in the medium in dissolution zone 20.
[0090] The medium formed in dissolution zone 20 can also comprise
recycled ionic liquid, as is discussed in more detail below with
reference to FIG. 2. The recycled ionic liquid can be introduced
into dissolution zone 20 via line 70. The medium formed in
dissolution zone 20 can comprise recycled ionic liquid in an amount
in the range of from about 0.01 to about 99.99 weight percent, in
the range of from about 10 to about 99 weight percent, or in the
range of from 90 to 98 weight percent based on the total amount of
ionic liquid in dissolution zone 20.
[0091] In one embodiment, the medium can optionally comprise
immiscible or substantially immiscible co-solvents. Such
co-solvents can comprise one or more co-solvents that are
immiscible or sparingly soluble with the cellulose-ionic liquid
mixture. Surprisingly, the addition of an immiscible or sparingly
soluble co-solvent does not cause precipitation of the cellulose
upon contacting the cellulose-ionic liquid mixture. However, upon
contact with an acylating reagent, as will be discussed in more
detail below, the cellulose can be esterified which can change the
solubility of the now cellulose ester-ionic liquid solution with
respect to the formerly immiscible or sparingly soluble co-solvent.
Accordingly, subsequent to esterification, the contact mixture can
become a single phase or highly dispersed mixture of cellulose
ester-ionic liquid in the co-solvent. The resulting single phase or
dispersed phase has much lower solution viscosity than the initial
cellulose-ionic liquid solution.
[0092] This discovery is significant in that heretofore highly
viscous cellulose solutions can now be used to make cellulose
esters while still maintaining the ability to mix and process the
solution. The discovery also provides a viable method to process
highly viscous cellulose-ionic liquid solutions at lower contact
temperatures.
[0093] Immiscible or sparingly soluble co-solvents suitable for use
in the present invention can comprise alkyl or aryl esters,
ketones, alkyl halides, hydrophobic ionic liquids, and the like.
Specific examples of immiscible or sparingly soluble co-solvents
include, but are not limited to, methyl acetate, ethyl acetate,
isopropyl acetate, methyl propionate, methyl butyrate, acetone,
methyl ethyl ketone, chloroform, methylene chloride, alkyl
immidazolium hexafluorophosphate, alkyl immidazolium triflimide,
and the like. In one embodiment, the immiscible or sparingly
soluble co-solvents can comprise methyl acetate, methyl propionate,
methyl butyrate, methyl ethyl ketone, and/or methylene chloride.
The weight ratio of immiscible or sparingly soluble co-solvents to
cellulose-ionic liquid mixture can be in the range of from about
1:20 to about 20:1. or in the range of from 1:5 to 5:1.
[0094] In one embodiment, the cellulose entering dissolution zone
20 via line 62 can initially be dispersed in the ionic liquid.
Dispersion of the cellulose in the ionic liquid can be achieved by
any mixing means known in the art. In one embodiment, dispersion of
the cellulose can be achieved by mechanical mixing, such as mixing
by one or more mechanical homogenizers.
[0095] After the cellulose has been dispersed in the ionic liquid,
dissolution of the cellulose in dissolution zone 20, along with
removal of at least a portion of any volatile components in the
mixture, can be achieved using any method known in the art. For
example, dissolution of the cellulose can be achieved by lowering
the pressure and/or raising the temperature of the cellulose/ionic
liquid dispersion initially formed in dissolution zone 20.
Accordingly, after the cellulose is dispersed in the ionic liquid,
the pressure can be lowered in dissolution zone 20. In one
embodiment, the pressure in dissolution zone 20 can be lowered to
less than about 100 millimeters mercury ("mm Hg"), or less than 50
mm Hg. Additionally, the cellulose/ionic liquid dispersion can be
heated to a temperature in the range of from about 60 to about
100.degree. C., or in the range of from 70 to about 85.degree. C.
After dissolution, the resulting solution can be maintained at the
above-described temperatures and pressures for a time in the range
of from about 0 to about 100 hours, or in the range of from about 1
to about 4 hours. The cellulose solution formed in dissolution zone
20 can comprise cellulose in an amount in the range of from about 1
to about 40 weight percent, or in the range of from 5 to 20 weight
percent, based on the entire weight of the solution. In another
embodiment, the cellulose solution formed in dissolution zone 20
can comprise dissolved cellulose in an amount of at least 10 weight
percent based on the entire weight of the solution.
[0096] After dissolution, at least a portion of the resulting
cellulose solution can be removed from dissolution zone 20 via line
66 and routed to esterification zone 40. In one embodiment, at
least one acylating reagent can be introduced into esterification
zone 40 to esterify at least a portion of the cellulose. As
mentioned above, in another embodiment, at least one acylating
reagent can be introduced into dissolution zone 20. Additionally,
the acylating reagent can be added after the cellulose has been
dissolved in the ionic liquid. Optionally, at least a portion of
the acylating reagent can be added to the ionic liquids prior to
dissolution of the cellulose in the ionic liquid. Regardless of
where the acylating reagent is added, at least a portion of the
cellulose in esterification zone 40 can undergo esterification
subsequent to being contacted with the acylating reagent.
[0097] As used herein, the term "acylating reagent" shall denote
any chemical compound capable of donating at least one acyl group
to a cellulose. As used herein, the term "acyl group" shall denote
any organic radical derived from an organic acid by the removal of
a hydroxyl group. Acylating reagents useful in the present
invention can be one or more C.sub.1 to C.sub.20 straight- or
branched-chain alkyl or aryl carboxylic anhydrides, carboxylic acid
halides, diketene, or acetoacetic acid esters. Examples of
carboxylic anhydrides suitable for use as acylating reagents in the
present invention include, but are not limited to, acetic
anhydride, propionic anhydride, butyric anhydride, isobutyric
anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic
anhydride, nonanoic anhydride, lauric anhydride, palmitic
anhydride, stearic anhydride, benzoic anhydride, substituted
benzoic anhydrides, phthalic anhydride, and isophthalic anhydride.
Examples of carboxylic acid halides suitable for use as acylating
reagents in the present invention include, but are not limited to,
acetyl, propionyl, butyryl, hexanoyl, 2-ethylhexanoyl, lauroyl,
palmitoyl, benzoyl, substituted benzoyl, and stearoyl chlorides.
Examples of acetoacetic acid esters suitable for use as acylating
reagents in the present invention include, but are not limited to,
methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl
acetoacetate, and tert-butyl acetoacetate. In one embodiment, the
acylating reagents can be C.sub.2 to C.sub.9 straight- or
branched-chain alkyl carboxylic anhydrides selected from the group
consisting of acetic anhydride, propionic anhydride, butyric
anhydride, 2-ethylhexanoic anhydride, and nonanoic anhydride.
[0098] The reaction medium formed in esterification zone 40 can
comprise cellulose in an amount in the range of from about 1 to
about 40 weight percent, in the range of from about 5 to about 25
weight percent, or in the range of from 10 to 20 weight percent,
based on the weight of the ionic liquid in the reaction medium.
Additionally, the reaction medium formed in esterification zone 40
can comprise ionic liquid in an amount in the range of from about
20 to about 98 weight percent, in the range of from about 30 to
about 95 weight percent, or in the range of from 50 to 90 weight
percent based on the total weight of the reaction medium.
Furthermore, the reaction medium formed in esterification zone 40
can comprise acylating reagent in an amount in the range of from
about 1 to about 50 weight percent, in the range of from about 5 to
about 30 weight percent, or in the range of from 10 to 20 weight
percent based on the total weight of the reaction medium.
Furthermore, the reaction medium formed in esterification zone 40
can have a cumulative concentration of nitrogen containing bases
and carboxylic acids in an amount less than 15 weight percent, less
than 5 weight percent, or less than 2 weight percent.
[0099] In one embodiment, the weight ratio of
cellulose-to-acylating reagent in esterification zone 40 can be in
the range of from about 90:10 to about 10:90, in the range of from
about 60:40 to about 25:75, or in the range of from 45:55 to 35:65.
In one embodiment, the acylating reagent can be present in
esterification zone 40 in an amount less than 5, less than 4, less
than 3, or less than 2.7 molar equivalents per anhydroglucose
unit.
[0100] In one embodiment of the present invention, when a halide
ionic liquid is employed as the cellulose dissolving ionic liquid,
a limited excess of acylating reagent can be employed in the
esterification of the cellulose to achieve a cellulose ester with a
particular DS. Thus, in one embodiment, less than 20 percent molar
excess, less than 10 percent molar excess, less than 5 percent
molar excess, or less than 1 percent excess of acylating reagent
can be employed during esterification.
[0101] In a preferred embodiment of the present invention when 2 or
more acylating reagents are employed in the esterification of
cellulose, the 2 or more acylating reagents can be added as a
mixture or the addition can be staged. In a staged addition, the
acylating reagents are added consecutively. Preferably, in a staged
addition at least about 80 molar percent of the first acylating
reagent is allowed to react with the cellulose prior to adding the
next acylating reagent.
[0102] Optionally, one or more catalysts can be introduced into
esterification zone 40 to aid in esterification of the cellulose.
The catalyst employed in the present invention can be any catalyst
that increases the rate of esterification in esterification zone
40. Examples of catalysts suitable for use in the present invention
include, but are not limited to, protic acids of the type sulfuric
acid, alkyl sulfonic acids, aryl sulfonic acids, functional ionic
liquids, and weak Lewis acids of the type MXn, where M is a
transition metal exemplified by B, Al, Fe, Ga, Sb, Sn, As, Zn, Mg,
or Hg, and X is halogen, carboxylate, sulfonate, alkoxide, alkyl,
or aryl. In one embodiment, the catalyst is a protic acid. The
protic acid catalysts can have a pKa in the range of from about -5
to about 10, or in the range of from -2.5 to 2.0. Examples of
suitable protic acid catalysts include methane sulfonic acid
("MSA"), p-toluene sulfonic acid, and the like. In one embodiment,
the one or more catalysts can be Lewis acids. Examples of Lewis
acids suitable for use as catalysts include ZnCl2, Zn(OAc)2, and
the like. When a catalyst is employed, the catalyst can be added to
the cellulose solution prior to adding the acylating reagent. In
another embodiment the catalyst can be added to the cellulose
solution as a mixture with the acylating reagent.
[0103] Additionally, functional ionic liquids can be employed as
catalysts during esterification of the cellulose. Functional ionic
liquids are ionic liquids containing specific functional groups,
such as hydrogen sulfonate, alkyl or aryl sulfonates, and
carboxylates, that effectively catalyze the esterification of
cellulose by the acylating reagent. Examples of functional ionic
liquids include 1-alkyl-3-methylimidazolium hydrogen sulfate,
methyl sulfonate, tosylate, and trifluoroacetate, where the alkyl
can be a C.sub.1 to C.sub.10 straight-chain alkyl group.
Additionally, suitable functional ionic liquids for use in the
present invention are those in which the functional group is
covalently linked to the cation. Thus, functional ionic liquids can
be ionic liquids containing functional groups, and are capable of
catalyzing the esterification of cellulose with an acylating
reagent.
[0104] An example of a covalently-linked functional ionic liquid
suitable for use in the present invention includes, but is not
limited to, the following structure:
##STR00004##
where at least one of the R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5 groups are replaced with the group (CHX).sub.nY, where X is
hydrogen or halide, n is an integer in the range of from 1 to 10,
and Y is sulfonic or carboxylate and the remainder R.sub.1,
R.sub.2, R.sub.3, R.sub.4, R.sub.5 groups are those previously
described in relation to the cations suitable for use as the
cellulose dissolving ionic liquid. Examples of cations suitable for
use in the functional ionic liquids to be used in the present
invention include, but are not limited to,
1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium,
1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium,
1-alkyl-3-(1-carboxy-2,2-difluoro-butyl)imidazolium,
1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium,
1-alkyl-3-(1-sulfonylethyl)imidazolium,
1-alkyl-3-(1-sulfonylpropyl)imidazolium,
1-alkyl-3-(1-sulfonylbutyl)imidazolium, and
1-alkyl-3-(1-sulfonylhexyl)imidazolium, where the alkyl can be a
C.sub.1 to C.sub.10 straight-chain alkyl group.
[0105] The amount of catalyst used to catalyze the esterification
of cellulose may vary depending upon the type of catalyst employed,
the type of acylating reagent employed, the type of ionic liquid,
the contact temperature, and the contact time. Thus, a broad
concentration of catalyst employed is contemplated by the present
invention. In one embodiment, the amount of catalyst employed in
esterification zone 40 can be in the range of from about 0.01 to
about 30 mol percent catalyst per anhydroglucose unit ("AGU"), in
the range of from about 0.05 to about 10 mol percent catalyst per
AGU, or in the range of from 0.1 to 5 mol percent catalyst per AGU.
In one embodiment, the amount of catalyst employed can be less than
30 mol percent catalyst per AGU, less than 10 mol percent catalyst
per AGU, less than 5 mol percent catalyst per AGU, or less than 1
mol percent catalyst per AGU. In another embodiment, when a
catalyst is employed as a binary component, the amount of binary
component employed can be in the range of from about 0.01 to about
100 mol percent per AGU, in the range of from about 0.05 to about
20 mol percent per AGU, or in the range of from 0.1 to 5 mol
percent per AGU.
[0106] The inventors have discovered a number of surprising and
unpredictable advantages apparently associated with employing a
catalyst as a binary component during the esterification of
cellulose. For example, the inventors have discovered that the
inclusion of a binary component can accelerate the rate of
esterification. Very surprisingly, the binary component can also
serve to improve solution and product color, prevent gellation of
the esterification mixture, provide increased DS values in relation
to the amount of acylating reagent employed, and/or help to
decrease the molecular weight of the cellulose ester product.
Though not wishing to be bound by theory, it is believed that the
use of a binary component acts to change the network structure of
the ionic liquid containing the dissolved cellulose ester. This
change in network structure may lead to the observed surprising and
unpredicted advantages of using the binary component.
[0107] As mentioned above, at least a portion of the cellulose can
undergo an esterification reaction in esterification zone 40. The
esterification reaction carried out in esterification zone 40 can
operate to convert at least a portion of the hydroxyl groups
contained on the cellulose to ester groups, thereby forming a
cellulose ester. As used herein, the term "cellulose ester" shall
denote a cellulose polymer having at least one ester substituent.
Furthermore, the term "`mixed cellulose ester" shall denote a
cellulose ester having at least two different ester substituents on
a single cellulose ester polymer chain. In one embodiment, at least
a portion of the ester groups on the resulting cellulose ester can
originate from the above-described acylating reagent. The cellulose
esters thus prepared can comprise the following structure:
##STR00005##
where R.sub.2, R.sub.3, and R.sub.6 can independently be hydrogen,
so long as R.sub.2, R.sub.3, and R.sub.6 are not all hydrogen
simultaneously, or a C.sub.1 to C.sub.20 straight- or
branched-chain alkyl or aryl groups bound to the cellulose via an
ester linkage.
[0108] In one embodiment, when the ionic liquid employed is a
carboxylated ionic liquid, one or more of the ester groups on the
resulting cellulose ester can originate from the ionic liquid in
which the cellulose is dissolved. The amount of ester groups on the
resulting cellulose ester that originate from the carboxylated
ionic liquid can be at least 10 percent, at least 25 percent, at
least 50 percent, or at least 75 percent.
[0109] Additionally, the ester group on the cellulose ester
originating from the carboxylated ionic liquid can be a different
ester group than the ester group on the cellulose ester that
originates from the acylating reagent. Though not wishing to be
bound by theory, it is believed that when an acylating reagent is
introduced into a carboxylated ionic liquid, an anion exchange can
occur such that a carboxylate ion originating from the acylating
reagent replaces at least a portion of the carboxylate anions in
the carboxylated ionic liquid, thereby creating a substituted ionic
liquid. When the carboxylate ion originating from the acylating
reagent is of a different type than the carboxylate anions of the
ionic liquid, then the substituted ionic liquid can comprise at
least two different types of carboxylate anions. Thus, so long as
the carboxylate anion from the carboxylated ionic liquid comprises
a different acyl group than is found on the acylating reagent, at
least two different acyl groups are available for esterification of
the cellulose. By way of illustration, if cellulose was dissolved
in 1-butyl-3-methylimidazolium acetate ("[BMIm]OAc" or
"[BMIm]acetate") and a propionic anhydride ("Pr.sub.2O") acylating
reagent were added to the carboxylated ionic liquid, the
carboxylated ionic liquid can become a substituted ionic liquid,
comprising a mixture of [BMIm]acetate and [BMIm]propionate. Thus,
the process of forming a cellulose ester via this process can be
illustrated as follows:
##STR00006##
As illustrated, contacting a solution of cellulose dissolved in
[BMIm]acetate with a propionic anhydride can result in the
formation of a cellulose ester comprising both acetate ester
substituents and propionate ester substituents. Thus, at least a
portion of the ester groups on the cellulose ester can originate
from the ionic liquid, and at least a portion of the ester groups
can originate from the acylating reagent. Additionally, at least
one of the ester groups donated by the ionic liquid can be an acyl
group. In one embodiment, all of the ester groups donated by the
ionic liquid can be acyl groups.
[0110] Therefore, in one embodiment, the cellulose ester prepared
by methods of the present invention can be a mixed cellulose ester.
In one embodiment, the mixed cellulose ester of the present
invention can comprise a plurality of first pendant acyl groups and
a plurality of second acyl groups, where the first pendant acyl
groups originate from the ionic liquid, and the second pendant acyl
groups originate from the acylating reagent. In one embodiment, the
mixed cellulose ester can comprise a molar ratio of at least two
different acyl pendant groups in the range of from about 1:10 to
about 10:1, in the range of from about 2:8 to about 8:2, or in the
range of from 3:7 to 7:3. Additionally, the first and second
pendant acyl groups can comprise acetyl, propionyl, and/or butyryl
groups.
[0111] In one embodiment, at least one of the first pendant acyl
groups can be donated by the ionic liquid or at least one of the
second pendant acyl groups can be donated by the ionic liquid. As
used herein, the term "donated," with respect to esterification,
shall denote a direct transfer of an acyl group. Comparatively, the
term "originated," with respect to esterification, can signify
either a direct transfer or an indirect transfer of an acyl group.
In one embodiment of the invention, at least 50 percent of the
above-mentioned first pendant acyl groups can be donated by the
ionic liquid, or at least 50 percent of the second pendant acyl
groups can be donated by the ionic liquid. Furthermore, at least 10
percent, at least 25 percent, at least 50 percent, or at least 75
percent of all of the pendant acyl groups on the resulting
cellulose ester can result from donation of an acyl group by the
ionic liquid.
[0112] In one embodiment, the above-described mixed cellulose ester
can be formed by a process where a first portion of the first
pendant acyl groups can initially be donated from the acylating
reagent to the carboxylated ionic liquid, and then the same acyl
groups can be donated from the carboxylated ionic liquid to the
cellulose (i.e., indirectly transferred from the acylating reagent
to the cellulose, via the ionic liquid). Additionally, a second
portion of the first pendant acyl groups can be donated directly
from the acylating reagent to the cellulose.
[0113] In a further embodiment of the present invention when 2 or
more acylating reagents are employed in the esterification of
cellulose, the 2 or more acylating reagents can be added as a
mixture or the addition can be staged. In a mixed addition, 2 or
more acylating reagents are added to the cellulose solution
simultaneously. In the case of carboxylated ionic liquids, where
one of the acyl groups are donated by the ionic liquid, addition of
one or more acylating reagents constitutes a mixed addition. In a
staged addition, the acylating reagents are added consecutively. In
one embodiment of the staged addition process, at least about 80
mol percent of the first acylating reagent is allowed to react with
the cellulose prior to adding the next acylating reagent.
[0114] In one aspect of the present invention, when contacting one
or more acylating reagents with the cellulose solution reaction
kinetics, the amount of acylating reagent that is added, and the
order of which they are added can also significantly influence
substituent distribution or regioselectivity when the total DS is
less than about 2.95.
[0115] Regioselectivity is most easily measured by determining the
relative degree of substitution (RDS) at C.sub.6, C.sub.3, and
C.sub.2 in the cellulose ester by carbon 13 NMR (Macromolecules,
1991, 24, 3050-3059). In the case of one acyl substituent or when a
second acyl substituent is present in a minor amount (DS.ltoreq.2),
the RDS can be most easily determined directly by integration of
the ring carbons. When 2 or more acyl substituents are present in
more equal amounts, in addition to determining the ring RDS it is
sometimes necessary to fully substitute the cellulose ester with an
additional substituent in order to independently determine the RDS
of each substituent by integration of the carbonyl carbons. In
conventional cellulose esters, regioselectivity is generally not
observed, and the RDS ratio of C.sub.6/C.sub.3, C.sub.6/C.sub.2, or
C.sub.3/C.sub.2 is generally near 1. In essence, conventional
cellulose esters are random copolymers.
[0116] In the present invention, we found that when adding one or
more acylating reagents, the C.sub.6 position of cellulose was
acylated much faster than C.sub.2 and C.sub.3. Consequentially, the
C.sub.6/C.sub.3 and C.sub.6/C.sub.2 RDS ratios are greater than 1
which is characteristic of a regioselectively substituted cellulose
ester. The degree of regioselectivity depends upon at least one of
the following factors: type of acyl substituent, contact
temperature, ionic liquid interaction, equivalents of acyl reagent,
order of additions, and the like. Typically, the larger the number
of carbon atoms in the acyl substituent, the C.sub.6 position of
the cellulose is acylated preferentially over the C.sub.2 and
C.sub.3 position. In addition, as the contact temperature is
lowered in the esterification zone 40, the C.sub.6 position of the
cellulose can be acylated preferentially over the C.sub.2 or
C.sub.3 position. As mentioned previously, the type of ionic liquid
and its interaction with cellulose in the process can affect the
regioselectivity of the cellulose ester. For example, when
carboxylated ionic liquids are utilized, a regioselectively
substituted cellulose ester is produced where the RDS ratio is
C.sub.6>C.sub.2>C.sub.3. When halide ionic liquids are
utilized, a regioselectively substituted cellulose ester is
produced where the RDS ratio is C.sub.6>C.sub.3>C.sub.2. This
is significant in that regioselective placement of substituents in
a cellulose ester leads to regioselectively substituted cellulose
esters with different physical properties relative to conventional
cellulose esters.
[0117] In one embodiment of this invention, no protective groups
are utilize to prevent reaction of the cellulose with the acylating
reagent.
[0118] In one embodiment of the present invention, the ring RDS
ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least 1.05. In
another embodiment, the ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 is at least 1.1. Another embodiment of the present
invention is when the ring R.sub.DS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 is at least 1.3.
[0119] In another embodiment of the present invention, the product
of the ring RDS ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times
the total DS [(C.sub.6/C.sub.3)*DS or (C.sub.6/C.sub.2)*DS] is at
least 2.9. In another embodiment, the product of the ring RDS ratio
for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the total DS is at
least 3.0. In another embodiment, the product of the ring RDS ratio
for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the total DS is at
least 3.2.
[0120] In another embodiment of the present invention, the ring RDS
ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least 1.05, and
the product of the ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 times the total DS is at least 2.9. In another
embodiment, the ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 is at least 1.1, and the product of the ring RDS
ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the total DS is
at least 3.0. In yet another embodiment, the ring RDS ratio for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least 1.3, and the product
of the ring RDS ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times
the total DS is at least 3.2.
[0121] As noted previously, when 2 or more acyl substituents are
present in more equal amounts, it is sometimes desirable to
integrate the carbonyl carbons in order to determine the RDS of
each substituent independently. Hence, in one embodiment of the
present invention, the carbonyl RDS ratio of at least one acyl
substituent for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least 1.3.
In another embodiment, the carbonyl RDS ratio of at least one acyl
substituent for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least 1.5.
In another embodiment, the carbonyl RDS ratio of at least one acyl
substituent for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least
1.7.
[0122] In another embodiment of the present invention, the product
of the carbonyl RDS ratio of at least one acyl substituent for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the DS of the acyl
substituent [(C.sub.6/C.sub.3)*DS.sub.acyl or
(C.sub.6/C.sub.2)*DS.sub.acyl] is at least 2.3. In another
embodiment, the product of the carbonyl RDS ratio for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the DS of the acyl
substituent is at least 2.5. In another embodiment, the product of
the carbonyl RDS ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times
the DS of the acyl substituent is at least 2.7. In another
embodiment of the present invention, the carbonyl RDS ratio of at
least one acyl substituent for C.sub.6/C.sub.3 or C.sub.6/C.sub.2
is at least 1.3, and the product of the carbonyl RDS ratio for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the acyl DS is at least
2.3. In another embodiment, the carbonyl RDS ratio for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at least 1.5, and the product
of the carbonyl RDS ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2
times the acyl DS is at least 2.5. In yet another embodiment, the
carbonyl RDS ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 is at
least 1.7 and the product of the carbonyl RDS ratio for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 times the acyl DS is at least
2.7.
[0123] Surprisingly, in one embodiment of the invention, staged
additions of the acylating reagent gave a relative degree of
substitution (RDS) different from that obtained in the mixed
addition of acylating reagent Moreover, both the staged and mixed
additions of the present invention provide a different RDS relative
to other means known in the prior art for making mixed cellulose
esters which generally provide cellulose esters with a RDS at
C.sub.6, C.sub.3, and C.sub.2 of about 1:1:1. In some cases, the
prior art methods provide a RDS where the RDS at C.sub.6 is less
than that of C.sub.2 and C.sub.3.
[0124] Referring still to FIG. 1, the temperature in esterification
zone 40 during the above-described esterification process can be in
the range of from about 0 to about 120.degree. C., in the range of
from about 20 to about 80.degree. C., or in the range of from 25 to
50.degree. C. Additionally, the cellulose can have a residence time
in esterification zone 40 in the range of from about 1 minute to
about 48 hours, in the range of from about 30 minutes to about 24
hours, or in the range of from 1 to 5 hours.
[0125] Subsequent to the above-described esterification process, an
esterified medium can be withdrawn from esterification zone 40 via
line 80. The esterified medium withdrawn from esterification zone
40 can comprise an initial cellulose ester. The initial cellulose
ester in line 80 can be a regioselectively substituted cellulose
ester. Additionally, as mentioned above, the initial cellulose
ester in line 80 can be a mixed cellulose ester.
[0126] The initial cellulose ester can have a degree of
substitution ("DS") in the range of from about 0.1 to about 3.5;
about 0.1 to about 3.08, about 0.1 to about 3.0, about 1.8 to about
2.9, or in the range of from 2.0 to 2.6. In another embodiment, the
initial cellulose ester can have a DS of at least 2. Additionally,
the initial cellulose ester can have a DS of less than 3.0, or less
than 2.9.
[0127] Furthermore, the degree of polymerization ("DP") of the
cellulose esters prepared by the methods of the present invention
can be at least 10, at least 50, at least 100, or at least 250. In
another embodiment, the DP of the initial cellulose ester can be in
the range of from about 5 to about 1,000, or in the range of from
10 to 250.
[0128] The esterified medium in line 80 can comprise the initial
cellulose ester in an amount in the range of from about 2 to about
80 weight pecent, in the range of from about 10 to about 60 weight
percent, or in the range of from 20 to 40 weight percent based on
weight of ionic liquid. In addition to the initial cellulose ester,
the esterified medium withdrawn from esterification zone 40 via
line 80 can also comprise other components, such as, for example,
altered ionic liquid, residual acylating reagent, and/or one or
more carboxylic acids. In one embodiment, the esterified medium in
line 80 can comprise a ratio of altered ionic liquid to initial
ionic liquid introduced into dissolution zone 20 in an amount in
the range of from about 0.01 to about 99.99 weight percent, in the
range of from about 10 to about 99 weight percent, or in the range
of from 90 to 98 weight percent based on the total amount of
initial ionic liquid. Additionally, the esterified medium in line
80 can comprise residual acylating reagent in an amount less than
about 20 weight percent, less than about 10 weight percent, or less
than 5 weight percent.
[0129] Furthermore, the esterified medium in line 80 can comprise a
total concentration of carboxylic acids in an amount in the range
of from about 0.01 to about 40 weight percent, in the range of from
about 0.05 to about 20 weight percent, or in the range of from 0.1
to 5 weight percent. In another embodiment, the esterified medium
in line 80 can comprise a total concentration of carboxylic acids
in an amount less than 40, less than 20, or less than 5 weight
percent. Carboxylic acids that can be present in the esterified
medium in line 80 include, but are not limited to, formic acid,
acetic acid, propionic acid, butyric acid, isobutyric acid, valeric
acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric
acid, palmitic acid, stearic acid, benzoic acid, substituted
benzoic acids, phthalic acid, and/or isophthalic acid.
[0130] The esterified medium in line 80 can be routed to cellulose
ester recovery/treatment zone 50. As is discussed in more detail
below with reference to FIG. 2, at least a portion of the cellulose
ester can optionally be subjected to at least one randomization
process in recovery/treatment zone 50, thereby producing a
randomized cellulose ester. Additionally, as is discussed in more
detail below with reference to FIG. 2, at least a portion of the
cellulose ester can be caused to precipitate out of the esterified
medium, at least a portion of which can thereafter be separated
from the resulting mother liquor.
[0131] Referring still to FIG. 1, at least a portion of the
cellulose ester precipitated and recovered in recovery/treatment
zone 50 can be withdrawn via line 90 as a final cellulose ester.
The final cellulose ester exiting recovery/treatment zone 50 via
line 90 can have a number average molecular weight ("Mn") in the
range of from about 1,200 to about 200,000, in the range of from
about 6,000 to about 100,000, or in the range of from 10,000 to
75,000. Additionally, the final cellulose ester exiting
recovery/treatment zone 50 via line 90 can have a weight average
molecular weight ("Mw") in the range of from about 2,500 to about
420,000, in the range of from about 10,000 to about 200,000, or in
the range of from 20,000 to 150,000. Furthermore, the final
cellulose ester exiting recovery/treatment zone 50 via line 90 can
have a Z average molecular weight ("Mz") in the range of from about
4,000 to about 850,000, in the range of from about 12,000 to about
420,000, or in the range of from 40,000 to 330,000. The final
cellulose ester exiting recovery/treatment zone 50 via line 90 can
have a polydispersity in the range of from about 1.3 to about 7, in
the range of from about 1.5 to about 5, or in the range of from 1.8
to 3. Additionally, the final cellulose ester in line 90 can have a
DP and DS as described above in relation to the initial cellulose
ester in line 80. Furthermore, the cellulose ester can be random or
non-random, as is discussed in more detail below with reference to
FIG. 2. Moreover, the final cellulose ester in line 90 can comprise
a plurality of ester substituents as described above. Also, the
final cellulose ester in line 90 can optionally be a mixed
cellulose ester as described above.
[0132] In one embodiment, the cellulose ester in line 90 can be in
the form of a wet cake. The wet cake in line 90 can comprise a
total liquid content of less than 99, less than 50, or less than 25
weight percent. Furthermore, the wet cake in line 90 can comprise a
total ionic liquid concentration of less than 1, less than 0.01, or
less than 0.0001 weight percent. Additionally, the wet cake in line
90 can comprise a total alcohol content of less than 100, less than
50, or less than 25 weight percent. Optionally, as is discussed in
greater detail below with reference to FIG. 2, the final cellulose
ester can be dried to produce a dry final cellulose ester
product.
[0133] The cellulose esters prepared by the methods of this
invention can be used in a variety of applications. Those skilled
in the art will understand that the specific application will
depend upon various characteristics of the cellulose ester, such
as, for example, the type of acyl substituent, DS, molecular
weight, and type of cellulose ester copolymer.
[0134] In one embodiment of the invention, the cellulose esters can
be used in thermoplastic applications in which the cellulose ester
is used to make film or molded objects. Examples of cellulose
esters suitable for use in thermoplastic applications include
cellulose acetate, cellulose propionate, cellulose butyrate,
cellulose acetate propionate, cellulose acetate butyrate, or
mixtures thereof.
[0135] In yet another embodiment of the invention, the cellulose
esters can be used in coating applications. Examples of coating
applications include but, are not limited to, automotive, wood,
plastic, or metal coating processes. Examples of cellulose esters
suitable for use in coating applications include cellulose acetate,
cellulose propionate, cellulose butyrate, cellulose acetate
propionate, cellulose acetate butyrate, or mixtures thereof.
[0136] In still another embodiment of the invention, the cellulose
esters can be used in personal care applications. In personal care
applications, cellulose esters can be dissolved or suspended in
appropriate solvents. The cellulose ester can then act as a
structuring agent, delivery agent, and/or film forming agent when
applied to skin or hair. Examples of cellulose esters suitable for
use in personal care applications include cellulose acetate,
cellulose propionate, cellulose butyrate, cellulose acetate
propionate, cellulose acetate butyrate, cellulose hexanoate,
cellulose 2-ethylhexanoate, cellulose laurate, cellulose palmitate,
cellulose stearate, or mixtures thereof.
[0137] In still another embodiment of the invention, the cellulose
esters can be used in drug delivery applications. In drug delivery
applications, the cellulose ester can act as a film former such as
in the coating of tablets or particles. The cellulose ester can
also be used to form amorphous mixtures of poorly soluble drugs,
thereby improving the solubility and bioavailability of the drugs.
The cellulose esters can also be used in controlled drug delivery,
where the drug can be released from the cellulose ester matrix in
response to external stimuli such as a change in pH. Examples of
preferred cellulose esters suitable for use in drug delivery
applications include cellulose acetate, cellulose propionate,
cellulose butyrate, cellulose acetate propionate, cellulose acetate
butyrate, cellulose acetate phthalate, or mixtures thereof.
[0138] In still another embodiment of the invention, the cellulose
esters of the present invention can be used in applications
involving solvent casting of film. Examples of such applications
include photographic film, protective film, and compensation film
for liquid crystalline displays. Examples of cellulose esters
suitable for use in solvent cast film applications include, but are
not limited to, cellulose triacetate, cellulose acetate, cellulose
propionate, and cellulose acetate propionate.
[0139] In an embodiment of the invention, films are produced
comprising cellulose esters of the present invention and are used
as protective and compensation films for liquid crystalline
displays (LCD). These films can be prepared by solvent casting as
described in US application 2009/0096962 or by melt extrusion as
described in US application 2009/0050842, both of which are
incorporated in their entirety in this invention to the extent they
do not contradict the statements herein.
[0140] When used as a protective film, the film is typically
laminated to either side of an oriented, iodinated polyvinyl
alcohol (PVOH) polarizing film to protect the PVOH layer from
scratching and moisture, while also increasing structural rigidity.
When used as compensation films (or plates), they can be laminated
with the polarizer stack or otherwise included between the
polarizer and liquid crystal layers. These compensation films can
improve the contrast ratio, wide viewing angle, and color shift
performance of the LCD. The reason for this important function is
that for a typical set of crossed polarizers used in an LCD, there
is significant light leakage along the diagonals (leading to poor
contrast ratio), particularly as the viewing angle is increased. It
is known that various combinations of optical films can be used to
correct or "compensate" for this light leakage. These compensation
films must have certain well-defined retardation (or birefringence)
values, which vary depending on the type of liquid crystal cell or
mode used because the liquid crystal cell itself will also impart a
certain degree of undesirable optical retardation that must be
corrected.
[0141] Compensation films are commonly quantified in terms of
birefringence, which is, in turn, related to the refractive index
n. For cellulose esters, the refractive index is approximately 1.46
to 1.50. For an unoriented isotropic material, the refractive index
will be the same regardless of the polarization state of the
entering light wave. As the material becomes oriented, or otherwise
anisotropic, the refractive index becomes dependent on material
direction. For purposes of the present invention, there are three
refractive indices of importance denoted n.sub.x, n.sub.y, and
n.sub.z, which correspond to the machine direction (MD), the
transverse direction (TD), and the thickness direction,
respectively. As the material becomes more anisotropic (e.g. by
stretching), the difference between any two refractive indices will
increase. This difference in refractive index is referred to as the
birefringence of the material for that particular combination of
refractive indices. Because there are many combinations of material
directions to choose from, there are correspondingly different
values of birefringence. The two most common birefringence
parameters are the planar birefringence defined as
.DELTA..sub.e=n.sub.x-n.sub.y, and the thickness birefringence
(.DELTA..sub.th) defined as:
.DELTA..sub.th=n.sub.z-(n.sub.x+n.sub.y)/2. The birefringence
.DELTA..sub.e is a measure of the relative in-plane orientation
between the MD and TD and is dimensionless. In contrast,
.DELTA..sub.th gives a measure of the orientation of the thickness
direction, relative to the average planar orientation.
[0142] Optical retardation (R) is related the birefringence by the
thickness (d) of the film:
R.sub.e=.DELTA..sub.ed=(n.sub.x-n.sub.y)d;
R.sub.th=.DELTA..sub.thd=[n.sub.z-(n.sub.x+n.sub.y)/2]. Retardation
is a direct measure of the relative phase shift between the two
orthogonal optical waves and is typically reported in units of
nanometers (nm). Note that the definition of R.sub.th varies with
some authors, particularly with regards to the sign (.+-.).
[0143] Compensation films or plates can take many forms depending
upon the mode in which the LCD display device operates. For
example, a C-plate compensation film is isotropic in the x-y plane,
and the plate can be positive (+C) or negative (-C). In the case of
+C plates, n.sub.x=n.sub.y<n.sub.z. In the case of -C plates,
n.sub.x=n.sub.y>n.sub.z. Another example is A-plate compensation
film which is isotropic in the y-z direction, and again, the plate
can be positive (+A) or negative (-A). In the case of +A plates,
n.sub.x>n.sub.y=n.sub.z. In the case of -A plates,
n.sub.x<n.sub.y=n.sub.z.
[0144] In general, aliphatic cellulose esters provide values of
R.sub.th ranging from about 0 to about -350 nm at a film thickness
of 60 .mu.m. The most important factors that influence the observed
R.sub.th is type of substituent and the degree of substitution of
hydroxyl (DS.sub.OH). Film produced using cellulose mixed esters
with very low DS.sub.OH in Shelby et al. (US 2009/0050842) had
R.sub.th values ranging from about 0 to about -50 nm. By
significantly increasing DS.sub.OH of the cellulose mixed ester,
Shelton et al. (US 2009/0096962) demonstrated that larger absolute
values of R.sub.th ranging from about -100 to about -350 nm could
be obtained. Cellulose acetates typically provide R.sub.th values
ranging from about -40 to about -90 nm depending upon
DS.sub.OH.
[0145] One aspect of the present invention relates to compensation
film comprising regioselectively substituted cellulose esters
wherein the compensation film has an R.sub.th range from about -400
to about +100 nm. In another embodiment of the invention,
compensation films are provided comprising regioselectively
substituted cellulose esters having a total DS from about 1.5 to
about 2.95 of a single acyl substituent (DS.ltoreq.0.2 of a second
acyl substituent) and wherein the compensation film has an R.sub.th
value from about -400 to about +100 nm.
[0146] In one embodiment of the invention, the regioselectively
substituted cellulose esters utilized for producing films are
selected from the group consisting of cellulose acetate, cellulose
propionate, and cellulose butyrate wherein the regioselectively
substituted cellulose ester has a total DS from about 1.6 to about
2.9. In another embodiment of the invention, the compensation film
has R.sub.th values from about -380 to about -110 nm and is
comprised of a regioselectively substituted cellulose propionate
having a total DS of about 1.7 to about 2.5. In yet another
embodiment, the compensation film has R.sub.th values from about
-380 to about -110 nm and is comprised of a regioselectively
substituted cellulose propionate having a total DS of about 1.7 to
about 2.5 and a ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 of at least 1.05. In another embodiment, the
compensation film has R.sub.th values from about -60 to about +100
nm and is comprised of regioselectively substituted cellulose
propionate having a total DS of about 2.6 to about 2.9. In yet
another embodiment, the compensation film has R.sub.th values from
about -60 to about +100 nm and is comprised of regioselectively
substituted cellulose propionate having a total DS of about 2.6 to
about 2.9 and a ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 of at least 1.05. In another embodiment, the
compensation film has R.sub.th values from about 0 to about +100 nm
and is comprised of a regioselectively substituted cellulose
propionate having a total DS of about 2.75 to about 2.9. In yet
another embodiment, the compensation film has R.sub.th values from
about 0 to about +100 nm and is comprised of a regioselectively
substituted cellulose propionate having a total DS of about 2.75 to
about 2.9 and a ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 of at least 1.05.
[0147] Another aspect of the present invention relates to
compensation film with an R.sub.th range from about -160 to about
+270 nm comprised of regioselectively substituted cellulose esters
having a total DS from about 1.5 to about 3.0 of a plurality of 2
or more acyl substituents. In one embodiment of this invention, the
cellulose esters can be selected from the group consisting of
cellulose acetate propionate, cellulose acetate butyrate, cellulose
benzoate propionate, and cellulose benzoate butyrate; wherein the
regioselectively substituted cellulose ester has a total DS from
about 2.0 to about 3.0. In another embodiment, the compensation
film has R.sub.th values from about -160 to about 0 nm and is
comprised of a regioselectively substituted cellulose acetate
propionate having a total DS of about 2.0 to about 3.0, a ring RDS
ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 of at least 1.05, and
a carbonyl RDS ratio for at least one acyl substituent for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 of at least about 1.3. In
another embodiment, the compensation film has R.sub.th values from
about +100 to about +270 nm and is comprised of a regioselectively
substituted cellulose benzoate propionate having a total DS of
about 2.0 to about 3.0, a ring RDS ratio for C.sub.6/C.sub.3 or
C.sub.6/C.sub.2 of at least 1.05, and a carbonyl RDS ratio for at
least one acyl substituent for C.sub.6/C.sub.3 or C.sub.6/C.sub.2
of at least about 1.3. In another embodiment, the compensation film
has R.sub.th values from about +100 to about +270 nm and is
comprised of a regioselectively substituted cellulose benzoate
propionate having a total DS of about 2.0 to about 3.0, a ring RDS
ratio for C.sub.6/C.sub.3 or C.sub.6/C.sub.2 of at least 1.05, a
carbonyl RDS ratio for at least one acyl substituent for
C.sub.6/C.sub.3 or C.sub.6/C.sub.2 of at least about 1.3, and the
benzoate substituent is located primarily at C2 or C3.
[0148] Referring still to FIG. 1, at least a portion of the mother
liquor produced in cellulose ester recovery/treatment zone 50 can
be withdrawn via line 86 and routed to ionic liquid
recovery/treatment zone 60. As will be discussed in further detail
below with reference to FIG. 2, the mother liquor can undergo
various treatments in ionic liquid recovery/treatment zone 60. Such
treatment can include, but is not limited to, volatiles removal and
reformation of the ionic liquid. Reformation of the ionic liquid
can include, but is not limited to, (1) anion homogenization, and
(2) anion exchange. Accordingly, a recycled ionic liquid can be
formed in ionic liquid recovery/treatment zone 60.
[0149] In one embodiment, at least a portion of the recycled ionic
liquid can be withdrawn from ionic liquid recovery/treatment zone
60 via line 70. The recycled ionic liquid in line 70 can have a
composition such as described above in relation to the ionic liquid
in line 64 of FIG. 1. The production and composition of the
recycled ionic liquid will be discussed in greater detail below
with reference to FIG. 2. As mentioned above, at least a portion of
the recycled ionic liquid in line 70 can be routed back to
dissolution zone 20. In one embodiment, at least about 80 weight
percent, at least about 90 weight percent, or at least 95 weight
percent of the recycled ionic liquid produced in ionic liquid
recovery/treatment zone 60 can be routed to dissolution zone
20.
[0150] Referring now to FIG. 2, a more detailed diagram for the
production of cellulose esters is depicted, including optional
steps for improving the overall efficacy and/or efficiency of the
esterification process. In the embodiment depicted in FIG. 2, a
cellulose can be introduced into an optional modification zone 110
via line 162. The cellulose fed to optional modification zone 110
can be substantially the same as the cellulose in line 62 described
above with reference to FIG. 1. In optional modification zone 110,
the cellulose can be modified employing at least one modifying
agent.
[0151] As mentioned above, water may be employed as the modifying
agent. Thus, in one embodiment of the present invention, a
water-wet cellulose can be withdrawn from optional modification
zone 110 and added to one or more ionic liquids in dissolution zone
120. In one embodiment, the cellulose can be mixed with water then
pumped into one or more ionic liquids as a slurry. Alternatively,
excess water can be removed from the cellulose, and thereafter the
cellulose can be added to the one or more ionic liquids in the form
of a wet cake. In this embodiment, the cellulose wet cake can
contain associated water in an amount in the range of from about 10
to about 95 weight percent, in the range of from about 20 to about
80 weight percent, in the range of from 25 to 75 weight percent,
based on the combined weight of the cellulose and associated
water.
[0152] Though not wishing to be bound by theory, the addition of
water wet cellulose has unexpectedly and unpredictably been found
to provide at least three heretofore unknown benefits. First, water
can increase dispersion of the cellulose in the one or more ionic
liquids so that when removal of water is initiated while heating
the cellulose, the cellulose rapidly dissolves in the one or more
ionic liquids. Secondly, water appears to reduce the melting points
of ionic liquids that are normally solids at room temperature, thus
allowing processing of ionic liquids at ambient temperatures. A
third benefit is that the molecular weight of cellulose esters
prepared using initially water wet cellulose is reduced during the
above-discussed esterification in esterification zone 40 when
compared to cellulose esters prepared using initially dry
cellulose.
[0153] This third benefit is particularly surprising and useful.
Under typical cellulose ester processing conditions, the molecular
weight of cellulose is not reduced during dissolution or during
esterification. That is, the molecular weight of the cellulose
ester product is directly proportionate to the molecular weight of
the initial cellulose. Typical wood pulps used to prepare cellulose
esters generally have a DP in the range of from about 1,000 to
about 3,000. However, the desired DP range of cellulose esters can
be from about 10 to about 500. Thus, in the absence of molecular
weight reduction during esterification, the cellulose must be
specially treated prior to dissolving the cellulose in the ionic
liquid or after dissolving in the ionic liquid but prior to
esterification. However, when employing water as at least one of
the optional modifying agents, pretreatment of the cellulose is not
required since molecular weight reduction can occur during
esterification. Accordingly, in one embodiment of the present
invention, the DP of the modified cellulose subjected to
esterification can be within about 10 percent of, within about 5
percent of, within 2 percent of, or substantially the same as the
DP of the initial cellulose subjected to modification. However, the
DP of the cellulose ester produced in accordance with embodiments
of the present invention can be less than about 90 percent, less
than about 70 percent, or less than 50 percent of the DP of the
modified cellulose subjected to esterification.
[0154] Referring still to FIG. 2, the optionally modified cellulose
in line 166 can be introduced into dissolution zone 120. Once in
dissolution zone 120, the optionally modified cellulose can be
dispersed in one or more ionic liquids, as described above with
reference to dissolution zone 20 in FIG. 1. Subsequently, at least
a portion of the modifying agent in the resulting cellulose/ionic
liquid mixture can be removed. In one embodiment, at least 50
weight percent of all modifying agents can be removed, at least 75
weight percent of all modifying agents can be removed, at least 95
weight percent of all modifying agents can be removed, or at least
99 weight percent of all modifying agents can be removed from the
cellulose/ionic liquid mixture. Removal of one or more modifying
agents in dissolution zone 120 can be accomplished by any means
known in the art for liquid/liquid separation, such as, for
example, distillation, flash vaporization, and the like. Removed
modifying agent can be withdrawn from dissolution zone 120 via line
124.
[0155] After removal of the modifying agent, dissolution zone 120
can produce a cellulose solution in substantially the same manner
as dissolution zone 20, as described above with reference to FIG.
1. Thereafter, a cellulose solution can be withdrawn from
dissolution zone 120 via line 176. The cellulose solution in line
176 can comprise ionic liquid, cellulose, and a residual
concentration of one or more optional modifying agents. The
cellulose solution in line 176 can comprise cellulose in an amount
in the range of from about 1 to about 40 weight percent, in the
range of from about 5 to about 30 weight percent, or in the range
of from 10 to 20 weight percent, based on the weight of the ionic
liquid. Furthermore, the cellulose solution in line 176 can
comprise a cumulative amount of residual modifying agents in an
amount of less than about 50 weight percent, less than about 25
weight percent, less than about 15 weight percent, less than about
5 weight percent, or less than 1 weight percent.
[0156] In the embodiment of FIG. 2, at least a portion of the
cellulose solution in line 176 can be introduced into
esterification zone 140. Esterification zone 140 can be operated in
substantially the same manner as esterification zone 40, as
described above with reference to FIG. 1. For example, an acylating
reagent can be introduced into esterification zone 140 via line
178. As in esterification zone 40, the acylating reagent can
esterify at least a portion of the cellulose in esterification zone
140. Additionally, as described above, at least a portion of the
resulting cellulose ester can comprise one or more ester
substituents that originated from and or were donated by the ionic
liquid.
[0157] After esterification in esterification zone 140, an
esterified medium can be withdrawn via line 180. The esterified
medium in line 180 can be substantially the same as the esterified
medium in line 80, as described above with reference to FIG. 1.
Thus, the esterified medium in line 180 can comprise an initial
cellulose ester and other components, such as, for example, altered
ionic liquid, residual acylating reagent, one or more carboxylic
acids, and/or one or more catalysts. The concentrations of the
initial cellulose ester and other components in the esterified
medium in line 180 can be substantially the same as the esterified
medium in line 80 described above with reference to FIG. 1.
[0158] Referring still to FIG. 2, as mentioned above, the initial
cellulose ester produced in esterification zone 140 can be a
non-random cellulose ester. In one embodiment, at least a portion
of the initial cellulose in line 180 can optionally be introduced
into randomization zone 151 to undergo randomization, thereby
creating a random cellulose ester. Randomization of the initial
cellulose can comprise introducing at least one randomizing agent
into randomization zone 151 via line 181. Additionally, as will be
discussed in further detail below, at least a portion of the
randomization agent introduced into randomization zone 151 can be
introduced via line 194.
[0159] The randomization agent employed in the present invention
can be any substance capable lowering the DS of the cellulose ester
via hydrolysis or alcoholysis, and/or by causing migration of at
least a portion of the acyl groups on the cellulose ester from one
hydroxyl to a different hydroxyl, thereby altering the initial
monomer distribution. Examples of suitable randomizing agents
include, but are not limited to water and/or alcohols. Alcohols
suitable for use as the randomizing agent include, but are not
limited to methanol, ethanol, n-propanol, i-propanol, n-butanol,
i-butanol, t-butanol, phenol and the like. In one embodiment,
methanol can be employed as the randomizing agent introduced via
line 181.
[0160] The amount of randomizing agent introduced into
randomization zone 151 can be in the range of from about 0.5 to
about 20 weight percent, or in the range of from 3 to 10 weight
percent, based on the total weight of the resulting randomization
medium in randomization zone 151. The randomization medium can have
any residence time in randomization zone 151 suitable to achieve
the desired level of randomization. In one embodiment, the
randomization medium can have a residence time in randomization
zone 151 in the range of from about 1 min. to about 48 hours, in
the range of from about 30 min. to about 24 hours, or in the range
of from 2 to 12 hours. Additionally, the temperature in
randomization zone 151 during randomization can be any temperature
suitable to achieve the desired level of randomization. In one
embodiment, the temperature in randomization zone 151 during
randomization can be in the range of from about 20 to about
120.degree. C., in the range of from about 30 to about 100.degree.
C., or in the range of from 50 to 80.degree. C.
[0161] Those skilled in the art will understand that the DS and DP
of the cellulose ester random copolymer might be less than that of
the cellulose ester non-random copolymer. Accordingly, in this
embodiment the non-random cellulose ester entering randomization
zone 151 may optionally have a greater DS and/or DP than the target
DS and/or DP of the randomized cellulose ester.
[0162] In one embodiment of the present invention, it may be
desirable to produce cellulose esters that are at least partially
soluble in acetone. Accordingly, the initial cellulose ester
produced in esterification zone 140 can bypass optional
randomization zone 151, thereby producing a final non-random
cellulose ester. Non-random cellulose esters prepared by the
methods of the present invention can be at least partially soluble
in acetone when they have a DS in the range of from about 2.1 to
about 2.4, in the range of from about 2.28 to about 2.39 or in the
range of from 2.32 to 2.37.
[0163] After optional randomization, an optionally randomized
medium can be withdrawn from randomization zone 151 via line 182.
The optionally randomized medium can comprise randomized cellulose
ester and residual randomizing agent. In one embodiment, the
optionally randomized medium in line 182 can comprise randomized
cellulose ester in an amount in the range of from about 2 to about
80 weight percent, in the range of from about 10 to about 60 weight
percent, or in the range of from 20 to 40 weight percent based on
the weight of the ionic liquid. Additionally, the optionally
randomized medium can comprise residual randomizing agent in the
range of from about 0.5 to about 20 weight percent, or in the range
of from 3 to 10 weight percent, based on the total weight of the
resulting randomized medium.
[0164] Additionally, the optionally randomized medium in line 182
can comprise other components, such as those described above with
reference to the esterified medium in line 180 and with reference
to the esterified medium in line 80 of FIG. 1. Such components
include, but are not limited to, altered ionic liquid, residual
acylating reagent, one or more carboxylic acids, and/or one or more
catalysts.
[0165] Following optional randomization, at least a portion of the
esterified and optionally randomized medium in line 182 can be
introduced into precipitation zone 152. Precipitation zone 152 can
operate to cause at least a portion of the cellulose ester from the
esterified and optionally randomized medium to precipitate. Any
methods known in the art suitable for precipitating a cellulose
ester can be employed in precipitation zone 152. In one embodiment,
a precipitating agent can be introduced into precipitation zone
152, thereby causing at least a portion of the cellulose ester to
precipitate. In one embodiment, the precipitating agent can be a
non-solvent for the cellulose ester. Examples of suitable
non-solvents that can be employed as the precipitating agent
include, but are not limited to, C.sub.1 to C.sub.8 alcohols,
water, or a mixture thereof. In one embodiment, the precipitating
agent introduced into precipitation zone 152 can comprise
methanol.
[0166] The amount of precipitating agent introduced into
precipitation zone 152 can be any amount sufficient to cause at
least a portion of the cellulose ester to precipitate. In one
embodiment, the amount of precipitating agent introduced into
precipitation zone 152 can be at least about 20 volumes, at least
10 volumes, or at least 4 volumes, based on the total volume of the
medium entering precipitation zone 152. The resulting precipitation
medium can have any residence time in precipitation zone 152
suitable to achieve the desired level of precipitation. In one
embodiment, the precipitation medium can have a residence time in
precipitation zone 152 in the range of from about 1 to about 300
min., in the range of from about 10 to about 200 min., or in the
range of from 20 to 100 min. Additionally, the temperature in
precipitation zone 152 during precipitation can be any temperature
suitable to achieve the desired level of precipitation. In one
embodiment, the temperature in precipitation zone 152 during
precipitation can be in the range of from about 0 to about
120.degree. C., in the range of from about 20 to about 100.degree.
C., or in the range of from 25 to 50.degree. C. The amount of
cellulose ester precipitated in precipitation zone 152 can be at
least 50 weight percent, at least 75 weight percent, or at least 95
weight percent, based on the total amount of cellulose ester in
precipitation zone 152.
[0167] After precipitation in precipitation zone 152, a cellulose
ester slurry can be withdrawn via line 184 comprising a final
cellulose ester. The cellulose ester slurry in line 184 can have a
solids content of less than about 50 weight percent, less than
about 25 weight percent, or less than 1 weight percent.
[0168] At least a portion of the cellulose ester slurry in line 184
can be introduced into separation zone 153. In separation zone 153,
at least a portion of the liquid content of the cellulose ester
slurry can be separated from the solids portion. Any solid/liquid
separation technique known in the art for separating at least a
portion of a liquid from a slurry can be used in separation zone
153. Examples of suitable solid/liquid separation techniques
suitable for use in the present invention include, but are not
limited to, centrifugation, filtration, and the like. In one
embodiment, at least 50 weight percent, at least 70 weight percent,
or at least 90 weight percent of the liquid portion of the
cellulose ester slurry can be removed in separation zone 153.
[0169] Furthermore, separation zone 153 can have any temperature or
pressure suitable for solid liquid separation. In one embodiment,
the temperature in separation zone 153 during separation can be in
the range of from about 0 to about 120.degree. C., in the range of
from about 20 to about 100.degree. C., or in the range of from 25
to 50.degree. C.
[0170] After separation in separation zone 153, a cellulose ester
wet cake can be withdrawn from separation zone 153 via line 187.
The cellulose ester wet cake in line 187 can have a total solids
content of at least 1 weight percent, at least 50 weight percent,
or at least 75 weight percent. Additionally, the cellulose ester
wet cake in line 187 can comprise cellulose ester in an amount of
at least 70 weight percent, at least 80 weight percent, or at least
90 weight percent. Additionally, as will be discussed in greater
detail below, at least a portion of the separated liquids from
separation zone 153 can be withdrawn via line 186.
[0171] Once removed from separation zone 153, at least a portion of
the cellulose ester solids from the cellulose ester wet cake can be
washed in wash zone 154. Any method known in the art suitable for
washing a wet cake can be employed in wash zone 154. An example of
a washing technique suitable for use in the present invention
includes, but is not limited to, a multi-stage counter-current
wash. In one embodiment, a wash liquid that is a non-solvent for
cellulose ester can be introduced into wash zone 154 via line 188
to wash at least a portion of the cellulose ester solids. Such wash
liquids include, but are not limited to, a C.sub.1 to C.sub.8
alcohol, water, or a mixture thereof. In one embodiment, the wash
liquid can comprise methanol. Additionally, as will be described in
greater detail below, at least a portion of the wash liquid can be
introduced into wash zone 154 via line 194.
[0172] In one embodiment, washing of the cellulose ester solids in
wash zone 153 can be performed in such a manner that at least a
portion of any undesired by-products and/or color bodies are
removed from the cellulose ester solids and/or ionic liquid. In one
embodiment, the non-solvent wash liquid can contain a bleaching
agent in the range of from about 0.001 to about 50 weight percent,
or in the range of from 0.01 to 5 weight percent based on the total
weight of the wash fluid. Examples of bleaching agents suitable for
use in the present invention include, but are not limited to,
chlorites, such as sodium chlorite (NaClO.sub.2); hypohalites, such
as NaOCl, NaOBr and the like; peroxides, such as hydrogen peroxide
and the like; peracids, such as peracetic acid and the like;
metals, such as Fe, Mn, Cu, Cr and the like; sodium sulfites, such
as sodium sulfite (Na.sub.2SO.sub.3), sodium metabisulfite
(Na.sub.2S.sub.2O.sub.5), sodium bisulfite (NaHSO.sub.3) and the
like; perborates, such as sodium perborate (NaBO.sub.3.nH.sub.2O
where n=1 or 4); chlorine dioxide (ClOC.sub.2); oxygen; and ozone.
In one embodiment, the bleaching agent employed in the present
invention can include hydrogen peroxide, NaOCl, sodium chlorite
and/or sodium sulfite. Washing in wash zone 153 can be sufficient
to remove at least 50, at least 70, or at least 90 percent of the
total amount of byproducts and/or color bodies.
[0173] After washing in wash zone 154, a washed cellulose ester
product can be withdrawn via line 189. The washed cellulose ester
product in line 189 can be in the form of a wet cake, and can
comprise solids in an amount of at least 1, at least 50, or at
least 75 weight percent. Additionally, the washed cellulose ester
product in line 189 can comprise cellulose ester in an amount of at
least 1, at least 50, or at least 75 weight percent.
[0174] The washed cellulose ester product can optionally be dried
in drying zone 155. Drying zone 155 can employ any drying methods
known in the art to remove at least a portion of the liquid content
of the washed cellulose ester product. Examples of drying equipment
suitable for use in drying zone 155 include, but are not limited
to, rotary dryers, screw-type dryers, paddle dryers, and/or
jacketed dryers. In one embodiment, drying in drying zone 155 can
be sufficient to produce a dried cellulose ester product comprising
less than 5, less than 3, or less than 1 weight percent
liquids.
[0175] After drying in drying zone 155, a final cellulose ester
product can be withdrawn via line 190. The final cellulose ester
product in line 190 can be substantially the same as the final
cellulose ester product in line 90, as described above with
reference to FIG. 1.
[0176] Referring still to FIG. 2, as mentioned above at least a
portion of the separated liquids generated in separation zone 153
can be withdrawn via line 186 as a recycle stream. The recycle
stream in line 186 can comprise altered ionic liquid, one or more
carboxylic acids, residual modifying agent, residual catalyst,
residual acylating reagent, residual randomizing agent, and/or
residual precipitation agent. As used herein, the term "altered
ionic liquid" refers to an ionic liquid that has previously passed
through a cellulose esterification step wherein at least a portion
of the ionic liquid acted as acyl group donor and/or recipient. As
used herein, the term "modified ionic liquid" refers to an ionic
liquid that has previously been contacted with another compound in
an upstream process step. Therefore, altered ionic liquids are a
subset of modified ionic liquids, where the upstream process step
is cellulose esterification.
[0177] In one embodiment, the recycle stream in line 186 can
comprise altered ionic liquid, one or more carboxylic acids, one or
more alcohols, and/or water. In one embodiment, the recycle stream
in line 186 can comprise altered ionic liquid in an amount in the
range of from about 10 to about 99.99 weight percent, in the range
of from about 50 to about 99 weight percent, or in the range of
from 90 to 98 weight percent, based on the total weight of the
recycle stream in line 186. In one embodiment, the altered ionic
liquid can comprise an ionic liquid having at least two different
anions: primary anions and secondary anions. At least a portion of
the primary anions in the altered ionic liquid originate from the
initial ionic liquid introduced into dissolution zone 120 via line
164, as described above. Additionally, at least a portion of the
secondary anions in the altered ionic liquid originate from the
acylating reagent introduced into esterification zone 140, as
described above. In one embodiment, the altered ionic liquid can
comprise primary anions and secondary anions in a ratio in the
range of from about 100:1 to about 1:100, in the range of from
about 1:10 to about 10:1, or in the range of from 1:2 to about 2:1.
Additionally, the altered ionic liquid can comprise a plurality of
cations, such as those described above with reference to the
initial ionic liquid in line 68 of FIG. 1.
[0178] The recycle stream in line 186 can comprise a total amount
of carboxylic acids in an amount in the range of from about 5 to
about 60 weight percent, in the range of from about 10 to about 40
weight percent, or in the range of from 15 to 30 weight percent
based on the total weight of ionic liquid in the recycle stream in
line 186. Examples of suitable carboxylic acids the recycle stream
in line 186 can comprise include, but are not limited to, acetic
acid, propionic acid, butyric acid, isobutyric acid, valeric acid,
hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid,
palmitic acid, stearic acid, benzoic acid, substituted benzoic
acids, phthalic acid, and isophthalic acid. In one embodiment, at
least 50 weight percent, at least 70 weight percent, or at least 90
weight percent of the carboxylic acids in the recycle stream in
line 186 are acetic, propionic, and/or butyric acids.
[0179] Furthermore, the recycle stream in line 186 can comprise a
total concentration of alcohols in an amount of at least 20
volumes, at least 10 volumes, or at least 4 volumes, based on the
total volume of the recycle stream. Examples of suitable alcohols
the recycle stream in line 186 can comprise include, but are not
limited to, C.sub.1 to C.sub.8 straight- or branched-chain
alcohols. In one embodiment, at least 50 weight percent, at least
70 weight percent, or at least 90 weight percent of the alcohol in
the separated ionic liquids in line 186 comprises methanol.
Moreover, the recycle stream in line 186 can comprise water in an
amount of at least 20 volumes, at least 10 volumes, or at least 4
volumes, based on the total volume of the recycle stream.
[0180] As depicted in FIG. 2, at least a portion of the recycle
stream in line 186 can be introduced into ionic liquid
recovery/treatment zone 160. Ionic liquid recovery/treatment zone
160 can operate to segregate and/or reform at least a portion of
the recycle stream from line 186. In one embodiment, at least a
portion of the recycle stream can undergo at least one flash
vaporization and/or distillation process to remove at least a
portion of the volatile components in the recycle stream. At least
40 weight percent, at least 75 weight percent, or at least 95
weight percent of the volatile components in the recycle stream can
be removed via flash vaporization. The volatile components removed
from the recycle stream can comprise one or more alcohols. In one
embodiment, the volatile components can comprise methanol. After
vaporization, the resulting volatiles-depleted recycle stream can
comprise a total amount of alcohols in the range of from about 0.1
to about 60 weight percent, in the range of from about 5 to about
55 weight percent, or in the range of from 15 to 50 weight
percent.
[0181] In one embodiment, at least a portion of the carboxylic
acids can be removed from the recycle stream. This can be
accomplished by first converting at least a portion of the
carboxylic acids to carboxylate esters. In this embodiment, at
least a portion of the recycle stream can be placed into a
pressurized reactor where the recycle stream can be treated at a
temperature, pressure, and time sufficient to convert the at least
a portion of the carboxylic acid to methyl esters, by reacting the
carboxylic acids with the alcohol present in the recycle stream.
During the esterification, the pressurized reactor can have a
temperature in the range of from 100 to 180.degree. C., or in the
range of from 130 to 160.degree. C. Additionally, the pressure in
the pressurized reactor during esterification can be in the range
of from about 10 to about 1,000 pounds per square inch gauge
("psig"), or in the range of from 100 to 300 psig. The recycle
stream can have a residence time in the pressurized reactor in the
range of from about 10 to about 1,000 minutes, or in the range of
from 120 to 600 minutes. Prior to the above-described
esterification, the alcohol and carboxylic acid can be present in
the recycle stream in a molar ratio in the range of from about 1:1
to about 30:1, in the range of from about 3:1 to about 20:1, or in
the range of from 5:1 to 10:1 alcohol-to-carboxylic acid. In one
embodiment, at least 5, at least 20, or at least 50 mole percent of
the carboxylic acids can be esterified during the above-described
esterification.
[0182] As mentioned above, at least a portion of the carboxylic
acids can be acetic, propionic, and/or butyric acids. Additionally,
as mentioned above, the alcohol present in the recycle stream can
be methanol. Accordingly, the above-described esterification
process can operate to produce methyl acetate, methyl propionate,
and/or methyl butyrate. Subsequent to esterification, at least 10,
at least 50, or at least 95 weight percent of the resulting
carboxylate esters can be removed from the recycle stream by any
methods known in the art. As depicted in FIG. 2, at least a portion
of the carboxylate esters produced by the above described
esterification can be routed to esterification zone 140 via line
196. Carboxylate esters introduced into esterification zone 140 can
be employed as immiscible cosolvents, as described above. In
another embodiment, at least a portion of the carboxylate esters
can be converted to anhydrides by CO insertion.
[0183] In another embodiment of the present invention, at least a
portion of the altered ionic liquid present in the recycle stream
can undergo reformation. Reformation of the altered ionic liquid
can optionally be performed simultaneously with the esterification
of the carboxylic acids in the recycle stream. Alternatively,
reformation of the altered ionic liquid can be performed
subsequently to the esterification of the carboxylic acids in the
recycle stream. Reformation of the altered ionic liquid can
comprise at least one anion exchange process.
[0184] In one embodiment, reformation of the altered ionic liquid
can comprise anion homogenization via anion exchange, such that
substantially all of the anions of the altered ionic liquid are
converted to the same type of anion. In this embodiment, at least a
portion of the altered ionic liquid can be contacted with at least
one alkyl formate. Alkyl formates suitable for use in the present
invention include, but are not limited to, methyl formate, ethyl
formate, propyl formate, isopropyl formate, butyl formate, isobutyl
formate, tert-butyl formate, hexyl formate, octyl formate, and the
like. In one embodiment, the alkyl formate can comprise methyl
formate. Additionally, reformation of the altered ionic liquid can
be performed in the presence of one or more alcohols. Alcohols
suitable for use in this embodiment of the invention include, but
are not limited to, alkyl or aryl alcohols such as methanol,
ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol,
phenol and the like. In one embodiment, the alcohol present during
reformation can comprise methanol.
[0185] The temperature during reformation of the altered ionic
liquid can be in the range of from about 100 to about 200.degree.
C., or in the range of from 130 to about 170.degree. C.
Additionally, the pressure during reformation of the altered ionic
liquid can be at least 700 kPa, or at least 1,025 kPa. Furthermore,
the reaction time of the reformation of the altered ionic liquid
can be in the range of from about 10 min. to about 24 hours, or in
the range of from 3 to 18 hours.
[0186] As mentioned above, reformation of the altered ionic liquid
can comprise anion homogenization. In one embodiment, the resulting
reformed ionic liquid can have an at least 90, at least 95, or at
least 99 percent uniform anion content. Additionally, the reformed
ionic liquid can comprise an alkyl amine formate. In one
embodiment, the amine of the alkyl amine formate can be an
imidazolium. Examples of alkyl amine formates suitable for use as
the reformed ionic liquid include, but are not limited to,
1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium
formate, 1-propyl-3-methylimidazolium formate,
1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium
formate, and/or 1-octyl-3-methylimidazolium formate.
[0187] Following reformation, at least a portion of the volatile
components of the reformed ionic liquid can optionally be removed
via any methods known in the art for removing volatile components.
Volatile components removed from the reformed ionic liquid can
include, for example, carboxylate esters, such as those formed via
the above described carboxylic acid esterification process.
Thereafter, at least a portion of the reformed ionic liquid can
undergo at least one anion exchange process to replace at least a
portion of the anions of the reformed ionic liquid thereby forming
a carboxylated ionic liquid. In one embodiment, the reformed ionic
liquid can be contacted with at least one carboxylate anion donor
to at least partially effect the anion exchange. Carboxylate anion
donors suitable for use in this embodiment include, but are not
limited to, one or more carboxylic acids, anhydrides, or alkyl
carboxylates. Additionally, the carboxylate anion donors can
comprise one or more C.sub.2 to C.sub.20 straight- or
branched-chain alkyl or aryl carboxylic acids, anhydrides, or
methyl esters. Furthermore, the carboxylate anion donor can be one
or more C.sub.2 to C.sub.12 straight-chain alkyl carboxylic acids,
anhydrides, or methyl esters. Moreover, the carboxylate anion donor
can be one or more C.sub.2 to C.sub.4 straight-chain alkyl
carboxylic acids, anhydrides, or methyl esters. The resulting
carboxylated ionic liquid can be substantially the same as the
carboxylated ionic liquid described above with reference to the
carboxylated ionic liquid in line 64 of FIG. 1.
[0188] When contacting the reformed ionic liquid with one or more
carboxylate anion donors, the contacting can be carried out in a
contact mixture further comprising alcohol or water. In one
embodiment, the alcohol or water can be present in the contact
mixture in the range of from 0.01 to 20 molar equivalents per alkyl
amine formate, or in the range of from 1 to 10 molar equivalents
per alkyl amine formate. In one embodiment, methanol can be present
in the contact mixture in the range of from 1 to 10 molar
equivalents per alkyl amine formate.
[0189] Referring still to FIG. 2, in one embodiment at least a
portion of the carboxylated ionic liquid produced in ionic liquid
recovery/treatment zone 160 can be in a treated ionic liquid
mixture further comprising at least one alcohol, at least one
residual carboxylic acid, and/or water. The one or more alcohols
and/or residual carboxylic acids can be substantially the same as
described above with reference to the recycle stream in line 186.
The treated ionic liquid mixture can be subjected to at least one
liquid/liquid separation process to remove at least a portion of
the one or more alcohols. Such separation process can comprise any
liquid/liquid separation process known in the art, such as, for
example, flash vaporization and/or distillation. Additionally, the
treated ionic liquid mixture can be subjected to at least one
liquid/liquid separation process to remove at least a portion of
the water. Such separation process can comprise any liquid/liquid
separation process known in the art, such as, for example, flash
vaporization and/or distillation.
[0190] In one embodiment, at least 50, at least 70, or at least 85
weight percent of the alcohols and/or water can be removed from the
treated ionic liquid mixture thereby producing a recycled
carboxylated ionic liquid. At least a portion of the alcohol
separated from the treated ionic liquid mixture can optionally be
removed from ionic liquid recovery/treatment zone 160 via line 194.
The one or more alcohols in line 194 can thereafter optionally be
routed to various other points depicted in FIG. 2. In one
embodiment, at least 50, at least 70, or at least 90 weight percent
of the alcohols removed from the treated ionic liquid mixture can
be routed to various other points in the process depicted in FIG.
2. In one optional embodiment, at least a portion of the alcohols
in line 194 can be routed to randomization zone 151 to be employed
as a randomizing agent. In another optional embodiment, at least a
portion of the alcohols in line 194 can be routed to precipitation
zone 152 to be employed as a precipitating agent. In yet another
optional embodiment, at least a portion of the alcohols in line 194
can be routed to wash zone 154 to be employed as a wash liquid.
[0191] In one embodiment, at least a portion of the water separated
from the treated ionic liquid mixture can optionally be removed
from ionic liquid recovery/treatment zone 160 via line 192.
Optionally, at least a portion of the water removed from ionic
liquid recovery/treatment zone 160 can be routed to modification
zone 110 to be employed as a modifying agent. At least about 5, at
least about 20, or at least 50 weight percent of the water
separated from the treated ionic liquid mixture can optionally be
routed to modification zone 110. Additionally, at least a portion
of the water in line 192 can optionally be routed to a waste water
treatment process.
[0192] After alcohol and/or water removal, the above-mentioned
recycled carboxylated ionic liquid can comprise residual carboxylic
acid in an amount in the range of from about 0.01 to about 25
weight percent, in the range of from about 0.05 to about 15 weight
percent, or in the range of from 0.1 to 5 weight percent based on
the entire weight of the recycled carboxylated ionic liquid.
Additionally, the recycled carboxylated ionic liquid can comprise
sulfur in an amount of less than 200 ppmw, less than 100 ppmw, less
than 50 ppmw, or less than 10 ppmw. Furthermore, the recycled
carboxylated ionic liquid can comprise halides in an amount less
than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than
10 ppmw. Moreover, the carboxylated ionic liquid can comprise
transition metals in an amount less than 200 ppmw, less than 100
ppmw, less than 50 ppmw, or less than 10 ppmw.
[0193] In one embodiment, at least a portion of the recycled
carboxylated ionic liquid produced in ionic liquid
recovery/treatment zone 160 can optionally be routed to dissolution
zone 120. At least 50 weight percent, at least 70 weight percent,
or at least 90 weight percent of the recycled carboxylated ionic
liquid produced in ionic liquid recovery/treatment zone 160 can be
routed to dissolution zone 120.
[0194] In dissolution zone 120, the recycled carboxylated ionic
liquid can be employed either individually or combined with the
carboxylated ionic liquid entering dissolution zone 120 via line
164 to thereby form the above-described cellulose dissolving ionic
liquid. In one embodiment, the recycled carboxylated ionic liquid
can make up in the range of from about 10 to about 99.99 weight
percent, in the range of from about 50 to about 99 weight percent,
or in the range of from about 90 to about 98 weight percent of the
cellulose dissolving ionic liquid in dissolution zone 120.
[0195] Further information concerning ionic liquids, their use in
the production of cellulose esters and cellulose derivatives, the
use of cosolvents with ionic liquids in processes to produce
cellulose esters and cellulose derivatives, and treatment of
cellulose esters are disclosed in U.S. patent application entitled
"Cellulose Esters and Their Production In Carboxylated Ionic
Liquids" filed on Feb. 13, 2008 and having Ser. No. 12/030,387;
U.S. patent application entitled "Cellulose Esters and Their
Production in Halogenated Ionic Liquids filed on Aug. 11, 2008 and
having Ser. No. 12/189,415 and its Continuation-In-Part Application
entitled "Regioselectively Substituted Cellulose Esters Produced In
A Halogenated Ionic Liquid Process and Products Produced Therefrom"
filed on Sep. 12, 2009; U.S. patent application "Production of
Ionic Liquids" filed on Feb. 13, 2008 having Ser. No. 12/030,425;
and U.S. patent application entitled "Reformation of Ionic Liquids"
filed on Feb. 13, 2008 having Ser. No. 12/030,424; U.S. patent
application entitled "Treatment of Cellulose Esters" filed on Aug.
11, 2008, having Ser. No. 12/189,421; U.S. patent application
entitled "Production of Cellulose Esters In the Presence of A
Cosolvent" filed on Aug. 11, 2008 having Ser. No. 12/189,753; U.S.
application entitled "Cellulose Solutions Comprising
Tetraalkylammonium Alkylphosphates and Products Produced Therefrom"
filed on Sep. 12, 2009; U.S. application entitled "Regioselectively
Substituted Cellulose Esters Produced In A Tetraalkylammonium
Alkylphosphate Ionic Liquid Process and Products Produced
Therefrom" filed on Sep. 12, 2009; and U.S. Provisional application
entitled "Regioselectively Substituted Cellulose Esters and Their
Production in Ionic Liquids" filed on Aug. 13, 2008 having Ser. No.
61/088,423; and U.S. Provisional Application entitled
"Tetraalkylammoinium Alkylphosphates" filed on Apr. 15, 2009 having
Ser. No. 61/169,560; all of which are incorporated by reference to
the extent they do not contradict the statements herein.
[0196] This invention can be further illustrated by the following
examples of embodiments thereof, although it will be understood
that these examples are included merely for purposes of
illustration and are not intended to limit the scope of the
invention unless otherwise specifically indicated.
EXAMPLES
Materials Used in Examples
[0197] Commercial grades of ionic liquids employed in the following
examples were manufactured by BASF and were obtained through Fluka.
These ionic liquids were used both as received and after
purification as described in the examples. Experimental alkyl
imidazolium carboxylates were also prepared as described in the
examples. Cellulose was obtained from Aldrich. The degree of
polymerization of the Aldrich cellulose (DP ca. 335) was determined
capillary viscometry using copper ethylenediamine (Cuen) as the
solvent. Prior to dissolution in ionic liquids, the cellulose was
typically dried for 14-18 h at 50.degree. C. and 5 mm Hg, except in
cases where the cellulose was modified with water prior to
dissolution.
[0198] The relative degree of substitution (RDS) at C.sub.6,
C.sub.3, and C.sub.2 in the cellulose ester of the present
invention was determined by carbon 13 NMR following the general
methods described in "Cellulose Derivatives", ACS Symposium Series
688, 1998, T. J. Heinze and W. G. Glasser, Editors, herein
incorporated by reference to the extent it does not contradict the
statements herein. Briefly, the carbon 13 NMR data was obtained
using a JEOL NMR spectrometer operating at 100 MHz or a Bruker NMR
spectrometer operating at 125 MHz. The sample concentration was 100
mg/mL of DMSO-d.sub.6. Five mg of Cr(OAcAc).sub.3 per 100 mg of
sample were added as a relaxation agent. The spectra were collected
at 80.degree. C. using a pulse delay of 1 second. Normally, 15,000
scans were collected in each experiment. Conversion of a hydroxyl
to an ester results in a downfield shift of the carbon bearing the
hydroxyl and an upfield shift of a carbon gamma to the carbonyl
functionality. Hence, the RDS of the C.sub.2 and C.sub.6 ring
carbons were determined by direct integration of the substituted
and unsubstituted C.sub.1 and C.sub.6 carbons. The RDS at C.sub.3
was determined by subtraction of the sum of the C.sub.6 and C.sub.2
RDS from the total DS. The carbonyl RDS was determined by
integration of the carbonyl carbons using the general assignments
described in Macromolecules, 1991, 24, 3050-3059, herein
incorporated by reference to the extent it does not contradict the
statements herein. In the case of cellulose mixed esters containing
a plurality of acyl groups, the cellulose ester was first converted
to fully substituted cellulose mixed p-nitrobenzoate ester. The
position of the p-nitrobenzoate esters indicate the location of the
hydroxyls in the cellulose mixed ester.
[0199] Color measurements were made following the general protocol
of ASTM D1925. Samples for color measurements were prepared by
dissolving 1.7 g of cellulose ester in 41.1 g of
n-methylpyrrolidone (NMP). A HunterLab Color Quest XE colorimeter
with a 20 mm pathlength cell operating in transmittance mode was
used for the measurements. The colorimeter was interfaced to a
standard computer running EasyMatch QC Software (HunterLab). Values
(L*; white to black, a*; +red to -green, b*; +yellow to -blue) were
obtained for NMP (no cellulose ester) and for the cellulose
ester/NMP solutions. Color difference (E*) between the solvent and
the sample solutions were then calculated
(E*=[(.DELTA.a*).sup.2+[(.DELTA.b*).sup.2+[(.DELTA.L*).sup.2].sup.0.5
where .DELTA. is the value for the sample solutions minus the value
for the solvent). As the value for E* approaches zero, the better
the color.
[0200] Viscosity measurements were made using an AR2000 rheometer
(TA Instruments LTD) interfaced with a computer running TA
Instruments Advantage Software. The 25 mm aluminum stage for the
rheometer was enclosed in a plastic cover with a nitrogen purge to
ensure that the samples did not pick up moisture during the
measurements. The ionic liquid-cellulose solutions were prepared by
the general methods disclosed in the examples.
[0201] Solvent casting of film was performed according to the
following general procedure: Cellulose ester solids and 10 wt %
plasticizer were added to a 90/10 wt % solvent mixture of
CH.sub.2Cl.sub.2/methanol (or ethanol) to give a final
concentration of 5-30 wt % based on cellulose ester+plasticizer.
The mixture was sealed, placed on a roller, and mixed for 24 hours
to create a uniform solution. After mixing, the solution was cast
onto a glass plate using a doctor blade to obtain a film with the
desired thickness. Casting was conducted in a fume hood with
relative humidity controlled at 50%. After casting, the film and
glass were allowed to dry for one hour under a cover pan (to
minimize rate of solvent evaporation). After this initial drying,
the film was peeled from the glass and annealed in a forced air
oven for 10 minutes at 100.degree. C. After annealing at
100.degree. C., the film was annealed at a higher temperature
(120.degree. C.) for another 10 minutes.
[0202] Film optical retardation measurements were made using a J.
A. Woollam M-2000V Spectroscopic Ellipsometer having a spectral
range of 370 to 1000 nm. RetMeas (Retardation Measurement) program
from J. A. Woollam Co., Inc. was used to obtain optical film
in-plane (R.sub.e) and out-of-plane (R.sub.th) retardations. Values
are reported at 589 or 633 nm at a film thickness of 60 .mu.m.
Example 1
Preparation of Cellulose Ester (Comparative)
[0203] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe (Mettler-Toledo
AutoChem, Inc., Columbia, Md., USA), and with an N.sub.2/vacuum
inlet. To the flask was added 61 g of 1-butyl-3-methylimidazolium
chloride. Prior to adding the [BMIm]Cl, the ionic liquid was melted
at 90.degree. C. then stored in a desiccator; during storage, the
[BMIm]Cl remained a liquid. While stirring rapidly, began adding
3.21 g of previously dried microcrystalline cellulose (DP ca. 335)
in small portions (3 min addition). The slurry was stirred for 5
min before applying vacuum. After ca. 3 h 25 min, most of the
cellulose had dissolved except for a few small pieces and 1 large
piece stuck to the probe. After 5.5 h, the oil bath temperature was
increased to 105.degree. C. to speed up dissolution of the
remaining cellulose. The solution was maintained at 105.degree. C.
for 1.5 h (47 min heat up) before allowing the solution to cool to
room temperature (6 h 25 min from the start of the cellulose
addition) and stand overnight at ambient temperature.
[0204] After standing overnight, the cellulose/[BMIm]Cl solution
was clear and the IR spectra indicated that all of the cellulose
was dissolved. The solution was heated to 80.degree. C. before
adding 10.11 g (5 eq) Ac.sub.2O drop wise (26 min addition). The
reaction was sampled throughout the reaction period by removing
6-10 g aliquots of the reaction mixture and precipitating in 100 mL
of MeOH. The solid from each aliquot was washed 2.times. with 100
mL portions of MeOH then 2.times. with 100 mL of MeOH containing 8%
of 35 wt % H.sub.2O.sub.2 before drying at 60.degree. C., 5 mm Hg.
The 1.sup.st sample was white, the 2.sup.nd sample was tan, and the
3.sup.rd sample was brown. During the course of the reaction, the
solution became progressively darker. Approximately 2 h 45 min
after the start of the Ac.sub.2O addition, the viscosity of the
reaction mixture abruptly increased then the reaction mixture
completely gelled. The oil bath was lowered and the contact
solution was allowed to cool to room temperature.
[0205] FIG. 3 is a plot of absorbance versus time for Example 1 and
it shows the dissolution of cellulose (1046 cm.sup.-1) and the
removal of residual water (1635 cm.sup.-1) from the mixture during
the course of the dissolution. The spikes in the cellulose trend
line are due to large cellulose gel particles sticking to the probe
which, are removed by the stirring action. Clumping occurs because
the surfaces of the cellulose particles become partially dissolve
before dispersion is obtained leading to clumping and large gel
particles. The dip in the trend lines near 6 h result from the
temperature increase from 80 to 105.degree. C. This figure
illustrates that ca. 6 h is required to fully dissolve the
cellulose when the cellulose is added to the ionic liquid that is
preheated to 80.degree. C.
[0206] FIG. 4 is a plot of absorbance versus time for Example 1 and
it illustrates the acetylation of cellulose (1756, 1741, 1233
cm.sup.-1), the consumption of Ac.sub.2O (1822 cm.sup.-1), and the
coproduction of acetic acid (1706 cm.sup.-1) during the experiment.
The DS values shown in FIG. 4 were determined by NMR spectroscopy
and correspond to the samples removed during the course of the
contact period. As illustrated, ca. 75% of the acetylation occurred
during the first hour after which the reaction rates slowed.
Approximately 2 h 45 from beginning the Ac.sub.2O addition
(DS=2.45), the solution viscosity suddenly increased followed by
gellation of the contact mixture. At this point, no further
reaction occurred and the remaining contact solution was processed
as described above. It should be noted that there was still a large
excess of Ac.sub.2O at the point of gellation. Furthermore, during
the course of the contact period, the solution became progressively
darker and the final product color was dark brown. Color
measurements of the final sample dissolved in NMP gave a L* value
of 82.74, an a* value of 2.23, a b* value of 56.94, and an E* value
of 59.55. In addition to determining the DS of each sample, the
molecular weight of each sample was determined by GPC (Table 1,
below). In general, Mw was approximately 55,000 and the
polydispersity ranged from 3-4. Based on the DP of the starting
cellulose, this analysis indicates that the molecular weight of the
cellulose polymer remained essentially intact during the contact
period.
Example 2
Modification of Cellulose with Water
[0207] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask was added 64.3 g of
1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl,
the IL was melted at 90.degree. C. then stored in a desiccator; the
[BMIm]Cl remained a liquid during storage. To the ionic liquid was
added 3.4 g (5 wt %) of microcrystalline cellulose (DP ca. 335) at
ambient temperature while stirring rapidly to disperse the
cellulose. Approximately 12 min after adding the cellulose, a
preheated 80.degree. C. oil bath was raised to the flask. After ca.
17 min in the 80.degree. C. oil bath, visually, all of the
cellulose appeared to be dissolved. After ca. 22 min in the
80.degree. C. oil bath, began applying vacuum. To insure complete
removal of water, 50 min after applying vacuum, the oil bath
setting was increased to 105.degree. C. and the solution was
stirred for 2 h 25 min before the oil bath was allowed to cool to
room temperature.
[0208] The temperature of the clear, amber cellulose solution was
adjusted to 80.degree. C. before adding 6.42 g of Ac.sub.2O (3 eq)
drop wise (5 min addition). The contact mixture was sampled
throughout the reaction period by removing 6-10 g aliquots of the
contact mixture and precipitating in 100 mL of MeOH. The solid from
each aliquot was washed 1.times. with 100 mL of MeOH then 2.times.
with MeOH containing 8 wt % 35% H.sub.2O.sub.2. The samples were
then dried at 60.degree. C., 5 mm Hg overnight. During the course
of the contact period, the color of the solution became darker
ultimately becoming dark brown. Approximately 2 h 10 min from the
start of Ac.sub.2O addition, the solution viscosity began to
increase significantly; 10 min later the solution completely gelled
out and started climbing the stir shaft. The experiment was aborted
and MeOH was added to the flask to precipitate the remaining
product.
[0209] The precipitation and the wash liquids from each aliquot
were combined and concentrated invacuo at 68.degree. C. until the
vacuum dropped to 24 mm Hg which provided 54.2 g of recovered
[BMIm]Cl. Analysis by .sup.1H NMR revealed that the ionic liquid
contained 4.8 wt % acetic acid when measured by this technique.
[0210] FIG. 5 is a plot of absorbance versus time for Example 2 and
it shows the dissolution of cellulose (1046 cm.sup.-1) and the
removal of residual water (1635 cm.sup.-1) from the mixture during
the course of the dissolution. As can be seen, the dissolution of
the cellulose was very rapid (17 min versus 360 min in Example 1).
This was due to adding the cellulose to the ionic liquid at room
temperature, stirring to get a good dispersion (higher surface
area), then heating to effect dissolution. Normally, [BMIm]Cl is a
solid that melts at ca. 70.degree. C. However, if water or a
carboxylic acid is allowed to mix with [BMIm]Cl, the [BMIm]Cl will
remain a liquid at room temperature thus allowing introduction of
the cellulose at ambient temperature. As can be seen from the water
loss in FIG. 5, the [BMIm]Cl contained significant water. This
example illustrates that the addition of water to an ionic liquid
followed by cellulose addition and good mixing to get a good
dispersion provides rapid dissolution of cellulose.
[0211] FIG. 6 is a plot of absorbance versus time for Example 2 and
it illustrates the acetylation of cellulose (1756, 1741, 1233
cm.sup.-1), the consumption of Ac.sub.2O (1822 cm.sup.-1), and the
coproduction of acetic acid (1706 cm.sup.-1) during the experiment.
The DS values shown in FIG. 6 were determined by NMR spectroscopy
and correspond to the samples removed during the course of the
contact period. Relative to Example 1, the reaction rate was slower
(Example 1, DS=2.44 @ 165 min; Example 2, DS=2.01 @ 166 min, cf.
Table 1, below). As was observed in Example 1, the solution
viscosity suddenly increased followed by gellation of the contact
mixture, but in Example 2, gellation occurred at a lower DS. Both
the slower reaction rate and gellation at a lower temperature can
be attributed to the use of less Ac.sub.2O. However, it should be
noted that there was still a large excess of Ac.sub.2O at the point
of gellation. As with Example 1, during the course of the contact
period, the solution became progressively darker and the final
product color was dark brown. Color measurements of the final
sample dissolved in NMP gave a L* value of 67.30, an a* value of
17.53, a b* value of 73.35, and an E* value of 82.22. In addition
to determining the DS of each sample, the molecular weight of each
sample was determined by GPC (Table 1, below). In general, Mw was
approximately 55,000 and the polydispersity ranged from 3-6. Based
on the DP of the starting cellulose, this analysis indicates that
the molecular weight of the cellulose polymer remained essentially
intact during the contact period.
Example 3
MSA Secondary Component, No Modification with Water
[0212] Cellulose (3.58 g, 5 wt %) was dissolved in 68 g of [BMIm]Cl
in a manner similar to Example 2. To the cellulose solution
(contact temperature=80.degree. C.) was added a mixture of 433 mg
MSA and 6.76 g of Ac.sub.2O (3 eq) drop wise (8 min). The reaction
was sampled throughout the reaction period by removing 6-10 g
aliquots of the reaction mixture and precipitating in 100 mL of
MeOH. The solid from each aliquot was washed 2.times. with 100 mL
portions of MeOH then dried at 60.degree. C., 5 mm Hg. The solid
samples were snow white. After ca. 2 h, all of the Ac.sub.2O
appeared to be consumed by IR. The experiment was aborted and the
remaining sample was processed as above.
[0213] The precipitation and the wash liquids from each aliquot
were combined and concentrated invacuo at 68.degree. C. until the
vacuum dropped to 24 mm Hg which provided 64 g of recovered
[BMIm]Cl. Unlike Example 2, analysis by .sup.1H NMR revealed that
the ionic liquid did not contain any acetic acid when measured by
this technique. This result indicates that MSA aids in the removal
of residual acetic acid from the ionic liquid, probably by
conversion of the residual acetic acid to methyl acetate.
[0214] FIG. 7 is a plot of absorbance versus time for Example 3 and
it illustrates the acetylation of cellulose (1756, 1741, 1233
cm.sup.-1), the consumption of Ac.sub.2O (1822 cm.sup.-1), and the
coproduction of acetic acid (1706 cm.sup.-1) during the experiment.
The DS values shown in FIG. 7 were determined by NMR spectroscopy
and correspond to the samples removed during the course of the
contact period. What is apparent from FIG. 7 is that the rates of
reaction are much faster compared to Examples 2 and 3. For example,
55 min was required to reach a DS of 1.82 in Example 1-1 (Table 1,
below) while only 10 min was required to reach a DS of 1.81 in
Example 3-1. Similarly, 166 min was required to reach a DS of 2.01
in Example 2-4 (Table 1, below) while only 20 min was required to
reach a DS of 2.18 in Example 3-2. Additionally, FIG. 7 shows that
no gellation occurred during the course of the experiment. In fact,
throughout the experiment, there was not any increase in solution
viscosity, the solution color was essentially unchanged from the
initial solution color, and the products isolated from the contact
mixture were all white. Color measurements of the final sample
dissolved in NMP gave a L* value of 97.65, an a* value of -2.24, a
b* value of 11.07, and an E* value of 11.54. Comparison of these
values to those obtained in Example 1 and 2 (E*=59.55 and 82.22,
respectively) shows that inclusion of a secondary component such as
MSA in the contact mixture significantly improves solution and
product color. This effect is particularly pronounced in view of
the fact that the samples in Examples 1 and 2 were bleached and the
samples in this Example were not bleached. As discussed in Example
36, bleaching can significantly improve product color for cellulose
esters prepared from cellulose dissolved in ionic liquids. Finally,
it should be noted in Table 1, below, that the Mw (ca. 40,000) for
the samples of Example 3 are less than those for Examples 1 and 2
and that the polydispersity (Mw/Mn) is lower and more narrow (2-3)
than those for Examples 1 and 2 (3-6). When compared to Examples 1
and 2, Example 3 shows that inclusion of a secondary component such
as MSA in the contact mixture accelerates the rates of reaction,
significantly improves solution and product color, prevents
gellation of the contact mixture, allows the achievement of high DS
values while using less acylating reagent, and helps to promote
lowering of the cellulose ester molecular weight.
TABLE-US-00001 TABLE 1 Properties of Cellulose Acetates Prepared
Without Water Modification Example Time (min) DS Mw Mw/Mn 1-1 55
1.82 59243 3.29 1-2 122 2.25 61948 4.34 1-3 165 2.44 51623 3.73 2-1
6 0.64 50225 2.93 2-2 34 1.49 56719 3.48 2-3 56 1.73 64553 5.4 2-4
166 2.01 66985 5.7 2-5 176 2.05 63783 5.83 3-1 10 1.81 41778 1.92
3-2 20 2.18 43372 2.01 3-3 27 2.39 41039 2.22 3-4 43 2.52 41483 2.4
3-5 66 2.62 40412 2.54 3-6 124 2.72 39521 2.55
Example 4
Modification with Water, MSA Secondary Component
[0215] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 58.07 g of
1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl,
the IL was melted at 90.degree. C. then stored in a desiccator. The
flask was placed in an oil bath and heated to 80.degree. C.
[0216] To 3.06 g (5 wt %) of microcrystalline cellulose (DP ca.
335), was added 3.06 g of water. The slurry was hand mixed and
allowed to stand for ca. 30 min before adding the slurry in small
portions to the [BMIm]Cl (5 min addition). This gave a hazy
solution in which the cellulose was surprisingly well dispersed.
The slurry was stirred for 27 min, before applying vacuum.
Visually, after 28 min under vacuum all of the cellulose had
dissolved which was confirmed by IR. By IR, there was still ca. 3
wt % water in the [BMIm]Cl when all of the cellulose was dissolved.
The system was maintained under vacuum at 80.degree. C. to remove
the remaining water. The sample was allowed to cool to room
temperature and left standing until the next step.
[0217] The cellulose solution was heated to 80.degree. C. before
adding a mixture of 5.78 g Ac.sub.2O (3 eq) and 368 mg MSA drop
wise (8 min). The reaction was sampled throughout the reaction
period by removing 6-10 g aliquots of the reaction mixture and
precipitating in 100 mL of MeOH. The solid from each aliquot was
washed 2.times. with 100 mL portions of MeOH then dried at
60.degree. C., 5 mm Hg. The isolated samples were snow white. The
solution color was excellent throughout the experiment and there
was no indication of a viscosity increase. After ca. 2 h 25 min,
infrared spectroscopy indicated that all of the Ac.sub.2O was
consumed. The experiment was aborted and the remaining sample was
processed as above.
[0218] FIG. 8 is a plot of absorbance versus time for Example 4 and
it shows the dissolution of cellulose (1046 cm.sup.-1) and the
removal of residual water (1635 cm.sup.-1) from the mixture during
the course of the dissolution. As can be seen, the dissolution of
the water wet (activated) cellulose was very rapid (28 min) despite
the presence of a significant amount of water. This is surprising
in view of the conventional teachings. The addition of water wet
cellulose to the ionic liquid enables one to obtain a good
dispersion of cellulose with little clumping. Upon application of a
vacuum to remove the water, the cellulose rapidly dissolves without
clumping to form large particles.
[0219] FIG. 9 is a plot of absorbance versus time for Example 4 and
it illustrates the acetylation of cellulose (1756, 1741, 1233
cm.sup.-1), the consumption of Ac.sub.2O (1822 cm.sup.-1), and the
coproduction of acetic acid (1706 cm.sup.-1) during the experiment.
The DS values shown in FIG. 9 were determined by NMR spectroscopy
and correspond to the samples removed during the course of the
contact period. Relative to Example 3, the reaction rate to produce
cellulose acetate was similar. However, the molecular weights (ca.
33,000) of the cellulose acetate samples (Table 2, below) were
notably lower that that observed in Example 3 and much lower than
that observed in Examples 1 and 2 (Table 1, above). Additionally,
the polydispersities for the samples of Example 4 are all less than
2, less than that observed for the samples of Examples 1, 2, and
3.
[0220] This example illustrates that water wet cellulose leads to
good cellulose dispersion in the ionic liquid and rapid cellulose
dissolution. The reaction rate for formation of cellulose acetate
is rapid. Surprisingly, water wet cellulose leads to lower
molecular weight cellulose acetate with low polydispersities
relative to dry cellulose. The cellulose acetate made from water
wet cellulose has better acetone solubility relative to when dry
cellulose is utilized.
Example 5
Modification with Water, MSA Secondary Component
[0221] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with a iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 67.33 g of
1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl,
the IL was melted at 90.degree. C. then stored in a desiccator. The
flask was placed in an oil bath and heated to 80.degree. C. To 7.48
g (10 wt %) of microcrystalline cellulose (DP ca. 335), was added
7.08 g of water. The cellulose slurry was hand mixed and allowed to
stand for ca. 60 min before adding the slurry in small portions to
the [BMIm]Cl (8 min addition). This gave a hazy solution in which
the cellulose was surprisingly well dispersed. The slurry was
stirred for 10 min, before applying vacuum. The cellulose
dissolution was left stirring overnight.
[0222] Infrared spectroscopy indicated that essentially all of the
cellulose was dissolved within 50 min after applying vacuum; ca.
3.5 h was required to remove the water. To the cellulose solution
was added a mixture of 14.13 g of Ac.sub.2O (3 eq) and 884 mg (0.2
eq) of MSA drop wise (11 min). The reaction was sampled throughout
the reaction period by removing 6-10 g aliquots of the reaction
mixture and precipitating in 100 mL of MeOH. The solid from each
aliquot was washed 2.times. with 100 mL portions of MeOH then dried
at 60.degree. C., 5 mm Hg. The isolated samples were snow white.
The solution color was excellent through out the experiment and
there was no indication of a viscosity increase. After ca. 2 h 10
min, all of the Ac.sub.2O appeared to be consumed by IR. The
experiment was aborted and the remaining sample was processed as
above.
[0223] FIG. 10 is a plot of absorbance versus time for Example 5
and it shows the dissolution of cellulose (1046 cm.sup.-1) and the
removal of residual water (1635 cm.sup.-1) from the mixture during
the course of the dissolution. As can be seen, the dissolution of
the water wet (activated) cellulose was very rapid (50 min) despite
the presence of a significant amount of water and the increase in
cellulose concentration relative to Example 4.
[0224] FIG. 11 is a plot of absorbance versus time for Example 5
and it illustrates the acetylation of cellulose (1756, 1741, 1233
cm.sup.-1), the consumption of Ac.sub.2O (1822 cm.sup.-1), and the
coproduction of acetic acid (1706 cm.sup.-1) during the experiment.
The DS values shown in FIG. 11 were determined by NMR spectroscopy
and correspond to the samples removed during the course of the
contact period. Despite the increase in cellulose concentration,
relative to Examples 3 and 4, the reaction rate to produce
cellulose acetate was similar. The molecular weights (ca. 22,000)
of the cellulose acetate samples (Table 2, below) were notably
lower that that observed in Example 4 and much lower than that
observed in Examples 1, 2, and 3 (Table 1, above). As was observed
for Example 4, the polydispersities for the samples of Example 5
are all less than 2, less than that observed for the samples of
Examples 1, 2, and 3.
[0225] This example illustrates that water wet cellulose leads to
good cellulose dispersion in the ionic liquid and rapid cellulose
dissolution even when the cellulose concentration is increased to
10 wt %. The reaction rate for formation of cellulose acetate is
rapid. Surprisingly, water wet cellulose at this concentrations
leads to even lower molecular weight cellulose acetates with low
polydispersities relative to dry cellulose. The cellulose acetate
made from water wet cellulose has better acetone solubility
relative to when dry cellulose is utilized.
Example 6
Modification with Water, MSA Secondary Component
[0226] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 51.82 g of
1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl,
the IL was melted at 90.degree. C. then stored in a desiccator. The
flask was placed in an oil bath and heated to 80.degree. C. To 9.15
g (15 wt %) of microcrystalline cellulose (DP ca. 335), added 53.6
g of water. After hand mixing, the cellulose was allowed to stand
in the water for 50 min before filtering which gave 18.9 g of a wet
cellulose cake. The water wet cellulose was then added in small
portions to the [BMIm]Cl (5 min addition). Within 2 min, the
cellulose was finely dispersed in the ionic liquid. Ten minutes
after adding the cellulose to the [BMIm]Cl, the flask was placed
under vacuum. After ca. 1 h, there were no visible cellulose
particles; the solution viscosity was very high and the solution
started climbing the stir rod. The solution was left stirring
overnight at 80.degree. C. under vacuum.
[0227] Infrared spectroscopy indicated that ca. 1 h was required
for cellulose dissolution and 2 h was required to strip the water
to the initial value. The cellulose solution was heated to
100.degree. C. prior to adding a mixture of 17.28 g Ac.sub.2O (3
eq) and 1.087 g (0.2 eq) of MSA drop wise (8 min). The reaction was
sampled throughout the reaction period by removing 6-10 g aliquots
of the reaction mixture and precipitating in 100 mL of MeOH. The
solid from each aliquot was washed 1.times. with 100 mL of MeOH
then 2.times. with MeOH containing 8 wt % 35% H.sub.2O.sub.2. The
solid samples were then dried at 60.degree. C., 5 mm Hg. After ca.
65 min, all of the Ac.sub.2O appeared to be consumed by IR. The
experiment was aborted and the remaining sample was processed as
above.
[0228] FIG. 12 is a plot of absorbance versus time for Example 6
and it shows the dissolution of presoaked water wet cellulose (1046
cm.sup.-1) and the removal of residual water (1635 cm.sup.-1) from
the mixture during the course of the dissolution. As can be seen,
the dissolution of the water wet (activated) cellulose was very
rapid (60 min) despite the presence of a significant amount of
water and the use of 15 wt % cellulose. Even more surprising was
the rapid removal of water (ca. 2 h) at this high cellulose
concentration.
[0229] FIG. 13 is a plot of absorbance versus time for Example 6
and it illustrates the acetylation of cellulose (1756, 1741, 1233
cm.sup.-1), the consumption of Ac.sub.2O (1822 cm.sup.-1), and the
coproduction of acetic acid (1706 cm.sup.-1) during the experiment.
The DS values shown in FIG. 13 were determined by NMR spectroscopy
and correspond to the samples removed during the course of the
contact period. Despite the increase in cellulose concentration (15
wt %), acetic anhydride could be easily mixed into the cellulose
solution at 100.degree. C. The higher reaction temperature led to
an increase in reaction rate. Again, the molecular weights (ca.
20,000) of the cellulose acetate samples (Table 2, below) were
notably lower that that observed in Examples 1, 2, and 3 (Table 1,
above) were the cellulose was dried prior to use; the
polydispersities for the samples of Example 6 are also less than
2.
[0230] This example illustrates that water wet cellulose leads to
good cellulose dispersion in the ionic liquid and rapid cellulose
dissolution even when the cellulose concentration is increased to
15 wt %. This example also shows that higher temperature
(100.degree. C.) increases reaction rates for formation of
cellulose acetate. Surprisingly, water wet cellulose at this
concentrations leads to even lower molecular weight cellulose
acetates with low polydispersities relative to dry cellulose. The
cellulose acetate made from water wet cellulose has better acetone
solubility relative to when dry cellulose is utilized.
TABLE-US-00002 TABLE 2 Effect of Water Modification on Properties
of Cellulose Acetates Example Time (min) DS Mw Mw/Mn 4-1 9 1.58
31732 1.73 4-2 13 1.94 33559 1.64 4-3 21 2.15 34933 1.63 4-4 35
2.28 31810 1.77 4-5 150 2.63 30771 1.89 5-1 11 1.95 24522 1.6 5-2
14 2.21 23250 1.67 5-3 18 2.35 22706 1.76 5-4 22 2.52 22692 1.79
5-5 31 2.59 21918 1.86 5-6 45 2.60 21628 1.89 5-7 70 2.66 19708
1.97 5-8 130 2.67 20717 1.99 6-1 10 2.63 20729 1.67 6-2 14 2.75
19456 1.78 6-3 18 2.80 19658 1.84 6-4 23 2.87 18966 1.84 6-5 32
2.89 20024 1.88 6-6 65 2.96 18962 1.85
Example 7
Miscible Cosolvent
[0231] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 58.79 g of
1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl,
the IL was melted at 90.degree. C. then stored in a desiccator. The
flask was placed in an oil bath and heated to 80.degree. C. After
reaching 80.degree. C., began collecting IR spectra before adding
1.82 g (3 wt %) of glacial acetic acid. The mixture was stirred for
12 min before adding 10.38 g (15 wt %) cellulose (DP ca. 335) as a
water wet cellulose cake (10.29 g water, prepared by soaking the
cellulose for 50 min in excess water, 9 min addition). The mixture
was stirred for ca. 9 min to allow the cellulose to disperse before
applying a vacuum. After ca. 65 min, infrared spectroscopy
indicated that all of the cellulose was dissolved (FIG. 14).
Stirring was continued for an additional 70 min before adding 1.82
g of glacial acetic acid (6 wt % total). In order to reduce the
solution viscosity, the stirring was turned off 8 min after adding
the acetic acid and the oil bath temperature was increased to
100.degree. C. After reaching 100.degree. C. (45 min) stirring was
resumed. Infrared spectroscopy indicated that upon resuming
stirring, the acetic acid mixed well with the cellulose solution.
The final solution was clear and no cellulose particles were
observed. After standing for 10 days, the cellulose solution was
still clear and could be hand stirred at room temperature which one
cannot do with a 15 wt % cellulose solution in [BMIm]Cl in the
absence of acetic acid.
[0232] This example shows that significant amount of a miscible
cosolvent such as a carboxylic acid compatible with cellulose
acylation can be mixed with a cellulose-ionic liquid sample while
still maintaining cellulose solubility. A cosolvent has the added
benefit of reducing solution viscosity.
Example 8
Randomization
[0233] A 3-neck 250 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 149.7 g of
1-butyl-3-methylimidazolium chloride. The flask was placed in an
oil bath and heated to 80.degree. C. Microcrystalline cellulose
(12.14 g, 7.5 wt %, DP ca. 335) was added to 68.9 g of water. After
hand mixing, the cellulose was allowed to stand in the water for 45
min at 60.degree. C. before filtering which gave 24.33 g of a wet
cellulose cake. The water wet cellulose was then added in small
portions to the [BMIm]Cl (5 min addition). Approximately 15 min
after adding the cellulose to the [BMIm]Cl, the flask was placed
under vacuum by gradually lowering the vacuum starting at ca. 120
mm Hg to ca. 1.4 mm Hg. After ca. 85 min, there were no visible
cellulose particles; IR spectroscopy indicated that all of the
cellulose was dissolved. The solution was left stirring overnight
at 80.degree. C. under vacuum.
[0234] To the cellulose solution heated to 80.degree. C. was added
a mixture of 22.93 g Ac.sub.2O (3 eq) and 1.427 g (0.2 eq) of MSA
drop wise (15 min). The reaction was sampled throughout the
reaction period by removing 6-10 g aliquots of the reaction mixture
and precipitating in 100 mL of MeOH. The solid from each aliquot
was washed 3.times. with 100 mL portions of MeOH then dried at
60.degree. C., 5 mm Hg. After removing an aliquot 192 min from the
start of the Ac.sub.2O addition, 1.21 g of MeOH was added to the
contact mixture. The contact mixture was stirred for an addition
120 min before adding 1.95 g of water. The contact mixture was then
stirred overnight at 80.degree. C. (14 h 40 min) at which time, the
experiment was aborted and the remaining sample was processed as
above.
[0235] The contact times, DS and molecular weights for isolated
samples removed from the contact mixture are summarized below in
Table 3.
TABLE-US-00003 TABLE 3 Effect of Randomization on Cellulose
Acetates Example Time (min) DS Mw Mw/Mn 8-1 16 1.95 26492 1.54 8-2
18 2.15 24838 1.57 8-3 21 2.24 23973 1.63 8-4 25 2.33 23043 1.7 8-5
32 2.42 23499 1.79 8-6 57 2.56 21736 1.82 8-7 190 2.73 20452 2.08
8-8 After MeOH Addition 2.73 20478 2.00 8-10 After H.sub.2O
Addition 2.59 21005 1.89
[0236] With increasing contact time, the DS increased (until water
was added) and the Mw decreased. Fifty-seven minutes after starting
the contact period, the cellulose acetate sample had a DS of 2.56
and a Mw of 21,736. Prior to adding the MeOH/water, the DS was 2.73
and the Mw was 20,452. After the water contact period, the isolated
cellulose acetate had a DS of 2.59 and a Mw of 21,005 indicating
that the DS was reduced but the Mw was unchanged.
[0237] FIG. 15 shows the proton NMR spectra of a cellulose acetate
prepared by direct acetylation (DS=2.56) and after randomization
(DS=2.59). Both the ring protons attached to the anhydroglucose
monomers and acetyl protons attached to the acetyl substituents are
shown. FIG. 15 demonstrates that even though these two cellulose
acetates have much essentially the same DS, they have a much
different monomer content.
Example 9
MSA Secondary Component, Minimal Acylating Reagent
[0238] A 3-neck 100 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with an iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 60.47 g of
1-allyl-3-methylimidazolium chloride. The flask was placed in an
oil bath and heated to 80.degree. C. Microcrystalline cellulose
(9.15 g, 7 wt %, DP ca. 335) was added to 27.3 g of water. After
hand mixing, the cellulose was allowed to stand in the water for 50
min at 60.degree. C. before filtering which gave 9.44 g of a wet
cellulose cake. The water wet cellulose was then added in small
portions to the [AMIm]Cl (5 min addition). Approximately 15 min
after adding the cellulose to the [AMIm]Cl, the flask was placed
under vacuum by gradually lowering the vacuum starting at ca. 120
mm Hg. After ca. 40 min, there were no visible cellulose particles;
IR spectroscopy indicated that all of the cellulose was dissolved.
The solution was left stirring overnight at 80.degree. C. under
vacuum.
[0239] To the cellulose solution heated to 80.degree. C. was added
a mixture of 8.58 g Ac.sub.2O (3 eq) and 537 mg (0.2 eq) of MSA
drop wise (5 min). The reaction was sampled throughout the reaction
period by removing 6-10 g aliquots of the reaction mixture and
precipitating in 100 mL of MeOH. The solid from each aliquot was
washed 3.times. with 100 mL portions of MeOH then dried at
60.degree. C., 5 mm Hg. After all of the Ac.sub.2O appeared to be
consumed by IR, the experiment was aborted and the remaining sample
was processed as above.
[0240] The contact times, DS and molecular weights for isolated
samples removed from the contact mixture are summarized below in
Table 4.
TABLE-US-00004 TABLE 4 Contact Times and Properties of Cellulose
Acetate Prepared in [AMIm]Cl. Example Time (min) DS Mw Mw/Mn 9-1 5
1.74 36192 1.69 9-2 8 2.24 35734 1.84 9-3 11 2.38 32913 1.9 9-4 15
2.48 31811 1.99 9-5 24 2.60 31970 2.14 9-6 50 2.74 31302 2.36 9-7
109 2.82 30808 2.48
[0241] Five minutes after starting the reaction, the first
cellulose acetate sample had a DS of 1.74 and a Mw of 36,192. With
increasing contact time, the DS increased and the Mw decreased.
After 109 min, the DS was 2.82 and the Mw was 30,808. This example
shows that, compared to the conventional method of Example 11 (5 eq
Ac.sub.2O, 6.5 h contact time), the method of Example 9 provides
for a higher DS and a significant reduction in cellulose acetate
molecular weight. For example, the conventional method of Example
11 requires 6.5 h to provide a cellulose acetate with a DS of 2.42
and a Mw of 50,839 while in Example 9, a cellulose acetate with a
DS of 2.48 and a Mw of 31,811 was achieved in 15 min.
Example 10
Conventional Cellulose Ester Preparation (Comparative)
[0242] A solution of cellulose (5 wt %) dissolved in 29.17 g of
[BMIm]Cl was heated to 80.degree. C. with an oil bath. The solution
was held under vacuum (ca. 7 mm Hg) while stirring for 2 h. To the
cellulose solution was added 4.6 g (5 eq) of Ac.sub.2O (5 min
addition). During the course of the reaction, the solution color
became gradually darker (brown). After 2.5 h, the solution had
gelled so the contact solution was allowed to cool to room
temperature. The product was isolated by adding the solution to
water then homogenizing to give a dispersed gel/powder. The mixture
was filtered and washed extensively with water. After drying the
solid invacuo at 50.degree. C., 2.04 g of a pink powder was
obtained that was insoluble in acetone. Analysis by .sup.1H NMR
indicated that the sample had a DS of 2.52 and a Mw of 73,261.
Example 11
Conventional Cellulose Ester Preparation (Comparative)
[0243] To a 3-neck 100 mL round bottom flask equipped for
mechanical stirring and with an N.sub.2/vacuum inlet added 33.8 g
of 1-allyl-3-methylimidazolium chloride. While stirring rapidly,
added 1.78 g of dry cellulose powder (DP ca. 335). The flask was
placed under vacuum (2 mm Hg) and the mixture was stirred at room
temperature to insure that the cellulose was well dispersed. After
15 min, the cellulose was well dispersed and the solution viscosity
was rising. The flask was placed in an oil bath which was heated to
80.degree. C. After 40 min, all of the cellulose was dissolved. The
solution was maintained at 80.degree. C. for 6.5 h before allowing
the solution to cool to room temperature and stand overnight.
[0244] The viscous solution was heated to 80.degree. C. before
adding 5.6 g (5 eq) of Ac.sub.2O drop wise (15 min). After 5 h, the
product was isolated by pouring the mixture into 300 mL of MeOH.
The MeOH/solid slurry was stirred for ca. 30 min before filtering
to remove the liquids. The solid was then taken up in two 200 mL
portions of MeOH and the slurry was stirred for ca. 30 min before
filtering to remove the liquids. The solids were dried overnight at
55.degree. C. (6 mm Hg) which gave 2.27 g of a powder that gave a
hazy acetone solution. Analysis by .sup.1H NMR and by GPC indicated
that the sample had a DS of 2.42 and a Mw of 50,839.
Example 12
MSA Secondary Component, Long Chain Aliphatic Cellulose Esters
[0245] A solution of cellulose (5 wt %) dissolved in [BMIm]Cl was
heated to 80.degree. C. with an oil bath. The solution was held
under vacuum (ca. 2.5 mm Hg) while stirring for 4 h. To the
cellulose solution was added a mixture of 10.88 g (5 eq) of
nonanoic anhydride and 141 mg of MSA (25 min addition). After 18.5
h, the solution was allowed to cool to room temperature before it
was poured into a solution of 80:20 MeOH:H.sub.2O. After filtering
the solid was washed extensively with 85:15 MeOH:H.sub.2O then with
95:5 MeOH:H.sub.2O. The sample was dried invacuo which gave 3.7 g
of a white powder soluble in isododecane. Analysis by .sup.1H NMR
indicated that the product was cellulose nonanoate with a DS of
2.49.
[0246] Obtainment of a cellulose nonanoate with a high degree of
substitution by the method of this example is surprising in view of
conventional teachings that long chain aliphatic cellulose esters
with a DS greater than ca. 1.5 cannot be prepared in ionic
liquids.
Example 13
MSA Secondary Component, C3 and C4 Alphatic Cellulose Esters
[0247] A solution of cellulose (5 wt %) dissolved in [BMIm]Cl was
heated to 80.degree. C. with an oil bath. The solution was held
under vacuum (ca. 6 mm Hg) while stirring overnight. To the
cellulose solution was added a mixture of 7.91 g (5 eq) of butyric
anhydride and 190 mg of MSA (25 min addition). After 2.6 h, the
solution was allowed to cool to room temperature before it was
poured into water. The solid was washed extensively with water
before drying invacuo which gave 2.62 g of a white powder soluble
in acetone and 90:10 CHCl.sub.3:MeOH. Analysis by .sup.1H NMR
indicated that the product was cellulose butyrate with a DS of
2.59.
[0248] This example shows that C3 and C4 aliphatic cellulose esters
with high degrees of substitution can be prepared by the methods of
this example.
Example 14
Homogenization of Cellulose Solution
[0249] To a 1 L flat bottom kettle was added 193.6 g of solid
[BMIm]Cl. A 3 neck top was placed on the kettle and the kettle was
fitted with a N.sub.2/vacuum inlet and for mechanical stirring. The
kettle was then placed in an 80.degree. C. oil bath and the
[BMIm]Cl was melted while stirring under a 6 mm Hg vacuum. After
the [BMIm]Cl was completely melted, 10.2 g of previously dried
cellulose (DP ca. 335) was added and the mixture was homogenized
with a Heidolph Silent Crusher. After ca. 3 min of homogenization,
essentially all of the cellulose was dissolved. The solution was
stirred under vacuum (6 mm Hg) for an additional 1.5 h at which
time, all of the cellulose was dissolved.
[0250] This example illustrates that high intensity mixing can be
used to disperse the cellulose (increased surface area) which leads
to rapid cellulose dissolution.
Example 15
Acetone Solubility
[0251] The solubilities of cellulose acetate in acetone were
evaluated as follows: Acetone (Burdick & Jackson high purity
grade) was dried prior to use using 4 A molecular sieves (purchased
from Aldrich and stored in an oven at 125.degree. C.). All of the
cellulose acetates were dried prior to use in a vacuum oven
(Eurotherm 91e) at 60.degree. C., 5 mm Hg for at least 12 h. Each
cellulose acetate was weighed into a 2 Dram vial (100 mg.+-.1 mg)
and 1 mL.+-.5 .mu.L of dry acetone was then added to the vial
(vials were obtained from VWR). The vials were then placed in an
ultrasonic bath (VWR, model 75HT) and ultrasonicated at room
temperature for 30-120 min then removed and vortexed (VWR
minivortexer) at room temperature using a speed setting of 10. If
the cellulose acetate appeared to be dissolving but the rate of
dissolution appeared to be slow, the vial was placed on a roller
and mixed (ca. 15 revolutions per min) overnight at ambient
temperature. Following the mixing period, the solubility of each
cellulose acetate was rated as follows:
TABLE-US-00005 Rating Description 1 Soluble, transparent with no
visible particles 2 Partially soluble, hazy 3 Partially soluble,
very hazy, visible particles 4 Gel 5 Swollen solid 6 Insoluble
Cellulose acetates with a rating of 1 are very useful in all
applications in which acetone solubility or solubility in related
solvents (e.g. diethyl phthalate) is a critical factor (e.g.
solvent spinning of acetate fiber or melt processing of plasticized
cellulose acetate). Cellulose acetates with a rating of 2 or 3
would require additional filtration to remove insoluble particles
and/or the use of co-solvents before they would have utility.
Cellulose acetates with a rating of 4-6 would not have utility in
these applications. Hence, cellulose acetates with a rating of 1
are highly desired.
[0252] The solubility in acetone of cellulose acetates prepared in
Examples 3-6,8,9 are compared (Table 5, below) to the solubilities
of the cellulose acetates in Examples 1, 2 and to cellulose
acetates (Examples 15-1 to 15-6) prepared by traditional methods.
The cellulose acetates prepared by traditional methods were
prepared by acetylation of cellulose to make cellulose triacetate
followed by H.sub.2SO.sub.4 catalyzed reduction of DS, a process
know to yield cellulose acetates that are random copolymers. In the
absence of water (dry acetone), the acetone solubility of these
cellulose acetates is known to be limited to a narrow range (from
about 2.48 to about 2.52).
TABLE-US-00006 TABLE 5 Solubility of Cellulose Acetate in Acetone
(100 mg/mL). Example DS Solubility 1-1 1.82 5 1-2 2.25 4 1-3 2.44 4
2-1 0.64 5 2-2 1.49 5 2-3 1.73 5 2-4 2.01 5 2-5 2.05 5 3-1 1.81 5
3-2 2.18 1 3-3 2.39 1 3-4 2.52 2 3-5 2.62 3 3-6 2.72 3 4-1 1.58 6
4-2 1.94 2 4-3 2.15 1 4-4 2.28 1 4-5 2.63 2 5-1 1.95 2 5-2 2.21 1
5-3 2.35 1 5-4 2.52 2 5-5 2.59 2 5-6 2.60 2 5-7 2.66 3 5-8 2.67 3
6-1 2.63 2 6-2 2.75 3 6-3 2.80 3 6-4 2.87 3 6-5 2.89 3 6-6 2.96 3
8-1 1.95 3 8-2 2.15 1 8-3 2.24 1 8-4 2.33 1 8-5 2.42 1 8-6 2.56 2
8-7 2.73 2 9-1 1.74 5 9-2 2.24 1 9-3 2.38 1 9-4 2.48 2 9-5 2.60 3
9-6 2.74 3 9-7 2.82 3 15-1 2.48 1 15-2 2.46 2 15-3 2.16 3 15-4 1.99
5 15-5 1.96 5 15-6 1.80 6
[0253] Careful examination of Table 5 reveals that the cellulose
acetates having a DS from about 2.42 to about 2.15 that were
produced by acetylation of cellulose dissolved in ionic liquids in
the presence of a secondary component (Examples 3-6,8,9) all have a
acetone solubility rating of 1. That is, all of these samples yield
transparent acetone solutions in which there are no visible
particles. In contrast, cellulose acetates produced by acetylation
of cellulose dissolved in ionic liquids in the absence of a
secondary component (Examples 1 and 2) have acetone solubility
ratings of 4-5 regardless of DS. For example, Example 1-2 (no
secondary component) has a DS of 2.25 and this cellulose acetate
forms a gel in acetone while Examples 8-3 and 9-2 (includes
secondary component) have a DS of 2.24 and these cellulose acetates
yield transparent acetone solutions. In agreement with what is
known about cellulose acetates prepared by traditional methods,
only one of the cellulose acetates examined (15-1, DS=2.48) has an
acetone solubility rating of 1. Example 15-3 (DS=2.16) has an
acetone solubility rating of 3 as opposed to Examples 4-3 and 8-2
(DS=2.15) which have acetone solubility ratings of 1.
[0254] This example shows that cellulose acetates produced by
acetylation of cellulose dissolved in ionic liquids in the presence
of a secondary component having a DS of about 2.4 to about 2.1
yield transparent acetone solutions. In the absence of a secondary
component, none of the cellulose acetates yield transparent acetone
solutions. Furthermore, the DS range that yield transparent acetone
solutions when using cellulose acetates produced by acetylation of
cellulose dissolved in ionic liquids in the presence of a secondary
component is broader and lower relative to cellulose acetates
produced by traditional methods. Without wishing to be bound by
theory, the evidence indicates that these solubility differences
reflect a difference in copolymer compositions.
Example 16
Purification of [BMIm]acetate
[0255] To a 1 L 3-neck round bottom flask was added 360 mL of
water, 1.30 g of acetic acid, and 5.68 g of Ba(OH).sub.2.H.sub.2O.
The mixture was heated to 80.degree. C. giving a translucent
solution. To this solution was added 300 g of commercial [BMIm]OAc
dropwise (1 h addition) containing 0.156 wt % sulfur as determined
by XRF. The solution was held at 80.degree. C. for an addition hour
before allowing the solution to cool to room temperature. The
solids formed during the reaction were removed by centrifuging
before concentration the solution in vacuo (60-65.degree. C., 20-80
mm Hg) to a pale yellow liquid. The liquid was extracted with two
300 mL portions of EtOAc. The liquid was concentrated first at
60.degree. C., 20-50 mm Hg then at 90.degree. C., 4 mm Hg leading
to 297.8 g of a pale yellow oil. Proton NMR confirmed the formation
of the [BMIm]OAc which, by XRF, contained 0.026 wt % sulfur.
Example 17
Preparation of [BMIm]propionate
[0256] To a 1 L 3-neck round bottom flask was added 400 mL of
water, 62.7 g of acetic acid, and 267 g of Ba(OH).sub.2.H.sub.2O.
The mixture was heated to 74.degree. C. giving a translucent
solution. To this solution was added 100 g of commercial
[BMIm]HSO.sub.4 dropwise (1.75 h addition). The solution was held
at 74-76.degree. C. for an addition 30 min before allowing the
solution to cool to room temperature and stand overnight (ca. 14
h). The solids formed during the reaction were removed by
filtration before concentration the solution in vacuo which gave an
oil containing solids which formed during concentration. The solids
were removed centrifuging giving an amber liquid. Additional
product was obtained by slurring the solids in EtOH and
centrifuging. The liquids were concentrated first at 60.degree. C.,
20-50 mmHg then at 90.degree. C., 4 mm Hg leading to 65.8 g of an
amber oil. Proton NMR confirmed the formation of the [BMIm]OPr
which, by XRF, contained 0.011 wt % sulfur.
Example 18
Preparation of [BMIm]formate
[0257] To 300 mL autoclave was added 25 g of 1-butylimidazole, 45.4
g (3.75 eq) of methyl formate, and 21 mL of MeOH (2.58 eq). The
autoclave was pressurized to 1035 kPa before heating the solution
to 150.degree. C. The contact solution was maintained at
150.degree. C. for 18 h. The solution was allowed to cool to room
temperature before removing the volatiles components in vacuo.
Proton NMR of the crude reaction mixture revealed that 89% of the
1-butylimidazole was converted to [BMIm]formate. Purified
[BMIm]formate was obtained by removal of 1-butylimidazole from the
crude product by distillation.
Example 19
Conversion of [BMIm]formate to [BMIm]acetate Using Methyl
Acetate
[0258] To 300 mL autoclave was added 25 g of [BMIm]formate, 50.3 g
(5.0 eq) of methyl acetate, and 50 mL of MeOH (9 eq). The autoclave
was pressurized to 1035 kPa before heating the solution to
170.degree. C. The contact solution was maintained 170.degree. C.
for 15.3 h. The solution was allowed to cool to room temperature
before removing the volatiles components in vacuo. Proton NMR of
the reaction mixture revealed that 57% of the [BMIm]formate was
converted to [BMIm]acetate.
Example 20
Conversion of [BMIm]formate to [BMIm]acetate Using Acetic
Anhydride
[0259] To 25 mL single-neck round bottom flask was added 11.1 g of
[BMIm]formate. Acetic anhydride (6.15 g) was added dropwise to the
[BMIm]formate. Evolution of gas was noted during the addition as
well as warming of the solution (47.degree. C.). The flask was then
placed in a preheated 50.degree. C. water bath for 45 min before
applying a vacuum (4 mm Hg) and heating to 80.degree. C. to remove
the volatile components. Analysis of the resulting liquid by
.sup.1H NMR indicated 100% conversion of the starting material to
[BMIm]acetate.
Example 21
Conversion of [BMIm]formate to [BMIm]acetate Using Acetic Acid
[0260] To 300 mL autoclave was added 25 g of [BMIm]formate, 87.4 g
(6.3 eq) of acetic acid, and 23.1 g of MeOH (5.3 eq). The autoclave
was pressurized to 1035 kPa before heating the solution to
150.degree. C. The contact solution was maintained 150.degree. C.
for 14 h. The solution was allowed to cool to room temperature
before removing the volatiles components in vacuo. Proton NMR of
the reaction mixture revealed that 41% of the [BMIm]formate was
converted to [BMIm]acetate.
Example 22
Conversion of [BMIm]acetate to [BMIm]formate Using Methyl
Formate
[0261] To 1 L autoclave was added 100.7 g of [BMIm]acetate, 152.5 g
(5 eq) of methyl formate, and 200 mL of MeOH (9.7 eq). The
autoclave was pressurized to 1035 kPa before heating the solution
to 140.degree. C. The contact solution was maintained 140.degree.
C. for 18 h. The solution was allowed to cool to room temperature
before removing the volatiles components in vacuo. Proton NMR of
the reaction mixture revealed that 100% of the [BMIm]acetate was
converted to [BMIm]formate.
Example 23
Comparison of High and Low Sulfur [BMIm]OAc
23A:
[0262] To a 100 mL 3-neck round bottom flask was added 32.75 g of
commercial high sulfur [BMIm]OAc (0.156 wt % sulfur) and 1.72 g of
cellulose powder. This mixture was briefly homogenized at ambient
temperature before the flask was placed in a preheated 80.degree.
C. oil bath. The mixture was stirred at 80.degree. C., 2 mm Hg for
1.75 h; ca. 15 min was required to completely dissolve the
cellulose. The straw colored solution was allowed to cool to room
temperature and stand under vacuum overnight (ca. 14 h).
[0263] To the mechanically stirred solution was added a solution of
methane sulfonic acid (MSA, 210 mg) and acetic anhydride (5.42 g, 5
eq/AGU) dropwise (23 min). At the end of the addition, the
temperature of the contact mixture was 35.degree. C. and the
solution was dark amber. After 1.5 h from the start of the
addition, 5.5 g of the contact mixture was removed and the product
was isolated by precipitation in MeOH. The contact mixture was then
heated to 50.degree. C. (25 min heat up time) and stirred for 1.5 h
before 6.5 g of solution was removed and poured into MeOH. The
remaining contact solution was heated to 80.degree. C. (25 min heat
up) and stirred for 2.5 h before pouring into MeOH. All of the
solids obtained by precipitation in MeOH were isolated by
filtration, washed extensively with MeOH, and dried overnight at
50.degree. C., 5 mm Hg.
23B:
[0264] An identical reaction to 23A was conducted side-by-side
using 37.02 g of low sulfur [BMIm]OAc (0.025 wt % sulfur, cf.
example 1), 1.95 g of cellulose, 6.14 g of acetic anhydride, and
222 mg of MSA.
[0265] The grams of product isolated and the analysis of each
product is summarized below in Table 6.
TABLE-US-00007 TABLE 6 Yield and Properties of CA Prepared in
[BMIm]OAc Entry Yield (g) DS Mn Mw Mz 23A-RT 0.37 2.53 15123 54139
135397 23A-50.degree. C. 0.45 2.65 12469 51688 123527
23A-80.degree. C. 1.36 2.62 15828 85493 237785 23B-RT 0.29 0.80
14499 65744 301858 23B-50.degree. C. 0.40 0.80 14768 57066 227833
23B-80.degree. C. 1.26 0.76 16100 70293 325094
[0266] As can be seen from Table 6, above, the DS of the CA made
using the high sulfur [BMIm]OAc as solvent was higher and the
molecular weight lower relative to the CA made using the low sulfur
[BMIm]OAc as solvent. Despite the increased temperature and
extended contact time, the DS did not increase significantly above
that observed after 1.5 h contact time at room temperature
regardless of which [BMIm]OAc was used as the solvent. Another
notable feature of this example was the color of the solutions and
products. The contact solution involving high sulfur [BMIm]OAc
solvent was black at all temperatures while the contact solution
involving low sulfur [BMIm]OAc solvent retained the straw color
typical of these solutions prior to the addition of the anhydride.
The CA solids obtained from the high sulfur [BMIm]OAc solvent were
brown to black in appearance while the CA solids obtained from the
low sulfur [BMIm]OAc solvent were white and provided colorless
solutions upon dissolution in an appropriate solvent.
[0267] This example shows that impurities (e.g., sulfur or halides)
in the high sulfur [BMIm]OAc can act as a catalyst in the
esterification of cellulose dissolved in the [BMIm]OAc. However,
the same impurities negatively impact the molecular weight and
quality of the product in such a manner that the CA does not have
practical value. When cellulose is dissolved in [BMIm]OAc
containing no or little of these impurities, high-quality CA can be
obtained. By introduction of an appropriate catalyst, high quality
CA with the desired DS can be obtained in a predictable manner.
Example 24
Acetylation of Cellulose in High Chloride [EMIm]OAc
[0268] Cellulose (1.19 g) was dissolved in 22.65 g of commercial
[EMIm]OAc which, by XRF, contained 0.463 wt % chloride following
the general procedure described in Example 8 with the exception
that the mixture was not homogenized prior to heating to 80.degree.
C.
[0269] To the mechanically stirred straw colored solution preheated
to 80.degree. C. was added a solution of MSA (141 mg) and acetic
anhydride (3.76 g, 5 eq/AGU) dropwise (10 min). By the end of the
addition, the contact mixture became dark brown-black. The contact
solution was stirred for 2.5 h before pouring into H.sub.2O. The
resulting solids were isolated by filtration, washed extensively
with H.sub.2O, and dried overnight at 50.degree. C., 5 mm Hg. This
yielded 1.57 g of a brown-black CA powder. Analysis revealed that
the CA had a DS of 2.21 and that the Mw was 42,206.
[0270] This example shows that [EMIm]OAc containing high levels of
halides is not a suitable solvent for esterification of
cellulose.
Example 25
Acetylation of Cellulose in [BMIn]Cl and [BMIm]OAc
25A:
[0271] Previously dried cellulose (13.2 g) and solid [BMIm]Cl
(250.9 g, mp=70.degree. C.) were combined in a glass jar. The glass
jar was placed in a preheated 40.degree. C. vacuum oven and heated
to 80.degree. C. over 3 h. The sample was allowed to stand under
vacuum at 80.degree. C. for ca. 14 h before the jar was removed.
The sample was immediately homogenized giving a clear solution of
cellulose.
[0272] To a 100 mL 3-neck round bottom flask was added 33.6 g of
the cellulose solution prepared above. The flask was placed in a
preheated 80.degree. C. oil bath and a vacuum was applied (7-8 mm
Hg). The solution was then stirred for 21 h while at 80.degree. C.
and under vacuum. The cellulose solution was then allowed to cool
to 38.degree. C.; the temperature could not be lowered further due
to the solution viscosity. Acetic anhydride (5.3 g, 5 eq/AGU) was
added dropwise over 7 min. The contact mixture was then stirred at
32-35.degree. C. for 2 h before a small amount of the solution was
removed and poured into MeOH resulting in precipitation of the
cellulose acetate. The remaining contact mixture was then heated to
50.degree. C. and held at that temperature for 1.6 h before
removing a small amount of the solution which was poured into MeOH
to precipitate the cellulose acetate. The remaining contact mixture
was then heated to 80.degree. C. and held at that temperature for
1.5 h before allowing the solution to cool and adding 60 mL of MeOH
to precipitate the cellulose acetate. All three samples were washed
extensively with MeOH then dried at 50.degree. C., 5 mm Hg
overnight.
25B:
[0273] To a 100 mL 3-neck round bottom flask was added 31.3 g of
the cellulose solution prepared above. The same general protocol as
used in the previous reaction was followed with the exception that
Zn(OAc).sub.2 (0.05 eq/AGU) was added to the cellulose solution
prior to cooling to 38.degree. C.
25C:
[0274] To a 100 mL 3-neck round bottom flask was added 27.41 g of
low sulfur [BMIm]OAc liquid (cf. example 16) and 1.44 g of
cellulose. The flask was placed in a preheated 80.degree. C. oil
bath and the mixture was allowed to stir overnight (ca. 14 h) under
a 2 mm Hg vacuum.
[0275] After cooling the solution to room temperature (25.1.degree.
C.), Ac.sub.2O (5 eq/AGU) was added to the cellulose solution
dropwise (25 min addition). The contact mixture was stirred for 1.8
h at room temperature before removing a small portion of the
solution which was poured into MeOH to precipitate the cellulose
acetate. The remaining contact mixture was heated to 50.degree. C.
and maintained at that temperature for 1.5 h before removing a
small portion of the solution which was poured into MeOH to
precipitate the cellulose acetate. The remaining contact mixture
was heated to 80.degree. C. and maintained at that temperature for
2.5 h before cooling and pouring into MeOH. All three samples were
washed extensively with MeOH then dried at 50.degree. C., 5 mm Hg
overnight.
25D:
[0276] To a 100 mL 3-neck round bottom flask was added 25.55 g of
low sulfur [BMIm]OAc liquid (cf. example 16) and 1.35 g of
cellulose. The flask was placed in a preheated 80.degree. C. oil
bath and the mixture was allowed to stir overnight (ca. 14 h) under
a 2 mm Hg vacuum. The same general protocol as used in the previous
reaction was followed with the exception that Zn(OAc).sub.2 (0.05
eq/AGU) was added to the cellulose solution prior to cooling to
room temperature.
[0277] Analysis of the cellulose acetates isolated from these 4
comparative reactions (25A-25D) is summarized below in Table 7.
TABLE-US-00008 TABLE 7 Physical properties of CA prepared in
[BMIm]Cl or [BMIm]OAc Entry Solvent Catalyst DS Mn Mw Mz 25A-RT
[BMIm]Cl none 0.57 7753 16777 32019 25A-50.degree. C. [BMIm]Cl none
1.42 9892 19083 33019 25A-80.degree. C. [BMIm]Cl none 2.27 11639
21116 34138 25B-RT [BMIm]Cl Zn(OAc).sub.2 1.77 8921 19468 36447
25B-50.degree. C. [BMIm]Cl Zn(OAc).sub.2 2.32 7652 18849 38367
25B-80.degree. C. [BMIm]Cl Zn(OAc).sub.2 2.75 7149 18964 38799
25C-RT [BMIm]OAc none 1.17 7039 41534 118265 25C-50.degree. C.
[BMIm]OAc none 1.17 7839 45116 136055 25C-80.degree. C. [BMIm]OAc
none 1.17 7943 48559 165491 25D-RT [BMIm]OAc Zn(OAc).sub.2 2.27
8478 47730 125440 25D-50.degree. C. [BMIm]OAc Zn(OAc).sub.2 2.30
11017 53181 136619 25D-80.degree. C. [BMIm]OAc Zn(OAc).sub.2 2.34
12096 56469 141568
[0278] This comparative example illustrates a number of important
points. In the case of [BMIm]Cl, the DS of the cellulose acetate
increases with each contact time-temperature from 0.57 to 2.27. The
same trend is observed with [BMIm]Cl+Zn(OAc).sub.2 with the
exception that the DS at each contact time-temperature is higher
due to the Zn(OAc).sub.2 which acts as a catalyst. In the case of
[BMIm]OAc, with or without Zn(OAc).sub.2, the DS does not
significantly change from that obtained at room temperature with
increasing contact time-temperature; the total DS is significantly
increased by the action of the Zn(OAc).sub.2. This unexpected
observation indicates that acetylation of cellulose dissolved in
[BMIm]OAc is much faster at lower temperatures relative to that
observed in acetylation of cellulose dissolved in [BMIm]Cl. It
should also be noted that a transition metal like Zn is very
effective in catalyzing or promoting the acylation of cellulose
dissolved in ionic liquids. Finally, it should also be noted that
the molecular weights of the cellulose acetates obtained by
acetylation of cellulose dissolved in [BMIm]OAc is significantly
greater relative to when cellulose is dissolved in [BMIm]Cl.
Example 26
Preparation of Mixed Cellulose Esters
[0279] The following general procedure was used to prepare
cellulose mixed esters. To a 100 mL 3-neck round bottom flask was
added the desired amount of 1-butyl-3-methylimidazolium
carboxylate. While stirring at room temperature, 5 wt % cellulose
was slowly added to the ionic liquid. After the cellulose was
dispersed in the ionic liquid, the flask was placed under vacuum
(2-5 mm Hg) and the contact mixture was heated to 80.degree. C. The
contact solution was then stirred for ca. 2 h before adding 0.1
eg/AGU of Zn(OAc).sub.2. The contact solution was stirred for ca.
30 min before the solution was allowed to cool to room temperature
and stand overnight (ca. 14 h).
[0280] The contact solution was placed under N.sub.2 before the
dropwise addition of 5 eq/AGU of the desired carboxylic anhydride.
When the addition was complete, the flask was placed in a preheated
40.degree. C. oil bath. The contact mixture was stirred for 5 h
before the solution was allowed to cool and poured into MeOH. The
resulting solids were isolated by filtration, washed extensively
with MeOH, and dried in vacuo (50.degree. C., 5 mm Hg). The
products were characterized by .sup.1H NMR and the results are
summarized below in Table 8.
TABLE-US-00009 TABLE 8 Cellulose Esters Prepared in Different Alkyl
Imidazolium Carboxylates Entry Ionic liquid Anhydride DS.sub.Total
DS.sub.Ac DS.sub.Pr DS.sub.Bu 1 [BMIm]OAc Bu.sub.2O 2.40 2.43 --
0.45 2 [BMIm]OBu Ac.sub.2O 2.43 2.30 -- 0.70 3 [BMIm]OPr Bu.sub.2O
2.52 -- 1.95 1.05
[0281] Note that in Table 8, above, the DS of the individual
substituents have been normalized to 3.0 for comparison purposes.
As this example illustrates, when cellulose is dissolved in an
alkyl imidazolium carboxylate and contacted with an carboxylic
anhydride different from the anion of the ionic liquid, the product
is a cellulose mixed ester. That is, the cellulose substituents
come from the added anhydride and from the alkyl imidazolium
carboxylate. In effect, the alkyl imidazolium carboxylate is acting
as an acyl donor.
Example 27
Removal of Carboxylic Acid
[0282] To each vessel of a 4 vessel Multimax high pressure reactor
equipped with an in situ infrared probe was added previously dried
[BMIm]OAc, 1 molar equivalent of acetic acid based on ionic liquid,
different molar amounts of MeOH based on acetic acid, and
optionally, a catalyst (2 mol %). The pressure in each vessel was
increased to 5 bar over a 3 min period before the contact
temperature was increased to 140.degree. C. over a 25 min period.
The contact mixtures were then held at 140.degree. C. for 10-15 h
and the reaction in each vessel was monitored by infrared
spectroscopy. The vessels were allowed to cool to 25.degree. C.
over a 30 min period. The contents of each vessel were then
concentrated invacuo to remove all volatile components before
analyzing each sample by proton NMR. FIG. 16 shows a plot of wt %
acetic acid versus time as determined by infrared spectroscopy; the
final concentration of acetic acid was confirmed by .sup.1H NMR.
FIG. 16 shows that in all cases, the reactions were complete within
9-10 h. The most significant factor affecting the rates and extend
of reaction was the number of molar equivalents of MeOH. The wt %
acetic acid remaining in the [BMIm]OAc ranged from 7.4 wt % to 2.2
wt %.
[0283] With typical distillation techniques, it is extremely
difficult to get the excess carboxylic acid concentration below 1
molar equivalent based on carboxylated ionic liquid. In the case of
acetic acid in [BMIm]OAc, this corresponds to ca. 23 wt % acetic
acid. This example shows that, by conversion of the acetic acid to
methyl acetate which is much more easily removed, the amount of
residual acetic acid can be reduced well below 23 wt %. The amount
of acetic acid removed will depend upon the amount of acetic acid
initially present, concentration of MeOH, contact times, and
contact temperature. As shown in this example, it is not necessary
to remove all of residual carboxylic acid; in many instances, it is
desirable to have residual carboxylic acid.
Example 28
Solubility of Cellulose in Ionic Liquid
[0284] Samples of 1-butyl-3-methylimmidazolium acetate containing
different amounts of acetic acid in 2 oz jars were dried at
80.degree. C..+-..degree.5, ca. 3 mm Hg overnight (ca. 14 h).
Examples 28-1 through 28-5 were prepared by the method of Example
27. Examples 28-6 through 28-8 were prepared by adding a known
amount of acetic acid to neat [BMIm]OAc (Table). Cellulose (5 wt %,
DP 335), was added to each [BMIm]OAc sample and the each sample was
briefly homogenized. Each sample was transferred to a microwave
reaction vessel which was then capped with an air tight lid then
placed in a 48 cell microwave rotor. The rotor was placed in a
Anton Paar Synthos 3000 microwave and the cellulose-[BMIm]OAc
mixtures were heated to 100.degree. C. using a 3 min ramp and held
for 10 min before heating to 120.degree. C. using a 3 min ramp and
held for 5 min. Inspection of each vessel indicated that the
cellulose in each example was dissolved in the [BMIm]OAc.
TABLE-US-00010 TABLE 9 Solubility of Cellulose in [BMIm] OAc
Example wt % HOAc IL (g) Soluble 28-1 2.2 6.16 y 28-2 2.8 8.78 y
28-3 5.8 8.48 y 28-4 6.6 8.48 y 28-5 7.4 8.15 y 28-6 10.0 10.23 y
28-7 12.5 10.26 y 28-8 14.5 10.18 y
[0285] This example shows that excess residual carboxylic acid in
ionic liquids can be reduced by the method of Example 27 and that
the recycled ionic liquid can then be used to dissolve cellulose so
that the solutions can be used for preparing cellulose esters. This
example also shows that cellulose can be dissolved in an ionic
liquid containing up to about 15 wt % carboxylic acid.
Example 29
Recycling of Ionic Liquid
[0286] To a 500 mL flat bottom kettle was added 299.7 g of
[BMIm]OAc. A 4-neck top was placed on the kettle and the kettle was
fitted with a N.sub.2/vacuum inlet, a React IR 4000 diamond tipped
IR probe, a thermocouple, and for mechanical stirring. The kettle
contents were placed under vacuum (ca. 4.5 mm Hg) and heated to
80.degree. C. using an oil bath. The removal of water from the
[BMIm]OAc was followed by infrared spectroscopy (FIG. 17). After
ca. 16 h, the oil bath was removed and the kettle contents were
allowed to cool to room temperature.
[0287] To the ionic liquid was added 3.77 g of Zn(OAc).sub.2. The
mixture was stirred for ca. 75 minutes to allow the Zn(OAc).sub.2
to dissolve before slowly adding 33.3 g (10 wt %) of previously
dried cellulose (DP ca. 335) over a 26 min period. The mixture was
stirred at room temperature for ca. 4 h at which time no particles
or fiber were visible in the translucent solution; infrared
spectroscopy indicated that all of the cellulose was dissolved
(FIG. 18). The solution was heated to 80.degree. C. By the time the
temperature reached 60.degree. C., the translucent solution was
completely clear. After reaching 80.degree. C., the solution was
cooled to room temperature.
[0288] To the cellulose-[BMIm]OAc solution was added 104.9 g of
Ac.sub.2O (5 eq) dropwise over a 70 min period. During the
Ac.sub.2O addition, the contact temperature rose from an initial
value of 21.4.degree. C. to a maximum value of 44.7.degree. C.
Infrared spectroscopy indicated that the Ac.sub.2O was consumed
nearly as fast as it was added (FIG. 19). When all of the Ac.sub.2O
was added, the contact temperature immediately began to decline and
the contact mixture went from a fluid liquid to a flaky gel.
Stirring was continued for an additional 3.5 h but no changes were
observed by infrared spectroscopy.
[0289] The gel was then added to 800 mL of MeOH while stirring
resulting in the precipitation of a white powder. After separation
by filtration, the solids were then washed 3 times with ca. 800 mL
portions of MeOH then 1 time with ca. 900 mL of MeOH containing 11
wt % of 35 wt % H.sub.2O.sub.2. The solids were then dried at
40.degree. C., 3 mm Hg resulting in 60.4 g of a white solid.
Analysis by proton NMR and GPC revealed that the solid was a
cellulose triacetate (DS=3.0) having a Mw of 58,725. The cellulose
triacetate (13.6 wt %) was completely soluble in 90/10
CH.sub.2Cl.sub.2/MeOH from which clear films can be cast. Such
films are useful in constructing liquid crystalline displays and in
photographic film base.
[0290] The precipitation and wash liquids from the cellulose
triacetate isolation were concentrated invacuo at 50.degree. C.
until the vacuum dropped to ca. 3 mm Hg which gave 376.6 g of a
liquid. Proton NMR showed that the liquid was [BMIm]OAc containing
ca. 17 wt % excess acetic acid. To a 1.8 L autoclave was added the
376.8 g of recovered [BMIm]OAc along with 483.8 g of MeOH. The
pressure in autoclave was adjusted to 100 psi with N.sub.2 before
the vessel contents were heated to 140.degree. C. and held for 9 h.
After cooling to room temperature, the volatile components were
removed invacuo which gave 299.8 g of a liquid. Proton NMR showed
the liquid to be [BMIm]OAc containing 2.6 wt % excess acetic acid.
When the weight of the initial [BMIm]OAc is corrected for water
content, the amount of recycled [BMIm]OAc corresponds to 100%
recovery.
[0291] This example shows that cellulose triacetate can rapidly be
prepared from cellulose dissolved in ionic liquids. This example
also shows that excess carboxylic acid can be removed from the
ionic liquid and the recycled ionic liquid can be recovered in high
yield. The recycled ionic liquid can then be used to dissolve
cellulose so that the solutions can be used again for preparing
cellulose esters.
Example 30
Anion Exchange to Form Carboxylated Ionic Liquid
[0292] To a vial containing a small magnetic stir bar was added 4.2
g of [BMIm]formate. An iC10 diamond tipped IR probe was inserted
into the vial so that the reaction could be monitored in situ by
infrared spectroscopy. To the [BMIm]formate was added 0.5 eq of
Ac.sub.2O in one portion. As FIGS. 20 and 21 show, 50% of the
[BMIm]formate was immediately converted to [BMIm]OAc. Additional
spectra were collected to allow the system to stabilize before
adding another 0.5 eq of Ac.sub.2O in one portion. Infrared
spectroscopy indicated that the remaining [BMIm]formate was
immediately converted to [BMIm]OAc.
[0293] This example shows that [BMIm]formate is rapidly converted
to [BMIm]OAc with the addition of Ac.sub.2O. The reaction rate is
so rapid that the [BMIm]formate can be titrated with Ac.sub.2O
until no gas is evolved.
Example 31
Effect of MeOH During Anion Exchange
[0294] To a vial containing a small magnetic stir bar was added
3.15 g of [BMIm]formate. An iC10 diamond tipped IR probe was
inserted into the vial so that the reaction could be monitored in
situ by infrared spectroscopy. To the [BMIm]formate was added 2 eq
of MeOH. After the system thermally stabilized, 1 eq of Ac.sub.2O
was added to the [BMIm]formate in one portion. As FIGS. 22 and 23
show, infrared spectroscopy indicated that the [BMIm]formate was
immediately converted to [BMIm]OAc.
[0295] This example shows that the reaction of [BMIm]formate with
Ac.sub.2O to form [BMIm]OAc is much faster than the reaction of
Ac.sub.2O with MeOH to form MeOAc. Hence, it is not necessary to
remove MeOH from [BMIm]formate prior to converting the
[BMIm]formate to [BMIm]OAc.
Example 32
Effects of Water Modification and MSA
[0296] A 3-neck 250 mL round bottom flask, fitted with two double
neck adapters giving five ports, was equipped for mechanical
stirring, with a iC10 diamond tipped IR probe, and with an
N.sub.2/vacuum inlet. To the flask added 62.37 g of
1-butyl-3-methylimidazolium acetate.
[0297] To 5.06 g (7.5 wt %) of cellulose (DP ca. 335) was added
20.68 g of water. After hand mixing, the cellulose was allowed to
stand in the water for 65 min at 60.degree. C. before filtering
which, gave 10.78 g of a wet cellulose cake. The water wet
cellulose was then added in small portions to the [BMIm]OAc (5 min
addition). Within 5 min, the cellulose was well dispersed in the
ionic liquid (a few small clumps were visible). The mixture was
stirred for 7 min before a preheated 80.degree. C. oil bath was
raised to the flask. The mixture was then stirred for 28 min
(visually, nearly all of the cellulose was dissolved) before slowly
placing the flask contents under vacuum with the aid of a bleed
valve (FIG. 24). After 1.5 h, the vacuum was 1.9 mm Hg. The clear
mixture was then stirred overnight under vacuum at 80.degree.
C.
[0298] The clear solution was allowed to cool to room temperature
15 h 45 min from the point of cellulose addition before adding a
mixture of 12.11 g (3.8 eq) of Ac.sub.2O and 600 mg of MSA dropwise
(28 min addition). The maximum temperature reached during the
Ac.sub.2O addition was 46.degree. C. Eight minutes after completing
the Ac.sub.2O addition, a preheated 50.degree. C. oil bath was
raised to the flask. The mixture was stirred for 16 min before 1.46
g of water was slowly added to the solution (2 min addition). The
solution was then stirred for 17 min before adding an additional
0.47 g of water. The solution was then stirred for 5 h 9 min before
cooling the solution to room temperature. The reaction was sampled
(FIG. 25) throughout the contact period by removing 6-10 g aliquots
of the reaction mixture and precipitating in 100 mL of MeOH. The
solid from each aliquot was washed once with a 100 mL portion of
MeOH then twice with 100 mL of MeOH containing 8 wt % of 35 wt %
H.sub.2O.sub.2. The samples were then dried at 60.degree. C., 5 mm
Hg overnight.
[0299] This example illustrates a number of benefits of the methods
employed herein. As can be seen from FIG. 24, water wet cellulose
can be readily dissolved in carboxylated ionic liquid even when a
significant amount of water still remains in the ionic liquid. As
shown in FIG. 25, the rate of reaction in the acylation of this
cellulose in a carboxylated ionic liquid is very rapid; a
significant concentration of Ac.sub.2O is never observed indicating
that the Ac.sub.2O is consumed as fast as it is added. The rapid
rates of reaction can lead to a much different monomer distribution
relative to that observed in other ionic liquids. For example, FIG.
26 compares the proton resonances of the protons attached to the
anhydroglucose rings of cellulose acetates (DS=2.56) prepared from
cellulose dissolved in [BMIm]OAc (top spectrum) and dissolved in
[BMIm]Cl (bottom spectrum). The major resonances in the top
spectrum centered near 5.04, 5.62, 4.59, 4.29, 4.04, 3.73, and 3.69
correspond to trisubstituted monomers. In the bottom spectrum,
there are much less of these resonances relative to the other type
of monomer resonances. This discovery is significant in that the
rapid rates of reaction provide a means to produce nonrandom
cellulose ester copolymers with different levels of block segments.
The extent and the size of the block segments will depends upon
factors such as mixing, prior water treatment or no water treatment
of the cellulose, concentration and type of catalyst, contact
temperature, and the like. As shown in FIG. 24, 3 samples were
taken prior to the addition of water. These 3 samples ranged in DS
from 2.48-2.56 and at 10 wt % in acetone, they were soluble giving
slightly hazy solutions (solubility rating of 2). In contrast, the
2 samples taken after water addition (DS ca. 2.52) were insoluble
in acetone (solubility rating of 6). FIG. 27 compares the ring
proton resonances for cellulose acetates prepared from cellulose
dissolved in [BMIm]OAc before and after addition of water. The top
spectrum corresponds to a cellulose acetate after water addition
(DS=2.53) and the bottom spectrum corresponds to a cellulose
acetate before water addition (DS=2.56). The differences between
these 2 spectra are consistent with different monomer compositions
in the copolymers.
Example 33
Production of Cellulose Triacetate
[0300] To a 3-neck 100 mL round bottom flask equipped for
mechanical stirring and with an N.sub.2/vacuum inlet added 34.63 g
of 1-ethyl-3-methylimidazolium acetate. While stirring rapidly,
added 6.11 g (15 wt %) of dry cellulose powder (DP ca. 335). The
flask was placed in a 90.degree. C. oil bath and the mixture was
stirred for 10 min before applying vacuum (2 mm Hg). After 50 min,
the oil bath temperature was increased to 100.degree. C. After 2 h
25 min, the oil bath was turned off and left the solution was left
standing under vacuum overnight.
[0301] To the cellulose solution was added a mixture of 731 mg of
MSA and 19.24 g (5 eq) of Ac.sub.2O dropwise. Initially, the
solution was stirred slowly so that the solution did not bunch
around the stir shaft. As the Ac.sub.2O was added, the solution
viscosity dropped; after adding ca. 5 mL, the solution stirred
easily and the stir rate was increased. During the addition, the
solution viscosity did not increase and no localized gels were
observed until the last few drops of Ac.sub.2O were added (40 min
addition). At this point the entire contact mixture suddenly
gelled. The contact temperature rose from 24.1.degree. C. to
47.5.degree. C. by the end of addition. During the addition, there
was little change in the color of the solution. After the reaction
gelled, 11.54 g of the reaction mixture was removed with a spatula
and solids were obtained by precipitation in MeOH (Sample 1). The
flask containing the remaining reaction mixture was then placed in
a preheated 50.degree. C. oil bath. After 20 min at 50.degree. C.,
there was no evidence of the gel softening. Hence, the gel was
allowed to cool to room temperature and 50 mL of MeOH was added to
the flask. The flask contents were then dumped into 400 mL of MeOH
which gave a white precipitate (Sample 2). Both fractions were
processed by stirring the initial slurry for ca. 1 h before
isolating the solids by filtration. The solids were washed by
taking them up in 300 mL of MeOH and stirring the slurry for ca. 1
h before the solids were isolated by filtration. The solids were
twice taken up in 300 mL of 12/1 MeOH/35% H.sub.2O.sub.2 and the
slurry was stirred for ca. 1 h before the solids were isolated by
filtration. The solids were then dried overnight at 50.degree. C.,
ca. 20 mm Hg.
[0302] The combined yield for Sample 1 and 2 was 10.2 g of a white
solid. Analysis by .sup.1H NMR showed that Samples 1 and 2 were
identical and that they were cellulose triacetates with a DS of
3.0. By GPC, both samples have a Mw of ca. 54,000.
[0303] This example shows that cellulose triacetate can rapidly be
prepared from cellulose dissolved in [EMIm]OAc. Cellulose
triacetate can be used to prepare film useful in liquid crystalline
displays and photographic film base.
Example 34
Immiscible Co-Solvent (Effect on IL Viscosity)
[0304] To a 3-neck 50 mL round bottom flask equipped for mechanical
stirring and with an N.sub.2/vacuum inlet added 20.03 g of
1-ethyl-3-methylimidazolium acetate. While stirring rapidly, added
1.05 g of dry cellulose powder (DP ca. 335). The flask was placed
under vacuum (2 mm Hg) and placed in an oil bath preheated to
90.degree. C. After 1 h 45 min, the oil bath temperature was
increased to 100.degree. C. and stirred an additional 55 min (2 h
40 min total contact time) before allowing the solution to cool to
ambient temperature while under vacuum.
[0305] To the cellulose solution was added 20 mL of methyl acetate
resulting in a 2-phase reaction mixture. While stirring rapidly, a
mixture of 131 mg of MSA and 4.63 g of Ac.sub.2O was added drop
wise (10 min). The contact temperature increased from 23.3.degree.
C. to 35.4.degree. C. and, at the end of the addition, the contact
mixture was a single phase and the viscosity of the single phase
was much less than that of the original cellulose-[EMIm]OAc
solution. Twenty-five minutes after beginning the addition, the
flask was placed in a preheated 50.degree. C. oil bath. The contact
mixture was stirred for 2 h at 50.degree. C. before allowing the
contact mixture to cool to ambient temperature over 50 min. The
product was precipitated in 350 mL of MeOH and the slurry was
stirred for ca. 1 h before the solids were isolated by filtration.
The solids were washed by taking them up in 300 mL of MeOH and
stirring the slurry for ca. 1 h before the solids were isolated by
filtration. Twice, the solids were taken up in 300 mL of 12/1
MeOH/35% H.sub.2O.sub.2 and the slurry was stirred for ca. 1 h
before the solids were isolated by filtration. The solids were then
dried overnight at 50.degree. C., ca. 20 mm Hg which gave 1.68 g of
a white solid. Analysis by .sup.1H NMR revealed that the solid was
a cellulose acetate with a DS of 2.67. Analysis by GPC indicated
that the cellulose acetate had a Mw of 51,428 and a Mw/Mn of
4.08.
[0306] This example shows that a cellulose solution in an ionic
liquid can be contacted with an immiscible or sparingly soluble
co-solvent without causing precipitation of the cellulose. Upon
contact with an acylating reagent, the cellulose is esterified
changing the solubility of the now cellulose ester-ionic liquid
solution with the formerly immiscible co-solvent so that the
contact mixture becomes a single phase. The resulting single phase
has much lower solution viscosity than the initial cellulose-ionic
liquid solution. This discovery is significant in that highly
viscous cellulose solutions can be used to make cellulose esters
while still maintaining the ability to mix and process the
solution. The discovery also provides a means to process highly
viscous cellulose-ionic liquid solutions at lower contact
temperatures. The cellulose ester product can be isolated from the
new single phase by conventional means. The cellulose ester product
has desirable degrees of substitution, molecular weights, and
solubility in solvents such as acetone, and can be readily melt
processed when plasticized with plasticizers such as diethyl
phthalate and the like.
Example 35
Immiscible Co-Solvent (Biphasic to Single Phase)
[0307] A 3-neck 100 mL round bottom flask containing 28.84 g of a 5
wt % cellulose solution in [BMIm]Cl was equipped for mechanical
stirring and with an N.sub.2/vacuum inlet. The flask was placed in
a preheated 80.degree. C. oil bath and the flask contents were
placed under vacuum (ca. 7 mm Hg) for 2 h. To the solution was
added 25 mL of methyl ethyl ketone that had been previously dried
over 4 A molecular sieves resulting in two well defined phases. To
the biphasic mixture was added 4.54 g of Ac.sub.2O while stirring
vigorously. After ca. 75 min, the contact mixture appeared to be
homogeneous. After 2.5 h, the contact mixture was allowed to cool
to room temperature. Phase separation did not occur even when a
small amount of water and methyl ethyl ketone was added to the
homogeneous mixture. The product was isolated by addition of the
contact mixture to 200 mL of MeOH followed by filtration to
separate the solids. The solids were washed twice with MeOH and
three times with water before they were dried at 50.degree. C., ca.
5 mm Hg. Analysis by .sup.1H NMR and by GPC revealed that the
product was a cellulose acetate with a DS of 2.11 and Mw of
50,157.
[0308] This example shows that a cellulose solution in an ionic
liquid such as [BMIm]Cl can be contacted with an immiscible or
sparingly soluble co-solvent such as methyl ethyl ketone without
causing precipitation of the cellulose. Upon contact with an
acylating reagent, the cellulose is esterified changing the
solubility of the now cellulose ester-ionic liquid solution with
the formerly immiscible co-solvent so that the contact mixture
became a single phase from which the cellulose ester could be
isolated by precipitation with an alcohol.
Example 36
Color Measurements for Cellulose Esters Prepared from Cellulose
Dissolved in Ionic Liquids
[0309] Color development during esterification of cellulose
dissolved in ionic liquids depend upon a number of factors. These
factors include the type of ionic liquid used to dissolve the
cellulose, impurities contained in the ionic liquid, type of
cellulose, the presence or absence of binary components (cf.
Example 3), cellulose dissolution contact time and temperature,
esterification contact time and temperature, among others.
Understanding those factors and the mechanism involved in color
formation is the best means for preventing color formations. Even
when the best practices are followed, colored product is still
often obtained. Hence, a means for removing or minimizing the color
is very important. In this regard, we have found that we can
minimize color by contacting the cellulose ester with a bleaching
agent while dissolved in ionic liquid or after separation of the
cellulose ester from the ionic liquid.
[0310] Example of a general method for bleaching cellulose esters
while dissolved in ionic liquid: To a 7.5 wt % solution of
cellulose dissolved in [BMIm]Cl was added a mixture of 2.9 eq
Ac.sub.2O and 0.1 eq MSA. After 65 minutes, in situ IR indicated
that the reaction was complete. To the solution was added a
bleaching agent (in this case, 0.75 wt % of a 2.25 wt % solution of
KMnO.sub.4 dissolved in MeOH). The mixture was stirred for 2 h
before the cellulose ester was isolated by precipitation in water,
washed with water, and dried. The concentration of bleaching agent
and bleaching contact time depends upon the particular process.
[0311] Example of a general method for bleaching cellulose esters
after separation from the ionic liquid: After completing the
reaction, the cellulose ester is isolated from the ionic liquid by
precipitation in a nonsolvent such as water or alcohol. The liquids
are separated from the cellulose ester and, optionally, the
cellulose ester can be washed further before contacting the solid
product with a bleaching agent (e.g. 35 wt % aqueous
H.sub.2O.sub.2). Specific examples of this process can be found in
Examples 33 and 34. The concentration of bleaching agent, the
number of bleaching cycles, and bleaching contact time depends upon
the particular process.
[0312] Values of L*, a*, b*, and E* for cellulose ester solutions
before and after bleaching are provided in Table 10. Comparing
entries 1-3 to entries 4-6 (no bleaching) it is evident that more
color is created during cellulose esterification when the anion of
the ionic liquid is a carboxylate relative to when the anion is a
halide. When the anion was a halide, in the absence of bleaching L*
and E* ranged from 93.6-97.7 and 19.1-11.5, respectively (entries
1-3). Bleaching with H.sub.2O.sub.2 after separation of the
cellulose ester from the ionic liquid increased a* and decreased b*
resulting in improvement of color which is reflected in a lower E*
value (entries 7 and 8). Bleaching the cellulose ester while it is
dissolved in the ionic liquid led to a similar improvement in color
(entry 9). In this case L* and a* increased while b* decreased
resulting in an E* value of 4.85. When the anion was a carboxylate,
in the absence of bleaching L* and E* ranged from 46.6-74.5 and
108.6-89.9, respectively (entries 4-6). Bleaching with
H.sub.2O.sub.2 after separation of the cellulose ester from the
ionic liquid led to a dramatic improvement of color. L* increased
while a* and b* decreased resulting in E* values of 0.9-11.2
(entries 10-16).
TABLE-US-00011 TABLE 10 Values of L*, a*, b*, and E* for cellulose
ester solutions before and after bleaching. Entry L* a* b* E* IL-BC
CE Bleach 1 97.65 -2.24 11.07 11.54 [BMIm]Cl-(MSA) CA None 2 94.28
-1.85 17.83 18.83 [BMIm]Cl-(MSA) CA None 3 93.56 -1.74 17.84 19.06
[BMIm]Cl-(MSA) CA None 4 46.56 41.45 77.89 103.19 [BMIm]OAc-(MSA)
CA None 5 50.35 35.44 89.8 108.59 [BMIm]OAc CA None 6 74.52 12.66
85.28 89.91 [BMIm]OAc CAP None 7 96.89 -1.44 10.10 10.68
[BMIm]Cl-(MSA) CA H.sub.2O.sub.2 8 98.24 -1.09 4.37 4.85
[BMIm]Cl-(MSA) CA H.sub.2O.sub.2 9 98.37 -1.04 5.69 6.02
[BMIm]Cl-(MSA) CA KMnO.sub.4 10 98.43 -3.00 10.72 11.24 [EMIm]OAc
CA H.sub.2O.sub.2 11 98.10 -3.06 10.34 10.95 [BMIm]OAc CA
H.sub.2O.sub.2 12 98.44 -1.51 5.87 6.27 [BMIm]OBu CAB
H.sub.2O.sub.2 13 97.91 -2.43 10.68 11.15 [EMIm]OAc-(MSA) CA
H.sub.2O.sub.2 14 99.44 0.00 0.58 0.87 [BMIm]OAc--(Zn(OAc).sub.2)
CA H.sub.2O.sub.2 15 99.02 0.05 1.63 1.94
[BMIm]OAc--(Zn(OAc).sub.2) CA H.sub.2O.sub.2 16 99.32 -0.48 1.98
2.16 [BMIm]OPr-(MSA) CP H.sub.2O.sub.2
[0313] This example illustrates that contacting a cellulose ester
with a bleaching agent while dissolved in ionic liquid or after
separation of the cellulose ester from the ionic liquid can lead to
very significant improvements in color.
Example 37
Viscosity of Solutions of Cellulose Dissolved in Ionic Liquids
Containing Miscible Cosolvents
[0314] Solutions of cellulose dissolved in [BMIm]Cl containing
different levels of acetic acid were prepared by the following
general procedure: To a 3-neck 50 mL round bottom flask equipped
for mechanical stirring and with a N2/vacuum inlet was added
[BMIm]Cl. The flask contents were heated to 80.degree. C. and
placed under vacuum (0.8 mm Hg). After 1.7 h, 5 wt % acetic acid
was added to the [BMIm]Cl before allowing the solution to cool to
room temperature. Cellulose (5 wt %) was added to the solution
before heating the mixture to 80.degree. C. The mixture was stirred
until a homogeneous solution was obtained (ca. 80 min), The
solution was then cooled to room temperature.
[0315] FIG. 28 compares the viscosities of cellulose solutions
containing no acetic acid, 5 wt % acetic acid, and 10 wt % acetic
acid at 25, 50, 75, 100.degree. C. The viscosity of the
cellulose-[BMIm]Cl-5 wt % acetic acid solution is significantly
less than that of cellulose-[BMIm]Cl at all temperatures. For
example, at 25.degree. C. and 0.2 rad/sec the viscosity of the
cellulose-[BMIm]Cl-5 wt % acetic acid solution is 466 poise versus
44,660 poise for the cellulose-[BMIm]Cl solution. Comparing the
viscosities of the cellulose-[BMIm]Cl-10 wt % acetic acid solution
to the cellulose-[BMIm]Cl-5 wt % acetic acid and cellulose-[BMIm]Cl
solutions at 25.degree. C., it is evident that the viscosity of the
cellulose-[BMIm]Cl-10 wt % acetic acid solution is less than that
of the cellulose-[BMIm]Cl solution but greater than that of the
cellulose-[BMIm]Cl-5 wt % acetic acid solution. At 25.degree. C.
and 0.2 rad/sec, the viscosities of the cellulose-[BMIm]Cl-10 wt %
acetic acid, cellulose-[BMIm]Cl-5 wt % acetic acid, and
cellulose-[BMIm]Cl solutions are 22,470, 466, and 44,660 poise,
respectively. With increasing temperature, the differences in the
viscosities between the cellulose-[BMIm]Cl-10 wt % acetic acid and
cellulose-[BMIm]Cl solutions diminish and the observed viscosities
depend upon the shear rate.
[0316] This example shows that the viscosity of a cellulose-ionic
liquid solution can be dramatically altered by adding a miscible
cosolvent such as a carboxylic acid to the solution. The viscosity
drops with increasing miscible cosolvent reaching a minimum before
increasing again as addition cosolvent is added.
Example 38
Viscosity of Solutions of Cellulose Dissolved in Ionic Liquids
Containing Immiscible Cosolvents
[0317] To determine the impact of an immiscible cosolvent which,
forms two layers with the initial cellulose-ionic liquid solution,
on solution viscosity it is necessary to convert the cellulose to a
cellulose ester prior to making the viscosity measurement.
[0318] To a 3-neck 100 mL round bottom flask equipped for
mechanical stirring and with an N2/vacuum inlet was added 33.18 g
of 1-butyl-3-methylimidazolium chloride. While stirring rapidly,
added 1.75 g of dry cellulose (5 wt %). The flask was placed under
vacuum (2 mm Hg) and placed in an oil bath preheated to 80.degree.
C. After 30 min in the oil bath all of the cellulose was dissolved.
The oil bath and stirring was turned off and the solution was left
under vacuum overnight.
[0319] To the cellulose solution was added 30 mL of methyl ethyl
ketone resulting in a 2-phase reaction mixture. While stirring
rapidly, added a mixture of 104 mg of MSA and 5.51 g of Ac.sub.2O
dropwise (3 min). At the end of the addition, the reaction mixture
was two phases. After stirring for ca. 70 min from the start of
addition, the reaction mixture was a single phase; the viscosity of
the phase was much less than that of the original cellulose
solution. Stirring was continued for an additional 150 min before
10.9 g of the solution was removed for viscosity measurements. The
remaining solution was then cooled to room temperature and the
product was isolated by precipitating in 350 mL of MeOH. The slurry
was stirred for ca. 1 h before the solids were isolated by
filtration. The solids were washed 4 times with 250 mL of MeOH. The
solids were then dried overnight at 50.degree. C., 5 mm Hg which
gave 1.66 g of a white solid. Analysis revealed that the solid was
the expected cellulose acetate. A second reaction was conducted in
the same fashion except that the cosolvent was omitted. Again, a
sample was removed for viscosity measurements just prior to
precipitation of the cellulose acetate.
[0320] FIG. 29 compares the solution viscosity of the contact
mixtures with and without cosolvents at 25.degree. C. Inclusion of
a cosolvent dramatically reduces the viscosity of the solution. For
example at 25.degree. C. and 1 rad/sec, inclusion of methyl ethyl
ketone resulted in a solution with a viscosity of 24.6 poise versus
6392 poise for the solution without methyl ethyl ketone.
Example 39
Impact of Miscible Cosolvents on Reaction Rates and Total DS
[0321] A 3-neck 100 mL round bottom flask was equipped with a
double neck adapter giving four ports, an iC10 diamond tipped IR
probe, for mechanical stirring, and a N.sub.2/vacuum inlet. To the
flask was added 50.15 g of 1-butyl-3-methylimidazolium propionate
([BMIm]OPr). While stirring rapidly, cellulose (4.07 g, 7.5 wt %)
was added to the [BMIm]OPr at room temperature. Vacuum was applied
with the aid of a bleed valve. After reaching 0.6 mm Hg, a
preheated 80.degree. C. oil bath was raised to the flask. A clear
solution was obtained 8 min after raising the oil bath. Stirring
was continued for an additional 2.8 h before the solution was
allowed to cool to room temperature and stand under N.sub.2 for 12
h.
[0322] To the cellulose solution at room temperature was added a
mixture of propionic anhydride (12.09 g, 3.7 eq) and MSA (482 mg,
0.2 eq) dropwise (20 min). During the course of the reaction,
aliquots were removed and the product was isolated by precipitation
in 200 mL of MeOH and filtering. The reaction was complete 20 min
after the end of addition. The experiment was terminated and the
remaining reaction mixture was processed as the aliquots. The solid
from each sample was washed 3 times with 200 mL portions of MeOH
then 1 time with 250 mL of MeOH containing 8 wt % of 35 wt %
H.sub.2O.sub.2. The white solids were then dried at 60.degree. C.,
5 mm Hg.
[0323] A second experiment was conducted following the same
procedure. The only difference was that the [BMIm]OPr contained
11.9 wt % propionic acid as a miscible cosolvent.
[0324] FIG. 30 shows a plot of absorbance for a band at 1212
cm.sup.-1 (propionate ester and propionic acid) versus contact
time. The DS indicated in FIG. 30 correspond to the DS values for
the samples obtained in each experiment. Relative to the reaction
of cellulose dissolved in [BMIm]OPr (no propionic acid), the
reaction rate of cellulose dissolved in [BMIm]OPr+11.9 wt %
propionic acid is slower and the DS of each sample is higher than
the corresponding sample in the other experiment. Thus, this
example shows in addition to impacting solution viscosity, a
cosolvent can also have a dramatic impact on reaction rates and
total DS obtained.
Example 40
Regioselective Esterification of Cellulose Dissolved in Ionic
Liquids by the Controlled Addition of Anhydrides
[0325] Series 1: A 3-neck 100 mL round bottom flask which contained
a solution 4.9 g (7.5 wt %) of cellulose dissolved in [BMIm]Cl was
equipped for mechanical stirring, with an iC10 diamond tipped IR
probe, and with an N.sub.2/vacuum inlet. The flask contents were
heated to 80.degree. C. before adding mixture of 5.9 g Pr.sub.2O
(1.5 eq) and 0.29 g MSA (0.1 eq) to the cellulose solution (4 min
addition). The consumption of anhydride and the production of
cellulose ester and carboxylic acid was followed in situ using
infrared spectroscopy. Forty minutes after the start of the
Pr.sub.2O addition, 4.66 g of Ac.sub.2O (1.5 eq) was added to the
contact mixture (2 min addition). The contact mixture was stirred
for an additional 2 h at 80.degree. C. before adding 1 g of
n-propanol to quench the remaining anhydride. During the course and
at the end of the contact period, the contact mixture was sampled
by removing 6-10 g aliquots of the contact mixture and cellulose
ester was obtained by precipitation in aqueous methanol. The solid
from each aliquot was washed 4.times. with aqueous methanol then
dried at 60.degree. C., 5 mm Hg.
[0326] FIG. 31 is a plot of absorbance versus time for series 1,
and it illustrates the esterification of cellulose (1756, 1233,
1212 cm.sup.-1), the consumption of anhydride (1815 cm.sup.-1), and
the coproduction of carboxylic acid (1706 cm.sup.-1) during the
experiment. The DS values shown in FIG. 31 were determined by
proton NMR spectroscopy and correspond to the samples removed
during the course of the contact period. The change in the acetyl
methyl (centered near 1.9 ppm) and propionyl methyl (centered near
1.0 ppm) resonances (FIG. 32) clearly indicated a nonrandom
distribution of the acyl substituents. This finding is surprising
in that cellulose esters prepared by conventional processes
typically have a random distribution of acyl substituents. That is,
the relative degree of substitution at the C.sub.6, C.sub.3, and
C.sub.2 anhydroglucose monomer is close to a 1:1:1 ratio.
[0327] Series 2: Following the general procedure of series 1,
cellulose dissolved in [BMIm]Cl was esterified by first adding a
mixture of 1.5 eq Ac.sub.2O and 0.1 eq MSA. Twenty minutes after
adding the Ac.sub.2O, 1.5 eq Pr.sub.2O was added to the contact
mixture. The contact mixture was stirred for an additional 7 h at
80.degree. C. As with series 1, during the course and at the end of
the contact period, the contact mixture was sampled by removing
6-10 g aliquots of the contact mixture and cellulose ester was
obtained by precipitation in aqueous methanol. Proton NMR again
indicated a nonrandom distribution of the acyl substituents
different from that obtained with series 1.
[0328] Series 3: Following the general procedure of series 1,
cellulose dissolved in [BMIm]Cl was esterified by adding a mixture
of 1.5 eq Ac.sub.2O, 1.5 eq Pr.sub.2O, and 0.1 eq MSA. The contact
time was 2 h 5 min. As with series 1 and 2, during the course and
at the end of the contact period, the contact mixture was sampled
by removing 6-10 g aliquots of the contact mixture, and cellulose
ester was obtained by precipitation in aqueous methanol. Proton NMR
again indicated a nonrandom distribution of the acyl substituents
different from that obtained with series 1 and 2.
[0329] In order to measure the differences in RDS obtained by the
different order of anhydride additions, selected aliquots (400 mg
each) from each sample series was dissolved in pyridine and
contacted with p-nitrobenzoyl chloride (1 g) at 70.degree. C. for
ca. 23 h before precipitating and washing with EtOH. This process
converted the cellulose acetate propionate esters to fully
substituted cellulose acetate propionate p-nitrobenzoate esters.
These samples were then analyzed by carbon 13 NMR, and the RDS
could be determined by integration of the carbonyl resonances. The
position of the p-nitrobenzoate esters indicate the location of the
hydroxyls in the cellulose acetate propionate. FIG. 33 compares the
carbonyl region in the .sup.13C NMR spectra of a sample from each
series having a similar DS; the RDS for each sample is given in the
Figure.
[0330] Examination of the RDS for each series shows that in each
case the order of reactivity is C.sub.6>>C.sub.3>C.sub.2.
For example, for series 1 in which the propionate was added first,
RDS C.sub.6=1.00, RDS C.sub.3=0.89, and RDS C.sub.2=0.73. In terms
of acetate versus propionate selectivity, the RDS.sub.Pr at C.sub.6
was 0.78 and the RDS.sub.Ac at C.sub.6 was 0.26. Comparing the RDS
for acetate versus propionate at C.sub.3 and C.sub.2, it is evident
that that there is more acetate than propionate at C.sub.3 (0.50
versus 0.39) and C.sub.2 (0.47 versus 0.26). That is, placement of
the acyl substituents was regioselective leading to a cellulose
acetate propionate enriched in 6-propionyl-2,3-diacetyl cellulose.
In series 1, the propionate carbonyl C.sub.6/C.sub.2 and
C.sub.6/C.sub.2 ratios were large (2.0 and 3.0, respectively) as
were the propionate carbonyl C.sub.6/C.sub.3*DS (2.8) and
C.sub.6/C.sub.2*DS (4.2) values. In the case of series 2 in which
the Ac.sub.2O was added first, RDS C.sub.6=1.00, RDS C.sub.3=0.93,
RDS C.sub.2=0.86. In terms of acetate versus propionate
selectivity, the RDS.sub.Pr at C.sub.6 was 0.25 and the RDS.sub.Ac
at C.sub.6 was 0.75 opposite from that observed with series 1. In
series 2, the acetate carbonyl C.sub.6/C.sub.2 and C.sub.6/C.sub.2
ratios were large (1.5 and 2.0, respectively) as were the acetate
carbonyl C.sub.6/C.sub.3*DS (2.3) and C.sub.6/C.sub.2*DS (3.1)
values. In the case of Series 3, in which the Ac.sub.2O and the
Pr.sub.2O were added as a mixture, regioselectivity was still
observed; RDS C.sub.6=1.00, RDS C.sub.3=0.68, RDS C.sub.2=0.50. In
terms of acetate versus propionate selectivity, the RDS.sub.Pr at
C.sub.6 was 0.56 and the RDS.sub.Ac at C.sub.6 was 0.44. At C3, the
RDS for propionate and acetate were roughly equivalent. At C.sub.2,
the RDS.sub.Pr was 0.20 and the RDS.sub.Ac was 0.30. In series 3,
the propionate carbonyl C.sub.6/C.sub.2 and C.sub.6/C.sub.2 ratios
were large (1.6 and 2.8, respectively) as were the propionate
carbonyl C.sub.6/C.sub.3*DS (1.7) and C.sub.6/C.sub.2*DS (3.1)
values.
[0331] Regioselective placement of substituents in a cellulose
ester leads to polymers with different physical properties in a
fashion analogous to classical random copolymers versus block
copolymers. As an example, FIG. 34 shows a plot of DS versus glass
transition temperature (Tg) for the polymers prepared in series
1-3. At a given DS, the Tg for series 1 is shifted 5.degree. C.
lower relative to series 2. In turn, the Tg for series 2 is shifted
5.degree. C. lower relative to series 3. That is, the Tg can be
shifted as much as 10.degree. C. at a constant DS by controlling
the placement of the acyl substituents. FIG. 35 shows a plot of
DS.sub.pr versus Tg for the same series 1-3. The slope of the lines
for series 2 and 3 are similar and are ca. twice that of series 1.
This means that when the propionate substituent is located
predominately at C.sub.6, small changes in DS.sub.Pr will result in
large changes in Tg. This illustrates that these new cellulose
ester compositions surprisingly leads to polymers having different
and novel physical properties relative to conventional cellulose
ester that impacts their use in many applications.
Example 41
Casting of Film and Film Optical Measurements Using Cellulose
Esters Containing a Minor Amount (DS 50.2) of a Second Acyl
Group
[0332] Cellulose esters that are essentially 6,3- and
6,2-regioselectively substituted (high C.sub.6 RDS, Examples
41.1-41.3) were prepared according to the methods of the present
invention in Examples 1-3. Commercial (Comparative examples 41.6
and 41.7) cellulose esters available from Eastman Chemical Company,
were produced by the general procedures described in US
2009/0096962 and US 2009/0050842. Comparative examples 41.4 and
41.5 were prepared as described in US 2005/0192434. The cellulose
esters in examples 41.4 and 41.5 are essentially
2,3-regioselectively substituted and differs from the examples of
the present invention in that they have a low RDS at C.sub.6 while
the cellulose esters of the present invention have a high RDS at
C.sub.6. The ring RDS was determined for each sample before film
was cast and the film optical properties determined. The results
are summarized in Table 11.
TABLE-US-00012 TABLE 11 The degree of substitution, relative degree
of substitution, and out-of- plane retardation (nm) for
compensation film for cellulose esters containing a minor amount
(DS .ltoreq. 0.2) of a second acyl group prepared by the methods of
the present invention versus comparative (C) cellulose esters.
Example IL DS DS.sub.Pr DS.sub.Ac RDS C.sub.6 RDS C.sub.3 RDS
C.sub.2 R.sub.th (589) 41.1 [EMIm]OAc 2.81 0.00 2.81 1.00 0.86 0.95
-55.9 41.2 [BMIm]OPr 2.81 2.77 0.04 1.00 0.86 0.95 36.1 41.3
[BMIm]OPr 1.68 1.65 0.03 0.85 0.42 0.41 -342.5 41.4 (C) 1.99 1.94
0.05 0.36 0.80 0.83 -80.2 41.5 (C) 1.53 1.48 0.05 0.24 0.63 0.66
-119.0 41.6 (C) 2.73 2.69 0.04 0.83 0.98 0.90 -29.2 41.7 (C) 1.93
1.77 0.16 0.56 0.71 0.66 -209.9
[0333] Examples 41.1 and 41.2 are essentially identical except that
Example 41.1 was a cellulose acetate, and Example 41.2 was a
cellulose propionate. As shown in Table 11, the cellulose
propionate had a higher R.sub.th (+36 nm) relative to the cellulose
acetate (-56 nm). Comparing the values of R.sub.th for the low DS
6,3-, 6,2-cellulose propionate (Example 41.3, DS=1.68,
C.sub.6/C.sub.3=2.0, C.sub.6/C.sub.2=2.1, DS*C.sub.6/C.sub.3=3.4,
DS*C.sub.6/C.sub.2=3.5) to the two 2,3-cellulose propionates
(Example 41.4, DS=1.99 C.sub.6/C.sub.3=0.45, C.sub.6/C.sub.2=0.43,
DS*C.sub.6/C.sub.3=0.9, DS*C.sub.6/C.sub.2=0.9 and Example 41.5,
DS=1.53, C.sub.6/C.sub.3=0.38, C.sub.6/C.sub.2=0.36,
DS*C.sub.6/C.sub.3=0.6, DS*C.sub.6/C.sub.2=0.6) it was evident that
the 6,3-, 6,2-cellulose propionate provided a much more negative
R.sub.th value (-343 nm versus -80 and -119 nm) even though the
cellulose esters have similar DS values. Similarly, comparison of
the R.sub.th value for Example 41.3 to the R.sub.th value for
Example 41.7 (DS=1.93, C.sub.6/C.sub.3=0.79, C.sub.6/C.sub.2=0.85,
DS*C.sub.6/C.sub.3=1.5, DS*C.sub.6/C.sub.2=1.6) revealed that the
regioselectively substituted cellulose propionate had a much lower
R.sub.th value (-343 nm versus -210 nm). Comparison of the R.sub.th
value for the high DS regioselectively substituted cellulose
propionate (Example 41.2, DS=2.81, C.sub.6/C.sub.3=1.16,
C.sub.6/C.sub.2=1.05, DS*C.sub.6/C.sub.3=3.3,
DS*C.sub.6/C.sub.2=3.0) to the R.sub.th value for the high DS
conventional cellulose propionate (Example 41.6, DS=2.73,
C.sub.6/C.sub.3=0.85, C.sub.6/C.sub.2=0.92, DS*C.sub.6/C.sub.3=2.3,
DS*C.sub.6/C.sub.2=2.3) revealed that the regioselectively
substituted cellulose propionate has a much higher R.sub.th (+36
nm) than the conventional cellulose propionate (-29 nm).
[0334] This example illustrated several important aspects of the
present invention. As the comparison of Examples 41.1 and 41.2
demonstrated, a propionate substituent increased R.sub.th more that
an acetate substituent at an equivalent DS and substitution
pattern. As expected, the total hydroxyl DS had a significant
influence on the R.sub.th values regardless of the substitution
pattern. However, the regioselectively substituted cellulose esters
of the present invention provided for a much wider range of
R.sub.th relative to other substitution patterns. At the lower DS
range, R.sub.th was much more negative for the regioselectively
substituted cellulose esters relative to conventional cellulose
esters. At higher DS range, R.sub.th was less negative and even
positive for the regioselectively substituted cellulose esters
relative to other cellulose esters.
Example 42
Casting of Film and Film Optical Measurements Using Cellulose
Esters Containing a Second Acyl Group (DS.gtoreq.0.2).
[0335] Regioselectively substituted cellulose acetate propionates
(Examples 42.1-42.6) were prepared according to the methods of the
present invention (high C.sub.6 RDS) in Examples 1-6. Comparative
example 42.7 cellulose ester was a cellulose acetate propionate
that was prepared by the general procedures described in US
2009/0096962 and US 2009/0050842 and is available from Eastman
Chemical Company. The ring and carbonyl RDS were determined for
each sample before film was cast, and the film optical properties
were determined. Table 12 provides the ring RDS versus R.sub.th,
Table 13 provides the carbonyl RDS versus R.sub.th, and Table 14
provides the propionate and acetate ratios of C.sub.6/C.sub.3 and
C.sub.6/C.sub.2 as well as C.sub.6/C.sub.3*DS and
C.sub.6/C.sub.2*DS.
TABLE-US-00013 TABLE 12 The degree of substitution, relative degree
of substitution, and out-of-plane retardation (nm) for compensation
film for cellulose esters containing a second acyl group (DS
.gtoreq. 0.2) prepared by the methods of the present invention from
cellulose dissolved in [BMIm]Cl versus comparative (C) cellulose
esters. Example DS DS.sub.Pr DS.sub.Ac RDS C.sub.6 RDS C.sub.3 RDS
C.sub.2 R.sub.th (589) 42.1 1.99 1.15 0.85 1.00 0.62 0.42 -109.5
42.2 2.14 0.90 1.24 1.00 0.69 0.48 -54.2 42.3 2.34 0.99 1.35 1.00
0.77 0.60 -137.2 42.4 2.61 1.41 1.20 1.00 0.89 0.73 -17.4 42.5 2.77
1.25 1.52 1.00 0.93 0.86 -33.7 42.6 2.17 1.10 1.07 1.00 0.68 0.50
-156.9 42.7 (C) 2.47 0.88 1.59 0.75 0.90 0.82 -161.7
TABLE-US-00014 TABLE 13 The degree of substitution, carbonyl carbon
relative degree of substitution, and out-of-plane retardation (nm)
for compensation film for cellulose propionates prepared from
cellulose dissolved in [BMIm]Cl by the methods of the present
invention versus comparative (C) cellulose esters. Example DS
DS.sub.Pr DS.sub.Ac Pr C.sub.6 Pr C.sub.3 Pr C.sub.2 Ac C.sub.6 Ac
C.sub.3 Ac C.sub.2 R.sub.th (589) 42.1 1.99 1.15 0.85 0.52 0.39
0.24 0.48 0.23 0.18 -109.5 42.2 2.14 0.90 1.24 0.48 0.28 0.14 0.52
0.41 0.34 -54.2 42.3 2.34 0.99 1.35 0.56 0.28 0.18 0.44 0.49 0.42
-137.2 42.4 2.61 1.41 1.20 0.78 0.39 0.26 0.22 0.50 0.47 -17.4 42.5
2.77 1.25 1.52 0.25 0.44 0.49 0.75 0.49 0.37 -33.7 42.6 2.17 1.10
1.07 0.56 0.36 0.20 0.44 0.32 0.30 -156.9 42.7 (C) 2.47 0.88 1.59
0.29 0.26 0.31 0.52 0.53 0.53 -161.7
TABLE-US-00015 TABLE 14 The ratios of C.sub.6/C.sub.3 and
C.sub.6/C.sub.2 as well as C.sub.6/C.sub.3*DS and
C.sub.6/C.sub.2*DS products for propionate and acetate and the
corresponding Rth values (nm) for compensation film for cellulose
acetate propionates prepared from cellulose dissolved in [BMIm]Cl
by the methods of the present invention versus comparative (C)
cellulose esters. Pr Pr C.sub.6/C.sub.3* C.sub.6/C.sub.2* Ac Ac
C.sub.6/C.sub.3* C.sub.6/C.sub.2* R.sub.th Example C.sub.6/C.sub.3
C.sub.6/C.sub.2 DS.sub.Pr DS.sub.Pr C.sub.6/C.sub.3 C.sub.6/C.sub.2
DS.sub.Ac DS.sub.Ac (589) 42.1 1.33 2.17 1.53 2.49 2.09 2.67 1.77
2.27 -109.5 42.2 1.71 3.43 1.54 3.09 1.27 1.53 1.57 1.90 -54.2 42.3
2.00 3.11 1.98 3.08 0.90 1.05 1.21 1.41 -137.2 42.4 2.00 3.00 2.82
4.23 0.44 0.47 0.53 0.56 -17.4 42.5 0.57 0.51 0.71 0.64 1.53 2.03
2.33 3.08 -33.7 42.6 1.56 2.80 1.71 3.08 1.38 1.47 1.47 1.57 -156.9
42.7 (C) 1.12 0.94 0.98 0.82 0.98 0.98 1.56 1.56 -161.7
[0336] Upon comparing Examples 42.1-42.6 to Example 42.7 (Table
12), it is evident that the regioselectively substituted cellulose
acetate propionates gave R.sub.th values that were less negative
than that provided by the conventional cellulose acetate propionate
regardless of DS.sub.OH. As an illustration, Example 42.3 had a
slightly lower DS relative to Example 42.7, but the R.sub.th value
of Example 42.3 (R.sub.th=-137 nm) was still less negative than
Example 42.7 (R.sub.th=-162 nm). Even upon further reduction in
total DS (increasing DS.sub.OH, Examples 42.1, 42.2, and 42.6), the
R.sub.th values for the regioselectively substituted cellulose
acetate propionates were still less negative.
[0337] As Table 12 shows, Examples 42.1-42.6 had high ring RDS
C.sub.6/C.sub.3 and C.sub.6/C.sub.2 ratios but there was variation
in R.sub.th at similar total DS values. As an illustration,
Examples 42.6 and 42.2 had similar DS values but significantly
different R.sub.th values (-157 nm versus -54 nm). Upon examination
of the carbonyl RDS C.sub.6/C.sub.3 and C.sub.6/C.sub.2 ratios for
these two Examples, it was evident that Example 42.2 (R.sub.th=-54
nm) had a much higher C.sub.6/C.sub.3 and C.sub.6/C.sub.2 Pr RDS
than did Example 42.6. Similarly, Example 42.4 had a lower DS
(2.61) than did Example 42.5 (2.77), but yet the R.sub.th value for
Example 42.4 (-17 nm) was less negative than Example 42.5 (-34 nm).
Again, examination of the carbonyl RDS C.sub.6/C.sub.3 and
C.sub.6/C.sub.2 ratios for these two Examples revealed that Example
42.4 had a much higher C.sub.6/C.sub.3 and C.sub.6/C.sub.2 Pr RDS
than did Example 42.5. That is, having propionate at C.sub.6 with a
high C.sub.6/C.sub.3 and C.sub.6/C.sub.2 Pr RDS ratios had a
significant influence on R.sub.th.
[0338] In Example 41 (single acyl substituent), it was shown that a
propionate substituent increased R.sub.th more that an acetate
substituent at an equivalent DS and substitution pattern and that
the total hydroxyl DS had a significant influence on the R.sub.th
values. The regioselectively substituted cellulose esters provided
for a much wider range of R.sub.th relative to other substitution
patterns. The present Example illustrated the influence that a
second acyl group can have on R.sub.th values. That is, for
regioselectively substituted cellulose esters of the present
invention, the combination of acetyl and propionyl substituents led
to a narrower and less negative R.sub.th range relative to
conventional cellulose esters. Higher propionate DS and high
C.sub.6/C.sub.3 and C.sub.6/C.sub.2 Pr RDS ratios at equivalent
total DS served to further modify R.sub.th.
* * * * *