U.S. patent application number 14/527902 was filed with the patent office on 2015-08-20 for dissolving-grade pulp compositions.
The applicant listed for this patent is Celanese Acetate LLC. Invention is credited to Leslie Allen, Dinesh Arora, Monica Boatwright, Christopher M. Bundren, Michael T. Combs, Denis G. Fallon, Bin Li, Rongfu Li, Jay Mehta, Tianshu Pan.
Application Number | 20150233055 14/527902 |
Document ID | / |
Family ID | 51932586 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150233055 |
Kind Code |
A1 |
Fallon; Denis G. ; et
al. |
August 20, 2015 |
Dissolving-Grade Pulp Compositions
Abstract
Dissolving-grade pulp compositions are prepared by treating a
cellulosic material with an extractant comprising a cellulose
solvent and co-solvent. The dissolving-grade pulp compositions
comprise at least 90 wt. % glucan, from 0.6 to 5 wt. % xylan, and
have distinct molecular weights, and elemental metal ions from
known and commercially available dissolving-grade pulp
compositions.
Inventors: |
Fallon; Denis G.;
(Blacksburg, VA) ; Allen; Leslie; (Blacksburg,
VA) ; Arora; Dinesh; (League City, TX) ;
Boatwright; Monica; (Blacksburg, VA) ; Bundren;
Christopher M.; (Blacksburg, VA) ; Combs; Michael
T.; (Shady Spring, WV) ; Li; Bin; (Blacksburg,
VA) ; Li; Rongfu; (Blacksburg, VA) ; Mehta;
Jay; (Blacksburg, VA) ; Pan; Tianshu;
(Charlotte, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Celanese Acetate LLC |
Irving |
TX |
US |
|
|
Family ID: |
51932586 |
Appl. No.: |
14/527902 |
Filed: |
October 30, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61941938 |
Feb 19, 2014 |
|
|
|
Current U.S.
Class: |
162/100 |
Current CPC
Class: |
D21H 11/00 20130101;
B01D 11/0288 20130101 |
International
Class: |
D21H 11/00 20060101
D21H011/00 |
Claims
1. A dissolving-grade pulp composition comprising at least 90 wt. %
glucan and from 0.6 to 5 wt. % xylan, wherein the composition has a
weight-average molecular weight of at least 500,000 g/mol.
2. The composition of claim 1, wherein the composition comprises
less than 175 ppm sodium.
3. The composition of claim 1, wherein the composition comprises
less than 25 ppm sodium.
4. The composition of claim 1, wherein the dissolving-grade pulp is
a hardwood dissolving-grade pulp.
5. The composition of claim 1, wherein the dissolving-grade pulp is
a softwood dissolving-grade pulp.
6. The composition of claim 1, wherein the composition further
comprises from 1 to 2 wt. % mannan.
7. The composition of claim 1, wherein the composition comprises
from 1.1 to 5 wt. % mannan.
8. The composition of claim 1, wherein the composition further
comprises arabinan and galactan.
9. The composition of claim 1, wherein the composition has a
weight-average molecular weight from 500,000 to 3,000,000
g/mol.
10. The composition of claim 1, wherein the composition has a
number-average molecular weight from 150,000 to 600,000 g/mol.
11. The composition of claim 1, wherein the composition has a
number-average molecular weight from 175,000 to 450,000 g/mol.
12. The composition of claim 1, wherein the composition has a
Z-average molecular weight from 900,000 to 50,000,000 g/mol.
13. The composition of claim 1, wherein the composition comprises
less than 7 ppm silicon.
14. The composition of claim 1, wherein the composition comprises
less than 10 ppm potassium.
15. The composition of claim 1, wherein the composition comprises
less than 0.01 wt. % dichloromethane extractables.
16. The composition of claim 1, wherein the weight ratio of xylan
to mannan is from 1:1 to 3:1.
17. The composition of claim 1, wherein the weight ratio of xylan
to mannan is less than 1:2.
18. A dissolving-grade pulp composition comprising at least 90 wt.
% glucan and from 0.6 to 5 wt. % xylan, wherein the composition
comprises less than 175 ppm sodium.
19. The composition of claim 18, wherein the composition comprises
less than 25 ppm sodium.
20. The composition of claim 18, wherein the weight ratio of xylan
to mannan is from 1:1 to 3:1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional App.
No. 61/941,938, filed Feb. 19, 2014, the entirety of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to dissolving-grade
pulp compositions and to processes for producing dissolving-grade
pulp compositions. In particular, the present invention relates to
dissolving-grade pulp compositions comprising at least 90 wt. %
glucan and from 0.6 to 5 wt. % xylan.
BACKGROUND OF THE INVENTION
[0003] Dissolving-grade pulp, also referred to as dissolving-grade
cellulose, is a bleached wood pulp or cotton linter that has a high
cellulose content, e.g., at least 90%. Dissolving-grade cellulose
is characterized by a high .alpha.-cellulose content, i.e., it is
composed of long-chain molecules, relatively free from lignin and
hemicelluloses, and other short-chain carbohydrates.
Dissolving-grade pulp may be further categorized into pulp grades
of varying levels of purity, brightness, and viscosity suitable for
the manufacture of cellulose esters (cellulose acetate, cellulose
butyrate, cellulose propionate), nitrates, ethers, viscose, and
microcrystalline cellulose.
[0004] Dissolving-grade pulps, and in particular high purity
dissolving-grade pulps such as acetate-grade cellulose pulps, are
useful in forming various cellulose derivatives For example,
cellulose acetate is the acetate ester of cellulose and is used for
a variety of products, including textiles (e.g., linings, blouses,
dresses, wedding and party attire, home furnishings, draperies,
upholstery and slip covers), industrial uses (e.g., cigarette and
other filters for tobacco products, and ink reservoirs for fiber
tip pens, decking lumber), high absorbency products (e.g., diapers,
sanitary napkins, and surgical products), thermoplastic products
(e.g., film applications, plastic instruments, and tape), cosmetic
and pharmaceutical (extended capsule/tablet release agents and
encapsulating agent), medicinal (hypoallergenic surgical products)
and others.
[0005] High purity .alpha.-cellulose is commonly required as a
starting material to make many cellulose derivatives, such as
cellulose acetate. Acetate-grade pulps are specialty raw materials
produced in commercial pulp processes, but the cost for such pulps
is high. Commercial paper grade pulps contain less than 90%
.alpha.-cellulose and are potential crude cellulosic sources for
making cellulose derivatives. Paper grade pulp contains a high
amount of impurities, such as hemicellulose, rendering it
incompatible with certain industrial uses, such as making cellulose
acetate flake or tow.
[0006] Zhou et al. discusses the use of dimethyldioxirane (DMDO), a
pulp bleaching agent, to treat birch pulp and obtain acetate-grade
pulp. However, currently, DMDO is not commercially available due to
its instability. Therefore, it is not an ideal solvent for
producing large quantities of high .alpha.-cellulose content pulp.
Zhou et al. "Acetate-grade pulp from birch," BioResources, (2010),
5(3), 1779-1778.
[0007] Studies have been done regarding the treatment of biomass to
form biofuels. Specifically, it is known that various ionic liquids
can be used to dissolve cellulosic material. S. Zhu et al. in Green
Chem. 2006, 8, pp. 325-327, describe the possibility of dissolving
cellulose in ionic liquids and recovering it by addition of
suitable precipitating agents such as water, ethanol, or
acetone.
[0008] Others have used ionic liquids to break down the cellulosic
materials to make biofuels by way of glucose. For example, U.S.
Pub. No. 2010/0112646 discloses a process for preparing glucose
from a cellulose material, in which a cellulose-comprising starting
material is provided and treated with a liquid treatment medium
comprising an ionic liquid and an enzyme. Similarly, U.S. Pub. No.
2010/0081798 discloses a process for preparing glucose from a
material containing ligno-cellulose, in which the material is first
treated with an ionic liquid and then subjected to enzymatic
hydrolysis. U.S. Pub. No. 2010/0081798 describes obtaining glucose
by treating a material containing ligno-cellulose with an ionic
liquid and subjecting same to an enzymatic hydrolysis and
fermentation. However, in order to turn cellulose containing
materials into glucose, the methods disclosed in these references
result in breaking down the cellulose molecules, making them
unsuitable for use as starting materials to make cellulose
derivatives.
[0009] U.S. Pat. No. 7,828,936 describes a method for dissolving
cellulose in which the cellulose based raw material is admixed with
a mixture of a dipolar aprotic intercrystalline swelling agent and
an ionic liquid. This method results in the complete dissolution of
the cellulose and destruction of the fiber morphology of the
cellulose. Although the cellulose may be regenerated using a
non-solvent, the crystallinity of the regenerated cellulose is
lower than the original cellulose sample.
[0010] The need exists for processes for producing dissolving-grade
pulp from lower grade starting materials without destroying the
fiber morphology and other characteristics of the cellulose
structure. In particular, the need exists for dissolving-grade pulp
compositions comprising at least 90% glucan and from 0.6 to 5 wt. %
xylan and for cost effective methods for producing such
compositions.
SUMMARY OF THE INVENTION
[0011] In a first embodiment, the invention is directed to a
dissolving-grade pulp composition comprising at least 90 wt. %
glucan and from 0.6 to 5 wt. % xylan, wherein the composition has a
weight-average molecular weight of at least 500,000 g/mol. In some
aspects, the composition may be a hardwood dissolving-grade pulp.
In other aspects, the composition may be a softwood
dissolving-grade pulp. The composition may comprise from 1 to 2 wt.
% mannan. The composition may comprise arabinan and galactan. The
composition may have a weight-average molecular weight from 500,000
to 3,000,000 g/mol. The composition may have a number-average
molecular weight from 150,000 to 600,000 g/mol or from 175,000 to
450,000 g/mol. The composition may have a Z-average molecular
weight from 900,000 to 50,000,000 g/mol. The composition may
comprise less than 175 ppm sodium or less than 25 ppm sodium. The
composition may comprise less than 7 ppm silicon. The composition
may comprise less than 10 ppm potassium. The composition may
comprise less than 0.01 wt. % dichloromethane extractables. In some
aspects, the composition may have a weight ratio of xylan to mannan
from 1:1 to 3:1. In other aspects, the weight ratio of xylan to
mannan is less than 1:2.
[0012] In a second embodiment, the invention is directed to a
dissolving-grade pulp composition comprising at least 90 wt. %
glucan and from 0.6 to 5 wt. % xylan, wherein the composition
comprises less than 175 ppm sodium. In some aspects, the
composition is a hardwood dissolving-grade pulp. In other aspects,
the composition is a softwood dissolving-grade pulp. The
composition may comprise from 1.1 to 5 wt. % mannan. The
composition may have a weight-average molecular weight of at least
500,000 g/mol, or from 500,000 to 3,000,000 g/mol. The composition
may comprise less than 25 ppm sodium. The composition may comprise
less than 7 ppm silicon. The composition may comprise less than 10
ppm potassium.
BRIEF DESCRIPTION OF THE DRAWING
[0013] The present invention will be better understood in view of
the appended non-limiting figures, in which:
[0014] FIG. 1 shows an exemplary purification process in accordance
with one embodiment of the present invention;
[0015] FIG. 2 shows an exemplary purification process in accordance
with another embodiment of the present invention; and
[0016] FIG. 3 shows an exemplary purification process in accordance
with yet another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
I. Introduction
[0017] The present invention relates to dissolving-grade pulp
compositions and to processes for producing dissolving-grade pulp
compositions. The dissolving-grade pulp compositions comprise at
least 90 wt. % glucan and from 0.6 to 5 wt. % xylan. Further, the
dissolving-grade pulp compositions of the present invention
preferably have distinct molecular weights and elemental metal ion
contents which are different from commercially available
dissolving-grade pulp compositions.
[0018] In one embodiment, the dissolving-grade pulp composition
comprises at least 90 wt. % glucan, from 0.6 to 5 wt. % xylan, and
has a weight-average molecular weight of at least 500,000
g/mol.
[0019] In some other embodiments, the dissolving-grade pulp
composition may comprise at least 90 wt. % glucan, from 0.6 to 5
wt. % xylan, and less than 175 ppm sodium.
[0020] The present invention also relates to processes for
producing dissolving-grade pulp compositions. In one aspect, the
invention is to a process comprising separating, e.g., extracting,
hemicellulose and other cellulosic impurities (e.g.,
dichloromethane (DCM) extractables and degraded cellulose) from a
cellulosic material with an extractant to form an intermediate
cellulosic material having a reduced hemicellulose content; and
concentrating the intermediate cellulosic material to form a
concentrated cellulosic material having an increased solids
content. The extractant used in the separating step comprises a
cellulose solvent and a cellulose co-solvent. The cellulose solvent
should be suitable for dissolving hemicellulose, and preferably
degraded cellulose and other impurities in the cellulosic material,
and in combination with a co-solvent, should have little solubility
for .alpha.-cellulose. The cellulose solvent is preferably selected
from the group consisting of an ionic liquid, an amine oxide and
combinations thereof, and the cellulose co-solvent is preferably
selected from the group consisting of dimethyl sulfoxide ("DMSO"),
tetramethylene sulfone, tetramethylene sulfoxide, N-methyl
pyrrolidone, dimethyl formamide ("DMF"), acetonitrile, acetic acid,
water, and mixtures thereof. The concentrated cellulosic material
may be dried to form a finished cellulosic product, preferably a
dissolving-grade pulp.
[0021] The processes of the invention are particularly suitable for
separating and removing impurities, such as hemicellulose and/or
degraded cellulose, from a cellulosic material to form a
dissolving-grade pulp, the purity of which may vary somewhat
depending largely on the composition of the starting cellulosic
material, the composition of the extractant used, and extraction
conditions. In preferred aspects, the finished cellulosic product
comprises at least 90 wt. % cellulose and may be referred to as a
dissolving-grade pulp.
II. Dissolving-Grade Pulp Compositions
[0022] As described herein, the present invention relates to
dissolving-grade pulp compositions that comprise at least 90 wt. %
glucan and from 0.6 to 5 wt. % xylan, based on a dried sample
weight. As used herein, glucan refers to .beta.-glucan.
.beta.-Glucans (beta-glucans) are polysaccharides of D-glucose
monomers linked by .beta.-glycosidic bonds. Cellulose is glucan
with beta(1,4)-linkage. In terms of ranges, the dissolving-grade
pulp composition may comprise 90 to 98.3 wt. % glucan, e.g., from
92 to 98 wt. %, or from 93 to 98 wt. % glucan and from 0.6 to 5 wt.
% xylan, e.g., from 0.9 to 5 wt. %, from 1.7 to 4 wt. %, or from
1.9 to 3.5 wt. %. In some aspects, the xylan content may vary
depending on whether the dissolving-grade pulp is a hardwood
dissolving-grade pulp or a softwood dissolving-grade pulp. The
softwood dissolving-grade pulp my comprise from 0.6 to 5 wt. %
xylan while the hardwood dissolving-grade pulp may comprise from
1.7 to 5 wt. % xylan.
[0023] The dissolving-grade pulp compositions may further comprise
arabinan, galactan, and mannan, generally in amounts totaling less
than 20 wt. %, e.g., less than 10 wt. % or less than 5 wt. %. The
dissolving-grade pulp compositions may comprise less than 0.2 wt. %
arabinan, e.g., less than 0.1 wt. %, or less than 0.05 wt. %. In
terms of ranges, the dissolving-grade pulp compositions may
comprise from 0.01 to 0.2 wt. % arabinan, e.g., from 0.01 to 0.1
wt. % or from 0.01 to 0.05 wt. %. The dissolving-grade pulp
compositions may comprise less than 0.2 wt. % galactan, e.g., less
than 0.1 wt. %, or less than 0.05 wt. %. In terms of ranges, the
dissolving-grade pulp compositions may comprise from 0.01 to 0.2
wt. % galactan, e.g., from 0.01 to 0.1 wt. % or from 0.01 to 0.05
wt. %. The dissolving-grade pulp compositions may comprise less
than 5 wt. % mannan, e.g., less than 3 wt. % or less than 1.5 wt.
%. In terms of ranges, the hemicellulose compositions may comprise
from 0.01 to 5 wt. % mannan, e.g., from 1.1 to 5 wt. %, or from 1.1
to 2 wt. %. By using the processes described herein to form the
dissolving-grade pulp, xylan is selectively removed in a greater
amount than mannan. The selective removal of xylan may allow for
fewer downstream processing steps for the dissolving-grade pulp,
e.g., bleaching.
[0024] In some embodiments, the dissolving-grade pulp may be
derived from hardwood and may have a weight ratio of xylan to
mannan is from 1:1 to 3:1, e.g., from 1.5:1 to 3:1 or from 2:1 to
3:1. In some preferred aspects, the xylan is present in a larger
weight amount than mannan. In further embodiments, the
dissolving-grade pulp may be derived from softwood and may have a
weight ratio of xylan to mannan of less than 1:2, e.g. less than
1:3, or less than 1:5.
[0025] Although weight percents of the polysaccharides in the
dissolving-grade pulp compositions are reported, i.e., xylan,
arabinan, galactan, glucan and mannan, these weight percents may be
readily converted to corresponding monosaccharide content. For
example, the xylan content in the sample may be calculated from the
xylose content of carbohydrate analysis by multiplying by a factor
of 0.88, and glucan or mannan by multiplying by a factor of
0.9.
[0026] The dissolving-grade pulp compositions may have increased
molecular weights as compared to the cellulosic material from which
they were derived. Without being bound by theory, the use of a
cellulose solvent results in the selected dissolution of
hemicellulose and other impurities which reduce or substantially
eliminate cellulose dissolution. Thus, the dissolving-grade pulp
may have a weight-average molecular weight higher than the starting
cellulosic material, e.g., at least 10% greater, at least 20%
greater or at least 30% greater. In some aspects, the
dissolving-grade pulp compositions may have a weight-average
molecular weight of at least 500,000 g/mol, e.g., at least 600,000
g/mol, at least 700,000 g/mol, or at least 750,000 g/mol. In terms
of ranges, the dissolving-grade pulp may have a weight-average
molecular weight from 500,000 to 3,000,000 g/mol, e.g., from
600,000 to 3,000,000 g/mol, e.g., from 700,000 to 3,000,000 g/mol
or from 750,000 to 3,000,000 g/mol. The dissolving-grade pulp
compositions may have a number-average molecular weight from
150,000 to 600,000 g/mol, e.g., from 175,000 to 450,000 g/mol or
from 250,000 to 450,000 g/mol. The dissolving-grade pulp
compositions may have a Z-average molecular weight from 900,000 to
50,000,000 g/mol, e.g., from 1,250,000 to 50,000,000 g/mol, or from
1,500,000 to 50,000,000 g/mol. The dissolving-grade pulp
compositions may have a peak molecular weight from 400,000 to
2,000,000 g/mol, e.g., from 500,000 to 2,000,000 g/mol or from
600,000 to 2,000,000 g/mol. The polydispersity index of the
dissolving-grade pulp compositions, calculated by dividing the
weight-average molecular weight by the number-average molecular
weight, may range from 1 to 5, e.g., from 1.5 to 5 or from 2 to
5.
[0027] Elemental metals and non-metals may be present in the
hemicellulose compositions, including but not limited to silver,
tin, bismuth, aluminum, arsenic, boron, barium, beryllium, cadmium,
calcium, cobalt, chromium, copper, iron, potassium, magnesium,
manganese, molybdenum, sodium, nickel, phosphorous, lead, sulfur,
antimony, selenium, silicon, titanium, thallium, vanadium, and
zinc. The presence and level of the above listed elemental metals
and non-metals may be controlled by the dissolving-grade pulp
preparation method. In particular, calcium content may be
influenced by washing agents and sodium content may be influenced
by the preparation process. In some aspects, the dissolving-grade
pulp compositions may comprise less than 175 ppm Group IA metals,
e.g., less than 100 ppm Group IA metals, less than 50 ppm Group IA
metals or less than 25 ppm Group IA metals. In some aspects, the
dissolving-grade pulp compositions may comprise less than 175 ppm
sodium, e.g., less than 100 ppm sodium, less than 50 ppm sodium or
less than 25 ppm sodium. In further aspects, the dissolving-grade
pulp compositions may comprise less than 10 ppm potassium, e.g.,
less than 7 ppm potassium or less than 5 ppm potassium. In still
further aspects, the dissolving-grade pulp compositions may
comprise less than 7 ppm silicon, e.g., less than 5 ppm or less
than 3 ppm. Without being bound by theory, by producing a
dissolving-grade pulp having low silicon content, the hardness of
the pulp may be improved, relative to dissolving-grade pulps
comprising higher amounts of silicon. In some aspects, the total
amount of elemental metals and non-metals disclosed above may be
present at less than 1 wt. %, e.g., less than 0.5 wt. %, or less
than 0.2 wt. % (2,000 ppm). In terms of ranges, the total amount of
elemental metals and non-metals disclosed above may range from 100
ppm to 10,000 ppm, e.g. from 100 ppm to 5,000 ppm or from 100 ppm
to 2,000 ppm. As used herein, parts per million (ppm) are
determined on a weight basis.
III. Cellulosic Material
[0028] The dissolving-grade pulp compositions of the present
invention may be formed from natural cellulosic materials,
including plant and plant-derived materials. As used herein, the
term "cellulosic material" refers to any material comprising
cellulose, such as a pulp, and which may contain, for example,
.alpha.-cellulose, hemicellulose and degraded cellulose. In
preferred embodiments, the cellulosic material comprises wood pulp,
e.g., paper grade wood pulp. When the cellulosic material is paper
grade wood pulp, the processes described herein may be
advantageously used to produce hemicellulose compositions and also
to produce cellulose compositions, although the processes of the
invention are not limited to the use of paper grade wood pulp as
the starting cellulosic material.
[0029] In some embodiments, the cellulosic material may comprise a
cellulosic raw material, which may include, without limitation,
plant derived biomass, corn stover, sugar cane stalk, bagasse and
cane residues, rice and wheat straw, agricultural grasses, hard
wood, hardwood pulp, soft wood, softwood pulp, herbs, recycled
paper, waste paper, wood chips, pulp and paper wastes, waste wood,
thinned wood, cornstalk, chaff, and other forms of wood, bamboo,
soyhull, bast fibers, such as kenaf, hemp, jute and flax,
agricultural residual products, agricultural wastes, excretions of
livestock, microbial, algal cellulose, and all other materials
proximately or ultimately derived from plants. Such cellulosic raw
materials are preferably processed in pellet, chip, clip, sheet,
attritioned fiber, powder form, or other form rendering them
suitable for extraction with the extractant. In some exemplary
embodiments, the hemicellulose compositions are derived from hard
wood pulps.
[0030] Generally, cellulosic material may be derived from
lignin-containing materials, where lignin has been removed
therefrom. In cellulosic materials, hemicellulose is linked to
cellulose by hydrogen bonds. Overall, the cellulose material has a
linear shape of fiber morphology, which is surrounded by
hemicellulose via hydrogen bonds. These bonds between cellulose and
hemicellulose may become weakened by treating the cellulosic
material with an extractant to selectively dissolve the
hemicellulose while maintaining the fiber morphology of the
cellulose material, e.g., leaving the fiber morphology
unchanged.
[0031] In one embodiment of the invention, the cellulosic material
is a paper grade pulp provided in a form such as, but not limited
to, a roll, a sheet, or a bale. Preferably, the paper grade pulp
comprises at least 70 wt. % .alpha.-cellulose, e.g., at least 75
wt. % .alpha.-cellulose or at least 80 wt. % .alpha.-cellulose.
Paper grade pulp typically also comprises at least 15 wt. %
hemicellulose, at least 20 wt. % hemicellulose or at least 25 wt. %
hemicellulose. In another embodiment, the cellulosic material may
be another .alpha.-cellulose containing pulp, such as viscose grade
pulp, rayon grade pulp, semi-bleached pulp, unbleached pulp, bleach
pulp, kraft pulp, absorbent pulp, dissolving-grade pulp, or fluff.
While these cellulosic materials comprise various concentrations of
.alpha.-cellulose, the inventive processes may advantageously treat
them, based on an optimized process design, to produce higher
purity .alpha.-cellulose products.
[0032] Cellulose is a straight chain polymer and is derived from
D-glucose units, which condense through .beta.-1,4-glycosidic
bonds. This linkage motif contrasts with that for
.alpha.-1,4-glycosidic bonds present in starch, glycogen, and other
carbohydrates. Unlike starch, there is no coiling or branching in
cellulose and cellulose adopts an extended and rather stiff
rod-like conformation, which is aided by the equatorial
conformation of the glucose residues. The multiple hydroxyl groups
on the glucose from one chain form hydrogen bonds with oxygen atoms
on the same or on a neighboring chain, holding the chains firmly
together side-by-side and forming microfibrils with high tensile
strength, which then overlay to form the macrostructure of a
cellulose fiber. In preferred embodiments of the invention, the
finished cellulosic product retains its fiber structure throughout
and after the extraction step.
[0033] As used herein, the term "hemicellulose" refers to any of
several heteropolymers, e.g., polysaccharides, present in plant
cell walls. Hemicellulose can include any one of xylan,
glucuronoxylan, arabinoxylan, glucomannan, galactomannan, and
xyloglucan. These polysaccharides contain many different sugar
monomers and can be hydrolyzed to monosaccharides, such as xylose,
mannose, galactose, rhamnose and arabinose. Xylose is typically the
primary sugar present in hardwoods and either mannose or xylose is
the primary sugar present in softwoods.
[0034] The processes of the present invention are particularly
beneficial in that they are effective for use with paper grade wood
pulp that is derived from softwoods and hardwoods. The processes of
the present invention provide a technique for recovering
dissolving-grade pulp compositions and also for recovering a
hemicellulose composition produced from hardwood and softwood
species.
[0035] Softwood species are generally more abundant and faster
growing than most hardwood species. Softwood is a generic term
typically used in reference to wood from conifers (i.e.,
needle-bearing trees from the order Pinales). Softwood-producing
trees include pine, spruce, cedar, fir, larch, douglas-fir,
hemlock, cypress, redwood and yew. Conversely, the term hardwood is
typically used in reference to wood from broad-leaved or angiosperm
trees. The terms "softwood" and "hardwood" do not necessarily
describe the actual hardness of the wood. While, on average,
hardwood is of higher density and hardness than softwood, there is
considerable variation in actual wood hardness in both groups, and
some softwood trees can actually produce wood that is harder than
wood from hardwood trees. One feature separating hardwoods from
softwoods is the presence of pores, or vessels, in hardwood trees,
which are absent in softwood trees. On a microscopic level,
softwood contains two types of cells, longitudinal wood fibers (or
tracheids) and transverse ray cells. In softwood, water transport
within the tree is via the tracheids rather than the pores of
hardwoods.
IV. Extractant
[0036] As described above, hemicellulose, and optionally degraded
cellulose, is extracted from the cellulosic material using an
extractant. The extractant comprises a cellulose solvent and a
co-solvent. The cellulose solvent is selected from the group
consisting of an ionic liquid, an amine oxide and mixtures thereof,
examples of which are described below. The cellulose solvent may or
(more preferably) may not fully dissolve .alpha.-cellulose, but
preferably dissolves at least hemicellulose and degraded cellulose.
.alpha.-cellulose preferably is less soluble in the co-solvent than
in the cellulose solvent.
[0037] a. Ionic Liquid
[0038] Ionic liquids are organic salts with low melting points,
preferably less than 200.degree. C., less than 150.degree. C., or
less than 100.degree. C., many of which are consequently liquid at
room temperature. Specific features that make ionic liquids
suitable for use in the present invention are their general lack of
vapor pressure, their ability to dissolve a wide range of organic
compounds and the versatility of their chemical and physical
properties. In addition, ionic liquids are non-flammable making
them particularly suitable for use in industrial applications. In
some embodiments, the cellulose solvent comprises one or more ionic
liquids.
[0039] It has been found that, in addition to these beneficial
properties, when contacted with cellulosic materials, including
plant matter and plant matter derivatives, the ionic liquids are
capable of acting as a cellulose solvent, dissolving the
hemicellulose and cellulose contained therein. In addition, with
the appropriate choice of treatment conditions (for example,
duration of contact, temperature, and co-solvent composition),
ionic liquids penetrate the structure of the cellulose-containing
material to break down the material and extract organic species
therein. In particular when used in combination with one or more
co-solvents, .alpha.-cellulosic components remaining in the
cellulosic material are preserved and the fiber morphology is
advantageously retained.
[0040] Ionic liquids, in pure form, generally are comprised of ions
and do not necessitate a separate solvent for ion formation. Ionic
liquids existing in a liquid phase at room temperature are called
room temperature ionic liquids. Generally, ionic liquids are formed
of large-sized cations and a smaller-sized anion. Cations of ionic
liquids may comprise nitrogen, phosphorous, sulfur, or carbon.
Because of the disparity in size between the cation and anion, the
lattice energy of the compound is decreased resulting in a less
crystalline structure with a low melting point.
[0041] Exemplary ionic liquids include the compounds expressed by
the following Formula (1):
[A].sup.+[B].sup.- (1)
[0042] In one embodiment, the ionic liquid is selected from the
group consisting of substituted or unsubstituted imidazolium salts,
pyridinium salts, ammonium salts, triazolium salts, pyrazolium
salt, pyrrolidinium salt, piperidium salt, and phosphonium salts.
In preferred embodiments, [A].sup.+ is selected from the group
consisting of:
##STR00001##
[0043] wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6
and R.sub.7 are each independently selected from the group
consisting of hydrogen, C.sub.1-C.sub.15 alkyls, C.sub.2-C.sub.15
aryls, and C.sub.2-C.sub.20 alkenes, and the alkyl, aryl or alkene
may be substituted by a substituent selected from the group
consisting of sulfone, sulfoxide, thioester, ether, amide, hydroxyl
and amine. [B].sup.- is preferably selected from the group
consisting of Cl.sup.-, Br.sup.-, I.sup.-, OH.sup.-,
NO.sub.3.sup.-, SO.sub.4.sup.2-, CF.sub.3CO.sub.2.sup.-,
CF.sub.3SO.sub.3.sup.-, BF.sub.4.sup.-, PF.sub.6.sup.-,
CH.sub.3COO.sup.-, (CF.sub.4SO.sub.2).sub.2N.sup.-,
AlCl.sub.4.sup.-, HCOO.sup.-, CH.sub.3SO.sub.4.sup.-,
(CH.sub.3).sub.2PO.sub.4.sup.-,
(C.sub.2H.sub.5).sub.2PO.sub.4.sup.- and
CH.sub.3HPO.sub.4.sup.-.
[0044] Examples of ionic liquids include tetrabutylammonium
hydroxide 30 hydrate (TBAOH.30H.sub.2O), benzyltriethylammonium
acetate (BnTEAAc), tetraethylammonium acetate tetrahydrate
(TEAAc.4H.sub.2O), benzyltrimethylammonium hydroxide (BnTMAOH),
tetramethylammonium hydroxide (TMAOH), ammonium acetate,
hydroxyethylammonium acetate, hydroxyethylammonium formate,
tetramethylammonium acetate, tetraethylammonium acetate,
tetrabutylammonium acetate, tetrabutylammonium hydroxide,
1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl
imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium
hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate,
methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate,
1,3-diethylimidazolium acetate (EEIMAc), 1-butyl-3-methyl
imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium
methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate,
1-ethyl-3-methyl imidazolium methanesulfonate,
methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl
imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride,
1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl
imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, and
mixtures or complexes thereof, but the disclosed concept of
utilizing ionic liquids is not limited to the disclosed
species.
[0045] In some embodiments, the ionic liquid is selected from the
group consisting of ammonium-based ionic substances,
imidazolium-based ionic substances, phosphonium-based ionic
substances, and mixtures thereof. The ammonium-based ionic liquid
may be selected from the group consisting of ammonium acetate,
hydroxyethylammonium acetate, hydroxyethylammonium formate,
tetramethylammonium acetate, tetrabutylammonium acetate,
tetraethylammonium acetate, benzyltriethylammonium acetate,
benzyltributyl ammonium acetate and combinations thereof. The
imidazolium-based ionic liquid may be selected from the group
consisting of 1-butyl-3-methyl imidazolium tetrachloroaluminate,
1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl
imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium
hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl
imidazolium acetate, 1,3-diethylimidazolium acetate (EEIMAc),
1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl
ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium
ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate,
methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl
imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride,
1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl
imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride,
1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl
diethyl phosphate (EMIMDEP), 1,3-dimethylimidazolium dimethyl
phosphate (DMIMDMP) and mixtures or complexes thereof. The ionic
liquid may also be selected from the group consisting of
N,N-dimethylpyrrolidinium acetate, N,N-dimethylpiperidinium
acetate, N,N-dimethylpyrrolidinium dimethyl phosphate,
N,N-dimethylpiperidinium dimethyl phosphate,
N,N-dimethylpyrrolidinium chloride, N,N-dimethylpiperidinium
chloride, and combinations thereof.
[0046] In still other embodiments, the ionic liquid may be selected
from the group consisting of 1-butyl-3-methylimidazolium
tetrachloroaluminate, 1-ethyl-3-methyl imidazolium
tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium
hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate,
methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate,
1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl
ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium
ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate,
methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl
imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride,
1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl
imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride,
1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl
diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and
combinations and complexes thereof.
[0047] In further embodiments, the ionic liquid may be selected
from the group consisting of ethyltributylphosphonium
diethylphosphate, methyltributylphosphonium dimethylphosphate,
tetrabutylphosphonium bromide, tetrabutylphosphonium chloride,
tributylmethylphosphonium methylsulfate,
trihexyltetradecylphosphonium decanoate,
trihexyltetradecylphosphonium dicyanamide,
ethyltriphenylphosphonium acetate, ethyltributylphosphonium
acetate, benzyltriethylphosphonium acetate,
benzyltributylphosphonium acetate, tetrabutylphosphonium acetate,
tetraethylphosphonium acetate, tetramethylphosphonium acetate, and
combinations thereof.
[0048] The ionic liquid may be commercially available, and may
include Basionic.TM. AC 01, Basionic.TM. AC 09, Basionic.TM. AC 25,
Basionic.TM. AC 28, Basionic.TM. AC 75, Basionic.TM. BC 01,
Basionic.TM. BC 02, Basionic.TM. FS 01, Basionic.TM. LQ 01,
Basionic.TM. ST 35, Basionic.TM. ST 62, Basionic.TM. ST 70,
Basionic.TM. ST 80, Basionic.TM. VS 01, and Basionic.TM. VS 02, but
the invention is not limited to use of these species.
[0049] In preferred embodiments, the ionic liquid compound, as
shown below, may be 1-ethyl-3-methyl imidazolium acetate (EMIMAc)
of the structural formula (2), 1-butyl-3-methyl imidazolium acetate
(BMIMAc) of the structural formula (3), 1-ethyl-3-methyl
imidazolium dimethylphosphate of structural formula (4),
1-ethyl-3-methyl imidazolium formate of the structural formula (5),
tetrabutylammonium acetate (TBAAc) of the structural formula (6),
1-allyl-3-methyl imidazolium chloride of the structural formula
(7), or 1-n-butyl-3-methyl imidazolium chloride of the structural
formula (8):
##STR00002##
[0050] b. Amine Oxide
[0051] Amine oxides are chemical compounds that contain the
functional group R.sub.3N.sup.+--O.sup.-, which represents an N--O
bond with three additional hydrogen and/or hydrocarbon side chains.
Amine oxides are also known as tertiary amines, N-oxides,
amine-N-oxide and tertiary amine N-oxides. In one embodiment, amine
oxides that are stable in water may be used.
[0052] In some embodiments, the amine oxide may be selected from
the group consisting of compounds with chemical structure of
acyclic R.sub.3N.sup.+--O.sup.-, compounds with chemical structure
of N-heterocyclic compound N-oxide, and combinations thereof. In
further embodiments, the amine oxide may be an acyclic amine oxide
compound with structure of R.sub.1R.sub.2R.sub.3N.sup.+--O.sup.-,
wherein R.sub.1, R.sub.2 and R.sub.3 are alkyl or aryl chains, the
same or different, with chain length from 1 to 18, e.g.
trimethylamine N-oxide, triethylamine N-oxide, tripropylamine,
N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide,
dimethylethylamine N-oxide, methyldipropylamine N-oxide,
tribenzylamine N-Oxide, benzyldimethylamine N-oxide,
benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide,
monomethyldiethylamine, dimethylmonoethylamine,
monomethyldipropylamine, N-dimethyl-, N-diethyl- or
N-dipropylcyclohexylamine, N-dimethylmethylcyclohexylamine,
pyridine, and pyridine N-oxide.
[0053] In some embodiments, the amine oxide may be a cyclic amine
oxide compound including the structures such as pyridine, pyrrole,
piperidine, pyrrolidine and other N-heterocyclic compounds, e.g.
N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or
4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine
N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide.
N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide.
N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide
N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide.
N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide. In some
embodiments, the amine oxide may be the combination of the above
mentioned acyclic and/or cyclic amine oxides.
[0054] In specific embodiments, the amine oxide may be selected
from the group consisting of trimethylamine N-oxide, triethylamine
N-oxide, tripropylamine N-oxide, tributylamine N-oxide,
methyldiethylamine N-oxide, dimethylethylamine N-oxide,
methyldipropylamine N-oxide, tribenzylamine N-Oxide,
benzyldimethylamine N-oxide, benzyldiethylamine N-oxide,
dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO),
pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine
N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide,
N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide,
N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide,
N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide,
N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide,
N-hexylpyrrolidine N-oxide, and combinations thereof.
[0055] Cellulose is insoluble in most solvents because of its
strong and highly structured intermolecular hydrogen bonding
network. Without being bound by theory, NMMO is able to break the
hydrogen bonding network that keeps cellulose insoluble in most
solvents. Therefore, the use of NMMO alone would destroy the fiber
morphology of cellulose. It has now been discovered that by using
the proper ratio of an amine oxide, such as NMMO, with a
co-solvent, .alpha.-cellulosic components in the cellulosic
material may be beneficially preserved and the fiber morphology
retained. NMMO is typically stored in 50 to 70 vol. %, e.g., 60
vol. %, aqueous solution as pure NMMO tends toward oxygen
separation. See, e.g., U.S. Pat. No. 4,748,241, the entirety of
which is incorporated herein by reference. Further contaminants in
commercial NMMO product, e.g., N-methylmorpholine, peroxides, and
acid components, tend to degrade the storage stability. In other
words, further application of NMMO needs to address all stability
concerns. For example, developed stabilizers like propyl gallate
may be added.
[0056] c. Co-Solvent
[0057] As stated above, the extractant also comprises a co-solvent.
Co-solvents in the context of this invention include solvents that
do not have the ability to readily dissolve .alpha.-cellulose. In
exemplary embodiments, the co-solvent is selected, with various
concentrations, from the group consisting of water, acetic acid,
alcohols such as methanol, ethanol, n-propanol, isopropanol,
n-butanol, tert-butanol, diols and polyols such as ethanediol and
propanediol, amino alcohols such as ethanolamine, diethanolamine
and triethanolamine, aromatic solvents, e.g., benzene, toluene,
ethylbenzene or xylenes, halogenated solvents, e.g.
dichloromethane, chloroform, carbon tetrachloride, dichloroethane
or chlorobenzene, aliphatic solvents, e.g. pentane, hexane,
heptane, octane, ligroin, petroleum ether, cyclohexane and decalin,
ethers, e.g. tetrahydrofuran, diethyl ether, methyl tert-butyl
ether and diethylene glycol monomethyl ether, ketones such as
acetone and methyl ethyl ketone, esters, e.g. ethyl acetate,
dimethyl carbonate, dipropyl carbonate, propylene carbonate,
amides, e.g., formamide, dimethylformamide (DMF),
N,N-dimethylacetamide (DMAC), DMSO, acetonitrile and mixtures
thereof. Since the boiling points of co-solvents vary
significantly, the efficient purification processes associated with
each co-solvent may not be exactly the same.
[0058] In one embodiment, a second co-solvent may be used in
conjunction with the first co-solvent and the cellulose solvent,
e.g., amine oxide or ionic liquid, as described above. In one
embodiment, the second co-solvent decreases the viscosity of the
extractant. The second co-solvent may have a viscosity, for
example, of less than 2.0 mPas, e.g., less than 1.8 mPas or less
than 1.5 mPas at 25.degree. C. In some embodiments, the second
co-solvent is selected from the group consisting of formamide, DMF,
dimethylacetamide, DMSO, N-methylpyrrolidone, propylene carbonate,
acetonitrile and mixtures thereof. It is postulated that using a
low viscosity second co-solvent in the extractant, the extraction
rate is enhanced and a smaller amount of ionic liquid is needed to
extract the hemicellulose in the cellulosic material.
[0059] Without being bound by theory, the insolubility of the
.alpha.-cellulose in the co-solvent and the resulting extractant
maintains the cellulose fiber morphology, e.g., leaving the fiber
morphology unchanged, while the extractant penetrates the
cellulosic material, dissolves and extracts the hemicellulose and
preferably degraded cellulose from the cellulosic material.
Depending on the specific co-solvent used in the extractant, the
weight percentage of the cellulose solvent and the co-solvent in
the extractant may vary widely.
[0060] d. Extractant Compositions
[0061] The specific formulation of the extractant employed may vary
widely, depending, for example, on the hemicellulose and degraded
cellulose content of the starting cellulosic material, and the
processing scheme employed. In one embodiment, the extractant
optionally comprises at least 0.1 wt. % amine oxide, e.g., at least
2 wt. % or at least 4 wt. %. In terms of upper limits, the
extractant optionally comprises at most 85 wt. % amine oxide, e.g.,
at most 75 wt. %, or at most 70 wt. % amine oxide. In terms of
ranges, the extractant optionally comprises from 0.1 wt. % to 85
wt. % amine oxide, e.g., from 2 wt. % to 75 wt. %, or from 4 wt. %
to 70 wt. %. The extractant optionally comprises at least 0.1 wt. %
co-solvent, e.g., at least 1 wt. %, or at least 3 wt. % co-solvent.
In terms of upper limits, the extractant optionally comprises at
most 99.9 wt. %, at most 98 wt. %, or at most 97 wt. % co-solvent.
In terms of ranges, the extractant optionally comprises from 0.1
wt. % to 99.9 wt. % co-solvent, e.g., from 1 wt. % to 98 wt. %, or
from 3 wt. % to 97 wt. % co-solvent.
[0062] In one embodiment, the extractant comprises an aqueous
co-solvent, e.g., water, and an amine oxide. For example, the
extractant optionally comprises at least 40 wt. % amine oxide,
e.g., at least 50 wt. % or at least 60 wt. %. In terms of upper
limits, the extractant optionally comprises at most 90 wt. % amine
oxide, e.g., at most 85 wt. %, or at most 80 wt. % amine oxide. In
terms of ranges, the extractant optionally comprises from 40 wt. %
to 90 wt. % amine oxide, e.g., from 50 wt. % to 85 wt. %, or from
60 wt. % to 80 wt. % amine oxide. The extractant optionally
comprises at least 1 wt. % aqueous co-solvent, e.g., at least 5 wt.
%, or at least 10 wt. % aqueous co-solvent. In terms of upper
limits, the extractant optionally comprises at most 50 wt. %
aqueous co-solvent, at most 40 wt. %, or at most 30 wt. %. In terms
of ranges, the extractant optionally comprises from 1 wt. % to 50
wt. % aqueous co-solvent, e.g., from 5 wt. % to 40 wt. %, or from
10 wt. % to 30 wt. %.
[0063] In one embodiment, the extractant comprises an organic
co-solvent and an amine oxide. In this aspect, the extractant
optionally comprises at least 0.1 wt. % amine oxide, e.g., at least
1 wt. % or at least 2 wt. % amine oxide. In terms of upper limits,
the extractant optionally comprises at most 85 wt. % amine oxide,
e.g., at most 80 wt. %, or at most 70 wt. %. In terms of ranges,
the extractant optionally comprises from 0.1 wt. % to 85 wt. %
amine oxide, e.g., from 1 wt. % to 80 wt. %, or from 2 wt. % to 70
wt. %. In this aspect, the extractant optionally comprises at least
15 wt. % organic co-solvent, e.g., at least 20 wt. %, or at least
30 wt. %. In terms of upper limits, the extractant optionally
comprises at most 99.9 wt. % organic co-solvent, at most 98 wt. %,
or at most 97 wt. %. In terms of ranges, the extractant optionally
comprises from 15 wt. % to 99.9 wt. % organic co-solvent, e.g.,
from 20 wt. % to 98 wt. %, or from 30 wt. % to 97 wt. %. In one
embodiment, the organic co-solvent is DMSO.
[0064] In one embodiment, the extractant includes an amine oxide, a
first co-solvent and a second co-solvent. In one embodiment, the
extractant includes an amine oxide, an aqueous co-solvent, e.g.,
water, and an organic co-solvent, e.g., DMSO. In this aspect, the
amine oxide concentration may range, for example, from 1 wt. % to
85 wt. %, the water concentration may range from 1 wt. % to 35 wt.
%, and the organic co-solvent, e.g., DMSO, concentration may range
from 1 wt. % to 98 wt. %.
[0065] In other embodiments, the cellulose solvent used in the
extractant comprises one or more ionic liquids. For example, the
extractant optionally comprises at least 0.1 wt. % ionic liquid,
e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper
limits, the extractant optionally comprises at most 95 wt. % ionic
liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of
ranges, the extractant optionally comprises from 0.1 wt. % to 95
wt. % ionic liquid, e.g., from 1 wt. % to 90 wt. %, or from 2 wt. %
to 85 wt. %. The extractant optionally comprises at least 5 wt. %
co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, or at least
20 wt. %. In terms of upper limits, the extractant optionally
comprises at most 99.9 wt. % co-solvent, at most 99 wt. %, or at
most 98 wt. %. In terms of ranges, the extractant optionally
comprises from 5 wt. % to 99.9 wt. % co-solvent, e.g., from 10 wt.
% to 99 wt. %, or from 20 wt. % to 98 wt. %.
[0066] In one embodiment, the cellulose solvent comprises one or
more ionic liquids and the co-solvent comprises an aqueous
co-solvent, e.g., water. In this aspect, the extractant preferably
comprises at least 50 wt. % ionic liquid, e.g., at least 65 wt. %
or at least 80 wt. %. In terms of upper limits, the extractant
optionally comprises at most 95 wt. % ionic liquid, e.g., at most
90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant
optionally comprises from 50 wt. % to 95 wt. % ionic liquid, e.g.,
from 65 wt. % to 90 wt. %, or from 70 wt. % to 85 wt. %. The
extractant optionally comprises at least 5 wt. % aqueous
co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, or at least
20 wt. %. In terms of upper limits, the extractant optionally
comprises at most 50 wt. % aqueous co-solvent, e.g., at most 35 wt.
%, or at most 20 wt. % aqueous co-solvent. In terms of ranges, the
extractant may comprise from 5 wt. % to 50 wt. % aqueous
co-solvent, e.g., from 10 wt. % to 35 wt. %, or from 15 wt. % to 20
wt. %.
[0067] In one embodiment, when the extractant comprises one or more
ionic liquids as cellulose solvent and an organic co-solvent, the
extractant preferably comprises at least 0.1 wt. % ionic liquid,
e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper
limits, the extractant optionally comprises at most 20 wt. % ionic
liquid, e.g., at most 15 wt. %, or at most 10 wt. %. In terms of
ranges, the extractant may comprise from 0.1 wt. % to 20 wt. %
ionic liquid, e.g., from 1 wt. % to 15 wt. %, or from 2 wt. % to 10
wt. %. The extractant optionally comprises at least 80 wt. %
organic co-solvent, e.g., at least 85 wt. %, or at least 90 wt. %.
In terms of upper limits, the extractant may comprise at most 99.9
wt. % organic co-solvent, e.g., at most 98 wt. %, or at most 97 wt.
%. In terms of ranges, the extractant optionally comprises from 80
wt. % to 99.9 wt. % organic co-solvent, e.g., from 85 wt. % to 98
wt. %, or from 90 wt. % to 97 wt. %. In one embodiment, the organic
co-solvent is DMSO.
[0068] In one embodiment, the extractant includes a cellulose
solvent, e.g., amine oxide or ionic liquid, a first co-solvent and
a second co-solvent. In this aspect, the weight ratio of first
co-solvent to second co-solvent is preferably from 20:1 to 1:20,
e.g. from 15:1 to 1:15 or from 10:1 to 1:10. Since the production
costs of ionic liquids are generally higher than those of
co-solvents, the use of a large amount of the second co-solvent
beneficially reduces the cost of purifying the cellulosic
material.
[0069] In one embodiment, the extractant includes an ionic liquid,
a first co-solvent and a second co-solvent. In one embodiment, the
extractant includes an ionic liquid, an aqueous co-solvent, e.g.,
water, and an organic co-solvent, e.g., DMSO. In the tertiary
extractant system, the extractant may include at most 50 wt. %
ionic liquid, e.g., at most 40 wt. %, or at most 30 wt. %. In terms
of lower limit, the extractant may include at least 0.1 wt. % ionic
liquid, e.g., at least 5 wt. % or at least 10 wt. %. In terms of
ranges, the extractant may include from 0.1 wt. % to 50 wt. % ionic
liquid, e.g., from 5 wt. % to 40 wt. %, or from 10 wt. % to 30 wt.
%. In some embodiments, the extractant may include at most 20 wt. %
the first co-solvent, i.e., at most 16 wt. %, or 10 wt. %. In terms
of ranges the extractant may include from 0.5 wt. % to 20 wt. % the
first co-solvent, e.g., from 3 wt. % to 16 wt. % or from 5 wt. % to
10 wt. %. In one embodiment, water is the first co-solvent. In one
embodiment, DMSO is the second co-solvent. Without being bound by
theory, it is postulated that the decrease in viscosity in the
extractant by using the second co-solvent beneficially enhances the
extraction rate and increases the amount of hemicellulose extracted
from the cellulosic material.
[0070] In one embodiment, the extractant comprises an aqueous
co-solvent, an ionic liquid and an amine oxide. In this aspect, the
co-solvent concentration may range, for example, from 5 wt. % to 50
wt. %, the ionic liquid concentration may range from 0.1 wt. % to
50 wt. %, and the amine oxide concentration may range from 0.1 wt.
% to 85 wt. %.
[0071] In one embodiment, the extractant comprises an organic
co-solvent, an ionic liquid and an amine oxide. In this aspect, the
co-solvent concentration may, for example, range from 5 wt. % to 99
wt. %, the ionic liquid concentration may range from 0.1 wt. % to
50 wt. %, and the amine oxide concentration may range from 0.1 wt.
% to 50 wt. %.
V. Process for Forming a Dissolving-Grade Pulp Composition
[0072] As described herein, cellulosic material may be purified
through an inventive extraction process to produce a
dissolving-grade pulp composition and also to recover hemicellulose
from a cellulosic material. FIG. 1 illustrates one non-limiting
exemplary system for purifying a cellulosic material, and
recovering a hemicellulose composition. As shown in FIG. 1, the
cellulosic material may be purified in purification process 100. As
shown, the cellulosic material is fed via line 103 to extractor
105. Line 103 may represent, for example, a pneumatic lock hopper,
a screw feeder, a belt feeder, a rotary valve feeder, or another
type of solid transport equipment. Extractant, comprising a
cellulose solvent and co-solvent, as described above, is fed to
extractor 105 via line 104. Although cellulosic material 103 and
extractant 104 are shown as fed separately to extractor 105, it is
contemplated that they may be completely or partially mixed prior
to being fed to extractor 105. As shown in FIG. 1, cellulosic
material 103 and extractant 104 may be combined in extractor 105 to
form an extraction mixture. The extraction mixture within extractor
105 may comprise, for example, from 0.1 to 20 wt. % solids, e.g.,
from 0.5 to 15 wt. % or from 1.25 to 10 wt. % solids.
[0073] Extractant 104 for extracting cellulosic material 103 may be
any extractant capable of dissolving preferably at least 50% of the
hemicellulose, more preferably at least 75% or at least 90% of the
hemicellulose, in cellulosic material 103, as determined by UV
absorbance analysis of hemicellulose concentration for hardwood and
mass measurements of the feed, cellulosic product, and
hemicellulose product. Extractant 104 comprises a cellulose solvent
and co-solvent in relative amounts that do not overly degrade or
dissolve the cellulose. For example, in one embodiment, the
extractant dissolves less than 15% of the .alpha.-cellulose in
cellulosic material 103, e.g., less than 10%, or less than 5%, as
determined similarly by UV absorbance analysis and mass
measurements.
[0074] As described above, amine oxides and ionic liquids may tend
to dissolve .alpha.-cellulose. The extractant preferably comprises
sufficient co-solvent to reduce .alpha.-cellulose solubility in the
overall extractant to a point that the .alpha.-cellulose does not
readily dissolve therein. Preferably, the .alpha.-cellulose is
substantially insoluble in the co-solvent. Extractant 104 in
accordance with the present invention, therefore, has the property
of selectively dissolving the hemicellulose and preferably degraded
cellulose that is in cellulosic material 103.
[0075] Exemplary compositions for the cellulosic material and
extractant fed to the extractor, and for the resulting extraction
mixture are provided in Table 1.
TABLE-US-00001 TABLE 1 EXTRACTOR 105 Conc. Conc. Conc. (wt. %) (wt.
%) (wt. %) Cellulosic Material 103 "Cellulose"* 50 to 90 55 to 85
60 to 80 "Hemicellulose"** 1 to 40 .sup. 5 to 30 10 to 25 Water 0.1
to 49 .sup. 1 to 40 1 to 29 Extractant 104 Solvent 0.1 to 99.9
.sup. 2 to 90 3 to 80 Co-solvent 0.1 to 99.9 10 to 98 20 to 97
Extraction Mixture in Extractor 105 Cellulose 0.3 to 14 0.3 to 13
0.3 to 12 Hemicellulose*** 0.005 to 6 0.03 to 5 0.05 to 4 Water
0.001 to 3 0.005 to 3 0.005 to 2 Solvent 0.09 to 99.4 1.7 to 90 2.6
to 80 Co-solvent 0.09 to 99.4 8.5 to 98 17 to 97 *"Cellulose"
refers to cellulose of all forms including degraded cellulose
**"Hemicellulose" in cellulosic material 103 refers to
hemicellulose alone excluding non-hemicellulose impurities
***"Hemicellulose" after being dissolved in extractant 104 refers
to hemicellulose, degraded cellulose, and other impurities
[0076] The treatment of cellulosic material 103 with extractant 104
may be conducted at an elevated temperature, and preferably occurs
at atmospheric pressure or slightly above atmospheric pressure.
Preferably, the contacting is conducted at a temperature from
30.degree. C. to 300.degree. C., e.g., from 40.degree. C. to
200.degree. C., or from 50.degree. C. to 150.degree. C. In terms of
upper limits, the treatment of cellulosic material 103 may be
conducted at a temperature of less than 300.degree. C., e.g., less
than 200.degree. C., or less than 150.degree. C. In terms of lower
limit, the treatment of cellulosic material 103 may be conducted at
a temperature of greater than 30.degree. C., e.g., greater than
40.degree. C., or greater than 50.degree. C. The pressure
(absolute, unless otherwise indicated) is in the range from 100 kPa
to 10 MPa, preferably from 100 kPa to 5000 kPa, more preferably
from 100 kPa to 1100 kPa. In some embodiments, the pressure may be
reduced below 100 kPa, e.g., from 1 to 99 kPa.
[0077] Cellulosic material 103 may contact extractant 104 (or have
a residence time in extractor 105 for continuous processes) between
5 minutes to 1000 minutes, e.g., between 20 minutes to 500 minutes,
or from 40 minutes to 200 minutes. In terms of lower limits, the
treatment of cellulosic material 103 may be for at least 5 minutes,
e.g., at least 20 minutes or at least 40 minutes. In terms of upper
limits, the treatment of cellulosic material 103 may be for at most
1000 minutes, e.g., at most 500 minutes, or at most 200
minutes.
[0078] The extraction process may be conducted in a batch, a
semi-batch or a continuous process with material flowing either
co-current or counter-current in relation to one another. In a
continuous process, cellulosic material 103 contacts extractant 104
in one or more extraction vessels. In one embodiment, extractant
104 may be heated to the desired temperature before contacting
cellulosic material 103. In one embodiment, the extraction
vessel(s) may be heated by any suitable means to the desired
temperature. Additionally, an inert gas (not shown), e.g., nitrogen
or CO.sub.2, may be supplied to the extractor to improve turbulence
in the extractor and thus improving heat and mass transfers. The
flow rate of inert gas will be controlled not to cause hydrodynamic
problem, e.g. flooding. When the size and concentration of solid
materials along with the flow rate of inert gas are well
controlled, the addition of an inert gas may cause the solids in
extractor 105 to float on the surface of the extraction mixture
allowing for the solids to be skimmed off the surface of the liquid
phase contained in extractor 105.
[0079] In the extraction step, the mass ratio of extractant to
cellulosic material may range from 5:1 to 500:1, e.g., from 7:1 to
300:1, or from 10:1 to 100:1. The solid:liquid volume ratio may
range from 0.005:1 to 0.17:1, e.g., from 0.01:1 to 0.15:1 or from
0.02:1 to 0.1:1, depending on the extraction apparatus and set-up.
In one embodiment, a solid:liquid ratio of from 0.01:1 to 0.02:1 or
about 0.0125:1 may be used to facilitate the filtration operation
in a batch process. In another embodiment, a solid:liquid ratio of
0.1:1 to 0.17:1 can be used, in particular for extractors employing
countercurrent extraction. The amount of extractant employed has a
significant impact on process economics. Counter-current extraction
may achieve greater extraction efficiency while maintaining
reasonable extractant usage. Counter-current extraction of solubles
from pulp can be accomplished in a variety of commercial equipment
such as, but not limited to, a series of agitated tanks,
hydrapulpers, continuous belt extractors, and screw extractors.
Twin-screw extractors are generally more efficient than
single-screw extractors. After extraction, the separation of solid
and liquid phases can be completed in suitable commercial
equipment, which includes filters, centrifuges, and the like.
[0080] In one embodiment, the cellulosic material is subjected to
repeated extraction steps. For example, the cellulosic material may
be treated with the extractant in an initial extraction step
followed by one or more additional extraction steps, in the same or
multiple extractors, to further extract residual hemicellulose
and/or degraded cellulose. In one embodiment, the cellulosic
product may be subjected to an initial extraction step, followed by
an extractant wash step, followed by a second extraction step. In
some embodiments, the cellulosic product may be subjected to a
third or fourth extraction step. When multiple extraction steps are
employed, the extractant in each extraction step may be the same or
varied to account for the different concentrations of hemicellulose
and degraded cellulose in intermediate cellulosic materials between
extraction steps. For example, a first extraction may use an
extractant comprising an ionic liquid and a co-solvent and a second
extraction may use an extractant comprising an amine oxide and a
co-solvent, or vice versa, optionally with one or more extractant
wash steps between and/or after the second extraction step. Similar
configurations can be designed and optimized based upon the general
chemical engineering principles and process design theory.
[0081] In another embodiment (not shown), the process may further
include enzymatic digestion of hemicellulose, extraction and/or
isolation of digested hemicellulose and recovery of a cellulosic
product with reduced hemicellulose content. Without being bound by
theory, by treating the cellulosic material first with the
extractant, enzymes may be better able to penetrate the cellulosic
material to hydrolyze residual hemicellulose and/or degraded
cellulose contained therein. On the contrary, experimental data has
shown that less hemicellulose may be removed from the cellulosic
material if it is first treated with an enzyme cocktail under
optimum enzyme hydrolysis conditions, followed by an extraction
step. For enzymes to be effective in hydrolyzing hemicellulose, a
pretreatment step (e.g., prehydrolysis) is preferred in order to
make the cellulosic materials amenable to enzymatic hydrolysis. The
pretreatment step preferably comprises treating the cellulosic
material with high pressure steam, optionally at low or high acid
concentrations, or ammonia treatment. Some modification to the
process flow scheme may be desired since the enzyme treatment would
likely necessitate increased residence time to complete enzymatic
hydrolysis. In addition, acidity (pH), temperature and ionic
strength would likely need to be adjusted for effective enzymatic
treatment.
[0082] In this embodiment, after the extraction step, the
cellulosic material may be treated with an enzyme, preferably a
hemicellulase, to break down residual hemicellulose contained in
the cellulosic material. The hemicellulase includes one or more
enzymes that hydrolyze hemicellulose to form simpler sugars,
ultimately yielding monosaccharides, such as glucose, hexoses and
pentoses. Suitable hemicellulase include one or more of
xyloglucanase, .beta.-xylosidase, endoxylanase,
.alpha.-L-arabinofuranosidase, .alpha.-glucuronidase, mannanase,
and acetyl xylan esterase. Preferably, the enzymes include a
combination of both endo-enzymes (i.e., enzymes hydrolyzing
internal polysaccharide bonds to form smaller poly- and
oligosaccharides) and exo-enzymes (i.e., enzymes hydrolyzing
terminal and/or near-terminal polysaccharide bonds) to facilitate
the rapid hydrolysis of large polysaccharide molecules. Suitable
commercial hemicellulase include SHEARZYME (available from
Novozymes A/S, Bagsvaerd, Denmark), PULPZYME (available from
Novozymes A/S, Bagsvaerd, Denmark), FRIMASE B210 (available from
Puratos, Groot-Bijgaarden, Belgium), FRIMASE B218 (available from
Puratos, Groot-Bijgaarden, Belgium), GRINDAMYL (available from
Danisco, Copenhagen, Denmark), ECOPULP TX200A (available from AB
Enzymes, Darmstadt, Germany), MULTIFECT Xylanase (available from
Genencor/Danisco, Palo Alto, USA), PENTOPAN Mono BG (available from
Novozymes, Bagsvaerd, Denmark), and PENTOPAN 500 BG (available from
Novozymes, Bagsvaerd, Denmark).
[0083] The enzymes generally can be used in amounts that are not
particularly limited. For example, hemicellulase can be used in
amounts ranging from about 0.001 mg/g to about 500 mg/g (e.g.,
about 0.05 mg/g to about 200 mg/g, about 0.1 mg/g to about 100
mg/g, about 0.2 mg/g to about 50 mg/g, or about 0.3 mg/g to about
40 mg/g). The concentration units are milligrams of enzyme per gram
of cellulosic material to be treated.
[0084] After the desired contacting time, an extraction mixture is
removed from extractor 105 via line 106. The extraction mixture 106
comprises extractant, dissolved hemicellulose, dissolved degraded
cellulose, side products, e.g., mono-, di-, and oligo-saccharide,
and an intermediate cellulosic material having reduced
hemicellulose content and preferably reduced degraded cellulose
content. As shown in FIG. 1, extraction mixture 106 may be fed to
filter/washer 108 to remove extractant, dissolved hemicellulose,
and dissolved degraded cellulose. Removal of the extractant in the
filtering step reduces the amount of residual hemicellulose that
must be further processed with the intermediate cellulosic
material. It also reduces the amount of extractant that must be
separated from the intermediate cellulose in subsequent steps.
Filter/washer 108 may comprise solid-liquid separation equipment,
including but not limited to, for example, rotary vacuum drums,
belt filters and screw presses. Filter/washer 108 forms a washed
intermediate cellulosic material 114 and an extraction filtrate
109.
[0085] Prior to exiting filter/washer 108, optionally while on a
vacuum belt filter, the intermediate cellulosic material may be
washed with extractant wash 107 to further reduce the amount of
extractant remaining in the filtered extraction mixture. The
washing may be conducted in a batch, a semi-batch or a continuous
process with material flowing either co-current or counter-current
in relation to one another. In some embodiments, the intermediate
cellulosic material may be washed more than once in separate
washing units from filter/washer 108. When more than one washing
step is used, the composition of the extractant wash may vary in
the different washing steps. For example, a first washing step may
use DMSO as an extractant wash to remove residual hemicellulose and
ionic liquid and a second washing step may use water as an
extractant wash to remove residual DMSO. A similar configuration
can be designed and optimized based upon the general chemical
engineering principles and process design theory.
[0086] Extractant wash 107 preferably comprises a co-solvent, which
dissolves residual hemicellulose and/or degraded cellulose from the
cellulosic material, but may also include some low level of
extractant resulting from the sequence of washing steps. In one
embodiment, the extractant wash is selected from the group
consisting of water, acetonitrile, DMF, DMAC, ketones (e.g.
acetone), aldehydes, esters (e.g. methyl acetate, ethyl acetate),
ethers (e.g., MTBE), lactones, carboxylic acids (e.g., acetic
acid), alcohols, polyols, amino alcohols, DMSO, formamide,
propylene carbonate, aromatic solvents, halogenated solvents,
aliphatic solvents, vinyl acetate, nitriles (propionitrile,
chloroacetonitrile, butyonitrile), chloroform, dichloromethane, and
mixtures thereof. In another embodiment, extractant wash 107 is
selected from the group consisting of DMSO, DMF, N-methyl
pyrrolidone, methanol, ethanol, isopropanol, dimethyl carbonate,
propylene carbonate, acetone, water, and mixtures thereof. In some
embodiments, at least two extractant washes are used in series,
such as DMSO and water. It should be understood that, depending on
the amount of residual hemicellulose contained in the cellulosic
material, the amount of extractant wash may be minimized to reduce
capital cost and energy requirements for subsequent separation and
recycle, described below. Additionally, it should be understood
that the one or more extractant washes may also be used to remove
side products, e.g., mono-, di-, and oligo-saccharides from the
extraction mixture.
[0087] The extractant wash may further comprise one or more washing
aids that improve the removal of extractant from the cellulosic
material, improve operability, or otherwise improve the physical
properties of the intermediate cellulose material. The washing aids
may include, for example, defoamers, surfactants, and mixtures
therefore. The amount of washing agent can vary widely based upon
the amount of residual extractant, quality requirement for
cellulosic product, and process operability.
[0088] The extractant wash may then be removed via line 113, e.g.,
as used extractant wash filtrate. The washed intermediate
cellulosic material exits filter/washer 108 as an intermediate
cellulosic material 114 having reduced hemicellulose content and
preferably reduced degraded cellulose content. Intermediate
cellulosic material 114 may comprise less than 6 wt. % extractant,
e.g., less than 5 wt. % or less than 4 wt. % extractant. In some
embodiments, the intermediate cellulosic material 112 may comprise
less than 0.5 wt. % cellulose solvent (ionic liquid and/or amine
oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or less
than 0.001 wt. %. Intermediate cellulosic material 112 may comprise
from 9.9 to 99% solids, e.g., from 19 to 90% or from 28 to 85%.
[0089] Exemplary compositions using DMSO as the co-solvent and
water as the extractant wash for the intermediate cellulosic
material are provided in Table 2. When DMSO is used as the
co-solvent and water is used as the extractant wash, at least 90%
of the cellulose in cellulosic material 103 is maintained in
cellulose product 116, as described herein.
TABLE-US-00002 TABLE 2 FILTER/WASHER 108 Conc. Conc. Conc. (wt. %)
(wt. %) (wt. %) Extraction Mixture 106 Cellulose 0.24 to 14.sup.
0.26 to 13 0.29 to 12.sup. Hemicellulose* 0.008 to 7 0.03 to 5 0.05
to 5 Solvent (e.g., Ionic 0.09 to 99.4 1.7 to 90 2.6 to 80 Liquid)
Co-solvent (e.g., 0.09 to 99.4 8.5 to 98 17 to 97 DMSO) Washed
Intermediate Cellulosic Material 114 Cellulose 9.9 to 99 19 to 90
28 to 85 Hemicellulose* 0.003 to 12 0.02 to 9 0.06 to 7 Extractant
wash (e.g., 1 to 90 10 to 80 15 to 70 water) Extraction Filtrate
109 Cellulose 0.002 to 1.4 0.003 to 1.3.sup. 0.003 to 1.2
Hemicellulose* 0.008 to 6.7 0.03 to 5.2 0.05 to 4.4 Solvent (e.g.,
Ionic 0.09 to 99.9 1.7 to 90 2.6 to 80 Liquid) Co-solvent (e.g.,
0.09 to 99.9 .sup. 8.5 to 99.6 17.0 to 99.3 DMSO) Used Extractant
wash (Filtrate) 113 Water .sup. 91 to 99.8 93 to 99.7 .sup. 94 to
99.7 Solvent (e.g., Ionic 0.004 to 2.7 0.004 to 2.0.sup. 0.004 to
1.5 Liquid) Co-solvent (e.g., 0.01 to 2.7 0.02 to 2.2 0.03 to 1.9
DMSO) *"Hemicellulose" in these streams includes hemicellulose,
degraded cellulose and other impurities
[0090] In another aspect, as shown in FIGS. 2 and 3, which depict
purification processes 101 and 102, filter/washer 108 is replaced
with filter 110. In this aspect, extraction mixture 106 is sent to
filter 110 to form filtered intermediate cellulosic material 112
and extraction filtrate 111. Exemplary compositions using
acetonitrile as the co-solvent are provided in Table 3.
TABLE-US-00003 TABLE 3 FILTER 110 Conc. Conc. Conc. (wt. %) (wt. %)
(wt. %) Extraction Mixture 106 Cellulose 0.2 to 14 0.3 to 13 0.3 to
12 Hemicellulose*** 0.008 to 7 0.03 to 5 0.05 to 4 Water 0.001 to
10 0.01 to 8 0.1 to 5 Solvent 0.09 to 99.4 1.7 to 90 2.6 to 80
Co-solvent (e.g., 0.09 to 99.4 8.5 to 98 17 to 97 Acetonitrile)
Intermediate Cellu- losic Material 112 Cellulose 25 to 80 29 to 79
33 to 78 Hemicellulose* 0.003 to 15 0.02 to 10 0.05 to 8 Solvent
(e.g., Ionic 0.02 to 70.sup. 0.34 to 63 0.51 to 56 Liquid)
Co-solvent (e.g., 0.02 to 70.sup. 1.7 to 68 3.4 to 68 Acetonitrile)
Water 0.0003 to 7 0.002 to 6 0.02 to 4 Extraction Filtrate 111
Cellulose 0.002 to 5.2 0.003 to 3.9.sup. 0.004 to 2.9.sup.
Hemicellulose* 0.01 to 5.6 0.05 to 5.5 0.07 to 5.4 Solvent (e.g.,
Ionic 0.08 to 99.3 1.7 to 90 .sup. 2 to 80 Liquid) Co-solvent
(e.g., 0.08 to 99.3 8 to 97.4 16 to 96.4 Acetonitrile)
[0091] Intermediate cellulosic material 114 may then be further
de-liquored, e.g., mechanically concentrated in a concentrator 115
to form a concentrated cellulosic material 117 having an increased
solids content and a residual extractant wash 116, which may be
recycled to and combined with either extractant wash 107 or stream
112. The solids content in concentrated cellulosic material 117 may
range from 10 to 99 wt. %, e.g., from 20 to 90 wt. % or from 30 to
85 wt. %. The concentrator may include squeeze rolls, rotating
rolls, and/or ringer rolls as well as optional heat exchangers to
vaporize the liquids. Additional water removal methods may be used
to concentrate the cellulosic material, depending on the desired
solids content and available energy supply. The concentrated
cellulosic material may comprise from 2 to 99 wt. % cellulose
(e.g., from 3 to 95 wt. % cellulose), from 1 to 60 wt. % water
(e.g., from 1 to 50 wt. % water), and from 0.01 to 20 wt. %
hemicellulose (e.g., from 0.5 to 10 wt. % hemicellulose).
[0092] In some embodiments, when the process comprises more than
one washing step, a concentrator may be utilized between washing
steps or after all washing steps in order to maximize the washing
separation of hemicellulose, as well as improve washing efficiency
for the solvent and co-solvent thereby reducing total washing agent
quantity required and associated energy and disposal costs.
[0093] Concentrated cellulosic material 117 or 114 may then be
further dried in dryer 120. Hot gas may be fed to dryer 120 via
line 121 and may exit dryer 120 via line 122. A finished cellulose
product, e.g., dissolving-grade pulp, may then exit dryer 120 via
line 123. The dryer may function to remove residual extractant
wash. The finished cellulose product may comprise from 80 to 99.9
wt. % cellulose (e.g., from 90 to 95 wt. % cellulose), from 0.01 to
25 wt. % hemicellulose (e.g., from 0.1 to 15 wt. % hemicellulose)
and from 0.1 to 20 wt. % water (e.g., from 3 to 15 wt. % water).
Exemplary dryers include disintegrator dryers, flash dryers, apron
dryers, rotary dryers, heated rolls, infrared dryers, ovens and
vacuums. Without being bound by theory, the disintegrator dryer may
be used to further open the cellulosic material, which may be
advantageous for subsequent processing, e.g., in the formation of
cellulose acetate, and derivatives thereof. In another embodiment,
dryer 120 comprises heated rolls which may be used to form baled
sheets or product rolls of cellulosic material. Finished cellulose
product 123 may comprise less than 20 wt. % water, e.g., less than
15 wt. %, less than 10 wt. % or less than 5 wt. % water.
[0094] In another embodiment, as shown in FIG. 2, after exiting
filter 110 and optional de-liquoring steps, intermediate cellulosic
material 112 may be directed to washer 125 where it is washed with
extractant wash 128 to further reduce the amount of extractant
remaining in the intermediate cellulosic product. The washing may
be conducted in a batch, a semi-batch or a continuous process with
material flowing either co-current or counter-current in relation
to one another. In some embodiments, only one washing step is used.
In other embodiments, as shown in FIG. 2, the intermediate
cellulosic material may be washed more than once in separate
washers 125 and 135. When more than one washing step is used, the
composition of the extractant wash may vary in the different
washing steps. For example, a first washing step may use
co-solvent, e.g. acetonitrile as extractant wash 128 to remove
residual cellulose solvent and residual hemicellulose and a second
washing step may use water as extractant wash 138 to remove
residual acetonitrile. A similar configuration can be designed and
optimized based upon the general chemical engineering principles
and process design theory and it is understood that multiple
washing steps, optionally with de-liquoring and/or drying steps in
between, may be used. The washing step may be conducted at a higher
temperature in order to enhance mass transfer and to increase the
solubility. The temperature may be from 10.degree. C. to
100.degree. C., e.g., from 15.degree. C. to 90.degree. C., or from
20.degree. C. to 80.degree. C.
[0095] Extractant washes 128 and 138 preferably each comprise a
co-solvent, which dissolves residual cellulose solvent and residual
hemicellulose and/or degraded cellulose from the cellulosic
material, but may preferably be substantially free of cellulose
solvent. Extractant wash 128 preferably comprises a co-solvent,
which can be used to wash away the residual first co-solvent in the
cellulose material. In one embodiment, the extractant wash is
selected from the group consisting of acetonitrile, acetone,
methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate,
vinyl acetate, propionitrile, dichloromethane, chloroform,
butyronitrile, chloroacetonitrile, water, and combinations thereof.
In other embodiments, the extract wash is selected from the group
consisting of water, ethylene glycol, glycerin, formamide,
N,N-dimethylformamide, N-methylpyrrolidinone,
N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and
combinations thereof. In some embodiments, first extractant wash
128 may comprise greater than 85 wt. % acetonitrile, e.g., greater
than 90 wt. % or greater than 95 wt. %; and second extractant wash
138 may comprise greater than 90 wt. % washing solvent, preferably
water, e.g., greater than 95 wt. % water, greater than 99 wt. %
water or greater than 99.5 wt. % water. It should be understood
that, depending on the amount of residual solvent contained in the
cellulosic material, the amount of extractant wash may be minimized
to reduce capital cost and energy requirements for subsequent
separation and recycle, described below.
[0096] The extractant wash may further comprise one or more washing
aids that improve the removal of extractant from the cellulosic
material, improve operability, or otherwise improve the physical
properties of the intermediate cellulose material. The washing aids
may include, for example, defoamers, surfactants, and mixtures
thereof. The amount of washing agent can vary widely based upon the
amount of residual extractant, quality requirement for cellulosic
product, and process operability.
[0097] The first extractant wash may then be removed via line 127
and the second extractant wash may be removed via line 137, e.g.,
as used extractant wash filtrates. In some embodiments, used
extractant wash filtrate 127 may be returned to extractor 105,
either directly to extractor 105 or combined with solvent 104. Used
extractant wash filtrate 137 may be used in hemicellulose recovery
section 130. The intermediate cellulosic material exits filter 110,
washer 125 and washer 135 via line 136. Washed intermediate
cellulosic material 136 has reduced hemicellulose content and
preferably reduced degraded cellulose content. Washed intermediate
cellulosic material 136 may comprise less than 6 wt. % extractant,
e.g., less than 5 wt. % or less than 4 wt. % extractant. In some
embodiments, washed intermediate cellulosic material 136 may
comprise less than 0.5 wt. % cellulose solvent (ionic liquid and/or
amine oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or
less than 0.001 wt. %. Washed intermediate cellulosic material 136
may comprise from 9.9 to 99% solids, e.g., from 19 to 90% or from
28 to 85%.
[0098] As shown in FIG. 3, instead of directing used extractant
wash filtrate 127 directly to extractor 105 or to extractant 104,
used extractant wash filtrate 127 may be separated in vaporizer 140
to form a recycled co-solvent stream 142 comprising, for example,
from 60 to 95 wt. % co-solvent, e.g., from 70 to 95 wt. % or from
80 to 90 wt. % co-solvent and from 5 to 40 wt. % ionic liquid,
e.g., from 7 to 30 wt. % or from 10 to 20 wt. % ionic liquid, and a
second recycled co-solvent stream 141 comprising, for example, at
least 90 wt. % co-solvent, e.g., at least 95 wt. %, at least 99 wt.
% or at least 99.5 wt. % co-solvent. Recycled co-solvent stream 142
may be directed to extractor 105 or combined with extractant 104.
Second recycled co-solvent stream 141 may be used within the
process, optionally after further separation.
[0099] Exemplary compositions using acetonitrile as the co-solvent,
acetonitrile as the first extractant wash and water as the second
extractant wash for the intermediate cellulosic material are
provided in Table 4. When acetonitrile is used as the co-solvent
and first extractant wash 128, and water is used as second
extractant wash 138, at least 90% or at least 95% of the cellulose
in cellulosic material 103 is maintained in washed intermediate
cellulosic material 136, as described herein. If no further
processing is required, washed intermediate cellulosic material 136
may be referred to as finished cellulosic material, e.g.,
dissolving-grade pulp.
TABLE-US-00004 TABLE 4 WASHER 125 and WASHER 135 Conc. Conc. Conc.
(wt. %) (wt. %) (wt. %) Washed Intermediate Cellulosic Material 126
Cellulose 25 to 88 29 to 83 33 to 78 Hemicellulose* 0.003 to 15
0.02 to 11.sup. 0.05 to 8.1 Extraction Wash 8 to 70 14 to 66 19 to
63 (Acetonitrile) Water 0 to 12 .sup. 0 to 6.5 0.001 to 2.9 Used
Extractant Wash 127 Water 0 to 16 .sup. 0 to 8.3 0.001 to 3.9
Solvent (Ionic Liquid) 0 to 23 0.02 to 21.sup. 0.03 to 19.sup.
Co-solvent (Acetonitrile) 61 to 100 71 to 100 78 to 100 Washed
Intermediate Cellulosic Material 136 Cellulose 25 to 88 29 to 83 33
to 78 Hemicellulose* 0.003 to 15 0.02 to 11.sup. 0.05 to 8.1
Acetonitrile 0 to 9 0 to 7 0.001 to 6 Water 11 to 70 13 to 67 15 to
63 Used Extractant Wash 137 Water 69 to 99.6 .sup. 71 to 99.3 .sup.
73 to 99.0 Solvent (Ionic Liquid) 0 to 7.7 .sup. 0 to 7.0 .sup. 0
to 6.5 Co-solvent (Acetonitrile) 0.4 to 24.sup. 0.7 to 23 1.0 to 21
*"Hemicellulose" in these designated streams includes
hemicellulose, degraded cellulose and other impurities.
[0100] Used extractant washes 127 and 137 may be subjected to
further separation (not shown) and reused within the process.
[0101] In some embodiments (not shown), washed intermediate
cellulosic material 126 or 136 may then be further de-liquored,
e.g., mechanically concentrated in a concentrator to form a
concentrated cellulosic material having an increased solids
content, e.g., from 10 to 99 wt. %, from 20 to 90 wt. % or from 30
to 85 wt. %. In some embodiments, the solids content is at least 90
wt. %. The concentrator may include squeeze rolls, rotating rolls,
and/or ringer rolls as well as optional heat exchangers to vaporize
the liquids. Additional water removal methods may be used to
concentrate the cellulosic material, depending on the desired
solids content and available energy supply. The concentrated
cellulosic material may comprise from 2 to 99 wt. % cellulose
(e.g., from 3 to 95 wt. % cellulose), from 1 to 60 wt. % water
(e.g., from 1 to 50 wt. % water), and from 0.01 to 20 wt. %
hemicellulose (e.g., from 0.5 to 10 wt. % hemicellulose). The
concentrated cellulosic material may then be further dried in a
dryer (not shown) as described herein.
[0102] In some embodiments, as described herein, when the process
comprises more than one washing step, a concentrator may be
utilized between washing steps or after all washing steps in order
to improve washing efficiency for the cellulose solvent and
co-solvent, as well as to maximize separation of any remaining
hemicellulose, thereby reducing total washing agent quantity
required and associated energy and disposal costs.
[0103] Depending on the purity of the starting cellulosic material,
high purity .alpha.-cellulose product may be produced. In preferred
embodiments, the finished cellulose product, e.g., dissolving-grade
pulp, comprises high purity .alpha.-cellulose products such as high
purity dissolving-grade pulps comprising at least 90 wt. % glucan,
from 1.7 to 5 wt. % xylan, and less than 5 wt. % hemicellulose,
e.g., less than 2 wt. % hemicellulose or less than 1 wt. %
hemicellulose. In one embodiment, the cellulosic product has an UV
absorbance of less than 2.0 at 277 nm, e.g., less than 1.6 at 277
nm, or less than 1.2 at 277 nm for hardwood species. Paper grade
pulp typically has an UV absorbance of greater than 4.7 at 277 nm,
as determined by standard UV absorbance measurements. Conveniently
and accurately, purity of the .alpha.-cellulose product may be
indicated by a lower absorbance at a certain wavelength.
[0104] In addition to retaining the fiber morphology of the
cellulosic product, the dissolving-grade pulp also may
advantageously retain other beneficial characteristics such as
brightness. Further, the dissolving-grade pulp may have a
weight-average molecular weight than the starting cellulosic
material, e.g., at least 200% higher, at least 300% higher or at
least 500% higher. The dissolving-grade pulp may be further
processed to make cellulose derivatives, such as cellulose ether,
cellulose esters, cellulose nitrate, other derivatives of
cellulose, or regenerated cellulose fiber, such as viscose,
lyocell, rayon, etc. Preferably, the dissolving-grade pulp may be
used to make cellulose acetate.
[0105] Returning to extractant filtrate 109 or 111 as shown in
FIGS. 1-3, the stream may be sent to a hemicellulose recovery unit
130 to form recovered extractant 131 and hemicellulose product 132.
The recovered extractant 131 may contain cellulose solvent and
co-solvent which can be recycled to extractor 105. Hemicellulose
recovery unit 130 may comprise a filtration unit or an evaporator,
a precipitator, distillation columns, washers, and dryers. The
finished hemicellulose product, has a broad application to generate
high value chemicals. Some, but not all, examples are described
briefly here. Firstly, it may be advantageously used as an
intermediate in ethanol, xylitol, furfural, methyl furfural, or
valerolactone production. Secondly, the finished hemicellulose
product may also be used as a feedstock to produce ethanol and/or
as a fuel to a recovery boiler. Thirdly, hemicellulose can be used
as a starting material to produce functional chemicals, such as
adhesives and sweeteners. Fourthly, it can be recycled back to
paper mill to make papers with special features.
[0106] While the above invention is applicable to processes in
which mono-, di-, and oligo-saccharide and/or other side products
may be generated in the extraction process, flashing process,
and/or other operating steps, several other technologies can also
be chosen to remove them from the system in order to maintain
continuous operation. In some embodiments, evaporation, membrane,
ion exchange, activated carbon bed, simulated moving bed
chromatographic separation, flocculant, e.g.
polydiallyldimethylammonium chloride (polyDADMAC), and/or their
combinations may be employed to separate mono-, di-, and
oligo-saccharide from the liquid stream. In other embodiments,
polymer-bound boronic acid has been demonstrated to be able to form
complex with sugars so that the sugars are separated from the
liquid stream. In yet other embodiments, the small sugars may be
converted by either enzymatic treatment or acid-catalytic process
into furfural, ethanol, acetic acid, and/or other products which
can be further separated out from the system. In still other
embodiments, mono-, di-, and oligo-saccharide and other side
products can be removed in one or more operations, which are
located before the separation of the extraction filtrate, after
precipitation step, in the hemicellulose wash steps, and/or in
other steps. The operating conditions are also determined by the
stability of the extractant. Without being bound by theory, this
allows for the minimization of degradation products of the
extractant. For a continuous operation, degradation products may be
removed by directly purging a degradation products stream.
Additionally, distillation may be used to purge degradation
products from a column as a distillate or a residue, depending on
the boiling point(s) of the degradation product(s). In some
embodiments, combinations of these degradation product removal
strategies may be employed.
[0107] Similarly, accumulated dissolved and/or suspended solids may
be removed from the system in order to maintain continuous
operation. In some embodiments, evaporation, membrane filtration,
ion exchange, activated carbon bed, simulated moving bed
chromatographic separation, flocculant, e.g.
polydiallyldimethylammonium chloride (polyDADMAC), and/or their
combinations may be employed to separate the accumulated dissolved
and/or suspended solids from the system.
[0108] It is understood that the processes described herein may be
further modified based upon the extraction capability, stability,
and costs of ionic liquid and co-solvent.
[0109] The present invention will be better understood in view of
the following non-limiting examples.
VI. Examples
Example 1
Hardwood Pulp Single Extraction
[0110] A carbohydrate analysis and a gel permeation chromatography
(GPC)/size exclusion chromatography (SEC) analysis of a
dissolving-grade pulp prepared according to the present invention
were conducted. The dissolving-grade pulp was prepared from a
hardwood paper grade pulp (Comp. Ex. D in Table 5). The extractant
composition comprised 3 wt. % EMIM Ac and 97 wt. % DMSO. The
extraction was conducted at 95.degree. C. for 1 hour with a pulp
solid loading of 5 wt. %. After extraction, the pulp was deliquored
with centrifugation and washed with fresh extractant (3 wt. % EMIM
Ac and 97 wt. % DMSO), and then washed with water four times. After
the water wash, the pulp was dispersed in water, and filtered with
a Busch funnel under vacuum. The filter cake was washed one more
time with acetone to remove additional water. Finally, the pulp
cake was dried at room temperature in a chemical hood to a moisture
content from 7 to 8 wt. % moisture content.
[0111] The carbohydrate analysis was conducted in the following
manner. The samples were prepared according to TAPPI T249.
Approximately 0.3 grams of pulp was prehydrolyzed in 3 mL of 72%
H.sub.2SO.sub.4 at 30.degree. C. for 1 hour, and then diluted to 4%
H.sub.2SO.sub.4 concentration by adding water. The sample was
autoclaved at 120.degree. C. to completely hydrolyze the
polysaccharides into monosaccharides. The hydrolyzed sample was
then analyzed by Dionex ion chromatography with a pulsed
amperometric detector (PAD). The results were calculated relative
to sample weight on an oven-dried basis.
[0112] The SEC was conducted using three detectors in series:
refractive index (RI), right angle and low angle light scattering
(RALS/LALS), and four-capillary differential viscometer. The system
was calibrated use a poly(methyl methacrylate) standard. The run
conditions were as follows: a mobile phase contained 0.5% lithium
chloride in N,N-dimethylacetamide (DMAC); the run was conducted at
60.degree. C., with an injection volume of 100 .mu.L and a flow
rate of 0.70 mL/min using Viscotek I-MBLMW and MBHMW SEC/GPC
columns.
[0113] The dissolving-grade pulp sample was prepared by placing
approximately 0.05 g of the dissolving-grade pulp in 10 mL water at
40.degree. C. to swell for 45 minutes. This was repeated. The
sample was then washed twice with 8 m: methanol for 45 minutes at
ambient temperature. 8 mL anhydrous DMAC was added twice
consecutively at ambient temperature. The first wash of anhydrous
DMAC was left for 45 minutes and the second wash was left
overnight. The sample was then added to 5 mL of 8% dry
LiCl/anhydrous DMAC, and stirred at ambient temperature for 48
hours for complete dissolution. The final dissolved sample was a
clear viscous mixture of 8% LiCl/DMAC at a concentration of 10
mg/mL. The sample was then diluted to approximately 1 mg/mL before
injection into the GPC instrumentation.
[0114] The UV measurement was conducted as follows. 1 mL of 72%
sulfuric acid was added to 0.1 g of dry pulp. The mixture was
incubated at 30.degree. C. for 1 hour with stirring every 10 min.
After incubation, the clear solution was diluted by 5 mL of
deionized water. The UV absorbance at 277 nm of the diluted
solution was measured. After hydrolysis by 72% sulfuric acid at
30.degree. C. for 1 hour, the xylan in the pulp was converted into
furfural which was measured by UV. Cellulose and mannose cannot be
converted into 5-hydroxymethylfurfural (HMF) under these
conditions. Therefore the UV purity is related to the xylan content
in purified pulp. The higher the UV absorbance at 277 nm, the
higher the xylan content in pulp. The pulp had a UV purity of 1 to
1.1, which approximately represents the xylan content in pulp to be
3 to 3.5 wt. %.
[0115] The results of the analysis are shown in Table 5.
Example 2
Hardwood Pulp Double Extraction
[0116] A carbohydrate analysis and a GPC/SEC analysis of a
dissolving-grade pulp prepared according to the present invention
were conducted as in Example 1. The dissolving-grade pulp was
prepared as in Example 1, except that the pulp was subjected to a
second extraction using the same extractant under the same
extraction condition. The pulp had a UV purity of 0.7 to 0.8,
corresponding to a xylan content from 1.2 to 1.7 wt. %. An
elemental metal analysis was also conducted on the pulp of Example
2.
Example 3
Hardwood Pulp Double Extraction
[0117] The UV purity of a dissolving-grade pulp prepared according
to the present invention was determined as in Example 1. The
dissolving-grade pulp was prepared from a hardwood paper grade pulp
(Comp. Ex. D in Table 5). The extractant composition comprised 3
wt. % EMIM Ac and 97 wt. % DMSO. The extraction was conducted at
95.degree. C. for 1 hour with a pulp solid loading of 5 wt. %.
After extraction, the pulp was de-liquored with centrifugation, and
then the de-liquored wet pulp was returned to the extractor and
fresh extractant was added (3 wt. % EMIM Ac and 97 wt. % DMSO). The
extraction composition had a 5% pulp solid loading and the
extraction was conducted for 1 hour at 95.degree. C. After the
second extraction, the pulp was washed and dried as in Example 1,
except that there no fresh extractant wash was used before the
water wash steps. Finally, the pulp cake was dried at room
temperature in a chemical hood to a moisture content of
approximately 7 to 8 wt. %. The purified pulp had a UV purity of
1.0 to 1.1, which represented an approximate xylan content from 3
to 3.5 wt. %
Comparative Example A
Hardwood
[0118] A carbohydrate analysis and a GPC/SEC analysis of a
commercial acetate grade pulp were conducted as in Example 1. The
pulp was prepared from a hardwood according to a pH kraft process.
The results of the analysis are shown in Table 5.
Comparative Example B
Hardwood
[0119] A carbohydrate analysis and a GPC/SEC analysis of a
commercial acetate grade pulp were conducted as in Example 1. The
pulp was prepared from a hardwood according to a pH kraft process.
The results of the analysis are shown in Table 5.
Comparative Example C
Hardwood
[0120] A carbohydrate analysis and a GPC/SEC analysis of a hardwood
pulp were conducted as in Example 1. The pulp was prepared from a
hardwood according to a sulfite process. The results of the
analysis are shown in Table 5.
Comparative Example D
Hardwood
[0121] A carbohydrate analysis and a GPC/SEC analysis of a
commercial paper grade pulp were conducted as in Example 1. The
pulp was prepared from a hardwood and was the starting cellulosic
material used in Examples 1-3. The results of the analysis are
shown in Table 5.
TABLE-US-00005 TABLE 5 CARBOHYDRATE AND GPC/SEC ANALYSIS Comp.
Comp. Comp. Comp. Example 1 Example 2 Example 3 Ex. A Ex. B Ex. C
Ex. D Carbohydrate Analysis Arabinan (wt. %) <0.1 0.1 -- <0.1
<0.1 N/A 0.2 Xylan (wt. %) 3.5 1.9 3 to 3.5 1.6 1.4 N/A 20.3
Mannan (wt. %) 1.2 1.1 -- 0.3 0.6 N/A 1.0 Galactan (wt. %) <0.1
0.1 -- <0.1 <0.1 N/A 0.2 Glucan (wt. %) 92.6 93.3 -- 96.4
97.4 N/A 77.3 Acid Insoluble (wt. %) 0.7 0.4 -- 0.2 0.7 N/A 0.6
Total (wt. %) 98 96.9 -- 98.6 100 N/A 99.6 GPC/SEC Analysis
Weight-Average 793,320 845,725 835,268 422,451 361,014 359.685
700,708 Molecular Weight (g/mol) Number-Average 273,901 269,540
178,361 76,651 149,729 88,577 143,951 Molecular Weight (g/mol)
Z-Average Molecular 1,498,000 1,707,000 1,958,000 830.376 768,853
823,311 1,993,333 Weight (g/mol) Peak Molecular Weight 727,083
661,129 623,267 349,115 213,764 196,808 619,425 (g/mol)
Polydispersity Index 2.90 3.12 4.68 5.51 2.42 4.06 4.79
Example 4
Elemental Analysis
[0122] The pulps of Examples 1-2 and of Comparative Examples A-B
and D were subjected to elemental analysis. The metal scan analysis
for these samples was determined by inductively coupled
plasma-optical emission spectroscopy (IEP-OES). The results are
shown in Table 6.
TABLE-US-00006 TABLE 6 ELEMENTAL ANALYSIS Elemental Comp. Comp.
Comp. Analysis (ppm) Example 1 Example 2 Ex. A Ex. B Ex. D Al 1.3
1.8 1.1 1.1 2.8 As 0.5 <0.05 <0.5 <0.5 <0.5 Ba .69 0.53
0.27 0.42 4.03 B <0.2 <0.2 0.7 0.2 0.2 Cd <0.02 <0.02
0.02 <0.02 <0.02 Ca 204 164 15.8 20 279 Cr 0.41 0.49 0.08
0.05 0.11 Co 0.04 <0.02 0.02 <0.02 0.04 Cu 1.87 1.9 0.33 0.15
0.21 Fe 18.7 18.6 3.09 2.17 2.66 Pb 2.6 <0.2 <0.2 <0.2 0.2
Li 0.03 0.03 0.07 0.05 0.02 Mg 82.7 66.5 29.2 12.7 30 Mn 0.37 0.23
0.06 0.75 2.21 Hg <0.01 <0.01 <0.01 <0.01 <0.01 Mo
0.18 0.12 <0.05 <0.05 <0.05 Ni 0.64 0.44 0.15 0.14 0.17 P
0.8 0.7 0.6 0.6 0.6 K 2 2 8 2 12 Si 3.78 4.96 8.78 15.9 9.92 Na 13
12 217 289 729 Sr 0.57 0.46 0.15 0.24 1.61 Ti 0.26 0.41 0.22 0.16
0.37 V <0.05 <0.05 <0.05 <0.05 <0.05 Zn 11.1 10.9
1.68 0.80 1.81
Example 5
[0123] The pulps of Examples 1-2 and of Comparative Examples A-B
and D were tested for carboxyl content, aldehyde content, copper
number, and DCM extractives. The carboxyl content was analyzed per
ESM 055B (ref: TAPPI T237, the entirety of which is hereby
incorporated by reference); the aldehyde content was analyzed per
ESM055B (ref: Rayonier Standard Procedure, the entirety of which is
hereby incorporated by reference); the copper number was analyzed
per ESM 071B (ref: TAPPI T430, the entirety of which is hereby
incorporated by reference); and the DCM extractives were analyzed
per ESM 077B (ref: PAPTAC G.13 & TAPPI T204, the entireties of
which are hereby incorporated by reference). The results are shown
in Table 7.
TABLE-US-00007 TABLE 7 PULP QUALITIES Comp. Comp. Comp. Example 1
Example 2 Ex. A Ex. B Ex. D Carboxyl 1.77 2.25 2.36 1.51 5.91
Content (meq/100 g) Aldehyde 0.22 <0.01 0.07 0.03 0.52 Content
(meq/100 g) Copper 0.14 0.15 0.25 0.13 0.42 number Carbonyl 0.12
0.13 0.30 0.10 0.58 Content (meq/100 g) DCM <0.01 <0.01 0.03
0.02 0.13 Extractives
Example 6
Softwood Pulp Single Extraction
[0124] A carbohydrate analysis and a GPC/SEC analysis of a
dissolving-grade pulp prepared according to the present invention
were conducted as in Examples 1 and 5. The dissolving-grade pulp
was prepared from paper grade softwood pulp. The extractant
composition comprised 3 wt. % EMIM Ac and 97 wt. % DMSO. The
extraction was conducted at 95.degree. C. for 1 hour with a pulp
solid loading of 5 wt. %. After extraction, the pulp was deliquored
with centrifugation, washed with fresh extractant (3 wt. % EMIM Ac
and 97 wt. % DMSO), and then washed with water four times. After
the water wash, the pulp was dispersed in water and filtered with a
Busch funnel under vacuum. The filter cake was washed one more time
with acetone to remove water. Finally, the pulp cake was dried at
room temperature in a chemical hood to a moisture content from 7 to
8 wt. %. The results of the analysis are shown in Table 8.
Example 7
Softwood Pulp Double Extraction
[0125] A carbohydrate analysis and a GPC/SEC analysis of a
dissolving-grade pulp prepared according to the present invention
were conducted as in Examples 1 and 5. The dissolving-grade pulp
was prepared as in Example 2, except that a softwood pulp was used
as a starting material. The results of the analysis are shown in
Table 8.
Comparative Example E
Softwood
[0126] A GPC/SEC analysis of a commercial acetate grade pulp was
conducted as in Example 1. The pulp was prepared from a softwood
according to a sulfite process. The results of the analysis are
shown in Table 8.
Comparative Example F
Softwood
[0127] A carbohydrate analysis and a GPC/SEC analysis of a
commercial acetate grade pulp were conducted as in Example 1. The
pulp was prepared from a softwood according to a sulfite process.
The results of the analysis are shown in Table 8.
Comparative Example G
Softwood
[0128] A carbohydrate analysis and a GPC/SEC analysis of a
commercial acetate grade pulp were conducted as in Example 1. The
pulp was prepared from a softwood according to a sulfite process.
The results of the analysis are shown in Table 8.
Comparative Example H
Softwood
[0129] A GPC/SEC analysis of a commercial acetate grade pulp was
conducted as in Example 1. The pulp was prepared from a softwood
according to a sulfite process. The results of the analysis are
shown in Table 8.
Comparative Example I
Softwood
[0130] A GPC/SEC analysis of a commercial acetate grade pulp was
conducted as in Example 1. The pulp was prepared from a softwood
according to a sulfite process. The results of the analysis are
shown in Table 8.
Comparative Example J
Softwood
[0131] A GPC/SEC analysis of a commercial acetate grade pulp was
conducted as in Example 1. The pulp was prepared from a softwood
according to a sulfite process. The results of the analysis are
shown in Table 8.
Comparative Example K
Softwood
[0132] A carbohydrate analysis and a GPC/SEC of a commercial paper
grade pulp were conducted as in Examples 6 and 7. The pulp was
prepared from a softwood according to a pH kraft process. The
results of the analysis are shown in Table 8.
Comparative Example L
Softwood
[0133] A carbohydrate analysis of a commercial paper grade pulp was
conducted as in Examples 6 and 7. The results of the analysis are
shown in Table 8.
TABLE-US-00008 TABLE 8 CARBOHYDRATE AND GPC/SEC ANALYSIS Comp.
Comp. Comp. Example 6 Example 7 Ex. E Ex. F Ex. G Carbohydrate
Analysis Arabinan (wt. %) 0.2 0.1 -- <0.1 <0.1 Xylan (wt. %)
1.8 0.9 -- 1.5 1.8 Mannan (wt. %) 5.6 4.9 -- 1.1 1.1 Galactan (wt.
%) 0.2 0.1 -- <0.1 <0.1 Glucan (wt. %) 86.9 90.1 -- 96.3 93.2
Acid Insoluble (wt. %) 0.1 <0.1 -- 0.5 0.4 Total (wt. %) 94.7
96.1 -- 98.7 96.5 GPC/SEC Analysis Weight-Average 2,368,500 N/A
671,393 638,516 500,753 Molecular Weight (g/mol) Number-Average
264,594 N/A 232,340 278,234 141,785 Molecular Weight (g/mol)
Z-Average Molecular 26,860,000 N/A 1,256,000 1,127,000 953,861
Weight (g/mol) Peak Molecular Weight 305,714 N/A 589,350 589,350
396,680 (g/mol) Polydispersity Index 8.95 N/A 2.89 2.89 3.53 Comp.
Comp. Comp. Comp. Comp. Ex. H Ex. I Ex. J Ex. K Ex. L Carbohydrate
Analysis Arabinan (wt. %) -- -- -- 0.5 0.6 Xylan (wt. %) -- -- --
8.9 9.5 Mannan (wt. %) -- -- -- 7.0 6.4 Galactan (wt. %) -- -- --
0.3 0.2 Glucan (wt. %) -- -- -- 76.5 79.6 Acid Insoluble (wt. %) --
-- -- <0.1 <0.1 Total (wt. %) -- -- -- 93.2 96.4 GPC/SEC
Analysis Weight-Average 565,102 423,975 429,182 2,237,500 --
Molecular Weight (g/mol) Number-Average 180,471 141,909 129,235
454,867 -- Molecular Weight (g/mol) Z-Average Molecular 1,069,333
807,799 842,857 12,700,000 -- Weight (g/mol) Peak Molecular Weight
510,524 364,948 306,513 546,395 -- (g/mol) Polydispersity Index
3.13 2.99 3.32 4.92 --
Example 8
Silicon Content
[0134] The analysis of the silicon content for the pulps of
Comparative Examples A-B, F-H and J was provided by atomic
spectroscopy and is shown in Table 9.
TABLE-US-00009 TABLE 9 SILICON CONTENT Silicon Target Silicon
Maximum (ppm) (ppm) Comp. Ex. A 7 23 Comp. Ex. B 19 47 Comp. Ex. F
5 14 Comp. Ex. G 12 37 Comp. Ex. H 12 28 Comp. Ex. J 12 37
[0135] While the invention has been described in detail,
modifications within the spirit and scope of the invention will be
readily apparent to those of skill in the art. It should be
understood that aspects of the invention and portions of various
embodiments and various features recited above and/or in the
appended claims may be combined or interchanged either in whole or
in part. In the foregoing descriptions of the various embodiments,
those embodiments which refer to another embodiment may be
appropriately combined with other embodiments as will be
appreciated by one of ordinary skill in the art. Furthermore, those
of ordinary skill in the art will appreciate that the foregoing
description is by way of example only, and is not intended to limit
the invention.
* * * * *