U.S. patent application number 13/286998 was filed with the patent office on 2012-05-10 for recovery of organic acids.
This patent application is currently assigned to ZeaChem, Inc.. Invention is credited to Timothy J. Eggeman, Dan W. Verser.
Application Number | 20120112127 13/286998 |
Document ID | / |
Family ID | 34831209 |
Filed Date | 2012-05-10 |
United States Patent
Application |
20120112127 |
Kind Code |
A1 |
Verser; Dan W. ; et
al. |
May 10, 2012 |
RECOVERY OF ORGANIC ACIDS
Abstract
A method is disclosed for the recovery of an organic acid from a
dilute salt solution in which the cation of the salt forms an
insoluble carbonate salt. A tertiary amine and CO.sub.2 are
introduced to the solution to form the insoluble carbonate salt and
a complex between the acid and an amine. A water immiscible
solvent, such as an alcohol, is added to extract the acid/amine
complex from the dilute salt solution to a reaction phase. The
reaction phase is continuously dried and a product between the acid
and the solvent, such as an ester, is formed.
Inventors: |
Verser; Dan W.; (Menlo Park,
CA) ; Eggeman; Timothy J.; (Lakewood, CO) |
Assignee: |
ZeaChem, Inc.
Menlo Park
CA
|
Family ID: |
34831209 |
Appl. No.: |
13/286998 |
Filed: |
November 1, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12548312 |
Aug 26, 2009 |
8048655 |
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13286998 |
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11046206 |
Jan 28, 2005 |
7601865 |
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12548312 |
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60570134 |
May 10, 2004 |
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60550659 |
Mar 5, 2004 |
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60540606 |
Jan 29, 2004 |
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Current U.S.
Class: |
252/182.12 ;
252/183.11; 252/183.13 |
Current CPC
Class: |
Y02E 50/17 20130101;
C07C 51/48 20130101; C07C 51/02 20130101; C07C 51/487 20130101;
Y02E 50/10 20130101; C07C 51/48 20130101; C07C 53/08 20130101; C07C
51/48 20130101; C07C 53/122 20130101; C07C 51/487 20130101; C07C
53/122 20130101; C07C 51/487 20130101; C07C 53/08 20130101; C07C
51/02 20130101; C07C 59/10 20130101; C07C 51/02 20130101; C07C
53/122 20130101; C07C 51/02 20130101; C07C 55/10 20130101; C07C
51/02 20130101; C07C 53/02 20130101; C07C 51/02 20130101; C07C
59/08 20130101; C07C 51/02 20130101; C07C 59/06 20130101; C07C
51/02 20130101; C07C 59/265 20130101; C07C 51/02 20130101; C07C
53/08 20130101; C07C 51/02 20130101; C07C 53/124 20130101 |
Class at
Publication: |
252/182.12 ;
252/183.11; 252/183.13 |
International
Class: |
C09K 3/00 20060101
C09K003/00 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] This invention was supported in part with funding provided
by Grant No. DE-FG36-03G013010, awarded by the United States
Department of Energy. The government may have certain rights to
this invention.
Claims
1-34. (canceled)
35. A composition comprising an aqueous phase and a non-aqueous
phase, wherein the non-aqueous phase comprises: a. a complex
between an organic acid and a tertiary amine; and b. normal
alcohol.
36. The composition of claim 35, wherein the water immiscible
solvent is an alcohol.
37. The composition of claim 35, wherein the water immiscible
solvent is an alcohol selected from the group consisting of
n-octanol, n-hexanol, n-pentanol, and n-butanol.
38. The composition of claim 35, wherein the tertiary amine is
tributylamine or dicyclohexyl methyl amine.
39. The composition of claim 35, wherein the complex is
tributylammonium acetate.
40. The composition of claim 35, wherein the composition further
comprises an aqueous phase.
41. The composition of claim 35, wherein the composition further
comprises an insoluble carbonate salt.
42. A composition comprising: a. an ester of an organic acid and a
water immiscible solvent; and, b. a tertiary amine.
43. The composition of claim 42, wherein the water immiscible
solvent is an alcohol.
44. The composition of claim 42, wherein the water immiscible
solvent is an alcohol selected from the group consisting of
n-octanol, n-hexanol, n-pentanol, and n-butanol.
45. The composition of claim 42, wherein the tertiary amine is
tributylamine or dicyclohexyl methyl amine.
46. The composition of claim 42, wherein the composition is
substantially anhydrous.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority from U.S.
Provisional Patent Application Ser. No. 60/540,606, filed Jan. 29,
2004, and from U.S. Provisional Patent Application Ser. No.
60/550,659, filed Mar. 5, 2004, and from U.S. Provisional Patent
Application Ser. No. 60/570,134, filed May 10, 2004. All three
provisional applications are incorporated herein by reference in
their entirety.
FIELD OF THE INVENTION
[0003] The present invention is related to methods for recovery of
organic acids from dilute salt solutions, such as fermentation
broths.
BACKGROUND OF THE INVENTION
[0004] Organic acids are valuable products in their own right as
food and feed ingredients, for example, or as intermediates.
Organic acids can be converted chemically to alcohols, which can
subsequently be converted to olefins. Such a process could be
envisioned as the basis for a biorefinery to convert biomass
resources into a range of products for the energy and chemical
industries. Organic acids can be produced by fermentation at very
high carbon yield from a wide range of biomass resources.
[0005] Many valuable carboxylic acids such as acetic, lactic and
propionic acids can be produced by fermentation. Holten, Lactic
Acid: Properties and Chemistry of Lactic Acid and Derivatives,
Verlag Chemie, 1971; Benninga, (1990), A History of Lactic Acid
Making: A Chapter in the History of Biotechnology, Kluwer Academic
Publishers, London; Partin, L., Heise, W. (1993), in Acetic Acid
and Its Derivatives, Agreda, V., Zoeller, J., ed., Marcel Dekker,
New York, pp. 3-13; Playne, 1985 Propionic and butyric acids pp.
731-759, In M. Moo-Young (ed.) Comprehensive Biotechnology, vol. 3,
Pergamon, Oxford. However, today almost all carboxylic acids are
produced from petrochemicals.
[0006] One reason why fermentation routes have failed to compete is
that the micro-organisms used to produce these acids are inhibited
by low pH. In order to achieve high yields, the pH of the
fermentation step has to be kept near neutral by the addition of a
base such as ammonia, sodium hydroxide or calcium hydroxide. In
addition, even at neutral pH, the acids generally inhibit the
growth of the organisms used in the fermentation and limit the
broth to low concentrations of the acid salt. Thus, the
fermentation routes typically produce a dilute aqueous solution of
the organic acid salt rather than the organic acid in its
protonated form. The salts are highly water-soluble, have a
negligible vapor pressure and the carbonyl group is unreactive.
These properties make recovery of the salt difficult since
distillation, extraction, crystallization and other common
industrial separation methods for large-scale production are either
technically or economically infeasible.
[0007] One way to ease the recovery of organic acid salts is to add
a mineral acid to lower the pH of the broth, thereby converting the
organic acid into its protonated form. In its protonated form, the
organic acid can be more easily recovered by known means such as
distillation, extraction or reactive separation processes. Direct
acidification with a mineral acid is usually regarded as a
troublesome option for recovery of organic acid salts because a
salt byproduct is inevitably formed. This byproduct is often of
very low value. For example, gypsum is historically the salt
co-produced in lactic acid production. (Holten, 1971, Benninga,
1990)
Calcium lactate+sulfuric acid=>calcium sulfate+lactic acid
[0008] Markets either have to be found or an environmentally
responsible disposal method has to be identified. Because of these
limitations, much research has gone into alternative methods to
recover organic acids.
[0009] Recovery of fermentation-derived acetate has been summarized
by Busche (Busche, R. M., "Recovering Chemical Products from Dilute
Fermentation Broths", Biotechnology and Bioengineering Symp. No.
13, p. 597-615, 1983 and co-workers at Du Pont (Busche et al.,
"Recovery of Acetic Acid from Dilute Acetate Solution",
Biotechnology and Bioengineering Symp. No. 12, p. 249-262, 1982)
and by Partin and Heise, 1993.
[0010] Once the organic acid has been produced in solution in its
protonated form by direct acidification, various means can be used
for its recovery from the broth (Othmer, "Acetic Acid Recovery
Methods", Chemical Engineering Progress, Vol. 54, No, 7, July,
1958, Baniel et al., U.S. Pat. No. 4,275,234). For example, solvent
extraction of organic acids from dilute solution has been studied
in detail. (King, et al., "Solvent Equilibrium for Extraction of
Carboxylic Acids from Water", Journal of Chemical and Engineering
Data, Vol. 23, No. 2, 1978). Baniel (U.S. Pat. No. 5,780,276) also
mentions the use of enhancers in extraction of amines including
small amounts of alcohols. However, Baniel (U.S. Pat. No.
5,780,276) provides processes for the recovery of the small amount
(10%) of enhancer alcohol and does not suggest its reaction with
the organic acid.
[0011] Busche (Busche, 1983) discusses general concepts that apply
for recovery of organic chemicals present in dilute fermentation
broths. He concludes that distillation is preferred for recovery of
species with boiling points lower than water (e.g. ethanol) since
the product is distilled overhead. If the species has a boiling
point higher than water (e.g. acetic acid, propionic acid, lactic
acid), then distillation is not preferred since the energy required
to boil water and remove it as the overhead product is excessive.
He also surveys other means for recovery of high boilers such as
extraction, crystallization, evaporation and electrodialysis.
[0012] Although not considered by Busche (Busche, 1983), reactive
distillation converts a carboxylic acid (a high boiler) into
volatile ester (a low boiler), thus sidestepping the energy penalty
associated with boiling water. (Xu and Chuang, "Kinetics of Acetic
Acid Esterification over Ion Exchange Catalysts", Can. J. Chem.
Eng., pp. 493-500, Vol. 74, 1996, Scates et al, "Recovery of Acetic
Acid from Dilute Aqueous Streams Formed During a Carbonylation
Process", U.S. Pat. No. 5,599,976, Feb. 4, 1997).
[0013] Many advances have been made in membrane processes during
the last two decades. Crossflow microfilters and ultrafilters are
routinely used to clarify broths by removing cell mass and
insoluble materials. Further clarification by nanofiltration
removes high molecular weight soluble impurities such as proteins
and residual carbohydrates, and provides the additional benefit of
concentrating the organic acid salt prior to downstream recovery.
Bipolar electrodialysis can be used to acidify the broth. A patent
assigned to Chronopol, Inc. (Miao, "Method and Apparatus for the
Recovery and Purification of Organic Acids", U.S. Pat. No.
5,681,728, Oct. 28, 1997) gives an example of how to sequence the
various membrane units to recover and acidify lactic acid from a
fermentation broth. Economics for membrane-based processes are
favorable today for high value, low volume products. Scale-up of
capital cost is nearly linear, so membrane systems are not always
competitive for large-scale production of bio-commodities unless
high flux is achieved. This is especially true when considering the
more complex membrane processes such as bipolar
electrodialysis.
[0014] Work at DuPont (Yates, "Removal and Concentration of Lower
Molecular Weight Organic Acids From Dilute Solutions", U.S. Pat.
No. 4,282,323, Aug. 4, 1981 and Busche et. al., 1982) discusses the
use of carbon dioxide as an acidulant to convert
fermentation-derived acetate salts into acetic acid and subsequent
solvent extraction. Researchers at Cargill (Baniel et. al., "Lactic
Acid Production, Separation, and/or Recovery Process", U.S. Pat.
No. 5,510,526, Apr. 23, 1996) have investigated a related method
for recovery of lactate by acidification with CO.sub.2 and
concurrent extraction with an amine. However, this reaction
requires high pressure and produces multiple phases (4) at the same
point in the process.
[0015] Researchers at CPC International (Urbas, "Recovery of Acetic
Acid from a Fermentation Broth", U.S. Pat. No. 4,405,717, Sep. 20,
1983 and Urbas, "Recovery of Organic Acids from a Fermentation
Broth", U.S. Pat. No. 4,444,881, Apr. 24, 1984) also discuss the
use of carbon dioxide as an acidulant. Tributylamine (TBA) is
normally immiscible with water, but the tributyl amine: acetic acid
complex (TBA:HAc) is water soluble. When a dilute aqueous solution
of calcium acetate at near neutral pH is mixed with TBA, and then
carbon dioxide is bubbled through the mixture, the following
reaction occurs at or near ambient temperatures:
Ca(Ac).sub.2+H.sub.2O+CO.sub.2+2TBA=>2TBA:HAc+CaCO.sub.3
[0016] Use of a stoichiometric amount of TBA produces a single
aqueous liquid phase containing the tributyl amine:acetic acid
complex. The reaction is driven to the right since calcium
carbonate precipitates upon formation. The amine must be suitably
chosen such that its acid/amine complex is completely water
soluble. Urbas (Urbas, U.S. Pat. No. 4,405,717) also mentions
dicyclohexyl methyl amine.
[0017] In one embodiment of the Urbas process, the aqueous amine
complex is extracted into an organic solvent, the solvent is
stripped off, and the complex is thermally split apart giving the
acetic acid product and regenerating both the solvent and amine for
recycle. The amine used in the extraction process must be
extractable. Urbas shows that amine:acid complexes that are too
water soluble cannot be extracted including trimethyl and triethyl
amine acid complexes. For extraction, Urbas teaches the use of low
boiling, non-reactive solvents that do not azeotrope with acetic
acid, with preference given to chloroform. These are severe
limitations on solvent selection. Furthermore, use of chlorinated
solvents, such as chloroform, would be problematic at industrial
scale.
[0018] In another embodiment of the Urbas process, the amine acid
complex is concentrated by the removal of the water and then
thermally cracked to generate the free acid and regenerate the
amine. In general, there have been two approaches to recovery of
acid/amine complexes, back extraction into water or an aqueous
base, or evaporation of the water and then recovery of the acid.
However, water removal is extremely energy intensive as outlined
previously.
[0019] The thermal regeneration reaction has been found by the
present inventors to be difficult in practice, leading to a viscous
intractable residue and low yield of acetic acid.
[0020] In the Urbas process, the calcium carbonate can be recycled
for use as a base for neutralization of the fermentation step. No
other salt byproduct is created, and this feature is a significant
advantage for this route. The use of calcium carbonate as a base in
an organic acid fermentation produces CO.sub.2 which can be
utilized in the reaction step to form the acid/amine complex and
the calcium carbonate, so there is not net production of
CO.sub.2.
[0021] Urbas teaches away from the use of solvents which can form
esters with the organic acid. However, the present inventors have
found that an ester may be a valuable intermediate or product. For
example, the use of an alcohol solvent that potentially forms an
ester with the acid can be integrated into an indirect ethanol
process for example as disclosed in U.S. Pat. No. 6,509,180 (Verser
and Eggeman, to ZeaChem) incorporated herein in its entirety by
reference. The ZeaChem process describes the production of ethanol
by production of acetic acid, esterification of the acid with an
alcohol and subsequent hydrogenation of the ester.
[0022] The production of esters of organic acids is well known.
Esters have been used as an intermediate in the recovery and
purification of organic acids. Methods such as reactive
distillation as mentioned previously can be used if the acid is in
the protonated form, i.e., the free acid. (Benninga 1990, Scates)
Various catalysts have been explored to facilitate this reaction
including cationic ion exchange resins, strong mineral acids such
as sulfuric, hydrochloric and nitric, and strong organic acids such
as methane sulfonic acid or toluene sulfonic acid. (Xu and Chuang,
1996, Filachione et al., "Production of Esters", U.S. Pat. No.
2,565,487, Aug. 28, 1951)
[0023] Since esterification is an equilibrium reaction, the reverse
reaction of hydrolysis occurs at the same time as the forward
reaction. In most processes either water, or the product ester, are
removed continuously during the reaction to drive the reaction in
the desired forward direction.
[0024] Direct esterification of acid/amine complexes have been
reported by several groups (Filachione, 1951, Tung et al, "Sorption
and Extraction of Lactic and Succinic Acids at pH>pKa, 2.
Regeneration and Process Considerations", Industrial and
Engineering Chemistry, Vol. 33, pgs. 3224-3229, 1994, Sterzel et
al, "Preparation of Lactates, U.S. Pat. No. 5,453,365, Sep. 26,
1995). Each of these references reports the esterification of the
concentrated complex in which the bulk of the water is removed by
evaporation or distillation overhead. Thus, these processes suffer
from the energy penalty of vaporizing the water.
[0025] The hydrogenation or hydrogenolysis of esters to produce an
alcohol from the organic acid moiety and to regenerate the alcohol
of the ester is well known. McKee, WO 00/53791 Alcohols produced by
hydrogenation of esters can also be converted to an olefin derived
from the organic acid moiety. The dehydration of alcohols to
olefins has been described (Tsao et al., "Dehydrate Ethanol to
Ethylene", Hydrocarbon Processing, 57 (2), p. 133-136, February
1978). The process has been practiced at the commercial scale for
ethanol dehydration to ethylene. The process is carried out in a
fluidized bed with a phosphoric acid catalyst on an inert
support.
[0026] Similarly, propionic acid can be produced by fermentation,
converted to propanol by hydrogenation of a suitable ester and then
dehydrated to propylene. (Playne, 1985)
[0027] In addition, various esters can be interconverted by
transesterification, by reacting one ester with an excess of a
second alcohol to form the ester of the second alcohol. Various
processes are known in the art for transesterification such as
reactive distillation.
[0028] Esters may also be hydrolyzed to regenerate the organic acid
and the alcohol. Lactic acid has been recovered and purified by
esterification with methanol and subsequent hydrolysis. (Benninga,
1990)
SUMMARY OF THE INVENTION
[0029] One embodiment of the present invention is a method for
recovery of an organic acid from a dilute salt solution that
includes an organic acid salt. The cation of the salt forms an
insoluble carbonate salt. The method includes introducing a
tertiary amine and carbon dioxide to the dilute salt solution to
form an acid/amine complex, as well as the insoluble carbonate
salt. A water immiscible solvent is introduced to the dilute salt
solution to form a reaction phase that includes the acid/amine
complex and the water immiscible solvent. The method further
includes continuously drying the reaction phase and forming a
product between the acid and the water immiscible solvent.
[0030] A further embodiment of the present invention is a method
for recovery of an organic acid from a dilute salt solution that
includes a calcium salt of an organic acid. The method includes
introducing a tertiary amine and carbon dioxide to the dilute salt
solution, forming an acid/amine complex and calcium carbonate. The
dilute salt solution is mixed with a water immiscible alcohol
having a distribution coefficient of at least about 0.5, and the
acid/amine complex is extracted into the water immiscible alcohol.
The method further includes continuously drying the water
immiscible alcohol and forming an ester from the acid and the
alcohol. In this manner, a mixture comprising the ester, residual
water immiscible alcohol, and the tertiary amine is produced.
[0031] A still further embodiment of the present invention is a
method for recovery of an organic acid selected from acetic acid,
lactic acid and propionic acid from a fermentation broth that
includes a calcium salt of the organic acid. The method includes
introducing carbon dioxide and either tributylamine or dicyclohexyl
methyl amine to the dilute salt solution to form an acid/amine
complex and calcium carbonate. The dilute salt solution is mixed
with a water immiscible alcohol that is selected from n-octanol,
n-hexanol, n-pentanol, or n-butanol. In this manner, the acid/amine
complex is extracted into the water immiscible alcohol. The method
further includes continuously drying the alcohol and forming an
ester from the acid and the alcohol to produce a mixture that
includes the ester, the alcohol and the tertiary amine. The method
further includes separating the ester, the tertiary amine, and the
alcohol. The separated tertiary amine is used as the tertiary amine
for introduction to the dilute salt solution to form the acid/amine
complex. The separated water immiscible alcohol is used as the
alcohol to be mixed with the dilute salt solution for extraction of
the acid/amine complex. The separated ester is treated for further
recovery by either hydrogenating the ester to form an alcohol of
the acid and regenerate the solvent alcohol, transesterifying the
ester with a second alcohol to form a second ester, or hydrolyzing
the ester to form the acid and regenerate the solvent alcohol.
[0032] A still further embodiment of the present invention is a
method for recovery of an organic acid from an acid/amine complex
in an aqueous solution. The method includes introducing a water
immiscible solvent to the aqueous solution to form a reaction phase
and an aqueous phase. The reaction phase includes the acid/amine
complex and the water immiscible solvent. The method further
includes continuously drying the reaction phase and forming a
product of the acid and the water immiscible solvent.
[0033] In various embodiments of the invention, the water
immiscible solvent can be an alcohol, and in that instance, the
acid/solvent product can be an ester. The alcohol can be selected
from the group of n-octanol, n-hexanol, n-pentanol, and n-butanol.
The water immiscible solvent can also be a mixed solvent that
includes a solvent reactive with the acid portion of the acid/amine
complex and a solvent that is inert with the acid portion of the
acid/amine complex. In various other embodiments, the water
immiscible solvent can have a distribution coefficient of at least
about 0.5, at least about 0.75, or at least about 1. In still
further embodiments, the water immiscible solvent can have a
selectivity value of at least about 8, at least about 15, or at
least about 20.
[0034] The tertiary amine, in various embodiments, can be either
tributylamine or dicyclohexyl methyl amine.
[0035] The organic acid of the invention can be selected from
acetic acid, lactic acid, propionic acid, butyric acid, succinic
acid, citric acid, 3-hydroxypropionic acid, glycolic acid, or
formic acid.
[0036] The step of continuously drying a reaction phase in various
embodiments of the present invention can include either removing
water as an azeoptrope with the solvent by azeotropic distillation
or removing water by contacting the reaction phase with a water
adsorbent.
[0037] The step of forming the acid/solvent product can comprise
forming an ester between the acid and an alcohol solvent by the
production of water. Further, the step of forming the acid/solvent
product can include adding a catalyst to the solvent. The catalyst
can be a strong acid catalyst, such as acid catalysts having a pKa
greater than the organic acid and solid catalysts. The catalyst can
be selected from sulfuric acid, hydrochloric acid and methane
sulfonic acid.
[0038] In further embodiments of the invention, the method can
include separating the acid/solvent product, the tertiary amine,
and the solvent from the reaction phase. The separated tertiary
amine can be used as the amine which is introduced to the dilute
salt solution to form the acid/amine complex. Further, the
separated solvent can be used as the water immiscible solvent to be
added to the dilute salt solution. The step of separating can be
conducted by distilling the acid/solvent product from the tertiary
amine and the solvent. Further, the step of separating can include
distilling the solvent from the tertiary amine.
[0039] When the acid/solvent product is an ester formed between the
acid and an alcohol, the method can further include hydrogenating
the ester to form an alcohol of the acid and regenerate the solvent
alcohol. In this embodiment, the alcohol of the acid can be
dehydrated to form an olefin. Further, in this embodiment, the
regenerated solvent can be used as the solvent to be introduced to
the dilute salt solution. In a further embodiment, an acid/solvent
ester product can be transesterified with a second alcohol to form
a second ester. Still further, an acid/solvent ester product can be
hydrolyzed to form an acid and regenerate the solvent alcohol,
which can be recycled for introduction into a dilute salt
solution.
BRIEF DESCRIPTION OF THE FIGURES
[0040] FIG. 1 is a block flow diagram of an embodiment of the
present invention.
[0041] FIG. 2 is a phase diagram for n-pentanol, water and TBA:HAc
complex.
[0042] FIG. 3 is a phase diagram for n-hexanol, water and TBA:HAc
complex.
[0043] FIG. 4 plots the water generated during esterification in
Example 8 and reports the observed range of pot temperatures.
DETAILED DESCRIPTION OF THE INVENTION
[0044] In one embodiment of the present invention, a method for
recovery of an organic acid from a dilute salt solution is
provided. The dilute salt solution includes an organic acid salt,
the cation of which forms an insoluble carbonate salt. The process
includes introducing a tertiary amine and CO.sub.2 to the salt
solution to form an acid/amine complex and the insoluble carbonate
salt. The process further includes introducing a water immiscible
solvent to the dilute solution to form a reaction phase that
includes the acid/amine complex in the water immiscible solvent.
The reaction phase is continuously dried. The method further
includes forming a product of the acid and the water immiscible
solvent.
[0045] This embodiment of the present invention is particularly
suitable for use with organic acids in dilute salt solutions that
are produced by fermentation. For example, such organic acids can
include acetic acid, lactic acid, propionic acid, butyric acid,
succinic acid, citric acid, 3-hydroxypropionic acid, glycolic acid,
formic acid, and others, and preferably, includes acetic acid,
lactic acid, and propionic acid. The organic acid salt in this
embodiment comprises a cation that forms an insoluble carbonate
salt. For example, calcium carbonate is insoluble. Other suitable
cations in addition to Ca include Zn, Ba, and Mg.
[0046] The step of introducing a tertiary amine and CO.sub.2 to the
dilute salt solution is typically conducted at near neutral pH
while the solution is mixed with the tertiary amine with the
CO.sub.2 being bubbled through the mixture. In this manner, the
organic acid salt reacts with water, CO.sub.2 and the tertiary
amine to form an acid/amine complex and the insoluble carbonate
salt. The carbonate salt will fall out of the solution, thereby
driving the reaction in the direction of forming the acid/amine
complex, essentially to completion. A significant advantage of the
present invention is that this reaction can be conducted under
ambient conditions of temperature and pressure and at near neutral
pH, such as the pH of a fermentation broth.
[0047] The insoluble carbonate salt, such as calcium carbonate, can
be easily recovered by conventional solid-liquid separation. In one
embodiment, this salt can be used as a base in an organic acid
fermentation for pH control during an initial production of an
organic acid. Such use of calcium carbonate during a fermentation
produces CO.sub.2 which can be used in various embodiments of the
invention to form an acid/amine complex and insoluble carbonate
salt. In this integrated process, there is not net production of
CO.sub.2. Thus, the step of introducing CO.sub.2 to a dilute salt
solution as an acidulant provides significant advantages because it
overcomes the consumption of mineral acid and the issue of salt
disposal in the recovery of organic acids.
[0048] Any tertiary amine, the acid/amine complex of which is
soluble in a dilute salt solution, is suitable for use in this step
of the process. In particular, the tertiary amine can be selected
from the group consisting of tributylamine (TBA) and dicyclohexyl
methyl amine.
[0049] This embodiment of the present invention further includes
introducing a water immiscible solvent to the dilute salt solution
to form a reaction phase that includes the acid/amine complex and
the water immiscible solvent. Thus, the acid/amine complex must be
at least partially soluble in the water immiscible solvent. This
step in which the acid/amine complex can be extracted from a dilute
aqueous solution provides the significant advantage of eliminating
the high-energy cost of vaporizing the bulk of the water as a means
to separate the acid/amine complex from an aqueous solution. The
design of liquid-liquid extraction systems is well known to those
in the art.
[0050] The water immiscible solvent can be an alcohol, such as an
alcohol that is known to form esters with organic acids, and
particularly, primary alcohols. More particularly, when the water
immiscible solvent is an alcohol, it can be selected from
n-octanol, n-hexanol, n-pentanol, and n-butanol.
[0051] The water immiscible solvent can be further characterized by
its distribution coefficient, K.sub.D, which is defined as the
weight fraction of the acid/amine complex in the solvent divided by
the weight fraction of the acid/amine complex in a second phase,
such as an aqueous phase. More particularly, the water immiscible
solvent can have a distribution coefficient of at least about 0.5,
at least about 0.75, or at least about 1. Therefore, the use of a
solvent in the extraction with a high K.sub.D is very advantageous
from a process point of view because it leads to lower solvent
inventory, smaller vessels and lower capital and operating
cost.
[0052] The water immiscible solvent is selected so that it reacts
with the acid/amine complex to form a product with the acid portion
of the acid/amine complex. For example, when a water immiscible
solvent is an alcohol, it reacts with the acid to form an ester.
Using a solvent that reacts with the acid portion of the acid/amine
complex to form a highly useful intermediate product, such as an
ester, provides a high yield efficient process for recovery of the
acid from the acid/amine complex.
[0053] The solvent, such as an alcohol, can be slightly soluble in
water and conversely, water can be slightly soluble in the solvent.
Water immiscible solvents useful in the present invention can also
be characterized by their selectivities. Selectivity, defined as
the distribution coefficient times the ratio of the mass fraction
of water in an aqueous phase divided by the mass fraction of water
in the solvent. This value is a measure of the solvent's ability to
preferentially separate the acid/amine complex from water in an
aqueous phase. A higher selectivity indicates that less water is
brought into the water immiscible solvent, resulting in less energy
being needed to remove free water in subsequent processing steps.
In preferred embodiments, the water immiscible solvent has a
selectivity value of at least about 8, at least about 15, or at
least about 20.
[0054] In a further embodiment, the water immiscible solvent can be
a mixed solvent which includes a solvent that is reactive with the
acid portion of the acid/amine complex to form the acid/solvent
product, as well as including a solvent that is inert with the acid
portion of the acid/amine complex. For example, such mixed solvents
can include as inert components toluene, xylene, aromatics, and
alkanes. Such components, being relatively hydrophobic, are thought
to assist by keeping water out of the water immiscible solvent,
thereby improving the effective selectivity of the solvent.
[0055] In a further embodiment, the water immiscible solvent can be
a mixed solvent which includes a solvent that is reactive with the
acid portion of the acid/amine complex to form the acid/solvent
product, as well as including another component such as an ester,
that is hydrophobic. Such a component is thought to assist in the
effective selectivity of the water immiscible solvent by keeping
water out of the solvent phase. Such a component may also be
reactive with either the acid and/or the solvent.
[0056] The reaction phase forms a separate phase from the aqueous
dilute salt solution and the acid/amine complex is extracted into
the reaction phase. The two phases can be separated at this point
and the reaction phase further treated as described in detail
below. The aqueous phase can be stripped of any residual solvent
and amine by known processes such as steam stripping or carbon
absorption, and the recovered solvent recycled to the process and
the water discharged or recycled to the fermentation.
[0057] This embodiment of the present invention further includes
continuously drying the reaction phase. As noted, the reaction
phase includes the acid/amine complex and the water immiscible
solvent and provides the environment for reaction between the water
immiscible solvent and the acid portion of the acid/amine complex.
By continuously drying the reaction phase, the presence of water
which can interfere with reaction of the acid and water immiscible
solvent is reduced. For example, in the instance where the water
immiscible solvent is an alcohol and reacts with the acid by
elimination of a water molecule, the presence of water is
detrimental to the reaction proceeding to formation of an ester. By
drying the reaction phase, any water initially present in the
solvent is removed. Further, in this example, a water molecule is
produced upon reaction of the acid and the solvent and should be
removed by drying to drive the reaction in the direction of ester
formation. Reference to continuously drying the reaction phase
suggests making water unavailable in the reaction phase to
interfere with formation of the acid/solvent product to such an
extent that the product can be formed. For example, in one
embodiment, the step of continuously drying the reaction phase can
include removing water as an azeotrope with the solvent by
azeotropic distillation. In this manner, any water initially
present in the reaction phase is removed. Further, as water is
generated by formation of the acid/solvent product, the water
product is removed as an azeotrope by azeotropic distillation.
Drying can also be conducted by the use of solid adsorbents, such
as molecular sieves.
[0058] The process finally includes forming a product from the acid
and the water immiscible solvent. One example of an acid/solvent
product in the present invention is the formation of an ester
between an acid and an alcohol solvent as discussed above. In the
instance of formation of an ester between an acid and an alcohol
solvent, the step of forming the product includes driving the
reaction in the direction of formation of the ester by removal of
water. Formation of esters can be achieved by known methods such as
reactive distillation. The design of the reactive distillation is
done by means known to those skilled in the art in terms of
temperature, rate, residence time and other design features. The
reaction may be carried out in batch or continuously.
[0059] In addition, the step of forming the product can further
include addition of a catalyst to the solvent. For example, the
catalyst can be a strong acid catalyst, such as a catalyst having a
pKa greater than the organic acid and solid acid catalysts,
including both Bronsted and Lewis acids. In specific embodiments,
the catalyst can be sulfuric acid, hydrochloric acid, and methane
sulfonic acid.
[0060] Some of the significant advantages of the present invention
are that various components of the process can be recovered and
recycled for reuse in the process. Therefore, upon formation of the
acid/solvent product, the process can optionally include separating
the acid/solvent product, the tertiary amine, and the solvent. For
example, the acid/solvent product can be distilled from the
mixture, leaving the tertiary amine and the solvent, with the
solvent the being distilled from the tertiary amine. In this
manner, the reaction phase at the end of the process can be
separated into three streams. The tertiary amine can be recycled
for use in the process to be introduced with CO.sub.2 to a dilute
salt solution to form an acid/amine complex and the insoluble
carbonate salt. Likewise, the separated solvent can be used to form
the reaction phase with the acid/amine complex. Alternatively, the
reaction mixture can be sent directly to hydrogenolysis after which
the solvent alcohol and the product alcohol can be separated.
[0061] The acid/solvent product is a useful form in which to
recover organic acids because it allows for ready formation of the
acid or conversion of the acid/solvent product into other useful
product forms. For example, in the instance where the acid/solvent
product is an ester, the method for recovery of the organic acid
can further include hydrolyzing the ester to form the acid and
regenerate the solvent alcohol. In this instance, the regenerated
solvent alcohol can be recycled for use as the water immiscible
solvent. The conditions for conducting the step of hydrolysis of an
ester are well known in the art.
[0062] Alternatively, when the acid/solvent product is an ester,
the method for recovery of the organic acid can included
hydrogenating the ester to form an alcohol of the acid and
regenerate the solvent alcohol. Again, the regenerated solvent
alcohol can be recycled for use as the water immiscible solvent. In
this embodiment, the organic acid is recovered as an alcohol. The
conditions for such a hydrogenation reaction are known to those of
skill in the art. In a further embodiment, the alcohol of the acid
can be dehydrated to form an olefin. The dehydration of alcohols to
olefins has been described (Tsao et al. 1978), and the process has
been practiced at the commercial scale. The process can be carried
out in a fluidized bed with a phosphoric acid catalyst on an inert
support. Similarly, the production of propionic acid by
fermentation, conversion to propanol by hydrogenation of a suitable
ester and dehydration to propylene is known. (Playne, Comprehensive
Biotech, Chapter 37).
[0063] In a further embodiment, where the acid/solvent product is a
first ester, the method can further include transesterifying the
first ester with a second alcohol to form a second ester. Such
transesterification reactions are known to those in the art.
[0064] With reference to FIG. 1, an embodiment of the present
invention is described. In an acidification unit 100, a dilute salt
solution comprising calcium acetate (Ca(Ac).sub.2) is introduced.
Also introduced into the acidification unit 100 is CO.sub.2 and a
tertiary amine (TBA). In this unit, an acid/amine complex between
the acid and TBA is formed. Also, the insoluble carbonate salt,
calcium carbonate, is formed. The dilute salt solution is then
filtered to remove the calcium carbonate in a filtration unit 110.
The calcium carbonate is washed in the filtration unit 110 and can
be used in a recycle stream as a neutralizing base in a
fermentation. The TBA:HAc amine/acid complex and water is then
transferred to an extraction unit 120. Also introduced to the
extraction unit 120 as a water immiscible solvent is n-pentanol.
The TBA:HAc amine/acid complex is extracted from the water to the
n-pentanol phase. The water and solvent phases are separated, with
the water being recycled. The n-pentanol phase, containing the
TBA:HAc amine/acid complex is conducted to an esterification unit
130. In the esterification unit 130, the solution is continuously
dried to remove any residual water. In addition, water formed by
reaction of the n-pentanol with the acetic acid is taken off in the
esterification unit 130. The resulting reaction mixture is then
conducted to a distillation unit 140 in which the ester formed from
the n-pentanol and acetic acid and residual n-pentanol are
distilled off and recovered. The remaining TBA is then conducted
back to the acidification unit 100 for reuse.
[0065] A particular embodiment of the present invention is a method
for recovery of an organic acid from a dilute salt solution
containing a calcium salt of an organic acid. This method includes
introducing a tertiary amine and CO.sub.2 to the dilute salt
solution to form an acid/amine complex and calcium carbonate. The
dilute salt solution is mixed with a water immiscible alcohol
characterized by a distribution coefficient of at least about 0.5.
In this manner, the acid/amine complex is extracted into the water
immiscible alcohol. The method further includes continuously drying
the water immiscible alcohol, and forming an ester from the acid
and the water immiscible alcohol to produce a mixture comprising
the ester, residual water immiscible alcohol, and the tertiary
amine.
[0066] A further particular embodiment of the present invention is
a method for recovery of an organic acid selected from acetic acid,
lactic acid, or propionic acid from a fermentation broth having a
calcium salt of the organic acid. The method includes introducing a
tertiary amine and CO.sub.2 to the dilute salt solution to form an
acid/amine complex and calcium carbonate. The tertiary amine can be
selected from tributylamine and dicyclohexyl methyl amine. The
method further includes mixing the dilute salt solution with a
water immiscible alcohol selected from n-octanol, n-hexanol,
n-pentanol, or n-butanol. The acid/amine complex is extracted into
the water immiscible alcohol, and the water immiscible alcohol is
continuously dried. The method includes forming an ester from the
acid and the water immiscible alcohol to produce a mixture
including the ester, residual water immiscible alcohol, and the
tertiary amine. The ester, the tertiary amine and the water
immiscible alcohol are separated. The separated tertiary amine is
recycled for introduction into the dilute salt solution, and the
separated water immiscible alcohol is recycled for mixing with the
dilute salt solution. The separated ester is treated by one of
three processes. The first is hydrogenating the ester to form an
alcohol of the acid and regenerate the solvent alcohol. The second
is transesterifying the ester with a second alcohol to form a
second ester. The third is hydrolyzing the ester to form the acid
and regenerate the solvent alcohol.
[0067] A further particular embodiment of the present invention is
a method for recovery of an organic acid from an acid/amine complex
in an aqueous solution. The method includes introducing a water
immiscible solvent to the aqueous solution to form a reaction phase
and an aqueous phase. The reaction phase includes the acid/amine
complex and the water immiscible solvent. The method further
includes continuously drying the reaction phase. Finally, a product
of the acid and the water immiscible solvent is formed.
[0068] The following examples are provided for the purpose of
illustration and are not intended to limit the scope of the present
invention.
EXAMPLES
Analytical Methods
[0069] Concentrations of acid/amine complex in both aqueous and
organic solutions were determined by potentiometric titration of
10-20 ml samples diluted with 30 ml of methanol and titrated with
standardized KOH in methanol following the method of Ricker, et.
al., "Solvent Properties of Organic Bases for Extraction of Acetic
Acid from Water", Journal of Separation Process Technology, Vol. 1,
No. 1, 1979.
[0070] The water content of the organic phases was determined by
Karl Fischer analysis.
[0071] Examples 1-3 illustrate the formation of an acid/amine
complex and calcium carbonate using various acids and various
amines. Example 4 illustrates the use of trioctyl amine which
failed to react to form an acid/amine complex. Example 5
illustrates the use of a dilute salt solution, the cation of which
does not form an insoluble carbonate, thereby preventing completion
of formation of an acid/amine complex.
Example 1
[0072] 500 ml of an aqueous calcium acetate solution (0.6 molar as
acetate) was added to a 1 liter graduated cylinder and the pH was
adjusted to 6.9-7.0 using acetic acid. A 5% molar excess of TBA was
added, which formed a separate layer, then the solution was sparged
with CO.sub.2 for 30 minutes at ambient pressure. The liquid
mixture became homogeneous with a single layer. A copious white
precipitate of CaCO.sub.3 was formed. The solution was filtered,
the CaCO.sub.3 cake was washed once with water, washed again with
acetone, dried and then weighed. The acidification experiments were
conducted four times with CaCO.sub.3 yields ranging from 91.0-96.1%
of theoretical. The resulting CaCO.sub.3 precipitates were easy to
filter and wash. A fine white powder was generated in all
cases.
Example 2
[0073] The experiment of Example 1 was scaled down to about 50 mls.
Side by side experiments were conducted using the acetate solution
from Example 1, 0.6 molar calcium lactate, 0.6 molar calcium
propionate. After gassing with CO.sub.2 for 30 minutes each
reaction produced the same volume of CaCO.sub.3 precipitate.
Example 3
[0074] Example 2 was reproduced except that instead of gassing with
CO.sub.2, the reaction mixture was gassed with a mixture of
nitrogen and CO.sub.2 in a ratio of N:CO.sub.2 of 10:1. The results
were identical to those of Example 2.
Example 4
[0075] An experiment similar to Example 2 was run using only the
acetate solution, but substituting trioctyl amine for the TBA.
After gassing with CO.sub.2 for 30 minutes there was no obvious
reaction at all. There was no CaCO.sub.3 precipitate and there were
still two liquid layers. It is believed that trioctyl amine failed
to react due to the acid/amine complex not being soluble in the
calcium acetate solution.
Example 5
[0076] An experiment similar to Example 1 was run, except that a
sodium acetate solution was used. No reaction appeared to have
taken place. It is believed that since NaCO.sub.3 is soluble and
does not precipitate, that a reaction forming an acid/amine complex
was not driven forward.
Example 6
[0077] This example illustrates the use of a variety of water
immiscible solvents for extraction of an acetic acid/TBA complex
from water.
[0078] All extraction experiments were conducted at room
temperature (25.degree. C.). For solvent screening, typically 100 g
of an aqueous mixture containing 4.08 g of acetic acid (HAc) and
12.56 g of TBA, a 1:1 molar ratio, were mixed in a separatory
funnel with 100 g of organic solvent. The mixture was shaken by
hand and then allowed to separate. Each phase was recovered and
weighed. Samples were taken and analyzed for acid/amine by the
method of Ricker (Ricker et al., 1979) described above, and water
by Karl Fischer.
[0079] A similar procedure was used to generate data for the
liquid-liquid phase diagrams except the starting concentration of
TBA:HAc was varied to generate different tie-lines.
[0080] The following table presents the data for solvent extraction
of tri-butyl amine/acetate from water for a number of solvents. The
solvent was mixed with an equal volume of an equimolar TBA:HAc salt
in water. The sample were shaken by hand and allowed to settle. The
organic phase was sampled and analyzed for acetate using the method
of Ricker et al., 1979. The distribution coefficient, K.sub.D, was
determined. Phase volume changes were not measured so the results
are only approximate, but give an indication of the merits of
various solvents.
TABLE-US-00001 TABLE 1 Distribution Coefficients Solvent
Distribution Coefficient - K.sub.D 2-octanone 0.087 Chloroform
0.987 butyl acetate 0.082 Toluene 0.0392 ethyl acetate 0.105 ethyl
acetate/ethanol (2/1) 0.293 ethyl propionate/ethanol (1/1) 0.249
1-hexanol 0.96 1-pentanol 1.87 1-butanol 2.48
[0081] As seen in Table 1, higher alcohols give very good
distribution coefficients and are potentially reactive with the
acetic acid to form esters.
Example 7
[0082] This example illustrates the use of a series of higher
alcohols (n-butanol, n-pentanol, n-hexanol, and n-octanol) for
extraction of an acetic acid/TBA complex from water.
[0083] Primary separation was achieved quickly (<30 seconds) for
all solvents included in the solvent extraction experiments.
Secondary separation was also very quick for all solvents, only
taking a few minutes to obtain clear solutions in both phases.
[0084] Table 2 reports the distribution coefficients and
selectivities.
TABLE-US-00002 TABLE 2 Solvent Distribution Coefficient Selectivity
n-Butanol 2.40 8.79 n-Pentanol 1.45 14.77 n-Hexanol 1.13 19.26
n-Octanol 0.75 21.91
[0085] The example shows there is a trade-off between distribution
coefficient and selectivity. Low molecular weight alcohols have
more favorable distribution, but the mutual solubility of water
with the low molecular weight alcohol lowers selectivity. Both
n-pentanol and n-hexanol have high distribution coefficients and
high selectivity.
Example 8
[0086] This example shows the steps for recovery of propionic acid
from a dilute salt solution using a process of the present
invention.
[0087] Precipitation of CaCO.sub.3 using TBA and CO.sub.2:
[0088] 22.42 gms of TBA was added to 100 mls of 0.6 molar
Ca(Pr).sub.2 solution (106 gms/liter) and gassed with CO.sub.2 for
30 min. A white precipitate of CaCO.sub.3 formed and was filtered
and weighed with a recovery of 90.8%.
[0089] Extraction of TBA/Pr:
[0090] A TBA/Pr amine/acid complex was prepared by mixing 199.92
gms of H.sub.2O, 10.46 gms propionic acid, and 21.66 gms of TBA. 50
gms of the H.sub.2O/TBA/HPr solution was mixed with 50 gms of each
of n-butanol, n-pentanol and n-hexanol in three flasks, and
separated in a separatory funnel. TBA/HPr in the organic phase was
sampled and measured by the method of Ricker et al., 1979. The
distribution coefficients for each of the three solvents were
determined to be: n-butanol--1.39; n-pentanol--1.46; and
n-hexanol--1.38.
[0091] Esterification of TBA/HPr in n-hexanol:
[0092] A mixture of 325.44 gms n-hexanol, 74.48 gms of HPr, and
155.64 gms of TBA was prepared and introduced to the distillation
apparatus as described in Example 10. An initial pot sample and a
final pot sample after reaction were taken. Reaction time was about
12 hours not including heat up and cool down time. The pot
temperature ranged from 157 C initially to 163 C at the end point.
The samples were analyzed by the method of Ricker et al., 1979. The
disappearance of HPr in the pot showed conversion to the ester of
92.2%.
Example 9
[0093] This example shows liquid-liquid phase equilibrium diagrams
constructed for n-pentanol and n-hexanol. FIGS. 2 and 3are the
experimentally measured phase diagrams. The tie lines are created
by varying the starting concentration of the TBA:HAc concentration
in a series of extractions as described above. The two phase
regions are fairly broad and the tie-lines have a favorable slope.
Distribution coefficients become more favorable at higher TBA:HAc
concentrations. Only a few stages are needed to produce a
concentrated TBA:HAc extract from a dilute aqueous solution.
Example 10
[0094] This example shows the production of an acid/solvent product
between acetic acid and the four alcohol solvents of Example 7. The
n-hexanol solvent was run with and without a sulfuric acid
catalyst.
[0095] A simple distillation of alcohol solvent and the acid/amine
complex was conducted at atmospheric pressure (.about.630 mm Hg) in
a glass still consisting of a electric heating mantle, a 1 liter
round bottom flask, a vacuum jacketed 30 cm distillation column
packed with 4 mm.times.4 mm glass rings, and an overhead condenser
and product splitter allowing the removal of a variable amount of
distillate and return of reflux to the column. A two-step process
was observed. Initially, the water dissolved in the extract was
removed by azeotropic distillation using the alcohol itself as the
drying solvent for the extract producing a dry solution of the
amine complex in the alcohol solvent. The overhead splitter was
configured so that the water was removed continuously as it was
produced and the solvent was returned to the still as reflux. All
of the alcohols tested form heterogeneous azeotropes with water and
forming two liquid phases overhead.
[0096] Initial water removal rate was quite fast, only a few
minutes. Then after the extract was dried, the distillation process
was continued with total reflux of the solvent alcohol, and there
was a continuous slow production of water overhead in the still
usually over several hours. This water was produced from the
esterification reaction of the alcohol solvent with the acid.
Residual acetate in the still was measured by taking a sample from
the still and measuring the acetate concentration by the method of
Ricker et al., 1979 described above. The difference between the
initial concentration and the sample at various times was taken to
be the conversion to ester.
[0097] The esterification reactions were conducted in the setup
described above, at atmospheric pressure (.about.630 mm Hg) for
each of the solvents tested. 450 g of a room temperature solution
containing a 3:1 molar ratio of alcohol to TBA:HAc complex were
added to the still. The catalyzed run with n-hexanol included
H.sub.2SO.sub.4 in the starting solution at a 0.1:1 mole ratio with
respect to the TBA:HAc complex. The heating mantle was turned on
and approximately thirty minutes later the solution began to boil.
Water formed a second phase in the overheads as the reaction
progressed. The water was collected and the volume recorded over
time. Conversion was calculated as the percent of the maximum
theoretical water if all of the acetic acid were converted to ester
and confirmed by titration of residual TBA:HAc in the still pot
samples. Ester formation was verified by gas chromatography using
known ester samples as standards. The results of this experiment in
terms of esterification yield are shown in Table 3.
TABLE-US-00003 TABLE 3 Solvent Esterification Yield at 4 hr, %
Theoretical n-Butanol 12.6 n-Pentanol 38.1 n-Hexanol 82.7/93.6 (No
Catalyst/H.sub.2SO.sub.4 Catalyst) n-Octanol 88.8
[0098] FIG. 4 plots the water generated during esterification and
reports the observed range of pot temperatures during the time the
solutions were boiling. The pot temperature rose over time, further
evidence of reaction. The curves in FIG. 4 are useful for comparing
rates, but can only be qualitatively used to compare yield since
different molar amounts of TBA:HAc were present in the starting
solutions and differing amounts of materials were taken for samples
over the course of the experiment. The values in Table 3 are more
useful for comparing yields.
[0099] Both esterification rate and yield increased with increasing
molecular weight of the alcohol. Rather than being related to the
chain length of the alcohol, this improvement in performance was
probably caused by the higher boiling point and thus higher
reaction temperature for the higher molecular weight alcohols.
Adequate esterification rate and yield could be achieved with the
lower molecular weight alcohols if the reaction was conducted at
elevated pressure. The pressures required are not extreme; for
example, n-butanol will boil at 170.degree. C. and 482.6 kPa, well
within the range of industrial importance.
[0100] Esterification rate and yield can also be improved by using
a catalyst. Comparison of the non-catalyzed n-hexanol run with the
catalyzed run shows that sulfuric acid is potentially a good
catalyst.
[0101] While various embodiments of the present invention have been
described in detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled in the
art. It is to be expressly understood, however, that such
modifications and adaptations are within the scope of the present
invention, as set forth in the following claims.
* * * * *