U.S. patent number RE39,175 [Application Number 11/149,502] was granted by the patent office on 2006-07-11 for microbial process for the preparation of acetic acid as well as solvent for its extraction from the fermentation broth.
This patent grant is currently assigned to Bioengineering Resources, Inc., Celanese International Corporation. Invention is credited to Edgar C. Clausen, James L. Gaddy, Ching-Whan Ko, Leslie E. Wade, Carl V. Wikstrom.
United States Patent |
RE39,175 |
Gaddy , et al. |
July 11, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Microbial process for the preparation of acetic acid as well as
solvent for its extraction from the fermentation broth
Abstract
A modified water-immiscible solvent useful in the extraction of
acetic acid from aqueous streams is a substantially pure mixture of
isomers of highly branched di-alkyl amines. This solvent is
substantially devoid of mono-alkyl amines and alcohols. Solvent
mixtures formed of such a modified solvent with a desired
cosolvent, preferably a low boiling hydrocarbon which forms an
azeotrope with water are useful in the extraction of acetic acid
from aqueous gaseous streams. An anaerobic microbial fermentation
process for the production of acetic acid employs such solvents,
under conditions which limit amide formation by the solvent and
thus increase the efficiency of acetic acid recovery. Methods for
the direct extraction of acetic acid and the extractive
fermentation of acetic acid also employ the modified solvents and
increase efficiency of acetic acid production. Such increases in
efficiency are also obtained where the energy source for the
microbial fermentation contains carbon dioxide and the method
includes a carbon dioxide stripping step prior to extraction of
acetic acid in solvent.
Inventors: |
Gaddy; James L. (Fayetteville,
AR), Clausen; Edgar C. (Fayetteville, AR), Ko;
Ching-Whan (Fayetteville, AR), Wade; Leslie E.
(Pearland, TX), Wikstrom; Carl V. (Benton, AR) |
Assignee: |
Bioengineering Resources, Inc.
(Fayetteville, AR)
Celanese International Corporation (Dallas, TX)
|
Family
ID: |
27493060 |
Appl.
No.: |
11/149,502 |
Filed: |
September 7, 1999 |
PCT
Filed: |
September 07, 1999 |
PCT No.: |
PCT/US99/20416 |
371(c)(1),(2),(4) Date: |
March 07, 2001 |
PCT
Pub. No.: |
WO00/14052 |
PCT
Pub. Date: |
March 16, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60099438 |
Sep 8, 1998 |
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60099439 |
Sep 8, 1998 |
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60099440 |
Sep 8, 1998 |
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60099475 |
Sep 8, 1998 |
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Reissue of: |
09786544 |
Mar 7, 2001 |
06368819 |
Apr 9, 2002 |
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Current U.S.
Class: |
435/42;
435/252.7; 435/170; 435/140 |
Current CPC
Class: |
C07C
51/47 (20130101); C07C 51/44 (20130101); C07C
51/48 (20130101); C07C 211/07 (20130101); C12P
7/54 (20130101); C07C 51/44 (20130101); C07C
53/08 (20130101); C07C 51/47 (20130101); C07C
53/08 (20130101); C07C 51/48 (20130101); C07C
53/08 (20130101) |
Current International
Class: |
C12P
39/00 (20060101); C12P 7/54 (20060101) |
Field of
Search: |
;435/42,140,170 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Ricker et al., "Solvent Extraction with amines for recovery of
acetic acid from dilute aqueous industrial streams"J. Sep Proc.
Tech. 1980 1 (2) pp. 23-30 1980. cited by examiner .
Gaddy, J. "Biological Production of Products from Waste Gases",
U.S. Appl. No. 09/219,395, filed Dec. 23, 1998. cited by examiner
.
Ricker et al., "Solvent properties of organic bases for extraction
of acetic acid from water", J. Sep. Proc. Technol. 1979 1(1):36-41.
cited by other .
J. Vega et al., "The Biological Production of Ethanol from
Synthesis Gas", Applied Biochemistry and Biotechnology, 20/21
781-797 (1989). cited by examiner .
J. Vega et al., "Study of Gaseous Substrate Fermentations: Carbon
Monoxide Conversion to Acetate. 2. Continuous Culture",
Biotechnology and Bioengineering, 34:785-793 (1989). cited by
examiner .
K. Klasson et al., "Bioconversion of Synthesis Gas into Liquid or
Gaseous Fuels", Enzyme Microb. Technol., 14:602-608 (Aug., 1992).
cited by examiner .
K. Klasson et al., "Biological Production of Liquid and Gaseous
Fuels from Synthesis Gas", Applied Biochemistry and Biotechnology,
24/25:857-873 (1990). cited by examiner.
|
Primary Examiner: Lilling; Herbert J.
Attorney, Agent or Firm: Howson and Howson
Government Interests
This invention has been partially supported by grants from the
United States Department of Energy, Cooperative Agreement No.
DE-FC02-90CE40939. The United States government has an interest in
this invention.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a 371 of PCT/US99/20416, which claims the benefit of the
priorities of U.S. patent application Ser. No. 60/099,438, filed
Sep. 8, 1998; U.S. patent application Ser. No. 60/099,439, filed
Sep. 8, 1998; U.S. patent application Ser. No. 60/099,440, filed
Sep. 8, 1998; and U.S. patent application Ser. No. 60/099,475,
filed Sep. 8, 1998.
Claims
What is claimed is:
1. A water-immiscible solvent/co-solvent mixture comprising: (a) a
water-immiscible solvent comprising greater than 50% by volume of a
mixture of isomers of highly branched di-alkyl amines, and
.[.from.]. .Iadd.less than .Iaddend.about .[.0.01% to 20%.].
.Iadd.1% .Iaddend.by volume of mono-alkyl amines said solvent
having a coefficient of distribution greater than 10; and (b) at
least 10% by volume of a non-alcohol co-solvent having a boiling
point lower than the boiling point of said solvent (a), wherein
said mixture extracts acetic acid from aqueous streams.
2. The mixture according to claim 1 wherein said co-solvent is
immiscible with water and readily separates therefrom, and has low
toxicity to anaerobic acetogenic bacteria.
3. The mixture according to claim 1 wherein said co-solvent forms
an azeotrope with water and acetic acid.
4. The mixture according to claim 1 wherein said co-solvent
comprises a hydrocarbon having from 9 to 11 carbon atoms.
5. The mixture according to claim 1 wherein said solvent (a)
contains greater than 80% by volume said di-alkyl amines and is
reduced to less than about 1% by volume of low boiling compounds
and mono-alkyl amines wherein said low boiling compounds boil at or
below 115.degree. C. at 69.9 Torr. 6.The mixture according to claim
1 wherein said solvent (a) contains from about 1% to 10% by volume
tri-alkyl amines.
7. The mixture according to claim 1, wherein said solvent (a) is
produced by distilling from a solvent containing low boiling
compounds, mono-alkyl amines, di-alkyl amines and tri-alkyl amines
substantially all low boiling compounds and monoalkyl amines to
improve acetic acid extractive capacity wherein said low boiling
compounds boil at or below 115.degree. C. at 69.9 Torr.
8. The mixture according to claim 7, wherein said solvent (a) is
produced by subjecting said distilled solvent to a second
distillation to reduce substantially all tri-alkyl amines.
9. A process for obtaining acetic acid from an aqueous phase
comprising acetic acid comprising the steps of: (a) contacting the
aqueous phase with the solvent/co-solvent mixture .[.of claim 1.].
.Iadd.comprising: (i) a water-immiscible solvent comprising greater
than 50% by volume of a mixture of isomers of highly branched
di-alkyl amines, and from about 0.01% to 20% by volume of
mono-alkyl amines said solvent having a coefficient of distribution
greater than 10; and (ii) at least 10% by volume of a non-alcohol
co-solvent having a boiling point lower than the boiling point of
said solvent (i), wherein said mixture extracts acetic acid from
aqueous streams; .Iaddend. (b) extracting acetic acid from said
aqueous phase into the resulting solvent phase; and (c) distilling
acetic acid from said solvent phase under a temperature not
exceeding 160.degree. C.
10. An anaerobic microbial fermentation process for the production
of acetic acid, said process comprising the steps of: (a)
fermenting in a bioreactor an aqueous stream comprising an
anaerobic acetogenic bacteria in a nutrient medium and a gas stream
comprising at least one gas selected from the group consisting of
(1) carbon monoxide, (2) carbon dioxide and hydrogen, (3) carbon
monoxide, carbon dioxide and hydrogen; and (4) carbon monoxide and
hydrogen; thereby producing a fermentation broth comprising acetic
acid; (b) separating said bacteria from other components in said
broth to provide a substantially cell-free stream; (c) continuously
extracting acetic acid from said cell-free stream into a solvent
phase by contacting said cell-free stream with a solvent mixture of
claim 1; and (d) continuously distilling from the product of (c)
the acetic acid separately from the solvent phase under a
temperature not exceeding 160.degree. C.; wherein said extracting
and distilling steps occur without substantially degrading said
amine to an amide, thus enhancing the efficiency of production of
acetic acid.
11. The process according to claim 10 wherein said separating step
employs a centrifuge, a hollow fiber membrane, or a solid-liquid
separation device.
12. The process according to claim 10 further comprising as step
(e) recycling said solvent to the distillation device of step (d)
and said cell-free stream to said bioreactor in step (a).
13. The process according to claim 10 wherein said distillation
step occurs in a substantially oxygen-free vacuum.
14. The process according to claim 10 wherein step (d) further
employs a vacuum between about 0.5 to about 10 psia.
15. The process according to claim 10 wherein said anaerobic
bacteria is selected from the group consisting of Acetobacterium
kivui, A. woodii, Butyribacterium methylotrophicum, Clostridium
aceticum, C. acetobutylicum, C. formoaceticum, C. kluyveri, C.
thermoaceticum, C. thermocellum, C. thermosaccharolyticum,
Eubacterium limosum, Peptostreptococcus productus, and C.
ljungdahlii, and mixtures thereof.
16. The process according to claim 15 wherein said C. ljungdahlii
is selected from the strains consisting of: PETC ATCC 55383, O-52
ATCC 55989, ERI2 ATCC 55380 and C-01 ATCC 55988, and mixtures
thereof.
17. A method for enhancing the efficiency of acetic acid recovery
from a fermentation broth comprising an aqueous stream containing
an anaerobic acetogenic bacterium and nutrient medium, said
bacterium having been fermented in the presence of a gas stream
comprising at least one gas selected from the group consisting of
(1) carbon monoxide, (2) carbon dioxide and hydrogen, (3) carbon
monoxide, carbon dioxide and hydrogen; and (4) carbon monoxide and
hydrogen; said method comprising contacting said stream with a
solvent mixture of claim 1; continuously extracting said acetic
acid from said stream in said solvent mixture; and distilling said
acetic acid from said solvent at a distillation temperature not
exceeding 160.degree. C. therefrom, without substantially degrading
said amine to amide.
18. An anaerobic microbial fermentation process for the production
of acetic acid, said process comprising the steps of: (a) providing
in a fermenter an anaerobic acetogenic bacterium in a nutrient
mixture and a solvent mixture of claim 1 for a time sufficient to
acclimate said bacteria to said solvent; (b) introducing into said
fermenter an aqueous stream comprising at least one gas selected
from the group consisting of (1) carbon monoxide, (2) carbon
dioxide and hydrogen, (3) carbon monoxide, carbon dioxide and
hydrogen, and (4) carbon monoxide and hydrogen; and producing a
fermentation broth comprising said bacteria, nutrient medium,
acetic acid, solvent and water; (c) introducing said fermentation
broth into a settling tank, wherein an aqueous phase containing
said bacteria and nutrient medium settles to the bottom of said
tank from the solvent phase which contains acetic acid, solvent and
water, without filtration; (d) continuously distilling from the
solvent phase of (c) the acetic acid separately from the solvent
phase under a temperature not exceeding 160.degree. C.; wherein
said distilling step occurs without substantially degrading said
amine to an amide, thus enhancing the efficiency of acetic acid
production.
19. The process according to claim 18 further comprising recycling
said solvent and said aqueous phase containing said bacteria into
said fermenter.
20. The process according to claim 19 wherein said distillation
step occurs in a substantially oxygen-free vacuum.
21. The process according to claim 18 wherein step (d) further
employs a vacuum between about 0.5 to about 10 psia.
22. The process according to claim 18 wherein said anaerobic
bacteria is selected from the group consisting of Acetobacterium
kivui, A. woodii, Butyribacterium methylotrophicum, Clostridium
aceticum, C. acetobutylicum, C. formoaceticum, C. kluyveri, C.
thermoaceticum, C. thermocellum, C. thermosaccharolyticum,
Eubacterium limosum, Peptostreptococcus productus, and C.
ljungdahlii, and mixtures thereof.
23. The process according to claim 22 wherein said C. ljungdahlii
is selected from the strains consisting of PETC ATCC 55383, O-52
ATCC 55989, ERI2 ATCC 55380 and C-01 ATCC 55988, and mixtures
thereof.
24. An anaerobic microbial fermentation process for the production
of acetic acid, said process comprising the steps of: (a)
fermenting in a bioreactor an aqueous stream comprising a nutrient
mixture with an anaerobic acetogenic bacteria and at least one gas
selected from the group consisting of (1) carbon monoxide, (2)
carbon dioxide and hydrogen, (3) carbon monoxide, carbon dioxide
and hydrogen; and (4) carbon monoxide and hydrogen; thereby
producing a broth comprising acetic acid, water, and bacterial
cells; (b) introducing into an extraction device containing either
a continuous solvent phase or a continuous aqueous phase and having
exits and entrances therefrom, (i) said broth with no cell
separation and (ii) a solvent comprising a solvent mixture of claim
1; wherein a solvent phase containing acetic acid, solvent and
water exits said extraction device separately from an aqueous phase
comprising said bacteria and nutrient media; (c) continuously
distilling from the solvent phase of (b) the acetic acid and water
separately from the solvent at a temperature not exceeding
160.degree. C.; wherein said steps (b) and (c) occur without
substantially degrading said amine to an amide, thus enhancing the
efficiency of acetic acid production.
25. The process according to claim 24 wherein said step (b)
comprises introducing said solvent into said extraction device in a
flow concurrent or countercurrent of that of said broth.
26. The process according to claim 24 further comprises recycling
said solvent and said aqueous phase containing said bacteria into
said fermenter.
27. The process according to claim 24 wherein said distillation
step occurs in a substantially oxygen-free vacuum.
28. The process according to claim 24 wherein step (c) further
employs a vacuum between about 0.5 to about 10 psia.
29. The process according to claim 24 wherein said anaerobic
bacteria is selected from the group consisting of Acetobacterium
kivui, A. woodii, Butyribacterium methylotrophicum, Clostridium
aceticum, C. acetobutylicum, C. formoaceticum, C. kluyveri, C.
thermoaceticum, C. thermocellum, C. thermosaccharolyticum,
Eubacterium limosum, Peptostreptococcus productus, and C.
ljungdahlii, and mixtures thereof.
30. The process according to claim 29 wherein said C. ljungdahlii
is selected from the strains consisting of PETC ATCC 55383, O-52
ATCC 55989, ERI2 ATCC 55380 and C-01 ATCC 55988, and mixtures
thereof.
31. An anaerobic microbial fermentation process for the production
of acetic acid, said process comprising the steps of: (a)
fermenting in a bioreactor an aqueous stream comprising at least
one gas selected from the group consisting of (1) carbon monoxide,
(2) carbon dioxide and hydrogen, (3) carbon monoxide, carbon
dioxide and hydrogen; and (4) carbon monoxide and hydrogen; in a
nutrient mixture with an anaerobic acetogenic bacteria, thereby
producing a fermentation broth comprising acetic acid and dissolved
carbon dioxide; (b) removing said carbon dioxide from the
fermentation broth prior to extraction; (c) contacting said broth
(b) with a solvent mixture comprising: (i) a water-immiscible
solvent comprising greater than 50% by volume of a mixture of
isomers of highly branched di-alkyl amines, and .[.from.].
.Iadd.less than .Iaddend.about .[.0.01% to 20%.]. .Iadd.1%
.Iaddend.by volume of mono-alkyl amines said solvent having a
coefficient of distribution greater than 10; and (ii) at least 10%
by volume of a non-alcohol co-solvent having a boiling point lower
than the boiling point of said solvent (i); wherein a solvent phase
is formed and comprises acetic acid, said solvent and water; and
(d) continuously distilling acetic acid from said solvent
phase.
32. The process according to claim 31 wherein said distilling step
occurs at a temperature not exceeding 160.degree. C., without
substantially degrading said amine to an amide, thus enhancing the
efficiency of production of acetic acid.
33. The process according to claim 31 wherein said distillation
step occurs in a substantially oxygen-free vacuum.
34. The process according to claim 32 wherein said distilling step
further employs a vacuum between about 0.5 to about 10 psia.
Description
FIELD OF THE INVENTION
The present invention relates generally to improved methods for the
microbial production of acetic acid. More particularly, the
invention relates to extraction of acetic acid from aqueous
streams, and from the microbial fermentation of desirable chemical
products from gaseous streams, such as waste gas streams,
industrial gas streams, or from gas streams produced from the
gasification of carbonaceous materials.
BACKGROUND OF THE INVENTION
Methods for the anaerobic fermentation of carbon monoxide, and/or
hydrogen and carbon dioxide to produce acetic acid, acetate salts
or other products of commercial interest, such as ethanol, have
been performed at laboratory bench scale. See, e.g., Vega et al,
(1989) Biotech. Bioeng., 34:785-793; Klasson et al (1990) Appl.
Biochem. Biotech., 24/25: 1; Vega et al (1989) Appl. Biochem.
Biotech., 20/21: 781-797; and Klasson et al (1992) Enz. Microbio.
Tech., 19: 602-608, among others. More recently, the present
inventors have discussed large-scale methods for the fermentation
of industrial gas streams, particularly waste gas streams, into
products of commercial use by using methods employing fermentation
of the gas stream, an aqueous nutrient medium and an anaerobic
bacteria or mixtures thereof in a bioreactor. See, e.g., U.S. Pat.
Nos. 5,173,429; 5,593,886 and International Patent Publication No.
WO98/00558, incorporated herein by reference.
According to the above-cited prior art of the inventors, one such
large scale process involves the following summarized steps.
Nutrients are continuously fed to a bioreactor or fermenter in
which resides a culture, either single or mixed species, or
anaerobic bacteria. A gas stream is continuously introduced into
the bioreactor and retained in the bioreactor for sufficient time
to maximize efficiency of the process. Exhaust gas containing inert
and unreacted substrate gases, are then released. The liquid
effluent is passed to a centrifuge, hollow fiber membrane, or other
solid-liquid separation device to separate out microorganisms that
are entrained. These microorganisms are returned to the bioreactor
to maintain a high cell concentration which yields a faster
reaction rate. Separation of the desired biologically produced
product(s) from the permeate or centrifugate occurs by passing the
permeate or centrifugate to an extractor where it is contacted with
a solvent, such as a di-alkyl and tri-alkyl amine in a suitable
cosolvent, or tributyl phosphate, ethyl acetate, tri-octyl
phosphine oxide and related compounds in a co-solvent. Suitable
cosolvents include long chain alcohols, hexane, cyclohexane,
chloroform, and tetracholoroethylene.
The nutrients and materials in the aqueous phase passes back to the
bioreactor and the solvent/acid/water solution passes to a
distillation column, where this solution is heated to a sufficient
temperature to separate the acid and water from the solvent. The
solvent passes from the distillation column through a cooling
chamber to lower the temperature to the optimum temperature for
extraction, then back to the extractor for reuse. The acid and
water solution passes to a final distillation column where the
desired end product is separated from the water and removed. The
water is recirculated for nutrient preparation.
Further, a variety of acetogenic bacteria are well known to produce
acetic acid and other commercially interesting products when
subjected to such fermentation processes, including novel strains
of Clostridium ljungdahlii [See e.g., U.S. Pat. Nos. 5,173,429 and
5,593,886 and International Patent Publication No. WO98/00558].
Despite such knowledge and advances in the art of microbial
fermentation of a variety of gas streams, acetic acid production is
limited by the acetic acid loading potential of the solvent used,
and by the degradation of the solvent as it travels through the
production process, among other issues. In view of the
ever-increasing need to produce acetic acid, as well as to convert
industrial waste gases into useful non-polluting products, there
remains a need in the art for processes which are more efficient in
producing the desired commercial product and compositions which can
enhance performance of such methods.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a modified
water-immiscible solvent useful in the extraction of acetic acid
from aqueous streams comprising a substantially pure mixture of
isomers of highly branched di-alkyl (or secondary) amines. This
solvent can extract the acid in the absence of a co-solvent. In a
preferred embodiment, this solvent is a modified form of
Adogen283.RTM. solvent [Witco Corp.] which is substantially reduced
in its content of alcohols and monoalkyl (or primary) amines. In
another preferred embodiment, the solvent is further reduced in
content (i.e. substantially purified) or tri-alkyl (or tertiary)
amines.
In another aspect, the invention provides a method for treating a
solvent comprising alcohols, monoalkyl amines, a mixtures of
isomers of highly branched di-alkyl amines and tri-alkyl amines to
improve its acetic acid extractive capacity comprising distilling
from the solvent substantially all the alcohols and monoalkyl
amines. In another embodiment, the method involves subjecting the
distilled solvent to a second distillation to remove substantially
all tri-alkyl amines.
In yet a further aspect, the invention provides a novel
water-immiscible solvent/co-solvent mixture useful for the
extraction of acetic acid, preferably at concentrations less than
10%, from an aqueous stream comprising an above-described modified
water-immiscible solvent useful in the extraction of acetic acid
from aqueous streams comprising a substantially pure mixture of
isomers of highly branched di-alkyl amines and a selected
cosolvent. In a preferred embodiment, the cosolvent is a low
boiling hydrocarbon having from 9 to 11 carbon atoms, which
hydrocarbons forms an azeotrope with water and acetic acid.
In still another aspect, the invention provides a non-fermenting
process for obtaining acetic acid from an aqueous stream comprising
contacting the stream with a modified solvent/cosolvent mixture as
described above; extracting the acetic acid from the aqueous phase
into the solvent phase; and distilling the acetic acid from its
admixture with the solvent under a temperature not exceeding
160.degree. C.
In yet a further aspect, the invention provides a non-fermenting
process for obtaining acetic acid from an aqueous stream comprising
contacting the stream with a solvent/cosolvent mixture as described
above; extracting the acetic acid from the aqueous phase into the
solvent/cosolvent phase; and distilling the acetic acid from its
admixture with the solvent/cosolvent under a temperature not
exceeding 160.degree. C. under a vacuum.
In a further aspect, the present invention provides an anaerobic
microbial fermentation process for the production of acetic acid,
the process comprising the steps of (a) fermenting in a bioreactor
an aqueous stream comprising a gas selected from the group
consisting of carbon monoxide, carbon monoxide and hydrogen,
hydrogen and carbon dioxide, and carbon monoxide, carbon dioxide
and hydrogen, in a nutrient mixture with an anaerobic acetogenic
bacterium, thereby producing a broth comprising acetic acid; (b)
continuously extracting acetic acid from the broth with a modified
solvent/cosolvent mixture as described above; (c) continuously
distilling from the product of (b) the acetic acid separately from
the solvent at a temperature not exceeding 160.degree. C., and (d)
optionally recycling the solvent and the broth through the
bioreactor. The extracting and distilling steps occur without
substantially degrading the amine to an amide, thus enhancing the
efficiency of acetic acid recovery from the broth.
In still another aspect, the present invention provides a method
for enhancing the recovery of acetic acid from a fermentation broth
comprising an aqueous stream containing one or more of carbon
monoxide, carbon dioxide and hydrogen, and an anaerobic acetogenic
bacterium, and nutrient medium, the method comprising contacting
the stream with a solvent comprising the above-described modified
di-alkyl amine and a selected co-solvent; continuously extracting
the acetic acid from the stream in the solvent mixture, and
distilling acetic acid from the solvent mixture, under a vacuum at
a distillation temperature of below 160.degree. C. therefrom,
without substantially degrading the amine to amide.
In still another aspect, the invention provides an improved method
for enhancing the recovery of acetic acid from anaerobic microbial
fermentation of an aqueous stream comprising carbon monoxide,
carbon monoxide and hydrogen, carbon monoxide, carbon dioxide and
hydrogen, or carbon dioxide and hydrogen, wherein the method
comprises the steps of contacting the fermentation product of the
stream with a water-immiscible solvent, extracting the fermentation
product from the stream, and distilling acetic acid therefrom. The
improvement comprises employing as the solvent the modified
solvent/cosolvent mixture described above and performing the
distillation step at a temperature not exceeding 160.degree. C.
without substantially degrading the amine to amide.
In yet a further aspect, the invention provides an anaerobic
microbial fermentation process (i.e., an extractive fermentation
process) for the production of acetic acid which is accomplished
without filtration or cell separation occurring prior to
extraction. In one embodiment, this method involves providing in a
fermenter an anaerobic acetogenic bacterium in a nutrient mixture
and a modified water-immiscible solvent comprising a substantially
pure mixture of isomers of highly branched di-alkyl amines with a
selected cosolvent, for a time sufficient to acclimate the bacteria
to the solvent. Into the fermenter is introduced a gas stream
comprising one or more of carbon dioxide, carbon monoxide and
hydrogen and a fermentation broth comprising the bacteria, nutrient
medium, acetic acid, solvent mixture and water. The fermentation
broth containing the cells and solvent mixture is introduced into a
settling tank, wherein an aqueous phase containing the bacteria and
nutrient medium settles to the bottom of the tank from the solvent
phase which contains acetic acid, solvent and water, without
filtration. Continuous distillation under a temperature not
exceeding 160.degree. C. removes the acetic acid separately from
the solvent. The distilling step occurs without substantially
degrading the amine to an amide, thus enhancing the efficiency of
acetic acid recovery from the broth.
In still another aspect, the invention provides an anaerobic
microbial fermentation process (i.e., a direct contact extraction
process) for the production of acetic acid, which involves no
filtration of bacterial cells. The process comprises the steps of:
(a) fermenting in a bioreactor an aqueous stream comprising a gas
containing one or more of carbon monoxide, carbon dioxide and
hydrogen in a nutrient mixture with an anaerobic acetogenic
bacteria, thereby producing a broth comprising acetic acid, water,
and bacterial cells; (b) introducing into a conventional extraction
device, such as a column with either solvent or water as the
continuous phase (i) the broth with no cell separation and (ii) a
solvent mixture comprising a modified water-immiscible solvent
useful in the extraction of acetic acid from aqueous streams
comprising a substantially pure mixture of isomers of highly
branched di-alkyl amines and a selected co-solvent, wherein a
solvent phase containing acetic acid, solvent and water exits the
column separately from an aqueous phase comprising the bacteria and
nutrient media; and (c) continuously distilling from the solvent
phase of (b) the acetic acid separately from the solvent at a
temperature not exceeding 160.degree. C. The steps (b) and (c)
occur without substantially degrading the amine to an amide, thus
enhancing the efficiency of acetic acid recovery from the
broth.
In still another aspect, the invention provides an anaerobic
microbial fermentation process for the production of acetic acid
which comprises the step(s) of removing dissolved carbon dioxide,
and optionally dissolved hydrogen sulfide, from the fermentation
broth before extraction. The steps of this process can include (a)
fermenting in a bioreactor a gas stream comprising one or more of
carbon monoxide, carbon dioxide and hydrogen in a nutrient mixture
with an anaerobic acetogenic bacteria, thereby producing a
fermentation broth comprising acetic acid and dissolved carbon
dioxide; (b) removing the carbon dioxide from the fermentation
broth prior to extraction; (c) contacting the broth (b) with a
solvent containing a di-alkyl amine, preferably the modified
solvent/cosolvent mixture of this invention for a time sufficient
to cause the formation of a solvent phase containing acetic acid,
the solvent and water: and (d) continuously distilling acetic acid
from the solvent phase. The carbon dioxide/hydrogen sulfide removal
step may be accomplished with a stripping gas, by preheating the
broth or by reducing the fermentation broth pressure rapidly.
Other aspects and advantages of the present invention are described
further in the following detailed description of the preferred
embodiments thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph charting solvent phase acetic acid (HAc)
concentration in g/L vs. aqueous phase HAc concentration in g/L for
acetic acid recovery processes employing 60% of the modified
solvent. Adogen283.RTM.LA in an azeotroping solvent. SX-18.
Experimental points are represented by triangles theoretical points
by squares and coefficients of extraction (K.sub.d) by circles.
FIG. 2 is a similar graph, except that the solvent mixture is 33%
modified solvent in cosolvent.
FIG. 3 is a schematic drawing of an exemplary apparatus set-up
useful for the microbial fermentation of gases for the production
of acetic acid, using the modified process step of carbon dioxide
and hydrogen sulfide stripping of the fermentation broth prior to
extraction and also employing only two distillation columns. See,
e.g., Example 6. The auxiliary apparatus which controls the
temperature of the various stages of this production process are
identified in the figure as cold water condensers, heat exchangers
or steam.
FIG. 4 is a graph illustrating amide formation rate temperature
dependency, according to the formula Y=kX, wherein Y is the amide
concentration after 16 hours in weight per cent; X is the acetic
acid in the feed in weight per cent; and k is the amide formate
rate constant. The formula for which points are noted on the graph
is ln(k)=-9163.21 (1/T)+27.41, where T is the absolute temperature
in Kelvin. See, e.g., Example 2 below.
DETAILED DESCRIPTION OF THE INVENTION
The compositions and processes of the present invention are
directed towards the improvement of processes for obtaining acetic
acid from aqueous phases, including aqueous phases formed by
fermentation processes. Thus, in one embodiment, the acetic acid
recovery processes of the prior art are improved and recovery of
acetic acid from dilute aqueous streams is enhanced by employing in
an extraction and distillation process a solvent comprising a
mixture of highly branched di-alkyl amines, and preferably a
mixture of that solvent with a selected cosolvent in which limited
solvent degradation occurs. In another embodiment, use of the same
modified solvent/cosolvent mixture can enhance acetic acid recovery
from a microbial fermentation process for gaseous streams which
include extraction/distillation steps.
Other improvements in acetic acid recovery, from conventional
fermentation processes provided by this invention involve
eliminating the requirement for the separation of bacteria cells
from the acetic acid-containing broth in the process and/or
replacing the use of an expensive extractor, by directly contacting
the bacterial cells with the selected modified solvent/cosolvent
mixture.
Still other improvements in the efficiency of acetic acid recovery
from conventional fermentation processes as well as the processes
described below include removing dissolved carbon dioxide and
optionally hydrogen sulfide from the fermentation broth prior to
extraction.
A. The Modified Solvent and Solvent/Co-solvent Mixture
This invention provides a modified solvent and a solvent/co-solvent
mixture which display highly desirable characteristics for
extraction of acetic acid from aqueous phases containing the acid.
This solvent and solvent mixture are useful for both extraction of
acetic acid in non-fermenting processes as well as for extraction
and distillation from a fermentation broth including an anaerobic
acetogenic microorganism, aqueous nutrient medium, and energy and
carbon sources from gas streams.
The desired solvent (for shorthand purposes, the "modified
solvent") of this invention is defined as a water-immiscible
solvent useful in the extraction of acetic acid from aqueous
streams comprising a substantially pure mixture of isomers of
highly branched di-alkyl mines. Such a modified solvent preferably
has a coefficient of distribution (K.sub.d) of greater than 10, and
more preferably greater than 15. This solvent can extract acetic
acid in the absence of a co-solvent.
By the term "substantially pure" is meant that the solvent contains
greater than 50% by volume di-alkyl amines, and has as small a
percentage as possible of monoalkyl amines. More preferably, the
solvent contains greater than 70% di-alkyl amines. In another
preferred embodiment, the solvent contains greater than 80%
di-alkyl amines. In still a more preferred embodiment, the solvent
contains between 80 to 100% di-alkyl amines. Such a substantially
pure mixture further contains a percentage of mono-alkyl amines in
the solvent which can range between 0.01% to about 20% by volume.
More specifically, the monoalkyl amine content can range from less
than 1% to about 10%. In some embodiments, the mono-alkyl amine
percentage ranges from about 5% to about 15%. In still other
embodiments of this invention, the solvent contains less than 5%
and preferably less than 1% by volume mono-alkyl amines. Another
embodiment of such a modified solvent is one that has an amount of
tri-alkyl amines that is less than a maximum of 50% by volume, and
preferably as low as 0% tri-alkyl amines. In some embodiments, the
amount of tri-alkyl amines in the solvent is less than 40% by
volume. Still another embodiment contains less than 25% by volume
tri-alkyl amines. A preferred embodiment contains less than 10% by
volume tri-alkyl amines, and preferably less than 5% by volume
tri-alkyl amines. Still a preferred embodiment contains less than
about 1% by volume tri-alkyl amines. Still other solvents of this
invention contain optionally as small a percentage as possible of
alcohols, desirably less than 25% by volume to about 0%. Another
embodiment contains less than 10% by volume alcohol, desirably less
than 5% by volume and preferably less than 1% by volume
alcohol.
For example, one desirable modified solvent contains about 90% of a
mixture of isomers of highly branched di-alkyl amines and about 10%
of tri-alkyl amines. Thus, useful modified solvents may have small
amounts of the alcohol, monoalkyl amines and trialkyl amines, and
still increase the efficiency of the acetic acid production in the
methods of this invention.
One embodiment of a modified solvent as described above may be
prepared by modification of a commercial solvent, i.e., removing
alcohols and monoalkyl amines to create a desirable modified
solvent for the processes of the present invention as described
above. The commercial product Adogen283.RTM. solvent (Witco
Corporation) is a di-alkyl amine, i.e., di(tridecyl)amine or
N-tridecyl-1-tridecanamine (CAS No. 5910-75-8 or 68513-50-8).
Essentially Adogen283.RTM. solvent is a complex mixture of isomers
which can be classified as monoalkyl, di-alkyl and tri-alkyl
amines. The unmodified Adogen283.RTM. solvent has an average
molecular weight of 395, and a total amine value of 144.0, and
contains, for example, 0.29 percent alcohols, 5.78 percent
mono-alkyl amine, and 85.99 percent di-alkyl amine. Mass
spectrometry analysis of the higher boiling amines of
Adogen283.RTM. solvent is indicated below in Table 1.
TABLE-US-00001 TABLE I Amine Formulae Amine Type Molecular Wt Mole
Percent (C.sub.13H.sub.27).sub.2NH Di-alkyl 381 54
(C.sub.13H.sub.27)(C.sub.12H.sub.25)NH Di-alkyl 367 27
(C.sub.13H.sub.27)(C.sub.14H.sub.29)NH Di-alkyl 395 10
(C.sub.13H.sub.27).sub.3N Tri-alkyl 563 5
(C.sub.13H.sub.27).sub.2(C.sub.12H.sub.25)N Tri-alkyl 549 4
Although this commercial Adogen283.RTM. solvent is recognized as a
useful extraction solvent for extracting dilute acetic acid from
aqueous phases, until the present invention, the art recognized
that when Adogen283.RTM. solvent was distilled, it would degrade
substantially, i.e., about 40% converted to unwanted amides by
reaction of the amine with acetic acid over a period of 3 hours
under distillation conditions [J. W. Althouse and L. L. Tazlarides,
J. Indus. Eng. Chem. Res., 31 1971-1981 (1992)], thereby making it
undesirable for acetic acid recovery processes involving
distillation. According to the above report, the alcohols is
Adogen283.RTM. solvent also can react with acetic acid at
distillation temperatures to form esters. Further, an
Adogen283.RTM. solvent or modifications thereof, even in
combination with a co-solvent, has previously been rejected for
processes involving distillation, because of its undesirable amide
formation [N. L. Ricker el al, J. Separation Technol., 1:36-41
(1979)].
Thus, a key aspect of the present invention was the determination
by the inventors of a method for modifying a solvent, such as
Adogen 283.RTM. solvent, having a high coefficient of distribution
(e.g., K.sub.d greater than or equal to 5, and preferably between
about 10 to 20) to eliminate its unwanted characteristics. A
further aspect of this invention is the combination of the modified
solvent with a selected cosolvent, to make a suitable solvent
mixture for acetic acid recovery processes involving distillation.
The modification of Adogen283 .RTM. solvent to substantially remove
or reduce the percentages of alcohols and monoalkyl amines is
accomplished as follows. The commercial solvent is subjected to
distillation, preferably in a wiped-film evaporator; and the
distilled solvent is then subjected to an acid wash step. The acid
wash step is accomplished at ambient temperature, preferably using
a dilute organic acid at a pH of less than 5. One exemplary acid is
dilute acetic acid (at about 1-50 g/L, preferably less than 30 g/L
and more preferably less than 3 g/L. The acid is generally used at
a ratio of dilute acid to solvent of at least 1:1. A preferred
ratio is about 5:1 acid to solvent. These two steps of distillation
and acid washing remove low boiling organic materials and
mono-alkyl amines. Preferably by "low boiling" is meant below about
115.degree. C., preferably below about 100.degree. C., of about 70
torr.
In one specific example, the distillation was performed in a
laboratory wiped-film evaporator, with a feed rate of 56.4 g
Adogen283.RTM. solvent/hour, a temperature of 164.3.degree. C., and
a pressure of 69.9 torr. The alcohols and monoalkyl amines separate
out and are removed at the top of the distillation column by this
process, leaving the resulting modified solvent containing a
mixture of highly branched di-alkyl amines and tri-alkyl amines to
be removed at the bottom of the distillation column. This modified
solvent was referred to as Modified Solvent A.
Modified Solvent A was characterized by containing 0.02 percent low
boiling organic materials, 0.16 percent mono-alkyl amine, 90.78
percent di-alkyl amine and 9.04 percent tri-alkyl amine. Table II
provides a comparison of the fractions (in percentages) which make
up the unmodified Adogen283.RTM. solvent, the Modified Solvent A,
and the fractions removed as a result of the above-described
process:
TABLE-US-00002 TABLE II Unmodified Adogen283 .RTM. Modified Removed
Fractions Solvent Solvent A Distillate Low boiling 0.29% 0.02%
3.06% organic materials Mono-alkyl Amines 5.78% 0.16% 53.36%
Di-alkyl Amines 85.99% 90.78% 43.59% Tri-alkyl Amines 7.95% 9.04%
0% Total Weight 218.91 g 195.96 g 22.95 g
This more preferred Modified Solvent A has an extraction
coefficient of about 10 or higher, and contains among other
components a mixture of isomers of highly branched di-alkyl amines,
modified to substantially reduce the alcohol content and the amount
of mono-alkyl amines therefrom. The Modified Solvent A is an
excellent acetic acid concentrating solvent, particularly for use
in the methods of this invention. The coefficient of extraction of
this modified solvent increases as the concentration of acetic acid
decreases.
Modified Solvent A may then be further purified to provide yet
another desirable modified solvent, referred to as Modified Solvent
B. Modified Solvent A is introduced into another distillation
column under the same conditions as above. This distillation
enables the di-alkyl amines in Modified Solvent A to be distilled
and removed at the top of the distillation column, resulting in
Modified Solvent B, while the tri-alkyl amines are removed at the
bottom of the column. Modified Solvent B is characterized by a
slightly better coefficient of extraction (greater than 10) and
even better performance in the methods of this invention when
combined with a selected cosolvent.
Based on the disclosures herein relating to the modification of
commercial Adogen283.RTM. solvent and the Modified Solvents A and
B, it is anticipated that other conventional solvents containing
isomeric mixtures of highly branched di-alkyl amines, with some
tri-alkyl amines, along with monoalkyl amines, alcohols and other
components, such as Amberlite LA-2 MW=375 [Rohm & Haas] and
others mentioned in H. Reisinger and C. J. King, Ind. Eng. Chem.
Res., 34:845-852 (1995), may be similarly treated to substantially
remove alcohols mono-alkyl amines, and where desired, tri-alkyl
amines, as described herein to create suitable modified solvents
for use in processes involving extraction and distillation of acids
from aqueous phases. One of skill in the art can readily apply this
teaching to such other solvents without undue experimentation.
Another aspect of this invention involves a mixture of a modified
solvent of this invention with a selected cosolvent, which mixture
also has preferred characteristics for use in extraction and
distillation processes for the recovery of acetic acid. A wide
variety of non-alcohol cosolvents may be selected for admixture
with the modified solvents identified above, as well as with the
commercially available Adogen283.RTM. solvent. Because of the high
distribution coefficient that is possible with the use of Adogen
283.RTM. solvent and modified versions thereof, a wide variety of
co-solvents may be employed in these admixtures. The cosolvent
merely decreases the K.sub.d in proportion to the fraction of
cosolvent employed in the mixture. As an example, a mixture of 50%
Adogen 283.RTM. solvent or a modified version thereof and 50%
cosolvent of any type has one half of the K.sub.d of pure Adogen
283.RTM. solvent. While this phenomenon is true with other amine
based solvents, e.g., Alamine 336.RTM.solvent, Adogen 381.RTM.
solvent, Adogen 260.RTM. solvent, among others), the values of
K.sub.d for these latter pure solvents are very low (1 to 3), so
the dilution with cosolvents results in uneconomically low K.sub.d
values (0.5 to 1.5 lower). In using other solvents, such as the
commercially available, Alamine 336.RTM.solvent, Adogen 381.RTM.
solvent, etc., the cosolvent must be chosen carefully to enhance
the distribution coefficient.
Although the K.sub.d is dependent on the acid concentration in the
fermenter (normally about 3-6 g/L), the desired K.sub.d of the
solvent mixture is desirably between about 1 and 20. For an acid
concentration of about 4.5-5.5 g/L, the K.sub.d of the solvent
mixture is desirably between about 8-11. Still another K.sub.d of
the solvent mixture is about 6-20. However, other values for the
coefficient may be used in the practice of this invention.
The solvent/co-solvent mixture must be immiscible with water and
readily separate from water at reduced temperatures. The selected
cosolvent must have a boiling point lower than that of the
commercial solvent or modified solvents described above. For
example, a preferred co-solvent boils between 125.degree. C. and
250.degree. C. More preferably the cosolvent boils at between about
150.degree. C. and 200.degree. C. In one embodiment, the cosolvent
boils at about 165.degree. C. Alcohols are to be avoided in
selection of a cosolvent because they react with acetic acid to
form esters, and also cause emulsification. The selected cosolvent
can improve physical properties such as viscosity of the mixture
and can also aid in the reduction of the boiling point of the
solvent. The selection of suitable cosolvents can be made by one of
skill in the art, further taking into account that low toxicity
cosolvents are essential for any water solubility and return to the
fermenter, and where the cosolvent will come into contact with the
bacteria. Obviously, the selected cosolvent must be able to be
tolerated by the bacteria.
A preferred co-solvent for use in the solvent mixture of this
invention is one that forms an azeotrope (i.e., a mixture that is
not easily separated and behaves "as one") with water and acetic
acid when in the vapor form. The azeotroping cosolvent enhances the
volatility of at least one of the components, e.g., water. The
formation of an azeotrope permits the cosolvent and the
water/acetic acid as vapor to move together (essentially as one) up
and out the top of a distillation column. When the vapor is
condensed, the cosolvent and the acetic acid/water separate. In the
distillation processes described below, this permits the cosolvent
to be decanted and returned to the first distillation column. The
acetic acid and water (and some residual cosolvent) can then go
onto a second distillation column for acetic acid recovery. The
primary advantage of an azeotroping cosolvent is that it permits
acetic acid recovery in two distillation columns rather than the
three required for non-azeotroping cosolvents.
Some cosolvents displaying the required characteristics include
low-boiling point hydrocarbon co-solvents that form azeotropes with
acetic acid. Particularly desirable cosolvents fitting this
description include alkanes, particularly those in the range of C-9
to C-11. Among such useful co-solvents are n-nonane, n-decane,
n-undecane, ethers, and Orfom.RTM. SX-18.TM. solvent (Phillips
Mining, Inc.), i.e., which is a mixture of C9-C11 isoalkanes. Still
other cosolvents useful for mixture with the modified solvents of
this invention include those non-alcohol solvents, among others
listed in Table 3, page 1976 of Althouse (1992), cited above and
incorporated herein by reference.
Such co-solvents, when admixed with a modified di-alkyl amine
solvent as described above, can reduce the boiling point of the
solvent system, particularly when the solvent system is distilled
under vacuum. The reduced boiling temperature also prevents or
limits amide formation from the di-alkyl amine. Such a
solvent/azeotroping co-solvent mixture permits the distillation
process to be carried out in two columns. Generally, the amount of
modified solvent in the solvent/cosolvent mixture can range in the
mixture from about 10 to about 90% by volume. Desirably, the amount
of modified, di-alkyl amine-containing solvent of this invention is
between about 30 to about 70% by volume of the solvent/cosolvent
mixture. In preferred embodiments, the modified solvent is present
in the mixture at about 60% by volume. At least 10% of cosolvent is
necessary to form a modified solvent/cosolvent mixture of this
invention. The amount of cosolvent can range from about 10 to about
90%; more desirably from about 30 to 70% by volume. In preferred
embodiments, the modified solvent is present in the mixture at
about 40% by volume. Thus one preferred and exemplary
solvent/cosolvent mixture of the present invention comprises 60%
Modified Solvent A and 40% Orfom.RTM. SX18 solvent.
One of skill in the art is expected to be able to adjust the
percentages of modified solvent and cosolvent as desired for any
particular distillation apparatus or process. Adjustments to the
proportion of modified solvent to cosolvent to prepare a desired
mixture will be based on factors such as the identity and contents
of the modified solvent and cosolvent, their relative distribution
coefficients, their viscosities, as well as practical
considerations, such as the availability of heat, the size of the
equipment, and the relative costs of the two solvent components.
For example, the best extraction coefficient appears to correlate
with a high amine content, which increases the expense of the
solvent system. Thus for some uses the high expense would influence
the desired proportions of the modified solvent/cosolvent. Also
restricting the upper value of the modified solvent in the mixture
is its viscosity and boiling point, both of which are reduced with
the cosolvent.
As one example, the SX-18 co-solvent proportionally reduces the
distribution coefficient of the modified solvent mixture (e.g., 50%
Modified Solvent A in SX-18 solvent has one half the distribution
coefficient of 100% Modified Solvent A), but is easier to work with
because of lowered viscosity and increased ability to recover due
to the presence of the co-solvent. The cosolvent SX-18 boils at
between about 160-167.degree. C. and therefore also lowers the
boiling point of the mixture, thereby reducing amide formation. One
of skill in the art is expected to have the ability to balance
these factors to prepare any desired mixture of the modified
solvent and cosolvent.
The desirable characteristics of the modified solvent/cosolvent
mixtures of this invention particularly suit them for use in
extraction and distillation processes for acetic acid. For
extraction., the desirable properties of the solvent mixture of
this invention include a high coefficient of extraction (i.e.,
about 3 or more, and preferably about 10 or more), immiscibility in
water, good water/solvent separation, low toxicity to bacterial
culture, a clear difference in viscosity and density from that of
water, and good selectivity for acetic acid over other products of
fermentation, such as ethanol, salts, and water. For distillation,
the desirable properties of the solvent and solvent mixture of this
invention include, for example, a distinct boiling point difference
between the acetic acid (i.e., 118.degree. C.) and co-solvent
(e.g., 165.degree. C.). These differences are also useful in
performance of the processes of this invention, because the greater
the differences between the boiling points of these components, the
smaller can be the distillation column, resulting in efficiency and
cost improvements in the acetic acid recovery processes.
Significantly, use of the modified solvent/cosolvent mixtures of
this invention involve only negligible solvent losses due to
thermal or reactive degradation, e.g., oxidation. See, e.g., FIG. 4
and Example 2. The solvent and cosolvent also are characterized by
limited reactivity with the acetic acid, media components,
biomaterials, and other unknowns in the aqueous phase or broth and
low miscibility in water. Desirably, the processes of this
invention for using the solvent/cosolvent reduces or substantially
eliminates any tendency for acetic acid and the solvent/cosolvent
to form unwanted byproducts, such as amides, which could be formed
from a reaction involving the amines in the novel modified solvent
and solvent mixtures of this invention.
It is expected that one of skill in the art will readily be able to
modify the solvent/cosolvent mixture of this invention in light of
the teachings of this specification and with regard to knowledge
available as to the above-noted factors. Such modifications are
believed to be encompassed by the scope of the appended claims.
B. Use of Novel Solvent/Co-solvent Mixtures in Recovering Acetic
Acid
The methods of this invention employ the modified
solvent/co-solvent mixtures described above and particular process
steps to avoid formation of unwanted amides. The use of the
modified solvent/cosolvent mixtures permit improved recovery of
acetic acid from aqueous phases, in either non-fermentation
processes of microbial fermentation processes.
Thus according to one embodiment of this invention, a
non-fermenting process for obtaining acetic acid from an aqueous
phase may employ the modified solvent/cosolvent mixtures described
above. Such a process employs as a first step continuously
contacting the aqueous phase with a solvent mixture comprising a
modified di-alkyl amine solvent/cosolvent mixture as described
above, to permit the acetic acid from the aqueous phase to be
extracted into the solvent phase. This step may employ conventional
extraction devices, such as columns, mixing and settling tanks and
similar apparatus designed for extraction and well-known to the
art. Additionally, extraction conditions may be optimized also be
resorting to teachings in the art. The extraction temperature is
desirably ambient temperature, i.e., about 20.degree. C. to about
80.degree. C. At about 80.degree. C., any carbon dioxide is
essentially all relieved from the solvent, but extraction is still
efficient.
Thereafter, the acetic acid is distilled from the solvent phase
under a distillation temperature which reduces the conversion of
the amines in the solvent to amides. The distillation temperature
as used herein means the temperature at the bottom of column.
According to the present invention, the distillation temperature
may range from about 115.degree. C. to about 160.degree. C. to
reduce amide formation. Most significantly, the processes of this
invention require the distillation temperatures to be below
130.degree. C. to limit amide formation, while permitting acetic
acid recovery.
In a preferred embodiment, the distillation step is performed under
an oxygen-free vacuum, which also serves to reduce the temperature
to minimize amide formation and oxidative degradation of the
solvent or solvent/cosolvent mixture. The higher the vacuum (i.e.,
lower absolute pressure) the lower the temperature and the less
amide formation and oxidative degradation. Desirably a vacuum of
less than 10 psia is required for this step. Preferably, the vacuum
is selected from between about 0.1 psia and 5 psia for the
distillation step. More preferably, a vacuum of 4 psia or less is
useful in this distillation step to enhance recovery of the acetic
acid. As yet a further advantage of the use of the modified
solvent/azeotroping cosolvent mixture of this invention is the use
of two distillation columns to enhance the efficiency of recovery
of acetic acid from aqueous phases in comparison to processes of
the prior art.
The control of distillation temperature in the processes of this
invention to limit solvent degradation may be accomplished by a
combination of factors, such as selection of the cosolvent, ratio
of solvent to cosolvent and conditions of vacuum for the
distillation step. Given the teachings of this specification, one
of skill in the art may select the appropriate combination of
factors to control the distillation temperature as required. For
example, one of skill in the art may readily adjust the temperature
and vacuum conditions of the distillation step within the above
ranges to achieve a desired efficiency of acetic acid recovery
while minimizing amide formation and oxidative degradation of the
solvent according to this invention. Such modifications are
encompassed within the appended claims.
According to yet another embodiment of this invention, an anaerobic
microbial fermentation process for the production of acetic acid
employs the modified solvent/cosolvent mixture of this invention to
enhance the efficiency of recovery of acetic acid. In this process,
a fermentation broth containing, among other components, acetic
acid, is formed by fermenting in a bioreactor with an anaerobic
acetogenic microorganism, an aqueous stream comprising a source of
nutrients, and a gas containing various mixtures of carbon
monoxide, or carbon dioxide or hydrogen. Thus, in one embodiment,
the gas stream contains carbon monoxide. In another embodiment the
gas stream contains carbon dioxide and hydrogen. In still another
embodiment the gas stream contains carbon dioxide, carbon monoxide
and hydrogen. In yet another embodiment the gas stream contains
carbon monoxide and hydrogen. Such gases may desirably be obtained
from waste gases of various industrial processes.
Also, as mentioned, in the fermentation broth is an anaerobic
acetogenic bacterium and a nutrient medium necessary for growth of
the bacterium. The anaerobic bacteria may be one strain of bacteria
or a mixed culture containing two or more of acetogenic bacteria,
including, without limitation, Acetobacterium kivui, A woodii,
Butyribacterium methylotrophicum, Clostridium aceticum, C.
acetobutylicum, C. formoaceticum, C. kluyveri, C. thermoaceticum,
C. thermocellum, C. thermohydrosulfuricum, C.
thermosaccharolyticum, Eubacterium limosum, Peptostreptococcus
productus, and C. ljutigdahlii, and mixture thereof. Particularly
desirable acetogenic bacteria are those strains previously
discovered by the inventors, namely, C. ljutngdahlii strain PETC
ATCC 49587, strain O-52 ATCC 55989 deposited on Jun. 27, 1997,
strain ER12 ATCC 55380 deposited on Dec. 8, 1992 and strain C-01
ATCC 55988 deposited on Jun. 27, 1997, and mixtures thereof. These
acetogenic bacteria are generally available from depositories such
as the American Type Culture Collection, 10801 University
Boulevard, Manassas, Va. 20110-2209 or from commercial or
educational institutions. The above-identified microorganisms are
deposited pursuant to the Budapest Treaty for the Deposit of
Microorganisms for Patent Purposes, and such deposits comply with
all the requirements thereof.
Nutrients are continuously fed to the fermenter. The nutrient media
useful in such fermentation broth are conventional and include
those nutrients known to be essential for the growth of such
acetogenic bacteria. An exemplary nutrient medium formation (Medium
A plus Medium B) for the growth of acetogenic bacteria at
atmospheric pressure, and which is sulfide based is illustrated in
the following Table III. However, many different formulae of
nutrient media may be used with components of differing
concentrations. One of skill in the art can readily formulate other
suitable nutrient media for the processes described herein. The
formula of Table III is merely one suitable formulation.
TABLE-US-00003 TABLE III Component Quantity per liter water Medium
A Mg(CH.sub.3COO).sub.2.4H.sub.2O 0.1452 g
Ca(CH.sub.3COO).sub.2.H.sub.2O 0.00677 g CH.sub.3COOK 0.5574 g
Nitrilotriacetic acid 0.0141 g 85% H.sub.3PO.sub.4 0.56 ml
FeCl.sub.2.4H.sub.2O 113 mg ZnSO.sub.4.7H.sub.2O 5.6 mg
MnCl.sub.2.4H.sub.2O 1.7 mg H.sub.3BO.sub.5 17 mg
CoCl.sub.3.6H.sub.2O 11 mg CuCl.sub.2.H.sub.2O 1.1 mg
NiCl.sub.2.6H.sub.2O 2.3 mg Na.sub.2SeO.sub.3 0.6 mg
Ca-D-Pantothenate 0.846 mg Thiamine 0.706 mg Biotin 0.212 mg Medium
B (NH.sub.4).sub.2HPO.sub.4 1.2 g NH.sub.4OH 5.62 ml
Na.sub.2S.9H.sub.2O 1.251 mg NaMoO.sub.4.2H.sub.2O 1.8 mg
Na.sub.2WO.sub.4.2H.sub.2O 6.0 mg
The selection of nutrients and other conditions for fermentation
may be readily made by one of skill in the art with resort to
existing knowledge, and depend on a variety of factors, such as the
microorganism used, the size and type of the equipment, tanks and
columns employed, the composition of the gas stream or energy
source, etc. Such parameters may be readily selected by one of
skill in the art in view of the teachings of this invention and are
not a limitation of this invention.
As the fermentation occurs, exhaust gas containing inert and
unreacted substrate gases, are released and the liquid fermentation
broth or effluent is passed to a centrifuge, hollow fiber membrane,
or other solid-liquid separation device to separate out
microorganisms that are entrained and preferably return them to the
fermenter.
Thereafter, the essentially cell-free aqueous stream from the
fermentation broth (hereinafter "cell-free stream") is subjected to
extraction with the modified solvent/cosolvent mixture in an
extractor. The solvent to feed ratio (ratio of solvent volume to
cell-free stream volume) can vary significantly from nearly zero to
10, for example. The lower the solvent to feed ratio, the higher
the concentration of acid in the solvent and the lower the
requirements for solvent. According to this invention, a solvent
comprising a mixture of isomers of highly branched di-alkyl amines
modified to remove mono-alkyl amines and a selected co-solvent,
e.g., a low boiling hydrocarbon cosolvent mixture described above,
is employed in the extraction step. As described in the above
embodiment, this extraction is maintained at a temperature of
between about 20.degree. C. to about 80.degree. C., depending on
the viscosity of the solvent mixture. This extraction step removes
the acetic acid from the cell-free stream and permits separation of
the acetic acid from the nutrient media and other materials in the
aqueous phase (which are recycled to the bioreactor) into a phase
which includes the solvent, a very small amount of water and the
acetic acid. Additionally, some components, such as Se, Mo, W and S
from the medium are extracted into the solvent.
Still another step in the process involves continuously distilling
the acetic acid and water component away from the extraction
product's solvent and water. To accomplish this step, the
solvent/acid/water solution passes to a first distillation column,
where this solution is heated to a temperature which reduces the
conversion of the amines in the solvent to amides. As described
above, the distillation temperature must range between 115.degree.
C., to a maximum of about 160.degree. C. to permit acetic acid
recovery, while limiting solvent degradation and amide formation.
Preferably, the temperature of the distillation step does not
exceed about 130.degree. C., in order to prevent amide formation. A
key advantage of the present invention is that the extracting and
distilling steps occur without substantially degrading the solvent
amine to an amide, and thus enhances the efficiency of acetic acid
recovery from the broth.
Where the solvent/co-solvent mixture of this invention employs an
azeotroping cosolvent, the distillation columns used in the process
operate more efficiently. The formation of an azeotrope permits the
cosolvent and the acid/water to move together (essentially as one)
up and out the top of the first distillation column during the
distillation step. In the liquid form, the cosolvent and the acetic
acid/water separate. Once separated, the cosolvent can be
reintroduced into the distillation column. The acetic acid and
water (and some residual cosolvent) then pass to a second
distillation column where the cosolvent again forms an azeotrope
with water and acid, and the three components flow as a vapor out
the top of the column. The vapor is condensed and most of the
liquid is refluxed. Because the condensed liquid contains a small
amount of cosolvent, a small stream is continuously returned to the
solvent distillation column. The product acetic acid is pulled out
just above the first theoretical stage, i.e., the portion of the
column where the solvent and acid separate.
A preferred embodiment of this method involves performing the
distillation step under an oxygen-free vacuum, which also serves to
reduce the temperature and avoid oxidative degradation of the
solvent of solvent/cosolvent mixture. The higher the vacuum (i.e.,
lower absolute pressure) the lower the temperature and the less
amide formation and oxidative degradation. As described above, the
vacuum is preferably less than 10 psia. Desirably a vacuum of
between about 0.1 psia and 5 psia is useful in the distillation
step. More preferably, a vacuum of 4 psia or less is useful in this
distillation step to further reduce the boiling point of the
solvent/acid/water mixture, further reducing amide formation and
enhancing recovery of the acetic acid. As yet a further advantage
of the use of the modified solvent/azeotroping cosolvent mixture of
this invention is the use of two distillation columns to accomplish
enhanced recovery of acetic acid from aqueous phases in comparison
to processes of the prior art.
The control of distillation temperature in the processes of this
invention to limit solvent degradation may be accomplished by a
combination of factors, such as selection of the cosolvent, ratio
of solvent to cosolvent and conditions of vacuum for the
distillation step. Given the teachings of this specification, one
of skill in the art may select the appropriate combination of
factors to control the distillation temperature as required. For
example, one of skill in the art may readily adjust the temperature
and vacuum conditions of the distillation step within the above
ranges to achieve a desired efficiency of acetic acid recovery
according to this invention. Such modifications are encompassed
within the appended claims.
C. Extractive Fermentation and Direct Contact Extraction Method
According to yet another embodiment of this invention, the
above-described novel modified solvent/cosolvent mixtures are
useful in a process of "direct contact extraction" and "extractive
fermentation", i.e., modifications of the anaerobic fermentation
production process for the recovery of acetic acid described above.
The modifications of the process allow the production of acetic
acid via microbial fermentation without the need for bacterial cell
separation prior to extraction or distillation. Further, these
solvent mixtures when used in microbial fermentation of acetic acid
can eliminate the need for use of a separate extractor. In addition
to reducing the complexity of the process, this invention reduces
the capital, operating and maintenance costs of the equipment
needed to perform the process of producing acetic acid, as well as
the time to obtain the product.
Thus, the "extractive fermentation" method of the invention
provides an anaerobic microbial fermentation process for the
production of acetic acid, which is a modification of the process
described above. As a first step, the bioreactor or fermenter
containing anaerobic acetogenic bacteria in a suitable nutrient
mixture necessary for growth of the bacteria is contacted with the
modified solvent/cosolvent mixture described above at about
37.degree. C. and at least about one atmosphere of pressure (i.e.,
14.7 psia) for a time sufficient to acclimate the bacteria to the
presence of the solvent, i.e. to permit the bacteria to grow in the
presence of the solvent. The anaerobic bacteria may be one strain
of bacteria or a mixed culture containing two or more strains of
acetogenic bacteria; the bacterial strains listed above in Part B
may also be used in this modification of the invention. As many
solvents are toxic to bacterial growth, this aspect of the
invention involving direct contact between the bacteria and the
solvent reflects the acclimation of the cells to solvent mixture,
which is obtained by gradually increasing contact between the cells
and solvent mixture over time.
Thereafter, an aqueous stream comprising a source of nutrients, and
a gas containing various mixtures of carbon monoxide, or carbon
dioxide or hydrogen, is introduced into the fermenter. Thus, in one
embodiment, the gas stream contains carbon monoxide. In another
embodiment the gas stream contains carbon dioxide and hydrogen. In
still another embodiment the gas stream contains carbon dioxide,
carbon monoxide and hydrogen. In yet another embodiment the gas
stream contains carbon monoxide and hydrogen. As above, these gases
may be obtained from industrial waste gases. According to this
step, a fermentation broth containing, among other components,
acetic acid, solvent, bacterial cells and water is formed.
Nutrients are continuously fed to the fermenter. The selection of
the particular nutrients, media and other conditions of temperature
and pressure, etc. for fermentation may be readily made by one of
skill in the art given the teachings of this invention, and depend
on a variety of factors, such as the microorganism used, the size
and type of the equipment, tanks and columns employed, the
composition of the gas stream or energy source, the gas retention
time, and liquid retention time in the fermenter, etc. Such
parameters may be readily balanced and adjusted by one of skill in
the art and are not considered to be limitations on this
invention.
As the fermentation occurs, exhaust gas containing inert and
unreacted substrate gases, are released. Within the fermentation
broth, the presence of the solvent continuously separates the
acetic acid and a small amount of water into a lighter "solvent
phase", from the heavier bacteria and nutrient medium and other
heavier materials in the aqueous phase. The mixture of cell-free
stream and solvent is continuously removed into a settling tank,
where the lighter solvent phase is decanted from the heavier
aqueous phase simply by the operation of gravity. No other
solid-liquid separation methods are used. The heavier phase is
recycled to the bioreactor/fermenter, and the lighter phase which
includes the solvent, a small amount of water and the acetic acid
solution passes to a first distillation column.
As described above, this solution is heated to a temperature for
acetic acid recovery which minimizes the conversion of the amines
in the solvent to amides. Preferably, the temperature of the
distillation step does not exceed about 160.degree. C., and more
preferably 130.degree. C., in order to prevent amide formation. A
key advantage of the present invention is that the distilling steps
occur without substantially degrading the solvent amine to an
amide, and thus enhance the efficiently of acetic acid
production.
Where the solvent/co-solvent mixture of this invention employs an
azeotroping cosolvent, the distillation columns used in the process
operate more efficiently. The formation of an azeotrope permits the
cosolvent and the acid/water to move together (essentially as one)
up and out the top of the first distillation column during the
distillation step. In the liquid form, the cosolvent and the acetic
acid/water separate. Once separated, the cosolvent can be
reintroduced into the distillation column. The acetic acid and
water (and some residual cosolvent) then pass to a second
distillation column where the cosolvent again forms an azeotrope
with water and acid, and the three components flow as a vapor out
the top of the column. The vapor is condensed and most of the
liquid is refluxed. Because the condensed liquid contains a small
amount of cosolvent, a small stream is continuously returned to the
solvent distillation column. The product acetic acid is pulled out
just above the first theoretical stage.
A preferred embodiment of this method involves performing the
distillation step under an oxygen-free vacuum as described above,
which also served to reduce the temperature and avoid oxidative
degradation of the solvent or solvent/cosolvent mixture. The higher
the vacuum (i.e., lower absolute pressure) the lower the
temperature and the less amide formation and oxidative degradation.
Desirably a vacuum of less than 10 psia, desirably between about
0.1 psia and 5 psia, and more preferably, a vacuum of 4 psia or
less is useful in this distillation step to further reduce the
boiling point of the solvent/acid/water mixture, further reducing
amide formation and enhancing recovery of the acetic acid. As yet a
further advantage of the use of the modified solvent/ azeotroping
cosolvent mixture of this invention is the use of two distillation
columns to accomplish enhanced efficiency of acetic acid recovery
from aqueous phases in comparison to processes of the prior
art.
The control of distillation temperature in the processes of this
invention to limit solvent degradation may be accomplished by a
combination of factors, such as selection of the cosolvent, ratio
of solvent to cosolvent and conditions of vacuum for the
distillation step. Given the teachings of this specification, one
of skill in the art may select the appropriate combination of
factors to control the distillation temperature as required. For
example, one of skill in the art may readily adjust the temperature
and vacuum conditions of the distillation step within the above
ranges to achieve a desired efficiency of acetic acid recovery
according to this invention. Such modifications are encompassed
within the appended claims.
In an alternative "direct contact extraction" method of this
invention, rather than separate the cellular materials from the
acetic acid and water by filtration or centrifugation prior to
extraction, the entire fermentation broth containing cells is
introduced directly into an extractor. Among conventional
extraction devices are columns with either the solvent phase or
aqueous phase as the continuous phase. These columns also have
entrances and exits for solvent and aqueous phase culture. The
fermentation broth including the bacterial cells flows downward
through the solvent filled column and solvent flows upward,
countercurrent to the broth. The opposite flow can also occur with
the water-filled column. These columns differ depending upon the
type of packing in the column and sizes of same. Alternatively,
other extraction devices, like mixing and settling tanks can be
used to accomplish the same tasks, and are readily selected by one
of skill in the art without undue experimentation to accomplish
this step as taught herein.
The presence of the solvent continuously separates the acetic acid
and a small amount of water into a "solvent phase", from the
heavier phase containing bacteria and nutrient media, acetate
salts, a small amount of acetic acid, and other heavier materials
in the aqueous phase. The solvent phase containing acetic acid and
a small amount of water is continuously removed and passed to a
first distillation column, and then further distilled as described
in the embodiment immediately above. The aqueous phase containing
the cellular materials exits the bottom of the extractor. Because
the aqueous phase and the solvent phase are substantially
immiscible, they separate naturally along the column, aided also by
the operation of gravity. No other solid-liquid separation methods
are used. The heavier aqueous phase is recycled to the
bioreactor/fermenter. Any cellular or proteinaceous material formed
at the culture/solvent interface is periodically removed from the
extractor. Various speeds and directions of solvent or water flows
may be adjusted depending on the type of extractor selected.
An example of the extractive fermentation method first described
above is represented in Example 6. Examples of the direct contact
extraction method are shown in Example 4, which employs a
solvent-filled column and Example 5, which uses an aqueous filled
column. The aqueous filled system is a less expensive alternative
to a solvent filled column, requiring less solvent than the
solvent-filled system. Both columns are commercial
alternatives.
One of skill in the art is expected to readily alter the specific
conditions under which the extractive fermentation and direct
extraction methods of this invention function without departing
from the scope of this invention.
D. Carbon Dioxide Stripping
According to yet another embodiment of this invention, the process
of microbial fermentation of a gas stream (particularly a gas
stream containing carbon monoxide, carbon monoxide and hydrogen and
optionally carbon dioxide, or carbon dioxide and hydrogen) to
produce acetic acid or another product, e.g., an alcohol, salt
etc., may be modified to increase its efficiency by substantially
reducing from the fermentation broth the presence of any carbon
dioxide and optionally sulfur (in the form of hydrogen sulfide). In
microbial fermentations of such gases, such as those of the prior
art (see PCT WO98/00558) or those taught herein, carbon dioxide and
hydrogen sulfide are present both in the gas stream exiting the
fermenter/bioreactor and in the liquid fermentation broth exiting
from the fermenter/bioreactor to the next step in the process. For
example, at 6 atmospheres pressure in the fermenter (.about.75
psig) the exit gas contains about 50 percent CO.sub.2 and 700 ppm
H.sub.2S, and the fermentation broth contains roughly 3 g/L
CO.sub.2 and 0.01 g/L H.sub.2S. During extraction, the CO.sub.2 and
H.sub.2S are removed along with acetic acid by the solvent. This is
true for processes employing conventional amine solvents, as well
as for the use of the modified solvent/cosolvent mixtures described
in this invention.
Anything that is extracted into the solvent, reduces the solvent
capacity for the acid. Because the concentration of CO.sub.2 in the
fermentation broth is similar to the concentration of acetic acid
(5 g/L) in the fermentation broth, it represents a real threat to
acetic acid loading in the solvent. Thus, the CO.sub.2 present in
the fermentation broth limits the loading potential of the solvent
for acetic acid. Hydrogen sulfide is not a significant threat to
acetic acid loading because of its low concentration, but H.sub.2S
as sulfide ion is an essential nutrient for the culture. The
removal of sulfur from the fermenter in the fermentation broth also
reduces the available sulfur for the bacteria in the fermenter.
Although it appears that the exhaust gas from the reactor has
hydrogen sulfide and therefore is in itself removing sulfur, having
the sulfur extracted increases the cost for sulfur as a nutrient.
Similarly since carbon dioxide is required for conversion of
hydrogen to acetic acid, its removal in the fermentation broth
during the production process reduces the utilization of
hydrogen.
Therefore, the present invention provides an improved method of
microbial fermentation of gases for the production of acetic acid
by including as a step of the process the removal of carbon dioxide
from the fermentation broth prior to extraction. An optional, but
desirable step involves the removal of hydrogen sulfide from the
fermentation broth prior to extraction. Preferably, both carbon
dioxide and hydrogen sulfide are removed from the fermentation
broth, and optionally returned to the fermenter.
One embodiment of this process involves contacting the fermentation
broth (which may be composed of bacterial cells, acetic acid,
nutrient media, salts and other components from the fermentation)
or the cell-free stream (which may have been first filtered or
centrifuged to remove most of the bacterial cells and other heavier
materials therefrom) with a "stripping" gas stream that is devoid
of carbon dioxide and preferably devoid of hydrogen sulfide. This
"stripping" gas can include, without limitation, nitrogen, helium,
argon, methane or the original dilute gas it is contains little to
no carbon dioxide and preferably no hydrogen sulfide. Essentially
any non-reactive gas or mixture of non-reactive gases is useful in
this context. Introduction of the stripping gas, e.g., N.sub.2, to
the fermentation broth or cell-free stream exiting the fermenter
reverses the equilibrium between the dissolved CO.sub.2 (or
H.sub.2S) in the liquid phase and the gas phase, and strips the
gases from the liquid phase. The preferred method of contact with
the stripping gas is in a countercurrent stripper column. Just as
equilibrium exists between the CO.sub.2 (or H.sub.2S) gas that is
dissolved in the fermentation liquid exiting the fermenter, an
equilibrium is also established between the broth or cell-free
stream entering the counter-current column and the gas leaving
therefrom. As the stripping gas and the CO.sub.2 laden fermentation
broth or cell-free stream contact each other, equilibrium between
the stripping gas, e.g., N.sub.2, and the CO.sub.2 in the water is
continually updated. The packing in the column ensures good surface
area between the liquid and the stripping gas.
Although the liquid exiting the countercurrent column at the bottom
has had its CO.sub.2 concentration significantly reduced, the fresh
nitrogen stripping has coming in has complete capacity for reaching
equilibrium with the CO.sub.2 in the water. When the nitrogen
finally leaves the top of the stripper column, it is saturated with
CO.sub.2 (and H.sub.2S). The CO.sub.2 (or H.sub.2S) laden nitrogen
can be scrubbed to remove or recycle the CO.sub.2 and H.sub.2S back
to the fermenter. The "stripped" or scrubbed fermentation broth or
cell-free stream then enters the next step of the acetic acid
production process, e.g., the extraction with solvent or the
contact with solvent in the direct extraction process described
above, and distillation. See, e.g., the schematic drawing of FIG. 3
and Example 6A.
Still another embodiment of this aspect of the invention is
provided by altering the method of the carbon dioxide stripping. As
exemplified in Example 6C, this process involves subjecting the
fermentation broth (which may be composed of bacterial cells,
acetic acid, nutrient media, salts and other components from the
fermentation) or the cell-free stream (which may have been first
filtered or centrifuged to remove most of the bacterial cells and
other heavier materials therefrom) to a rapid decrease in pressure
prior to introduction into the extractor or into a solvent
extraction column. For example, the pressure of the fermentation
broth or cell-free stream may be decreased from 6 atmospheres (or
greater) to a lower pressure, e.g., atmospheric pressure, which
causes the carbon dioxide in the broth or cell-free stream to
approach its equilibrium concentration. Preferably this decrease in
pressure occurs after the fermentation broth or cell-free stream
exits the fermenter and is in a separate container. The CO.sub.2 is
preferably recycled back to the fermenter.
The "stripped" fermentation broth or cell-free stream then enters
the next step of the acetic acid production process, e.g., the
extraction with solvent or the contact with solvent in the direct
extraction process described above, and distillation. See, e.g.,
Example 6C.
Yet a further embodiment of this aspect of the invention is
provided by altering the method of the carbon dioxide stripping. As
exemplified in Example 6D, this process involves removing the
fermentation broth (which may be composed of bacterial cells,
acetic acid, nutrient media, salts and other components from the
fermentation) or the cell-free stream (which may have been first
filtered or centrifuged to remove most of the bacterial cells and
other heavier materials therefrom) from the fermenter, and heating
the broth or cell-free stream to a temperature of about 80.degree.
C. or more prior to extraction. The high temperature causes the
carbon dioxide in the broth or cell-free stream to approach its
equilibrium concentration. The CO.sub.2 and H.sub.2S preferably are
recycled to the fermenter via a variety of common engineering
methods.
The "stripped" fermentation broth or cell-free stream then enters
the next step of the acetic acid production process, e.g., the
extraction with solvent or the contact with solvent in the direct
extraction process described above, and distillation. See, e.g.,
Example 6D The only disadvantage of this modification of the
process is that after extraction, the aqueous broth component
cannot be recycled back into the fermenter, due to the killing
effect of the heating temperature upon the bacteria, and must be
discarded.
One of skill in the art is expected to readily alter the specific
conditions under which the carbon dioxide and optionally hydrogen
sulfide stripping occurs departing from the scope of this
invention.
The following examples illustrate various aspects of this invention
and do not limit the invention, the scope of which is embodied in
the appended claims.
EXAMPLE 1
Recovery of Acetic Acid from the Fermentation Product Stream Using
the Solvent/Azeotroping Cosolvent Mixture of the Invention
A. 60% Modified Solvent A and 40% Orfom.RTM. SX-18 Cosolvent
An apparatus and method for producing acetic acid from a variety of
aqueous gaseous streams is described in detail in published
International Patent Application No. PCT WO98/00588, incorporated
by reference herein. The process described therein is modified
according to one aspect of the present invention, as follows.
A gas stream containing 45% carbon monoxide, 45% hydrogen and 10%
carbon dioxide was introduced into a continuous stirred tank
fermenter containing C. ljungdahlii strain ER12 and suitable
nutrient medium. The liquid product stream from the fermenter with
cell recycle (i.e., cell separation utilizing a hollow fiber
membrane) containing 5 g/l free acetic acid and 5 g/l acetate at pH
4.75 (i.e., the cell-free stream) was sent to a multi-state
countercurrent extraction column. In the extraction column, the
cell-free stream is contacted with a solvent/cosolvent mixture of
this invention containing 60% Modified Solvent A and 40% Orfom.RTM.
SX-18 cosolvent at a temperature of 37.degree. C. and using a 0.09
(v/v) solvent to feed ratio. The solvent exiting the extractor
contained 50 g/l acetic acid, and the aqueous stream (which was
sent back to the fermenter as recycle) contained 5 g/l acetate and
0.5 g/l acetic acid.
The solvent stream containing the modified solvent/cosolvent and
acetic acid was sent to a distillation system containing a first
"solvent" column, an accumulator and a second "acid" column. In
operating the first distillation column, the combination of a
low-boiling co-solvent and a mild vacuum of 0.3 atm pressure
permits the column temperature to be minimized and permits the
separation of acid, water and cosolvent in the overhead product
from the Modified Solvent A and some co-solvent, which stay in the
bottom of the column. The bottom temperature is kept at a maximum
temperature of 130.degree. C. by vacuum operation. The modified
solvent and cosolvent at the bottom of the column are sent back to
the extractor as recycle. The mixture at the top of the column,
i.e., water, acetic acid and some co-solvent, separates at the top
of the column and is then cooled to allow the co-solvent to
condense and separate from the water/acid.
By removing most of the co-solvent from the water/acid, the lower
co-solvent concentration in the water/acid is below the azeotrope.
This mixture, which contains acetic acid and water and a small
amount of cosolvent, is sent to the second "acid" distillation
column. In this second column, the water and co-solvent and some
acid go out the top of the column and the acetic acid goes to the
bottom which has a temperature of 118.degree. C. Part of the
water/acid phase is refluxed to the column and the remaining
water/acid phase and co-solvent are recirculated back to
extraction. Glacial acetic acid is removed near the bottom of this
column as product, and the overhead is sent back to the process as
recycle.
B. 30% Adogen283.RTM.LA (Witco) Solvent and 70% SX-18 Cosolvent
As another example of a fermentation method conducted according to
the present invention, the liquid product stream described in Part
A containing 5 g/l free acid and 10 g/l acetate at pH 5.0 was
contacted with a solvent mixture containing 30% Adogen283.RTM.LA
solvent (Witco) and 70% SX-18 cosolvent in a multi-state extractor.
A 0.09 solvent to feed ratio is used. The solvent exiting the
extractor contains 25 g/l acetic acid and the aqueous stream
contains 10 g/l acetate and 2.75 g/l acetic acid. Thus, the acid
distribution coefficient is reduced by dilution with additional
SX-18 cosolvent. The process for product recovery by distillation
is thereafter the same as described above.
C. 30% Modified Solvent A and 70% Decane Cosolvent
An extraction similar to that of Part B was carried out with 30%
Modified Solvent A in a cosolvent, decane. The distribution
coefficient remains the same as in Part B, and the process for
product recovery by distillation is equivalent.
D. 60% Adogen283.RTM.LA (Witco) solvent and 40% n-dodecane
Cosolvent
The extraction of Part A is carried out with 60% Adogen283.RTM.LA
solvent (Witco) in n-dodecane cosolvent. The extraction process
remains the same as in Part B, yielding 50 g/l acid in the solvent,
and 10 g/l acetate and 0.5 g/l acetate acid in the aqueous
phase.
The aqueous stream containing acetate is again sent back to the
fermenter as recycle. The solvent stream containing acetic acid is
sent to a distillation system very similar to the system presented
in Part B, except that the pressure in the solvent column is 0.2
atmosphere and the temperature at the bottom of the column is
127.degree. C.
EXAMPLE 2
Amide Formation
This example demonstrates the basis for the invention, that is,
determination by the inventors that temperature control is vital to
the efficient functioning of an amine-containing solvent in an
acetic acid production process when an amine-containing solvent is
employed in distillation and extraction steps.
The amide formation from amine in the solvent is a first order rate
expression in acetic acid concentration illustrated by the formula:
Y=kX, where Y represents amide concentration after 16 hours,
measured in weight percent; X=acetic acid concentration after 16
hours, measured in weight percent, and k=the amide formation rate
constant.
The rate of amide formation and thus the rate constant, k,
increases with temperature by an Arrhenius type rate expression,
represented by the formula: ln(k)=-9163.21 (1/T)+27.41, where T=the
absolute temperature in Kelvin.
FIG. 4 illustrates a plot of ln(k) as a function of the inverse
absolute temperature which is used in finding the Arrhenius rate
expression. For example, at a temperature of 150.degree. C.
(1/T=0.00236), the rate of amide formation is 9 times greater than
at a temperature of 110.degree. C. (1/T=0.00261)
EXAMPLE 3
Direct Extraction of Acetic Acid Using a Continuous Solvent Phase
Column
Fermentation broth obtained from a fermenter similar to that of
Example 1 contained 2.6 g/l cells (dry weight), excess nutrients, 5
g/l acetic acid and 5.0 g/l acetate at pH 4.75. This broth is sent
to a continuous solvent phase extraction column containing 60%
Adogen283.RTM.LA (Witco) solvent in SX-18 cosolvent. The extraction
column is a cylindrical column, packed or unpacked, which has
entrances and exits for solvent and aqueous phase culture. Culture
flows downward through the solvent filled column, and solvent flows
upward, countercurrent to the culture. The exiting solvent from the
column contains 50 g/l acetic acid and is sent to distillation for
acid recovery prior to recycle back to the column. The exiting
culture stream at the bottom of the column contains 5.0 g/l
acetate, 0.5 g/l acetic acid, cells and nutrients and is sent back
to the fermenter as recycle. Because the solvent and culture are
immiscible, little to no water (culture) is present in the solvent
and little to no solvent is present in the culture recycle stream.
A small rag layer consisting of cellular proteinaceous material is
formed at the culture/solvent interface which must be removed
periodically.
EXAMPLE 4
Extraction of Acetic Acid Using a Continuous Aqueous Phase
Column
The fermentation broth of Example 3 is passed through a continuous
aqueous phase extraction column containing 60% Adogen283.RTM.LA
solvent (Witco) in SX-18 cosolvent. The column is constructed
similarly as in Example 3 except that the column is filled with
aqueous phase culture instead of solvent. Again solvent and culture
flow countercurrently, with solvent exiting the top of the column
and culture exiting the bottom of the column. Exiting aqueous phase
and solvent phase concentrations are the same as in Example 3.
EXAMPLE 5
Internal Extractive Fermentation for Acetic Acid Production from
CO, CO.sub.2 and H.sub.2
Industrial waste gas containing 7.52 percent carbon dioxide, 31.5
percent carbon monoxide, 27.96 percent hydrogen and 33.02 percent
nitrogen is fermented to acetic acid/acetate at pH 5.0 in a
fermenter/reactor as described in Example 1A, using Clostridium
ljungdahlii, BRI isolate ER12. The gas retention time (ratio of
reactor volume to gas flow rate) is 10 minutes and the liquid
dilution rate (ratio of liquid medium flow rate to reactor volume)
is 0.03 hour.sup.-1. Medium containing essential vitamins and
minerals flows continuously into the reactor. The agitation rate is
1000 rpm. The reactor also contains a solvent phase of 60% Modified
Solvent A of this invention in SX-18 cosolvent. As the culture
produces acetic acid from CO, CO.sub.2 and H.sub.2, it is extracted
by the solvent.
A mixture of solvent and culture exit the fermenter and are
separated in a small settling tank. A portion of the aqueous phase,
equal in rate to the medium feed rate, flows from the system as
waste purge. The balance of the aqueous phase from the separator is
returned to the reactor. Solvent containing extracted acid is sent
to distillation for recovery. After recovery the solvent is
recycled to the reactor.
EXAMPLE 6
Stripping of Culture Prior to Acid Extraction
A. Nitrogen Stripping
Culture from the reactor of Examples 1-4 containing bacterial
cells, 5 g/l acetic acid, 9.3 g/l acetate and dissolved sulfide and
carbonate at pH 5.0 is passed through a nitrogen stripping column
to remove dissolved CO.sub.2 and sulfide as H.sub.2S before passing
the culture through an extraction column. This operation is
required in order to prevent solvent loading of CO.sub.2 and
H.sub.2S instead of acetic acid, and to return H.sub.2S as a sulfur
source and reducing agent back to the culture. The N.sub.2 gas
stream which contains H.sub.2S and CO.sub.2 is sent back to the
reactor as a secondary gas feed. By using the nitrogen stripper,
the solvent is loaded to 50 g/l acetic acid. Without CO.sub.2 and
H.sub.2S removal prior to extraction, the solvent is loaded to
25-30 g/l acetic acid.
B. Stripping with Alternative Gases
The culture of Part A is stripped with gases other than N.sub.2,
including methane or CO.sub.2-free synthesis gas containing
H.sub.2, CO, CH.sub.4. All other aspects of the example are the
same.
C. Stripping via Pressure Reduction to Relieve Dissolved
CO.sub.2
The pressure of the fermentation broth in Part A is rapidly
decreased from 6 or 3 atmospheres to atmospheric pressure in order
to release CO.sub.2 prior to loading in the extractor. The CO.sub.2
pressure in the culture approaches the equilibrium concentration
according to Henry's law at one atmosphere, a greatly reduced level
which helps maximize acid extraction by the solvent.
D. Stripping via Preheating to Relieve Dissolved CO.sub.2
The cell-free stream in Part A is preheated prior to extraction to
relieve CO.sub.2 in much the same manner as noted in Part C. The
broth cannot be reused after heating.
All published documents are incorporated by reference herein.
Numerous modifications and variations of the present invention are
included in the above-identified specification and are expected to
be obvious to one of skill in the art. Such modifications and
alterations to the compositions and processes of the present
invention are believed to be encompassed in the scope of the claims
appended hereto.
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