U.S. patent application number 10/627254 was filed with the patent office on 2005-01-27 for process for production of acetyl anhydrides and optionally acetic acid from methane and carbon dioxide.
This patent application is currently assigned to THE REGENTS OF THE UNIVERSITY OF CALIFORINIA. Invention is credited to Bell, Alexis T., Gaemers, Sander, Mukhopadhyay, Sudip, Sunley, John Glenn, Zerella, Mark.
Application Number | 20050020856 10/627254 |
Document ID | / |
Family ID | 34080602 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050020856 |
Kind Code |
A1 |
Bell, Alexis T. ; et
al. |
January 27, 2005 |
Process for production of acetyl anhydrides and optionally acetic
acid from methane and carbon dioxide
Abstract
Acetyl anhydrides such as acetyl sulfate are produced by a
process for comprising contacting methane and carbon dioxide in an
anhydrous environment in the presence of effective amounts of a
transition metal catalyst and a reaction promoter, and an acid
anhydride compound, and optionally an acid. The acetyl anhydride
can be contacted with water to produce acetic acid or with an
alcohol to produce a product comprising an acetate ester and that
may also comprise acetic acid.
Inventors: |
Bell, Alexis T.; (Oakland,
CA) ; Mukhopadhyay, Sudip; (Williamsville, NY)
; Zerella, Mark; (Berkeley, CA) ; Sunley, John
Glenn; (East Yorkshire, GB) ; Gaemers, Sander;
(Bishop Burton, GB) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
THE REGENTS OF THE UNIVERSITY OF
CALIFORINIA
OAKLAND
CA
|
Family ID: |
34080602 |
Appl. No.: |
10/627254 |
Filed: |
July 24, 2003 |
Current U.S.
Class: |
562/888 |
Current CPC
Class: |
C07C 309/00 20130101;
C07C 67/08 20130101; C07C 51/56 20130101; C07C 53/18 20130101; C07C
69/14 20130101; C07C 67/08 20130101; C07C 51/56 20130101; C07C
381/00 20130101 |
Class at
Publication: |
562/888 |
International
Class: |
C07C 069/02 |
Claims
What is claimed is:
1. A process for producing an acetyl anhydride comprising
contacting methane and carbon dioxide in an anhydrous environment
in the presence of effective amounts of a transition metal catalyst
and a reaction promoter, and an acid anhydride compound, and
optionally an acid, to produce a product comprising the acetyl
anhydride.
2. A process according to claim 1 further comprising: (b)
contacting the product comprising the acetyl anhydride with
water.
3. A process according to claim 2 further comprising recovering
acetic acid from step (b).
4. A process according to claim 1 further comprising: (b)
contacting the product comprising the acetyl anhydride with an
alcohol.
5. A process according to claim 4 further comprising recovering an
acetate ester from the product of step (b).
6. A process according to claim 4 further comprising recovering
acetic acid from the product of step (b).
7. A process according to claim 1 in which the catalyst is a
vanadium-containing catalyst.
8. A process according to claim 7 in which the catalyst is selected
from vanadium pentoxide, vanadium trioxide, sodium metavanadate,
vanadium-containing heteropolyacid catalysts and vanadyl
acetylacetonate.
9. A process according to claim 7 in which the catalyst is vanadyl
acetylacetonate.
10. A process according to claim 1 in which the reaction promoter
is selected from K.sub.2S.sub.2O.sub.8, K.sub.4P.sub.2O.sub.8,
calcium dioxide, urea-hydrogen peroxide, and m-chloroperbenzoic
acid.
11. A process according to claim 10 in which the reaction promoter
is K.sub.2S.sub.2O.sub.8.
12. A process according to claim 1 in which the acid anhydride
compound comprises sulfur trioxide, sulfur dioxide, trifluoroacetic
acid anhydride, fluoromethanesulfonic acid anhydride,
trifluoromethanesulfonic acid anhydride, fluorosulfonic acid
anhydride, methanesulfonic acid anhydride, NO, NO.sub.2,
N.sub.2O.sub.5, P.sub.2O.sub.5, SeO.sub.3, As.sub.2O.sub.5,
TeO.sub.3, or B.sub.2O.sub.3 or a mixture of two or more of the
foregoing.
13. A process according to claim 1 in which the acid anhydride
compound comprises trifluoroacetic acid anhydride.
14. A process according to claim 1 in which the acid anhydride
compound comprises trifluoromethanesulfonic acid anhydride.
15. A process according to claim 1 in which the acid anhydride
compound comprises sulfur trioxide.
16. A process according to claim 1 in which the acid anhydride
compound comprises fuming sulfuric acid.
17. A process according to claim 1 in which an acid is present
during the contacting.
18. A process according to claim 17 in which the acid comprises
trifluoroacetic, methanesulfonic, fluorosulfonic,
fluoromethanesulfonic, trifluoromethanesulfonic, sulfuric, fuming
sulfuric, sulfurous, nitric, nitrous, phosphoric, phosphorous,
superphosphoric, or boric acid, or a selenium- and
tellurium-containing analog of the sulfur-containing acids, or a
mixture of two or more of the foregoing.
19. A process according to claim 17 in which the acid comprises
fuming sulfuric acid.
20. A process according to claim 17 in which the acid comprises
trifluoroacetic acid.
21. A process according to claim 17 in which the acid comprises
trifluoromethanesulfonic acid.
22. A process according to claim 1 in which the acetyl anhydride
comprises acetyl sulfate.
23. A process according to claim 1 in which the acetyl anhydride
comprises acetyl trifluoroacetate.
24. A process according to claim 1 in which the acetyl anhydride
comprises acetyl trifluoromethanesulfonate.
25. A process according to claim 1 in which the temperature is from
about 10 to about 200.degree. C.
26. A process according to claim 1 in which the temperature is from
about 60 to about 100.degree. C.
27. A process for producing acetic acid comprising: (a) contacting
methane and carbon dioxide in an anhydrous environment in the
presence of effective amounts of a transition metal catalyst and a
reaction promoter, and an acid anhydride compound, and optionally
an acid, to produce a product comprising an acetyl anhydride; and
(b) contacting the product of step (a) with water.
28. A process according to claim 27, further comprising: (c)
recovering acetic acid from the product of step (b).
29. A process according to claim 27 in which the catalyst is a
vanadium-containing catalyst.
30. A process according to claim 29 in which the catalyst is
selected from vanadium pentoxide, vanadium trioxide, sodium
metavanadate, vanadium-containing heteropolyacid catalysts and
vanadyl acetylacetonate.
31. A process according to claim 29 in which the catalyst is
vanadyl acetylacetonate.
32. A process according to claim 29 in which the reaction promoter
is selected from K.sub.2S.sub.2O.sub.8, K.sub.4P.sub.2O.sub.8,
calcium dioxide, urea-hydrogen peroxide and m-chloroperbenzoic
acid.
33. A process according to claim 32 in which the reaction promoter
is K.sub.2S.sub.2O.sub.8.
34. A process according to claim 27 in which the acid anhydride
compound comprises sulfur trioxide, sulfur dioxide, trifluoroacetic
acid anhydride, trifluoromethanesulfonic acid anhydride,
fluoromethanesulfonic acid anhydride, fluorosulfonic acid
anhydride, methanesulfonic acid anhydride, NO, NO.sub.2,
N.sub.2O.sub.5, P.sub.2O.sub.5, SeO.sub.3, AS.sub.2O.sub.5,
TeO.sub.3, or B.sub.2O.sub.3, or a mixture of two or more of the
foregoing.
35. A process according to claim 27 in which the acid anhydride
compound comprises trifluoroacetic acid anhydride.
36. A process according to claim 27 in which the acid anhydride
compound comprises trifluoromethanesulfonic acid anhydride.
37. A process according to claim 27 in which the acid anhydride
compound comprises sulfur trioxide.
38. A process according to claim 27 in which the acid anhydride
compound comprises fuming sulfuric acid.
39. A process according to claim 27 in which an acid is present
during the contacting.
40. A process according to claim 39 in which the acid comprises
trifluoroacetic, fluorosulfonic, methanesulfonic,
fluoromethanesulfonic, trifluoromethanesulfonic, sulfuric, fuming
sulfuric, sulfurous, nitric, nitrous, phosphoric, phosphorous,
superphosphoric or boric acid, or a selenium- or
tellurium-containing analog of the sulfur-containing acids, or a
mixture of two or more of the foregoing.
41. A process according to claim 39 in which the acid comprises
fuming sulfuric acid.
42. A process according to claim 39 in which the acid comprises
trifluoroacetic acid.
43. A process according to claim 39 in which the acid comprises
trifluoromethanesulfonic acid.
44. A process according to claim 27 in which the acetyl anhydride
comprises acetyl sulfate.
45. A process according to claim 27 in which the acetyl anhydride
comprises acetyl trifluoroacetate.
46. A process according to claim 27 in which the acetyl anhydride
comprises acetyl trifluoromethanesulfonate.
47. A process according to claim 27 in which step (a) is conducted
at a temperature of from about 10 to about 200.degree. C.
48. A process according to claim 27 in which the step (a) is
conducted at a temperature of from about 60 to about 100.degree.
C.
49. A process according to claim 27 further comprising recovering
acetic acid from step (b).
50. A process according to claim 39 in which an acid corresponding
to the acid used in step (a) is recovered from step (b), and said
acid is recycled to step (a).
51. A process for the production of an acetate ester comprising:
(a) contacting methane and carbon dioxide in an anhydrous
environment in the presence of effective amounts of a transition
metal catalyst and a reaction promoter, and an acid anhydride
compound, and optionally an acid, to produce a product comprising
an acetyl anhydride; and (b) reacting the product of step (a) with
an alcohol to produce a product comprising an acetate ester.
52. A process according to claim 51, further comprising (c)
recovering the acetate ester from the product of step (b).
53. A process according to claim 51 in which the product of step
(b) further comprises acetic acid, said process further comprising:
(c) recovering acetic acid from the product of step (b).
54. A compound having the formula
CH.sub.3C(O)--O--SO.sub.2CF.sub.3.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to the production of acetyl
anhydrides, and optionally of acetic acid, and particularly to a
process for the production of such substances from methane and
carbon dioxide.
[0002] The primary process route used today for production of
acetic acid is by catalytic reaction of methanol and carbon
monoxide. Such a process, typically termed "carbonylation", is
described in a number of patents and publications. Rhodium,
palladium or iridium-containing catalysts have been found
especially useful for conducting this reaction. A recent example of
a patent on such a process is U.S. Pat. No. 6,472,558 of Key et
al., which describes a process for reaction of methanol (and/or a
reactive derivative of methanol such as methyl acetate or dimethyl
ether) and carbon monoxide in a liquid reaction composition that
comprises methyl acetate, methyl iodide, acetic acid, water and a
polydentate phosphine oxide, in addition to the iridium
catalyst.
[0003] Another process route that has been found useful for the
production of acetic acid involves the catalytic oxidation of
ethane. Such processes are disclosed, for instance, in U.S. Pat.
No. 6,383,977 of Karim et al. and U.S. Pat. No. 6,399,816 of
Borchert et al. In the processes described in both patents, a mixed
oxide catalyst containing multiple metals is used. Karim et al.
discloses catalysts containing molybdenum, vanadium, niobium and
palladium, while Borchert et al. discloses containing molybdenum
and palladium, plus preferably vanadium, niobium, antimony, nickel
and calcium.
[0004] Methane is the lowest molecular weight, and simplest in
structure, of the hydrocarbons. Because of the existence of large
reserves of methane worldwide it has been considered desirable for
some time to develop processes to convert methane to more valuable
chemicals. Processes for production of acetic acid from methanol
represent an ultimate use of methane, but in current commercial
practice, the methane first must be converted to methanol. A
process that produces acetic acid directly from methane would be
more desirable.
[0005] A small amount of work has been conducted so far on the
direct conversion of methane to acetic acid, for instance by
reaction of methane with carbon dioxide. A process for production
of acetic acid by such a reaction was disclosed in the 1924 British
patent 226,248 of Dreyfus. The patent describes a process involving
gas phase reaction of methane with carbon monoxide and/or carbon
dioxide in the presence of a catalyst that preferably contains
nickel carbonate. Apparently a mixture of acetic acid, acetaldehyde
and possibly acetone is obtained. No data on yields or conversions
is contained in this patent.
[0006] PCT application WO 96/05163 of Hoechst A. G. describes a gas
phase reaction of methane and carbon dioxide to produce acetic
acid, using a catalyst containing one or more Group VIA, VIIA
and/or VIIIA metals. Selectivities of 70-95% based on methane are
asserted; however the application contains no exemplary data.
[0007] A number of researchers have investigated production of
acetic acid by liquid phase carbonylation of methane with carbon
monoxide, due to the favorable thermodynamics of this reaction.
See, for instance, Bagno, et al. J. Org. Chem. 1990, 55, 4284-4289;
Lin, et al., Nature 1994, 368, 613-615, Chaepaikin, et al., J. Mol.
Catal. A: Chem. 2001, 169, 89-98; Nishiguchi, et al., Chem. Lett.
1992, 1141-1142; Nakata, et al. J. Organomet. Chem. 1994, 473,
329-334; Kurioka, et al., Chem. Lett. 1995, 244; Fujiwara, et al.,
Studies in Surface Science and Catalysis 1998, 119, 349-353;
Taniguchi, et al., Org. Lett. 1999, 1(4), 557-559; Asadullah, et
al., Tetrahedron Lett. 1999, 40, 8867-8871; and Asadullah, et al.,
Chem. Int. Ed. 2000, 39(14), 2475-2478.
[0008] Kurioka et al. (1995, supra) also reported a liquid phase
experiment in which methane was reacted with carbon dioxide in the
presence of palladium acetate, cupric acetate, potassium persulfate
and trifluoroacetic acid, reportedly producing acetic acid. The
yield was said to have been 1650% (based on the palladium). This
work was continued and further reported on by Taniguchi et al.,
Studies in Surface Science and Catalysis 1998, 439-442. That
publication described a series of experiments in which methane and
carbon dioxide were reacted in the presence of catalysts, primarily
vanadium-containing catalysts such as vanadium(acac).sub.2
[acac=acetylacetonate], sodium metavanadate, and vanadium
pentoxide, and in the presence of liquids including pure
trifluoroacetic acid ("TFA") and aqueous solutions of TFA,
hydrochloric acid, sulfuric acid, and sodium hydroxide, as well as
simply in water. The best results were obtained in a system that
contained only TFA; the worst results were with water alone.
[0009] Taniguchi et al. (1998) hypothesized that the acetic acid
was produced by reaction of methane and carbon dioxide, but
subsequent work by others (and by us) showed that this was not
correct; in the Taniguchi et al. work the acetic acid would have
been produced primarily if not entirely by reaction of methane and
TFA, with concomitant production of one mole of fluoroform for each
mole of acetic acid produced by this reaction. TFA, however, is an
expensive feedstock for the production of acetic acid. In addition,
it is difficult to reconvert the fluoroform byproduct to TFA for
recycle or reuse.
[0010] Nizova et al., Chem. Commun. 1998, 1885 reported results of
reactions of methane with carbon monoxide in aqueous systems to
produce acetic acid. The authors mention that they had also
produced acetic acid by reaction of methane and carbon dioxide in
an aqueous system, in the presence of a sodium
metavanadate/pyrazine-2-carboxylic acid catalyst. However, the
yield (based on methane) appears to have been quite low and
pressures rather high (50 bar). Piao et al., J. Organomet. Chem.
1999, 574, 116-120 and Yin et al., Appl. Organomet. Chem. 2000, 14,
438-442 reported on catalytic partial oxidation of methane to
methyl trifluoroacetate, in the presence of trifluoroacetic acid
and a small amount of trifluoroacetic acid anhydride, but with no
CO or CO.sub.2 present. More recently, Reis et al., Angew. Chem.
Int. Ed. 2003, 42, 821 described production of acetic acid from
methane in a single-pot reaction, with trifluoroacetic acid and
various vanadium-containing catalysts, notably amavadine,
Ca[V[ON(CH(CH.sub.3)COO).sub.2).sub.2], but in the absence of
carbon dioxide.
[0011] It would be desirable to provide a process for production of
acetic acid more directly from methane, and particularly from a
process that involves methane and carbon dioxide rather than carbon
monoxide since carbon dioxide is relatively cheap, and additional
oxygen is not needed. A process conducted under relatively mild
conditions, adaptable to industrial use rather than a laboratory
curiosity, and with good conversions and/or yields, would be highly
desirable.
[0012] An improved process for the production of acetyl anhydrides
also would be desirable. An acetyl anhydride compound can be
defined as a compound, which upon reaction with water liberates
acetic acid and another non-hydrohalogenoic acid. Alternatively an
acetyl anhydride compound may be described as a compound in which
the hydroxy group of acetic acid has been replaced with the anion
of a non-hydrohalogenoic acid. Acetyl sulfate is one example of an
acetyl anhydride. It typically is produced by reacting acetic
anhydride with sulfuric acid and has a number of uses, for instance
as a sulfonating agent and as a chemical intermediate.
BRIEF SUMMARY OF THE INVENTION
[0013] This invention relates to a process for producing an acetyl
anhydride comprising:
[0014] contacting methane and carbon dioxide in an anhydrous
environment in the presence of effective amounts of a transition
metal catalyst and a reaction promoter, an acid anhydride compound,
and optionally an acid, to produce a product comprising the acetyl
anhydride.
[0015] In addition, the invention relates to a process for
producing a product comprising acetic acid from methane and carbon
dioxide comprising producing an acetyl anhydride as above, and then
reacting the product of this step with water.
[0016] In another aspect, the invention relates to a process for
producing a product comprising an acetate ester by reacting the
acetyl anhydride-containing product with an alcohol. Alternatively,
the acetyl anhydride could be hydrogenated to produce products
comprising ethanol, ethyl bisulfate, ethyl acetate, etc., depending
on the non-acetyl component of the anhydride.
[0017] Acetyl anhydrides produced as above may be novel compounds
and thus form another aspect of this invention.
[0018] In a further embodiment, the invention also comprises the
step of recovering acetic acid from the reaction product of the
acetyl anhydride and water, or recovering the acetate ester from
the reaction product of the acetyl anhydride and alcohol.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 depicts .sup.1H NMR analysis of a product obtained by
contacting methane, carbon dioxide, trifluoroacetic acid and
trifluoroacetic anhydride, then contacting the product with
water.
[0020] FIG. 2 depicts .sup.1H NMR analysis of a product produced by
contacting methane, carbon dioxide and fuming sulfuric acid, then
contacting the product with water.
[0021] FIG. 3 depicts .sup.1H NMR analysis of a product obtained by
contacting methane, carbon dioxide and fuming sulfuric acid, before
addition of water.
DETAILED DESCRIPTION OF THE INVENTION
[0022] This invention comprises a process for producing an acetyl
anhydride comprising contacting methane and carbon dioxide in an
anhydrous environment in the presence of effective amounts of a
transition metal catalyst and a reaction promoter, and an acid
anhydride compound, and optionally an acid, to produce a product
comprising the acetyl anhydride.
[0023] The invention further comprises a process for producing a
product comprising acetic acid in two steps, comprising:
[0024] (a) contacting methane and carbon dioxide in an anhydrous
environment in the presence of effective amounts of a transition
metal catalyst and a reaction promoter, and an acid anhydride
compound, and optionally an acid, to produce a product comprising
an acetyl anhydride; and
[0025] (b) contacting the reaction product of step (a) with
water.
[0026] In a further embodiment, the invention also comprises the
step of:
[0027] (c) recovering acetic acid from the product of step (b).
[0028] In another embodiment the invention comprises a process for
the production of a product comprising an acetate ester
comprising:
[0029] (a) contacting methane and carbon dioxide in an anhydrous
environment in the presence of effective amounts of a transition
metal catalyst and a reaction promoter and an acid anhydride
compound, and optionally an acid, to produce a product comprising
an acetyl anhydride; and
[0030] (b) reacting the product of step (a) with an alcohol to
produce a product comprising an acetate ester.
[0031] The product of step (b) may also comprise acetic acid.
[0032] The invention also comprises a process as above, and
additionally:
[0033] (c) recovering the acetate ester from the product of step
(b), and/or recovering acetic acid from the product of step
(b).
[0034] In the first step of the process of this invention, methane
and carbon dioxide are contacted, in the presence of a transition
metal catalyst, a reaction promoter and an acid anhydride compound,
and optionally an acid. The term "acid anhydride compound" as used
herein refers generally to a compound that reacts with water to
produce an acid. More particularly, for use in the processes of
this invention, an acid anhydride must be capable of maintaining
the reaction environment in an anhydrous state during the contact
of the methane and the carbon dioxide. Acid anhydrides suitable for
use in the processes of this invention include, for example, sulfur
trioxide, sulfur dioxide, trifluoroacetic acid anhydride,
trifluoromethanesulfonic acid anhydride, anhydrides of other
sulfonic acids such as fluorosulfonic acid anhydride,
fluoromethanesulfonic acid anhydride, methanesulfonic acid
anhydride, etc., NO, NO.sub.2, N.sub.2O.sub.5, P.sub.2O.sub.5,
SeO.sub.3, As.sub.2O.sub.5, TeO.sub.3, and B.sub.2O.sub.3. Some
acid anhydrides, such as anhydrides of longer chain carboxylic
acids, might not be suitable for use in the processes of this
invention, however, as they contain secondary methylene groups that
could interact with the reaction promoter.
[0035] The methane, carbon dioxide, and other materials preferably
are contacted in the presence of an acid that one the one hand acts
as a solvent but that may also participate as a reagent in the
process. Suitable acids include organic acids such as
trifluoroacetic, fluorosulfonic, methanesulfonic,
fluoromethanesulfonic, and trifluoromethanesulfonic acids, and
inorganic acids such as sulfuric, sulfurous, nitric, nitrous,
phosphoric, phosphorous, superphosphoric, and boric acids, as well
as selenium- and tellurium-containing analogs of the
sulfur-containing acids. Preferably the acid is the corresponding
acid of the acid anhydride compound used, e.g., when the acid
anhydride compound is trifluoroacetic acid anhydride the reaction
is conducted in the presence of trifluoroacetic acid, and when the
acid anhydride compound is sulfur trioxide the acid is sulfuric
acid, or in that case, more preferably fuming sulfuric acid is used
to supply both the acid and the anhydride. Mixtures of acid
anhydride compounds or of acids may be used, if desired.
[0036] In general, the molar ratios of the three substances
(methane: CO.sub.2: acid anhydride compound) are from about 0.5:1:1
to about 1:6:10, preferably from about 1:1:1 to about 1: 2:2
respectively. The amount of methane generally ranges from about 10
to about 50 mmol (from about 1 to about 5 mol/dm.sup.3, assuming
all the methane enters the liquid phase). The amount of carbon
dioxide generally ranges from about 5 to about 60 mmol (from about
0.5 to about 6 mol/dm.sup.3, assuming all the CO.sub.2 enters the
liquid phase). In general, this reaction is conducted at a
temperature of from about 10 to about 200.degree. C., preferably
from about 60 to about 100.degree. C., and for a time of from about
2 to about 48 hours, preferably from about 10 to about 20 hours.
The process can be either a batch or continuous process, but is
preferably a continuous process. The total pressure of the reaction
is suitably in the range 5 barg to 200 barg. The partial pressure
of methane is suitably in the range 2.5 barg to 100 barg, and the
partial pressure of carbon dioxide is suitably in the range 2.5
barg to 100 barg.
[0037] The liquid phase initially comprises the acid anhydride
compound and optionally the acid. The acid anhydride compound is
present in an amount constituting from about 1% to about 100% of
the liquid reaction composition, excluding catalysts and reaction
promoters (i.e., if no acid is present, the anhydride is the sole
initial liquid component in the process, not including catalyst and
reaction promoter). If an acid is used in the process, it is
present in the liquid reaction composition in an amount of from
about 0.1% to about 99% by weight, preferably from about 1% to
about 80% by weight. The acid concentration range is suitably
chosen depending on the acid and acid anhydride compound used in
the processes. The use of a higher amount of acid may be desirable
in order to improve solubility of a particular catalyst and/or
promoter in the liquid reaction composition. The acid should be
used in as dry a state as practicable.
[0038] Also present at this stage are a catalyst and a reaction
promoter.
[0039] Catalysts suitable for use in this process are transition
metal catalysts, particularly compounds of vanadium, chromium,
tantalum and niobium. Preferably the transition metal catalyst is a
vanadium-containing catalyst such as those known in the art to
catalyze reactions between methane and carbon dioxide. A preferred
catalyst is vanadyl acetylacetonate, VO(acac).sub.2, where "acac"
represents the group CH.sub.3COCHCOCH.sub.3. Other suitable
vanadium-containing catalysts include sodium metavanadate,
NaVO.sub.3, vanadium trioxide, vanadium pentoxide, and
heteropolyacid catalysts containing vanadium and other metallic
and/or non-metallic elements such as phosphorus, silicon,
molybdenum and tungsten. Suitable heteropolyacid catalysts are
disclosed in Taniguchi et al (1998) and Piao et al. (1999), both
supra. Still other suitable catalysts are the vanadium-containing
catalysts disclosed in Reis et al. (2003), supra, i.e.:
[0040] [VO(N(CH.sub.2CH.sub.2O).sub.3)],
[0041] [VO(N(CH.sub.2CH.sub.2O).sub.2(CH.sub.2COO)],
[0042] Ca[V(ON(CH(CH.sub.3)COO).sub.2).sub.2],
[0043] Ca[V(ON(CH.sub.2COO).sub.2).sub.2],
[0044] [VO(maltolate).sub.2] (maltolate is the basic form of
3-hydroxy-2-methyl-4-pyrone),
[0045] [VO(HOCH.sub.2CH.sub.2N(CH.sub.2CO.sub.2).sub.2)],
[0046] [VO(CF.sub.3COO).sub.2],
[0047] [VO(CF.sub.3SO.sub.3).sub.2], and
[0048] VOSO.sub.4.
[0049] Preferred catalysts of chromium, tantalum and niobium
include analogous substances such as the acetylacetonates, oxides,
salts of acids whose anions contain the metal (e.g., chromates),
and heteropolyacid catalysts containing them.
[0050] In general, the catalyst is used in an amount of from about
0.05 mmol to about 0.5 mmol (from about 0.005 to about 0.05
mol/dm.sup.3). The molar ratio of methane to catalyst is about
150:1.
[0051] Also used in the process is a reaction initiator, that is, a
compound that assists in commencement of the reaction through
free-radical initiation or other mechanism. Most of the well-known
and commonly used reaction initiators may be employed in this
process, providing they do not react with other components to form
side products or are otherwise undesirable. The preferred initiator
is potassium peroxysulfate, K.sub.2S.sub.2O.sub.8. Other suitable
initiators include K.sub.4P.sub.2O.sub.8, calcium dioxide,
urea-hydrogen peroxide and m-chloroperbenzoic acid. In general, the
initiator is used in an amount of from about 0.5 to about 20 mmol
(from about 0.05 to about 2 mol/dm.sup.3), preferably from about
3.5 to about 3.7 mmol (from about 0.35 to about 0.37
mol/dm.sup.3).
[0052] The overall reaction taking place in this process can
generally be depicted as
CH.sub.4+CO.sub.2+XO.sub.n.fwdarw.CH.sub.3C(O)--O--XO.sub.nH
[0053] where XO.sub.n is a binary acid anhydride compound, for
example SO.sub.3, and where the acid form of the binary anhydride
is optionally used as the solvent for the reaction, or it can be
depicted as
CH.sub.4+CO.sub.2+Z.sub.2O.fwdarw.CH.sub.3C(O)--O-Z+ZOH
[0054] where Z.sub.2O is an acid anhydride compound and where ZOH
is an oxygen-containing acid compound, which is optionally used as
the solvent for the reaction.
[0055] For example the overall reaction taking place in this
process can be depicted as
CH.sub.4+CO.sub.2+H.sub.2S.sub.2O.sub.7.fwdarw.CH.sub.3C(O)--O--SO.sub.3H+-
H.sub.2SO.sub.4
[0056] where fuming sulfuric acid (H.sub.2S.sub.2O.sub.7) is used
in the process, which may be alternatively written as
CH.sub.4+CO.sub.2+SO.sub.3.fwdarw.CH.sub.3C(O)--O--SO.sub.3H
[0057] (i.e. when fuming sulfuric acid is described as
H.sub.2SO.sub.4 plus SO.sub.3), and
CH.sub.4+CO.sub.2+(CF.sub.3SO.sub.2).sub.2O.fwdarw.CH.sub.3C(O)--O--SO.sub-
.2CF.sub.3+CF.sub.3SO.sub.3H
[0058] where trifluoromethanesulfonic anhydride is used, optionally
in the presence of trifluoromethanesulfonic as the acid
anhydride.
[0059] The product of this process, still in an anhydrous
environment, is a mixed anhydride of acetic acid and the acid
anhydride compound and/or a mixed anhydride of acetic acid and the
acid, if an acid is also used in the process. We term this mixed
anhydride an "acetyl anhydride".
[0060] If sulfuric or fuming sulfuric acid is used to produce the
acetyl anhydride, the product of the reaction is generally also
known as acetyl sulfate, which typically is used as a sulfonating
agent or as a chemical intermediate. For example, it can be
hydrogenated to provide ethanol, ethyl acetate or ethyl bisulfate.
Reaction of acetyl sulfate with alcohols produces alkyl acetates
and sulfuric acid. Acetyl sulfate is generally produced by reacting
acetic anhydride with sulfuric acid; consequently step (a) of the
process may serve as an alternate process for producing acetyl
sulfate. The acetyl anhydride resulting from a process in which
trifluoromethanesulfonic acid is used, or its anhydride is used
without the acid, is a novel compound, having the formula
CH.sub.3C(O)--O--SO.sub.2CF.sub.3, and forms an aspect of this
invention. Subsequent reaction of it with water produces acetic
acid and trifluoromethanesulfonic acid.
[0061] The addition of water to the acetyl anhydride is generally
performed at a temperature of from about 0 to about 100.degree. C.,
preferably from about 30 to about 60.degree. C., and is exothermic.
The resulting product is a mixture of acetic acid and the acid used
in the acetyl anhydride production, or of acetic acid and the acid
anhydride compound, if no acid is employed. The product may also
contain small amounts of by-products such as the methyl ester of
the starting acid. The acetic acid may readily be separated from
the reaction products by techniques such as azeotropic distillation
or membrane separation. The other acid may conveniently be recycled
to the acetyl anhydride production step.
[0062] If the acetyl anhydride is reacted with an alcohol to
produce a product comprising an acetate ester, the ester similarly
may be recovered from the reaction products by techniques such as
azeotropic distillation or membrane separation. The products of
such a reaction usually also include acetic acid and/or esters of
the other acid component of the acetyl anhydride (e.g.
trfluoroacetates, trifluoromethanesulfonates, etc.). The
proportions of these products would depend on factors such as
reaction stoichiometry, the nature of the reacting compounds, and
the like. Accordingly, acetic acid and/or esters of the other acid
could also be recovered from the products of this step, if
desired.
EXAMPLES
[0063] The following examples are presented as representative of
the invention. However, the invention is not limited thereby, as
those skilled in the art would readily recognize variants and
modifications of the processes as being within the nature and scope
of this invention.
[0064] General Procedure
[0065] In a typical reaction, CH.sub.4 and CO.sub.2 were reacted at
85.degree. C. in a high pressure, glass-lined autoclave.
K.sub.2S.sub.2O.sub.8 and a small amount of VO(acac)2 were
dissolved in [a mixture of?] an anhydrous acid and its
corresponding anhydride (fuming sulfuric acid,
H.sub.2SO.sub.4SO.sub.3, a mixture of H.sub.2SO.sub.4 and SO.sub.3;
CF.sub.3SO.sub.3H and trifluoromethanesulfonic acid anhydride;
trifluoroacetic acid and its anhydride, respectively). Reactions
were carried out for 16 h. Upon completion of the reaction, 2 g of
water were added to the liquid phase in order to hydrate any
anhydrides. The acetic acid thus formed was identified and
quantified by .sup.1H NMR.
[0066] To prepare acetic acid from fuming sulfuric acid or a
combination of trifluoromethanesulfonic acid and its anhydride, 3.7
mmol (0.37 mol/dm.sup.3) K.sub.2S.sub.2O.sub.8, 0.16 mmol
(1.6.times.10.sup.-2 mol/dm.sup.3) VO(acac).sub.2, and either 37.5
mmol (3.75 mol/dm.sup.3) of SO.sub.3 or 10.6 mmol (1.06
mol/dm.sup.3) of trifluoromethanesulfonic acid anhydride were
charged to a 100 ml glass lined Parr autoclave, together with a
small Teflon coated magnetic stir bar. For the preparation of
acetic acid using a combination of trifluoroacetic acid and its
anhydride, the amounts used were 3.7 mmol K.sub.2S.sub.2O.sub.8,
0.16 mmol VO(acac).sub.2, 10.0 g trifluoroacetic acid and 3.0 g of
its anhydride. The solvent was chilled to 5-8.degree. C. during
these additions to minimize the thermal decomposition of
K.sub.2S.sub.2O.sub.8. The reactor was then purged with N.sub.2 to
expel the air out of the system. It was then pressurized first with
120 psig CO.sub.2 and then finally with 80 psig methane from
adjacent connecting cylinders. The reactor was heated to 85.degree.
C. under stirring and maintained for 16-17 h. After that time, the
reactor was quenched with ice and opened to collect the reaction
mixture. Then 2.0 g of water were slowly added to the mixture,
which was then filtered. .sup.1H NMR analysis was then conducted.
The results for the reaction using trifluoroacetic acid/anhydride
are given in FIG. 1; those for fuming sulfuric acid are given in
FIG. 2(a). D.sub.2O was used in a capillary as the lock reference.
The corresponding chemical shifts for acetic acid was 2.3 ppm to
2.4 ppm, depending on the concentration of acetic acid in the
mixture.
[0067] Table 1 shows the effect of the starting acid on the
conversion of CH.sub.4 to acetic acid. The highest conversion (16%)
was obtained with trifluoroacetic anhydride and trifluoroacetic
acid. Approximately 7% conversion of CH.sub.4 to acetic acid was
obtained when fuming sulfuric acid was used, and 13% conversion
when trifluoromethanesulfonic acid anhydride and
trifluoromethanesulfonic acid were used. Small amounts of methyl
esters of the starting acids were produced as byproducts in each
reaction. To ensure that any CO or CO.sub.2 produced by the
oxidation of CH.sub.4 by K.sub.2S.sub.2O.sub.8 under the reaction
conditions was not responsible for acetic acid formation, a blank
reaction was performed in the absence of CO.sub.2. .sup.1H NMR
analysis of the product is shown in FIG. 2(b). Only byproducts were
detected. The absence of an acetic acid peak in the .sup.1H NMR
spectrum demonstrates clearly that the only source of CO.sub.2 is
that which was originally supplied to the reactor. The excess water
added to the mixture after completion of the reaction enables the
hydrolysis of byproduct CH.sub.3OSO.sub.3H to methanol and sulfuric
acid.
1 Direct reaction of CH.sub.4 and CO.sub.2 with different acid
anhydride compounds in the presence of various acids % conversion,
CH.sub.4 to Acid acetic acid Byproduct CF.sub.3COOH.sup.a 16
CF.sub.3COOCH.sub.3 H.sub.2SO.sub.4.sup.b 7 CH.sub.3OSO.sub.3H
CF.sub.3SO.sub.3H.sup.c 13 CF.sub.3SO.sub.3CH.sub.3 Reaction
conditions: CH.sub.4, 80 psig; CO.sub.2, 120 psig;
K.sub.2S.sub.2O.sub.8, 1 g (3.7 mmol); VO(acac).sub.2, 0.043 g
(0.16 mmol); solvent, 10.0 g; 85.degree. C.; 16 h.
.sup.aTrifluoroacetic acid anhydride, 3.0 g, was added.
.sup.bSO.sub.3, 3.0 g, was added. .sup.cTrifluoromethane-sulfoni- c
acid anhydride, 3.0 g, was added.
[0068] To aid in elucidating the pathway of acetic acid formation
from CH.sub.4 and CO.sub.2 in these acids, the same reaction in
sulfuric acid was run, but .sup.1H NMR was performed prior to
addition of water to the product mixture. The analytical results
are shown in FIG. 3. The product obtained in this reaction was
identified as the mixed anhydride of acetic acid and sulfuric acid,
CH.sub.3C(O)--OSO.sub.3H. Upon the addition of water, this mixed
anhydride hydrolyzes to produce acetic acid and H.sub.2SO.sub.4.
The presence of acetic acid was confirmed by distilling a
water-acetic acid azeotrope and then analyzing this mixture by
.sup.1H NMR and Raman spectroscopy (not shown).
[0069] All publications and patent applications cited in this
specification are herein incorporated by reference as if each
individual publication or patent application were specifically and
individually indicated to be incorporated by reference.
[0070] The use of the words "a" or "an" herein is intended to
include both singular and plural. This, for instance, "an acid",
"an anhydride compound", etc. may refer to a single acid or
anhydride or a mixture of such compounds
[0071] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it will be readily apparent to those of ordinary
skill in the art in light of the teachings of this invention that
certain changes and modifications may be made thereto without
departing from the spirit or scope of the appended claims.
* * * * *