U.S. patent application number 14/220893 was filed with the patent office on 2014-07-24 for method and system for production of oxalic acid and oxalic acid reduction products.
This patent application is currently assigned to Liquid Light, Inc.. The applicant listed for this patent is Liquid Light, Inc.. Invention is credited to Robert Augustine, Alexander Bauer, Emily Barton Cole, Farah Dhun, Robert Farrauto, Jerry J. Kaczur, Mohanreddy Kasireddy, Kate A. Keets, Theodore J. Kramer, George Leonard, Paul Majsztrik, Rishi Parajuli, Narayanappa Sivasankar, Setrak Tanielyan, Kyle Teamey, Yizu Zhu.
Application Number | 20140206896 14/220893 |
Document ID | / |
Family ID | 51208197 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140206896 |
Kind Code |
A1 |
Sivasankar; Narayanappa ; et
al. |
July 24, 2014 |
Method and System for Production of Oxalic Acid and Oxalic Acid
Reduction Products
Abstract
The present disclosure is a method and system for production of
oxalic acid and oxalic acid reduction products. The production of
oxalic acid and oxalic acid reduction products may include the
electrochemical conversion of CO.sub.2 to oxalate and oxalic acid.
The method and system for production of oxalic acid and oxalic acid
reduction products may further include the acidification of oxalate
to oxalic acid, the purification of oxalic acid and the
hydrogenation of oxalic acid to produce oxalic acid reduction
products.
Inventors: |
Sivasankar; Narayanappa;
(Plainsboro, NJ) ; Farrauto; Robert; (Monmouth
Junction, NJ) ; Augustine; Robert; (Monmouth Juction,
NJ) ; Tanielyan; Setrak; (Monmouth Junction, NJ)
; Kasireddy; Mohanreddy; (Monmouth Junction, NJ) ;
Cole; Emily Barton; (Houston, TX) ; Keets; Kate
A.; (Lawrenceville, NJ) ; Parajuli; Rishi;
(Kendell Park, NJ) ; Kaczur; Jerry J.; (North
Miami Beach, FL) ; Zhu; Yizu; (North Andover, MA)
; Dhun; Farah; (Monmouth Junction, NJ) ; Teamey;
Kyle; (Washington, DC) ; Bauer; Alexander;
(Monmouth Junction, NJ) ; Kramer; Theodore J.;
(New York, NY) ; Majsztrik; Paul; (Cranbury,
NJ) ; Leonard; George; (Princeton, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Liquid Light, Inc. |
Monmouth Junction |
NJ |
US |
|
|
Assignee: |
Liquid Light, Inc.
Monmouth Junction
NJ
|
Family ID: |
51208197 |
Appl. No.: |
14/220893 |
Filed: |
March 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US13/77610 |
Dec 23, 2013 |
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14220893 |
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13724996 |
Dec 21, 2012 |
8691069 |
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PCT/US13/77610 |
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61745204 |
Dec 21, 2012 |
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61794230 |
Mar 15, 2013 |
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61816531 |
Apr 26, 2013 |
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61844755 |
Jul 10, 2013 |
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61846944 |
Jul 16, 2013 |
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61720670 |
Oct 31, 2012 |
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61703232 |
Sep 19, 2012 |
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61675938 |
Jul 26, 2012 |
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Current U.S.
Class: |
560/204 ;
205/440; 205/443; 562/588; 568/864 |
Current CPC
Class: |
Y02P 20/10 20151101;
C07C 51/347 20130101; Y02P 20/127 20151101; C25B 9/08 20130101;
C25B 3/04 20130101; C07C 29/149 20130101; C07C 67/08 20130101; C07C
67/08 20130101; C07C 69/36 20130101; C07C 29/149 20130101; C07C
31/202 20130101 |
Class at
Publication: |
560/204 ;
562/588; 205/443; 205/440; 568/864 |
International
Class: |
C25B 3/04 20060101
C25B003/04; C07C 51/347 20060101 C07C051/347; C07C 29/149 20060101
C07C029/149; C07C 67/08 20060101 C07C067/08 |
Claims
1. A method for reduction of oxalic acid into products by a
reactor, comprising: receiving a solution of oxalic acid in a
reactor; receiving a feed of hydrogen in the reactor; reacting the
solution of oxalic acid and the hydrogen with a catalyst in the
reactor at a temperature in a range of 50.degree. to 170.degree. C.
to produce at least one of glycolic acid or mono-ethylene glycol,
the catalyst including at least one of cobalt, copper, ruthenium,
ruthenium dioxide, cobalt nickel alloys, nickel, Pt group metals,
rhenium, copper chromite, zinc copper chromite, barium chromite,
ammonium copper chromate, zinc chromate, Raney nickel, manganese
chromate, and alloys thereof.
2. The method according to claim 1, wherein the reacting the
solution of oxalic acid and the hydrogen with a catalyst includes
stirring a mixture of a rate of 200 RPM to 800 RPM.
3. The method according to claim 1, wherein the feed of hydrogen is
maintained at a pressure 300 psi to 1500 psi.
4. The method according to claim 1, wherein the reactor is Teflon
lined or glass lined.
5. The method according to claim 1, wherein the reactor includes
Hastelloy, Hastelloy 276, Hastelloy C or Elgiloy
6. A method for reduction of oxalic acid into products in an
electrochemical cell, the electrochemical cell including a first
region having a cathode and a second region having an anode, the
method comprising the steps of: contacting the first region with a
catholyte comprising oxalic acid; contacting the second region with
an anolyte; and applying an electrical potential between the anode
and the cathode sufficient to produce a glyoxylic acid recoverable
from the first region.
7. The method according to claim 6, wherein the anolyte includes
water.
8. The method according to claim 7, wherein oxygen is recoverable
from the second region.
9. The method according to claim 6, wherein the anolyte includes
HX, where X is selected from a group consisting of F, Cl, Br, I and
mixtures thereof.
10. The method according to claim 9, wherein a halogen is
recoverable from the second region.
11. A method of reduction of oxalic acid into products, comprising:
receiving oxalic acid in a reactive distillation column; receiving
an alcohol in the reactive distillation column; and reacting the
oxalic acid with the alcohol in the reactive distillation column,
wherein a dialkyl oxalate is generated from reacting the oxalic
acid with the alcohol and is separated from a solution of the
reactive distillation column in a section of the reactive
distillation column.
12. The method according to claim 11, wherein said alcohol is one
of ethanol, butanol or methanol.
13. The method according to claim 11, wherein the reactive
distillation column includes an upper section, a middle section and
a lower section.
14. The method according to claim 13, wherein the dialkyl oxalate
is generated from reacting the oxalic acid with the alcohol and is
separated from a solution of the reactive distillation column in
the lower section of the reactive distillation column.
15. The method according to claim 14, wherein the middle section
includes an acid catalyst.
16. The method according to claim 15, wherein the oxalic acid is
received in the upper section of the reactive distillation column
and the alcohol is received in the lower section of the reactive
distillation column.
17. The method according to claim 11, further comprising: receiving
the dialkyl oxalate at a hydrogenation device to produce a dialkyl
oxalate reduction product.
18. A method for producing a first product from a first region of
an electrochemical cell having a cathode and a second product from
a second region of the electrochemical cell having an anode, the
electrochemical cell having a separator that separates the first
region and the second region, the method comprising the steps of:
contacting the first region with a catholyte comprising carbon
dioxide and a non-aqueous solvent; contacting the second region
with an anolyte, the anolyte comprising MX and the non-aqueous
solvent; and applying an electrical potential between the anode and
the cathode sufficient to produce an oxalate recoverable from the
first region and a halogen recoverable from the second region.
19. The method according to claim 18, wherein the cathode is formed
of one or more of metal plates, packed bed of metal spheres or
fibers, screens, meshes, metal foams, metal non-woven materials,
sintered non-wovens, metal wools, sintered metal fibers, woven
metal felts, metal woven fibrous materials, metal coated carbon
materials and metal coated ceramic materials.
20. The method according to claim 18, wherein the anode is formed
of one or more of plates, RVC, carbon cloth, PTFE, carbon tissue,
carbon felts, carbon fibers, conductive diamond films, iridium
oxide on titanium, ruthenium oxide, graphine and graphite.
21. The method according to claim 18, wherein the separator is
formed of one or more of polymeric porous materials, inorganic
filtration materials, perfluorinated ionomers, combination hybrid
organic-Inorganic membranes, hydrocarbon based membranes and solid
state ion conductors.
22. The method according to claim 18, where X is selected from a
group consisting of F, Cl, Br, I and mixtures thereof.
23. The method according to claim 18, wherein the halogen includes
at least one of F.sub.2, Cl.sub.2, Br.sub.2, I.sub.2, F.sub.3--,
Cl.sub.3--Br.sub.3-- or I.sub.3--.
24. The method according to claim 18, wherein the cathode includes
at least one of Al, Au, Ag, Bi, C, Cd, Co, Cr, Cu, Cu.sub.2O, Cu,
Fe, Ga, Hg, In, Mo, Nb, Ni, NiCo.sub.2O.sub.4, Ni--Fe, Pb, Pd Pt,
Rh, Sn, Ti, V, W, Zn, stainless steel, austenitic steel, ferritic
steel, duplex steel, martensitic steel, Nichrome, elgiloy
Hastelloy, metal carbides and alloys thereof.
25. The method according to claim 24, said cathode includes nickel
or a nickel alloy.
26. The method according to claim 18, wherein the non-aqueous
solvent includes at least one of propylene carbonate, ethylene
carbonate, dimethyl carbonate, diethyl carbonate,
dimethylsulfoxide, dimethylformamide, acetonitrile, ammonia,
acetone, tetrahydrofuran, N,N-dimethylacetaminde, dimethoxyethane,
diethylene glycol dimethyl ester, butyrolnitrile,
1,2-difluorobenzene, .gamma.-butyrolactone, N-methyl-2-pyrrolidone,
sulfolane, 1,4-dioxane, nitrobenzene, nitromethane, acetic
anhydride, alkanes, cycloalkanes, perfluorocarbons, linear
carbonates, aromatics such as benzene and toluene and their
derivatives, dichloromethane, chloroform, ethers, chlorobenzene,
polyols, glymes, diglymes, triglymes, tetraglymes, alcohols,
alkenes, trifluorotoluene, anisole, m-cresol, and ionic liquids to
include those containing cations of the types: 1,3
dialkyimidazolium, N,N dialkylpyrrolidinium, and
1-alkyl-2,3-dimethylimidazolium where N=2 or 4 and anions of the
type hexafluorophosphate, tetrafluroborate,
bis(trifluoromethanesulfonyl)imide, perfluoroalkylphosphate, and
halide ions such as Br--
27. The method according to claim 18, wherein the oxalate is
M.sub.NC.sub.2O.sub.4, N is 1 or 2.
28. The method according to claim 18, wherein M is Li.sup.+,
Na.sup.+, K.sup.+, Ca.sup.++, Ba.sup.++, Sr.sup.++, Mg.sup.++, a
R.sub.1R.sub.2R.sub.3R.sub.4N.sup.+, K.sup.- where each of
R.sub.1-4 is independently selected from the group consisting of
alkyl, branched alkyl, cycloalkyl, and aryl, tetraalkyl ammonium,
tetramethylammonium, tetraethylammonium, tetrabutylammonium,
tetraphenylphosphonium, tetrabutylphosphonium,
tetraethylphosphonium, tetrahexylammonium, tetraoctylammonium,
methyl tributylammonium, butyltrimethylammonium,
1-n-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium,
1-ethyl-1-methylpyrrolidinium, di-n-decyldimethylammonium, choline,
or ammonium.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit under 35 U.S.C.
.sctn.120 of PCT application, International application No.
PCT/US2013/077610 filed Dec. 23, 2013. PCT application,
International application No. PCT/US2013/077610 filed Dec. 23, 2013
is incorporated by reference in its entirety.
[0002] PCT application, International application No.
PCT/US2013/077610 filed Dec. 23, 2013 claims the benefit under 35
U.S.C. .sctn.119(e) of U.S. Provisional Application Ser. No.
61/745,204 filed Dec. 21, 2012, U.S. Provisional Application Ser.
No. 61/794,230 filed Mar. 15, 2013, U.S. Provisional Patent
Application Ser. No. 61/816,531 filed Apr. 26, 2013, U.S.
Provisional Patent Application Ser. No. 61/844,755 filed Jul. 10,
2013 and U.S. Provisional Patent Application No. 61/846,944 filed
Jul. 16, 2013. Said U.S. Provisional Application Ser. No.
61/745,204 filed Dec. 21, 2013, U.S. Provisional Application Ser.
No. 61/794,230 filed Mar. 15, 2013, U.S. Provisional Patent
Application Ser. No. 61/816,531 filed Apr. 26, 2013, U.S.
Provisional Patent Application Ser. No. 61/844,755 filed Jul. 10,
2013 and U.S. Provisional Patent Application No. 61/846,944 filed
Jul. 16, 2013 are hereby incorporated by reference in their
entireties.
[0003] PCT application, International application No.
PCT/US2013/077610 filed Dec. 23, 2013 claims the benefit under 35
U.S.C. .sctn.120 of U.S. patent application Ser. No. 13/724,996
filed Dec. 21, 2012. U.S. patent application Ser. No. 13/724,996
claims the benefit under 35 U.S.C. .sctn.119(e) of U.S. Provisional
Application Ser. No. 61/720,670 filed Oct. 31, 2012, U.S.
Provisional Application Ser. No. 61/703,232 filed Sep. 19, 2012 and
U.S. Provisional Application Ser. No. 61/675,938 filed Jul. 26,
2012. Said U.S. patent application Ser. No. 13/724,996, said U.S.
Provisional Application Ser. No. 61/720,670 filed Oct. 31, 2012,
U.S. Provisional Application Ser. No. 61/703,232 filed Sep. 19,
2012 and U.S. Provisional Application Ser. No. 61/675,938 filed
Jul. 26, 2012 are incorporated by reference in their
entireties.
TECHNICAL FIELD
[0004] The present disclosure generally relates to the field of
electrochemical reactions, and more particularly to a method and
system for production of oxalic acid and oxalic acid reduction
products.
BACKGROUND
[0005] The combustion of fossil fuels in activities such as
electricity generation, transportation, and manufacturing produces
billions of tons of carbon dioxide annually. Research since the
1970s indicates increasing concentrations of carbon dioxide in the
atmosphere may be responsible for altering the Earth's climate,
changing the pH of the ocean and other potentially damaging
effects. Countries around the world, including the United States,
are seeking ways to mitigate emissions of carbon dioxide.
[0006] A mechanism for mitigating emissions is to convert carbon
dioxide into economically valuable materials such as fuels and
industrial chemicals. If the carbon dioxide is converted using
energy from renewable sources, both mitigation of carbon dioxide
emissions and conversion of renewable energy into a chemical form
that can be stored for later use will be possible.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0007] The present disclosure is directed to a method and system
for production of oxalic acid and oxalic acid reduction products.
The production of oxalic acid and oxalic acid reduction products
may include the electrochemical conversion of CO.sub.2 to oxalate
and oxalic acid. The method and system for production of oxalic
acid and oxalic acid reduction products may further include the
acidification of oxalate to oxalic acid, the purification of oxalic
acid and the hydrogenation of oxalic acid to produce oxalic acid
reduction products.
[0008] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not necessarily restrictive of the
present disclosure. The accompanying drawings, which are
incorporated in and constitute a part of the specification,
illustrate subject matter of the disclosure. Together, the
descriptions and the drawings serve to explain the principles of
the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The numerous advantages of the disclosure may be better
understood by those skilled in the art by reference to the
accompanying figures in which:
[0010] FIG. 1 is a schematic illustrating a system for the
electrochemical reduction of carbon dioxide to oxalate; the
conversion of oxalate to oxalic acid; and the conversion of oxalic
acid to other products.
[0011] FIG. 2 is a schematic illustrating a system for the
electrochemical reduction of carbon dioxide to oxalate; the
conversion of oxalate to oxalic acid; and the conversion of oxalic
acid to other products.
[0012] FIG. 3 is a schematic illustrating a system for the
electrochemical reduction of carbon dioxide to oxalate; the
conversion of oxalate to oxalic acid; and the conversion of oxalic
acid to other products.
[0013] FIG. 4 is a schematic illustrating a process for converting
oxalate salts to oxalic acid.
[0014] FIG. 5 is a schematic illustrating a process for converting
oxalate salts to oxalic acid.
[0015] FIGS. 6A-6C are schematics illustrating hydrogenation
devices for reducing oxalic acid to products.
[0016] FIG. 7 is a schematic illustrating an electrochemical cell
for converting oxalate salts to oxalic acid.
[0017] FIG. 8 is a schematic illustrating a system for converting
carbon dioxide to oxalic acid.
[0018] FIGS. 9A-9C are schematics illustrating a electrochemical
cells for converting carbon dioxide to oxalic acid.
[0019] FIG. 10 is a schematic illustrating a system for the
conversion of carbon dioxide to mono-ethylene glycol.
[0020] FIG. 11 is a schematic illustrating a system for the
conversion of carbon dioxide to mono-ethylene glycol.
[0021] FIG. 12 is a schematic illustrating a system for the
conversion of carbon dioxide to mono-ethylene glycol.
[0022] FIG. 13 is a schematic illustrating a system for the
conversion of carbon dioxide to mono-ethylene glycol.
[0023] FIG. 14 is a schematic illustrating a system for the
conversion of carbon dioxide to mono-ethylene glycol and other
two-carbon products.
[0024] FIG. 15 is a schematic illustrating the possible
intermediates in the catalytic hydrogenation of oxalic acid to
mono-ethylene glycol.
[0025] FIG. 16 is a schematic illustrating the components of a
thermal catalytic hydrogenation system.
[0026] FIG. 17 is a schematic illustrating a reactive distillation
column.
[0027] FIG. 18 is a schematic illustrating a process for the
conversion of carbon dioxide to two-carbon products such as
mono-ethylene glycol.
[0028] FIG. 19 is a schematic illustrating a process for purifying
oxalic acid.
[0029] FIG. 20 is a schematic illustrating a process for purifying
oxalic acid.
[0030] FIG. 21 is a schematic illustrating a process for purifying
oxalic acid.
[0031] FIG. 22 is a schematic illustrating a process for purifying
oxalic acid.
[0032] FIG. 23 is a schematic illustrating an electrochemical
acidification cell and a process for the conversion of oxalate to
oxalic acid.
[0033] FIG. 24 is a schematic illustrating a process for the
conversion of an oxalate salt to oxalic acid.
[0034] FIG. 25 is a schematic illustrating a process for the
electrochemical reduction of halide and trihalide.
[0035] FIG. 26 is a schematic illustrating a process for the
conversion of oxalic acid to mono-ethylene glycol.
[0036] FIG. 27 is a schematic illustrating a process for the
conversion of oxalic acid to mono-ethylene glycol.
[0037] FIG. 28 is a schematic illustrating an electrochemical
process for the conversion of carbon dioxide to oxalate.
[0038] FIG. 29 is a schematic illustrating an integrated
acidification-esterification-hydrogenation system.
[0039] FIG. 30 is a schematic illustrating an integrated
acidification-esterification-hydrogenation system is shown.
DETAILED DESCRIPTION
[0040] Reference will now be made in detail to the subject matter
disclosed, which is illustrated in the accompanying drawings.
[0041] The present disclosure is directed to a method and system
for production of oxalic acid and oxalic acid reduction
products.
[0042] Before any embodiments of the disclosure are explained in
detail, it is to be understood that the embodiments may not be
limited in application per the details of the structure or the
function as set forth in the following descriptions or illustrated
in the figures. Different embodiments may be capable of being
practiced or carried out in various ways. Also, it is to be
understood that the phraseology and terminology used herein is for
the purpose of description and should not be regarded as limiting.
The use of terms such as "including," "comprising," or "having" and
variations thereof herein are generally meant to encompass the item
listed thereafter and equivalents thereof as well as additional
items. Further, unless otherwise noted, technical terms may be used
according to conventional usage. It is further contemplated that
like reference numbers may describe similar components and the
equivalents thereof.
[0043] The following definitions are used: TAA--tetraalkylammonium;
TAAX--tetraalkylammonium halide; TBA--tetrabutylammonium;
TBAX--tetrabutylammonium halide; TBABr--tetrabutylammonium bromide;
TBAP--tetrabutylammonium perchlorate; TPABr--tetrapropylammonium
bromide; TBAOx or TBA.sub.2Ox or TBAO--tetrabutylammonium oxalate;
PC--propylene carbonate; ACN--acetonitrile; CO.sub.2--carbon
dioxide; HBr--Hydrobromic acid; BUTY--Gamma butyrolactone,
.gamma.-butyrolactone; OA--oxalic acid; DEO--diethyl oxalate;
DMO--dimethyl oxalate; EtOH--ethanol; BuOH--butanol; DBO--dibutyl
oxalate
[0044] Electrochemical conversion of CO.sub.2 to oxalate may be
undertaken in non-aqueous media to achieve high yields. However,
oxalate is a salt that has limited utility. The acid form of
oxalate, oxalic acid, has many more industrial uses and may
advantageously be used as an intermediate for the production of a
large variety of chemical compounds such as glyoxylic acid,
glyoxylate, glycolic acid, glycolate, glyoxal, glycolaldehyde,
ethylene glycol, acetic acid, acetaldehyde, ethanol, ethane,
ethylene, and certain metal oxalates such as ferrous oxalate. An
economical process of acidifying oxalate to oxalic acid in a
combined process with CO.sub.2 to oxalate conversion is therefore
advantageous. As used herein, it should be understood that ethylene
glycol may also be referred as monoethylene glycol and
mono-ethylene glycol and may be simply referred as (MEG). As used
herein, ethylene glycol, mono-ethylene glycol, monoethylene glycol
and MEG may be used interchangeably and may refer to the chemical
of C.sub.2H.sub.6O.sub.2.
[0045] A second problem in non-aqueous CO.sub.2 electrochemical
conversion is finding an appropriate anodic process. Halogens may
be produced, but these are not always marketable because of their
high toxicity. The present disclosure may include a method and
system for production of oxalic acid and oxalic acid reduction
products which advantageously produces no toxic compounds. When
production of a halogen is desired, however, another embodiment may
include the anodic generation of a halogen and cathodic production
of oxalate or oxalic acid depending upon the specific process
employed.
[0046] Referring to FIG. 1, a schematic illustrating a system 100
for the electrochemical reduction of carbon dioxide to oxalate; the
conversion of oxalate to oxalic acid; and the conversion of oxalic
acid to other products is shown. System 100 may be configured for
production of oxalic acid and oxalic acid reduction products in
accordance with an embodiment of the present disclosure.
[0047] It is contemplated that system 100 may operate according to
the overall chemical equation:
4CO.sub.2+2H.sub.2O.fwdarw.2H.sub.2C.sub.2O.sub.4+O.sub.2 [1]
[0048] Advantageously, a halogen and halide salt may be recycled
and may not be consumed in the reactions of system 100.
[0049] System 100 may include an electrochemical cell (also
referred as a container, electrolyzer, or cell) 102.
Electrochemical cell 102 may be implemented as a divided cell. The
divided cell may be a divided electrochemical cell. Electrochemical
cell 102 may include a first region 116 and a second region 118.
First region 116 and second region 118 may refer to a compartment,
section, or generally enclosed space, and the like without
departing from the scope and intent of the present disclosure.
First region 116 may include a cathode 122. Second region 118 may
include an anode 124. First region 116 may include a catholyte, the
catholyte including carbon dioxide which may be dissolved in the
catholyte. Second region 118 may include an anolyte which may
include MX 117.
[0050] Electrochemical cell 102, and all electrochemical cells
described herein, uses an energy source, not shown, which may
generate an electrical potential between the anode 124 and the
cathode 122. The electrical potential may be a DC voltage. Energy
source 114 may also be configured to supply a variable voltage or
constant current to electrochemical cell 102 or any electrochemical
described herein.
[0051] Separator 120 may selectively control a flow of ions between
the first region 116 and the second region 118. Separator 120 may
include an ion conducting membrane, separator, or diaphragm
material.
[0052] Electrochemical cell 102 is generally operational to reduce
carbon dioxide in the first region 116 to a first product, such as
an oxalate. Oxalate 113 may be referred as an oxalate salt and may
include a general formula of M.sub.nC.sub.2O.sub.4 where N=1 or 2.
Oxalate 113 may be recoverable from the first region 116 while a
second product, such as a halogen or trihalide anion 115, may be
recoverable from the second region 118. Carbon dioxide source 106
may provide carbon dioxide to the first region 116 of
electrochemical cell 102. In some embodiments, the carbon dioxide
is introduced directly into the region 116 containing the cathode
122. It is contemplated that carbon dioxide source 106 may include
a source of a mixture of gases in which carbon dioxide has been
separated from the gas mixture.
[0053] It is contemplated that a first product, such as oxalate,
may be extracted by a first product extractor, not shown. First
product extractor may implement an organic product and/or inorganic
product extractor. First product extractor may be generally
operational to extract (separate) the first product, such as
oxalate 113, from the first region 116. The extracted oxalate 113
may be presented through a port of the system 100 for subsequent
storage and/or consumption by other devices and/or processes.
[0054] The anode side of the reaction occurring in the second
region 118 of electrochemical cell 102, and any other
electrochemical cells described herein, may include MX 117 supplied
to the second region 118. MX 117 may also comprise MX.sub.2 if two
anions are need for charge balance. Salt MX 117 may act as both an
anodic reactant as well as a supporting electrolyte. The second
product recoverable from the second region 118 may be a halogen or
trihalide ion 115. MX 117 may include a cation, as M may be
Li.sup.+, Na.sup.+, K.sup.+, Ca.sup.++, Ba.sup.++, Sr.sup.++,
Mg.sup.++, a R.sub.1R.sub.2R.sub.3R.sub.4N.sup.+, K.sup.- where
each of R.sub.1-4 is independently selected from the group
consisting of alkyl, branched alkyl, cycloalkyl, and aryl,
tetraalkyl ammonium, tetramethylammonium, tetraethylammonium,
tetrabutylammonium, tetraphenylphosphonium, tetrabutylphosphonium,
tetraethylphosphonium, tetrahexylammonium, tetraoctylammonium,
methyl tributylammonium, butyltrimethylammonium,
1-n-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium,
1-ethyl-1-methylpyrrolidinium, di-n-decyldimethylammonium, choline,
or ammonium. To increase electrolyte solubility, crown ethers, such
as 12-crown-4, 15-crown-5, diphenyl-18-crown-6, and 18-crown-6, may
be used with the cation such as Li.sup.+, Na.sup.+, or K.sup.+. The
electrolyte used will also determine the type of membrane or
separator that may be selected for the electrochemical cell 102.
Ionic liquids may also be employed as electrolytes, as well as
CTAB, hexadecyltributyl phosphonium bromide, and the Stark
catalyst. X may include F, Cl, Br, I, BF.sub.4, PF.sub.6,
ClO.sub.4, or an anion; and mixtures thereof.
[0055] It is contemplated that a second product, such as halogen or
trihalide anion 115, may be extracted by a second product
extractor, not shown. Second product extractor may implement an
organic product and/or inorganic product extractor. Second product
extractor may be generally operational to extract (separate) the
second product, such as a halogen or trihalide anion 115, from the
second region 118. The extracted halogen or trihalide anion 115 may
be presented through a port of the system 100 for subsequent
storage and/or consumption by other devices and/or processes. It is
contemplated that first product extractor 110 and/or second product
extractor 112 may be implemented with electrochemical cell 102, or
may be remotely located from the electrochemical cell 102.
Additionally, it is contemplated that first product extractor
and/or second product extractor 112 may be implemented in a variety
of mechanisms and to provide desired separation methods, such as
fractional distillation or molecular sieve drying, without
departing from the scope and intent of the present disclosure.
[0056] In one embodiment, electrochemical cell 102 may reduce
CO.sub.2 to an oxalate salt (M.sub.2O.sub.2O.sub.4) at the cathode
122 and may oxidize a halogen containing salt of the formula MX,
where M is a cation and X is a halide anion, at the anode 124
produce a halogen or trihalide anion 115. This liberates the cation
(M.sup.+) to be transferred across a membrane or separator 120 to
pair with the oxalate anion in the first region 116, or also
referred as the catholyte compartment. An oxidation resistant
cation exchange membrane or separator may be employed as the
separator 120.
[0057] Halogen or trihalide anion 115 may be fed to an
electrochemical reduction cell 130. It is contemplated that
electrochemical reduction cell 130 may be similar to
electrochemical cell 102. For example, electrochemical reduction
cell 130 may include a first region and a second region. First
region and second region may refer to a compartment, section, or
generally enclosed space, and the like without departing from the
scope and intent of the present disclosure. First region may
include a cathode. Second region 118 may include an anode 124.
Electrochemical reduction cell 130 may reduce halogen or trihalide
anion 115 to HX 132 at the cathode and oxidizes water 134 at the
anode, producing oxygen (O.sub.2) and liberating hydrogen ions
(H.sup.+) to be transferred across the membrane of the
electrochemical reduction cell 130 to generate the HX 132.
[0058] Oxalate 113 may be fed to an anion exchanger 140. Anion
exchanger 140 may refer to an ion exchanger that exchange
negatively charged ions, the anions. Anion exchanger 140 may
convert oxalate 113 to oxalic acid 144 using the HX 132 produced
from electrochemical reduction cell 130. Anion exchanger 140 may
further produce MX 117 which may be recycled to the second region
118 of electrochemical cell 102.
[0059] Oxalic acid 144 may be further converted to a range of more
reduced two-carbon (or O.sub.2) species. Oxalic acid 144 may be fed
to a hydrogenation device 150, such as a thermal catalytic
hydrogenation device or electrochemical reduction device. Oxalic
acid 144 may be converted to an oxalic acid reduction product 152.
Oxalic acid reduction product 152 may include two-carbon species
such as glyoxylic acid, glyoxal, glycolic acid, glycolaldehyde,
acetaldehyde, ethylene glycol, ethanol, acetic acid, ethane, or
ethylene. Oxalic acid may also be converted to alkyl oxalates such
as dimethyl oxalate by reaction with an alcohol.
[0060] Referring to FIG. 2, a schematic illustrating a system 200
for the electrochemical reduction of carbon dioxide to oxalate; the
conversion of oxalate to oxalic acid; and the conversion of oxalic
acid to other products is shown. System 200 may include
electrochemical cell 102, electrochemical cell 210 and
hydrogenation device 150.
[0061] Similar to system 100, electrochemical cell 102 of system
200 may reduce CO.sub.2 from carbon dioxide source 106 to an
oxalate salt (M.sub.2O.sub.2O.sub.4) at the cathode 122 and
oxidizes a halogen containing salt of the formula MX, where M is a
cation and X is a halide anion, at the anode 124 to produce a
halogen or trihalide anion 115. This liberates the cation (M.sup.+)
to be transferred across a membrane or separator 120 to pair with
the oxalate anion in the first region 116, or also referred as the
catholyte compartment. An oxidation resistant cation exchange
membrane may be employed as the separator 120.
[0062] Electrochemical cell 210, also referred to an
electrochemical acidification unit, may include three regions or
compartments. Electrochemical cell 210 may include a first region
116, a second region 118 and a third region 212. Third region 212
may be a central ion exchange region bounded by two cation exchange
membranes or separators 214, 216. First region 116 may include a
cathode 116 and may be fed halogen or trihalide anion 115 from the
second region of electrochemical cell 102. Second region 118 may
include an anode 124 and may be fed water 220. Electrochemical cell
210 may be configured to acidify the oxalate salt fed to the
central ion exchange region 212 to produce oxalic acid 144. MX may
be recoverable from first region 116 of electrochemical cell 210
and recycled to the second region 118 of electrochemical cell 102.
In the second region 118 of electrochemical cell 210, the anode
reaction may generate hydrogen ions that pass through the adjoining
cation membrane 216 into the ion exchange region 212. Oxygen 222
may be produced from the oxidation of water that may be recoverable
from the second region 118. It is contemplated that the second
region 118 of electrochemical cell 210 may include an acid
electrolyte such as sulfuric acid.
[0063] Oxalic acid 144 may be further converted to a range of more
reduced two-carbon species. Oxalic acid 144 may be fed to a
hydrogenation device 150, such as a thermal catalytic hydrogenation
device or electrochemical reduction device. Oxalic acid 144 may be
converted to an oxalic acid reduction product 152. It is
contemplated that system 200 may operate according to the overall
chemical equation:
4CO.sub.2+2H.sub.2O.fwdarw.2H.sub.2O.sub.2O.sub.4+O.sub.2 [2]
[0064] Referring to FIG. 3, a schematic illustrating a system 300
for the electrochemical reduction of carbon dioxide to oxalate; the
conversion of oxalate to oxalic acid; and the conversion of oxalic
acid to other products is shown. System 300 may include an
electrochemical cell 102, an anion exchanger 140, and a
hydrogenation device 150.
[0065] Similar to system 100, electrochemical cell 102 of system
300 may reduce CO.sub.2 from carbon dioxide source 106 to an
oxalate salt (M.sub.2O.sub.2O.sub.4) at the cathode 122 and oxidize
a halogen containing salt of the formula MX, where M is a cation
and X is a halide anion, at the anode 124 to produce a halogen or
trihalide anion 115. This liberates the cation (M.sup.+) to be
transferred across a membrane or separator 120 to pair with the
oxalate anion in the first region 116, or also referred as the
catholyte compartment. An oxidation resistant cation exchange
membrane may be employed as the separator 120.
[0066] It is contemplated that halogen or trihalide anion 115
recoverable from the second region 118 of electrochemical cell 102
may be extracted as a saleable product or as a product that may be
used in a separate process, such as a bromination reaction with an
organic producing a brominated organic, such as the reaction of
bromine with ethane to produce bromoethane, as well as other
bromination reactions in producing fine chemicals.
[0067] Oxalate 113 may be fed to anion exchanger 140. Anion
exchanger 140 may refer to an ion exchanger that exchanges
negatively charged ions, the anions. Anion exchanger 140 may
convert oxalate 113 to oxalic acid 144 using the HX received from
an HX source 310. Anion exchanger 140 may further produce MX 117
which may be recycled to the second region 118 of electrochemical
cell 102. The overall chemical reaction of system 300 may be
represented by:
2CO.sub.2+2HX.fwdarw.H.sub.2O.sub.2O.sub.4+X.sub.2 [3]
[0068] The HX source 310, configured to flow as a HX stream could
be a purchased reagent in the process or could be utilized as part
of a larger process scheme involving further reactions, such that
the HX is recycled--for example, from the bromination of organics,
which produces an HX byproduct.
[0069] Referring to FIG. 4, a schematic illustrating a process for
converting oxalate salts to oxalic acid is shown. The inputs of the
anion exchange resin may include primary inputs such as a solvent,
oxalate, and MX with regenerants such as water and HX. The anion
exchange resin may produce a recycle stream that may include a
solvent and MX and may produce a product stream of oxalic acid,
water and HX. FIG. 5 is a schematic illustrating a process for
converting oxalate salts to oxalic acid. Process may include an
oxalate absorption process, a water rinse process, an oxalate
desorption process 530 and a solvent rinse process.
[0070] Referring to FIGS. 6A-6C, schematics illustrating
hydrogenation devices 150 for reducing oxalic acid to products are
shown. FIG. 6A depicts a thermal catalytic hydrogenation device 610
that may receive oxalic acid and hydrogen and may produce an oxalic
acid reduction product and water. FIG. 6B depicts an
electrochemical hydrogenation cell 620. Electrochemical
hydrogenation cell 620 may include an oxalic acid input to the
catholyte region and a water input to the anolyte region. An oxalic
acid reduction product may be recovered from the catholyte region
and oxygen may be recovered from the anolyte region of the
electrochemical reduction cell 620. FIG. 6C depicts an
electrochemical reduction cell 630 in accordance with another
embodiment of the present disclosure. Electrochemical reduction
cell 630 may include an oxalic acid input to the catholyte region
and a HX input to the anolyte region. An oxalic acid reduction
product may be recovered from the catholyte region and a halogen
may be recovered from the anolyte region of the electrochemical
hydrogenation cell 630. It is contemplated that the structure of
electrochemical hydrogenation cell 620, 630 may be similar to
electrochemical cell 102 as previously described, including a first
region having a cathode, such as a catholyte region and a second
region having an anode, such as an anolyte region. The regions may
be separated by a membrane or separator.
[0071] Referring to FIG. 7, a schematic illustrating an
electrochemical cell 700 for converting oxalate salts to oxalic
acid is shown. Electrochemical cell 700 may reduce CO.sub.2 to an
oxalate salt (M.sub.2O.sub.2O.sub.4) at the cathode.
Electrochemical cell 700 may be pre-charged with oxalic acid and
the oxalate salt to enhance conductivity. The catholyte may include
a non-aqueous aprotic solvent such as acetonitrile or propylene
carbonate (PC). The oxalate ion may be transferred to the anolyte
region through an anion exchange membrane (AEM). The anode reaction
may include oxidation of water, a hydrogen halide, or any organic
or inorganic species that when oxidized may liberate protons. The
anolyte may include an aqueous solvent. The oxalate that would be
transferred through the AEM would then be acidified by the
generated protons to produce oxalic acid.
[0072] Referring to FIG. 8, a schematic illustrating a system 800
for converting carbon dioxide to oxalic acid is shown. System 800
may include a first electrochemical cell 810 and a second
electrochemical cell 820. In the first electrochemical cell 810,
the anodic reaction in the first electrochemical cell 810 may
involve a Cu(I)/Cu(II) couple. The advantage of using this reaction
may be a lower half-cell voltage required compared to the likely
voltages for operation of the electrochemical cell 700 of FIG. 7.
Because of the low half-cell voltage achieved by using the
Cu(I)/Cu(II) couple, the undesired oxidation of oxalic acid may be
minimized. Therefore, a copper oxalate salt, CuC.sub.2O.sub.4 may
be recoverable from the electrochemical cell 810. The copper
oxalate salt may be acidified in a second electrochemical cell 820.
In electrochemical cell 820, the anodic reaction may be water
splitting, or oxidation of a hydrogen halide or other organic or
inorganic species that under oxidation liberates protons. These
protons would migrate across a cation exchange membrane or
separator to the catholyte. The copper oxalate salt may be
acidified to oxalic acid and the Cu(II) species reduced to Cu(I) to
be recycled to the anodic compartment of the first electrochemical
cell 810. System 800 would be operable to produce oxalic acid by
employing the Cu(I)/Cu(II) couple acting as a mediator to the
reaction.
[0073] Referring to FIGS. 9A-9C, schematics illustrating
electrochemical cells 910, 920, 930 for converting carbon dioxide
to oxalic acid are shown. In each of electrochemical cells 910,
920, 930, a non-aqueous aprotic solvent (or solvents) is used for
both the catholyte and the anolyte. In these modes of operation, a
solvent used in the electrochemical cell 910, 920, 930 may be a
non-aqueous solution and the anodes of electrochemical cells 910,
920, 930 are fed a hydrogen gas stream. The AEM would not be
necessary, and likely a simple separator material may be employed.
In this mode of operation, the hydrogen may serve as the anodic
reactant and would be oxidized to hydrogen ions. In a similar mode
of operation, the oxalate salt produced in the cathode compartment
may be acidified in the anolyte to produce oxalic acid in
electrochemical cell 910 as shown in FIG. 9A.
[0074] Referring to FIG. 9B, an electrochemical cell 920 which
includes a mix of H.sub.2/CO.sub.2 fed into the catholyte region of
the electrochemical cell 920. Electrochemical cell 920 may reduce
the CO.sub.2 to oxalate and the H.sub.2 may be oxidized at the
anode. Electrochemical cell 920 may be configured for convective
flow-through of the catholyte to the anolyte region to ensure
H.sub.2 is available anodically and CO.sub.2 is available
cathodically. This may simplify the required gas feed to the
electrochemical cell 920. In another embodiment, a stream of
H.sub.2 may be fed to the anolyte and a feed of CO.sub.2 could be
fed to the catholyte separately.
[0075] Referring to FIG. 9C, electrochemical cell 930 is shown.
Electrochemical cell 930 may include a liquid permeable gas
separator. H.sub.2 gas could be fed either flow-by (as shown) or in
a flow-through mode. It is contemplated that electrochemical cells
910, 920, 930 may include a similar structure as electrochemical
cell 102 as previously described, unless otherwise described
without departing from the scope and intent of the present
disclosure.
[0076] Referring to FIG. 10, a schematic illustrating a system 1000
for the conversion of carbon dioxide to mono-ethylene glycol is
shown. System 1000 may include electrochemical cell 102, reactor
1010, acidification reactor 1030 and a hydogenation device 150. In
electrochemical cell 102, carbon dioxide may be reduced to an
oxalate salt, at the cathode of an electrochemical cell 102. A
halide salt may be oxidized to a halogen or trihalide anion at the
anode of the electrochemical cell 102. The reactions of
electrochemical cell 102 may preferably occur in a non-aqueous
solvent.
[0077] In a reactor 1010, halogen or trihalide anion produced by
electrochemical cell 102 may be reacted with hydrogen to form a
hydrogen halide. Reactor 1010 may be a burner or combustor wherein
a significant amount of thermal energy is produced in addition to
hydrogen halide. The thermal energy may then be used in other
operations, such as distillation, the separation of products, and
electric power generation. Alternatively, reactor 1010 may be a
fuel cell. The resulting electricity may be used in a variety of
ways, for example to offset some of the electrical requirements of
the CO.sub.2 reduction in electrochemical cell 102. Hydrogen halide
from reactor 1010 may be reacted with oxalate salt from
electrochemical cell 102 in an acidification reactor 1030 to
produce a oxalic acid, and a halide salt. The halide salt may then
be recycled to the electrochemical cell 102. The oxalic acid may be
fed to hydrogenation device 150 where it is reduced to an oxalic
acid reduction product, such as monoethylene glycol.
[0078] Referring to FIG. 11, a schematic illustrating a system 1100
for the conversion of carbon dioxide to mono-ethylene glycol is
shown. System 1100 may include electrochemical cell 102, reactor
1010, acidification reactor 1030, esterification device 1110 and
hydogenation device 150. System 1100 may include an esterfication
device 1110 which may receive oxalic acid from reactor 1030 whereby
the oxalic acid is reacted with an alcohol in the esterfication
device 1110 to produce an oxalate ester or oxalate diester that is
fed to hydrogenation device 150. In one embodiment, the oxalate
ester or oxalate diester may be hydrogenated to make mono-ethylene
glycol (MEG). Other products may include glyoxylic acid, glycolic
acid, glyoxal, glycolaldehyde, acetic acid, acetaldehyde, ethanol,
ethane, diethylene glycol, triethylene glycol, ethers, esters,
polyglycols, unsaturated chemicals such as crotonaldehyde,
alcohols, diols, carboxylic acids, aldehydes, and four carbon
products. It is contemplated that hydrogenation device may recycle
the alcohol and any oxalate ester or oxalate diester to the
esterification device 1110.
[0079] Referring to FIG. 12, a schematic illustrating a system 1200
for the conversion of carbon dioxide to mono-ethylene glycol is
shown. System 1200 may include electrochemical cell 102, an anolyte
recovery electrochemical cell 130, acidification reactor 1030 and
hydrogenation device 150. Anolyte recovery electrochemical cell 130
may receive a halogen from electrochemical cell 102. Anolyte
recovery electrochemical cell 130 may also receive water and
produce HX and an oxygen byproduct. Acidification reactor 1030 is
configured to receive oxalate and HX and produce a carboxylic acid,
such as oxalic acid, and a halide salt. The halide salt may then be
recycled to the electrochemical cell 102. The oxalic acid may be
fed to hydrogenation device 150 where it is reduced to an oxalic
acid reduction product, such as monoethylene glycol.
[0080] Referring to FIG. 13, a schematic illustrating a system 1300
for the conversion of carbon dioxide to mono-ethylene glycol is
shown. System 1300 may include an electrochemical cell 1310 which
includes a hydrogen fed anode, an esterification device 1110 and a
hydrogenation device 150. Electrochemical cell 1310 may be
implemented as electrochemical cells 910, 920, 930 as shown in
FIGS. 9A-9C.
[0081] Referring to FIG. 14, a schematic illustrating a system 1400
for the conversion of carbon dioxide to mono-ethylene glycol and
other two-carbon products. System 1400 may include electrochemical
cell 102, acidification reactor 1030 and hydogenation device 150.
Hydrogen halide may be reacted with carboxylate salt, such as an
oxalate, from electrochemical cell 102 in an acidification reactor
1030 to produce a carboxylic acid, such as oxalic acid, and a
halide salt. The halide salt may then be recycled to the
electrochemical cell 102. The oxalic acid may be fed to
hydrogenation device 150 where it is reduced to an oxalic acid
reduction product, such as monoethylene glycol.
[0082] In addition to mono-ethylene glycol, systems 1000, 1100,
1200, 1300 and 1400 may produce a variety of multi-carbon
chemicals. If oxalic acid is produced, it may be further reduced,
for example, by electrochemical reduction, catalytic reduction or
other reduction methods.
Electrochemical Cell Operating Conditions
[0083] Referring once again to electrochemical cell 102 as shown in
at least FIG. 1, a solvent may be employed. The solvent may be a
non-aqueous solvent or mix of solvents including propylene
carbonate, ethylene carbonate, dimethyl carbonate, diethyl
carbonate, dimethylsulfoxide, dimethylformamide, acetonitrile,
ammonia, acetone, tetrahydrofuran, N,N-dimethylacetaminde,
dimethoxyethane, diethylene glycol dimethyl ester, butyrolnitrile,
1,2-difluorobenzene, .gamma.-butyrolactone, N-methyl-2-pyrrolidone,
sulfolane, 1,4-dioxane, nitrobenzene, nitromethane, acetic
anhydride, alkanes, cycloalkanes, perfluorocarbons, linear
carbonates, aromatics such as benzene and toluene and their
derivatives, dichloromethane, chloroform, ethers, chlorobenzene,
polyols, glymes, diglymes, triglymes, tetraglymes, alcohols,
alkenes, trifluorotoluene, anisole, m-cresol, and ionic liquids to
include those containing cations of the types: 1,3
dialkyimidazolium, N,N dialkylpyrrolidinium, and
1-alkyl-2,3-dimethylimidazolium where N=2 or 4 and anions of the
type hexafluorophosphate, tetrafluroborate,
bis(trifluoromethanesulfonyl)imide, perfluoroalkylphosphate, and
halide ions such as Br--.
[0084] Many cathode materials may be used to effect the reduction
of CO.sub.2 to oxalate. Cathode materials may include Al, Au, Ag,
Bi, Carbon (e.g. graphite), Cd, Co, Cr, Cu, Cu.sub.2O, Cu alloys
(e.g., brass and bronze), Fe, Fe alloys (e.g. Fe--Ti), Ga, Hg, In,
Mo, Mo alloys (e.g. Mo--Ni), Nb, Ni, NiCo.sub.2O.sub.4, Ni alloys
(e.g., Ni 625, NiHX), Ni--Fe alloys, Pb, Pb alloys, Pd alloys
(e.g., PdAg), Pt, Pt alloys (e.g., PtRh), Rh, Sn, Sn alloys (e.g.,
SnAg, SnPb, SnSb), Ti, V, W, W alloys, Zn, stainless steel (SS)
(e.g., SS 2205, SS 304, SS 316, SS 321), austenitic steel, ferritic
steel, duplex steel, martensitic steel, Nichrome in various ratios
(e.g., NiCr 60:16 (with Fe)), elgiloy (e.g., Co--Ni--Cr), and
various Haynes International Inc. trade name nickel-cobalt alloys
called Hastelloys, such as Hastelloy 276, Hastelloy C. Metal
carbides as cathodes may also be used and could include iron
carbide, molybdenum carbide, and chromium carbide.
[0085] A range of screens/meshes, non-woven materials, sintered
metals, layered materials, foams, and gradients are suitable for
use as cathode materials for the electrochemical cell. Cathodes may
be coated with nanoparticles and nano-features through template
electroplating, etching, and deposition. For example, nickel
nanoparticles may be used to coat the cathode surfaces. An
exemplary cathode may comprise of multilayers of 316 SS screen made
of alternating layers of 400 mesh and 15 mesh stainless steel. A
quantity of 12 or 22 micron non-woven 316 stainless steel, such as
those available from Bekaert, may be used as a flow
channel/electrical contact between the back plate and the layered
mesh assembly. Another cathode may comprise corrugated screens with
flow channels built in, wherein layers are spot welded or sintered
together. The 3D electrode may be sintered or welded to suitable
thickness 316 SS plate current distributor to make a complete
integrated cathode assembly.
[0086] Cathode structures
[0087] Suitable cathode structures also include the following
forms:
[0088] Metal plates
[0089] Packed bed consisting of metal spheres or fibers
[0090] Assembly of screens/meshes
[0091] Metal foams
[0092] Metal non-woven materials including needeled felts
[0093] Sintered or partially sintered non-wovens
[0094] Metal wools
[0095] Layered materials
[0096] Layered metal meshes or screens
[0097] Welded layered meshes, such as those used as filtration
media for PE extrusion
[0098] Sintered metal fibers and powders
[0099] Woven metal felts
[0100] Other metal woven fibrous metals in various weaves or twills
comprising various metal fiber sizes and thicknesses
[0101] Metal coated carbon materials, such as nickel on carbon
fibers, or metal coated ceramic fibers
[0102] The electrochemical cell cathode may also comprise one or
more cathode materials, one or more structure types, and with one
or more combinations of metal and metal coating compositions. For
example, the cathode may consist of a nickel fiber structure
adjacent to the separator, and utilize a 304 SS structure towards
the cathode backplate, which may be 304 SS or another metal alloy.
The selection of the metal alloys and metallic coatings on the
cathode is used to maximize the cathode reduction of carbon dioxide
reaction. Cathode coatings on the cathode structure materials may
be applied by electroplating, chemical vapor deposition (CVD) or
other methods to all or various sections of the cathode structure.
The cathode coatings may be metal or metal oxides, or converted to
the metal or oxide by hydrogen reduction (metal oxide to metal) or
thermal oxidation in air (formation of oxide coatings). The metals
are the same group noted as the single metals or alloys specified.
The coatings may also consist of multiple coatings of different
layers of materials for providing stability.
[0103] Table 0 shows the effect of cathode materials on oxalate
faradaic yield operated at constant current of -3.5 to .about.5
mA/cm.sup.2. The working electrode, as listed, was immersed in a
0.2M TBABr solution in propylene carbonate saturated with CO.sub.2.
The reference electrode was a Ag wire. A three chamber
electrochemical cell was used, with the compartments separated by
porous glass frits. A two compartment electrochemical cell was used
in some cases, the compartments separated by a Vicor.RTM. glass
frit. The counter electrode was a Zn foil immersed in 0.2M
tetrabutylammonium perchlorate (TBAP) in propylene carbonate.
[0104] Typically, the water content was 100-200 ppm at the start of
the experiment and 120-150 at the end of the experiment.
Experiments were typically run for 6 hrs. Approximately 10%
Faradaic yield of oxalate was lost to the center compartment
chamber when the three compartment cell was used, therefore true
oxalate Faradaic yields are typically higher than listed.
TABLE-US-00001 TABLE 0 Oxalate FY Cathodes (%) Stainless steel 2205
47-56 Stainless steel 304 63-85 Stainless steel 316 50-72 Ni:Cr
(60:16) 40-53 Ni:Cr (80:20) 80-100 Ni:Fe:Mo 68-86 Ni (99.994%
purity) 74-80 Nickel 58-67 Mo 72 Fe:Co (80:20) 68* Co:Cr:Mo
(60:30:10) 0 Hastelloy C Mesh 28-35 Co 73-85 W 78-88 Cu:Ni (55:45)
31 Fe:Mo (80:20) 72* Co:Cr:Mo (60:30:10) 68* Fe:Ni:B:Mo Metallic
Glass 6* FeTi 0* FeB 0* MoB.sub.2 2* Ni:Mo (80:20) 37* Mo:Ti
(80:20) 9* W:Co (50:50) 2* WC:Co (94:6) 0 *Represents the average
of 2-3 independent experiments
[0105] In addition, the cathode material could be chemically
modified to improve or enhance the cathode reaction efficiency and
selectivity. For metallic surfaces, modification may include using
thiols, primary amines, pyrrolidones, heterocyclic amines, and
surfactants containing carboxylate groups, phosphonate groups,
phosphine groups, and citrate groups. For oxide and carbide
materials, silanes, diazomethanes, alkyl ammonium ions,
cycloketones, cycloalkylidenes, and ionic liquid cations may be
employed to modify the cathode surfaces.
[0106] To passivate stainless steel electrodes, electrodes of a
required size are cut from bulk material. The electrodes are
cleaned by polishing with alumina powder, followed by rinsing with
deionized water, then dipping in acetone for approximately 2
minutes, followed by rinsing and sonication in deionized water. A
15 wt % citric acid in deionized water solution is prepared.
Cleaned electrodes are immersed in 15 wt % solution of citric acid
for approximately four hours at room temperature (25.degree. C.).
The electrodes are taken out of the solution, rinsed 3 times with
deionized water and dried under argon. Treated electrodes may then
be stored in closed glass vials until needed.
[0107] It is contemplated that the high surface area cathode/anode
electrode may include the following characteristics, such as a
preferred void volume ranging from 30% to 98%. The electrodes may
include specific surface areas from 2 cm.sup.2/cm.sup.3 to 500
cm.sup.2/cm.sup.3 or higher. Surface areas also may be defined as
total area in comparison to the current distributor/conductor back
plate, with a preferred range of 2.times. to 1000.times. or
more.
[0108] Table 00 shows the effect of corrosion inhibitors on oxalate
faradaic yield when an electrochemical cell is operated at constant
current of -3.5 mA/cm.sup.2. The working electrode (304 SS) was
immersed in a 0.2M TBABr solution in propylene carbonate saturated
with CO.sub.2. The reference electrode was a Ag wire. A three
chamber electrochemical cell was used, with the compartments
separated by porous glass frits. The counter electrode was a Zn
foil immersed in 0.2M TBAP in propylene carbonate.
TABLE-US-00002 TABLE 00 Cathode Concentration (ppm) Yield Oxalate
(%) Imidizole 500 45.5 +/- 26% 2-pyrrolydinone 500 82.4 +/- 6.4%
EDTA 500 82.2
[0109] Electrochemical Flow Cell Examples
[0110] An electrochemical cell was assembled with a 316 SS back
conductor plate on the cathode side and a graphite back conductor
plate on the anode side. A single layer of hydrophobic PVDF with a
pore diameter of about 0.45 micron and thickness of about 150
micron was used as a separator between the cathode compartment and
anode compartment. The cathode compartment contained a
multi-layered high surface area 316 SS cathode. The cathode
consisted of a non-woven fiber mat with a fiber diameter of 22
micron, which was in direct contact with the back plate. The
thickness of the fiber mat was approximately 0.5 mm in its
compressed state when installed in the cell. Between the non-woven
material and the separator an assembly of layers of mesh was placed
having two alternating opening sizes, fine (400.times.400) mesh
with a thickness of 0.15 mm and an opening size of 0.0015 inches
and an open area of 38%, and a coarse (15.times.15) mesh with a
thickness of 0.4 mm and an opening size of 0.057 inches and an open
area of 73%. In total eight layers of mesh were used. A 0.35 mm
thick porous PTFE screen was placed between the separator and the
cathode to minimize the risk of a short circuit. The anode
compartment contained 4 layers of carbon cloth, the first of which
was in direct contact with the separator. A sheet of porous glassy
carbon, i.e., reticulated vitreous carbon with a pore density of 60
pores per inch, was placed between the layer and the other 3 carbon
cloth layers. The thickness of a single carbon cloth layer and the
RVC was 0.35 mm and 3.65 mm, respectively. Both electrode
compartments were assembled in a zero-gap configuration, i.e., no
open space left on either side of the separator.
[0111] The electrochemically active area of the cell was in the
range of 50-100 cm.sup.2. Electrolyte was fed to the respective
electrodes via high density polyethylene flow plates having flow
channels with a circular cross section. The flow entered the active
electrode compartment on the bottom of the cell and was directed
upward, parallel to the separator.
Example 1
PC Room Temperature Operation
[0112] A flow cell experiment was run using propylene carbonate
with 0.5 M TBABr as the electrolyte. The anolyte and catholyte were
purged with nitrogen and sparged with carbon dioxide, respectively.
The current density was 75 mA/cm2 and was conducted at room
temperature (25.degree. C.). The flow rate for the catholyte was
150 ml/min and for the anolyte was 100 ml/min. The cell voltage was
about 15V. The current efficiency was approximately 30% while the
highest oxalate concentration was 0.37% by weight (3700 ppm).
Example 2
PC High Temperature Operation
[0113] A flow cell experiment was executed using propylene
carbonate with 0.5 M TBA-Br and 10 mM benzonitrile as the
electrolyte. The anolyte and catholyte were purged with nitrogen
and sparged with carbon dioxide, respectively. The current density
was 75 mA/cm.sup.2 and was conducted at 60.degree. C. The flow
rates for both the anode and cathode were 1.1 L/min. The cell
voltage was between 6.8 and 7 volts. The current efficiency was
between 15% and 30%. The highest oxalate concentration was 0.24% by
weight (2400 ppm).
Example 3
ACN as a Anolyte/Catholyte Solvent
[0114] A flow cell experiment was performed using acetonitrile as a
solvent with 0.75 M TBABr as the electrolyte. The anolyte and
catholyte were purged with nitrogen and sparged with carbon
dioxide, respectively. The current density was 75 mA/cm2. The run
was conducted at ambient temperature and pressure. The anode and
cathode flow rate was 1.1 L/min. The cell voltage was in the range
of 5.7-6.5 V. The current efficiency was 50% for oxalate and 40%
for the anolyte tribromide generation. The highest oxalate
concentration was 2.5% by weight (25,000 ppm).
Example 4
Nickel Cathode
[0115] In an embodiment of the disclosure, it has been found that
nickel cathodes may improve cell voltages. When using stainless
steel cathodes, voltages of 5.5V at 75 mA/cm2 are typically
observed. With thick Ni cathodes voltages of about 5 V or less are
observed. (Table 1). As shown in Table 2, a thin electrode
configuration in conjunction with Ni brings the voltage to about
4.1V. Both tests were executed with a PTFE separator (0.45 micron
pore size). A PVDF separator (0.1 micron pore size) may also be
used. A test of a PTFE separator using a stainless steel cathode
resulted in yields similar to what is shown on Table 1 (about 70%
for the first hour of the run, see Table 3).
[0116] The nickel cathode may be formed as a mesh including either
2 or 4 layers of mesh bonded together. To form the cathodes used in
the experiments, three to five pieces of mesh were cut (depending
on cathode thickness), which were then folded once, yielding 6 or
10 layers of bonded mesh in the cathode compartment. The current
collector plate may also comprise nickel.
TABLE-US-00003 TABLE 1 Thick Nickel Cathode Run With PTFE Separator
Cell Configuration: 5x double layer (folded) of multi-layer Ni-mesh
[85 .times. 70 0.006], 1 PTFE Screen, 0.45 micron PTFE hydrophilic
separator (rough side facing anode. Description: Run with 0.75M
TBA-Br in ACN thick electrode configuration (1/4'') Oxalate
Faradaic I Cell Oxalate Yield % Time Current Voltage Concentration
At Time (min) (Amperes) (Volts) mg/L Intervals 0 7.7 5.06 593.60 30
7.7 4.74 2953.98 77.9% 60 7.7 4.82 5293.01 75.2%
TABLE-US-00004 TABLE 2 Thin Nickel Cathode Run With PTFE Separator
Cell Configuration: 3x double layer (folded) of multi-layer Ni-mesh
[85 .times. 70 0.006], 0.45 micron PTFE hydrophilic separator
(rough side facing anode) Description: Run with 0.75M TBA-Br, thin
electrode configuration (1/8'') Oxalate Faradaic I Cell Oxalate
Yield % Time Current Voltage Concentration At Time (min) (Amperes)
(Volts) mg/L Intervals 0 7.7 4.36 413.52 30 7.7 4.14 2356.78 64.4%
60 7.7 4.05 4017.87 54.4% 90 7.7 4.09 5543.32 49.5% 120 7.7 4.06
6839.26 42.2%
TABLE-US-00005 TABLE 3 Stainless Steel Cathode with PTFE separator
Cell configuration: PTFE, hydrophilic PTFE separator. (0.45 .mu.m),
C cloth Run Description: Run with 0.75M TBABr in ACN, 0.45M
hydrophilic PTFE separator Oxalate Faradaic I Cell Oxalate Yield %
Time Current Voltage Concentration At Time (min) (Amperes) (Volts)
mg/L Intervals 0 7.7 6.11 122.27 30 7.7 7.04 2139.99 69.0% 60 7.7
6.74 4116.19 67.1% 90 7.7 6.82 5979.04 55.0% 120 7.7 6.95 7738.92
56.8%
[0117] It is further contemplated that additives may be utilized to
increase salt solvation and conductivity in electrochemical cell
102. Additives may be used to enhance salt solvation and may also
increase conductivity in an additive or co-solvent role. Additive
concentrations may range from ppm levels to 100% by weight. In
general, the additive or multiple additives will be used in
addition to one or more solvents listed above. Additives may
include carbonates such as dimethyl carbonate, ethylmethyl
carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl
carbonate. Carbonates with other akyl groups are also claimed. In
addition phosphates such as benzyl phosphate, denzyl dimethyl
phosphate, allyl phosphate, dibenzyl phosphate, and diallyl
phosphates may be used. Some organic sulfates such as methyl benzyl
sulfate, ethylbenzylsulfate, diallyl sulfate, propyl allyl sulfate
and butylallylsulfate may also be used as additives to increase the
conductivity.
[0118] Additives may also include the ionic liquids listed
previously as well as their mixtures and other variations.
Surfactants may also be used. Crown ethers may be added to increase
the solvation of hard cations such as Li.sup.+, Na.sup.+, and K.
The crown ether employed for Li.sup.+, Na.sup.+ and K.sup.+ are
12-crown-4, 15-crown-5, diphenyl-18-crown-6, and 18-crown-6,
respectively. Similarly, cryptands may also be used to increase
solvation for hard cations. These include 2.2.2-cryptand,
2.2.1-cryptand, 2.1.1-cryptand, 2.2.2B-cryptand, and
5-decyl-4,7,13,16,21-pentaoxa-1,10-diazabicyclo(8.8.5)tricosane.
Larger cryptands and those available from EMD Millipore under the
trade name of Kryptofix may also be employed.
[0119] Anion acceptors may also be used to increase solvation of
the halide anion. These include borane and boroxine derivatives to
include, but not limited to, tris(isopropyl)borane and
trimethoxyboroxin.
[0120] Glymes may increase conductivity, increasing ion solvation
and also may lower solution viscosity. Glymes include glyme,
diglyme, triglyme, and tetraglyme as well other glyme variations.
Metal nanoparticles, zwitterions, and micelles or reverse micelles
could also be employed.
[0121] A range of organic homogenous catalysts, capable of being
reduced to a radical anion at the cathode interface and
transferring an electron to CO.sub.2 may be used. These include,
but are not limited to, benzophenone methyl
4-methyl-3-nitrobenzoate, tetracyanoquinodimethane,
cyclooctatetraene, diphenylethanedione (benzil) and
benzonitrile.
[0122] Anion catalysts to help effect the oxidation of halide ions
to halogens could include nitroxides, nitronyl nitroxides,
azephenylenyls, perchlorophenylmethyl radicals, TEMPO
(2,2,6,6-Tetramethyl-1-piperidinyloxy) and
tris(2,4,6-trichlorophenyl) methyl radicals. The radical of each
compound may also be used. Other catalysts could include
succinimide, N-bromosuccinimide, or other imides.
[0123] minimum voltage for the cathodic half cell may be -0.71 V
vs. SCE. The operating cathodic half cell voltage is usually
between -1.2 and -3 V vs. SCE. The minimum voltage for the anodic
half cell is 0.83 V vs. SCE. The operating anodic half cell voltage
is usually between 1 and 3 V vs. SCE. The overall voltage for the
complete cell is usually between 2 and 20 V.
[0124] Catholyte operating temperature may be in a range of -10 to
240.degree. C., and more preferably 5-60.degree. C. The lower
temperature may be limited by the electrolytes used and their
freezing points. In general, the lower the temperature, the higher
the solubility of CO.sub.2 in the solution phase of the
electrolyte. Higher carbon dioxide concentrations may help in
obtaining higher conversion and current efficiencies. The drawback
is that the operating electrolyzer cell voltages may be higher, so
there is an optimization that would be done to produce the
chemicals at the lowest operating cost. Anolyte operating
temperature operating temperature may be in a range of -10 to
240.degree. C., more preferably 5-60.degree. C.
[0125] Operating the electrochemical cell catholyte at a higher
operating pressure allows more dissolved CO.sub.2 to dissolve in
the solvent. Typically, electrochemical cells may operate at
pressures up to about 20 to 30 psig in multi-cell stack designs,
although with modifications, they could operate at up to 100 psig.
The electrochemical cell anolyte would also need to be operated in
the same pressure range to minimize the pressure differential on
the membrane separating the two electrode compartments. Special
electrochemical designs are required to operate electrochemical
units at higher operating pressures up to about 60 to 100
atmospheres or greater, which is in the liquid CO.sub.2 and
supercritical CO.sub.2 operating range.
[0126] In another embodiment, a portion of the catholyte recycle
stream may be separately pressurized using a flow restriction with
backpressure or using a pump, with CO.sub.2 injection, such that
the pressurized stream is then injected into the catholyte region
of the electrochemical cell, and potentially increasing the amount
of dissolved CO.sub.2 in the aqueous solution to improve the
conversion yield.
[0127] The catholyte cross sectional area flow rate range may be
2-3,000 gpm/ft.sup.2 or more (0.0076-11.36 m.sup.3/m.sup.2) and may
include a flow velocity range of 0.002 to 20 ft/sec (0.0006 to 6.1
m/sec).
[0128] The electrochemical cell design may include Zero-Gap,
flow-through with a recirculating catholyte electrolyte with
various high surface area cathode materials. Additional designs may
include flooded co-current packed and trickle bed designs with the
various high surface area cathode materials. Bipolar stack cell
designs and High pressure cell designs may also be employed for the
electrochemical cells.
[0129] The operating cell voltages for the electrochemical cells
disclosed in the embodiments in this disclosure may range from
about 1.0 to about 20 volts depending on the anode and cathode
chemistry employed in addition to the cell operating current
density. The operating current density of the electrochemical cells
may range from 5 ma/cm.sup.2 to as high as 500 ma/cm.sup.2 or
more.
[0130] For bromine and iodine anode oxidation chemistry, carbon and
graphite are particularly suitable for use as anodes. The anode may
include electrocatalytic coatings applied to the surfaces of the
base anode structure. For the oxidation of HBr, acid anolytes, and
oxidizing water generating oxygen, the preferred electrocatalytic
coatings may include precious metal oxides such as ruthenium and
iridium oxides, as well as platinum and gold and their combinations
as metals and oxides on valve metal substrates such as titanium,
tantalum, zirconium, or niobium. For bromine and iodine anode
chemistry, carbon and graphite are particularly suitable for use as
anodes. Polymeric bonded carbon material may also be used. High
surface area anode structures that may be used which would help
promote the reactions at the anode surfaces. The high surface area
anode base material may be in a reticulated form composed of
fibers, sintered powder, sintered screens, and the like, and may be
sintered, welded, or mechanically connected to a current
distributor back plate that is commonly used in bipolar
electrochemical cell assemblies. In addition, the high surface area
reticulated anode structure may also contain areas where additional
applied catalysts on and near the electrocatalytic active surfaces
of the anode surface structure to enhance and promote reactions
that may occur in the bulk solution away from the anode surface
such as the reaction between bromine and the carbon based reactant
being introduced into the anolyte. The anode structure may be
gradated, so that the density of the may vary in the vertical or
horizontal direction to allow the easier escape of gases from the
anode structure. In this gradation, there may be a distribution of
particles of materials mixed in the anode structure that may
contain catalysts, such as precious metals such as platinum and
precious metal oxides such as ruthenium oxide in addition to other
transition metal oxide catalysts.
[0131] The electrochemical cell anode may comprise flat
carbon/graphite plates, RVC (reticulated vitreous carbon) foams,
carbon cloth, carbon felts/tissue may be used. Carbon cloth may be
used as an electrically conductive material to ensure good
electrical contact with the anode back plate.
[0132] Suitable Anode structures include:
[0133] Plates (carbon/graphite/graphene)
[0134] RVC
[0135] Carbon cloth
[0136] Woven with and without activated carbon layer
[0137] Various loadings of PTFE
[0138] Carbon tissue
[0139] Carbon felts
[0140] Carbon fibers
[0141] Conductive diamond films
[0142] Iridium oxide on titanium
[0143] Ruthenium oxide plated or deposited onto a carbon felt or
carbon cloth as a catalyst
[0144] Graphene
[0145] Cation ion exchange type membranes may be preferred as
separators for 120 in embodiments for electrochemical cell 102,
especially those that have a high rejection efficiency to anions
and allowing cations to pass. Examples of these membrane types
having a fluorinated hydrocarbon backbone are perfluorinated
sulfonic acid based cation ion exchange membranes such as DuPont
Nafion.RTM. brand unreinforced types N117 and N120 series, more
preferred PTFE fiber reinforced N324 and N424 types, and similar
related membranes manufactured by Japanese companies under the
supplier trade names such as Flemion.RTM..
[0146] Other multi-layer perfluorinated ion exchange membranes used
in the chlor alkali industry have a bilayer construction of a
sulfonic acid based membrane layer bonded to a carboxylic acid
based membrane layer, which efficiently operates with an anolyte
and catholyte above a pH of about 2 or higher. These membranes have
a much higher anion rejection efficiency. These are sold by DuPont
under their Nafion.RTM. trademark as the N900 series, such as the
N90209, N966, N982, and the 2000 series, such as the N2010, N2020,
and N2030 and all of their types and subtypes.
[0147] Hydrocarbon based membranes, which are made from of various
cation ion exchange materials may also be used if the anion
rejection is not as critical, such as those sold by Sybron under
their trade name Ionac.RTM., AGC Engineering (Asahi Glass) under
their Selemion.RTM. trade name, and Tokuyama Soda among others on
the market. These hydrocarbon based membranes may be specially
prepared from ion exchange materials that are bonded together in a
suitable bonding matrix such as polyethylene, polypropylene, and
polyvinylchlorine (PVC) as examples. Other membrane types may use a
microporous separator and have an impregnated ion exchange material
that may be chemically bonded or adhered to the separator, such as
Nafion infused or bonded to a PVDF or PTFE separator, or other
ionic materials, such as ionic liquids that can be used to prepare
solid gel-type membranes and the like, as long as they are
chemically suitable with the liquid phase solutions contemplated in
electrochemical cell 102. All of the membrane and separator
materials suggested or described in this invention may also be
employed in the various other electrochemical cells designs and
methods disclosed in this application which are non-aqueous or
aqueous based.
[0148] Microporous separators may also be employed in some
electrochemical system options such as microporous PVDF
(polyvinylidiene difluoride) based, PTFE (polytetrafluoroethylene),
or glass fiber based materials as well as commercial diaphragms
available for the chlor alkali industry. These microporous
separators may also be prepared and constructed in various other
plastics or polymers or their combinations that are chemically
suitable for the solvent and salts employed in electrochemical cell
102. In addition, multiple layers may be employed using one or more
separator types. In addition, ceramic based porous separators,
which may be in flexible sheet forms, may be employed, for example
aluminum oxide (alumina) based, silicon oxide based, and zirconium
oxide based and their various combinations in addition to boron
carbides and the like.
[0149] Another suitable membrane separator material, being marketed
by CeramHyd, under the trade name CERAPEM, employs an activated
boron nitride in a PTFE matrix may also be suitable for some of the
various electrochemical cells described in this disclosure.
[0150] Alternative ceramic based membranes may also be employed as
separators, especially those that may conduct and operate at the
low temperatures, 5.degree. C. to 200.degree. C., for the various
electrochemical cells that may be used in this disclosure. These
membranes may be selective in various cations such as alkali metal
or even hydrogen ions.
[0151] Suitable electrochemical separators include commercially
available PVDF (polyvinylidene difluoride) filtration material with
a 0.1-0.45 micron pore size, available with a thickness of
approximately 145 microns thick may be used. Such as material is
manufactured by Meissner and distributed by Tisch scientific.
Lithium ion battery materials, for example from W. L. Gore and
Associates (polytetrafluoroethylene PTFE based), may also be used.
Other lithium battery battery separator materials may include
inorganic compounds tomprovide dimensional stability The selection
of the separator is based on the compatibility of the separator or
membrane with the solvent(s) selected and stability to the anode
reaction product.
[0152] Other separator materials that may be used in the
electrochemical cell include:
[0153] Polymeric porous separators for lithium ion batteries and
filtration processes [0154] a. PVDF, PTFE, Polyolefin, HDPE, PEEK
(polyether ether ketone), nylon [0155] b. Composite polymer matrix
with inorganic particle and fiber fillers [0156] c. Fiber (woven
polymer) supported polymers
[0157] Inorganic Filtration Materials [0158] a. Ceramics comprising
silica, alumina, titania, and zirconia in a woven or nonwoven form,
with and without binders [0159] b. Partially sintered glass fiber
and and ceramic materials
[0160] Perfluorinated Ionomers [0161] a. Nafion.RTM. brand
perfluorinated sulfonic acid based membranes and cation exchange
related membrane materials [0162] b. Composite perfluorinated
ionomers which incorporate inorganic particles or fibers in the
ionomer matrix
[0163] Combination hybrid Organic-Inorganic membranes having an
inorganic within a polymer matrix Partially fluorinated and
hydrocarbon-based ionomers (e.g., PEEK-S)
[0164] Solid State Ion Conductors and Composites Including these
Materials [0165] a. E.g., ceramic membrane composed of boron
nitride with PTFE matrix
[0166] Hydrocarbon based membranes, which may be fabricated from
ion exchange resin materials
[0167] The electrochemical cells described herein may be
independently configured in three ways: Three major flow
configurations may be used: [0168] Flow-in (flow inside a 3D
electrode structure parallel to the separator) [0169] Flow-by (flow
in a plenum/open mesh along the 3D electrode surface parallel to
separator) [0170] flow along either the side facing the separator
or the side facing the back plate [0171] Flow-thru (flow through
the electrode, perpendicular to separator) [0172] flow towards and
away from separator
[0173] Referring once again to FIGS. 1 and 12, electrochemical
reduction cell 130, also referred as the anolyte recovery
electrochemical cell, may be similar to electrochemical cell 102.
Electrochemical reduction cell 130 may include a first region and a
second region. First region and second region may refer to a
compartment, section, or generally enclosed space, and the like
without departing from the scope and intent of the present
disclosure. First region 116 may include a cathode. Second region
118 may include an anode. Electrochemical reduction cell 130 may
reduce a halogen or trihalide anion 115 to HX 132 at the cathode
and oxidize water 134 at the anode, producing oxygen (O.sub.2) and
liberating hydrogen ions (H.sup.+) to be transferred across the
membrane of the electrochemical reduction cell 130 to generate the
HX 132.
[0174] Electrochemical reduction cell 130 may produce an acid, such
as HX, that may be used to acidify oxalate and allow the recycle of
the halogen or multivalent material for reuse to electrochemical
cell 102. There are several ways to configure the electrochemical
cell 130. A two region electrochemical reduction cell, including a
catholyte region and an anolyte region separated by a cation ion
exchange membrane may be used. The anode reaction may be the
oxidation of water in an inorganic acid producing hydrogen ions and
oxygen. The hydrogen ions may then pass through the membrane into
the cathode compartment. In the cathode compartment, the feed of
halogen, such as Br.sub.2, may then be reduced at the cathode to
bromide ions (Bo, and then combine with the hydrogen ions to
produce HBr. The cathode reaction may require a high surface area
structure to efficiently convert the X.sub.2 halogen or
X.sub.3.sup.- halide anion to the HX acid. An aqueous or
non-aqueous catholyte with the addition of water may also be used.
For instance, the non-aqueous solvent from the anode region 118 of
electrochemical cell 102 may be fed directly into electrochemical
cell 130 for bromine reduction, or the bromine might be separated
from the anolyte of electrochemical cell 102 and introduced to the
catholyte of electrochemical cell 130 for reduction. The HX may
then passed on to the next reactor the acidification reactor 1030
to acidify and convert alkali metal oxalate or tetraalkylammonium
oxalate to oxalic acid.
[0175] Referring once again to FIG. 2, electrochemical cell 210,
also referred as an electrochemical acidification cell, is
configured to convert oxalate to oxalic acid. Hydrogen ions may be
generated in the anode, or anolyte region 118 and pass through a
central ion exchange region 212 bounded by two cation ion exchange
membranes 214, 216. The M-oxalate solution is passed through the
ion exchange compartment 212 where the M-cations are exchanged for
the hydrogen ions, producing oxalic acid, and the M-cations pass
through the adjoining second cation membrane 214 into the catholyte
region 116. In the catholyte region, the X.sub.2 or X.sub.3.sup.-,
such as bromine or tribromide, is reduced at the cathode 122,
forming X.sup.-, such as bromide, which combines with the M-cations
to form an MX reduced product. The MX 117 may then be recycled to
electrochemical cell 102.
[0176] Electrochemical cell 210 may include three regions, a first
region 116 such as a catholyte region, a second region 118 such as
an anolyte region and a third region 212 such as central ion
exchange region by two cation exchange membranes on each side. The
second region 118 includes an anode 124 suitable to oxidize water.
In a preferred implementation, the anode 124 is a titanium anode
having an anode electrocatalyst coating which faces the adjacent
cation exchange membrane 216. The first region 116 includes a
cathode 122 suitable to reduce water and to generate an alkali
metal hydroxide.
[0177] In a preferred implementation, hydrogen ions (H.sup.+) or
protons are generated in the second region 118 a potential and
current are applied to the electrochemical cell 210. The hydrogen
ions (H.sup.+) or protons pass through the adjacent cation exchange
membrane 216 into the central ion exchange region 212. An alkali
metal oxalate, or tetraalkylammonium oxalate, stream is preferably
introduced to the electrochemical cell 210 into the bottom of the
central ion exchange region 212, where the hydrogen ions (H.sup.+)
or protons displace the ions (e.g., lithium or tetraalkylammonium
ions) in the product stream to acidify the stream and produce the
oxalic acid 144. The displaced cations may pass through the
adjoining cation exchange membrane 214 into the first region 116 to
combine with hydroxide ions (OH.sup.-) formed from water reduction
at the cathode 122 to form a hydroxide, such as lithium or
tetraalkylammonium hydroxide.
[0178] The central ion exchange region 212 may include a plastic
mesh spacer (not shown) to maintain the dimensional space in the
central ion exchange region 212 between the cation exchange
membranes 214, 216. In an embodiment, a cation ion exchange
material may be included in the central ion exchange region 212
between the cation exchange membranes 212, 214. It is contemplated
that the cation ion exchange material may increase electrolyte
conductivity in the ion exchange region solution.
[0179] The second region 118 generally may include an anode feed
stream that includes an acid anolyte solution, such as a sulfuric
acid solution, or an HX solution, and may produce a gaseous oxygen
product 222. A deionized water source 220 and an acid make-up
source may maintain anolyte acid strength and volume for the anode
recycle loop, not shown.
[0180] The first region 116 may include a cathode feed stream that
includes water and may include an alkali metal hydroxide that
circulates through the catholyte recycle loop. The reaction
products, which may include an alkali metal hydroxide and hydrogen
gas, may exit the first region 116.
[0181] It is contemplated that electrochemical cell 210 may include
a catholyte disengager configured to process a cathode exit stream
into a hydrogen stream, a catholyte recycle stream, and a catholyte
overflow stream which may include hydroxide. The hydrogen stream
may be vented from the catholyte disengager. The catholyte recycle
stream preferably includes an alkali metal hydroxide, such as
lithium hydroxide, or tetraalkylammonium hydroxide. The catholyte
stream may have a deionized water source to control the
concentration of the hydroxide.
[0182] It is contemplated that electrochemical cell 210 may include
a variety of characteristics to improve performance. High surface
area cathode structures are preferred. Carbon materials such as
high surface area carbon and graphite felts may be employed for the
reduction of the halogen. The cathode may include preferred void
volume, ranging from 30% to 98%, a specific surface area from 2
cm.sup.2/cm.sup.3 to 500 cm.sup.2/cm.sup.3 or higher. The surface
area also can be defined as total area in comparison to the current
distributor/conductor back plate, with a preferred range of
2.times. to 1000.times. or more.
[0183] For the anode reaction with the generation of oxygen,
electrocatalytic coatings of precious metals, such as platinum, and
precious metal oxides such as ruthenium and iridium oxides and
their combinations as metals and oxides on valve metal substrates
such as titanium, tantalum, or niobium are suitable. As described
herein, high surface area anode structures may also be used.
[0184] Dilute inorganic acids may be used as the anolyte, such as
HX acids or sulfuric acid or phosphoric acid with the addition of
water into the anolyte compartment to compensate for water losses
as needed.
[0185] Referring once again to FIG. 3, anion exchanger 140, also
referred as an acidification and separation unit, is configured to
recycle salt to electrochemical cell 102 and to acidify oxalate
salt to oxalic acid 144. In one embodiment, anion exchanger 140 may
include an anion exchange column. Oxalate salt 113 in solution may
be passed through the column and oxalate salt may adsorb to the
column material, causing another anion to desorb and combine with
the cation(s) from the oxalate to form salt or salts. The anion
would typically be the conjugate base of an acid. When an acid
solution is introduced to the column, the oxalate may be desorbed
as oxalic acid and the conjugate base of the acid, such as
Cl.sup.-, Br.sup.-, or I.sup.- is adsorbed to the column. The
overall effect may be to achieve acidification of oxalic acid and
separation of the oxalic acid from the salt used in electrochemical
cell 102. The oxalic acid 144 may then be utilized as a product or
further processed to another chemical. The salt used in the first
electrochemical cell may be recycled so there may be few byproducts
of the process.
[0186] The separation, acidification, and solvent transfer process
of anion exchanger 140 may be effected by a basic anion exchange
resin. An embodiment of the process is illustrated in FIG. 4, which
includes absorbing oxalate ions using a basic anion exchange resin
and desorbing the oxalate with a desired mineral acid. Referring to
FIG. 5, a more detailed series of flow diagrams illustrating the
oxalate absorption, water rinsing, regeneration, and solvent rinse
steps is shown.
[0187] Step 1: The process starts with primary inputs of solvent
mix A which may be either a single solvent or mixture of solvents,
oxalate ions of the form M.sub.nC.sub.2O.sub.4 where M is a cation
that is monovalent or divalent, and X is an anion such as Cl.sup.-,
Br.sup.-, or I.sup.-. The input solution may be passed through a
strong base ion exchange resin in the X.sup.- form; oxalate is
absorbed by the anion exchange resin, liberating X.sup.-. The
effluent recycle stream may include solvent A and salt
M.sub.nX.sub.m.
[0188] Step 2: When the ion exchange bed is exhausted and oxalate
begins to break through the bed, the bed may be drained and rinsed
with water. Rinsing may remove solvent A from the resin bed.
[0189] Step 3: The bed may be regenerated with an aqueous HX
solution of sufficient concentration to cause the desorption of
oxalate ions. Regeneration may result in a mixed stream of oxalic
acid and HX in water.
[0190] Step 4: After regeneration, the bed may be drained and
rinsed with solvent A. The process may now be restarted by
returning to Step 1.
[0191] In this embodiment, the oxalate salt may be removed from one
solvent and re-dissolved as oxalic acid in an aqueous phase. This
is specifically useful coupled with the electrochemical
hydrogenation cells 620, 630 of FIG. 6 which may which require
oxalic acid in an aqueous electrolyte.
[0192] In a different embodiment, a solvent used in the anion
exchange process as the regenerate could be solvent A or another
non-aqueous solvent. In this embodiment, oxalic acid may be
re-dissolved in solvent A or another non-aqueous solvent followed
by thermal catalytic hydrogenation of oxalic acid as shown in
thermal hydrogenation device 610 of FIG. 6. Catalytic hydrogenation
of oxalic acid may be performed in either aqueous or non-aqueous
solution.
[0193] In another embodiment, the oxalate salt may be precipitated
from the non-aqueous phase recovered from electrochemical cell 102
by using a combination of a cation and solvent to give low
solubility oxalate salt. This may be described as shown in FIG. 24.
After isolation of the salt it may be dissolved in an aqueous
solution and acidified with HX. In order to recover the MX for
reuse, an appropriate solvent may be added to the aqueous solution
of oxalic acid and MX to cause MX precipitation. The MX may be
dried and recycled, and a second solvent separated from the aqueous
phase to recover the second solvent. This may provide oxalic acid
in aqueous solution for use in electrochemical hydrogenation cells
620, 630 of FIG. 6B and FIG. 6C.
[0194] In another embodiment, the oxalate salt may be precipitated
from the non-aqueous phase from electrochemical cell 102 by using a
combination of a cation and solvent to give a low solubility
oxalate salt. After isolation this salt may be dissolved in an
aqueous solution and acidified with HX. Using liquid-liquid
extraction, oxalic acid may be extracted into a second phase, as
shown in FIG. 23. The extraction solvent may be separated from the
oxalic acid and recovered, leaving oxalic acid to be re-dissolved
in an aqueous solution. The MX left in the aqueous phase may be
dried and recycled, for example to electrochemical cell 102.
[0195] Oxalic acid may be recovered as a saleable product or may be
further reduced to more reduced C.sub.2 or C.sub.4 chemicals. The
methods of reduction may involve either thermal catalytic
hydrogenation or electrochemical reduction as shown in FIGS. 6A, 6B
and 6C.
[0196] It is contemplated that hydrogenation device 150 as depicted
in FIGS. 1-3 and 10-14 may be implemented as one of devices 610,
620, 630 as shown in FIGS. 6A, 6B, 6C, and 16. Referring
specifically to FIG. 6A, thermal catalytic hydrogenation device 610
may be configured to retain oxalic acid in a non-aqueous solvent
through the anion exchanger 140. Oxalic acid may also be in an
aqueous solution. It may then be hydrogenated to a more reduced
chemical such as glyoxylic acid, glycolic acid, glycolaldehyde,
ethylene glycol, ethanol, acetaldehyde, acetic acid, ethane,
ethylene, or glyoxal via the addition of heat, pressure, and/or
introduction of a hydrogenation catalyst. C.sub.4 chemicals may
also be produced. For instance, oxalic acid in propylene carbonate
might be pumped into a high-pressure reactor, pressurized with
H.sub.2, and heated in the presence of a supported hydrogenation
catalyst. Ethylene glycol, or glycolic acid, may then be recovered
upon completion of the reaction.
[0197] The overall equation for hydrogenation device 610 for
C.sub.2 products is:
H.sub.2O.sub.2O.sub.4+zH.sub.2.fwdarw.H.sub.xC.sub.2O.sub.y+zH.sub.2O
[0198] For hydrogenation device 610, catalysts may include cobalt,
copper, ruthenium, ruthenium dioxide, cobalt nickel alloys, nickel,
Pt group metals, rhenium, copper chromite, zinc copper chromite,
barium chromite, ammonium copper chromate, zinc chromate, Raney
nickel, manganese chromate, and alloys of copper and the other
metals listed. These catalysts may be supported on carbon, alumina,
silica, diatomaceous earth, pumice, zeolites, or molecular
sieves.
[0199] Promotors such as trivalent phosphorus compounds, ammonia,
and alkylammonium salts may be employed. The operation may be
either batch mode or continuous flow mode with either a fixed bed
or a fluidized bed. Contact time of the reactant with the catalyst
may be greater than 0.1 seconds.
[0200] The reactant for hydrogenation device 610 may be either
oxalic acid, an oxalate salt, oxalic acid dihydrate, or the diester
of oxalic acid. The H.sub.2 pressure may be greater than 10
atmospheres and may be between 10-1000 atmospheres. The H.sub.2
concentration may be in excess of the stoichiometric amount
required to reduce oxalic acid to ethylene glycol. The temperature
may be between 50.degree. C. to 500.degree. C., preferably less
than 150.degree. C. to avoid thermal decomposition of oxalic
acid.
[0201] It is contemplated that the oxalic acid carrier may include
a non-aqueous solvent such as those which may be used in
electrochemical cell 102. In one embodiment, the oxalate salt will
be acidified where the solvent could include propylene carbonate or
acetonitrile. The cations liberated from the oxalate salt may be
recycled to the catholyte region of an electrochemical cell, while
the oxalate salt is acidified to oxalic acid in a non-aqueous
stream. A stream comprising oxalic acid, a non-aqueous solvent,
with or without a further salt, may be directed to the
hydrogenation device 610 for hydrogenation.
[0202] The hydrogenation of oxalic acid may take place in water, a
non-aqueous solvent, or in the gas phase. Oxalic acid may also be
contacted with an alcohol, such as methanol or ethanol or butanol,
to form esters to include dimethyl oxalate or diethyl oxalate or
dibutyl oxalate. These esters may then be hydrogenated, which
allows for the production of higher order products and the recovery
of the alcohol.
[0203] Hydrogenation of the oxalic acid mono and diesters is well
reported in the literature and is traditionally carried over
supported NiO/CuO catalysts in both gas and in liquid phase. The
liquid phase hydrogenation of oxalic acid may take place through a
series of intermediates, as shown in FIG. 15, leading to ethylene
glycol. According to this reaction scheme, the hydrogenation of
oxalic acid generates glyoxylic acid, which may be converted to
either glyoxal or glycolic acid, and further hydrogenation of
either of these two intermediates generates the glycolic aldehyde,
the glycolic aldehyde may be converted to ethylene glycol.
[0204] It is contemplated that the electrochemical hydrogenation
cells 620, 630 of FIGS. 6B and 6C may be suitable for hydrogenation
of oxalic acid to glyoxylic acid. It is further contemplated that
thermal catalytic hydrogenation device 610 may be suitable for
hydrogenation of oxalic acid to glycolic acid as a first possible
product or ethylene glycol as a second possible product.
[0205] Referring to FIG. 16, a schematic illustrating the
components of a thermal catalytic hydrogenation system is shown.
Thermal catalytic hydrogenation system 1600 may be one
implementation of hydrogenation device 150 of FIGS. 1-3 and FIGS.
10-14. Thermal catalytic hydrogenation system 1600 may include a
reactor configured for continuous monitoring of a hydrogen uptake
rate. Reactor may include a standard 100 mL stainless steel PARR
Autoclave 5. The entire vessel of the reactor may be removed from a
stand as a complete assembly for either charging or product
recovery. The reactor is equipped with a magnetically coupled drive
with a permanent magnet for the inner rotor, to which the stirring
shaft is attached. Additionally, a water cooling sleeve attached to
the drive protects the components from excessive heat arising from
a head of the reactor. The first port, 1 accommodates a safety
rupture disc intended to release pressure if a critical level is
exceeded. Port 2 is a combination port which holds liquid sampling
and gas inlet valves. The sampling valve allows removal of liquid
product samples without the need to open the reactor. A dip tube
fitted with stainless steel frit at the tip allows extraction of
liquid samples while allowing the catalyst to remain in the
reactor. The catalyst may then be reused in subsequent reactions.
Port 3A is a combination port configured to accommodate a pressure
gauge and a 1/8'' stainless steel needle valve. Port 3B is a second
combination port accommodating a pressure gage and a 1/8''
stainless steel needle valve. The latter is used as a primary gas
inlet port for initially purging and pressurizing the reactor and
the port itself is connected to the volumetric section of the
reactor system through a 1/8'' stainless steel tube. Port 4
comprises a J-type thermocouple while the remaining two ports can
be fitted with a cooling coil for accurate control of the reactor
temperature. The cooling coil may also be removed to produce two
additional ports. A first additional port may be left blank while a
second additional port, 6 may be fitted with 1/4'' on/off valve
used for loading reaction solutions using gas-tight syringes.
[0206] For catalyst activation (pre-reduction), the reactor may be
charged with 5 wt % Ru/C catalyst and 40 mL deionized water. The
reactor may be alternately purged with argon 5 times and hydrogen
also 5 times. The system 1600 may be pressurized to 800 psi, the
reactor heated to the desired temperature and stirred for 3 hours
at stirring rate of 200-300 RPM. The reactor may then be cooled to
ambient temperature, and without opening the reactor, the water may
be siphoned out through a dip tube, fitted with 2 mkm stainless
still fritted filter.
[0207] After catalyst activation (pre-reduction), the reactor may
be charged with 41.5 gm of 5% aqueous oxalic acid solution using a
gas-tight syringe. To remove dissolved oxygen, the feed solution
may be kept in a septa-sealed glass bottle and may be carefully
purged with inert gas for at least 30 min before injection into the
reactor. The reactor may be flushed 5 times and pressurized with
hydrogen to 800 psi, the stirring rate may be set initially to 200
RPM and the reactor heated to desired temperature (between
50.degree. C. and 170.degree. C.) over a period of 60 minutes. The
pressure may be adjusted to the desired setting, the stirring rate
increased to 800-900 RPM and monitoring of the hydrogen uptake was
initiated. During the first 6 hours, samples may be taken at 2 hour
intervals and hydrogenations were typically continued for 21
hours.
[0208] Catalysts employed in the hydrogenation reactions of thermal
catalytic hydrogenation system 1600 may include Ru/C, Ru/SiO.sub.2,
Ru/Al.sub.2O.sub.3, Pd/C, and Cu-Chromite. Temperatures may range
from approximately 50.degree. C. to approximately 170.degree. C.
Hydrogen may be employed at pressures of about 300 psi to about
1500 psi. Stirring rates may range from about 400 RPM to about 800
RPM. The hydrogenation reactor may be stainless steel, unlined or
Teflon lined, or glass lined. The reactor may also be made of
Hastelloy or Elgiloy or other corrosion resistant materials.
Starting material concentrations of oxalic acid may range from
about 5% by weight to about 50% by weight. Products from the
thermal catalytic hydrogenation reaction may include mono ethylene
glycol, glycolic acid, and acetic acid.
[0209] In one exemplary operation, to a container charged with 7.5%
by weight of activated (pre-reduced) Ru/C catalyst was added 100 gm
of a 25% by weight oxalic acid solution in water. The mixture was
subjected to thermal catalytic hydrogenation conditions as
described above at a temperature of 75.degree. C., with a stirring
rate of 400 RPM and a pressure of 1500 psi of hydrogen. After six
hours, the reaction was worked up to provide by weight 76.4%
glycolic acid, 6.6% mono-ethylene glycol, and 10.5% acetic acid
with a total recovered carbon balance of 93.5%.
[0210] In another embodiment, the temperature of the hydrogenation
may be initially held at a temperature between 50.degree. C. to
85.degree. C. for a period of 5 to 8 hours followed by an increase
in temperature to between 110.degree. C. and 150.degree. C. for a
period of 2 to 5 hours. At the end of the reaction monoethylene
glycol may be isolated. Initial hydrogenation at a lower
temperature may minimize thermal decomposition of oxalic acid.
[0211] In another embodiment, after the reaction mixture has
reached a reaction temperature between 50.degree. C. and
170.degree. C., the oxalic acid may be slowly added to the reaction
mixture in order to minimize the concentration of oxalic acid in
the reaction mixture.
[0212] Referring to FIG. 17, a schematic illustrating a reactive
distillation column is shown. Reactive distillation is a process
technology with the potential to simultaneously perform chemical
reactions and separations of product and reactants. The reactive
distillation process performed by the reactive distillation column
1700 may be configured for esterification of oxalic acid with
alcohol (1-butanol, ethanol and methanol) to produce dialkyl
oxalate (dibutyl oxalate (DBO), diethyl oxalate (DEO), dimethyl
oxalate (DMO), and the like.
[0213] Reactive distillation column 1700 may include a rectifying
zone, a reactive zone and a distillation zone. Reactive
distillation column 1700 may receive oxalic acid and an alcohol,
such as butanol. Reactive distillation column may simultaneously
reactive and separate the dibutyl oxalate which may then be
hydrogenated to mono-ethylene glycol.
[0214] Oxalic acid has unique properties. It is highly acidic
compared to other dicarboxylic acids and it is thermally unstable
due to the presence of the adjacent carboxylic acid groups. Acidity
and thermal stability must be carefully considered when designing a
process to selectively synthesize a dialkyl ester and separate it
from other chemical species.
[0215] Once formed, an oxalic acid diester may then be hydrogenated
to mono-ethylene glycol (MEG) with great selectivity and
efficiency. Oxalic acid diester may be obtained by condensing
oxalic acid with low molecular weight alcohols such as methanol,
ethanol, propanol, isopropanol, butanol or iso-butanol using an
acid. Protic Bronsted acids such as H.sub.2SO.sub.4, HCl,
H.sub.2PO.sub.4, p-TsOH, and MsOH have been used as the acid
catalysts in conventional esterification chemistry. Esterifications
may also be catalyzed with solid acids such as Amberlyt-15,
Amberlyst-35, Smopex 101, Zeolite-Y, H-USY, Zeolite-X,
Zeolite-.beta., Zeolite Mordenite, Silica-Alumina,
Molybdatophosphoric acid hydrate, sulfated zirconia, sulfated
SnO.sub.2, sulfated TiO.sub.2, sulfated Nb.sub.2O.sub.5, Tungstated
ZrO.sub.2, Nafion SiO.sub.2 composite (SAC-13), Mo/ZrO.sub.2,
Nb/ZrO.sub.2 etc.
[0216] The use of solid acids for esterifications may be
advantageous due to its simplicity at a process level. Solid acids
may be placed in a fixed-bed type system thereby reducing the
overall capital cost of the process by eliminating a need for a
separation of the acid from the reaction mixture. In most of the
cases, mineral acids that are used for esterification are lost
without recovery due to low concentration, which in turn increases
downstream purification and waste treatment costs.
[0217] Both conventional esterification methods (such as: Soxhlet
extraction, liquid-liquid extraction, Dean-Stark, in situ drying
methods, etc.) as well as advanced reactive distillation column
(RDC) methods may be used to form oxalate esters. Various alcohols,
catalysts, oxalic/alcohol ratio, catalyst loading, temperature and
other reaction conditions have been considered in order to enhance
the kinetics, product concentration, and yield.
[0218] Bench scale batch reactions of the esterification of oxalic
acid with methanol, ethanol, and butanol using solid acids such as
Amberlyst-15 and Silica-Alumina may be conducted to determine rate
and conditions for the optimal yield of the esterification. Removal
of water may generate optimal yields and rates. These parameters
may be utilized to design the reactive distillation column 1700 for
the esterification of oxalic acid with a solid acid catalyst, which
shifts the esterification of dialkyl oxalate reactions both
chemically and thermodynamically to overcome the theoretical limits
imposed by both chemical and phase equilibria of the highly
non-ideal systems.
Esterification Experiments
Diethyl Oxalate (In Situ Drying Agent):
[0219] An anhydrous oxalic acid (1 g, 11.1 mmol) was placed in a
round bottom flask and was dissolved in anhydrous ethanol (50 mL,
39.45 gm, 85.6 mmol). The mixture was stirred at room temperature
until the oxalic acid dissolved. Amberlyst 15 hydrogen form (2.00
gm) was added along with magnesium sulfate (2.5 gm, 20.77 mmol) and
a rubber septum used to seal the flask. The mixture was allowed to
stir at 60.degree. C. under a nitrogen filled balloon. After 2.5
hours, additional magnesium sulfate (2.5 gm, 20.77 mmol) was added
to the reaction mixture and then stirred for a total of 4.5 hours.
The reaction was cooled and filtered. The crude liquid reaction
mixture was concentrated via rotary evaporation affording a light
brown oil containing a small amount of residual magnesium
sulfate.
Dimethyl Oxalate (Soxhlet):
[0220] An anhydrous oxalic acid (12.22 gm, 0.135 mol) was dissolved
in anhydrous methanol (110 mL, 86.5 gm, 2.7 mol) in a round bottom
flask and stirred until the oxalic acid was dissolved. Toluene (110
mL) was added to the mixture along with p-toluene sulfonic acid
(1.28 gm, 6.75 mmol). A Soxhlet extractor containing a glass
thimble packed with magnesium sulfate was placed over the round
bottom flask. The mixture was refluxed for 18 hours. At the end of
this time, the reaction mixture was cooled to room temperature and
solvent was concentrated via a rotary evaporation yielding a white
solid (13.8 gm, 87% crude yield).
Dimethyl Oxalate (Dean-Stark)
[0221] An anhydrous oxalic acid (22.22 gm, 0.25 moles), p-toluene
sulfonic acid monohydrate (2.34 gm, 0.123 moles) and methanol (100
mL, 79.1 gm, 2.47 moles) were added to a round bottom flask. The
round bottom flask was attached to a dean-stark apparatus filled
with toluene. The reaction was refluxed for 18 hours. At the end of
this time, the reaction mixture was concentrated via a rotary
evaporation affording white solid (30.17, 95.5% crude yield).
Dimethyl Oxalate (Liquid-Liquid Extractor):
[0222] An anhydrous oxalic acid (66.68 g, 0.74 moles), methanol
(600 mL, 474.6 g, 14.81 moles) and deionized H.sub.2O (290 mL) were
added to a body of the liquid-liquid extractor. P-toluene sulfonic
acid monohydrate (27.06 gm, 0.142 moles) was added to a reactor
body along with toluene (100 mL). Toluene (500 mL) may also be
placed in the round bottom flask of the liquid-liquid extractor and
heated in a 150.degree. C. oil bath. The reaction was left to stir
for several hours. The organic solution was concentrated via a
rotary evaporation affording a white solid (44.3 gm, 51% crude
yield).
Note on Catalyst Activation (Silica-Alumina):
[0223] Silica alumina (50 gm) was placed in 1M ammonium chloride
(250 mL) and may be stirred for six hours at room temperature. The
silica-alumina was filtered off with a fritted Buchner funnel,
washed with deionized H.sub.2O, and dried for several hours. Around
8.65 gm was left to calcine for 5.5 hours under argon gas at
450.degree. C. in a tube oven. After cooling to room temperature,
the silica-alumina may be placed in a vacuum oven at 60.degree. C.
for 45 minutes prior to use.
Reactive Distillation
[0224] Reactive distillation involves the simultaneous reaction as
well as separation of the reaction components using a catalyst at
proper system temperature. Esterification is an exothermic process
and hence lot of heat is generated during the reaction. In
conventional process, this majority of the heat is extracted using
heat transfer methods and not utilized comprehensively. In RDC, the
heat is utilized internally to heat the reaction components in
order to carry out separation simultaneously. This advanced
simultaneous process reduces thermal energy cost considerably.
Based on the physical and chemical properties such as boiling
point, stability, miscibility, affinity, reactivity of the
reactants and products, RDC methods of producing dibutyl oxalate
(DBO) and diethyl oxalate (DEO) have been designed and tested.
Reactive Distillation of Dibutyl Oxalate
[0225] As shown in FIG. 17, oxalic acid in 1-butanol solution at
95.degree. C. or higher is fed into a location at the upper portion
of the column, and the rest of 1-butanol (total of 1:5 molar ratio
of oxalic acid to butanol) is fed at a location of the lower
portion of the column close to the column bottom at a temperature
of 100.degree. C. to 130.degree. C. The column is packed with solid
acid catalyst in the middle section, the lower and upper sections
of the column are packed with structural packing without catalytic
reactivity for separations purpose only, identified as rectifying
and distillation zones.
[0226] Esterification happens in the middle of the column. Water
and unreacted butanol are recovered at the top of the column in a
decanter, the butanol in the top phase is then recycled back for
further esterification. The bottom stream has a dibutyl oxalate
concentration of 46% wt to 75% wt, the rest of the mixture is
butanol along with a minor amount of water, the product stream may
be further separated to yield higher purity dibutyl oxalate for
subsequent use.
Reactive Distillation of Diethyl oxalate
[0227] Oxalic acid in ethanol (EtOH) solution at 79.4.degree. C.
may be fed into proper location at the upper portion 1710 of the
column and the rest of ethanol (total of 1:5 molar ratio of OA to
EtOH) may be fed at a proper location of the lower portion of the
column 1720 at a temperature of 80.5.degree. C. The column may be
packed with acid catalyst in the middle section 1730, the lower and
upper sections 1710, 1720 of the column are packed with structural
packing without catalytic reactivity for separations purpose
only.
[0228] Esterification happens in the middle of the column, 1730,
the reactive zone. Unreacted ethanol is recovered at less than 93%
weight at the top of the column 1710 (lower than the azeotrope
composition with water), it is then dried and recycled back for
further reaction. The bottom stream (product stream) has a diethyl
oxalate concentration of 87% weight, the rest is water and a minor
amount of ethanol, the stream may be further separated to yield
higher purity diethyl oxalate for subsequent use.
TABLE-US-00006 TABLE Comparison of the esterification rate of batch
and RDC method: Conventional batch method RDC method Rate of
dialkyl ester 30-150 gram/hour-liter 150-400 gram/hour-liter
formation
[0229] Due to the efficient removal of water in RDC method, the
rate may be much higher than that of conventional batch method.
[0230] The reactive distillation column 1700 may be designed in a
way that it can separate reactive mixtures involving azeotropes to
a large extent. Such separations may be difficult to achieve by
conventional "distillation after reaction" mechanism where
reactions are fully controlled by the equilibrium limit and phase
behavior is controlled by azeotrope properties.
[0231] The heat released by esterification of oxalic acid may be
used for vaporizing water without the need for heat exchange
equipment and heating and cooling resources, and without thermal
resistance.
[0232] Solid acid Amberlyst and Zeolites catalysts may be used,
instead of H.sub.2SO.sub.4 or other liquid acids which may be lost
in the process resulting in additional waste treatment costs. Solid
acid catalysts may be packed in a bed and have a lifetime of
several years.
[0233] The esterification reactions may occur at atmospheric
pressure and temperature ranges from 100.degree. C. to 160.degree.
C., depending on the catalyst used.
[0234] The oxalate esters obtained from reactive distillation may
be used in subsequent processes. For example, the esters may be
reduced to ethylene glycol via thermal catalytic hydrogenation.
[0235] Referring once again to FIGS. 6B and 6C, oxalic acid may be
electrochemically reduced to C.sub.2 and C.sub.4 products at the
cathode 122 of the electrochemical cell 620, 630. Various anodic
reactions that liberate available H+ may be employed. As shown in
FIG. 6B, electrochemical cell 620 may be configured for water
oxidation to H.sup.+ and O.sub.2 if a benign side product is
desired. This is given by the equation for C.sub.2 products:
H.sub.2O.sub.2O.sub.4.fwdarw.H.sub.xC.sub.2O.sub.y+zO.sub.2
[0236] As shown in FIG. 6C, electrochemical cell 630 may be
configured for HX oxidation to a halogen and H.sup.+ if a halogen
is desired as the product. This is given by the equation for
C.sub.2 products:
H.sub.2O.sub.2O.sub.4+2zHX.fwdarw.H.sub.xC.sub.2O.sub.y+zH.sub.2O+zX.sub-
.2
[0237] Similarly, the oxidation of other organic and inorganic
species may be employed as the anolyte reaction and are not limited
to these variations.
[0238] As shown in FIGS. 6B and 6C, electrochemical cells 620, 630
may have cathodes that may include and are not limited to Pb, C,
graphite, semiconductors, In, Sn, Zn, Cd, Hg, amalgams, Bi, Ga,
alloys containing Pb, In, Sn, Zn, Cd, Hg, Bi, Ga, bimetallics
containing Hg with another conductor, or other combinations of
bimetallics, and metal carbides. The catholyte may include
homogeneous catalysts. Homogeneous catalysts may include aromatic
heterocyclic amines and may include, but are not limited to,
unsubstituted and substituted pyridines and imidazoles. Substituted
pyridines and imidazoles may include, but are not limited to mono
and disubstituted pyridines and imidazoles. For example, suitable
catalysts may include straight chain or branched chain lower alkyl
(e.g., C1-C10) mono and disubstituted compounds such as
2-methylpyridine, 4-tertbutyl pyridine, 2,6 dimethylpyridine
(2,6-lutidine); bipyridines, such as 4,4'-bipyridine;
amino-substituted pyridines, such as 4-dimethylamino pyridine; and
hydroxyl-substituted pyridines (e.g., 4-hydroxy-pyridine) and
substituted or unsubstituted quinoline or isoquinolines. The
catalysts may also suitably include substituted or unsubstituted
dinitrogen heterocyclic amines, such as pyrazine, pyridazine and
pyrimidine. Other catalysts generally include azoles, imidazoles,
indoles, oxazoles, thiazoles, substituted species and complex
multi-ring amines such as adenine, pterin, pteridine,
benzimidazole, phenonthroline and the like.
[0239] For bromine and iodine anode chemistry, carbon and graphite
may be particularly suitable for use as anodes in electrochemical
cells 620, 630. Polymeric bonded carbon sheets may also be used.
For other chemistries, carbon, cobalt oxides, stainless steels,
their alloys and combinations may be employed as well as coatings
of precious metal oxides such as ruthenium and iridium oxides, as
well as platinum and gold and their combinations as metals and
oxides on valve metal substrates such as titanium, tantalum, or
niobium.
[0240] A desired salt in the catholyte region 116 of
electrochemical cells 620, 630 may include either HBr, HCl, HI,
H.sub.2SO.sub.4, bromide, chloride, or sulfate salts where the
cation is sodium, potassium, ammonium, tetraalkylammonium, or
another single or divalent cation. Concentrations of salts may
range from mM to M. A desired salt in the anolyte region may
include either HBr, HCl, HI, H.sub.2SO.sub.4, bromide, chloride, or
sulfate salts where the cation is sodium, potassium, ammonium,
tetraalkylammonium or another single or divalent cation. The
concentration may range from mM to M. The anodic chemistry may also
be operated in the gas phase. In this embodiment, anhydrous HBr or
HCl gas anolyte may be used as well as water vapor.
[0241] In a preferred embodiment, the solvent may be water with
concentrations of oxalic acid near saturation levels of about 12%
by weight. The solvent may also be a variety of non-aqueous
solvents with specifically added quantities of water. These
non-aqueous solvents could include but are not limited to propylene
carbonate, ethylene carbonate, dimethyl carbonate, diethyl
carbonate, dimethylsulfoxide, dimethylformamide, acetonitrile,
acetone, tetrahydrofuran, N,N-dimethylacetaminde, dimethoxyethane,
diethylene glycol dimethyl ester, butyrolnitrile,
1,2-difluorobenzene, .gamma.-butyrolactone, N-methyl-2-pyrrolidone,
sulfolane, 1,4-dioxane, nitrobenzene, nitromethane, acetic
anhydride, and ionic liquids. Oxalic acid may be soluble in the
solvent chosen. In one embodiment, oxalic acid in propylene
carbonate with the appropriate salt may be used as the
catholyte.
[0242] A preferred oxalic acid concentration may range from 1 mM to
about 12% by weight in aqueous solution. The solubility limit of
oxalic acid may be increased by using solvents other than water.
The solubility limit may also be increased by increasing the
temperature of the reaction and/or through the use of electrolytes
that have a salting effect on oxalic acid. These include
thiocyanates, perchlorates, tetrafluoroborates, and
hexafluorophosphates.
[0243] Generally, the solvent may be the same in both the catholyte
region 116 and anolyte region 118 of electrochemical cells 620,
630. However, in certain embodiments, the solvent used in the
catholyte region 116 and anolyte region 118 may differ. If a
halogen is produced in the anolyte region 118 of electrochemical
cell 630, the solvent of choice may be stable in the presence of
Br.sub.2, Cl.sub.2, or I.sub.2.
[0244] In the catholyte region 116, the pH may depend on the
concentration of oxalic acid and the electrolyte salt or acid
employed. In general, the pH may range from 0 to 5. In the anolyte
region 118, the pH may depend on the concentration of the
electrolyte acid employed. In general, the pH may range from 0 to
5.
[0245] The temperature used may depend on the solvent chosen. For
aqueous solution, the preferred temperature range may be 5.degree.
C. to 80.degree. C. Lower and higher temperature ranges may be
employed by using various solvents. A catholyte cross sectional
area flow rate range may be 2-3,000 gpm/ft.sup.2 or more
(0.0076-11.36 m.sup.3/m.sup.2). A flow velocity range may be 0.002
to 20 ft/sec (0.0006 to 6.1 m/sec).
[0246] Electrochemical cells 620, 630 may include zero-gap,
flow-by, and flow-through designs with a recirculating catholyte
electrolyte with various high surface area cathode materials. Also
flooded co-current packed and trickle bed designs with the various
high surface area cathode materials may be employed for the
electrochemical cells 620, 630. Bipolar stack cell designs, high
pressure cell designs and filter press, zero gap designs with gas
phase anodic chemistries and either aqueous or non-aqueous cathodic
chemistry may be employed for the electrochemical cell 620,
630.
[0247] In one embodiment, the catholyte may include oxalic acid, a
solvent, and a salt, with a gas phase HBr anolyte. The cathode and
anode materials may be in direct contact with the membrane and
there may be less than a few millimeters of depth to the anode or
cathode region. High surface area of the anode and cathode may be
achieved through micro and nano-structuring of the electrode
materials. Mixed Phase--Gas phase anodic chemistry with aqueous
phase or non-aqueous phase cathodic chemistry may also be
implemented.
[0248] The cathode/anode electrodes may include a preferred void
volume, ranging from 30% to 98% and a specific surface areas from 2
cm.sup.2/cm.sup.3 to 500 cm.sup.2/cm.sup.3 or higher. Surface areas
also may be defined as total area in comparison to the current
distributor/conductor back plate, with a preferred range of
2.times. to 1000.times. or more.
[0249] Cation ion exchange type membranes may be preferred,
especially those that have a high rejection efficiency to anions,
for example perfluorinated sulfonic acid based ion exchange
membranes such as DuPont Nafion brand unreinforced types N117 and
N120 series, more preferred PTFE fiber reinforced N324 and N424
types, and similar related membranes manufactured by Japanese
companies under the supplier trade names such as Flemion.
[0250] Other multi-layer perfluorinated ion exchange membranes used
in the chlor alkali industry may have a bilayer construction of a
sulfonic acid based membrane layer bonded to a carboxylic acid
based membrane layer, which efficiently operates with an anolyte
and catholyte above a pH of about 2 or higher. These membranes may
have much higher anion rejection efficiency. These are sold by
DuPont under their Nafion trademark as the N900 series, such as the
N90209, N966, N982, and the 2000 series, such as the N2010, N2020,
and N2030 and all of their types and subtypes.
[0251] Hydrocarbon based membranes, which are made from of various
cation ion exchange materials may also be used if the anion
rejection is not as critical, such as those sold by Sybron under
their trade name Ionac, ACG Engineering (Asahi Glass) under their
Selemion trade name, and Tokuyama Soda among others on the
market.
[0252] Microporous separators may also be employed in some system
options such as microporous PVDF (polyvinylidiene difluoride), PTFE
(polytetrafluoroethylene), or glass fiber based materials as well
as commercial diaphragms. Other separators as describe elsewhere
herein may also be used.
[0253] Referring to FIG. 18, a method 1800 for conversion of carbon
dioxide to oxalate, oxalic acid and oxalic acid reduction products
is shown.
[0254] Referring to FIG. 22, a method 2200 for purifying an oxalate
salt is shown. Method 2200 may begin with an oxalate salt, such as
tetrabutylammonium oxalate or other oxalate salt in a non-aqueous
aprotic solvent, such as acetonitrile, is received as a starting
material. The oxalate salt may be purified by reacting the oxalate
salt with a metal ion (MX.sub.2), optionally dissolved in a second
solvent (solvent A), to form a weakly soluble, or insoluble complex
(M-Oxalate). For example, metal ions such as Mg, Ca, Zn, Mn, Ni,
Fe, and Cu may be employed. The mixture may be filtered to yield
the solid M-Oxalate and a solution of salt, such as
tetraalkylammonium halide, in solvent or a mixture of solvents. The
salt solution and solvent(s) may be recycled. The solid M-Oxalate
may be treated with acid HX and solvent or a solvent mixture
(solvent NB) to yield oxalic acid and salt MX. Oxalic acid may then
be purified from the solution. Salt MX and solvent or solvent
mixture (solvent A/B) may be recycled.
[0255] In another embodiment, an oxalate salt solution may be
electrochemically acidified. Representative electrochemical
acidification cells have been discussed previously and are
illustrated in FIGS. 7, 8, 9A-C, and 23.
[0256] In another embodiment, an oxalate salt may be purified
through the use of an ion exchange column, such as an anion
exchange column, as shown in FIG. 26. An oxalate salt, such as a
tetraalkylammonium oxalate, in a non-aqueous aprotic solvent, such
as acetonitrile, and optionally tetraalkylammonium halide may be
flowed onto an ion exchange column to which the oxalate dianion
adheres. Oxalate salt solution may be flowed onto the column until
oxalate is detected flowing off the column, indicating column
saturation. Tetraalkylammonium halide and solvent flowing off the
column may be recovered and recycled, for example for use in an
electrochemical carbon dioxide reduction cell 102 in FIG. 1. After
oxalate salt has been adsorbed onto an ion exchange column, a
solution of acid, such a HX, may be flowed onto the column. The
acid may convert the oxalate salt to oxalic acid and oxalic acid
may flow out of the column with the solvent and unreacted acid. The
oxalic acid and acid HX may then be separated, with the HX being
recycled, and oxalic acid being isolated or being reacted to form
other products, such as further reduced two-carbon products.
[0257] In another embodiment, an oxalic acid and
tetraallkylammonium halide solution in a non-aqueous aprotic
solvent, such as acetonitrile, may be purified through solid
sorbent amine extraction. Solid-phase column materials may comprise
Dowex MWA-1, Amberlite IRA-910, Amberlite IRA-35, Reillex 425 or
similar materials. An oxalic acid solution in a non-aqueous aprotic
solvent, such as acetonitrile, and optionally tetraalkylammonium
halide may be flowed onto a solid sorbent amine column to which the
oxalic acid adheres. Oxalic acid solution may be flowed onto the
column until oxalic acid is detected flowing off the column,
indicating column saturation. Tetraalkylammonium halide and solvent
flowing off the column may be recovered and recycled, for example,
for use in an electrochemical carbon dioxide reduction cell 102 of
FIG. 1. After oxalic acid has been adsorbed onto a solid sorbent
amine column, forming a solid sorbent amine-oxalate salt, a
solution of amine base may be flowed onto the column. The base may
convert the solid sorbent amine-oxalate salt to soluble
amine-oxalate salt and the soluble amine-oxalic acid salt may flow
out of the column. The oxalic acid and soluble amine then be
separated, for example through heating, with the amine being
recycled and oxalic acid being isolated or being reacted to form
other products, such as further reduced two-carbon products.
[0258] In another embodiment, an oxalic acid and tetraalkylammonium
halide mixture may be purified through chromatography. The mixture
may be flowed onto a chromatographic medium, such as a hydrophilic
medium or a hydrophobic medium. Suitable chromatographic media
include silica gel, alumina, polymers, reverse phase silica gel,
and related chromatographic media. The oxalic acid and
tetraalkylammonium halide mixture may be flowed onto the
chromatographic medium in solution, or the mixture may be combined
with the chromatographic medium as a solid. After the mixture has
been flowed onto the chromatographic medium, or combined with the
chromatographic medium, a solvent, or mixture of solvents, may be
flowed onto the medium to separate the oxalic acid from the
tetraalkylammonium halide. Suitable solvents include water,
methanol, ethanol, 1-propanol, isopropanol, acetonitrile, hexane,
petroleum ether, diethyl ether, formic acid, acetic acid, ammonia,
and triethylamine. The separated oxalic acid may be further reduced
to two carbon products, and the tetraalkylammonium halide may be
recycled, for example for use in an electrochemical carbon dioxide
reduction cell.
[0259] In another embodiment, an oxalic acid and tetraalkylammonium
halide solution in a non-aqueous aprotic solvent, such as
acetonitrile, may be purified through nano-filtration. Two
different nano-filtration methods may be employed. Referring to
FIG. 19, a method 1900 may employ nano-filtration that may reject
oxalic acid and may allow tetraalkylammonium halide in solvent to
pass through the filter. The resulting permeate stream may be
recycled. The reject stream of oxalic acid in solvent may be sent
to distillation to remove the solvent, which may be recycled, and
yield purified oxalic acid. The purified oxalic acid may be further
processed to yield other products such as other two-carbon
containing compounds. Suitable nano-filtration membranes are
solvent stable membranes, such those manufactured by Evonik under
the trade name of DuraMem and PuraMem, which also come in different
molecular weight cutoffs (i.e., 150, 200, etc. in Daltons) which
may also improve the selected separations. The pH adjustment of the
solvent solution may also have a pH range where the separation
selectivity is also improved, with the addition of excess HX to the
solution. In another embodiment, if the ACN is replaced by water,
the salts may also be separated using nano-filtration membranes
that are suitable for use in aqueous solutions.
[0260] Referring to FIG. 20, a method 2000 may employ
nano-filtration that may reject tetraalkylammonium halide and may
allow passage of oxalic acid. The reject stream containing
tetraalklyammonium halide in solvent may be recycled. The permeate
stream containing oxalic acid may be sent to distillation to remove
the solvent, which may be recycled, and yield purified oxalic acid.
The purified oxalic acid may be further processed to yield other
products such as other two-carbon containing compounds.
[0261] Referring to FIG. 21, a method 2100 for purifying an oxalic
acid solution containing tetraalkylammonium halide through amine
extraction is shown. A solution of oxalic acid in a non-aqueous
aprotic solvent, such as acetonitrile, may be treated with an
amine, such as a trialkylamine to form an amine-oxalate salt. An
amine-oxalate salt may precipitate from solution or may form a two
phase liquid solution. Addition of an amine salt immiscible solvent
may optionally be added to achieve precipitation or phase
separation. The amine salt may then be filtered or the two liquid
phases may be separated to provide a solution of tetraalkylammonium
halide for recycling and an oxalic acid-amine salt, which may be a
solid or may be in solution. The oxalic acid-amine salt may then be
heated to provide purified oxalic acid, which may be used in
subsequent reactions, and amine, which may be recycled.
[0262] In another embodiment, an oxalic acid solution containing
tetraalkylammonium halide may be purified by liquid-liquid
extraction in an extractor apparatus. In this embodiment, either
the oxalic acid or the tetralalkylammonium halide or other salt may
have differing solubility in the different solvents employed. For
the case where oxalic acid may have higher solubility in a second
solvent, the oxalic acid concentration will increase in the second
solvent and decrease in the initial solution. This may leave the
tetralkylammonium halide salt in the solvent of the initial
solution which may be recycled. A series of extractor apparatuses
may be used to achieve the desired purity. For example,
counter-current extraction or dropping counter-current extraction
may be employed.
[0263] Referring again to FIG. 18, once purified oxalic acid has
been obtained it may be used in further chemistry. For example, the
oxalic acid may be reacted with alcohols to form the diester which
can then be reduced to form mono-ethylene glycol. Alternatively,
oxalic acid may be directly reduced via thermal catalytic
hydrogenation to form glycolic acid, or to form mono-ethylene
glycol. In addition, oxalic acid may be electrochemically reduced
to form glyoxylic acid.
[0264] As shown in FIG. 18, halide or trihalide anion formed during
the electrochemical reduction of carbon dioxide may be recycled
through thermal, catalytic, or electrochemical reduction systems.
For example, a stream of halogen may be reacted with a stream of
hydrogen to form HX and heat. Once the halogen and hydrogen streams
are mixed an ignition source would initiate the reaction.
Alternatively, halide or trihalide anion may be reacted with
hydrogen in the presence of a catalyst to form hydrogen halide and
heat. Catalysts such as Pt, Pd, Rh, Ru, Ni, Ir, and other
homogeneous or heterogeneous hydrogenation catalysts may be used.
Heat from the reaction of hydrogen and halide or trihalide anion
may be captured and used for energy production or to provide heat
for other processes. As illustrated in FIG. 25, an electrochemical
cell may be used to reduce halide or trihalide anion to HX.
Finally, halide or trihalide anion may be reacted in a fuel cell to
provide HX as well as electrical energy, which may be used in the
electrochemical reduction of carbon dioxide.
[0265] Referring to FIG. 28, electrochemical cell 2800 for
producing oxalate from the reduction of carbon dioxide in a
non-aqueous solvent in accordance with an another embodiment is
shown. An acetonitrile (ACN) solution with a dissolved conductive
salt, for example TBABr, may be introduced into a thin central flow
channel or compartment, such that all of the flow may be evenly
distributed in width and height from the flow channel into the
adjoining anolyte and catholyte regions containing the anode and
cathode electrode structures respectively. The central flow channel
may comprise a material, such as ionically conductive materials
that may include ion exchange beads or inert nonconductive
materials with a high open area such as plastic mesh screens,
plastic beads, and the like. Advantageously, the flow channel may
be kept open and preferably kept dimensionally stable in width or
thickness through the height of the flow channel. A separator may
be used on either side of the flow channel to help provide the flow
resistance required to have an evenly distributed flow into the
anolyte and catholyte regions. The separator may be a porous
material with a small pore size in the range of 0.01 to 5 microns
with an open area in the range of 20 to 80%. The separator may be
made from an inert material, such as a plastic material. Plastic
material may include PVDF (polyvinylidiene difluoride), HDPE (high
density polyethylene), PP (polypropylene), or PTFE
(polytetrafluoroethylene). The separator may also be made of an ion
conducting material. Ion conducting materials may include ion
exchange materials or membranes, such as sulfonated polystyrene,
cation ion exchange sulfonated tetrafluoroethylene materials sold
under the trade name of Nafion, as well as hydrocarbon based cation
ion exchange materials sold under the trade names of Selemion,
Flemion, Neosepta, and the like.
[0266] The use of the thin flow channel in this electrochemical
cell design may allow for an alternative method for controlling a
bulk flow of the solvent and salt into the cell 2800 which may not
be possible when using just a single separator between the anolyte
and catholyte regions and feeding in the required solvent into the
anolyte and catholyte regions separately. The use of porous
separators may allow a non-uniform bulk flow distribution from the
anolyte to catholyte region, or vice versa, because of pressure
differentials between the anolyte and catholyte region flow loops.
The electrochemical cell 2800 may be employed to prevent or
minimize any unwanted potential bulk flow from the anolyte to
catholyte and vice versa.
[0267] The electrochemical cell catholyte loop may include a pumped
recirculating catholyte solution where carbon dioxide is dissolved
into the ACN-TBABr solution and the carbon dioxide may be reduced
on a high surface area cathode structure. The high surface cathode
structure may incorporate a cathode current distributor. Cathode
materials include transition group metals and alloys, such as
stainless steel 316 or nickel as examples. The oxalate formed at
the cathode may then overflow the catholyte disengager as an ACN
solvent containing TBA.sub.2Oxalate and any excess or unreacted
TBABr. The catholyte product may then be processed in the next unit
operation where the oxalate is separated as oxalic acid from the
TBABr.
[0268] The electrochemical cell anolyte loop may include a pumped
recirculating anolyte solution where the dissolved bromide ion in
the ACN-TBABr solution may be oxidized at the high surface area
anode structure to bromine (Br.sub.2). The formed bromine may react
with any excess TBABr, such that the bromide ion may couple with
the formed bromine to form a tribromide complex, such as
TBABr.sub.3. The high surface anode structure may incorporate an
anode current distributor. Anode materials include carbon materials
such as carbon and graphite, which may be in the form of felts,
needled felts, or woven forms. These carbon based materials may
have catalysts impregnated into and onto the surfaces of the high
surface area carbon structure includes platinum group metals and
their oxides, mixtures, and alloys, such as gold, platinum,
ruthenium dioxide, iridium oxide, and the like that preferably may
be chemically resistant to the anode bromine formation chemistry
and may help to promote or catalyze the oxidation of bromide to
bromine. Other suitable anode materials may be valve metals, such
as titanium, niobium, and tantalum having an electrocatalyst
surface coating of the various precious metal group metals and
their oxides, mixtures, and their alloys. The TBABr.sub.3 formed at
the anode may then overflow the anolyte disengager as an ACN
solvent containing TBABr.sub.3 and any excess or unreacted TBABr.
The anolyte product may then be processed in the next unit
operation where the TBABr.sub.3 may be reacted with organics to
form brominated hydrocarbons, or reacted with hydrogen to form HBr,
which may be used to convert oxalate to oxalic acid.
[0269] Referring to FIGS. 29 and 30, an integrated
acidification-esterification-hydrogenation system is shown. Carbon
dioxide, recycled acetonitrile (ACN) and tetrabutylammonium bromide
(TBABr) or tetraalkylammonium halide (TBAX) may be fed into a
catholyte region of an electrochemical cell 2, such as described
above, where carbon dioxide 1 is electrochemically reduced to form
tetra-butyl-ammonium oxalate ((TBA).sub.2 oxalate, TBAO) or another
oxalate salt. An ACN solution, or other aprotic solvent solution,
of TBABr (TBAX) and TBAO from the cathode compartment of the
electrochemical cell (i.e., stream CATHOLYT 13) is withdrawn and
fed into a reactive extraction column 7. A halide or trihalide
anion anolyte stream (not shown) may be withdrawn from the anode
compartment of the electrochemical cell 2, or electrochemical cell
2 may comprise a hydrogen oxidizing anode as described above.
[0270] The reactive extraction column 7 comprises two sections
("Acidify" and "Rxt-Ext" as indicated in FIG. 29). The column
performs three functions: acidification, esterification, and
extraction. See FIG. 30 for an illustration of the column 7. As
shown in FIG. 30, the upper part of the column is packed with
structured packing 32, and it performs acidification of TBAO into
oxalic acid (OA) using hydrogen halide vapor, HX, which flows in
from the lower part of the Acidify section 35 of the column while
the catholyte stream is fed from the top of the column through a
liquid distributor to assure uniform distribution of the liquid.
Pump-around can be applied from the bottom of this acidifying
section to the top of the column to recycle fluids internally, as
needed, to ensure complete reaction of TBAO. This section of the
column has in-situ energy integration where the heat released by
the acidification reaction is used to vaporize the ACN without
using any heat transfer fluid or heat exchanger. ACN and unreacted
HX 16 vents at the top of the column. After a two phase FLASH, HX
30 is returned to the Acidify 35 section of the column, ACN 18 in
the liquid stream is merged with another ACN 17 stream to recycle
29 back to the cathode compartment of the cell 2.
[0271] The OA produced flows down with ACN to the lower section of
the column 7 for esterification with alcohol, such as 1-butabol
(BOH). The alcohol 15 is fed from the bottom of the column. As seen
in FIG. 30, this section of the column does esterification and
extraction simultaneously. The "Rxt-Ext" section of the column
consists of alternative zones of packed solid catalytic bed 33
(with Amberlyst 15, 35 or Zeolite Y) and unpacked rotating disks 34
for extraction. OA and BOH react to produce DBO and H.sub.2O. As
the products are formed, extraction action takes place, which means
that water continuously moves downwards with TBABr that has a
favorable partitioning into aqueous phase while DBO, unreacted BOH
and other trace organic species move up due to their lighter
densities than that of water.
[0272] The side-drain feeding of OA+ACN+TBABr to RXT-EXT section 31
goes to the bottom of the reactive zone of the column for
concurrent feeding of BOH with OA, which enhances the extraction
efficiency of the system as well as the reaction efficiency due to
the counter current flow of organic species and water. The downward
flow of produced water concentrates BOH in organic phase that is
moving up, which speeds up the esterification reaction. The
side-drain feeding of OA+ACN+TBABr to RXT-EXT 31 section can also
be split into more than one feeding points to optimize the column
performance.
[0273] As shown in FIG. 29, the bottom stream of the column is
TBABr+H2O 20, which is fed into the top of a spray-drying
crystallization tower 11 through a liquid distributor with fine
orifices. Hot air 23 is entering from the bottom of the tower to
evaporate water. The pelleted crystal form of TBABr or TBAX 21 is
then recycled back to the cathode compartment of electrochemical
cell 2.
[0274] The intermediate product DBO 19 plus unreacted BOH 19 exits
the upper end of the RXT-EXT section of the ACID-EST column, and
enters DISTILL column 10. In this DISTILL column 10, BOH is
vaporized and recycled back 28 to the Esterification section
(Rxt-Ext section) of the ACID-EST column 7, while the DBO product
25 leaves at the bottom of the DISTILL column 10 and then feeds
into a fixed bed reactive distillation column HYDROGN 12 for
hydrogenation. This may be a reactive column that is packed with
solid Cu--Cr-oxide catalyst, compressed hydrogen 24 at 20 to 50 atm
entering from the bottom while DBO is fed from the top. The column
has an optimum temperature profile. Product MEG 26 at fiber grade
purity of 99.9% exits from the bottom and regenerated BOH 22 is
recycled back to the feeding stage of RXT-EXT section of the
ACID-EST column 7.
[0275] It is understood that the specific order or hierarchy of
steps in the methods disclosed are examples of exemplary
approaches. Based upon design preferences, it is understood that
the specific order or hierarchy of steps in the method can be
rearranged while remaining within the disclosed subject matter. The
accompanying method claims present elements of the various steps in
a sample order, and are not necessarily meant to be limited to the
specific order or hierarchy presented.
[0276] It is believed that the present disclosure and many of its
attendant advantages will be understood by the foregoing
description, and it will be apparent that various changes may be
made in the form, construction and arrangement of the components
without departing from the disclosed subject matter or without
sacrificing all of its material advantages. The form described is
merely explanatory, and it is the intention of the following claims
to encompass and include such changes.
* * * * *