U.S. patent application number 15/320218 was filed with the patent office on 2017-05-04 for integrated process for co-production of carboxylic acids and halogen products from carbon dioxide.
The applicant listed for this patent is Liquid Light, Inc.. Invention is credited to Jerry J. Kaczur, Prasad Lakkaraju.
Application Number | 20170121831 15/320218 |
Document ID | / |
Family ID | 54935947 |
Filed Date | 2017-05-04 |
United States Patent
Application |
20170121831 |
Kind Code |
A1 |
Kaczur; Jerry J. ; et
al. |
May 4, 2017 |
Integrated Process for Co-Production of Carboxylic Acids and
Halogen Products from Carbon Dioxide
Abstract
The present disclosure is a method and system for production of
carboxylic based chemicals. A method for producing at oxalic acid
may include receiving an anolyte feed at an anolyte region of an
electrochemical cell including an anode and receiving a catholyte
feed including carbon dioxide and an alkali metal bicarbonate at a
catholyte region of the electrochemical cell including a cathode.
Method may include applying an electrical potential between the
anode and cathode sufficient to reduce the carbon dioxide to at
least one reduction product and converting the at least one
reduction product and an alkali metal hydroxide to an alkali metal
oxalate via a thermal reactor. The method may further include
converting the alkali metal oxalate to oxalic acid at the
electrochemical acidification electrolyzer. The method may further
include the co-production of halogen products from the anolyte
region of the electrochemical cell, by the oxidation of hydrogen
halides used as an anolyte feed. The halogen may then be further
reacted with other chemicals to produce chlorinated organics as
well as inorganic compounds such as sodium hypochlorite.
Inventors: |
Kaczur; Jerry J.; (North
Miami Beach, FL) ; Lakkaraju; Prasad; (East
Brunswick, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Liquid Light, Inc. |
Monmouth Junction |
NJ |
US |
|
|
Family ID: |
54935947 |
Appl. No.: |
15/320218 |
Filed: |
July 14, 2014 |
PCT Filed: |
July 14, 2014 |
PCT NO: |
PCT/US14/46555 |
371 Date: |
December 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62014465 |
Jun 19, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02P 20/125 20151101;
C25B 9/18 20130101; C25B 1/46 20130101; C25B 1/24 20130101; Y02E
60/36 20130101; C25B 15/08 20130101; C25B 1/10 20130101; C25B 3/04
20130101; Y02P 20/10 20151101; C25B 1/34 20130101; Y02E 60/366
20130101 |
International
Class: |
C25B 3/04 20060101
C25B003/04; C25B 15/08 20060101 C25B015/08; C25B 9/18 20060101
C25B009/18; C25B 1/34 20060101 C25B001/34 |
Claims
1. A method for producing oxalic acid and co-products, comprising:
receiving an anolyte feed including a hydrogen halide at an anolyte
region of a first electrochemical cell including an anode;
receiving a catholyte feed including carbon dioxide and an alkali
metal bicarbonate at a catholyte region of the first
electrochemical cell including a cathode; applying an electrical
potential between the anode and the cathode of the first
electrochemical cell sufficient to reduce the carbon dioxide to
formate and to oxidize the hydrogen halide to a halogen; converting
the formate to an alkali metal oxalate via a thermal reaction;
receiving the alkali metal oxalate at a first electrochemical
acidification electrolyzer; converting the alkali metal oxalate to
oxalic acid and co-producing alkali metal hydroxide, hydrogen, and
a halogen at the first electrochemical acidification electrolyzer;
converting an alkali metal halide in a second electrochemical
acidification electrolyzer to produce a hydrogen halide containing
solution, an alkali metal hydroxide, and hydrogen; and feeding at
least a portion of the hydrogen halide containing solution to the
anolyte region of the first electrochemical cell; feeding at least
a portion of the hydrogen halide containing solution to the first
electrochemical acidification electrolyzer.
2. The method of claim 1, wherein the anolyte feed to the first
electrochemical cell includes water and a hydrogen halide
containing solution generated from the second electrochemical
acidification cell, wherein the hydrogen halide solution comprises
a soluble mixture of hydrogen halide and alkali metal halide with
the hydrogen halide concentration ranging from about 5 wt % to 40
wt %.
3. The method of claim 1, wherein the hydrogen halide includes at
least one of hydrogen bromide or hydrogen chloride.
4. The method of claim 2, wherein an alkali metal halide content in
the hydrogen halide containing solution ranges from 0.01 wt % to a
solubility limit of the alkali metal halide in the hydrogen halide
solution.
5. The method of claim 2, wherein the alkali metal halide is at
least one of sodium chloride, potassium chloride, sodium bromide,
or potassium bromide.
6. The method of claim 1, wherein the alkali metal hydroxide from
the first and second electrochemical acidification cells includes
potassium or sodium hydroxide.
7. The method of claim 1, wherein the converting the formate to the
alkali metal oxalate via the thermal reaction includes receiving a
catalyst.
8. The method of claim 7, wherein the catalyst is selected from the
group consisting of alkali metal hydroxides, alkali metal
ethoxides, alkali metal methoxides, and alkali metal hydrides.
9. The method of claim 6, wherein converting the alkali metal
oxalate to oxalic acid at the first electrochemical acidification
electrolyzer comprises: passing the alkali metal oxalate through an
ion exchange region of the first electrochemical acidification
electrolyzer bounded by one or more cation ion exchange membranes;
producing an alkali metal hydroxide and hydrogen in the catholyte
compartment, and oxidizing a hydrogen halide containing solution in
the anode compartment to produce a halogen.
10. The method of claim 9, further comprising: converting the
oxalic acid to an oxalic acid ester with an alcohol.
11. The method of claim 10, further comprising: converting the
oxalic acid ester to ethylene glycol by hydrogenation.
12. The method of claim 1, further comprising: reacting the halogen
with an organic compound to produce a halogenated organic
compound.
13. The method of claim 1, further comprising: reacting the halogen
with an alkali metal hydroxide to produce an alkali metal
hypochlorite product.
14. The method of claim 12, wherein the organic compound is at
least one of ethylene or propylene.
15. The method of claim 14, wherein the halogenated organic is at
least one of ethylene chloride, propylene chloride, ethylene
bromide or propylene bromide.
16. A method for producing formic acid and co-products comprising:
receiving an anolyte feed including a hydrogen halide at an anolyte
region of a first electrochemical cell including an anode;
receiving a catholyte feed including carbon dioxide and an alkali
metal bicarbonate at a catholyte region of the first
electrochemical cell including a cathode; applying an electrical
potential between the anode and the cathode sufficient to reduce
the carbon dioxide to at least an alkali metal formate and to
oxidize the hydrogen halide to a halogen; converting the alkali
metal formate to formic acid and co-producing alkali metal
hydroxide, hydrogen, and halogen at a first electrochemical
acidification electrolyzer; converting an alkali metal halide in a
second electrochemical acidification electrolyzer to produce a
hydrogen halide containing solution, an alkali metal hydroxide, and
hydrogen; feeding at least a portion of the hydrogen halide
containing solution to the anolyte compartment of the first
electrochemical cell; and feeding at least a portion of the
hydrogen halide containing solution to the first electrochemical
acidification electrolyzer.
17. The method of claim 16, wherein the anolyte feed to the first
electrochemical cell includes water, hydrogen halide, and alkali
metal halide with the hydrogen halide concentration ranging from
about 5 wt % to 40 wt %.
18. The method of claim 16, wherein the hydrogen halide includes at
least one of hydrogen bromide or hydrogen chloride.
19. The method of claim 16, wherein the alkali metal halide content
in the hydrogen halide containing solution ranges from 0.01 wt % to
a solubility limit of the alkali metal halide in the hydrogen
halide solution.
20. The method of claim 16, wherein the alkali metal halide is at
least one of sodium chloride, potassium chloride, sodium bromide or
potassium bromide.
21. The method of claim 16, wherein the alkali metal hydroxide from
the first and second electrochemical acidification cells is at
least one of potassium hydroxide or sodium hydroxide.
22. The method of claim 16, wherein the alkali metal formate is at
least one of potassium formate or sodium formate.
23. The method of claim 16, wherein converting the alkali metal
formate to formic acid at the first electrochemical acidification
electrolyzer comprises: passing the alkali metal formate through an
ion exchange region of the first electrochemical acidification
electrolyzer bounded by one or more cation ion exchange membranes;
producing an alkali metal hydroxide and hydrogen in the catholyte
compartment; and oxidizing a hydrogen halide containing solution in
the anode compartment to produce a halogen.
24. The method of claim 23, further comprising: converting the
formic acid to a formate ester with an alcohol.
25. The method of claim 23, further comprising: converting the
formic acid to a formamide.
26. The method of claim 16, further comprising: reacting the
halogen with an organic compound to produce a halogenated organic
compound.
27. The method of claim 16, further comprising: reacting the
halogen with an alkali metal hydroxide to produce an alkali metal
hypochlorite product.
28. The method of claim 16, wherein the halogen is at least one of
bromine or chlorine.
29. The method of claim 26, wherein the organic compound is at
least one of ethylene or propylene.
Description
TECHNICAL FIELD
[0001] The present disclosure generally relates to the field of
electrochemical reactions, and more particularly to methods and/or
systems for producing carboxylic acids from carbon dioxide and
co-producing halogen products.
BACKGROUND
[0002] The combustion of fossil fuels in activities such as the
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,
may be seeking ways to mitigate emissions of carbon dioxide.
[0003] One implementation may be to convert carbon dioxide into
economically valuable materials such as fuels and industrial
chemicals. If the carbon dioxide may be converted using energy from
renewable sources, it will be possible to both mitigate carbon
dioxide emissions and to convert renewable energy into a chemical
form that may be stored for later use. Electrochemical and
photochemical pathways may be likely mechanisms for carbon dioxide
conversion.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0004] The present disclosure is a method and system for the
production of carboxylic acid based chemicals, including carboxylic
acids and salts, and producing halogen co-products. A method for
producing at oxalic acid may include receiving an anolyte feed at
an anolyte region of an electrochemical cell including an anode and
receiving a catholyte feed including carbon dioxide and an alkali
metal bicarbonate at a catholyte region of the electrochemical cell
including a cathode. The method may include applying an electrical
potential between the anode and cathode sufficient to reduce the
carbon dioxide to at least one reduction product and converting the
at least one reduction product and an alkali metal hydroxide to an
alkali metal oxalate via a thermal reactor. The method may further
include receiving the alkali metal oxalate at an electrochemical
acidification electrolyzer and converting the alkali metal oxalate
to oxalic acid at the electrochemical acidification
electrolyzer.
[0005] 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
[0006] The numerous advantages of the present disclosure may be
better understood by those skilled in the art by reference to the
accompanying figures in which:
[0007] FIG. 1A shows a system for production of oxalic acid
starting with the electrochemical generation of carbon monoxide
from carbon dioxide in accordance with an embodiment of the present
disclosure;
[0008] FIG. 1B shows a system for the production of oxalic acid
utilizing HBr in the anolyte to co-produce bromine in accordance
with an embodiment of the present disclosure;
[0009] FIG. 2A shows a system for production of oxalic acid
starting with the electrochemical generation of formate using
carbon dioxide in accordance with an embodiment of the present
disclosure;
[0010] FIG. 2B shows a system for production of oxalic acid via
electrochemical generation of formate using carbon dioxide and
utilizing a halogen halide in the anolyte to co-produce bromine in
accordance with an embodiment of the present disclosure;
[0011] FIG. 3 shows a system for production of alkali metal formate
using carbon dioxide in accordance with an embodiment of the
present disclosure; and
[0012] FIG. 4 shows a system for electrochemical acidification of
alkali metal oxalate in accordance with an embodiment of the
present disclosure.
[0013] FIG. 5 shows a system for production of alkali metal formate
using carbon dioxide and utilizing a alkali metal chloride brine in
the anolyte to co-produce chlorine and alkali metal bicarbonate in
accordance with an embodiment of the present disclosure;
[0014] FIG. 6 shows a system for production of alkali metal formate
using carbon dioxide and co-generating chlorine, alkali metal
hypochlorite (MOCl) and oxalic acid in accordance with an
embodiment of the present disclosure; and
[0015] FIG. 7 shows a system for production of downstream chemical
alternatives from the formate produced from the reduction of carbon
dioxide, such as formic acid, alkali metal formates, methyl
formate, and formamides in accordance with an embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0016] Reference will now be made in detail to the subject matter
disclosed, which is illustrated in the accompanying drawings.
[0017] The present disclosure describes a method and system for
production of carboxylic based chemicals, including carboxylic
acids and salts. The method may employ an electrochemical cell
reaction to produce carbon monoxide, CO, or alkali metal formate
from a carbon dioxide feedstock. A thermal reaction with an alkali
metal hydroxide, may be used to combine, for example, two alkali
metal formate molecules, into a alkali metal oxalate product.
[0018] The alkali metal oxalate may be then converted to oxalic
acid by a membrane based electrochemical acidification process,
where protons (H.sup.+ ions) formed at the anode may be used to
replace the alkali metal ions, and the alkali metal ions (M.sup.+)
may be captured as alkali metal hydroxide (MOH) at the cathode, and
may be recycled to be used as the alkali metal hydroxide used in
the intermolecular condensation process unit operation.
[0019] Alternatively the alkali metal oxalate may be converted to
oxalic acid through treatment with mineral acid, such as HCl, HBr,
HI, H.sub.2SO.sub.4, H.sub.3PO.sub.4, or the like. For example,
treating sodium oxalate with aqueous HCl may result in an oxalic
acid solution comprising NaCl. The oxalic acid may be extracted
from the solution via extraction with an organic solvent such as
alcohol, ether, halo-organic, ketone, amide, or ester. Useful
solvents include, but are not limited to, methanol, ethanol,
propanol, diethyl ether, methyl ethyl ether, methyl tert-butyl
ether, tetrahydrofuran, dioxane, methylene chloride, chloroform,
carbon tetrachloride, chlorobenzene, di-chlorobenzene, methyl
acetate, ethyl acetate, methyl propionate, ethyl propionate,
acetone, butanone, dimethylformamide, N-methyl pyrrolidone, and the
like. The oxalic acid may also be recovered from the solution
through crystallization from the aqueous solution. Crystallization
may require concentrating the solution and/or cooling the
solution.
[0020] After removal of oxalic acid, the aqueous solution
comprising salt, NaCl for example, may be recycled by sending it to
an anolyte compartment of an electrochemical cell. Halide ions, for
example chloride, may be oxidized to form halogen (for example
chlorine). The halogen may be isolated from an anolyte stream after
exiting an anolyte compartment of an electrochemical cell. The
halogen may be reacted with hydrogen, for example hydrogen produced
during a thermal alkali metal formate to alkali metal oxalate
calcination reaction. Hydrogen may also be obtained from another
source. The mineral acid (HCl for example) formed by the reaction
of hydrogen with halogen may be used to acidify alkali metal
oxalate, completing the cycle. The energy produced (heat or
electrical energy) by reacting halogen with hydrogen may be
captured and used in the process of the invention (in the thermal
calcination reaction for example) or may be used elsewhere.
[0021] 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.
[0022] Referring to FIG. 1A, a system 100 for production of
dicarboxylic acid, such as oxalic acid starting with the
electrochemical generation of formate from the electrochemical
reduction of carbon dioxide in accordance with an embodiment of the
present disclosure is shown. System 100 may include an
electrochemical cell 110. Electrochemical cell 110 (also referred
as a container, electrolyzer, or cell) may be implemented as a
divided cell. The divided cell may be a divided electrochemical
cell and/or a divided photo-electrochemical cell. Electrochemical
cell 110 may include an anolyte region and a catholyte region.
Anolyte region and catholyte 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.
[0023] Catholyte region may include a cathode. Anolyte region may
include an anode. An energy source (not shown) may generate an
electrical potential between the anode and the cathode of
electrochemical cell 110. The electrical potential may be a DC
voltage. Energy source may be configured to supply a variable
voltage or constant current to electrochemical cell 110. A
separator may selectively control a flow of ions between the
anolyte region and the catholyte region. Separator may include an
ion conducting membrane or diaphragm material.
[0024] Electrochemical cell 110 may operate to perform an
electrochemical reduction of carbon dioxide in an electrochemical
cell producing carbon monoxide (CO) and hydrogen as cathode
products and oxygen as an anode product when using an anolyte
comprising sulfuric acid (H.sub.2SO.sub.4).
[0025] The CO generated from electrochemical cell 110 may be
separated from the hydrogen and then passed to a thermal reactor
120. Thermal reactor may react the carbon monoxide with an alkali
metal hydroxide, such as KOH via a thermal intermolecular
condensation reaction to form alkali metal formate. Thermal reactor
120 may operate to perform a thermal decomposition reaction or a
carbonylation reaction, which may be reactions which incorporate CO
into organic and inorganic chemical structures.
[0026] Alkali metal formate formed from thermal reactor 120 may be
passed to another thermal reactor 130. Thermal reactor 130 may
perform a second thermal intermolecular condensation reaction
employing an alkali metal hydroxide (e.g. KOH) that may promote the
reaction to produce alkali metal oxalate. While system 100 of FIG.
1 depicts a thermal reactor 120 and thermal reactor 130, it is
contemplated that a single thermal reactor may be employed with
system 100 without departing from the scope and intent of the
present disclosure.
[0027] Alkali metal oxalate from thermal reactor 130 may be
dissolved in water and may be passed to an electrochemical
acidification electrolyzer 140. Electrochemical acidification
electrolyzer 140 may produce a dicarboxylic acid, such as oxalic
acid, and KOH along with oxygen and hydrogen byproducts.
Electrochemical acidification electrolyzer 140 may be a membrane
based unit including of at least three regions, including an anode
region, one or more central ion exchange regions, and a cathode
region. It is contemplated that an energy source (not shown) may
generate an electrical potential between the anode and the cathode
of electrochemical acidification electrolyzer 140 sufficient to
produce oxalic acid. Alkali metal oxalate may be passed through the
central ion exchange region where alkali metal ions may be replaced
with protons, and the displaced alkali metal ions pass through the
adjoining membrane into the cathode region to form MOH. The anode
reaction may utilize an acid, such as sulfuric acid, producing
oxygen and hydrogen ions.
[0028] The hydrogen byproduct resulting from electrochemical
acidification electrolyzer 140, as an alternative embodiment, may
be used as a fuel to produce steam or used in another chemical
process that may utilize hydrogen, such as a hydrogenation
process.
[0029] The dicarboxylic acid, such as an oxalic acid product may be
purified to produce a final purified product, or may be further
processed as a chemical intermediate to produce another product,
such as monoethylene glycol, using a reduction process such as an
electrochemical reduction or a catalytic hydrogenation.
[0030] Aqueous KOH from electrochemical acidification electrolyzer
140 may be passed to an evaporator 150. Evaporator 150 may
evaporate the water from aqueous KOH product using steam or another
heat source, converting it into a concentrated aqueous solution
and/or solid with 5% or less water content as needed in
electrochemical cell 110 and thermal reactor 120.
[0031] Referring to FIG. 1B, a system 105 for production of
dicarboxylic acid, such as oxalic acid, utilizing a hydrogen
halide, such as HBr, in the anolyte to co-produce bromine in
accordance with an embodiment of the present disclosure is shown.
System 105 may operate with a less energy intensive electrochemical
process, using HBr as the anolyte in the anode region of
electrochemical cell 110 and electrochemical acidification
electrolyzer 140, producing bromine and hydrogen ions at a
significantly lower anode potential. The bromine may then be used,
for example, in reactions to produce brominated chemical products,
such as brominated organic compounds, for example bromoethane,
which may then be converted into alcohols such as ethanol, or
converted to monoethylene glycol in a series of thermochemical
reactions. It is contemplated that system 105 shown with thermal
reactor 120 and thermal reactor 130 could be implemented with a
single thermal reactor without departing from the scope and intent
of the present disclosure.
[0032] Referring to FIG. 2A, a system 200 for production of
dicarboxylic acid, such as oxalic acid, starting with the
electrochemical generation of formate using carbon dioxide in
accordance with an embodiment of the present disclosure is shown.
System 200 may provide an alternative system for production of
oxalic acid as produced by systems 100, 105 of FIG. 1A and FIG.
1B.
[0033] System 200 may include an electrochemical cell 110.
Electrochemical cell 110 may operate to perform an electrochemical
reduction of carbon dioxide with a alkali metal carbonate cathode
feed, which may be formed from the reaction of CO.sub.2 with MOH,
to produce alkali metal formate along with oxygen as an anode
product when using an anolyte comprising sulfuric acid
(H.sub.2SO.sub.4). The alkali metal formate product solution
concentration from the catholyte compartment of electrochemical
cell 110 may range from 1 wt % to 30 wt % or more based on the
formate ion, and preferably range from 5 wt % to 20 wt % as
formate. The corresponding % weight as the alkali metal formate,
for example alkali metal formate may be based on the molecular
weight of the alkali metal compound.
[0034] Alkali metal formate may be passed to a thermal reactor 120.
Thermal reactor 120 may perform a thermal intermolecular
condensation reaction with an alkali metal hydroxide (e.g., KOH) to
produce alkali metal oxalate.
[0035] Alkali metal oxalate from thermal reactor 120 may be
dissolved in water and may be passed to an electrochemical
acidification electrolyzer 140. Electrochemical acidification
electrolyzer 140 may produce dicarboxylic acid, such as oxalic
acid, and KOH along with oxygen and hydrogen byproducts.
Electrochemical acidification electrolyzer 140 may be a membrane
based unit including of at least three regions, including an anode
region, one or more central ion exchange regions, and a cathode
region. Alkali metal oxalate may be passed through the central ion
exchange region where alkali metal ions may be replaced with
protons, and the displaced alkali metal ions pass through the
adjoining membrane into the cathode region to form KOH. The anode
reaction may utilize an acid, such as sulfuric acid, producing
oxygen and hydrogen ions.
[0036] The hydrogen byproduct resulting from electrochemical
acidification electrolyzer 140, as an alternative embodiment, may
be used as a fuel to produce steam or used in a side process that
may utilize hydrogen, such as in a chemical hydrogenation
process.
[0037] The dicarboxylic acid, such as oxalic acid product may be
purified to produce a final purified product, or may be further
processed as a chemical intermediate to produce another product,
such as monoethylene glycol, using an electrochemical reduction or
thermochemical process.
[0038] Aqueous KOH from electrochemical acidification electrolyzer
140 may be passed to an evaporator 150. Evaporator 150 may
evaporate the water from aqueous KOH product using steam or another
heat source, converting it into a concentrated aqueous solution
and/or solid with 5% or less water content as needed in the
electrochemical cell 110 or thermal reactor 120.
[0039] Referring to FIG. 2B, a system 205 for production of oxalic
acid dicarboxylic acid, such as oxalic acid via electrochemical
generation of formate using carbon dioxide and utilizing a halogen
halide in the anolyte to co-produce a halogen, such as bromine, in
accordance with an embodiment of the present disclosure is shown.
System 205 may be similar to system 200, where system 205 may use a
hydrogen halide, such as HBr as the anolyte in the anode regions of
electrochemical cell 110 and electrochemical acidification
electrolyzer 140. Electrochemical cell 110 may produce bromine and
hydrogen ions at a significantly lower anode potential. Bromine may
then be used, for example, in reactions to produce brominated
chemical products, such as bromoethane, which may then be converted
into alcohols such as ethanol, or converted to monoethylene glycol
in a series of thermochemical reactions.
[0040] Referring to FIG. 3, a system 300 for production of a
formate, such as alkali metal formate, using carbon dioxide in
accordance with an embodiment of the present disclosure is shown.
FIG. 3 illustrates the electrochemical reduction of carbon dioxide
in the production of an alkali metal formate as shown in
electrochemical cell 110 of FIG. 2A and FIG. 2B. Electrochemical
cell 110 may include an anolyte input feed 310 and a catholyte
input feed 312 to produce a product 314. Product 314 may be a
solution of alkali metal formate with an excess alkali metal
bicarbonate (KHCO.sub.3). Anolyte region 320 may have a titanium
anode 322 having an anode electrode catalyst coating facing cation
exchange membrane 330. Anode mesh screen 332 may be a folded
expanded titanium screen with an anode electrocatalyst coating and
provides spacing and contact pressure between anode 322 and cation
exchange membrane 332. Cation exchange membrane 330 may selectively
control a flow of ions between anolyte region 320 from catholyte
region 340.
[0041] Catholyte region 340 may have a mounted cathode 342, which
may be a metal electrode with an active electrocatalyst layer on
the front side facing membrane 330. High surface area cathode
structure 344 may be mounted with direct contact pressure between
the face of cathode 342 and cation membrane 330.
[0042] As shown in FIG. 1A and FIG. 2A, feeding anolyte region 320
may be stream 310 which may include anolyte, the anolyte comprising
an aqueous sulfuric acid electrolyte solution. Stream 310 may enter
the anolyte region 320 and flow by the face of anode 322 through
folded anode screen 332. Anode reactions may comprise splitting
water into oxygen (O.sub.2) and hydrogen ions (H.sup.+) or protons.
The gases and liquid mixture from anolyte region 320 may leave as
stream 350, which flows by temperature sensor 352 monitoring a
solution temperature in the stream, and into anolyte gas/liquid
disengager 354. In disengager 354, the gas may be vented as stream
356, and excess anolyte overflow leaves as stream 358. Stream 360
may be a gas-depleted exit stream from the anolyte disengager 354,
with a deionized water feed stream 362 and a sulfuric acid make-up
feed stream 364 added to the recirculation stream to maintain
anolyte acid strength and volume. Stream 360 with added streams 362
and 364 may then pass through an optional heat exchanger 370 with a
cooling water supply 372, and then becomes stream 310 feeding into
the anolyte region 320.
[0043] Electrochemical cell 110 may include a catholyte region 340
which includes cathode 342 having an electrocatalyst surface facing
membrane 330. High surface area cathode structure 344 may be
mounted between membrane 330 and cathode 342, relying on contact
pressure with cathode 342 for conducting electrical current into
the structure. The interface between high surface area structure
344 and membrane 330 may utilize a thin expanded plastic mesh
insulator screen (not shown) to minimize direct contact with the
high surface area cathode material with the membrane 330.
[0044] Feed stream 312 may feed into catholyte region 340, flowing
through the high surface area structure 344 and across the face of
cathode 342 where cathode reduction reactions between carbon
dioxide, electrolyte, and cathode material at the applied current
and voltage potential produce exit stream 314, the exit stream
including a formate.
[0045] Stream 314 may be the exit solution and gas mixture product
from the cathode reaction which flows by pH monitoring sensor 374
and temperature sensor 352 and then into catholyte gas/liquid
disengager 380 where the gas exits as stream 382 and
formate/electrolyte overflow exits as stream 384, and the
gas-depleted stream leaves the disengager as stream 386. Stream 386
may then enter an input of catholyte recirculation pump 390, which
then passes through heat exchanger 392 which uses cooling water
372, then passes by temperature sensor 352. A fresh catholyte
electrolyte feed 394 may be metered into stream 386 which may be
used to adjust the catholyte flow stream pH into the catholyte
region 340 and control a product overflow rate and sets the formate
product concentration, with the pH monitored by pH sensor 374.
Carbon dioxide flow stream 396 may be metered into the flow stream
which enters the catholyte region 340 as stream 312.
[0046] In an alternative embodiment, as shown in FIGS. 1B and 2B,
the anolyte comprising sulfuric acid shown in FIGS. 1A and 2A may
be replaced with an anolyte comprising hydrogen halide (e.g. HBr),
producing a halide (e.g. bromine) and hydrogen ions at a lower
voltage potential than required for the generation of oxygen at the
anode. The halide may then be used, for example, in reactions to
produce halide chemical products, such as bromoethane in the
reaction with an alkane, such as ethane, which may then be
converted into alcohols (e.g. ethanol) or converted to monoethylene
glycol in a series of thermochemical reactions.
[0047] Referring to FIG. 4, system 400 for electrochemical
acidification of alkali metal oxalate in accordance with an
embodiment of the present disclosure is shown. Electrochemical
acidification electrolyzer 140 may include an anolyte region 402, a
central ion exchange region 408 bounded by cation ion exchange
membranes 406a and 406b on each side, and a catholyte region 410
where an alkali metal hydroxide (e.g. KOH) may be formed. Hydrogen
ions (H.sup.+) or protons may be generated in the anolyte region
402, which then may pass through the adjoining membrane 406a into
the central ion exchange region 408 when a potential and current
may be applied to the cell. An alkali metal oxalate (e.g. alkali
metal oxalate) product solution 405, such as generated in thermal
reactor 120, 130 of FIGS. 1A and 2B, may pass through the central
ion exchange region 408, where protons displace the alkali metal
ions in the solution stream, thus acidifying the solution and
forming a dicarboxylic acid, such as oxalic acid. Stream 456, and
the displaced alkali metal ions may pass through the adjoining
cation exchange membrane 406b into the catholyte region 410, where
they combine with hydroxide ions (OH.sup.-) formed from water
reduction reaction at the cathode to form an alkali metal hydroxide
(e.g. KOH) stream 434.
[0048] Electrochemical acidification electrolyzer 140 may include
input feeds 430 and 432 and may produce a solution of dicarboxylic
acid (e.g. oxalic acid) 456, oxygen 420 from the anolyte region
402, and KOH 442 from the catholyte region 410. Anode region 402
may include a titanium anode 404 with an anode electrode catalyst
coating facing cation exchange membrane 406a. The central ion
exchange region 408 may contain a plastic mesh spacer to maintain
the space in the central ion exchange region between cation
exchange membranes 406a and 406b. Optionally, a preferred material
may be the use of a cation ion exchange material between the
membranes, so that there may be increased electrolyte conductivity
in the ion exchange region solution. Catholyte region 410 may
include a cathode 412.
[0049] Anolyte region 402 may have feed stream input 430 including
sulfuric acid, which may flow through the anolyte region 402 and
exit as stream 414 including a gas and liquid, passing by
temperature sensor 416 into anolyte disengager 418, where the gas
exits as stream 420 and liquid overflow as stream 422. Gas-depleted
stream 424 may exit the anolyte disengager 418 and deionized water
stream 426 may be metered into the stream 424 as well as sulfuric
acid make-up stream 428 to maintain acid electrolyte strength in
the anolyte region 402. Stream 424 may pass through optional heat
exchanger 426 which may have cooling water supply 428 to cool or
maintain the stream 424 temperature, and the stream 424 enters the
anolyte region 402 as stream 430.
[0050] Catholyte region 410 may include feed stream 432 which may
be the recirculating alkali metal hydroxide (e.g. KOH) in the
catholyte loop, which enters catholyte region 410 and flows by
cathode 412, which may generate hydrogen gas and hydroxide
(OH.sup.-) ions, and forms a alkali metal hydroxide from the
combination of alkali metal ions crossing the membrane 406b with
the hydroxide ions formed at the cathode 412 from the reduction of
water. Exit stream 434 from the cathode region 410 may contain
alkali metal hydroxide and hydrogen gas from the cathode reactions,
and passes by temperature sensor 436 and then into catholyte
disengager 438, where hydrogen gas 440 may be separated from the
catholyte solution, which exits catholyte disengager 438 as recycle
stream 444 and alkali metal hydroxide product overflow stream 442.
Recycle stream 444 may pass through optional recirculation pump 446
and then through optional heat exchanger 448, which uses cooling
water supply 450. The stream then passes by temperature sensor 452,
and then may have a deionized water addition stream 454 added to
the stream to control the alkali metal hydroxide concentration in
the catholyte recirculation loop, and then reenters the catholyte
region 410 as stream 432.
[0051] In an alternative embodiment, the anolyte comprising
sulfuric acid may be replaced with an anolyte comprising HBr,
producing bromine and hydrogen ions at a much lower voltage
potential than required for the generation of oxygen at the
anode.
[0052] FIG. 5 shows schematic drawing of system 500, an alternative
embodiment in operating a system utilizing a sodium-based compound
that may generate, for example, sodium formate from the
electrochemical reduction of carbon dioxide followed by the
conversion of the sodium formate to sodium oxalate, which may then
be converted to oxalic acid. The system produces oxalic acid in
addition to two additional co-products, which may be sodium
bicarbonate and sodium hydroxide.
[0053] Electrochemical formate cell 502 may be similarly configured
to the cell as shown and described in FIG. 3 except for
modifications to the feed solutions used in the anolyte and
catholyte. Formate cell 502 may comprise catholyte compartment 506
and anolyte compartment 504, and ion permeable separator 503,
preferably being a cation ion exchange type membrane. A feed stream
522 of saturated NaCl brine may be introduced into catholyte
compartment 504 of formate cell 502, where the chloride ion of the
NaCl salt solution may be oxidized to chlorine gas at the anode in
anode compartment 504. As the chloride ion of the NaCl salt may be
oxidized at the anode, sodium ions migrate in the potential field,
and pass through separator 503 into cathode compartment 506.
[0054] The anolyte product stream 508 from catholyte compartment
504 comprises a mixture of chlorine gas and NaCl depleted brine
solution. The chlorine gas may then be separated or disengaged as
stream 510 from stream 508 as a co-product, and the separated
depleted brine solution stream 512 may then be processed in a
series of steps typically used in chlor alkali processes comprising
dechlorination of the depleted brine, resaturation of the brine
solution with NaCl using a bed of solid NaCl salt, followed by a
brine purification step to remove impurities, such as metals and
hardness (such as Ca.sup.+, Mg.sup.+, and Ba.sup.+), from the brine
solution to impurity levels typically used to achieve long life
operation of separator 503, to produce a purified saturated NaCl
brine solution stream 522 which is electrolyzed in the anolyte
compartment 504 of formate cell 502.
[0055] Chlorine gas 510 may then be processed in various ways, such
as removal of water from the gas by condensation, and then the
chlorine gas may then be used for producing various useful
co-products from the system, for example, the generation of sodium
hypochlorite by a reaction with NaOH, the generation of HCl through
reaction with hydrogen, as well as reactions with organics, such as
to produce EDC (ethylene dichloride) by reaction with an external
supply of ethylene. Many other reaction co-products made with the
chlorine gas 510 may be envisioned.
[0056] Brine dechlorination unit 514 may be used to remove residual
chlorine from depleted brine solution 512 using a selected reducing
agent, which may be chosen from those typically used such as sodium
sulfite, sodium hydrosulfite, and hydrogen peroxide among others.
The dechlorinated brine then may be passed to brine saturator unit
516, where the depleted brine NaCl concentration may be increased
from a typical 150-240 gm/L as NaCl to a concentration of 300-320
gm/L as NaCl using a brine saturator, which may consist of a bed of
solid salt crystals in an apparatus typically called a briner. The
saturated brine may then be passed through brine purification
system 518, which may consist of chemical precipitation steps for
the removal of most of the hardness in the solution, typically by
the addition of NaOH and sodium carbonate under alkaline
conditions, followed by filtration to remove the precipitated
hardness containing solids, then followed by an ion exchange
purification step utilizing chelating ion exchange resin beds to
reduce the hardness levels in the brine to typically 20-50 ppb or
less. The sulfate component in the brine may be reduced by the
chemical precipitation, or by the use of commercial system that
utilizes nanofiltration to preferentially remove sulfate from
brine, for example the SRS system--sold by Aker Chemetics. The
purification chemicals also may include HCl and NaOH used for
regenerating the chelating ion exchange columns. Stream 520 may be
an effluent stream containing the precipitated carbonates,
sulfates, and metals effluent from the purification of the
saturated brine solution, which may be processed and recycled back
to the process with a minimum amount of material requiring
disposal. Purified brine solution 522 may then pass into anolyte
compartment 504 of electrochemical formate cell 502. The
recirculation of the anolyte loop is not shown, but the brine flow
rate may be metered so as to maintain the desired brine
concentration in the electrochemical cell anolyte loop and overflow
stream 508, with the brine concentration typically in the range of
150-240 gm/L as NaCl. In an embodiment, the anolyte brine
concentration may be operated lower NaCl concentrations, to as low
as about 100-140 gm/L, which may result in a decrease in chlorine
efficiency and the generation of more byproduct oxygen in the
chlorine gas stream, but which may be useful in reducing the brine
flow rate through the brine purification system with a reduction in
brine processing costs.
[0057] Solution feed stream 548, which may be an aqueous mixture of
sodium formate, sodium bicarbonate, and dissolved carbon dioxide
which may include a gaseous carbon dioxide component which may be
in the form of gaseous micro-bubbles, may be passed into catholyte
compartment of electrochemical cell 502. In catholyte compartment
506, which preferably incorporates a high surface area cathode
structure, carbon dioxide may be electrochemically reduced to
formate, and the formate may combine with the sodium ions
(Na.sup.+) passing through the adjacent separator 503 to form
sodium formate. In addition, any cathode inefficiency side
reactions forming hydrogen (H.sub.2) at the cathode may produce
hydroxide ions (OH.sup.-), and these hydroxide ions may react with
carbon dioxide to form sodium carbonate in the catholyte solution.
The sodium carbonate may then further react with excess carbon
dioxide to form sodium bicarbonate. In addition, it is believed
that the other sodium ions may combine with carbonic acid and the
other potential carbon dioxide equilibrium species at the operating
catholyte pH to further form additional sodium carbonate and sodium
bicarbonate.
[0058] The reduction reaction products may exit as stream 524,
where they may be separated or disengaged into gas stream 526 and
solution stream 530. Gas stream 526 may be passed into separator
528, which may separate carbon dioxide from any byproduct hydrogen
so that they may be reused or recycled in the other system 500 unit
operations. Gas separator 528 may be any suitable membrane-based or
molecular sieve pressure swing gas separation unit technology that
may be capable of the separation of carbon dioxide and hydrogen.
The separated gases may then be further purified and compressed as
needed for recycle or reuse to the process.
[0059] Solution stream 530 comprising mainly sodium formate and
sodium bicarbonate may then be split into recycle stream 532, which
may be recycled back to electrochemical formate cell 502 catholyte
compartment, and product stream 531 which may go to
evaporator-crystallizer 550. Recycle stream 532 may have several
input streams, including the introduction-of-carbon-dioxide stream
534, optionally a sodium bicarbonate stream 536 from
reactor-dissolver unit 560, a side stream 538 leaving stream 532
which may go into an optional electrochemical acidification cell A
540 and may have an acidified product stream 546 back into stream
532, and may have the addition of water to the stream as needed to
prevent precipitation in stream 532 and catholyte compartment 506,
and having all of the inputs/outputs into stream 532 ending up as
solution stream 548 which may be sent into catholyte compartment
506.
[0060] Electrochemical acidification cell 540 may be used to
acidify a small portion taken from catholyte loop stream 532, and
which may reenter anolyte recycle stream 532 as stream 546.
[0061] Electrochemical acidification cell 540 may be the same
design as the acidification cell as shown in FIG. 4. The cell
anolyte solution may utilize sulfuric acid such that the anode
reaction produces oxygen and produces hydrogen ions, which may be
used to acidify formate stream 538 as it passes through the ion
exchange compartment in the cell. The cathode reaction in this cell
may be the reduction of water, which produces hydrogen gas and
hydroxide ions (OH.sup.-). The sodium ions that may be displaced by
the hydrogen ions passing into the ion exchange compartment may
pass into the catholyte compartment to combine with the hydroxide
ions to produce a sodium hydroxide co-product. The hydrogen gas may
also be captured for use in the process. Deionized water may be
used in acidification cell 540 as needed to replace electrolyzed
water and for controlling the concentration of the NaOH in the
catholyte compartment.
[0062] Catholyte product stream 531, which may contain high
concentrations of alkali metal formate and alkali metal bicarbonate
may then be passed to evaporator-crystallizer unit 550, which may
evaporate sufficient water from the solution and continuously
precipitate a alkali metal bicarbonate crystal product as stream
556, a liquid concentrated alkali metal formate stream 554, and a
water product stream 552 which may be condensed and used elsewhere
as needed in the process, such as in oxalate solution dissolver
572. Evaporator-crystallizer 550 may utilize steam for providing
the energy requirements for evaporating the water from the stream
531 input stream to the unit. Evaporator-crystallizer 550 may be a
multiple evaporator effect unit, consisting of multiple units to
efficiently utilize the energy of the input steam, or any other
suitable types of units may be utilized.
[0063] In addition, Evaporator-crystallizer 550 may use steam as
well as mechanical means for producing a vacuum to further reduce
the energy requirements for the evaporation of the water from the
solution. Any suitable evaporator-crystallizer unit or system may
comprise suitable metallurgy for the operating conditions of the
system. Alkali metal formate may have a solubility in water that
may be about 8 to 10 times more than that of alkali metal
bicarbonate, so the solubility difference allows the easy
separation of alkali metal formate from alkali metal bicarbonate
using solution temperature differences to enhance the separation.
Other methods for the separation of alkali metal formate from
alkali metal bicarbonate may be employed including fractional
crystallization, falling film crystallization, and the like. A
continuous process for the separation may be preferred, although
batch processing may also be used.
[0064] The alkali metal bicarbonate crystal stream 556 from unit
550 may be in the form of an aqueous slurry, which may then be
separated, washed, and dried by any suitable means to produce a
dried alkali metal bicarbonate product 558. Equipment such as
centrifuges and vacuum belt filters may be used for the separation
of the alkali metal bicarbonate crystals from the 556 stream
slurry, and the mother liquor from any water rinses may be recycled
back to unit 550. The alkali metal bicarbonate product 558 may also
be recrystallized or further purified by any suitable means to
obtain a final product with purity suitable for specialty uses,
such as food grade quality product. A portion of the stream 556
slurry or stream 558 alkali metal bicarbonate product as stream 560
may be utilized in reactor-dissolver 561, which may be used to
convert alkali metal carbonate to alkali metal bicarbonate using an
additional carbon dioxide gas stream 563. Reactor-dissolver 561 may
also have an NaOH input stream 562, which may then be converted to
alkali metal bicarbonate. The NaOH may be supplied from one or both
of the electrochemical acidification units 540 and 576 if
required.
[0065] Alkali metal formate stream 554 may be a concentrated alkali
metal formate solution that contains 50 wt % or less water, and
preferably 40 wt % or less water, and more preferably 30 wt % or
less water. The formate solution stream 554 may be viscous and may
contain from 0.1 wt % to 30 wt % alkali metal bicarbonate depending
on the water solubility of alkali metal bicarbonate in the alkali
metal formate solution. The solution concentrations of the alkali
metal formate and residual alkali metal carbonate may be varied as
needed to achieve the desired final residual alkali metal
bicarbonate concentration in the alkali metal formate solution.
Alkali metal formate stream 554 may then passed to alkali metal
formate liquid dryer where the residual water may be removed by any
suitable means such as by vacuum evaporation and the like. The
alkali metal formate may be an alkali metal formate melt,
consisting of a small percentage of water, in the range of 0.01 wt
% to 5 wt % as water, and may have between 0.1 wt % to 20 wt %
alkali metal bicarbonate. The alkali metal formate melt stream 566
may then be passed into alkali metal formate thermal reactor 568
for high temperature conversion of the alkali metal formate to
alkali metal oxalate (calcination). A suitable catalyst 567, such
as NaOH, sodium hydride, sodium borohydride, sodium ethoxide,
sodium methoxide, KOH, KH, KOEt, KOMe, KOtBu and the like may be
added into the sodium formate before it enters thermal reactor 568.
The introduction of catalyst 567 may help to reduce the calcination
temperature and improve the conversion yield of alkali metal
formate to alkali metal oxalate to a range of 50% to 99% or more,
and preferably 70% to 99% or more. The reaction may also provide
suitable yields without the need for the addition of catalyst 567.
Hydrogen may be a major byproduct reaction from thermal reactor 568
and may be recovered for use in the process. Thermal reactor 568
may be operated in different configurations, such as under a
partial vacuum, under an inert atmosphere such as nitrogen, or with
the use of any suitable gas that may improve the efficiency of the
chemical conversion of the formate to oxalate. The addition of
other chemicals to thermal reactor 568 may also be useful, so as to
obtain a clean flowing purified product. Thermal reactor 568 may be
any suitable type equipment that may heat the alkali metal formate
to suitable temperatures and control the thermal or calcination
atmosphere. Thermal reactor 568 may include tunnel furnaces, rotary
kilns, high temperature spray dryers, high temperature rotating
drum/flaker units, fluid bed reactors, and other commercial
calcining equipment and designs that may be commercially
available.
[0066] The alkali metal oxalate product stream 570 leaving thermal
reactor 568 may be cooled, and passed to oxalate solution dissolver
572, where alkali metal oxalate solids are dissolved in water, and
may be filtered by various available methods to remove any
insoluble materials and obtain a clear, filtered product solution,
free of suspended solids. The alkali metal oxalate product may
contain alkali metal carbonate and/or alkali metal bicarbonate as
byproduct(s) of the calcination. The solution may be concentrated
sufficiently so that the alkali metal oxalate/alkali metal
bicarbonate solution may not require a larger amount of energy or
steam for water evaporation in evaporator-crystallizer 576.
[0067] Alkali metal oxalate solution stream 574 may then be passed
to electrochemical acidification cell 576, where the alkali metal
oxalate solution passes through the ion exchange compartment of the
cell and may be converted to oxalic acid stream 580 and carbon
dioxide stream 579 which may produced from the acidification of any
alkali metal carbonate present in alkali metal oxalate stream 574.
Electrochemical acidification cell 576 may utilize the same
chemistry and configuration as electrochemical acidification cell
540, producing oxygen and hydrogen a co-products, as well as NaOH
as stream 578.
[0068] Referring to FIG. 6, in another embodiment, a system 600 for
production of dicarboxylic acid, such as oxalic acid, starting with
the electrochemical generation of formate using carbon dioxide in
accordance with an embodiment of the present disclosure is shown.
System 600 may provide an alternative system for production of
oxalic acid as produced by systems 100, 105 of FIG. 1A and FIG. 1B
in addition to the production of alternative co-products.
[0069] System 600 may include an electrochemical cell 610.
Electrochemical cell 610 may operate to perform an electrochemical
reduction of carbon dioxide with a alkali metal bicarbonate cathode
feed, which may be formed from the reaction of CO.sub.2 with NaOH,
producing alkali metal formate along with chlorine gas as an anode
product when utilizing hydrochloric acid (HCl) as an anolyte, which
may be produced in electrochemical unit 670 which may use a
purified NaCl solution input feed stock. It is contemplated that
the alkali metal bicarbonate cathode feed, also referred as a
catholyte feed, may be a solution containing alkali metal
bicarbonate and alkali metal carbonate. Also, the catholyte feed
may be specified as an alkali metal bicarbonate containing
solution, such that it may contain alkali metal carbonate as well
as smaller amounts of other salts that may be added such as alkali
metal sulfates, alkali metal chlorides, alkali metal phosphates,
and the like where these added components may enhance the
electrochemical reduction of carbon dioxide to formate at the
cathode. In addition, the alkali metal containing solution may also
contain one or more organic homogeneous catalysts to also enhance
and lower the potential at the cathode for the reduction.
[0070] Alkali metal formate may be passed to a thermal reactor 620.
Alkali metal formate may be separated from bicarbonate present in
the catholyte by various means as described in FIG. 5 to provide a
suitable feed to thermal reactor 620. Thermal reactor 620 may
perform a thermal intermolecular condensation reaction with an
alkali metal hydroxide (e.g. KOH, NaOH) or use other catalysts to
produce alkali metal oxalate.
[0071] Alkali metal oxalate from thermal reactor 620 may then be
dissolved in water and may then be passed to an electrochemical
acidification electrolyzer 630. Electrochemical acidification
electrolyzer 630 may produce a dicarboxylic acid, such as oxalic
acid, and NaOH along with oxygen and hydrogen byproducts.
Electrochemical acidification electrolyzer 630 may be a membrane
based unit including of at least three regions, an anode region,
one or more central ion exchange regions, and a cathode region.
Alkali metal oxalate may be passed through the central ion exchange
region, where alkali metal ions may be replaced with protons, and
displaced alkali metal ions pass through the adjoining membrane
into the cathode region to form NaOH. The anode reaction may
produce chlorine gas when utilizing an HCl feed from
electrochemical unit 670. Alternative, the anode reaction may
utilize a different acid, such as sulfuric acid, producing oxygen
and hydrogen ions. Alternatively, electrochemical acidification
electrolyzer 630 may be an electrochemical electrodialysis unit,
utilizing bipolar membranes, producing oxalic acid as well as
smaller amounts of hydrogen and NaOH.
[0072] The hydrogen byproduct resulting from electrochemical
acidification electrolyzer 630, as an alternative embodiment, may
be used as a fuel to produce steam or used in a side process that
may utilize hydrogen, such as in a chemical hydrogenation process.
The chemical hydrogenation process may be, for example, the
hydrogenation of an oxalic acid solution or the hydrogenation of an
ester of oxalic acid, such as dimethylcarboxyalate (DMO) and
diethylcarboxalate (EDO), that may form high purity monoethylene
glycol (MEG).
[0073] Aqueous NaOH from electrochemical acidification electrolyzer
630 may be passed to an evaporator 640. Evaporator 640 may
evaporate the water from aqueous NaOH product using steam or
another heat source, converting it into a concentrated aqueous
solution and/or a solid with 5% or less water content. The NaOH may
be reacted in reactor 680 with CO.sub.2 to form an alkali metal
bicarbonate solution, which may be passed to the catholyte
compartment in electrochemical cell 610. NaOH may also be converted
to a solid for use as a catalyst in thermal reactor 620.
[0074] Electrochemical unit 670 may be an electrochemical
acidification electrolyzer, a type such as electrochemical
acidification electrolyzer 630, where a purified NaCl brine
solution is passed into the ion exchange compartment and may be
acidified, producing an HCl product stream as well as co-producing
NaOH and hydrogen in the cathode compartment. The anolyte may
utilize sulfuric acid and generate oxygen from the oxidation of
water. The purified brine may be produced by brine purification and
recycle unit 660, utilizing an NaCl solid feed and using various
purification chemicals as needed to produce the purified brine,
suitable for use in electrochemical unit 670. Electrochemical unit
670 may comprise other types of electrochemical units, such as
electrodialysis units which may utilize bipolar membranes, as well
as any other suitable type of electrolyzer that may produce
HCl.
[0075] System 600 in another embodiment, may also produce alkali
metal hypochlorite (for example NaOCl), as a co-product from the
system, utilizing chlorine and NaOH produced from electrochemical
unit 670 and electrochemical acidification electrolyzer 630.
Alternatively, chlorine may be reacted with organics to produce
various chlorinated chemical products, such as ethylene dichloride
(EDC). MOH may be a separate product of the process, or may be
converted to alkali metal carbonate or alkali metal bicarbonate,
thus converting more carbon dioxide to useful chemicals.
[0076] In another embodiment, the alkali metal formate, produced in
electrolyzer 610 may be passed directly to electrochemical
acidification electrolyzer 630, skipping thermal reactor 620,
producing formic acid. The formic acid may then be converted to
other suitable chemicals, such as methyl formate, or reacted with
various salts to produce alkali metal formates, such as calcium
formate. Methyl formate may also be converted to produce amides
such as formamide or dimethylformamide via reactions with
amines.
[0077] In another embodiment, electrochemical unit 670 may comprise
a two compartment cell having an anode compartment and a cathode
compartment separated by a separator or membrane. In this
embodiment, NaCl may be fed to the anolyte compartment producing
chlorine, and sodium hydroxide and hydrogen would be produced in
the cathode compartment.
[0078] Referring to FIG. 7, in another embodiment, system 700 may
be a process for producing downstream chemical alternatives from
the formate produced from the reduction of carbon dioxide, such as
formic acid, alkali metal formates, methyl formate, formamides, as
well other chemical derivatives such as formaldehyde. In addition
to the formate derived chemicals, the co-production of anolyte
products from the electrochemical cell and the other
electrochemical units including the electrochemical acidification
units may include chlorine, chlorinated organics, sodium
hypochlorite, sodium hydroxide, sodium bicarbonate, and sodium
bicarbonate. These products may be varied in their production
quantities and ratios as needed for system recycling and for
commercial product sales to maximize product sales and profit.
[0079] Referring to FIG. 7, system 700 for the production of
downstream formate products may include an electrochemical cell
705. Electrochemical cell 705 may operate to perform an
electrochemical reduction of carbon dioxide with a sodium
bicarbonate cathode feed, which may be formed from the reaction of
CO.sub.2 with NaOH, producing sodium formate along with chlorine
gas as an anode product when utilizing hydrochloric acid (HCl) as
an anolyte, which may produced in electrochemical unit 755 which
may use a purified NaCl solution input feed stock. It is
contemplated that the alkali metal bicarbonate cathode feed, also
referred as a catholyte feed, may be a solution containing alkali
metal bicarbonate and alkali metal carbonate. Also, the catholyte
feed may be specified as an alkali metal bicarbonate containing
solution, such that it may contain alkali metal carbonate as well
as smaller amounts of other salts that may be added such as alkali
metal sulfates, alkali metal chlorides, alkali metal phosphates,
and the like where these added components may enhance the
electrochemical reduction of carbon dioxide to formate at the
cathode. In addition, the alkali metal containing solution may also
contain one or more organic homogeneous catalysts to also enhance
and lower the potential at the cathode for the reduction.
[0080] The HCl product from electrochemical unit 755 may be
operated to produce a product stream containing HCl or a solution
mixture containing HCl and NaCl. The HCl--NaCl solution mixture
composition is such that the NaCl is soluble for the selected HCl
concentration in the solution mixture. The HCl solution product
concentration may range from 1 wt % to 35 wt %, and more preferably
in the range of 5 wt % to 30 wt %, and more preferably in the range
of 10 wt % to 25 wt %. The NaCl concentration, depending on it's
solubility in the specific HCl concentration, may range from ppm
amounts to 15 wt %, and more preferably from 0.01 wt % to 10 wt %
or less. The additional alkali metal in the HCl solution product
will produce additional alkali metal bicarbonate co-product with
the alkali metal formate in the first electrochemical cell, and is
a means of producing additional co-product. The HCl:NaCl ratio
product as a feed to electrochemical cell 705 anolyte compartment
may be used to control the pH in the catholyte of electrochemical
cell 705, since the hydrogen ions (H.sup.+) or protons may pass in
proportion to the sodium ions (Na.sup.+) present in the HCl
solution composition in the electrochemical cell anolyte. The
additional sodium ions crossing the membrane to the catholyte
compartment may also produce additional sodium bicarbonate as a
co-product from the entire process.
[0081] Sodium formate from the electrochemical cell 705 catholyte
compartment may then be passed through evaporator crystallizer 710,
where unreacted sodium bicarbonate may be separated from the sodium
formate product stream. Nanofiltration or other separation methods
may also be used in place of evaporator-crystallizer 710 or may be
used in conjunction with the 710 unit. The separated sodium
bicarbonate may be recycled to reaction unit 760, with any excess
sodium bicarbonate that may be passed to carbonate reactor 740.
[0082] The purified sodium formate stream from
evaporator-crystallizer 710 may then be passed onto electrochemical
acidification electrolyzer 715 where sodium formate may be
converted to formic acid.
[0083] Electrochemical acidification electrolyzer 715 may produce
formic acid in addition to preferably co-producing NaOH along with
chlorine and hydrogen. Electrochemical acidification electrolyzer
715 may be a membrane based unit comprising of at least three
regions, including an anode region, one or more central ion
exchange regions, and a cathode region. Sodium formate may be
passed through the central ion exchange region, where sodium ions
may be replaced with protons, and the displaced sodium ions may
pass through the adjoining membrane into the cathode region to form
NaOH. The anode reaction may produce chlorine gas when utilizing an
HCl feed from electrochemical unit 755. Alternatively, the anode
reaction may utilize a different acid, such as sulfuric acid,
producing oxygen and hydrogen ions. Alternatively, electrochemical
acidification electrolyzer 715 may be an electrochemical
electrodialysis unit, utilizing bipolar membranes, producing formic
acid as well as smaller amounts of hydrogen and NaOH.
[0084] The hydrogen byproduct resulting from electrochemical
acidification electrolyzer 715, as an alternative embodiment, may
be used as a fuel to produce steam or used in a side process that
may utilize hydrogen, such as in a chemical hydrogenation process
to produce downstream chemical products from formic acid.
[0085] Aqueous NaOH from electrochemical acidification electrolyzer
715 may be passed to an evaporator 735. Evaporator 735 may
evaporate the water from aqueous NaOH product using steam or
another heat source, converting it into a concentrated aqueous NaOH
solution ranging from 5 wt % to 70 wt %, and more preferably from
20 wt % to 50 wt %. The NaOH solution from evaporator 735 may then
be sold as the NaOH solution, preferably as a 50 wt % NaOH
solution, or converted to several co-products, including sodium
carbonate, sodium bicarbonate, and sodium hypochlorite. NaOH may
also be used, if required, in producing any of the downstream
formic acid based products.
[0086] A portion of the NaOH solution from evaporator 735 may then
be passed and reacted in reactor 740 with CO.sub.2 to form a sodium
bicarbonate and/or sodium carbonate solution, which may then be
precipitated, crystallized, and dried to produce solid products for
commercial sale.
[0087] The NaOH from evaporator 735 may also be converted to sodium
hypochlorite with any chlorine that may be produced from
electrochemical cell 705 and electrochemical acidification reactor
715. The NaOCl concentration from hypochlorite reactor may depend
on the concentration of the NaOH used in the reaction and any
dilution of the product with deionized water to achieve a specific
specification product, and the concentration may typically range
from 3% to 20 wt % as NaOCl.
[0088] Electrochemical unit 775 may an electrochemical
acidification electrolyzer, a type such as electrochemical
acidification electrolyzer 715, where a purified NaCl brine
solution is passed into one or more ion exchange compartments and
may be acidified, producing an HCl product stream as well as
co-producing NaOH and hydrogen in the cathode compartment. The HCl
product from electrochemical unit 755 may be operated to produce a
product stream containing HCl or a solution mixture containing HCl
and NaCl. The HCl--NaCl solution mixture composition is such that
the NaCl is soluble for the selected HCl concentration in the
solution mixture. The HCl solution product concentration may range
from 1 wt % to 35 wt %, and more preferably in the range of 5 wt %
to 30 wt %, and more preferably in the range of 10 wt % to 25 wt %.
The HCl product may then be passed onto the anolyte compartment of
electrochemical unit 705.
[0089] The anolyte of electrochemical unit 755 may alternatively
utilize sulfuric acid and generate oxygen from the oxidation of
water, and not produce chlorine or another halogen. The preference
may be to produce a co-product anolyte product, such as
chlorine.
[0090] The purified brine may be produced by brine purification and
recycle unit 750, utilizing an NaCl solid feed and using various
purification chemicals as needed to produce the purified brine,
suitable for use in electrochemical unit 755. Electrochemical unit
775 in an alternative embodiment may comprise other types of
electrochemical units utilizing an NaCl feed stock and converting
it into an acid and a base, such as electrodialysis units which may
utilize bipolar membranes, as well as any other suitable type of
electrolyzer that may split salts, such as NaCl, and produce HCl
and NaOH.
[0091] System 700 in another embodiment, may also produce sodium
hypochlorite (NaOCl), as a co-product from the system, utilizing
chlorine and NaOH that may be produced from electrochemical unit
705 and electrochemical acidification electrolyzer 715.
Alternatively, the chlorine may be reacted with organics to produce
various chlorinated chemical products from the process, such as
ethylene dichloride (EDC). The NaOH may also be a separate product
from the process, or may be converted to sodium carbonate or sodium
bicarbonate, thus converting more carbon dioxide to useful
chemicals.
Formate CO.sub.2 Reduction Chemistry
[0092] The postulated chemistry of the reduction of CO.sub.2 at the
cathode may proceed as follows.
[0093] Hydrogen atoms may be adsorbed at the electrode from the
reduction of water as shown in equation (1).
H.sup.++e.sup.-.fwdarw.H.sub.ad (1)
[0094] Carbon dioxide may be reduced at the cathode surface with an
adsorbed hydrogen atom to form formate, which may be adsorbed on
the surface as shown in equation (2) as follows:
CO.sub.2+H.sub.ad.fwdarw.HCOO.sub.ad (2)
[0095] The formate adsorbed on the surface then reacts with another
adsorbed hydrogen atom to form formic acid that may be released
into the solution as shown in equation (3):
HCOO.sub.ad+H.sub.ad.fwdarw.HCOOH (3)
[0096] A competing reaction at the cathode may be the reduction of
water where hydrogen gas may be formed as well as hydroxide ions as
shown in equation (4):
2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.- (4)
[0097] Operating the electrochemical cell at higher pressures
(above atmospheric), may increase the current efficiency and allow
operation of the cells at higher current densities.
Anode Reactions
[0098] The anode reaction may be the oxidation of water into oxygen
and hydrogen ions as shown in equation (5) as follows:
2H.sub.2O.fwdarw.4H.sup.++4e.sup.-+O.sub.2 (5)
[0099] Below may be the various preferred and alternative
embodiments for the process, arranged in different categories.
Formate Formation from CO
[0100] The thermal intermolecular reaction of alkali metal formate
CO with KOH may be as shown in equation (6) follows:
CO+KOH.fwdarw.HCOOK (6)
[0101] The KOH may be consumed in the reaction. Under the right
conditions, both formate and oxalate may both be produced, and
which may decrease the number of process steps. The production of
both would require the separation of these carboxylic acids from
each other.
[0102] Carbon monoxide may also be selectively absorbed in a alkali
metal carbonate and bicarbonate aqueous solutions to produce
formate, where M may be an alkali metal which may be shown as in
equations (7) and (8) as follows:
CO+MHCO3.fwdarw.MOOCH+CO.sub.2 (7)
2CO+M.sub.2CO.sub.3+H.sub.2O.fwdarw.2MCOCH+CO.sub.2 (8)
[0103] These reactions may not require MOH, such as NaOH or KOH, in
the reaction for the formation of M-formate as catalysts.
Oxalate from Formate
[0104] The thermal intermolecular reaction of alkali metal formate
with KOH may be as shown in equation (9) as follows:
2HCOOK+KOH.fwdarw.K.sub.2C.sub.2O.sub.4+H.sub.2 (9)
[0105] Optionally, sodium or potassium carbonate may also be used
for converting formate to oxalate, but the conversion yields have
been shown to be significantly lower. Under the right operating
conditions and temperatures, the yields may be significantly
improved.
Anode Oxidation Reactions
[0106] The anode reaction when utilizing sulfuric acid in the
anolyte, is the oxidation of water generating hydrogen ions and
oxygen as shown in equation (10) as follows:
2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4e.sup.- (10)
[0107] If hydrobromic acid, HBr, is used in the anolyte, the
reaction is the oxidation of the bromide to bromine as follows:
2HBr.fwdarw.Br.sub.2+2H.sup.++2e.sup.- (11)
[0108] If sodium chloride, NaCl, may be used in the anolyte, the
anode reaction, such as in the formate cell in FIG. 5, is the
oxidation of the chloride ion as shown in equation (12) as
follows:
2NaCl.fwdarw.Cl.sub.2+2Na.sup.++2e.sup.- (12)
[0109] Sodium ions may pass through the ion permeable separator
from the anolyte compartment to the catholyte compartment and
combine with any formate from the reduction of carbon dioxide to
form sodium formate and any by-product hydroxide ions formed from
the reduction of water at the cathode may form NaOH.
[0110] If hydrochloric acid, HCl, may be used in the anolyte, the
reaction may be the oxidation of the chloride to chlorine with the
co-production of hydrogen ions as shown in equation (13) as
follows:
2HCl.fwdarw.Cl.sub.2+2H.sup.++2e.sup.- (13)
Carbonate and Bicarbonate Reactions
[0111] Sodium carbonate, Na.sub.2CO.sub.3, dissolved in solution
may be converted to sodium bicarbonate, Na.sub.2HCO.sub.3, with
reaction with CO.sub.2 as shown in equation (14) as follows:
Na.sub.2CO.sub.3+CO.sub.2+H.sub.2O.fwdarw.2NaHCO.sub.3 (14)
[0112] Sodium hydroxide, NaOH, reaction with CO.sub.2 in solution
may be converted to sodium carbonate, Na.sub.2CO.sub.3, as shown in
equation (15) as follows:
2NaOH+CO.sub.2+H.sub.2O.fwdarw.2Na.sub.2CO.sub.3+H.sub.2O (15)
Chlorine Reaction with NaOH
[0113] Sodium hydroxide, NaOH, may be reacted with chlorine to
produce sodium hypochlorite, NaOCl, as shown in equation (16) as
follows:
2NaOH+Cl.sub.2.fwdarw.NaOCl+NaCl+H.sub.2O (16)
Electrolyzer Configurations
[0114] The following present various exemplary combinations of cell
configurations, electrode structures, and anolyte/catholyte
compositions that may be used in the electrochemical CO and/or
formate, and electrochemical acidification (EA) electrolyzers in
the above described processes.
[0115] The cathode of the electrochemical cell 110 and
electrochemical acidification electrolyzer 140 may be a high
surface area electrode. The void volume for the cathode may be from
about 30% to 98%. The surface area of the cathode may be from 2
cm.sup.2/cm.sup.3 to 2,000 cm.sup.2/cm.sup.3 or higher. The surface
areas may be further defined as a total area in comparison to the
current distributor/conductor back plate area with a preferred
range of from 2 to 1000 times the current distributor/conductor
back plate area.
[0116] The cathode of the electrochemical cell 110 may be
electrolessly plated indium or tin on a copper woven mesh, screen
or fiber structure. Indium-copper intermetallics may be formed on
the copper woven mesh, screen or fiber structure. The
intermetallics may be harder than the soft indium metal, and allow
better mechanical properties in addition to usable catalytic
properties. The indium electrocatalyst coating may also be prepared
by electroplating indium onto a suitable corrosion resistant metal
substrate, such as a tin plated copper or tin plated stainless
steel metal high surface area substrate. Alternatively, the indium
can be plated onto a high surface area carbon substrate, such as a
carbon felt or cloth composed of fibers, which may already have an
applied tin-based coating. Also, the indium electrocatalyst may be
applied by co-electroplating a mixture of indium with another
metal, such as Sn, Zn, Bi, or Pb, onto a suitably prepared coated
metal or carbon substrate, such that the coating is physically and
chemically compatible with the applied indium/co-metal
electroplated external layer. Suitable indium-based
electrocatalytic coatings are corrosion resistant to the catholyte
solutions, salts, and operating pH of the catholyte.
[0117] In the electrochemical reduction of carbon dioxide metals
including Pb, Sn, Hg, Tl, In, Bi, and Cd among others may produce
formic acid (or formate) as a major C.sub.1 product in aqueous
solutions. Alloy combinations of these metals such as Hg/Cu,
Sn--Cd, Sn--Zn, Cu--Sn, may form at various performance
efficiencies. One of the issues may be that a number of these
metals, such as Sn and Cu, may be that the surface changes and
deactivates or loses the Faradaic conversion activity in producing
formate. The surface then may have to be reactivated by a reverse
current or polarity. In the production for formation of C.sub.2+
chemicals, such as oxalic acid and glycolic acid, metals such as
Ti, Nb, Cr, Mo, Ag, Cd, Hg, Tl, As, and Pb as well as Cr--Ni--Mo
steel alloys among many others may result in the formation of these
higher C.sub.2+ products.
[0118] In another embodiment, the cathode surfaces may be renewed
by the periodic addition of indium salts or a mix of indium/tin
salts in situ during the electrochemical cell operation.
Electrochemical cell 110 may be operated at full rate during
operation, or temporarily operated at a lower current density with
or without any carbon dioxide addition during the injection of the
metal salts.
[0119] In another exemplary embodiment, in preparing cathode
materials for the production of C.sub.2+ chemicals, the addition of
metal salts that may reduce on the surfaces of the cathode
structure may be also used, such as the addition of Ag, Au, Mo, Cd,
Sn, etc. to provide a catalytic surface that may be difficult to
prepare directly during cathode fabrication or for renewal of the
catalytic surfaces.
[0120] In another exemplary embodiment, Magneli phase titanium
oxides, in particular Ti.sub.4O.sub.7 may be used as a cathode base
material, which may also be impregnated or coated with one or more
of the aforementioned suitable cathode metals, which may include
Ag, Au, In, Mo, Cd, Sn, Cu, Hg, Tl, Bi, Ti, Nb, Zr, As, Cr, Co, Zn,
Pb, and their alloys and combinations. These magneli phase
materials may be in the form of three dimensional porous materials
in the shape of plates, foams, pellets, powders, and the like. One
manufacturer, Atraverda, Ltd., manufactures these under the
tradename of Ebonex.
[0121] Cathode 412 for the electrochemical acidification
electrolyzer 140 may include stainless steels and nickel
electrodes. Cathode 412 may include coatings on the cathode to
reduce the hydrogen overpotential.
[0122] An alkali metal hydroxide range for the electrochemical
acidification electrolyzer 140 may be 5% to 50% by weight, and more
preferably 10% to 45% by weight. The alkali metal hydroxide
examples may be NaOH, KOH, CsOH and the like.
[0123] Cathode materials for the cathode of electrochemical cell
110 for carbon monoxide production from CO.sub.2 may include
precious and noble metals, Cu, Ag, Au, and their oxides,
specifically the oxides of copper. Other d-block metals, such as Zn
and Ni, may be selective for CO reduction in aqueous media.
Regardless of specificity for CO as a CO.sub.2 reduction product, a
cathode for electrochemical cell 110 for an aqueous system for
CO.sub.2 reduction to CO may have a high hydrogen overpotential to
prevent competing H.sub.2 formation.
[0124] Anions used for CO production at the cathode may be any
species stable at working potentials such as sulfate, chloride or
bicarbonate. CO.sub.2 reduction to CO may favor high pH due to
limited competing H.sub.2 formation; however there may be a
practical pH maximum at around 8.5 for a saturated CO.sub.2
solution due to the formation of carbonic acid on dissolution.
There may be no strict lower limit that may have been observed.
Depending on the chemistry of the system, the pH of the catholyte
region of electrochemical cell 110 may range from 3 to 12. The pH
may be a function of the catalysts used, such that there may be no
corrosion at the electrochemical cell 110 and catholyte operating
conditions.
[0125] Electrolytes for the electrochemical cell 110 for forming CO
and formates may include alkali metal bicarbonates, carbonates,
sulfates, and phosphates, borates, ammonium, hydroxides, chlorides,
bromides, and other organic and inorganic salts. The electrolytes
may also include non-aqueous electrolytes, such as propylene
carbonate, methanesulfonic acid, methanol, and other ionic
conducting liquids, which may be in an aqueous mixture, or as a
non-aqueous mixture in the catholyte. The introduction of micro
bubbles of carbon dioxide into the catholyte stream may improve
carbon dioxide transfer to the cathode surfaces.
[0126] The electrochemical cell catholyte solution may also
comprise an aqueous or non-aqueous based solution. The solution may
contain an organic solvent, for example methanol or ethanol, that
may help provide a higher solubility of carbon dioxide in the
solution over that of aqueous solutions. The organic solvent may be
fully soluble in the aqueous catholyte solution or may also be
present as an emulsion in the catholyte solution. The solvent may
be a polar or aprotic type solvent. Solvents may include
carbonates, such as propylene carbonate, acetone,
alcohols--including primary, secondary, and tertiary types,
dimethyl sulfoxide, dioxane, aromatic hydrocarbons such as toluene
and cyclohexane, chlorinated as well as fluorinated solvents such
as chloroform, aprotic solvents such as acetonitrile, and the like.
An aqueous solvent in this disclosure is defined as a solution
containing less than 50 wt % of organics in comparison to the water
content. The organics may be chosen in regards to improving carbon
dioxide solubility in the solution, as a moderator of the catholyte
salt solubility such as formate, and in improving or enabling the
cathode chemistry in the formation of C2+ compounds, which may be
promoted by the use of the organics which exclude water in the
cathode reaction. Examples of a C2+ carbon dioxide reduction
products are oxalate, glycolate, and glyoxylates. Other carbon
dioxide products may include acetic acid, ethanol, methanol, as
well as others.
[0127] Electrolytes for the anolyte region of the electrochemical
cell 110 may include: alkali metal hydroxides, (e.g. as KOH, NaOH,
LiOH) in addition to ammonium hydroxide; inorganic acids such as
sulfuric, phosphoric, and the like; organic acids such as
methanesulfonic acid in both non-aqueous and aqueous solutions; and
alkali halide salts, such as the chlorides, bromides, and iodine
salts such as NaF, NaCl, NaBr, LiBr, KF, KCl, KBr, KI, and NaI, as
well as their hydrogen halide forms, such as HCl, HF, HI, and HBr.
The alkali halide salts may produce, for example, fluorine,
chlorine, bromine, or iodine as halide gas or dissolved aqueous
products from the anolyte region. Methanol or other hydrocarbon
non-aqueous liquids may also be used, and they would form some
oxidized organic products from the anolyte. Selection of the
anolyte would be determined by the process chemistry product and
requirements for lowering the overall operating cell voltage. For
example, using HBr as the anolyte, with the formation of bromine at
the anode, which require a significantly lower anode voltage
potential than chlorine formation. Hydriodic acid, HI, may form
iodine at anode potential voltages even lower than that of
bromine.
[0128] Preferred anolytes for the system include alkali metal
hydroxides, such as KOH, NaOH, LiOH; ammonium hydroxide; inorganic
acids such as sulfuric, phosphoric, and the like; organic acids
such as methanesulfonic acid; non-aqueous and aqueous solutions;
alkali halide salts, such as the chlorides, bromides, and iodine
types such as NaCl, NaBr, LiBr, and NaI; and hydrogen halides such
as HCl, HBr and HI. The hydrogen halides and alkali halide salts
will produce for example chlorine, bromine, or iodine as a halide
gas or as dissolved aqueous products from the anolyte compartment.
Methanol or other hydrocarbon non-aqueous liquids can also be used,
and would form some oxidized organic products from the anolyte.
Selection of the anolyte would be determined by the process
chemistry product and requirements for lowering the overall
operating cell voltage. For example, the formation of bromine at
the anode requires a significantly lower anode voltage potential
than chlorine formation, and iodine is even lower than that of
bromine. This allows for a significant power cost savings in the
operation of both of the electrochemical units when bromine is
generated in the anolyte. The formation of a halogen, such as
bromine, in the anolyte may then be used in an external reaction to
produce other compounds, such as reactions with alkanes to form
bromoethane, which may then be converted to an alcohol, such as
ethanol, or an alkene, such as ethylene, and the halogen hydrogen
halide byproduct from the reaction can be recycled back to the
electrochemical cell anolyte.
[0129] Catholyte cross sectional area flow rates may range from 2
to 3,000 gpm/ft.sup.2 or more (0.0076-11.36 m.sup.3/m.sup.2). Flow
velocities may range from 0.002 to 20 ft/sec (0.0006 to 6.1
m/sec).
[0130] Catholyte region of the electrochemical cell 110 may include
at least one catalyst. The catalyst may be a homogeneous
heterocyclic catalyst which may be utilized in the catholyte region
to improve the Faradaic yield to formate. Homogeneous heterocyclic
catalysts may include, for example, one or more of pyridine, tin
2-picoline, 4-hydroxy pyridine, adenine, a heterocyclic amine
containing sulfur, a heterocyclic amine containing oxygen, an
azole, a benzimidazole, a bipyridine, a furan, an imidazole, an
imidazole related species with at least one five-member ring, an
indole, a lutidine, methylimidazole, an oxazole, a phenanthroline,
a pterin, a pteridine, pyridine, a pyridine related species with at
least one six-member ring, a pyrrole, a quinoline, or a thiazole,
and mixtures thereof.
[0131] Operating electrochemical cell 110 at a higher operating
pressure in the catholyte region may allow more dissolved CO.sub.2
to dissolve in the aqueous electrolyte. 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 110 anolyte may
also be operated in the same pressure range to minimize the
pressure differential on the membrane separating the two electrode
regions. Special electrochemical designs may be required to operate
electrochemical units at higher operating pressures up to about 60
to 100 atmospheres or greater, which may be in the liquid CO.sub.2
and supercritical CO.sub.2 operating range.
[0132] In another embodiment, a portion of the catholyte recycle
stream may be separately pressurized using a flow restriction with
back pressure or using a pump 390 with CO.sub.2 injection such that
the pressurized stream may be then injected into the catholyte
region of the electrochemical cell 110, and potentially increasing
the amount of dissolved CO.sub.2 in the aqueous solution to improve
the conversion yield.
[0133] Catholyte region and anolyte region of electrochemical cell
110 may have operating temperatures that may range from -10 to
95.degree. C., 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 aqueous solution phase of the
electrolyte which may result in obtaining higher conversion and
current efficiencies. However, operating electrochemical cell
voltages may be higher, such that an optimization may be required
to produce the chemicals at the lowest operating cost. In addition,
the operating temperatures of the anolyte and catholyte may be
different, whereby the anolyte is operated at a higher temperature
and the catholyte is operated at a lower temperature.
[0134] The electrochemical cell 110 and the electrochemical
acidification electrolyzer 140 may be zero gap, flow-through
electrolyzers with a recirculating catholyte electrolyte with
various high surface area cathode materials. For example, flooded
co-current packed and trickle bed designs with various high surface
area cathode materials may be employed. The stack cell design may
be bipolar and/or monopolar.
[0135] The anode of the electrochemical cell 110 and the
electrochemical acidification electrolyzer 140 may include one or
more anode coatings. For example, for acid anolytes and oxidizing
water under acid conditions, electrocatalytic coatings may include:
precious metal and 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 conductive substrates such as
titanium, tantalum, or niobium as typically used in the chlor
alkali industry or other electrochemical processes where they may
be stable as anodes. Magneli phase titanium oxides, in particular
Ti.sub.4O.sub.7 may be used as an anode material, which may also be
impregnated or coated with the aforementioned precious metals and
precious metal oxides. These magneli phase materials may be in the
form of three dimensional porous materials in the shape of plates,
foams, pellets, powders, and the like. One manufacturer, Atraverda,
Ltd., manufactures these under the tradename of Ebonex. For other
anolytes such as alkaline or hydroxide electrolytes, the
electrocatalytic coatings may include carbon, graphite, cobalt
oxides, nickel, stainless steels, and their alloys and combinations
which may be stable as anodes under these alkaline conditions.
[0136] Membrane 330, 406a, 406b may be cation ion exchange type
membranes such as those having a high rejection efficiency to
anions. For example perfluorinated sulfonic acid based 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..
Other multi-layer perfluorinated ion exchange membranes used in the
chlor alkali industry and having a bilayer construction of a
sulfonic acid based membrane layer bonded to a carboxylic acid
based membrane layer may be employed to efficiently operate with an
anolyte and catholyte above a pH of about 2 or higher. These
membranes may have a higher anion rejection efficiency. These may
be 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.
Hydrocarbon based membranes, which may be made from of various
cation ion exchange materials may also be used if the anion
rejection may be 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.
Electrochemical Formate Cell Examples
[0137] An electrochemical bench scale cell with an electrode
projected area of about 108 cm.sup.2 was used for much of the bench
scale test examples. The electrochemical cell was constructed
consisting of two electrode compartments machined from 1.0 inch
(2.54 cm) thick natural polypropylene. The outside dimensions of
the anode and cathode compartments were 8 inches (20.32 cm) by 5
inches (12.70 cm) with an internal machined recess of 0.375 inches
(0.9525 cm) deep and 3.0 inches (7.62 cm) wide by 6 inches (15.24
cm) tall with a flat gasket sealing area face being 1.0 inches
(2.52 cm) wide. Two holes were drilled equispaced in the recess
area to accept two electrode conductor posts that pass though the
compartment thickness, and having two 0.25 inch (0.635 cm) drilled
and tapped holes to accept a plastic fitting that passes through
0.25 inch (0.635 cm) conductor posts and seals around it to not
allow liquids from the electrode compartment to escape to the
outside. The electrode frames were drilled with an upper and lower
flow distribution hole with 0.25 inch pipe threaded holes with
plastic fittings installed to the outside of the cell frames at the
top and bottom of the cells to provide flow into and out of the
cell frame, and twelve 0.125 inch (0.3175 cm) holes were drilled
through a 45 degree bevel at the edge of the recess area to the
upper and lower flow distribution holes to provide an equal flow
distribution across the surface of the flat electrodes and through
the thickness of the high surface area electrodes of the
compartments.
[0138] For the anode compartment cell frames, an anode with a
thickness of 0.060 inch (0.1524 cm) and 2.875 inch (7.3025 cm)
width and 5.875 inch (14.9225 cm) length with two 0.25 inch (0.635
cm) titanium diameter conductor posts welded on the backside were
fitted through the two holes drilled in the electrode compartment
recess area. The positioning depth of the anode in the recess depth
was adjusted by adding plastic spacers behind the anode, and the
edges of the anode to the cell frame recess were sealed using a
medical grade epoxy. The electrocatalyst coating on the anode was a
Water Star WS-32, an iridium oxide based coating on a 0.060 inch
(0.1524 cm) thick titanium substrate, suitable for oxygen evolution
in acids. In addition, the anode compartment also employed an anode
folded screen (folded three times) that was placed between the
anode and the membrane, which was a 0.010 inch (0.0254 cm) thick
titanium expanded metal material from DeNora North America (EC626),
with an iridium oxide based oxygen evolution coating, and used to
provide a zero gap anode configuration (anode in contact with
membrane), and to provide pressure against the membrane from the
anode side which also had contact pressure from the cathode
side.
[0139] For the cathode compartment cell frames, 316L stainless
steel cathodes with a thickness of 0.080 inch (0.2032 cm) and 2.875
inch (7.3025 cm) width and 5.875 inch (14.9225 cm) length with two
0.25 inch (0.635 cm) diameter 316L SS conductor posts welded on the
backside were fitted through the two holes drilled in the electrode
compartment recess area. The positioning depth of the cathode in
the recess depth was adjusted by adding plastic spacers behind the
cathode, and the edges of the cathode to the cell frame recess were
sealed using a fast cure medical grade epoxy.
[0140] A copper bar was connected between the two anode posts and
the cathode posts to distribute the current to the electrode back
plate. The cell was assembled and compressed using 0.25 inch (0.635
cm) bolts and nuts with a compression force of about 60 in-lbs
force. Neoprene elastomer gaskets (0.0625 inch (0.159 cm) thick)
were used as the sealing gaskets between the cell frames, frame
spacers, and the membranes.
Example 1
[0141] The above cell was assembled with a 0.010 inch (0.0254 cm)
thickness indium foil mounted on the 316L SS back conductor plate
using a conductive silver epoxy. A multi-layered high surface area
cathode, comprising an electrolessly applied indium layer of about
1 micron thickness that was deposited on a previously applied layer
of electroless tin with a thickness of about 25 micron thickness
onto a woven copper fiber substrate. The base copper fiber
structure was a copper woven mesh obtained from an on-line internet
supplier, PestMall.com (Anteater Pest Control Inc.). The copper
fiber dimensions in the woven mesh had a thickness of 0.0025 inches
(0.00635 cm) and width of 0.010 inches (0.0254 cm). The prepared
high surface area cathode material was folded into a pad that was
1.25 inches (3.175 cm) thick and 6 inches (15.24 cm) high and 3
inches (7.62 cm) wide, which filled the cathode compartment
dimensions and exceeded the adjusted compartment thickness (adding
spacer) which was 0.875 inches (2.225 cm) by about 0.25 inches
(0.635 cm). The prepared cathode had a calculated surface area of
about 3,171 cm.sup.2, for an area about 31 times the flat cathode
plate area, with a 91% void volume, and specific surface area of
12.3 cm.sup.2/cm.sup.3. The cathode pad was compressible, and
provided the spring force to make contact with the cathode plate
and the membrane. Two layers of a very thin (0.002 inches thick)
plastic screen with large 0.125 inch (0.3175 cm) holes were
installed between the cathode mesh and the Nafion.RTM. 324
membrane. Neoprene gaskets (0.0625 inch (0.159 cm) thick) were used
as the sealing gaskets between the cell frames and the membranes.
The electrocatalyst coating on the anode in the anolyte compartment
was a Water Star WS-32, an iridium oxide based coating, suitable
for oxygen evolution in acids. In addition, the anode compartment
also employed a three-folded screen that was placed between the
anode and the membrane, which was a 0.010 inch (0.0254 cm) thick
titanium expanded metal material from DeNora North America (EC626),
with an iridium oxide based oxygen evolution coating, and used to
provide a zero gap anode configuration (anode in contact with
membrane), and to provide pressure against the membrane from the
anode side which also had contact pressure from the cathode
side.
[0142] The cell assembly was tightened down with stainless steel
bolts, and mounted into the cell station, which has the same
configuration as shown in FIG. 1 with a catholyte disengager, a
centrifugal catholyte circulation pump, inlet cell pH and outlet
cell pH sensors, a temperature sensor on the outlet solution
stream. A 5 micron stainless steel frit filter was used to sparge
carbon dioxide into the solution into the catholyte disengager
volume to provide dissolved carbon dioxide into the recirculation
stream back to the catholyte cell inlet.
[0143] The anolyte used was a dilute 5% by volume sulfuric acid
solution, made from reagent grade 98% sulfuric acid and deionized
water.
[0144] In this test run, the system was operated with a catholyte
composition containing 0.4 molar potassium sulfate aqueous with 2
gm/L of potassium bicarbonate added, which was sparged with carbon
dioxide to an ending pH of 6.60.
[0145] Operating Conditions:
Batch Catholyte Recirculation Run
[0146] Anolyte Solution: 0.92 M H.sub.2SO.sub.4 Catholyte Solution:
0.4 M K.sub.2SO.sub.4, 0.14 mM KHCO.sub.3 Catholyte flow rate: 2.5
LPM Catholyte flow velocity: 0.08 ft/sec Applied cell current: 6
amps (6,000 mA) Catholyte pH range: 5.5-6.6, controlled by periodic
additions of potassium bicarbonate to the catholyte solution
recirculation loop. Catholyte pH declined with time, and was
controlled by the addition of potassium bicarbonate.
[0147] Results:
Cell voltage range: 3.39-3.55 volts (slightly lower voltage when
the catholyte pH drops) Run time: 6 hours Formate Faradaic yield:
Steady between 32-35%, calculated taking samples periodically. The
final formate concentration: 9,845 ppm
Example 2
[0148] The same cell as in Example 1 was used with the same
cathode, which was only rinsed with water while in the
electrochemical cell after the run was completed and then used for
this run.
[0149] In this test run, the system was operated with a catholyte
composition containing 0.375 molar potassium sulfate aqueous with
40 gm/L of potassium bicarbonate added, which was sparged with
carbon dioxide to an ending pH of 7.05.
[0150] Operating Conditions:
Batch Catholyte Recirculation Run
[0151] Anolyte Solution: 0.92 M H.sub.2SO.sub.4 Catholyte Solution:
0.4 M K.sub.2SO.sub.4, 0.4 M KHCO.sub.3 Catholyte flow rate: 2.5
LPM Catholyte flow velocity: 0.08 ft/sec Applied cell current: 6
amps (6,000 mA) Catholyte pH range: Dropping from 7.5 to 6.75
linearly with time during the run.
[0152] Results:
Cell voltage range: 3.40-3.45 volts Run time: 5.5 hours Formate
Faradaic yield: Steady at 52% and slowly declining with time to 44%
as the catholyte pH dropped. Final formate concentration: 13,078
ppm
Example 3
[0153] The same cell as in Examples 1 and 2 was used with the same
cathode, which was only rinsed with water while in the
electrochemical cell after the run was completed and then used for
this run.
[0154] In this test run, the system was operated with a catholyte
composition containing 0.200 molar potassium sulfate aqueous with
40 gm/L of potassium bicarbonate added, which was sparged with
carbon dioxide to an ending pH of 7.10.
[0155] Operating Conditions:
Batch Catholyte Recirculation Run
[0156] Anolyte Solution: 0.92 M H.sub.2SO.sub.4 Catholyte Solution:
0.2 M K.sub.2SO.sub.4, 0.4 M KHCO.sub.3 Catholyte flow rate: 2.5
LPM Catholyte flow velocity: 0.08 ft/sec Applied cell current: 9
amps (9,000 mA) Catholyte pH range: Dropping from 7.5 to 6.65
linearly with time during the run, and then additional solid
KHCO.sub.3 was added to the catholyte loop in 10 gm increments at
the 210, 252, and 290 minute time marks which brought the pH back
up to about a pH of 7 for the last part of the run.
[0157] Results:
Cell voltage range: 3.98-3.80 volts Run time: 6.2 hours Formate
Faradaic yield: 75% declining to 60% at a pH of 6.65, and then
increasing to 75% upon the addition of solid potassium bicarbonate
to the catholyte to the catholyte loop in 10 gm increments at the
210, 252, and 290 minute time marks and slowly declining down with
time 68% as the catholyte pH dropped to 6.90. Final formate
concentration: 31,809 ppm.
Example 4
[0158] The same cell as in Examples 1, 2, and 3 was used with the
same cathode, which was only rinsed with water while in the
electrochemical cell after the run was completed and then used for
this run.
[0159] In this test run, the system was operated with a catholyte
composition containing 1.40 molar potassium bicarbonate (120 gm/L
KHCO.sub.3), which was sparged with carbon dioxide to an ending pH
of 7.8.
[0160] Operating Conditions:
Batch Catholyte Recirculation Run
[0161] Anolyte Solution: 0.92 M H.sub.2SO.sub.4
Catholyte Solution: 1.4 M KHCO.sub.3
[0162] Catholyte flow rate: 2.6 LPM Catholyte flow velocity: 0.09
ft/sec Applied cell current: 11 amps (11,000 mA) Catholyte pH
range: Dropping from around 7.8 linearly with time during the run
to a final pH of 7.48
[0163] Results:
Cell voltage range: 3.98-3.82 volts Run time: 6 hours Formate
Faradaic yield: 63% and settling down to about 54-55%. Final
formate concentration: 29,987 ppm.
Example 5
[0164] The same cell as in Examples 1, 2, and 3 was used, except
for using 701 gm of tin shot (0.3-0.6 mm diameter) media with an
electroless plated indium coating as the cathode. The cathode
compartment thickness was 0.875 inches.
[0165] In this test run, the system was operated with a catholyte
composition containing 1.40 molar potassium bicarbonate (120 gm/L
KHCO.sub.3), which was sparged with carbon dioxide to an ending pH
of 8.0
[0166] The cell was operated in a batch condition with no overflow
for the first 7.3 hrs, and then a 1.40 molar potassium bicarbonate
feed was introduced into the catholyte at a rate of about 1.4
mL/min, with the overflow collected and measured, and a sample of
the loop was collected for formate concentration analysis.
[0167] Operating Conditions:
Batch Catholyte Recirculation Run
[0168] Anolyte Solution: 0.92 M H.sub.2SO.sub.4
Catholyte Solution: 1.4 M KHCO.sub.3
[0169] Catholyte flow rate: 3.2 LPM Applied cell current: 6 amps
(6,000 mA) Catholyte pH range: Dropping slowly from around a pH of
8 linearly with time during the run to a final pH of 7.50
[0170] Results:
Cell voltage range: 3.98-3.82 volts Run time: Batch mode: 7.3 hours
Feed and product overflow: 7.3 hours to end of run at 47 hours.
[0171] The formate Faradaic efficiency was between 42% and 52%
during the batch run period where the formate concentration went up
to 10,490 ppm. During the feed and overflow period, the periodic
calculated efficiencies varied between 32% and 49%. The average
conversion efficiency was about 44%. The formate concentration
varied between 10,490 and 48,000 ppm during the feed and overflow
period. The cell voltage began at around 4.05 volts, ending up at
3.80 volts.
Example 6
[0172] The same cell as in Examples 1, 2, and 3 was used, except
for using 890.5 gm of tin shot (3 mm diameter) media and with a tin
foil coating as the cathode. The cathode compartment thickness was
1.25 inches and the system was operated in a batch mode with no
feed input. Carbon dioxide was sparged to saturate the solution in
the catholyte disengager.
[0173] Packed Tin Bed Cathode Detail:
Weight: 890.5 gm tin shot Tin shot: 3 mm average size Total
compartment volume: 369 cm.sup.3 Calculated tin bead surface area:
4,498 cm.sup.2 Calculated packed bed cathode specific surface area:
12.2 cm.sup.2/cm.sup.3 Calculated packed bed void volume: 34.6%
[0174] In this test run, the system was operated with a catholyte
composition containing 1.40 molar potassium bicarbonate (120 gm/L
KHCO.sub.3), which was sparged with CO.sub.2 to an ending pH of
about 8.0
[0175] The cell was operated in a batch condition with no overflow
and a sample of the catholyte loop was collected for formate
concentration analysis periodically.
[0176] Operating Conditions:
Batch Catholyte Recirculation Run
[0177] Anolyte Solution: 0.92 M H.sub.2SO.sub.4
Catholyte Solution: 1.4 M KHCO.sub.3
[0178] Catholyte flow rate: 3.0 LPM (upflow) Catholyte flow
velocity: 0.068 ft/sec Applied cell current: 6 amps (6,000 mA)
Catholyte pH range: Increasing slowly from around a pH of 7.62
linearly with time during the run to a final pH of 7.73
[0179] Results:
Cell voltage range: Started at 3.84 volts, and slowly declined to
3.42 volts Run time: Batch mode, 19 hours
[0180] The formate Faradaic efficiency started at about 65% and
declined after 10 hours to 36% and to about 18.3% after 19 hours.
The final formate concentration ended up at 20,500 ppm at the end
of the 19 hour run.
Example 7
[0181] The same cell as in Examples 1, 2, and 3 was used, except
for using 805 gm of indium coated tin shot (3 mm diameter) media
and with a 0.010 inch (0.0254 cm) thickness indium foil mounted on
the 316L SS back conductor plate using a conductive silver epoxy as
the cathode. The cathode compartment thickness was 1.25 inches and
the system was operated in a batch mode with no feed input. Carbon
dioxide was sparged to saturate the solution in the catholyte
disengager. The tin shot was electrolessly plated with indium in
the same method as used in Examples 1-4 on the tin-coated copper
mesh. The indium coating was estimated to be about 0.5-1.0 microns
in thickness.
[0182] Indium-Coated Tin Shot Packed Bed Cathode Detail:
Weight: 890.5 gm, indium coating on tin shot Indium coated tin
shot: 3 mm average size Total compartment volume: 369 cm.sup.3
Calculated tin bead surface area: 4498 cm.sup.2 Packed bed cathode
specific surface area: 12.2 cm.sup.2/cm.sup.3 Packed bed void
volume: 34.6%
[0183] In this test run, the system was operated with a catholyte
composition containing 1.40 molar potassium bicarbonate (120 gm/L
KHCO.sub.3), which was sparged with CO.sub.2 to an ending pH of
about 8.0
[0184] The cell was operated in a batch condition with no overflow
and a sample of the catholyte loop was collected for formate
concentration analysis periodically.
[0185] Operating Conditions:
Batch Catholyte Recirculation Run
[0186] Anolyte Solution: 0.92 M H.sub.2SO.sub.4
Catholyte Solution: 1.4 M KHCO.sub.3
[0187] Catholyte flow rate: 3.0 LPM (upflow) Catholyte flow
velocity: 0.068 ft/sec Applied cell current: 6 amps (6,000 mA)
Catholyte pH range: Decreased slowly from around a pH of 7.86
linearly with time during the run to a final pH of 5.51
[0188] Results:
Cell voltage range: Started at 3.68 volts, and slowly declined to
3.18 volts Run time: Batch mode, 24 hours
[0189] The formate Faradaic efficiency started at about 100% and
varied between 60% to 85%, ending at about 60% after 24 hours. The
final formate concentration ended up at about 60,000 ppm at the end
of the 24 hour run. Dilution error of the samples at the high
formate concentrations may have provided the variability seen in
the yield numbers.
Example 7
[0190] The same cell as in Examples 1, 2, and 3 was used with a
newly prepared indium on tin electrocatalyst coating on a copper
mesh cathode. The prepared cathode had calculated surface areas of
about 3,171 cm.sup.2, for an area about 31 times the flat cathode
plate area, with a 91% void volume, and specific surface area of
12.3 cm.sup.2/cm.sup.3.
[0191] In this test run, the system was operated with a catholyte
composition containing 1.40 M potassium bicarbonate (120 gm/L
KHCO.sub.3), which was sparged with CO.sub.2 to an ending pH of 7.8
before being used.
[0192] The cells were operated in a recirculating batch mode for
the first 8 hours of operation to get the catholyte formate ion
concentration up to about 20,000 ppm, and then a fresh feed of 1.4
M potassium bicarbonate was metered into the catholyte at a feed
rate of about 1.2 mL/min. The overflow volume was collected and
volume measured, and the overflow and catholyte loop sample were
sampled and analyzed for formate by ion chromatography.
[0193] Operating Conditions:
Cathode: Electroless indium on tin on a copper mesh substrate
Continuous Feed with Catholyte Recirculation Run--11.5 days Anolyte
Solution: 0.92 M H.sub.2SO.sub.4
Catholyte Solution: 1.4 M KHCO.sub.3
[0194] Catholyte flow rate: 3.2 LPM Catholyte flow velocity: 0.09
ft/sec Applied cell current: 6 amps (6,000 mA)
[0195] Results:
Cell voltage versus time, displaying a stable operating voltage of
about 3.45 volts over the 11.5 days after the initial start-up.
Continuous Run time: 11.5 days Formate Concentration Versus Time:
The formate concentration varied between 17,000 ppm and 28,000 ppm
based on samples taken daily. Formate Faradaic yield: The
calculated formate current efficiency versus time measuring the
formate yield from the collected samples. The formate yield varied
between about 30% to 60% based on the daily interval samples taken.
Final formate concentration: About 28,000 ppm. Catholyte pH: The
catholyte pH change over the 11.5 days, slowly declined from a pH
of 7.8 to a pH value of 7.5 at the end of the run. The feed rate
was not changed during the run, but could have been slowly
increased or decreased to maintain a constant catholyte pH in any
optimum operating pH range.
Example 8
[0196] The same cell as in Examples 1, 2, and 3 was used with a
newly prepared indium on tin electrocatalyst coating on a copper
mesh cathode. The prepared cathode had calculated surface areas of
about 3,171 cm.sup.2, for an area about 31 times the flat cathode
plate area, with a 91% void volume, and specific surface area of
12.3 cm.sup.2/cm.sup.3.
[0197] In this test run, the system was operated with a catholyte
composition containing 1.40 M potassium bicarbonate (120 gm/L
KHCO.sub.3), which was sparged with CO.sub.2 to an ending pH of 7.8
before being used.
[0198] The cells were operated in a recirculating batch mode for
the first 8 hours of operation to get the catholyte formate ion
concentration up to about 20,000 ppm, and then a fresh feed of 1.4
M potassium bicarbonate was metered into the catholyte at a feed
rate of about 1.2 mL/min. The overflow volume was collected and
volume measured, and the overflow and catholyte loop sample were
sampled and analyzed for formate by ion chromatography.
[0199] Operating Conditions:
Cathode: Electroless indium on tin on a copper mesh substrate
Continuous Feed with Catholyte Recirculation Run--21 days Anolyte
Solution: 0.92 M H.sub.2SO.sub.4
Catholyte Solution: 1.4 M KHCO.sub.3
[0200] Catholyte flow rate: 3.2 LPM Catholyte flow velocity: 0.09
ft/sec
[0201] Applied cell current: 6 amps (6,000 mA)
[0202] Results:
Cell voltage versus time: The cell showed a higher operating
voltage of about 4.40 volts, higher than all of our other cells,
because of an inadequate electrical contact pressure of the cathode
against the indium foil conductor back plate. The cell maintained
operation for an extended run. Continuous Run time: 21 days
[0203] Formate Faradaic yield: The calculated formate current
efficiency were measured versus time from the collected samples.
The formate Faradaic current efficiency declined from about 50%-60%
from the first 4 days, averaged at about 4%-45% in days 5 through
14, and slowly declined into the 20%-25% range in days 17 through
20.
[0204] Formate Concentration Versus Time: The formate concentration
averaged between about 20,000-30,000 ppm in days 1 through 16, and
then declined to about 10,000 to 14,000 ppm in days 17 through 20.
On day 21, 0.5 gm of indium (III) carbonate was added to the
catholyte while the cell was still operating at the 6 ampere
operating rate. The formate concentration in the catholyte
operating loop was 11,330 ppm before the indium addition, which
increased to 13,400 ppm after 8 hours, and increased to 14,100 ppm
after 16 hours when the unit was shut down after 21 days of
operation.
[0205] Catholyte pH: The catholyte pH change over the continuous
operation period, which stabilized at about 7.6 after 2 days, and
then operated in the 7.6 to 7.7 pH range until shutdown at about 20
days. The feed rate was not changed during the run, but could have
been increased or decreased to maintain a constant pH operation in
an optimum range.
Example 9
[0206] The same electrochemical cell as used in examples 1, 2, 3, 8
and 9 was assembled for some further test runs. The only difference
was that a previously used electroless indium on tin on copper mesh
cathode operated during the runs was rinsed and was then
electroplated with an additional indium surface coating layer using
an indium sulfamate electroplating solution (Indium Corporation).
The estimated applied indium coating thickness on the cathode was
about 1 micron. Experiments conducted with the electroplated
cathode provided formate Faradaic yield efficiencies of 60-65% with
cell operating at 10 to 11 amperes, a current density of 90-100
ma/cm.sup.2. The anolyte solution was 1 M sulfuric acid, and the
catholyte solution was a 1.0 M KHCO.sub.3 solution. Cell runs were
conducted in multiple 3 hour batch runs, using a catholyte
recirculation flowrate of 3 liters/min with carbon dioxide bubbled
into the catholyte disengager.
Example 10
[0207] The same cell as in Example 9 with the same indium
electroplated cathode (previously used in several cell runs) was
then used in an electrochemical system to demonstrate the reduction
of carbon dioxide at the cathode to produce an alkali metal formate
and co-producing chlorine at the anode from an alkali metal
halide.
[0208] A 300 gm/L solution of sodium chloride was made up from
reagent grade sodium chloride for use as an anolyte. The catholyte
solution was a 0.25 M Na.sub.2CO.sub.3 solution made from reagent
grade potassium bicarbonate. The chlorine evolved from the anolyte
disengager was absorbed in a sodium hydroxide solution containing
80 grams of NaOH in 250 mL of solution volume to produce sodium
hypochlorite. Carbon dioxide was sparged into the catholyte
solution disengager and the catholyte solution recirculation
flowrate was 9 liters/min.
[0209] The electrochemical cell was operated for 2 hours at an
applied current of 12 amperes (110 ma/cm.sup.2 current density).
The cell voltage started at about 5.16 volts and slowly declined to
about 4.15 volts at the end of the run as the catholyte solution
temperature increased from 24.2.degree. C. to about 32.9.degree. C.
The pH of the catholyte increased from a starting pH of about 7.75,
and the catholyte pH was controlled to a maximum pH of about 8.10
by the addition of dilute 10 wt % HCl in 10 mL aliquots. A total of
80 mL of the 10 wt % acid was added to the catholyte during the
run. At the end of the two hour run, the anolyte and catholyte were
drained from the cell and collected for analysis. The sodium
hydroxide solution absorber solution was analyzed for sodium
hypochlorite.
[0210] The anolyte and sodium hypochlorite solutions were analyzed
for chlorine content using a standard iodometric analysis method
using potassium iodide and dilute sulfuric acid and using 0.1 N
sodium thiosulfate for the titration. The final anolyte solution
volume (280 mL) as found to contain 3.19 gm/L chlorine, for a total
of 0.89 gm of chlorine. The NaOH absorber (260 mL final volume)
contained a concentration of about 113.34 gm/L NaOCl, which is
equivalent to 31.74 gm of NaOCl, or equivalent to 30.23 gm of
chlorine. Thus, the total amount of chlorine collected from the
cell anolyte and sodium hypochlorite absorber was determined to be
31.12 gm. The calculated theoretical amount of chlorine was
determined to be 31.74 gm, so the calculated anolyte Faradaic
efficiency of NaCl to chlorine was 98.0%.
[0211] The catholyte formate solution concentration was analyzed by
ion chromatography, and was found to contain 2,221 ppm of formate,
for a total of 2.24 gm as the formate ion. The calculated
theoretical as formate ion was 20.61 gm, for a calculated formate
Faradaic yield of 10.87%.
Example 11
[0212] The same cell as in example 10 was used with the same
cathode and anode (previously used in several cell runs) was then
used in an electrochemical system to demonstrate the reduction of
carbon dioxide at the cathode to produce an alkali metal formate
and co-producing chlorine at the anode from a hydrogen halide.
[0213] A 10 wt % solution of hydrochloric acid was made up from
reagent grade 37 wt % hydrochloric acid for use as an anolyte. The
catholyte solution was a 1.0 M NaHCO.sub.3 solution made from
reagent grade potassium bicarbonate. The chlorine evolved from the
anolyte disengager was absorbed in a sodium hydroxide solution
absorber containing 41 grams of NaOH in 210 mL of solution volume
to produce sodium hypochlorite. Carbon dioxide was sparged into the
catholyte solution disengager and the catholyte solution
recirculation flowrate was 9 liters/min.
[0214] The electrochemical cell was operated for 2 hours at an
applied current of 12 amperes (110 ma/cm.sup.2 current density).
The cell voltage started at about 3.38 volts and slowly increased
to about 3.53 volts at the end of the run as the catholyte solution
temperature increased from 25.9.degree. C. to about 30.2.degree. C.
The pH of the catholyte increased from a starting pH of about 7.82,
and the catholyte pH slowly increased to about a pH of 8.00 after
30 minutes, and then slowly declined to a pH of 7.80. At the end of
the two hour run, the anolyte and catholyte were drained from the
cell and collected for analysis. The sodium hydroxide solution
absorber solution was analyzed for sodium hypochlorite.
[0215] The final anolyte solution volume (430 mL) as found to
contain 3.01 gm/L chlorine, for a total of 1.30 gm of chlorine. The
NaOH absorber (220 mL final volume) contained a concentration of
about 130.27 gm/L NaOCl, which is equivalent to 28.66 gm of NaOCl,
or equivalent to 27.30 gm of chlorine. Thus, the total amount of
chlorine collected from the cell anolyte and sodium hypochlorite
absorber was determined to be 28.60 gm. The calculated theoretical
amount of chlorine was determined to be 31.74 gm, so the calculated
anolyte Faradaic efficiency of NaCl to chlorine was 90.1%.
[0216] The final catholyte formate solution concentration was
analyzed by ion chromatography, and was found to contain 4,811 ppm
formate, for a total of 3.71 gm present as the formate ion. The
calculated theoretical as formate ion was 20.61 gm, for a
calculated formate Faradaic yield of 18.0%.
[0217] The use of a higher HCl concentration would improve the
yield of HCl to chlorine. The final HCl concentration determined by
acid-base titration was found to be 34.9 gm/L, which is about 3.5
wt % as HCl. In a typical cell operation, the concentration would
be kept at a constant HCl concentration. The formate yield was
lower than expected, and may have been due to some cathode coating
degradation from the previous runs or during storage between
runs.
Thermal Conversion of Alkali Metal Formate to Oxalate
Experiments
[0218] Experiments were conducted to determine some process
conditions in the thermal conversion of alkali metal formate.
Temperature, calcination time, and the addition of various
catalysts that may improve the yields to oxalate were evaluated.
Carbonate was determined by a standard two step titration method
using standardized 0.1 N HCl as the titrant and phenolphthalein and
bromocresol green as the pH indicators.
Example 12
[0219] Table 1 shows the results of a set of experiments that were
conducted in a thermal furnace using a nitrogen atmosphere.
Experiments were conducted to evaluate the conditions and yields in
the thermal conversion of alkali metal formate. Temperature was
varied as well as calcination time, and the use of various
catalysts were evaluated. These samples were prepared using reagent
grade sodium formate crystal and the addition of reagent grade
potassium hydroxide pellets. The chemical reagents were mixed
together, and placed in a 100 mL nickel crucible. The crucible was
calcined at the times and temperatures as given in Table 1. At
420.degree. C., for time periods of 0.5 to 1.0 hrs, the percent
yield of the potassium formate to potassium oxalate using the
potassium hydroxide catalyst ranged from 73.71% to 78.53%. The
oxalate content was analyzed by both permanganate titration and by
Ion chromatography. At 440.degree. C., the conversion yield to
oxalate was about 77%.
TABLE-US-00001 TABLE 1 Mass of Percent Mass of Potassium Mass Yield
Potassium Hydroxide Percent Mass Potassium Calcination Formate
Catalyst of KOH Loss Oxalate Temperature .degree. C. Time (hr) (gm)
(gm) (%) (grams) (%) 420 0.5 4.0888 0 0.0000 0.1838 7.62 420 0.5
4.1784 0.2244 5.3705 0.2115 76.11 420 0.5 4.0156 0.3348 8.3375
0.1742 73.95 420 0.75 4.0267 0.3246 8.0612 0.2397 73.71 420 1.0
4.1087 0.2268 5.5200 0.2121 78.53 440 0.5 4.2935 0.3323 7.7396
0.2482 77.17 440 1.0 4.0391 0.2008 4.9714 0.2329 77.55
Example 13
[0220] Table 2 shows the results of the same procedure as in
Example 12, except that potassium bicarbonate was added to
potassium formate as a catalyst. The calcination temperature was
420.degree. C. for 30 minutes in a nitrogen atmosphere in the
thermal oven.
TABLE-US-00002 TABLE 2 Sample Catalyst Wt % % Oxalate 1 10%
KHCO.sub.3 11.38 1 5% KHCO.sub.3 14.44
Example 14
[0221] Table 3 shows the results of the same procedure as in
Example 12, KOH was added to potassium formate as a catalyst. The
calcination temperature was 440.degree. C. for 30 minutes in a
nitrogen atmosphere in the thermal oven. Table 4 shows the results
using no KOH catalyst.
TABLE-US-00003 TABLE 3 Wt % Potassium Potassium Sample KOH Oxalate
Carbonate # Catalyst Wt % Wt % 1 2.0 80.4 13.0 2 2.0 72.8 22.6 3
2.0 71.7 20.7
TABLE-US-00004 TABLE 4 Wt % Potassium Potassium Sample KOH Oxalate
Carbonate # Catalyst Wt % Wt % 1 0 14.3 23.8 2 0 43.9 51.0
Example 15
[0222] Table 5 shows the results of the same procedure as in
Example 12, KOH was added to potassium formate as a catalyst. The
calcination temperature was 480.degree. C. for 30 minutes in a
nitrogen atmosphere in the thermal oven. Table 6 shows additional
results using a KOH catalyst.
TABLE-US-00005 TABLE 5 Wt % Potassium Potassium Sample KOH Oxalate
Carbonate # Catalyst Wt % Wt % 1 2.0 75.9 21.6 2 2.0 75.7 21.7 3
2.0 74.6 21.5
TABLE-US-00006 TABLE 6 Wt % Potassium Potassium Sample KOH Oxalate
Carbonate # Catalyst Wt % Wt % 1 2.0 73.3 23.6 2 2.0 72.7 24.1 3
2.0 71.2 24.3
Example 16
[0223] Table 7 shows the results of the same procedure as in
Example 12, magnesium oxide powder was added to potassium formate
as a catalyst. The calcination temperature was 420.degree. C. in a
nitrogen atmosphere in the thermal oven.
TABLE-US-00007 TABLE 7 MgO Potassium Calcination Potassium Sample
Catalyst Formate MgO Time in Oxalate # (gm) (gm) Wt % Hrs Wt % 1
0.7567 4.2279 17.9 0.75 19.9 2 0.3603 3.7827 9.5 1.0 54.3 3 0.5644
3.9544 14.3 1.5 48.3
Example 17
[0224] Table 8 shows the results of the same procedure as in
Example 12, sodium borohydride (NaBH.sub.4) powder was added to
potassium formate as a catalyst. The calcination temperature was
440.degree. C. in a nitrogen atmosphere in the thermal oven. Table
9 shows the results using NaBH.sub.4 and KOH as co-catalysts at the
same temperature.
TABLE-US-00008 TABLE 8 NaBH.sub.4 Calcination Potassium Potassium
Sample Catalyst Time in Oxalate Carbonate # wt % min Wt % Wt % 1
2.47 3.5 66.2 11.0 2 2.77 2.66 75.6 11.2
TABLE-US-00009 TABLE 9 Potassium Potassium Sample Calcination
NaBH.sub.4 KOH Oxalate Carbonate # Time wt % wt % wt % wt % 1 5 min
25 sec 2 2 74.2 8.5 2 3 min 2.5 2.5 66.5 10.2 3 2 min 30 sec 2.5
2.5 81.3 10.7 4 3 min 10 sec 2.5 2.5 76.8 9.5 5 3 min 2.77 0 75.6
11.2 6 2 min 30 sec 2.5 3.0 81.3 11.1 7 2 min 30 sec 2.5 2.5 80.5
11.8
Example 18
[0225] Table 10 shows the results of the same procedure as in
Example 12, except that sodium hydride (NaH) powder was added to
sodium formate as a catalyst. The calcination temperature was
440.degree. C. in a nitrogen atmosphere in the thermal oven.
[0226] Table 11 shows the results using NaH added as a catalyst to
potassium formate at various time and temperatures.
TABLE-US-00010 TABLE 10 Calcination Calcination Potassium Potassium
Sample Time NaH Temp Oxalate Carbonate # (min) wt % .degree. C. wt
% wt % 1 3.75 2.86 440 85.49 7.36 2 3.75 2.86 440 84.48 7.14 3 3.75
2.59 440 89.12 5.32 4 4.25 2.96 430 86.99 7.15 5 3.25 2.19 430
89.46 5.14
TABLE-US-00011 TABLE 11 Calcination Potassium Potassium Sample
Calcination Temp NaH Oxalate Carbonate # Time .degree. C. wt % wt %
wt % 1 19.66 min 440 2.0 55.18 15.69 2 30 min 400 2.5 47.68
22.96
Alternative Embodiments
[0227] Alternative anolyte solutions may be employed to generate
chemical products such as bromine at the anode region of
electrochemical cell 110, which may be used to brominate organics
as intermediates in making ethanol, ethylene, and other chemicals
based on bromine chemistry. The oxidation of sulfur compounds in
the anolyte region, such as sodium sulfide or SO.sub.2, or the
direct or indirect oxidation of organics, and conducting the
partial oxidation of organics, such as methanol to formaldehyde,
are also contemplated.
[0228] Various alkali metal hydroxides may be employed at the
electrochemical cell 110 and/or a thermal reactor 120, 130. For
example, hydroxides of lithium, sodium, potassium, and rubidium,
and cesium may be used. Further, alkaline earth metal hydroxides
may also be used.
[0229] Thermal reactors 120, 130 may perform thermal intermolecular
condensation reactions using alkali metal hydroxides. Such
condensation reactions may include chemical reactions in which two
molecules or moieties (functional groups) combine to form one
single molecule, together with the loss of a small molecule. When
two separate molecules may be reacted, the condensation may be
termed intermolecular. Since the reaction occurs at elevated
temperatures, the reactions may be characterized as "thermal
intermolecular condensation step". If water may be lost, the
reactions may be characterized as "thermal intermolecular
dehydration step". These reactions may occur in an aqueous solution
phase, such as with the reaction of CO with the alkali metal
hydroxide, or as a melt of the alkali metal carboxylic acid and the
alkali metal hydroxide in the thermal reaction.
[0230] Thermal reactors 120, 130 may operate at about 40 to
500.degree. C., and more preferably at about 50-450.degree. C. The
operating temperatures may depend on the decomposition temperatures
of the carboxylic acid and the optimum temperature to get the
highest yields of the carboxylic product. A residence time of the
reaction at optimum reaction temperatures may range from 5 seconds
to hours, and the equipment chosen to conduct the reaction may be
designed to provide the rate of heating and cooling required to
obtain optimal conversion yields. This may include the use of cold
rotating metal that may rapidly chill the hot thermal product after
the thermal reaction period may be completed.
[0231] Thermal reactors 120, 130 may operate in air or an enriched
oxygen atmospheres, as well as inert gas atmospheres, such as
nitrogen, argon, and helium. Carbon dioxide and hydrogen
atmospheres may also be employed to obtain the highest yield in the
reaction, as well as partial CO atmospheres. Thermal reactors 120,
130 may be operated under a full or partial vacuum.
[0232] The use of CO from other sources, such as from the
production of syngas from methane or natural gas reforming may be
employed. CO may also come from other sources, such as process
waste streams, where may be it separated from carbon dioxide.
[0233] Alkali metal hydroxide concentration ranges may be 2% to
99%, more preferably 5 to 98% by weight. The alkali hydroxide may
run in molar excess of the alkali metal carboxylic acid being
thermally processed in the initial reaction mix or in a continuous
process where they may be mixed together. The anticipated molar
ratios of the alkali metal carboxylic acid to alkali metal
hydroxide may range from 0.005 to 100, and more preferably 0.01 to
50. It may be preferable to use the least amount of alkali metal
hydroxide as possible for the reaction to reduce the consumption of
the hydroxide in the process.
[0234] The process operating equipment that may be employed for
thermal reactors 120, 130 may include various commercially
available types. For the CO reaction with alkali metal hydroxide,
the equipment that may be used may be batch operation equipment,
where gas may be injected into a solution mix of the alkali
hydroxide. This may also be done in a continuous manner where there
may be a feed input of fresh alkali metal hydroxide into a
continuous stirred tank reactor (CSTR) with a CO feed into the
solution through a gas diffuser into the solution. Alternatively,
counter-current packed towers may be used where CO may be injected
into the tower counter-current to the flow of alkali metal
hydroxide.
[0235] For a alkali metal oxalate operation, thermal reactors 120,
130 may include equipment such as rotary kilns, and single pass
plug flow reactors that may be used if the process required the
thermal processing of a mixture of alkali metal formate and alkali
hydroxide as a solid or hot melt mix. Preferably, the equipment
would be operated in a continuous fashion, providing the required
residence time for the reaction to go to completion at the selected
temperatures, which may be followed by a cooling section.
[0236] A thermal intermolecular condensation process may also be
conducted to produce higher carbon content carboxylic acids as well
as converting the carboxylic acids into esters, amides, acid
chlorides, and alcohols. In addition, the carboxylic acid products
may be converted to the corresponding halide compounds using
bromine, chlorine, and iodine.
[0237] Catalysts for the thermal conversion of the alkali metal
formate may consist of various bases, including alkali metal
hydroxide as well as other compounds that are bases. In addition,
alkali metal and other hydrides may be used, since they also act as
bases. Any other suitable catalysts that may be compatible with the
formates in the calcination and provide high conversion yields are
suitable for the process.
[0238] It is contemplated that method for production of
dicarboxylic acid, such as oxalic acid, may include various steps
performed by systems 100, 105, 200 and 205. It may be 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 may be merely explanatory.
* * * * *