U.S. patent application number 13/021355 was filed with the patent office on 2011-06-23 for acid separation by acid retardation on an ion exchange resin in an electrochemical system.
Invention is credited to Ryan J. Gilliam, Nigel Antony Knott, Michael Kostowskyj.
Application Number | 20110147227 13/021355 |
Document ID | / |
Family ID | 44149573 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110147227 |
Kind Code |
A1 |
Gilliam; Ryan J. ; et
al. |
June 23, 2011 |
ACID SEPARATION BY ACID RETARDATION ON AN ION EXCHANGE RESIN IN AN
ELECTROCHEMICAL SYSTEM
Abstract
A method and system of separating an acid from an acid-salt
solution produced in an electrochemical system using an ion
exchange resin bed, by processing the acid-salt solution through
the ion exchange resin bed such that the acid is retarded at the
bottom of the bed and a de-acidified salt solution is recovered
from the top of the bed. After removing the salt solution from the
bed, the acid is recovered by back-flushing the resin bed with
water.
Inventors: |
Gilliam; Ryan J.; (San Jose,
CA) ; Knott; Nigel Antony; (Los Gatos, CA) ;
Kostowskyj; Michael; (Los Gatos, CA) |
Family ID: |
44149573 |
Appl. No.: |
13/021355 |
Filed: |
February 4, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12952665 |
Nov 23, 2010 |
|
|
|
13021355 |
|
|
|
|
12617005 |
Nov 12, 2009 |
|
|
|
12952665 |
|
|
|
|
12541055 |
Aug 13, 2009 |
|
|
|
12617005 |
|
|
|
|
12503557 |
Jul 15, 2009 |
|
|
|
12541055 |
|
|
|
|
61301878 |
Feb 5, 2010 |
|
|
|
Current U.S.
Class: |
205/349 ;
204/234; 204/242; 205/334; 205/464; 205/480; 205/508 |
Current CPC
Class: |
C25B 1/14 20130101; Y02E
60/36 20130101; Y02E 60/366 20130101; C02F 2201/46115 20130101;
C02F 2001/46166 20130101; C25B 1/26 20130101; C25B 1/04 20130101;
C02F 1/42 20130101; C01B 32/60 20170801; C02F 2303/16 20130101;
C25B 1/02 20130101; C02F 2201/4619 20130101; C25B 1/00 20130101;
C25B 1/16 20130101 |
Class at
Publication: |
205/349 ;
205/334; 205/464; 205/508; 205/480; 204/242; 204/234 |
International
Class: |
C25B 15/08 20060101
C25B015/08; C25B 1/00 20060101 C25B001/00; C25B 9/00 20060101
C25B009/00; C25B 15/00 20060101 C25B015/00 |
Claims
1. A method comprising: producing an acid in an anode electrolyte
in contact with an anode in an anode compartment of an
electrochemical system; and separating the acid from the anode
electrolyte by retarding the acid on an ion exchange resin to
produce a de-acidified anode electrolyte.
2. The method of claim 1, further comprising returning the
de-acidified anode electrolyte to the anode compartment.
3-4. (canceled)
5. The method of claim 1, comprising producing the acid in the
anode electrolyte by reducing hydrogen gas to protons at the anode
and migrating the protons into the anode electrolyte by applying a
voltage across the anode and a cathode in contact with a cathode
electrolyte in the electrochemical system.
6. The method of claim 5, comprising preventing formation of a gas
at the anode.
7. (canceled)
8. The method of claim 1, further comprising reducing water to
hydroxide ions and hydrogen gas at the cathode and producing a
hydroxide in the cathode electrolyte by migrating the hydroxide
ions into the cathode electrolyte.
9. The method of claim 8, wherein the anode electrolyte, the
cathode electrolyte, or both comprise salt solution and the salt
solution comprises sodium chloride or sodium sulfate and wherein
the anode electrolyte comprises hydrochloric acid or sulfuric acid
and the cathode electrolyte comprises sodium hydroxide.
10. (canceled)
11. The method of claim 9, further comprising contacting the
cathode electrolyte with carbon dioxide and producing carbonic acid
and/or bicarbonate ions and/or carbonate ions in the cathode
electrolyte.
12-13. (canceled)
14. The method of claim 1, comprising separating the acid from the
anode electrolyte by: feeding the anode electrolyte comprising the
acid into a lower portion of an ion exchange resin bed comprising a
resin selected to retard the acid on the resin without retarding
the salt; and removing the anode electrolyte comprising the salt
from the upper portion of the ion exchange resin bed.
15. The method of claim 14, further comprising eluting the acid
from the ion exchange resin bed by back-flushing the ion exchange
resin to produce an eluted acid.
16. The method of claim 15, wherein the ion exchange resin
comprises a strong base anion exchange resin comprising particle
sizes in the range of 525-625 microns.
17-18. (canceled)
19. The method of claim 16, further comprising dissolving a mineral
with the eluted acid in a mineral dissolution system to produce a
mineral solution comprising divalent cations and un-reacted acid
and processing the mineral solution through a nano-filtration
system to produce an acid-salt solution comprising the un-reacted
acid and the salt solution in a first solution stream, and a
divalent cation solution comprising calcium and/or magnesium ions
in a second solution stream.
20. (canceled)
21. The method of claim 19, further comprising processing the first
solution stream through a reverse osmosis system to separate the
salt solution from the un-reacted acid and produce a concentrated
salt solution and a dilute acid.
22. (canceled)
23. A system comprising: an electrochemical system comprising an
anode electrolyte in contact with an anode in an anode compartment
and configured to produce an acid in the anode electrolyte; and an
acid retardation system comprising an ion exchange resin bed
operatively connected to the anode compartment and configured to
receive the anode electrolyte and retard the acid on an ion
exchange resin and produce a de-acidified anode electrolyte.
24. The system of claim 23, wherein the acid retardation system is
configured to retard the acid in a lower portion of the ion resin
bed and produce the de-acidified anolyte in an upper portion of the
ion exchange resin bed.
25. The system of claim 24, wherein the ion exchange resin bed
comprises a short bed comprising a fine mesh resin.
26. (canceled)
27. The system of claim 24, wherein the acid retardation system is
configured to extract and return the de-acidified anode electrolyte
to the anode electrolyte compartment.
28-29. (canceled)
30. The system of claim 23, further comprising a mineral
dissolution system operatively connected to the acid retardation
system, wherein the mineral dissolution system is configured to
dissolve a mineral with the eluted acid to produce a mineral
solution comprising divalent cations.
31. (canceled)
32. The system of claim 30, wherein the electrochemical system
comprises a cathode in electrical communication with the anode and
in contact with a cathode electrolyte, wherein the electrochemical
system is configured to produce the acid in the anode electrolyte
by reducing hydrogen gas at the anode to protons and migrating the
protons into the anode electrolyte, on application of a voltage
across the anode and cathode.
33. The system of claim 32, wherein the electrochemical system
comprises a salt solution in the anode electrolyte and wherein the
cathode is configured to produce a hydroxide in the cathode
electrolyte by reducing water at the cathode to hydroxide ions and
hydrogen gas, migrate cations from the anode electrolyte to the
cathode electrolyte across a cation exchange membrane separating
anode electrolyte and the cathode electrolyte, and migrate the
hydroxide ions into the cathode electrolyte.
34. (canceled)
35. The system of claim 23, further comprising a carbonate
precipitation system operatively connected to the cathode
compartment, and wherein the carbonate precipitation system is
configured to mix the divalent cation solution with cathode
electrolyte and carbon dioxide, and sequester the carbon dioxide as
a divalent cation carbonate and/or bicarbonate comprising calcium
and/or magnesium.
36-37. (canceled)
Description
CROSS-REFERENCE
[0001] This application claims priority to and the benefits of U.S.
Provisional Patent Application No. 61/301,878 filed Feb. 5, 2010
herein incorporated by reference.
[0002] This application also is a continuation-in-part of, and
claims priority to, commonly assigned U.S. patent application Ser.
No. 12/952,665, filed Nov. 23, 2010, which is a
continuation-in-part of U.S. patent application Ser. No. 12/617,005
filed Nov. 11, 2009, which is a continuation-in-part of U.S. patent
application Ser. No. 12/541,055 filed Aug. 13, 2009, which is a
continuation-in-part of U.S. patent application Ser. No. 12/503,557
filed Jul. 16, 2009, all of which are herein incorporated by
reference in their entirety
BACKGROUND OF THE INVENTION
[0003] In producing a hydroxide solution by an electrochemical
process, an acid and a dilute salt solution are produced in some
processes. In some cases, the acid and dilute salt solutions are
produced in the same compartment of the electrochemical system,
i.e., in the anode electrolyte, and the acid and the salt are
mixed. As the salt without the acid can be recycled to produce more
hydroxide ions in the cathode electrolyte and as the acid without
the salt can be used elsewhere, it is desirable to separate the
salt and acid.
SUMMARY OF THE INVENTION
[0004] This invention pertains to a method and system of separating
an acid from an acid-salt solution produced in an electrochemical
system by processing the acid-salt solution through an ion exchange
resin bed to retard the acid at the bottom of the bed, and
accumulate the de-acidified salt solution at the top of the bed. In
some embodiments, the de-acidified salt solution is extracted from
the top of the bed, and the acid is recovered by back-flushing the
resin bed from the top of the bed with water after the salt
solution is extracted.
[0005] The methods, compositions, and apparatus of the invention
may be used in any suitable electrochemical system in which an acid
is produced. In some embodiments of the method, the acid-salt
solution is produced in the anode electrolyte of the system by
adding a concentrated salt solution e.g., a concentrated sodium
chloride solution, or a sodium sulfate solution, to the anode
electrolyte; reducing hydrogen gas to protons at the anode and
migrating the protons into the salt solution/anode electrolyte by
applying a voltage across the anode and a cathode in contact with a
cathode electrolyte; and migrating cations e.g., Na+ ions from the
salt solution/anode electrolyte into the cathode electrolyte. It
will be appreciated that while this embodiment is described and is
illustrative, any embodiment in which the methods, compositions,
and apparatus of the invention may be used is encompassed by the
invention.
[0006] In some embodiments of the method, the hydroxide is produced
in the cathode electrolyte by reducing water to hydroxide ions and
hydrogen gas at the cathode; migrating the hydroxide ions into the
cathode electrolyte; and migrating cations e.g., Na+ ions from the
salt solution to the cathode electrolyte across a cation exchange
membrane separating the salt solution from the cathode electrolyte.
It will be appreciated that other reactions might occur at the
cathode, for example the well-known reactions of the oxygen
depolarized electrode, so long as an acid is produced in some part
of the cell (e.g., at the anode).
[0007] In some embodiments of the method, the salt solution may
comprise sodium chloride or sodium sulfate; the acid may comprise
hydrochloric acid or sulfuric acid; and the hydroxide may comprise
sodium hydroxide.
[0008] In some embodiments of the method, hydrogen gas produced at
the cathode is directed to the anode for oxidation to protons that
produce the acid in the anode electrolyte.
[0009] In some embodiments of the method, the hydroxide produced in
the cathode electrolyte is used to sequester carbon dioxide as a
bicarbonate and/or carbonate; in certain embodiments this is done
by adding carbon dioxide to the cathode electrolyte to produce
bicarbonate ions or carbonate ions in the cathode electrolyte, and,
in some cases, mixing the cathode electrolyte with a divalent
cation solution comprising Ca++ ions or Mg++ ions to produce the
divalent cation carbonate or bicarbonate (e.g., calcium and/or
magnesium carbonate).
[0010] In some embodiments, the sequestered carbon dioxide is taken
from a waste gas emitted from an industrial facility. In certain
embodiments the industrial facility is a fossil fuelled power
generating plant, such as a coal-fired plant or natural gas-fired
plant, a cement production plant, an ore smelter or a carbon
fermentation plant.
[0011] In some embodiments of the method, the ion exchange resin
comprises a strong base anion exchange resin comprising particle
sizes in the range of 525-625 microns.
[0012] In some embodiments of the method, the recovered acid is
used to dissolve a mineral comprising divalent cations e.g., Ca++
ions or Mg++ ions to produce a divalent cation solution for use in
sequestering the carbon dioxide as a divalent carbonate and/or
bicarbonate.
[0013] In some embodiments of the method, the recovered salt
solution is cleaned in a nano-filtration system and concentrated in
a reverse osmosis system and reused as the anode electrolyte.
[0014] In some embodiments, the system or method comprises an
electrochemical system comprising an anode electrolyte in contact
with an anode in an anode compartment, and is configured to produce
an acid in the anode electrolyte; and an acid retardation system
comprising an ion exchange resin bed operatively connected to the
anode compartment and is configured to receive the anode
electrolyte and retard the acid on an ion exchange resin and
produce a de-acidified anode electrolyte.
[0015] In some embodiments, the system or method is configured to
retard the acid in the lower portion of the ion resin bed and
produce the de-acidified anode electrolyte in the upper portion of
the bed. In some embodiments, the ion exchange resin bed comprises
a strong base anion exchange resin comprising particles ranging in
size from 525 to 625 microns and is specially designed to retard
the acid without retarding the salt. In some embodiments, the acid
retardation system is configured to return the de-acidified salt
solution to the anode electrolyte compartment.
[0016] In some embodiments, the system or method comprises an
evaporating system operatively linked to the acid retardation
system and is configured to concentrate and return the recovered
salt solution to the anode electrolyte.
[0017] In some embodiments, the system or method comprises a
mineral dissolution system operatively connected to the acid
retardation system and is configured to dissolve a mineral with the
recovered acid to produce a mineral solution comprising divalent
cations; in some embodiments, the divalent cation solution is used
to sequester carbon dioxide as a divalent carbonate and/or
bicarbonate with the cathode electrolyte.
[0018] In some embodiments of the system or method the acid is
produced in the anode electrolyte by reducing hydrogen gas at the
anode to protons and migrating the protons into the anode
electrolyte; and migrating cations from the anode electrolyte, with
a voltage applied across the anode and cathode.
[0019] In some embodiments, the system or method is configured to
produce a hydroxide in the cathode electrolyte by reducing water at
the cathode to hydroxide ions and hydrogen gas; migrating cations
from the anode electrolyte to the cathode electrolyte across a
cation exchange membrane separating the anode electrolyte and the
cathode electrolyte; and migrating the hydroxide ions into the
cathode electrolyte. In some embodiments, the system or method
includes a hydrogen supply system configured to direct hydrogen gas
produced at the cathode to the anode.
[0020] In some embodiments, the system or method includes a
nano-filtration system configured to clean the salt solution, and a
reverse osmosis system configured to concentrate the recovered salt
solution.
[0021] In some embodiments, the system or method includes a
carbonate precipitation system operatively connected to the cathode
compartment and the nano-filtration system and configured to mix
the divalent cation solution with cathode electrolyte and carbon
dioxide to sequester the carbon dioxide as a divalent cation
carbonate and/or bicarbonate. In some embodiments, the carbon
dioxide gas is mixed with the cathode electrolyte to produce
bicarbonate ions or carbonate ions in the cathode electrolyte, and
this cathode electrolyte is used to sequester the carbon dioxide as
a divalent carbonate or biocarbonate.
[0022] Any suitable ion exchange medium may be used, such as
commercially available resin e.g., from the Dow Chemical Company
under the product name DOWEX*21K XLT.TM.. For example, the resin
may be used in an ion exchange column commercially available from
the Colgon Carbon Corporation in the USA or from Eco-tech Limited
in Canada.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The following drawings illustrate by way of examples and not
by limitation embodiments of the present system and method.
[0024] FIGS. 1 and 2 illustrate embodiments of an electrochemical
system configured to produce an acid-salt solution in an
electrolyte in the system and a hydroxide in the cathode
electrolyte, in accordance with the present system.
[0025] FIGS. 3 and 4 illustrate embodiment of a system configured
to separate the acid and salt from the acid-salt solution and
re-use the salt and acid, in accordance with the present
system.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The invention provides methods, compositions, and apparatus
directed at separating an acid and a salt solution from an
acid-salt solution produced in an electrochemical system. In
certain embodiments, the acid-salt solution is produced in the
anode electrolyte; for example, the anode reaction may produce
protons from the oxidation of hydrogen. It will be understood by
those of skill in the art that, while the latter embodiment is used
for illustrative purposes, many anodic reactions may produce an
acid in a salt solution and the methods, compositions, and
apparatus are directed to all such reactions for which they are
suitable.
[0027] With reference to the illustrative embodiments as
exemplified, but not limited, by FIGS. 1-4, in some embodiments the
system and method pertains to separating an acid (e.g., 306) and a
salt solution (e.g., 304) from an acid-salt solution (e.g., 102)
produced in an electrolyte in an electrochemical system (e.g, 100,
300, 400). In some embodiments, the acid-salt solution (e.g., 102)
is produced in the anode electrolyte (e.g., 104) by charging the
anode electrolyte with a concentrated salt solution (e.g., 126);
oxidizing hydrogen gas (e.g., 120) at the anode to form protons and
migrating the protons into the anode electrolyte in contact with
the anode (e.g., 106A, 106B) by applying a voltage (e.g., 118)
across the anode and cathode; and migrating cations from the anode
electrolyte (e.g., 104).
[0028] In some embodiments and with reference to FIG. 3 for
illustrative purposes, as the acid is produced in the anode
electrolyte (e.g., 104), it is continually withdrawn (e.g., 102)
from the system by withdrawing some of the anode electrolyte. Since
the anode electrolyte is continuously replenished with a
concentrated salt solution (e.g., 126), and since in some
embodiments not all the cations from the salt solution will migrate
from the anode electrolyte to the cathode electrolyte (e.g., 110),
the withdrawn anode electrolyte/salt solution may contain a
solution of the acid and salt.
[0029] However, as the salt solution without the acid can be reused
e.g., in the anode electrolyte and as the acid without the salt can
be used elsewhere for any purpose for which it is suited, e.g., to
dissolve a mineral in mineral dissolution system, such as the one
illustrated in FIG. 4, it is desired to separate the acid and salt
solution from the withdrawn acid-salt solution.
[0030] In some embodiments, as is shown in FIG. 3 for illustrative
purposes, the salt/acid separation is achieved by withdrawing a
portion of the anode electrolyte and passing the withdrawn anode
electrolyte through in an acid retardation system (e.g., 302A,
302B) operatively connected to the anode compartment (e.g., 108).
In the acid retardation system (e.g., 302A, 302B) the withdrawn
anode electrolyte is flowed upwards through an ion exchange resin
bed configured to retard the acid in the lower portion of the bed
(e.g., 302B), and produce a de-acidified anode electrolyte/salt
solution in the upper portion of the bed (e.g., 302A).
[0031] In some embodiments and with reference to FIG. 3 for
illustrative purposes, the de-acidified anode electrolyte (e.g.,
304) is extracted from the top of bed (e.g., 302A) and is reused as
anode electrolyte (e.g., 104) in the electrochemical system (e.g.,
300). In some embodiments, after the salt solution is removed from
the upper portion of the ions resin bed (e.g., 302A), the acid is
recovered by back-flushing the lower portion of the ion exchange
resin bed (e.g., 302B) with water (e.g., 310).
[0032] The systems and methods of the invention are suitable for
electrochemical systems in which an acid/salt solution is produced
in any compartment (e.g., the anode compartment) and where it is
desired to separate the acid and the salt; thus, the half-reaction
at the cathode, which generally does not produce an acid, may be
any half-reaction that is coupled with a half-reaction at the anode
that produces acid at the anode. In some embodiments of the system
and method and with reference to FIG. 1 for illustrative purposes,
as the acid is produced in the anode electrolyte (e.g., 104), a
hydroxide solution is concurrently produced in the cathode
electrolyte (e.g., 110) by reducing water at the cathode (e.g.,
114) to hydroxide ions and hydrogen gas (e.g., 124A); migrating the
hydroxide ions into the cathode electrolyte (e.g., 110); and
migrating cations from the salt solution (e.g., 104) into the
cathode electrolyte (e.g., 110).
[0033] In some embodiments, the hydrogen gas produced at the
cathode (e.g., 124A) is directed to the anode (e.g., 106A, 106B)
for oxidation to protons, and the protons are migrated into the
anode electrolyte to produce the acid in the anode electrolyte. In
some embodiments, the voltage (e.g., 118) across the anode and
cathode is regulated to prevent the formation a gas e.g., oxygen or
chlorine at the anode.
[0034] In some embodiments and with reference to FIGS. 1 and 3 for
illustrative purposes, carbon dioxide is added to the cathode
electrolyte (e.g., 110A, 110B) to form carbonic acid and/or
carbonate ions and/or bicarbonate ions in the cathode electrolyte
(e.g., 110), depending on the pH of the cathode electrolyte. Thus
in some embodiments wherein Na+ ions are migrated from the anode
electrolyte (e.g., 104) into the cathode electrolyte (e.g., 110),
the cathode electrolyte (e.g., 110) may comprise sodium hydroxide
and/or sodium carbonate and/or sodium bicarbonate.
[0035] In some embodiments and with reference to FIGS. 1 and 4 for
illustrative purposes, the cathode electrolyte (e.g., 110)
comprising bicarbonate ions and/or carbonate ions is reacted with a
divalent cation solution (e.g., 410) comprising e.g., Ca++ ions
and/or Mg++ ions in a carbonate precipitating system (e.g., 412) to
precipitate a divalent cation carbonate and/or bicarbonate and
thereby sequester the carbon dioxide in the precipitate. In some
embodiments the acid solution recovered from the anode electrolyte
(e.g., 306, 418) is utilized to dissolve a mineral, which may be
any suitable mineral, e.g. serpentine or olivine, that can be
contacted with the acid of the system to release divalent cations
and/or other useful species, e.g., in a mineral dissolution system
(e.g., 402) to obtain a portion or all of the divalent cation
solution used to produce the divalent carbonates and/ or
bicarbonates.
[0036] As can be appreciated by those of ordinary skill in the art
and with reference to FIGS. 1-4 for illustrative purposes, although
the present system and method are described herein with reference
to producing the acid-salt solution (e.g., 102) in the anode
electrolyte (e.g., 104) in contact with the anode (e.g., 106), in
some embodiments the system can be configured to produce the
acid/salt in another electrolyte that is not in direct contact with
the anode.
[0037] This can be accomplished, e.g., by separating the anode
electrolyte from a salt solution located in other electrolyte by a
cation exchange membrane (e.g., 127) such that protons from the
anode electrolyte will migrate into the salt solution (e.g., 106)
from the anode electrolyte through the cation exchange membrane
(e.g., 127).
[0038] In some embodiments, the salt solution can be separated from
the anode electrolyte by an anion exchange membrane such that
anions from the salt solution will migrate into the anode
electrolyte through the anion exchange membrane to produce the acid
in the anode electrolyte. In some embodiments of the system as is
illustrated in FIG. 1, since the cation exchange membrane (e.g.,
127) will prevent the migration of anions (e.g., e.g., Cl-- ions),
from the salt solution to the anode (e.g., 106), therefore the
acid/salt solution will not form in direct contact with the anode
(e.g., 106). However, as will be appreciated, while this feature
may be present in some embodiments, it is optional, depending on
the nature of the anode, the anions, and other factors that will be
apparent to those of skill in the art.
[0039] To the extent that one of ordinary skill in the art can
modify the present system based on the present disclosure, to
produce the acid/salt solution in any compartment of the
electrochemical system, such modifications are within the scope of
the present system and method as defined by the appended
claims.
[0040] Also, as can be appreciated by those of ordinary skill in
the art, although the present system and method are described
herein with reference to producing a salt/acid solution (e.g., 102)
comprising hydrochloric acid and sodium chloride, since the system
can be modified based on the present disclosure to use another salt
e.g., sodium sulfate to produce an salt/acid solution comprising
sulfuric acid and sodium sulfate, such modifications are also
within the scope of the present system and method as defined by the
appended claims. Other salt/acid combinations, such as but not
limited to salts and the corresponding acids formed from alkali
salts, such as where the alkali salt is a salt of the groups 1(IA)
or 2(IIA) of the periodic table. Exemplary electrolytes suitable
for use with the present invention include, but are not limited to,
the following: sodium chloride, potassium chloride, sodium sulfate,
potassium sulfate, calcium sulfate, magnesium sulfate, sodium
nitrate, potassium nitrate, sodium bicarbonate, sodium carbonate,
potassium bicarbonate, or potassium carbonate. Other suitable
electrolyte solutions include sea water and aqueous sea salt
solutions.
[0041] Further, as can be appreciated by those of ordinary skill in
the art, although the present system and method are described
herein with reference to producing a salt/acid solution (e.g., 102)
by oxidizing hydrogen gas (e.g., 120) at the anode to protons and
reducing water at the cathode to hydroxide ions and hydrogen gas,
since the system can be modified based on the present disclosure to
produce the acid/salt solution by another mechanism e.g., by
producing a gas e.g., chlorine gas at the anode and dissolving the
chlorine gas in the anode electrolyte, therefore such modifications
are also within the scope of the present system and method as
defined by the appended claims.
[0042] Also, as can be appreciated by those of ordinary skill in
the art, although the present system and method are described
herein with reference to producing a salt/acid solution (e.g., 102)
in an electrolyte in the system by using one or more cation ion
exchange membranes (e.g., 112, 127) to separate the electrolytes in
the system, and migrating cations from the salt solution (e.g.,
104) to the cathode electrolyte (e.g., 110) through cation exchange
membrane (e.g., 112), the system can be modified based on the
present disclosure to use other separation means such as a
diaphragm. Therefore, to the extent that one of ordinary skill can
modify the present system, based on the present disclosure, to
produce the acid/salt solution in any compartment of an
electrochemical system using any separation means, such
modifications are within the scope of the present system and method
as defined by the appended claims.
[0043] With reference to FIGS. 1-4 for illustrative purposes, in
some embodiments the system (e.g., 100, 200, 300, 400) comprises an
electrochemical system comprising an anode electrolyte (e.g., 104)
in contact with an anode (e.g., 106A, 106B) in an anode compartment
(e.g., 108) and configured to produce an acid-salt solution (e.g.,
102) in the anode electrolyte; and an acid retardation system
(e.g., 302A, 302B) comprising an ion exchange resin bed operatively
connected to the anode compartment (e.g., 108) and configured to
receive the acid-salt solution (e.g., 102) and retard the acid on
an ion exchange resin and produce a de-acidified anode electrolyte
(e.g., 304). In some embodiments as illustrated in FIGS. 3 and 4,
the system is configured to retard the acid in a lower portion of
the ion resin bed (e.g., 302B) and produce the de-acidified anolyte
in an upper portion of the ion exchange resin bed (e.g., 302A).
[0044] In some embodiments, the ion exchange resin bed (e.g., 302A,
302B) comprises a short bed comprising a fine mesh resin. In some
embodiments, the ion exchange resin comprises a strong base anion
exchange resin comprising particle sizes in the range of (e.g.,
525-625) microns and is specially designed to retard the acid
without retarding the salt. For all embodiments, the resin is
commercially available from several suppliers including the Dow
Chemical Company under the product name DOWEX*21K XLT.TM.. In some
embodiments the resin is used in an ion exchange column
commercially available from the Colgon Carbon Corporation in the
USA or from Eco-tech Limited in Canada and can be configured in an
ion retardation system as described in U.S. Pat. No. 4,673,507
herein incorporated by reference.
[0045] In some embodiments of the system as illustrated in FIGS. 3
and 4, the acid retardation system (e.g., 302A, 302B) is configured
to extract and return the de-acidified anode electrolyte (e.g.,
304) to the anode electrolyte compartment (e.g., 108). In some
embodiments also as are illustrated in FIGS. 3 and 4, the system
comprises an evaporating system (e.g., 306) operatively linked to
the acid retardation system (e.g., 302A, 302B) and the anode
compartment (e.g., 108). In some embodiments, the evaporating
system is configured to concentrate the de-acidified anode
electrolyte and return the concentrated de-acidified anode
electrolyte (e.g., 126) to the anode electrolyte compartment. In
some embodiments, the acid retardation system (e.g., 302A, 302B) is
configured to back-flush the acid from the ion resin after the salt
solution is removed, by flushing the ion exchange resin with water
(e.g., 310).
[0046] With reference to FIGS. 3 and 4 for illustrative purposes,
in some embodiments, the system 300, 400 comprises a mineral
dissolution system (e.g., 402) operatively connected to the acid
retardation system (e.g., 302A, 302B) and is configured to dissolve
a mineral with the recovered acid (e.g., 306) to produce a mineral
solution (e.g., 404) comprising divalent cations. In some
embodiments, the mineral dissolution system (e.g., 402) is
operatively connected to the anode compartment (e.g., 108) and is
configured to receive the recovered acid (e.g., 306) from the acid
retardation system and mix this recovered acid with anode
electrolyte comprising the acid/salt solution (e.g., 102) to
dissolve the mineral.
[0047] With reference to FIG. 1 for illustrative purposes, in some
embodiments, the system (e.g., 100) comprises a cathode (e.g., 114)
in electrical contact with the anode (e.g., 106A) which is in
contact with a cathode electrolyte (e.g., 108), and is configured
to produce the acid-salt solution (e.g., 102) in the anode
electrolyte (e.g., 104) by reducing hydrogen gas at the anode to
protons and migrating the protons into the anode electrolyte, on
application of a voltage (e.g., 118) across the anode and
cathode.
[0048] In some embodiments and with reference to FIG. 1 for
illustrative purposes, in the electrochemical system (e.g., 100), a
concentrated salt solution (e.g., 126) is added to the anode
electrolyte and the system is configured to: produce a hydroxide in
the cathode electrolyte (e.g., 110) by reducing water at the
cathode to hydroxide ions and hydrogen gas; migrate cations e.g.,
Na+ ions from the anode electrolyte (e.g., 104) to the cathode
electrolyte (e.g., 110) across a first cation exchange membrane
(e.g., 112) separating the anode electrolyte (e.g., 104) and the
cathode electrolyte (e.g., 110); and migrate the hydroxide ions
into the cathode electrolyte. As can be appreciated by one of
ordinary skill in the art, although a cation exchange membrane
(e.g., 126), as is illustrated in FIG. 1, is configured to separate
the anode from the anode electrolyte (e.g., 108), in some
embodiments the system as illustrated in FIG. 3, will function
without cation exchange membrane (e.g., 126) in which case the salt
solution (e.g., 102) will be produced in the anode electrolyte
(e.g., 104).
[0049] With reference to FIG. 4 for illustrative purposes, in some
embodiments, the system comprises a nano-filtration system (e.g.,
406), operatively connected to the mineral dissolution system
(e.g., 402) and is configured to filter the mineral solution and
produce an acid-salt solution comprising un-reacted acid and the
salt solution in a first solution stream (e.g., 408) and a divalent
cation solution comprising calcium and/or magnesium ions in a
second solution stream (e.g., 410).
[0050] In some embodiments of the system and with reference to
FIGS. 1 and 4 for illustrative purposes, the system includes a
carbonate precipitation system (e.g., 412) operatively connected to
the cathode compartment (e.g., 116) and the nano-filtration system
(e.g., 406). In some embodiments, the carbonate precipitation
system is configured to mix the divalent cation solution (e.g.,
410) with cathode electrolyte (e.g., 110) and carbon dioxide, and
sequester the carbon dioxide as a divalent cation carbonate and/or
bicarbonate comprising calcium and/or magnesium.
[0051] In some embodiments as illustrated in FIG. 4, the system
includes a reverse osmosis system (e.g., 414) operatively connected
to the nano-filtration system (e.g., 406) and the electrochemical
system 100, and is configured to separate a salt solution (e.g.,
416) from the un-reacted acid (e.g., 418). In some embodiments as
illustrated in FIG. 4, the anode compartment (e.g., 108) of the
electrochemical system (e.g., 100) is configured to utilize the
salt solution (e.g., 416) as the anode electrolyte, and the mineral
dissolution system is configured to utilize the dilute acid (e.g.,
418) to dissolve the mineral in the mineral dissolution system
(e.g., 402).
[0052] With reference to FIGS. 1, 2 and 3 for illustrative
purposes, in some embodiments of the system, the anode electrolyte
(e.g., 104) is separated from the cathode electrolyte (e.g., 110)
by a first cation exchange membrane (e.g., 112). In some
embodiments, the cathode electrolyte (e.g., 110) is in contact with
a cathode (e.g., 114) and both the cathode electrolyte and the
cathode are contained in a cathode electrolyte compartment (e.g.,
116).
[0053] In the system as illustrated in FIG. 1, a direct-current
voltage supply system (e.g., 118) is configured to electrically
connect the anode and the cathode, to oxidize hydrogen gas to
protons at the anode and reduce water to hydrogen gas and hydrogen
ions at the cathode, in accordance with Eq. 1 and 2:
At anode: H.sub.2.fwdarw.2H.sup.++2e- Eq. 1
At cathode: 2H.sub.20+e.sup.-.fwdarw.2OH-+2H.sub.2 Eq. 2
[0054] In some embodiments of the system, hydrogen gas (e.g., 120)
is provided to the anode (e.g., 106A, 106B) through a hydrogen
supply system (e.g., 122); in some embodiments, the system includes
a hydrogen recirculation loop (e.g., 124A) configured to
re-circulate un-reacted hydrogen to the anode (e.g., 106A, 106B).
In some embodiments, the hydrogen gas (e.g., 124B) generated at the
cathode is provided to the anode.
[0055] In some embodiments as illustrated in FIGS. 1 and 2, the
anode may comprise a gas diffusion anode (e.g., 106A, 106B). In
some embodiments as illustrated in FIG. 1, the anode may comprising
a second cation exchange membrane (e.g., 127) that contacts the
anode electrolyte (e.g., 104) and thus separates the anode (e.g.,
106A) from the anode electrolyte (e.g., 104). In some embodiments
as illustrated in FIG. 2, the system does not include the second
cation exchange membrane of FIG. 1 and hence the anode is in direct
contact with the anode electrolyte (e.g., 104).
[0056] In some embodiments as illustrated in FIG. 1, the system
includes a hydrostatic pressure system (e.g., 128) configured to
apply a hydrostatic pressure on to the anode electrolyte (e.g.,
104) and thus transmit the pressure on to the second cation
exchange membrane (e.g., 127) and against the anode (e.g., 106A).
In some embodiments, a column of anode electrolyte above the anode
compartment achieves the desired hydrostatic pressure on the cation
exchange membrane (e.g., 126). In some embodiments, compressed air
is used to apply the pressure on the anode electrolyte. In various
embodiments, the pressure applied to the second cation ion exchange
membrane assists in securing the cation exchange membrane (e.g.,
127) against the anode (e.g., 106A).
[0057] With reference to FIG. 2 for illustrative purposes, in some
embodiments the gas diffusion anode (e.g., 126B) may comprise a
catalyst (e.g., 130) configured to catalyze the oxidation of
hydrogen gas at the anode (e.g., 106A, 16B) to protons. In some
embodiments, the catalyst is supported on a substrate (e.g., 132).
In some embodiments the catalyst the may comprise platinum or a
platinum alloy.
[0058] In some embodiments as illustrated in FIG. 1, carbon dioxide
is added to the cathode electrolyte (e.g., 110) to produce an
alkaline solution comprising carbonate ions or bicarbonate ions in
the cathode electrolyte in accordance with Eq. 3:
CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3.fwdarw.H.sup.++HCO.sub.3.sup.-.-
fwdarw.2H.sup.++CO.sub.3.sup.- Eq. 3
[0059] In some embodiments, the carbon dioxide in gaseous form is
added directly to the cathode electrolyte (e.g., 110) by sparging
the gas directly into the cathode electrolyte in the cathode
compartment (e.g., 116); in some embodiments the carbon dioxide is
added to the cathode electrolyte by withdrawing a portion of the
cathode electrolyte (e.g., 134) from the cathode compartment and
contacting the carbon dioxide and cathode electrolyte in a carbon
dioxide contactor (e.g., 136) to absorb the gas in the cathode
electrolyte, and returning the cathode electrolyte/carbon
dioxide/carbonate ion/bicarbonate ion solution (e.g., 138) to the
cathode compartment.
[0060] In some embodiments as illustrated in FIG. 1, the system
comprises a partition (e.g., 134) that partitions the cathode
electrolyte (e.g., 110) into a first cathode electrolyte portion
(e.g., 110A) and a second cathode electrolyte portion (e.g., 110B).
In this embodiment of the system, the second cathode electrolyte
portion (e.g., 110B) comprising dissolved carbon dioxide is in
contact with the cathode (e.g., 114) and the first cathode
electrolyte portion (e.g., 110A) comprising dissolved carbon
dioxide and gaseous carbon dioxide is under partition (e.g., 134)
and is not in direct contact with the cathode. Thus in this
embodiment of the system, the partition will prevent gaseous carbon
dioxide in the first cathode electrolyte portion (e.g., 110A) from
coming in contact with the cathode electrolyte in the second
cathode electrolyte portion (e.g., 110B). Consequently in this
embodiment of the system, where hydrogen is generated at the
cathode and where it is desired to separate the hydrogen gas from
carbon dioxide gas or water vapor from the cathode electrolyte, the
partition will prevent mixing of the hydrogen gas with carbon
dioxide gas and the water vapor.
[0061] In some embodiments as illustrated in FIG. 1, the first
cation exchange membrane (e.g., 112) is located between the cathode
(e.g., 114) and anode (e.g., 106A) such the cation exchange
membrane separates the cathode electrolyte (e.g., 110) from the
anode electrolyte (e.g., 104). Thus as is illustrated in FIG. 1, on
applying a relatively low voltage, e.g., less than 2V or less than
1V, across the anode (e.g., 106A) and cathode (e.g., 114),
hydroxide ions (OH.sup.-) and hydrogen gas (H.sub.2) will be
produced at the cathode (e.g., 114), and hydrogen gas will be
oxidized at the anode (e.g., 106) to produce hydrogen ions at the
anode (e.g., 106A), without producing a gas at the anode. In some
embodiments, the hydrogen gas produced at the cathode (e.g., 114)
is directed to the anode through a hydrogen gas delivery system
(e.g., 122), and is oxidized to hydrogen ions at the anode. In some
embodiments, the use of hydrogen gas at the anode from the cathode
will reduce the need for externally produced hydrogen, which
consequently will reduce the energy required by the system to
produce the hydroxide in the cathode electrolyte.
[0062] Also, as illustrated in FIG. 1, under the applied voltage
(e.g., 118) across the anode (e.g., 106A) and cathode (e.g., 114),
hydrogen ions produced at the anode (e.g., 106A) will migrate from
the anode (e.g., 106) into the anode electrolyte (e.g., 104) to
produce an acid, e.g., hydrochloric acid, in the anode
electrolyte.
[0063] In some embodiments, the first cation exchange membrane
(e.g., 112) is selected to allow passage of cations therethrough
but restrict passage of anions therethrough. Thus, as is
illustrated in FIG. 1, on applying the low voltage across the anode
(e.g., 106A) and cathode (e.g., 114), cations in the anode
electrolyte (e.g., 104), e.g., sodium ions in the anode electrolyte
comprising sodium chloride, will migrate into the cathode
electrolyte through the first cation exchange membrane (e.g., 112),
while anions in the cathode electrolyte (e.g., 110), e.g.,
hydroxide ions, and/or carbonate ions, and/or bicarbonate ions,
will be blocked from migrating from the cathode electrolyte through
the first cation exchange membrane (e.g., 112) and into the anode
electrolyte 104.
[0064] Thus, as is illustrated in FIG. 1, where the anode
electrolyte (e.g., 104) comprises an aqueous salt solution such as
an aqueous sodium chloride solution, in the cathode electrolyte
(e.g., 110) an alkaline solution will be produced comprising sodium
ions that migrate from the anode electrolyte (e.g., 104), and
hydroxide ions produced at the cathode and/or carbonate ions and or
bicarbonate ions produced by dissolving carbon dioxide in the
cathode electrolyte.
[0065] Concurrently, in the system of FIG. 1 for illustrative
purposes, in the anode electrolyte (e.g., 104), an acid, e.g.,
hydrochloric acid, will be produced from hydrogen ions migrating
from the anode (e.g., 106A) and chloride ions present from the
anode electrolyte.
[0066] With reference to FIG. 1 for illustrative purposes, in some
embodiments an anode (e.g., 106A) comprising a second cation
exchange membrane (e.g., 127) is utilized to separate the anode
(e.g., 106) from the anode electrolyte (e.g., 104) such that on a
first surface, the cation exchange membrane (e.g., 126) is in
contact with the anode (e.g., 106), and an opposed second surface
it is in contact with the anode electrode electrolyte (e.g., 104).
Thus, in this embodiment of the system, since the second cation
exchange membrane (e.g., 126) will allow passage of cations, e.g.,
hydrogen ions, therefore the hydrogen ions produced in at the anode
will migrate through the second cation exchange membrane (e.g.,
126) and into the anode electrolyte (e.g., 104).
[0067] In some embodiments, suitable cation exchange membranes
(e.g., 112 and 126) are conventional and are available from Asahi
Kasei of Tokyo, Japan; or from Membrane International of Glen Rock,
N.J., or DuPont or DOW Chemicals, in the USA. However, it will be
appreciated that in some embodiments, depending on the need to
restrict or allow migration of a specific cation or an anion
species between the electrolytes, a cation exchange membrane that
is more restrictive and thus allows migration of one species of
cations while restricting the migration of another species of
cations may be used as, e.g., a cation exchange membrane that
allows migration of sodium ions into the cathode electrolyte from
the anode electrolyte while restricting migration of hydrogen ions
from the anode electrolyte into the cathode electrolyte, may be
used. Such restrictive cation exchange membranes are commercially
available and can be selected by one ordinarily skilled in the
art.
[0068] With reference to FIG. 1 for illustrative purposes, in some
embodiments of the system, the cathode electrolyte (e.g., 110A) is
operatively connected to a supply of carbon dioxide gas contained
in a waste gas from an industrial plant, e.g., a power generating
plant, a cement plant, or an ore smelting plant. As can be
appreciated, the concentration of carbon dioxide in the waste gases
from these sources is greater than the concentration of carbon
dioxide in the ambient atmosphere; this source of carbon dioxide
may also contain other gases and non-gases such as nitrogen,
SO.sub.X, NO.sub.X., as is described in co-pending and commonly
assigned U.S. Provisional Patent application No. 61/223,657, titled
"Gas, Liquids, Solids Contacting Methods and Apparatus", filed Jul.
7, 2009, herein fully incorporated by reference. In some
embodiments, although carbon dioxide is present in the atmosphere,
in view of the very low concentration of atmospheric carbon
dioxide, this source of carbon dioxide may not provide sufficient
carbon dioxide to achieve the results obtained with the present
system. Also, in some embodiments, since the cathode electrolyte is
contained in closed system wherein the pressure of the added carbon
dioxide gas within the system is greater than the ambient
atmospheric pressure, ambient air and hence ambient carbon dioxide
is typically prevented from infiltrating into the cathode
electrolyte.
[0069] In some embodiments of the system, and with reference to
FIG. 1 for illustrative purposes, carbon dioxide is added to the
cathode electrolyte (e.g., 110A) to produce carbonic acid that may
dissociate to hydrogen ions and carbonate ions and/or bicarbonate
ions, depending on the pH of the cathode electrolyte. Concurrently,
as described above, hydroxide ions, produced in the cathode
electrolyte from electrolyzing water in the cathode, may react with
the hydrogen ions to produce water in the cathode electrolyte.
[0070] Thus, depending on the degree of alkalinity desired in the
cathode electrolyte, the pH of the cathode electrolyte may be
adjusted and in some embodiments is maintained between and 7 and 14
or greater; or between 7 and 9; or between 8 and 11 as is well
understood in the art. In some embodiments, the pH of the cathode
electrolyte may be adjusted to any value between 7 and 14 or
greater, including a pH 7.0, 7.5, 8.0, 8.5. 9.0, 9.5, 10.0, 10.5,
11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0 and greater.
[0071] In some embodiments of the system, the pH of the anode
electrolyte is adjusted and is maintained between less than 0 and
up to 7 and/or between less than 0 and up to 4, by regulating the
concentration of hydrogen ions that migrate into the anode
electrolyte from oxidation of hydrogen gas at the anode, and/or the
withdrawal and replenishment of anode electrolyte in the system. In
this regard and with reference to FIG. 1 for illustrative purposes,
since the voltage across the anode and cathode is dependent on
several factors including the difference in pH between the anode
electrolyte and the cathode electrolyte as can be determined by the
Nernst equation, in some embodiments, the pH of the anode
electrolyte is adjusted to a value between 0 and 7, including 0,
0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 and
7, depending on the desired operating voltage across the anode and
cathode. Thus, as can be appreciated, where it is desired to reduce
the energy used and/ or the voltage across the anode and cathode,
e.g., as in the Chloralkali process, carbon dioxide can be added to
the electrolyte as disclosed herein to achieve a desired pH
difference between the anode electrolyte and cathode electrolyte.
Thus, to the extent that such systems utilize carbon dioxide, these
equivalent systems are within the scope of the present
invention.
[0072] With reference to FIGS. 1-4 for illustrative purposes, the
method in some embodiments comprises a step of changing the anode
electrolyte (e.g., 104) with a concentrated salt solution (e.g.,
126); reducing hydrogen gas (e.g., 120) to protons at the anode
(e.g., 106A, 106B) and migrating the protons into the anode
electrolyte, by applying a voltage (e.g., 118) across the anode and
a cathode in contact with a cathode electrolyte; and migrating
cations from the anode electrolyte.
[0073] In some embodiments of the method, a hydroxide is produced
in the cathode electrolyte (e.g., 110, 110B) by reducing water to
hydroxide ions and hydrogen gas at the cathode (e.g., 114);
migrating the hydroxide ions into the cathode electrolyte (e.g.,
110, 110B); and migrating cations e.g., Na+ ions from the salt
solution (e.g., 104, 126) to the cathode electrolyte across a
cation exchange membrane (e.g., 114) separating the salt solution
from the cathode electrolyte.
[0074] In some embodiments of the method, the salt solution (e.g.,
126) may comprise sodium chloride or sodium sulfate; the acid may
comprise hydrochloric acid or sulfuric acid; and the hydroxide in
the cathode electrolyte may comprise sodium hydroxide.
[0075] In some embodiments of the method, hydrogen gas produced at
the cathode (e.g., 124A) is directed to the anode (e.g., 106A,
106B) to be oxidized to protons and form the acid in the anode
electrolyte.
[0076] In some embodiments of the method and with reference to FIG.
4 for illustrative purposes, the cathode electrolyte is used to
sequester carbon dioxide as a divalent bicarbonate and/or carbonate
by mixing the cathode electrolyte with a divalent cation solution
comprising Ca++ ions or Mg++ ions in carbonate precipitation system
(e.g., 412). In some embodiments, the sequestered carbon dioxide is
obtained from a waste gas emitted from an industrial facility
comprising a fossil fuelled power generating plant, a cement
production plant, an ore smelter or a carbon fermentation
plant.
[0077] As described above with reference to embodiments of the
system and with reference to FIG. 3 for illustrative purposes, in
some embodiments of the method, the acid is separated from
acid-salt solution by feeding the acid-salt solution into a lower
portion of the ion exchange resin bed (e.g., 302B) comprising a
resin selected to retard the acid on the resin without retarding
the salt; removing the salt solution from the upper portion of the
ion exchange resin bed (e.g., 302A); and eluting or back-flushing
the acid (e.g., 306) from the ion exchange resin with water (e.g.,
310).
[0078] In some embodiments of the method, the ion exchange resin
comprises a strong base anion exchange resin comprising particle
sizes in the range of 525-625 microns and the bed is short e.g.,
less than 1 ft.
[0079] In some embodiments of the method, the eluted acid (e.g.,
306) is reacted in mineral dissolution system (e.g., 402) with a
mineral comprising divalent cations to produce the divalent cation
solution (e.g., 410) used in sequestering carbon dioxide as a
carbonate or bicarbonate.
[0080] In some embodiments of the method, the divalent cation
solution is subjected to nano-filtration in nano-filtration system
(e.g., 406) to clean the solution and reverse osmosis system (e.g.,
414) to concentrate the salt solution. In some embodiments, the
concentrated salt solution (e.g., 416) is reused as concentrated
salt solution (e.g., 126) added to the anode electrolyte (e.g.,
104).
[0081] With reference to FIGS. 2 and 4 for illustrative purposes,
in some embodiments, carbon dioxide is absorbed into the cathode
electrolyte (e.g., 110) utilizing a gas mixer/gas absorber (e.g.,
136). In some embodiments, the gas mixer/gas absorber comprises a
series of spray nozzles that produces a flat sheet or curtain of
liquid into which the gas is absorbed; in another embodiment, the
gas mixer/gas absorber comprises a spray absorber that creates a
mist and into which the gas is absorbed; in other embodiments,
other commercially available gas/liquid absorber, e.g., an absorber
available from Neumann Systems, Colorado, USA is used.
[0082] The carbon dioxide used in the system may be obtained from
various industrial sources that releases carbon dioxide including
carbon dioxide from combustion gases of fossil fuelled power
plants, e.g., conventional coal, oil and gas power plants, or IGCC
(Integrated Gasification Combined Cycle) power plants that generate
power by burning sygas; cement manufacturing plants that convert
limestone to lime; ore processing plants; fermentation plants; and
the like. In some embodiments, the carbon dioxide may comprise
other gases, e.g., nitrogen, oxides of nitrogen (nitrous oxide,
nitric oxide), sulfur and sulfur gases (sulfur dioxide, hydrogen
sulfide), and vaporized materials.
[0083] In some embodiments, the system includes a gas treatment
system (not illustrated) that removes constituents in the carbon
dioxide gas stream before the gas is utilized in the cathode
electrolyte.
[0084] In some embodiments, as illustrated in FIG. 1 a portion of,
or the entire amount of, cathode electrolyte (e.g., 110) comprising
bicarbonate ions and/or carbonate ions/ and or hydroxide ions is
withdrawn from the system and is contacted with carbon dioxide gas
in an exogenous carbon dioxide gas/liquid contactor (e.g., 136) to
increase the absorbed carbon dioxide content in the solution.
[0085] In some embodiments, the solution enriched with carbon
dioxide (e.g., 138) is returned to the cathode compartment (e.g.,
116); in other embodiments, the solution enriched with carbon
dioxide is reacted with a solution comprising divalent cations in a
carbonate precipitating system (e.g., 412) to produce divalent
cation hydroxides, carbonates and/or bicarbonates.
[0086] In some embodiments, the pH of the cathode electrolyte
(e.g., 110) is adjusted upwards by hydroxide ions that migrate from
the cathode, and/or downwards by dissolving carbon dioxide gas in
the cathode electrolyte to produce carbonic acid and carbonic ions
that react with and remove hydroxide ions. Thus, as can be
appreciated that the pH of the cathode electrolyte is determined,
at least in part, by the balance of these two processes.
[0087] With reference to FIG. 1 for illustrative purposes, in some
embodiments, the system includes a partition (e.g., 134) configured
into J-shape structure and positioned in the cathode electrolyte
(e.g., 110A, 110B) to define an upward-tapering channel (e.g., 144)
in the upper portion of the cathode electrolyte compartment. The
partition also defines a downward-tapering channel (e.g., 146) in
lower portion of the cathode electrolyte. Thus, with the partition
in the place, the cathode electrolyte (e.g., 110) is partitioned
into the first cathode electrolyte portion (e.g., 110A) and a
second cathode electrolyte portion (e.g., 110B). As is illustrated
in FIG. 1, cathode electrolyte in the first cathode electrolyte
portion (e.g., 110A) is in contact with cathode electrolyte in the
second cathode electrolyte portion (e.g., 110B); however, a gas in
the first electrolyte portion (e.g., 110A), e.g., carbon dioxide,
is prevented from mixing with cathode electrolyte in the second
cathode electrolyte (e.g., 110B).
[0088] With reference to FIG. 1 for illustrative purposes, the
system in some embodiments includes a cathode electrolyte
circulating system (e.g., 134) adapted for withdrawing and
circulating cathode electrolyte in the system. In one embodiment,
the cathode electrolyte circulating system comprises a carbon
dioxide gas/liquid contactor (e.g., 136) that is adapted for
dissolving carbon dioxide in the circulating cathode electrolyte,
and for circulating the electrolyte in the system. As can be
appreciated, since the pH of the cathode electrolyte can be
adjusted by withdrawing and/or circulating cathode electrolyte from
the system, the pH of the cathode electrolyte compartment can be by
regulated by regulating an amount of cathode electrolyte removed
from the system through the carbon dioxide gas/liquid contactor
(e.g., 136).
[0089] With reference to FIG. 1 for illustrative purposes,
depending on the pH of the cathode electrolyte, carbon dioxide gas
introduced into the first cathode electrolyte portion (e.g., 108A)
will dissolve in the cathode electrolyte and reversibly dissociate
and equilibrate to produce carbonic acid, protons, carbonate and/or
bicarbonate ions in the first cathode electrolyte compartment as
follows:
CO.sub.2+H.sub.2O<==>H.sub.2CO.sub.3<==>H.sup.++HCO.sub.3.su-
p.-<==>H.sup.++CO.sub.3.sup.2-
In the system, as cathode electrolyte in the first cathode
electrolyte portion (e.g., 110A) may mix with second cathode
electrolyte portion (e.g., 110B), the carbonic acid, bicarbonate
and carbonate ions formed in the first cathode electrolyte portion
(e.g., 110A) by absorption of carbon dioxide in the cathode
electrolyte may migrate and equilibrate with cathode electrolyte in
the second cathode electrolyte portion (e.g., 110B). Thus, in some
embodiments, first cathode electrolyte portion (e.g., 110A) may
comprise dissolved and un-dissolved carbon dioxide gas, and/or
carbonic acid, and/ or bicarbonate ions and/or carbonate ions;
while second cathode electrolyte portion (e.g., 108B) may comprise
dissolved carbon dioxide, and/or carbonic acid, and/ or bicarbonate
ions and/or carbonate ions.
[0090] With reference to FIG. 1 for illustrative purposes, on
applying a voltage across anode (e.g., 106) and cathode (e.g.,
114), the system (e.g., 100) may produce hydroxide ions and
hydrogen gas at the cathode from water, as follows:
2H.sub.2O+2e.sup.-=H.sub.2+2OH.sup.-
As cathode electrolyte in first cathode electrolyte portion (e.g.,
110A) can intermix with cathode electolyte in second cathode
electrolyte portion (e.g., 110B), hydroxide ions formed in the
second cathode electrolyte portion may migrate and equilibrate with
carbonate and bicarbonate ions in the first cathode electrolyte
portion (e.g., 110A). Thus, in some embodiments, the cathode
electrolyte in the system may comprise hydroxide ions and dissolved
and/or un-dissolved carbon dioxide gas, and/or carbonic acid, and/
or bicarbonate ions and/or carbonate ions. In the system, as the
solubility of carbon dioxide and the concentration of bicarbonate
and carbonate ions in the cathode electrolyte are dependent on the
pH of the electrolyte, the overall reaction in the cathode
electrolyte (e.g., 104) is either:
2H.sub.2O+2CO.sub.2+2e.sup.-=H.sub.2+2HCO.sub.3.sup.-; or Scenario
1:
H.sub.2O+CO.sub.2+2e.sup.-=H.sub.2+CO.sub.3.sup.2- Scenario 2:
or a combination of both, depending on the pH of the cathode
electrolyte.
[0091] In embodiments wherein it is desired to produce bicarbonate
and/or carbonate ions in the cathode electrolyte, the system as
illustrated in FIG. 1, and as described above with reference to
production of hydroxide ions in the cathode electrolyte, can be
configured to produce bicarbonate ions and/or carbonate ions in the
cathode electrolyte by dissolving carbon dioxide in cathode
electrolyte and applying a voltage of less than 3V, or less than
2.5 V, or less than 2V, or less than 1.5V such as less than 1.0V,
or even less than 0.8 V or 0.6V across the cathode and anode.
[0092] In some embodiments, hydroxide ions, carbonate ions and/or
bicarbonate ions produced in the cathode electrolyte, and
hydrochloric acid produced in the anode electrolyte are removed
from the system, while sodium chloride in the salt solution
electrolyte is replenished to maintain continuous operation of the
system. As can be appreciated, in some embodiments, the system can
be configured to operate in various production modes including
batch mode, semi-batch mode, continuous flow mode, with or without
the option to withdraw portions of the hydroxide solution produced
in the cathode electrolyte, or withdraw all or a portions of the
acid produced in the anode electrolyte, or direct the hydrogen gas
produced at the cathode to the anode where it may be oxidized.
[0093] In some embodiments, hydroxide ions, bicarbonate ions and/or
carbonate ion solutions are produced in the cathode electrolyte
when the voltage applied across the anode and cathode is less than
3V, 2.9V or less, 2.8V or less, 2.7V or less, 2.6V or less, 2.5V or
less, 2.4V or less, 2.3V or less, 2.2V or less, 2.1V or less, 2.0V
or less, 1.9V or less, 1.8V or less, 1.7V or less, 1.6V, or less
1.5V or less, 1.4V or less, 1.3V or less, 1.2V or less, 1.1V or
less, 1.0V or less, 0.9V or less or less, 0.8V or less, 0.7V or
less, 0.6V or less, 0.5V or less, 0.4V or less, 0.3V or less, 0.2V
or less, or 0.1 V or less.
[0094] In another embodiment, the voltage across the anode and
cathode can be adjusted such that gas will form at the anode, e.g.,
oxygen or chlorine, while hydroxide ions, carbonate ions and
bicarbonate ions are produced in the cathode electrolyte and
hydrogen gas is generated at the cathode. However, in this
embodiment, hydrogen gas is not supplied to the anode. As can be
appreciated by one ordinarily skilled in the art, in this
embodiment, the voltage across the anode and cathode will be
generally higher compared to the embodiment when a gas does not
form at the anode.
[0095] With reference to FIG. 1 for illustrative purposes, in some
embodiments, the invention provides for a system comprising one or
more ion exchange membrane 112, 126 located between the gas
diffusion anode (e.g., 106A, 106B) and the cathode (e.g., 114). In
some embodiments, the membranes should be selected such that they
can function in an acidic and/or basic electrolytic solution as
appropriate. Other desirable characteristics of the membranes
include high ion selectivity, low ionic resistance, high burst
strength, and high stability in an acidic electrolytic solution in
a temperature range of 0.degree. C. to 100.degree. C. or higher, or
a alkaline solution in similar temperature range may be used. In
some embodiments, a membrane that is stable in the range of
0.degree. C. to 80.degree. C., or 0.degree. C. to 90.degree. C.,
but not stable above these ranges may be used.
[0096] For other embodiments, it may be useful to utilize an
ion-specific ion exchange membranes that allows migration of one
type of cation but not another; or migration of one type of anion
and not another, to achieve a desired product or products in an
electrolyte. In some embodiments, the membrane should be stable and
functional for a desirable length of time in the system, e.g.,
several days, weeks or months or years at temperatures in the range
of 0.degree. C. to 80.degree. C., or 0.degree. C. to 90.degree. C.
and higher and/or lower. In some embodiments, for example, the
membranes should be stable and functional for at least 5 days, 10
days, 15 days, 20 days, 100 days, 1000 days or more in electrolyte
temperatures at 80.degree. C., 70.degree. C., 60.degree. C.,
50.degree. C., 40.degree. C., 30.degree. C., 20.degree. C.,
10.degree. C., 5.degree. C. and more or less.
[0097] As can be appreciated, the ohmic resistance of the membranes
will affect the voltage drop across the anode and cathode, e.g., as
the ohmic resistance of the membranes increase, the voltage drop
across the anode and cathode will increase, and vice versa.
Membranes currently available can be used and they include
membranes with relatively low ohmic resistance and relatively high
ionic mobility; similarly, membranes currently available with
relatively high hydration characteristics that increase with
temperatures, and thus decreasing the ohmic resistance can be used.
Consequently, as can be appreciated, by selecting currently
available membranes with lower ohmic resistance, the voltage drop
across the anode and cathode at a specified temperature can be
lowered.
[0098] In some embodiments, the cathode electrolyte, (e.g., 110A,
110B) is operatively connected to a waste gas treatment system
where the alkaline solution produced in the cathode electrolyte is
utilized, e.g., to sequester carbon dioxide contained in the waste
gas by contacting the waste gas and the cathode electrolyte with a
solution of divalent cations to precipitate hydroxides, carbonates
and/or bicarbonates as described in commonly assigned U.S. patent
application Ser. No. 12/344,019 filed on Dec. 24, 2008, herein
incorporated by reference in its entirety. The precipitates,
comprising, e.g., calcium and magnesium hydroxides, carbonates and
bicarbonates in some embodiments may be utilized as building
materials, e.g., as cements and aggregates, as described in
commonly assigned U.S. patent application Ser. No. 12/126,776 filed
on May 23, 2008, supra, herein incorporated by reference in its
entirety. In some embodiments, some or all of the carbonates and/or
bicarbonates are allowed to remain in an aqueous medium, e.g., a
slurry or a suspension, and are disposed of in an aqueous medium,
e.g., in the ocean depths or a subterranean site.
[0099] In some embodiments, the cathode and anode are also
operatively connected to an off-peak electrical power-supply system
that supplies off-peak voltage to the electrodes through the
voltage supply (e.g., 118 of FIG. 1 or of FIG. 3). Since the cost
of off-peak power is lower than the cost of power supplied during
peak power-supply times, the system can utilize off-peak power to
produce an alkaline solution in the cathode electrolyte at a
relatively lower cost.
[0100] With reference to FIG. 1 for illustrative purposes, on
applying a voltage (e.g., 118) across the anode (e.g., 106) and
cathode (e.g., 114), protons will form at the anode from oxidation
of hydrogen gas supplied to the anode, while hydroxide ions and
hydrogen gas will form at the cathode electrolyte from the
reduction of water, as follows:
H.sub.2=2H.sup.++2e.sup.- (anode, oxidation reaction)
2H.sub.2O+2e.sup.-=H.sub.2+2OH.sup.- (cathode, reduction
reaction)
[0101] Since protons are formed at the anode from hydrogen gas
provided to the anode; and since a gas such as oxygen does not form
at the anode; and since water in the cathode electrolyte forms
hydroxide ions and hydrogen gas at the cathode, the system will
produce hydroxide ions in the cathode electrolyte and protons in
the anode electrolyte when a voltage is applied across the anode
and cathode. Further, as can be appreciated, in the present system
since a gas does not form at the anode, the system will produce
hydroxide ions in the cathode electrolyte and hydrogen gas at the
cathode and hydrogen ions at the anode when less than 2V is applied
across the anode and cathode, in contrast to the higher voltage
that is required when a gas is generated at the anode, e.g.,
chlorine or oxygen. For example, in some embodiments, hydroxide
ions are produced when less than 2.0V, 1.5V, 1.4V, 1.3V, 1.2V,
1.1V, 1.0V, 0.9V, 0.8V, 0.7V, 0.6V, 0.5V, 0.4V, 0.3V, 0.2V, 0.1 V
or less is applied across the anode and cathode.
[0102] As discussed above, in the system, on applying a voltage
across the anode (e.g., 106) and cathode (e.g., 114) the positively
charged protons formed at the anode will attempt to migrate to the
cathode through the anode electrolyte (e.g., 104), while the
negatively charged hydroxide ions formed at the cathode will
attempt to migrate to the anode through the cathode electrolyte
(e.g., 110A, 110B). As is illustrated in FIG. 1 and with reference
to hydroxide ions in the cathode electrolyte (e.g., 110A, 110B),
since the first cation exchange membrane (e.g., 116) will restrict
the migration of anions from the cathode electrolyte (e.g., 110A,
110B), and since the anion exchange membrane (e.g., 120) will
prevent the migration of anions from the anode electrolyte (e.g.,
104) to the salt solution (e.g., 118), the hydroxide ions generated
in the cathode electrolyte will be prevented from migrating out of
the cathode electrolyte through the cation exchange membrane.
Consequently, on applying the voltage across the anode and cathode,
the hydroxide ions produced at the cathode will be contained in the
cathode electrolyte. Thus, depending on the flow rate of fluids
into and out of the cathode electrolyte and the rate of carbon
dioxide dissolution in the cathode electrolyte, the pH of the
cathode electrolyte will adjust, e.g., the pH may increase,
decrease or remain the same.
[0103] In some embodiments, depending on the ionic species desired
in cathode electroyte (e.g., 110A, 110B) and/or the anode
electolyte (e.g., 104) and/or the salt solution (e.g., 126),
alternative reactants can be utilized. Thus, for example, if a
potassium salt such as potassium hydroxide or potassium carbonate
is desired in the cathode electolyte (e.g., 108A, 108B), then a
potassium salt such as potassium chloride can be utilized in the
salt solution (e.g., 126). Similarly, if sulfuric acid is desired
in the anode electrolyte, then a sulfate such as sodium sulfate can
be utilized in the salt solution (e.g., 126). As described in some
embodiments herein, carbon dioxide gas is absorbed in the cathode
electrolyte; however, it will be appreciated that other gases,
including volatile vapors, can be absorbed in the electrolyte,
e.g., sulfur dioxide, or organic vapors to produce a desired
result. As can be appreciated, the gas can be added to the
electrolyte in various ways, e.g., by bubbling it directly into the
electrolyte, or dissolving the gas in a separate compartment
connected to the cathode compartment and then directed to the
cathode electrolyte as described herein.
[0104] In some embodiments, hydroxide ions are formed at the
cathode (e.g., 114) and in the cathode electrolyte (e.g., 110A,
110B) by applying a voltage of less than 2V across the anode and
cathode without forming a gas at the anode, while providing
hydrogen gas at the anode for oxidation at the anode. In some
embodiments, method (e.g., 300) does not form a gas at the anode
when the voltage applied across the anode and cathode is less than
3V or less, 2.9V or less, 2.8V or less, 2.7V or less, 2.6V or less,
2.5V or less, 2.4V or less, 2.3V or less, 2.2V or less, 2.1V or
less, 2.0V or less, 1.9V or less, 1.8V or less, 1.7V or less, 1.6V
or less, 1.5V or less, 1.4V or less, 1.3V or less, 1.2V or less,
1.1V or less, 1.0V or less, 0.9V or less, 0.8V or less, 0.7V or
less, 0.6V or less, 0.5V or less, 0.4V or less, 0.3V or less, 0.2V
or less, or 0.1 V or less, while hydrogen gas is provided to the
anode where it is oxidized to protons. As will be appreciated by
one ordinarily skilled in the art, by not forming a gas at the
anode and by providing hydrogen gas to the anode for oxidation at
the anode, and by otherwise controlling the resistance in the
system for example by decreasing the electrolyte path lengths and
by selecting ionic membranes with low resistance and any other
method know in the art, hydroxide ions can be produced in the
cathode electrolyte with the present lower voltages.
[0105] In the system as illustrated in FIG. 1, the solubility of
carbon dioxide in the cathode electrolyte is dependent on the pH of
the electrolyte. Also in the system, the voltage across the cathode
and anode is dependent on several factors including the pH
difference between the anode electrolyte and cathode electrolyte.
Thus, in some embodiments the system can be configured to operate
at a specified pH and voltage to absorb carbon dioxide and produce
carbonic acid, carbonate ions and/or bicarbonate ions in the
cathode electrolyte. In embodiments where carbon dioxide gas is
dissolved in the cathode electrolyte, as protons are removed from
the cathode electrolyte more carbon dioxide may be dissolved to
form carbonic acid, bicarbonate ions and/or carbonate ions.
Depending on the pH of the cathode electrolyte the balance is
shifted toward bicarbonate ions or toward carbonate ions, as is
well understood in the art and as is illustrated in the carbonate
specification diagram, above. In these embodiments the pH of the
cathode electrolyte solution may decrease, remain the same, or
increase, depending on the rate of removal of protons compared to
rate of introduction of carbon dioxide. It will be appreciated that
no carbonic acid, hydroxide ions, carbonate ions or bicarbonate
ions are formed in these embodiments, or that carbonic acid,
hydroxide ions, carbonate ions, bicarbonate ions may not form
during one period but form during another period.
[0106] For illustrative and descriptive purposes, the systems and
methods are described wherein a salt solution comprising sodium
chloride is used in the cathode electrolyte. Thus, in the systems
and methods herein, the acid produced in the anode catholyte
comprises hydrochloric acid and the alkaline solution produced in
the cathode electrolyte comprises sodium hydroxide. However, as can
be appreciated by those ordinarily skilled in the art, the present
system and method are not limited to using sodium chloride solution
since an equivalent salt solution can be used in the anode
electrolyte, e.g., a potassium sulfate solution, to produce an
equivalent alkaline solution in the cathode electrolyte, e.g.,
potassium hydroxide and/or potassium carbonate and/or potassium
bicarbonate, and since an equivalent acid, e.g., sulfuric acid, can
be produced in the anode electrolyte. Thus, to the extent that such
equivalents are based on the present system and method, these
equivalents are within the scope of the present system and method
as defined by the claims.
* * * * *