Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02696086 2014-02-12
ELECTROCHEMICAL PRODUCTION OF AN ALKALINE SOLUTION USING CO2
BACKGROUND OF THE INVENTION
[0002] In many chemical processes an alkaline solution is required to achieve
a chemical
reaction, e.g., to neutralize an acid, or buffer the pH of a solution, or
precipitate an insoluble
hydroxide and/or carbonate and/or bicarbonate from a solution. One method by
which the alkaline
solution is produced is by an electrochemical system as disclosed in US Patent
Application
publication Nos. US 2010-0140103 Al and US 2010-0230293 Al. In producing an
alkaline
solution electrochemically, a large amount of energy, salt and water may be
used; consequently,
lowering the energy and material used is highly desired. An alkaline solution
includes a solution
comprising hydroxide ions, and/or carbonate ions, and/or bicarbonate ions.
SUMMARY OF THE INVENTION
[0003] In one embodiment, this invention pertains to an electrochemical system
comprising a
cathode electrolyte comprising added carbon dioxide, and contacting a cathode;
and a first cation
exchange membrane separating the cathode electrolyte from an anode electrolyte
contacting an
anode. In another embodiment, the invention pertains to an electrochemical
method comprising
adding carbon dioxide into a cathode electrolyte separated from an anode
electrolyte by a first
cation exchange membrane; and producing an alkaline solution in the cathode
electrolyte without
producing a gas at the anode in contact with the anode electrolyte. In another
embodiment, the
invention pertains to a method comprising producing an acid in an
electrochemical system
comprising added carbon dioxide in the cathode electrolyte; and contacting a
mineral with the
acid.
[0004] In some embodiments, the system comprises a second cation exchange
membrane
contacting the anode electrolyte; the carbon dioxide is contained in a waste
gas; the waste gas
comprises emissions from an electrical power generating plant, a cement plant,
an ore
processing facility or a fermentation system; atmospheric carbon dioxide is
excluded from the
cathode electrolyte; the cathode electrolyte is operatively connected to the
industrial facility; the
pH of the cathode electrolyte is 7 and above; the pH of the cathode
electrolyte is between 7 and
14; the pH of the cathode electrolyte is between 7 and 9; the pH of the
cathode electrolyte is
between 8 and 11; the pH of the anode electrolyte is less than 7; the pH of
the anode electrolyte
is less than 4; the cathode electrolyte comprises hydroxide ions and/or
bicarbonate ions and/or
carbonate ions; the cathode electrolyte comprises sodium ions; the cathode
electrolyte is
operatively connected to a carbonate and/or bicarbonate precipitator; the
carbonates and/or
bicarbonates comprise calcium and/or magnesium; hydrogen is oxidized at the
anode; the
cathode is configured to produce hydrogen gas; a gas delivery system is
configured to direct
hydrogen
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gas from the cathode to the anode; the anode electrolyte comprises an acid and
a salt solution; the salt
solution comprises sodium ions and chloride ions; the system is configured to
produce hydrogen ions at
the anode with less than 1V across the anode and cathode, without producing a
gas at the anode; the
system is configured to migrate hydrogen ions into the anode electrolyte; the
system is configured to
produce hydroxide ions at the cathode; the system is configured to migrate
hydroxide ions into the
cathode electrolyte; the system is configured to migrate cations from the
anode electrolyte into the
cathode electrolyte; the cations comprise sodium ions; the anode electrolyte
is operatively connected to a
mineral dissolution system configured to dissolve minerals; the mineral
solution comprises calcium ions
and/or magnesium ions; the minerals comprises mafic minerals; the mineral
dissolution system is
operatively connected to a separator configured to separate sodium ions and
chloride ions from the
mineral solution; a concentrator is configured to concentrate sodium ions and
chloride ions into a salt
solution.
[0005] In some embodiments, the method comprises applying a voltage
across the cathode in
contact with the cathode electrolyte and the anode in contact with the anode
electrolyte, wherein a gas is
not produced at the anode; and wherein the voltage is less than 1V; and
wherein the anode comprises a
second cation exchange membrane contacting the anode electrolyte. In some
embodiments, the method
comprises producing hydroxide ions and/or bicarbonate ions and/or carbonate
ions in the cathode
electrolyte; wherein the carbon dioxide is contained in a waste gas, e.g., an
industrial waste gas; wherein
the waste gas is emitted from an industrial plant; wherein the industrial
plant comprises an electrical
power generating plant, a cement production plant or an ore processing
facility and the like; wherein
carbon dioxide in ambient air is excluded from the cathode electrolyte. In
some embodiments, the method
comprises maintaining a pH of 7 or greater in the cathode electrolyte;
maintaining a pH of between 7 and
9 in the cathode electrolyte; maintaining a pH of between 8 and 11 in the
cathode electrolyte; maintaining
a pH of less than 7 in the anode electrolyte; maintaining a pH of less than 4
in the anode electrolyte;
oxidizing hydrogen gas at the anode to produce hydrogen ions; migrating the
hydrogen ions through the
second cation exchange membrane into the anode electrolyte; producing
hydroxide ions and hydrogen
gas at the cathode and migrating hydroxide ions into the cathode electrolyte;
directing hydrogen gas from
the cathode to the anode; migrating cations ions through the first cation
exchange membrane into the
cathode electrolyte, wherein the cations comprise sodium ions; and producing
an acid in the anode
electrolyte.
[0006] In some embodiments, the method comprises producing an acid in
the anode electrolyte,
without generating a gas at the anode; oxidizing hydrogen gas at the anode;
wherein the acid produced
comprises hydrochloric acid; producing hydrogen gas at the cathode; producing
an alkaline solution in the
cathode electrolyte; migrating sodium ions into the cathode electrolyte;
wherein the alkaline solution
comprises sodium hydroxide, sodium bicarbonate and/or sodium carbonate; the
voltage is less than 1V;
the anode electrolyte is separated from the cathode electrolyte by first
cation exchange membrane; the
anode comprises a second cation exchange membrane in contact with the anode
electrolyte; the anode
electrolyte comprises a salt; the salt comprises sodium chloride. In some
embodiments, the method
comprises dissolving a mineral with the acid to produce a mineral solution;
producing calcium ions and/or
magnesium ions; the mineral comprises a mafic mineral; and the mineral
solution is filtered to produce a
filtrate comprising sodium ions and chloride ions solution. In other
embodiments, the method includes;
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concentrating the filtrate to produce a salt solution; utilizing the salt
solution as the anode electrolyte;
precipitating a carbonate and/or bicarbonate with the cathode electrolyte,
wherein the carbonate
and/or bicarbonate comprises calcium and/or magnesium carbonate and/or
bicarbonate.
[0007] Accordingly, with the system and method, by selectively placing ion
exchange membranes,
e.g., cation exchange membranes, between the anode electrolyte and the cathode
electrolyte; and
by controlling the voltage across the anode and cathode, e.g., maintaining
less than 2V; and by
controlling the pH of the cathode electrolyte and/or the anode electrolyte;
and by oxidizing hydrogen
gas at the anode without producing a gas at the anode, an alkaline solution
comprising hydroxide
ions and/or carbonate ions and/or bicarbonate ions is produced in the cathode
electrolyte; hydrogen
gas is produced at the cathode; hydrogen ions are produced at the anode from
hydrogen gas
supplied to the anode, without producing a gas at the anode, and hydrogen ions
are migrated into an
electrolyte, e.g., the anode electrolyte, to produce an acid in the anode
electrolyte. In various
embodiments, utilizing hydrogen gas at the anode from hydrogen generated at
the cathode,
eliminates the need for an external supply of hydrogen; consequently, the
overall utilization of
energy by the system to produce the alkaline solution is reduced.
[0008] In some embodiments, the alkaline solution produced is utilized to
sequester carbon dioxide,
e.g., from industrial waste gases, into cementitous carbonate materials as
disclosed, for example, in
US Patent Application publication no. US 2009-0020044A1, filed on May 23,2008
and titled
"Hydraulic Cements Comprising Carbonate Compound Compositions".
[0009] Advantageously, with the present system and method, since a relatively
low voltage is utilized
across the anode and cathode to produce the alkaline solution, and since
hydrogen generated at the
cathode is utilized at the anode, a relatively low amount of energy is
utilized to produce the alkaline
solution. Also, by the system and method, since carbon dioxide from industrial
waste gases is
utilized to produce the alkaline solution, the system and method can be
utilized to sequester large
amounts of carbon dioxide and thus reduce carbon dioxide emissions into the
atmosphere. Further,
the acid produced can be utilized in various ways including dissolving
materials, e.g., minerals and
biomass.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The following drawings illustrate by way of examples and not by
limitation some
embodiments of the present system and method.
[0011] Fig. 1 is an illustration of an embodiment of the present system.
[0012] Fig. 2 is an illustration of an embodiment of the anode portion of the
system.
[0013] Fig. 3 ¨ is an intentionally blank page.
[0014] Fig. 4 is an illustration of an embodiment of the system.
[0015] Fig. 5 is an illustration of the carbonate/bicarbonate ion speciation
in H20 v. the pH of the
solution at 25 C.
[0016] Fig. 6 is an illustration of a voltage difference across the anode and
cathode v. pH of the
cathode electrolyte in an embodiment of the system.
[0017] Fig. 7 is an illustration of an embodiment of the system.
[0018] Fig. 8 is an illustration of an embodiment of the system.
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[00191 Fig. 9 is an illustration of an embodiment of the system.
[0020] Fig. 107 is an intentionally blank page.
[0021] Fig. 11 ¨ is an intentionally blank page.
DETAILED DESCRIPTION OF THE INVENTION
[0022] This invention provides systems and methods for an
electrochemical production of an alkaline
solution in a cathode electrolyte and an acid in an electrolyte, e.g., the
anode electrolyte. In various
embodiments, carbon dioxide is added to the cathode electrolyte and a gas is
not produced at the anode;
in various embodiments, an alkaline solution comprising, e.g., sodium
hydroxide and/or sodium carbonate
and/or sodium bicarbonate is produced in the cathode electrolyte. In various
embodiments, a salt solution
comprising, e.g., sodium chloride, is used as the anode electrolyte to produce
the alkaline solution. Also,
as described herein, an acid solution, e.g., hydrochloric acid, is produced in
the anode electrolyte by
hydrogen ions migrating from the anode into the anode electrolyte, and with
cations, e.g., chloride ions,
present in the anode electrolyte.
[0023] In some embodiments, the acid solution produced is utilized to
dissolve a mineral, e.g.,
serpentine or olivine, to obtain a divalent cation solution, e.g., calcium and
magnesium ion solution, which
may in some embodiments be used with the alkaline solution to precipitate
carbonates and/ or
bicarbonates derived from carbon dioxide in a waste gas stream, e.g., carbon
dioxide in the exhaust
gases of a fossil fuelled power generating plant or a cement producing plant
In some embodiments, a
sodium chloride solution is used as the anode electrolyte.
[0024] Also, as disclosed herein, on applying a voltage across the anode
and cathode, cations, e.g.,
sodium ions in the anode electrolyte, migrate from the anode electrolyte
through the first cation exchange
membrane into the cathode electrolyte to produce an alkaline solution
comprising, sodium hydroxide
and/or sodium carbonate and/or sodium bicarbonate in the cathode electrolyte;
and anions in the anode
electrolyte, e.g., chloride ions, and hydrogen ions migrated from the anode to
produce an acid, e.g.,
hydrochloric acid in the anode electrolyte.
[0025] Further, as described herein, hydrogen gas and hydroxide ions are
produced at the cathode,
and in some embodiments, some or all of the hydrogen gas produced at the
cathode is directed to the
anode where it is oxidized to produce hydrogen ions.
[0026] However, as can be appreciated by one ordinarily skilled in the
art, since the present system
and method can be configured with an alternative, equivalent salt solution in
the anode electrolyte, e.g., a
potassium sulfate solution, to produce an equivalent alkaline solution, e.g.,
potassium hydroxide and/or
potassium carbonate and/or potassium bicarbonate in the cathode electrolyte,
and an equivalent acid,
e.g., sulfuric acid in the anode electrolyte, by applying the voltage as
disclosed herein across the anode
and cathode, the invention is not limited to the exemplarary embodiments
described herein, but is
adaptable for use with an equivalent salt solution, e.g., potassium sulfate,
to produce an alkaline solution
- in the cathode electrolyte, e.g., potassium carbonate and/or potassium
bicarbonate and an acid, e.g.,
sulfuric acid in the anode electrolyte.
[0027] Accordingly, to the extent that such equivalents are based on or
suggested by the present
system and method, these equivalents are within the scope of the appended
claims.
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[0028] With reference to Fig. 7, in one embodiment, the system 700
comprises a cathode 106 in
contact with a cathode electrolyte 108 comprising added carbon dioxide 107,
wherein the cathode
electrolyte is separated from an anode electrolyte 104 by first cation
exchange membrane 116. In an
embodiment as is illustrated in Fig. 8, the system 800 comprises an anode 102
that is separated from the
anode electrolyte by a second cation exchange membrane 122 that is in contact
with the anode 102.
[0029] In systems 700, 800 as illustrated in Figs. 7 and 8, the first
cation exchange membrane 116 is
located between the cathode 106 and anode 102 such it separates the cathode
electrolyte 108 from the
anode electrolyte 104. Thus as is illustrated in Figs. 7 and 8, on applying a
relatively low voltage, e.g., less
than 2V or less than 1V, across the anode 102 and cathode 106, hydroxide ions
(OH) and hydrogen gas
(H2) are produced at the cathode 106, and hydrogen gas is oxidized at the
anode 102 to produce
hydrogen ions at the anode 102, without producing a gas at the anode. In
certain embodiments, the
hydrogen gas produced at the cathode is directed to the anode through a
hydrogen gas delivery system
112, and is oxidized to hydrogen ions at the anode. In various embodiments,
utilizing hydrogen gas at the
anode from hydrogen generated at the cathode, eliminates the need for an
external supply of hydrogen;
consequently, the utilization of energy by the system to produce the alkaline
solution is reduced.
[0030] In certain embodiments as illustrated in Figs. 7 and 8, under the
applied voltage 114 across
the anode 102 and cathode 106, hydroxide ions are produced at the cathode 106
and migrate into the
cathode electrolyte 108, and hydrogen gas is produced at the cathode. In
certain embodiments, the
hydrogen gas produced at the cathode 106 is collected and directed to the
anode, e.g., by a hydrogen gas
delivery system 122, where it is oxidized to produce hydrogen ions at the
anode. Also, as illustrated in
Figs. 7 and 8, under the applied voltage 114 across the anode 102 and cathode
106, hydrogen ions
produced at the anode 102 migrate from the anode 102 into the anode
electrolyte 104 to produce an acid,
e.g., hydrochloric acid.
[0031] In certain embodiments, the first cation exchange membrane 116 is
selected to allow passage
of cations therethrough while restricting passage of anions therethrough.
Thus, as is illustrated in Figs.7
and 8, on applying the low voltage across the anode 102 and cathode 106,
cations in the anode
electrolyte 104 , e.g., sodium ions in the anode electrolyte comprising sodium
chloride, migrate into the
cathode electrolyte through the first cation exchange membrane 116, while
anions in the cathode
electrolyte 108, e.g., hydroxide ions, and/or carbonate ions, and/or
bicarbonate ions, are prevented from
migrating from the cathode electrolyte through the first cation exchange
membrane 116 and into the
anode electrolyte 104.
[0032] Thus, as is illustrated in Figs. 7 and 8, where the anode
electrolyte 104 comprises an
aqueous salt solution such as sodium chloride in water, a solution, e.g., and
alkaline solution, is produced
in the cathode electrolyte 108 comprising cations, e.g., sodium ions, that
migrate from the anode
electrolyte 104, and anions, e.g., hydroxide ions produced at the cathode 106,
and/or carbonate ions and
or bicarbonate ions produced by dissolving carbon dioxide 107 in the cathode
electrolyte.
[0033] Concurrently, in the anode electrolyte 104, an acid, e.g.,
hydrochloric acid is produced from
hydrogen ions migrating from the anode 102 and anions, e.g., chloride ions,
present from the anode
electrolyte.
[0034] With reference to Fig. 8, an anode comprising a second cation
exchange membrane 122 is
utilized to separate the anode 102 from the anode electrolyte 104 such that on
a first surface, the cation
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=
exchange membrane 122 is in contact with the anode 102, and an opposed second
surface it is in
contact with the anode electrode electrolyte 104. Thus, as can be appreciated,
in this
embodiment, since the second cation exchange membrane is permeable to cations,
e.g.,
hydrogen ions, the anode is in electrical contact with the anode electrolyte
through the second
cation exchange membrane. In some embodiments, the anode as illustrated in
Fig. 8 may
comprise a gas diffusion anode as described below.
[0035] Thus, in the embodiment of Fig. 8, as with the embodiment illustrated
in Fig.7, on applying
the low voltage across the anode 102 and cathode 106, hydrogen ions produced
at the anode 102
from oxidation of hydrogen gas at the anode migrate through the second cation
exchange
membrane 122 into the anode electrolyte 104. At the same time, cations in the
anode electrolyte,
e.g., sodium ions in the anode electrolyte comprising sodium chloride, migrate
from the anode
electrolyte 104 into the cathode electrolyte 108 through the first cation
exchange membrane 116,
while anions in the cathode electrolyte 108, e.g., hydroxide ions, and/or
carbonate ions, and/or
bicarbonate ions, are prevented from migrating from the cathode electrolyte
108 to the anode
electrolyte 104 through the first cation exchange membrane 116.
[0036] Also, In the embodiment as illustrated in Fig. 8, hydrogen ions
migrating from the anode
102 through the second cation exchange membrane 122 into the anode electrolyte
104 will
produce an acid, e.g., hydrochloric acid with the cations, e.g., chloride
ions, present in the anode
electrolyte; and in the cathode electrolyte 108, an alkaline solution is
produce from cations present
in the cathode electrolyte and anions, e.g., sodium ions, that migrate from
the anode to the
cathode electrolyte through the first cation exchange membrane 116.
[0037] In some embodiments, cation exchange membranes 116 and 122 are
conventional and are
available from, for example, Asahi Kasei of Tokyo, Japan; or from Membrane
International of Glen
Rock, NJ, or DuPont, 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.
[0038] As is illustrated in Fig. 8, the anode 102 comprises a second cation
exchange membrane
112 that separates the anode 102 from the anode electrolyte 104 and is
attached to the anode.
Thus, in some embodiments, the anode and second cation exchange membrane may
comprise an
integral gas diffusion anode that is commercially available, or can be
fabricated as described for
example in commonly assigned US Patent Application publication no. US2011-
0083968A1.
However, as can be appreciated by one ordinarily skilled in the art,
notwithstanding that a gas
diffusion anode is illustrated and utilized in Figs. 7 and 8 and described
herein, in the some
embodiments, any conventional anode that can be configured to oxidize hydrogen
gas to produce
hydrogen ions as described herein can be utilized.
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[0039] With reference to Fig. 7 and 8, in some embodiments, the cathode
electrolyte 108
is operatively connected to a supply of carbon dioxide gas 107, contained,
e.g., in an
industrial plant, e.g., a power generating plant, a cement plant, or an ore
smelting plant. If
necessary, this source of carbon dioxide comprises a gas wherein the
concentration of
carbon dioxide is greater than the concentration of carbon dioxide in the
ambient
atmosphere. This source of carbon dioxide may also contain other gaseous and
non-
gaseous components of a combustion process, e.g., nitrogen gas, SON, NOR, as
is
described in commonly assigned US Patent application publication no. US 2010-
0230830
Al. However, as can be appreciated, this source of carbon dioxide can be
cleaned and
utilized as the carbon dioxide added to the cathode electrolyte 108.
[0040] Although carbon dioxide is present in ordinary ambient air, in view of
its very low
concentration, ambient carbon dioxide may not provide sufficient carbon
dioxide to
achieve the results obtained with the present system and method that utilize
carbon
dioxide taken from an industrial waste gas steam, e.g., from the stack gases
of a fossil
fuelled power generating plant or a cement production plant. Also, in some
embodiments
of the system and method, 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.
[0041] In some embodiments, and with reference to Figs. 5 -8, carbon dioxide
is added to
the cathode electrolyte to dissolve and produce carbonic acid that dissociates
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 from
electrolyzing
water in the cathode electrolyte, may react with the hydrogen ions to produce
water in the
cathode electrolyte. 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, and as illustrated in carbonate speciation
diagram of Fig.
5. 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.
[0042] Similarly, 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 as can be
appreciated
by one ordinarily skilled in the art and with reference to Fig. 6, 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
Nerst
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, in equivalent systems, 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
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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.
[0043] With reference to Fig. 7 and 8, in some embodiments, the anode
electrolyte 102 comprises a salt
solution that includes sodium ions and chloride ions; the system 700, 800 is
configured to produce the
alkaline solution in the cathode electrolyte 108 while also producing hydrogen
ions at the anode 106, with
less than 1V across the anode 122 and cathode 106, without producing a gas at
the anode; the system
700, 800 is configured to migrate hydrogen ions from the anode into the anode
electrolyte; the anode
electrolyte comprises an acid; the system 700, 800 is configured to produce
bicarbonate ions and/or .
carbonate ions in the cathode electrolyte 108; migrate hydroxide ions from the
cathode 106 into the
cathode electrolyte; migrate cations, e.g., sodium ions, from the anode
electrolyte 104 into the cathode
electrolyte through the first cation exchange membrane 116; hydrogen gas is
provided to the anode; and
a hydrogen gas delivery system 112 is configured to direct hydrogen gas from
the cathode to the anode.
[0044] With reference to Figs. 7 - 9, in some embodiments the cathode
electrolyte 108 may be
operatively connected to a system for further processing of the cathode
electrolyte, e.g., a carbonate
and/or bicarbonate precipitating system 912 comprising a precipitator
configured to precipitate carbonates
and/or bicarbonates from a solution, wherein in some embodiments the
carbonates and/or bicarbonates
comprise calcium and/or magnesium carbonate and/or bicarbonate. Also as
illustrated in Fig. 9, in some
embodiments, the anode electrolyte 104 comprising an acid, e.g., hydrochloric
acid, and a depleted salt
solution comprising low amount sodium ions, is operatively connected to a
system for further processing
of an acid, e.g., a mineral dissolution system 904 that is configured to
dissolve minerals and produce a
mineral solution comprising calcium ions and/or magnesium ions, e.g., mafic
minerals such as olivine and
serpentine. In some embodiments, not shown in Fig. 9, the acid may used for
other purposes in addition
to or instead of mineral dissolution. Such use includes use as a reactant in
production of cellulosic
biofules, use the production of polyvinyl chloride (PVC), and the like. System
appropriate to such uses
may be operatively connected to the electrochemistry unit, or the acid may be
transported to the
appropriate site for use.
[0045) In the some embodiments, the mineral dissolution system 904 is
operatively connected to nano-
filtration system 910 that is configured to separate sodium ions and chloride
ions from the mineral solution
comprising, e.g., calcium ions, magnesium ions, silica, hydrochloric acid
and/or sodium hydroxide. In
some embodiments, the nano-filtration system 910 is configured with a reverse
osmosis system 914 that
is capable of concentrating sodium ions and chloride ions into a salt solution
that is used as the anode
electrolyte 104.
[00461 With reference to Figs. 1 - 9, the method 1000 in some embodiments
comprises a step 1002 of
adding carbon dioxide into a cathode electrolyte 108 in contact with a cathode
106 wherein the cathode
electrolyte is separated from an anode electrolyte 104 by a first cation
exchange membrane 116; and
producing an alkaline solution in the cathode electrolyte by applying a
voltage 114 of less that 1V across
the cathode 106 and an anode 102 in contact with the anode electrolyte without
producing a gas at the
anode.
[0047] In some embodiments of the method 1000, the anode 102 is in contact
with a second cation
exchange membrane 122 that separates the anode from the anode electrolyte; the
alkaline solution 108
comprises hydroxide ions and/or bicarbonate ions and/or carbonate ions; the
carbon dioxide 107 is
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contained in wastes gases of an industrial plant, e.g., an electrical power
generating plant, a cement
= production plant, a fermentation process or an ore processing facility.
[0048] In some embodiments, by the method 1000, ambient air is excluded the
cathode electrolyte 108;
a pH of between and 7 and 14 or greater us maintained in the cathode
electrolyte; a pH of between 7 and
9 is maintained in the cathode electrolyte; a pH of between 8 and 11 is
maintained in the cathode
electrolyte; a pH of from less than 0 and up to 7 is maintained in the anode
electrolyte; a pH of from less
than 0 and up to 4.is maintained in the anode electrolyte; hydrogen gas is
oxidized at the anode 102 to
produce hydrogen ions and hydrogen ions are migrated from the anode through
the second cation
exchange membrane 122 into the anode electrolyte; hydroxide ions and hydrogen
gas are produced at
the cathode 106; hydroxide ions are migrated from the cathode 106 into the
cathode electrolyte 108;
hydrogen gas is directed from the cathode 106 to the anode 102; cations ions
are migrated from the
anode electrolyte 104 through the first cation exchange membrane 122 into the
cathode electrolyte 108
wherein the cations comprise sodium ions.
[0049] In some embodiments, the method 1000 comprises producing sodium
hydroxide and/or sodium
carbonate ions and/or sodium bicarbonate ions in the cathode electrolyte 108;
producing an acid and a
depleted salt solution in the anode electrolyte 104 comprising sodium ions and
chloride ions; utilizing the
anode electrolyte to dissolve minerals 904 and produce a mineral solution
comprising calcium ions and/or
magnesium ions, wherein the minerals comprises mafic minerals; filtering the
mineral solution 914 to
produce a filtrate comprising sodium ions and chloride ions; concentrating the
filtrate to produce the salt
solution, wherein the concentrator comprises a reverse osmosis system 914;
utilizing the salt solution as
the anode electrolyte 104; precipitating a carbonate and/or bicarbonate with
the cathode electrolyte 912;
wherein the carbonate and/or bicarbonate comprises calcium and/or magnesium
carbonate and/or
bicarbonate. In some embodiments, the method includes disposing of the acid in
an underground storage
site where the acid can be stored in an un-reactive salt or rock formation and
hence does not an
environmental acidification.
[0050] With reference to Figs. 1 ¨ 9, the method 1100 in another embodiment
comprises a step
1102 of producing an acid 124 in an electrochemical system, e.g., system 900,
comprising added carbon
dioxide 106A, 107 in the cathode electrolyte 108; and contacting a mineral 906
with the acid 124. In some
embodiment the method further producing the acid in the anode electrolyte 104,
without generating a gas
at the anode 102, and oxidizing hydrogen gas 112 at the anode, wherein the
acid comprises hydrochloric
acid 124; and wherein the hydrogen gas 112 is produced at the cathode 106;
producing an alkaline
solution in the cathode electrolyte 108; migrating sodium ions into the
cathode electrolyte; wherein the
alkaline solution comprises sodium hydroxide, sodium bicarbonate and/or sodium
carbonate; wherein the
voltage is less than 2 V or less than 1V; wherein the anode electrolyte 104 is
separated from the cathode
electrolyte 108 by first cation exchange membrane 116; wherein the anode 102
comprises a second
cation exchange membrane 122 in contact with the anode electrolyte 102;
wherein the anode electrolyte
comprises a salt, e.g., sodium chloride; dissolving a mineral 906 with the
acid 124 to produce a mineral
solution; producing calcium ions and/or magnesium ions; wherein the mineral
comprises a mafic mineral,
e.g.. olivine or serpentine; filtering the mineral solution to produce a
filtrate comprising sodium ions and
chloride ions solution; concentrating the filtrate to produce a salt solution;
utilizing the salt solution as the
anode electrolyte 104; precipitating a carbonate and/or bicarbonate with the
cathode electrolyte; wherein
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CA 02696086 2014-02-12
=
the carbonate and/or bicarbonate comprises calcium and/or magnesium carbonate
and/or
bicarbonate. In some embodiments, the method includes disposing of the acid in
an underground
storage site where the acid can be stored in an un-reactive salt or rock
formation and hence does
not an environmental acidification.
[0051] With reference to Figs. 1 -6, as disclosed in U.S. Patent Application
publication no. US
2010-0230293 Al filed on July 16,2009, titled; "CO2 Utilization In
Electrochemical Systems", in
some embodiments, carbon dioxide is absorbed into the cathode electrolyte
utilizing a gas
mixer/gas absorber. In one embodiment, 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.
[0052] 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. In some embodiments, the system includes a gas treatment
system that
removes constituents in the carbon dioxide gas stream before the gas is
utilized in the cathode
electrolyte. In some embodiments, a portion of, or the entire amount of,
cathode electrolyte
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 to increase the absorbed carbon dioxide content in the solution. In
some embodiments,
the solution enriched with carbon dioxide is returned to the cathode
compartment; in other
embodiments, the solution enriched with carbon dioxide is reacted with a
solution comprising
divalent cations to produce divalent cation hydroxides, carbonates and/or
bicarbonates. In some
embodiments, the pH of the cathode electrolyte 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 it can be
appreciated that the pH of the cathode electrolyte is determined, at least in
part, by the balance of
these two processes.
[0053] Referring to Fig.1 herein, the system 100 in one embodiment comprises a
gas diffusion
anode 102 and a cathode 106 in contact with a cathode electrolyte 108, 108A,
108B comprising
dissolved carbon dioxide 107A. The system in some embodiments includes a gas
delivery system
112 configured to deliver hydrogen gas to the anode 102; in some embodiments,
the hydrogen gas
is obtained from the cathode 106. In the system, the anode 102 is configured
to produce protons,
and the cathode 106 is configured to produce hydroxide ions and hydrogen gas
when a low
voltage 114, e.g., less than 2V is applied across the anode and the cathode.
In the system, a gas
is not produced at the anode 102.
[0054] In the system as illustrated in Fig. 1, first cation exchange membrane
116 is positioned
between the cathode electrolyte 108, 108A, 108B and a salt solution 118; and
an anion exchange
membrane 120 is positioned between the salt solution 118 and the anode
electrolyte 104 in a
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CA 02696086 2010-03-24
,
configuration where the anode electrolyte 104 is separated from the anode 102
by second cation
exchange membrane 122. In the system, the second cation exchange membrane 122
is positioned
between the anode 102 and the anode electrolyte 104 such that anions may
migrate from the salt solution
118 to the anode electrolyte 104 through the anion exchange membrane 120;
however, anions are
prevented from contacting the anode 102 by the second cation exchange membrane
122 adjacent to the
anode 102.
[0055] In some embodiments, the system is configurable to migrate
anions, e.g., chloride ions, from
the salt solution 118 to the anode electrolyte 104 through the anion exchange
membrane 120; migrate
cations, e.g., sodium ions from the salt solution 118 to the cathode
electrolyte 108, 108A, 108B through
the first cation exchange membrane 116; migrate protons from the anode 102 to
the anode electrolyte
104; and migrate hydroxide ions from the cathode 106 to the cathode
electrolyte 108, 108A, 108B. Thus,
in some embodiments, the system can be configured to produce sodium hydroxide
and/or sodium
bicarbonate and/or sodium carbonate in the cathode electrolyte 108, 108A,
108B; and produce an acid
e.g., hydrochloric acid 124 in the anode electrolyte.
[0056] In some embodiments as illustrated in Fig.1, the system comprises a
partition 126 that
partitions the cathode electrolyte 108 into a first cathode electrolyte
portion 108A and a second cathode
electrolyte portion 108B, wherein the second cathode electrolyte portion 108B,
comprising dissolved
carbon dioxide, contacts the cathode 106; and wherein the first cathode
electrolyte portion 108A
comprising dissolved carbon dioxide and gaseous carbon dioxide is in contact
with the second cathode
electrolyte portion108B under the partition 126. In the system, the partition
is positioned in the cathode
electrolyte such that a gas, e.g., carbon dioxide in the first cathode
electrolyte portion 108A is isolated
from cathode electrolyte in the second cathode electrolyte portion 108B. Thus,
for example, where a gas,
e.g., hydrogen, is generated at the cathode and it is desired to separate this
cathode gas from a gas or
vapor that may evolve from the cathode electrolyte, the partition may serve as
a means to prevent mixing
of the gases form the cathode and the gases and or vapor from the cathode
electrolyte. While this system
is illustrated in Fig. 1, it is applicable to any of the electrochemical
system described herein, e.g., the
systems illustrated in Figs. 4, 7 and 8.
[0057] Thus, as can be appreciated, in some embodiments, on applying the
present voltage across
the anode and cathode, the system can be configured to produce hydroxide ions
and hydrogen gas at the
cathode 106; migrate hydroxide ions from the cathode into the cathode
electrolyte 108, 1088, 108A;
migrate cations from the salt solution 118 to the cathode electrolyte through
the first cation exchange
membrane 116; migrate chloride ions from the salt solution 118 to the anode
electrolyte 104 through the
anion exchange membrane 120; and migrate protons from the anode 102 to the
anode electrolyte 104.
Hence, depending on the salt solution 118 used, the system can be configured
to produce an alkaline
solution, e.g., sodium hydroxide in the cathode electrolyte.
[0058] In some embodiments, the system is operatively connected to a
carbon dioxide gas/liquid
contactor 128 configured to remove cathode electrolyte from the system and
dissolve carbon dioxide in
the cathode electrolyte in the gas/liquid contactor before the cathode
electrolyte is returned to the system.
[0059] In other embodiments, the cathode electrolyte is operatively
connected to a system (not
shown) that is configured to precipitate divalent cation carbonates and/or
divalent cation bicarbonates
and/or divalent cation hydroxides from a solution comprising carbon dioxide
gas and divalent cations.
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CA 02696086 2010-03-24
[0060] Fig. 2 illustrates a schematic of a suitable gas diffusion anode
that can be used in
embodiments of the system described herein. In some embodiments, the gas
diffusion anode comprises a
conductive substrate 130 infused with a catalyst 136 that is capable of
catalyzing the oxidation of
hydrogen gas to protons when the present voltages are applied across the anode
and cathode. In some
embodiments, the anode comprises a first side 132 that interfaces with
hydrogen gas provided to the
anode, and an opposed second side 134 that interfaces with the anode
electrolyte 104. In some
embodiments, the portion of the substrate 132 that interfaces with the
hydrogen gas is hydrophobic and is
relatively dry; and the portion of the substrate 134 that interfaces with the
anode electrolyte 104 is
hydrophilic and may be wet, which facilitates migration of protons from the
anode to the anode electrolyte.
In various embodiments, the substrate is porous to facilitate the movement of
gas from the first side 132
to the catalyst 136 that may be located on second side 134 of the anode; in
some embodiments, the
catalyst may also be located within the body of the substrate 130. The
substrate 130 may be selected for
its hydrophilic or hydrophobic characteristics as described herein, and also
for its low ohmic resistance to
facilitate electron conduction from the anode through a current collector
connected to the voltage supply
114; the substrate may also be selected for it porosity to ion migration,
e.g., proton migration, from the
anode to the anode electrolyte 116.
[0061] In some embodiments, the catalyst may comprise platinum,
ruthenium, iridium, rhodium,
manganese, silver or alloys thereof. Suitable gas diffusion anodes are
available commercially, e.g., from
E-TEK (USA) and other suppliers. In some embodiments of the anode as is
illustrated in Fig. 8, the anode
comprises a ion exchange membrane, .e.g., a cation exchange membrane 122 that
contacts the second
side 134 of the anode. In such embodiments, the ion exchange membrane can be
used to allow or
prevent migration of ions to or from the anode. Thus, for example, with
reference to Fig. 8, when protons
are generated at the anode, a cation exchange membrane may be used to
facilitate the migration of the
protons from the anode and/or block the migration of ions, e.g., cations to
the substrate. In the some
embodiments, the ion exchange membrane may be selected to preferentially allow
passage of one type of
cation, e.g., hydrogen ions, while preventing the passage of another type of
ions, e.g., sodium ions.
[0062] As is illustrated in Fig.1, the system includes a salt solution
118 located between the anode
electrolyte 104 and the cathode electrolyte 108, 108A, 108B. In some
embodiments, the cathode
electrolyte is separated from the salt solution by a first cation exchange
membrane 116 that is allows
migration of cations, e.g., sodium ions, from the salt solution to the cathode
electrolyte. The first cation
exchange membrane 116 is also capable of blocking the migration of anions from
the cathode electrolyte
108, 108A, 1086 to the salt solution 118. In some embodiments, the anode
electrolyte 104 is separated
from the salt solution 118 by an anion exchange membrane 108 that will allow
migration of anions, e.g.,
chloride ions, from the salt solution 118 to the anode electrolyte 104. The
anion exchange membrane,
however, will block the migration of cations, e.g., protons from the anode
electrolyte 104 to the salt
solution 118.
[0063] With reference to Figs. 1 and 2, the system includes a hydrogen
gas supply system 112
configured to provide hydrogen gas to the anode 102. The hydrogen may be
obtained from the cathode
106 or may be obtained from external source, e.g., from a commercial hydrogen
gas supplier, e.g., at
start-up of the system when the hydrogen supply from the cathode is
insufficient. In the system, the
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CA 02696086 2014-02-12
hydrogen gas is oxidized to protons and electrons; un-reacted hydrogen gas is
recovered and
circulated 140 at the anode.
[0064] Referring to Fig. 1, in operation, the cathode electrolyte 108, 108A,
108B is initially charged
with a alkaline electrolyte, e.g., sodium hydroxide solution, and the anode
electrolyte 104 is initially
charged with an acidic electrolyte, e.g., dilute hydrochloric acid. The
cathode electrolyte is also
initially charged with carbon dioxide gas 107A, 128, and hydrogen gas is
provided to the anode. In
the system, on applying a voltage across the anode and cathode, protons
produced at the anode will
enter into the anode electrolyte and attempt to migrate from the anode
electrolyte 104 to the cathode
106 via the salt solution 118 between the cathode and anode. However, since
the anion exchange
membrane will block the migration of protons to the salt solution, the protons
will accumulate in the
anode electrolyte 104.
(0065) Simultaneously at the cathode 106, the voltage across the anode and
cathode will produce
hydroxide ions and hydrogen gas at the cathode. In some embodiments, the
hydrogen produced at
the cathode is recovered and directed to the anode 102 where it is oxidized to
protons. In the system,
hydroxide ions produced at the cathode 106 will enter into the cathode
electrolyte 108, 108A, 108B
from where they will attempt to migrate to the anode 102 via the salt solution
118 between the
cathode and anode. However, since the cathode electrolyte 108, 108A, 108B is
separated from the
salt solution electrolyte by the first cation exchange membrane 116 which will
block the passage of
anions, the first cation exchange membrane will block the migration of
hydroxide ions from the
cathode electrolyte to the salt solution; consequently, the hydroxide ions
will accumulate in the
cathode electrolyte 108, 108A, 108B.
[0066] In the system as illustrated in Fig. 1, with the voltage across the
anode and cathode, since the
salt solution is separated from the cathode electrolyte by the first cation
exchange membrane 116,
cations in the salt solution, e.g., sodium ions, will migrate through the
first cation exchange membrane
116 to the cathode electrolyte 108, 108A, 108B, and anions, e.g., chloride
ions, will migrate to the
anode electrolyte through the anion exchange membrane 120. Consequently, in
the system, as
illustrated in Fig. 1, an acid, e.g., hydrochloric acid 124 will be produced
in the anode electrolyte 104,
and alkaline solution, e.g., sodium hydroxide will be produced in the cathode
electrolyte. As can be
appreciated, with the migration of cations and anions from the salt solution,
the system in some
embodiments can be configured to produce a partly de-ionized salt solution
from the salt solution 118.
In some embodiments, this partially de-ionized salt solution can be used as
feed-water to a
desalination facility (not shown) where it can be further processed to produce
desalinated water as
described in commonly assigned U.S. Patent Application publication no. US 2009-
0001020A1 filed on
June 27, 2008; alternatively, the solution can be used in industrial and
agricultural applications where
its salinity is acceptable.
[0067] With reference to Fig. 1, the system in some embodiments includes a
second cation exchange
membrane 124, attached to the anode substrate 105, such that it separates the
anode 102 from the
anode electrolyte. In this configuration, as the second cation exchange
membrane 122 is permeable
to cations, protons formed at the anode will migrate to the anode electrolyte
as described herein;
however, as the second cation exchange membrane 122 is impermeable to anions,
anions, e.g.,
chloride ions, in the anode electrolyte will be blocked from migrating to the
anode 102, thereby
avoiding interaction between the anode and the anions that may interact with
the anode, e.g., by
corrosion.
[0068] With reference to Fig. 1, in some embodiments, the system includes a
partition 128 configured
into J-shape structure and positioned in the cathode electrolyte 108, 108A,
108B to define an
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CA 02696086 2010-03-24
upward-tapering channel 144 in the upper portion of the cathode electrolyte
compartment. The partition
also defines a downward-tapering channel 146 in lower portion of the cathode
electrolyte. Thus, with the
partition in the place, the cathode electrolyte 108 is partitioned into the
first cathode electrolyte portion
108A and a second cathode electrolyte portion 108B. As is illustrated in Fig.
1, cathode electrolyte in the
first cathode electrolyte portion 108A is in contact with cathode electrolyte
in the second cathode
electrolyte portion 108B; however, a gas in the first electrolyte portion
108A, e.g., carbon dioxide, is
prevented from mixing with cathode electrolyte in the second cathode
electrolyte 108B. Although this is
illustrated in for the system of Fig.1, such a configuration may be used in
any system where it is desired to
partition an electrolyte solution, e.g., a cathode electrolyte such that a gas
that is introduced into one
portion remains separate from another portion. For example, such a
configuration may be used in any
system as described herein as, e.g., in Figs. 7 and 8.
[0069] With reference to Fig.1, the system in some embodiments includes
a cathode electrolyte
circulating system 142 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
128 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 128.
[0070] In an alternative as illustrated in Fig. 4, the system comprises a
cathode 106 in contact with a
cathode electrolyte 108 and an anode 102 in contact with an anode electrolyte
104. In this system, the
cathode electrolyte comprises a salt solution that functions as the cathode
electrolyte as well as a source
of chloride and sodium ions for the alkaline and acid solution produced in the
system. In this system, the
cathode electrolyte is separated from the anode electrolyte by an anion
exchange membrane 120 that
allows migration of anions, e.g., chloride ions, from the salt solution to the
anode electrolyte. As is
illustrated in Fig. 4, the system includes a hydrogen gas delivery system 112
configured to provide
hydrogen gas to the anode. The hydrogen may be obtained from the cathode
and/or obtained from an
external source, e.g., a commercial hydrogen gas supplier e.g., at start-up of
operations when the
hydrogen supply from the cathode is insufficient. In some embodiments, the
hydrogen delivery system is
configured to deliver gas to the anode where oxidation of the gas is catalyzed
to protons and electrons. In
some embodiments, un-reacted hydrogen gas in the system is recovered and re-
circulated to the anode.
[0071] Referring to Fig. 4, as with the system of Fig. 1, on applying a
voltage across the anode and
cathode, protons produced at the anode from oxidation of hydrogen will enter
into the anode electrolyte
from where they will attempt to migrate to the cathode electrolyte across the
anion exchange membrane
120. However, since the anion exchange membrane120 will block the passage of
cations, the protons will
accumulate in the anode electrolyte. At the same time, however, the anion
exchange membrane 120
being pervious to anions will allow the migration of anions, e.g., chloride
ions from the cathode electrolyte
to the anode, thus in this embodiment, chloride ions will migrate to the anode
electrolyte to produce
hydrochloric acid in the anode electrolyte. In this system, the voltage across
the anode and cathode is
adjusted to a level such that hydroxide ions and hydrogen gas are produced at
the cathode without
producing a gas, e.g., chlorine or oxygen, at the anode. In this system, since
cations will not migrate from
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CA 02696086 2010-03-24
the cathode electrolyte across the anion exchange membrane 116, sodium ions
will accumulate in the
cathode electrolyte 108 to produce an alkaline solution with hydroxide ions
produced at the cathode. In
embodiments where carbon dioxide gas is dissolved in the cathode electrolyte,
sodium ions may also
produce sodium bicarbonate and or sodium carbonate in the cathode electrolyte
as described herein with
reference to Fig.1.
[0072] With reference to Fig. 1, depending on the pH of the cathode
electrolyte, carbon dioxide gas
introduced into the first cathode electrolyte portion 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:
CO2 + H20 <==> H2CO3 <==> H+ + HCO3- <==> H+ + C032
Inthe system, as cathode electrolyte in the first cathode electrolyte portion
108A may mix with second
cathode electrolyte portion 108B, the carbonic acid, bicarbonate and carbonate
ions formed in the first
cathode electrolyte portion 108A by absorption of carbon dioxide in the
cathode electrolyte may migrate
and equilibrate with cathode electrolyte in the second cathode electrolyte
portion 108B. Thus, in some
embodiments, first cathode electrolyte portion 108A 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 108B may comprise dissolved carbon dioxide, and/or
carbonic acid, and/ or
bicarbonate ions and/or carbonate ions.
[0073] With reference to Fig. 1, on applying a voltage across anode 102
and cathode 108, the
system 100 may produce hydroxide ions and hydrogen gas at the cathode from
water, as follows:
2H20 + 2e- = H2 + 20H
As cathode electrolyte in first cathode electrolyte portion 108A can intermix
with cathode electolyte in
second cathode electrolyte portion 108B, hydroxide ions formed in the second
cathode electrolyte portion
may migrate and equilibrate with carbonate and bicarbonate ions in the first
cathode electrolyte portion
108A. 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 104 is either:
Scenario 1: 2H20 + 2CO2 + 2e- = H2 + 2HCO3- ; or
Scenario 2: H20 + CO2 + 2e- = H2 + C032
ora combination of both, depending on the pH of the cathode electrolyte. This
is illustrated in as a
arbonate speciation diagram in Fig. 5.
[0074] For either scenario, the overall cell potential of the system can
be determined through the
Gibbs energy change of the reaction by the formula:
Ecell = -AG/nF
Or, at standard temperature and pressure conditions:
Ecell = -AG /nF
where, Eco is the cell voltage, AG is the Gibbs energy of reaction, n is the
number of electrons
transferred, and F is the Faraday constant (96485 J/Vmol). The Eco of each of
these reactions is pH
dependent based on the Nernst equestion as illustrated in Fig.6.
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CA 02696086 2010-03-24
[0075] Also, for either scenario, the overall cell potential can be
determined through the combination
of Nernst equations for each half cell reaction:
E = ¨ R T In(Q) / n F
where, E is the standard reduction potential, R is the universal gas
constant, (8.314 J/mol K) T is the
absolute temperature, n is the number of electrons involved in the half cell
reaction, F is Faraday's
constant (96485 JN mol), and Q is the reaction quotient such that:
Etas! = Ecathode Eanode=
When hydrogen is oxidized to protons at the anode as follows:
H2 = 2H+ + 2e-,
E is 0.00 V, n is 2, and Q is the square of the activity of H+ so that:
Eanode = +0.059 pHa,
where pHa is the pH of the anode electrolyte.
When water is reduced to hydroxide ions and hydrogen gas at the cathode as
follows:
2H20 + 2e- = H2 + 20H-,
E is -0.83 V, n is 2, and Q is the square of the activity of OH- so that:
Ecathode = -0.059
where plic is the pH of the cathode electrolyte.
[0076] For either Scenario, the E for the cathode and anode reactions
varies with the pH of the
anode and cathode electrolytes. Thus, for Scenario 1 if the anode reaction,
which is occurring in an acidic
environment, is at a pH of 0, then the E of the reaction is OV for the half
cell reaction. For the cathode
reaction, if the generation of bicarbonate ions occur at a pH of 7, then the
theoretical E is 7 x (-0.059 V) =
-0.413V for the half cell reaction where a negative E means energy is needed
to be input into the half cell
or full cell for the reaction to proceed. Thus, if the anode pH is 0 and the
cathode pH is 7 then the overall
cell potential would be -0.413V, where:
Etotal = -0.059 (pHa - pH) = -0.059 ApH.
[0077] For Scenario 2 in which carbonate ions are produced, if the anode
pH is 0 and the cathode
pH is 10, this would represent an E of 0.59 V.
[0078] Thus, in some embodiments, directing CO2 gas into the cathode
electrolyte may lower the pH
of the cathode electrolyte by producing bicarbonate ions and/or carbonate ions
in the cathode electrolyte,
which consequently may lower the voltage across the anode and cathode in
producing hydroxide,
carbonate and/or bicarbonate in the cathode electrolyte.
[0079] Thus, as can be appreciated, if the cathode electrolyte is
allowed to increase to a pH of 14 or
greater, the difference between the anode half-cell potential (represented as
the thin dashed horizontal
line, Scenario 1, above) and the cathode half cell potential (represented as
the thick solid sloping line in
Scenario 1, above) will increase to 0.83V. With increased duration of cell
operation without CO2 addition
or other intervention, e.g., diluting with water, the required cell potential
will continue to increase. The cell
potential may also increase due to ohmic resistance loses across the membranes
in the electrolyte and
the cell's overvoltage potential.
[0080] Herein, an overvoltage potential refers to the voltage difference
between a thermodynamically
determined half-cell reduction potential, and the experimentally observed
potential at which the redox
reaction occurs. The term is related to a cell voltage efficiency as the
overvoltage potential requires more
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CA 02696086 2010-03-24
energy than is thermodynamically required to drive a reaction. In each case,
the extra energy is lost as
heat. Overvoltage potential is specific to each cell design and will vary
between cells and operational
conditions even for the same reaction.
[0081] In embodiments wherein it is desired to produce bicarbonate
and/or carbonate ions in the
cathode electrolyte, the system as illustrated in Figs. 1-2, 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 first cathode electrolyte by dissolving carbon
dioxide in the first 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] With reference to Figs.1-2, in some embodiments, the invention
provides for a system
comprising one or more anion exchange membrane 120, and cation exchange
membranes 116, 122
located between the gas diffusion anode 102 and the cathode 106. 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 C to 100 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 C to 80 C, or 0 C
to 90 C, but not stable
above these ranges may be used. 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,
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CA 02696086 2014-02-12
e.g., several days, weeks or months or years at temperatures in the range of 0
C to 80 C, or 0 C to
90 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 C, 70 C, 60 C, 50 C, 40 C, 30 C, 20 C, 10 C, 5
C and more or less.
[0086] 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.
[0087] Scattered through currently available membrane are ionic channels
consisting of acid groups.
These ionic channels may extend from the internal surface of the matrix to the
external surface and
the acid groups may readily bind water in a reversible reaction as water-of-
hydration. This binding of
water as water-of-hydration follows first order reaction kinetics, such that
the rate of reaction is
proportional to temperature. Consequently, currently available membranes can
be selected to provide
a relatively low ohmic and ionic resistance while providing for improved
strength and resistance in the
system for a range of operating temperatures. Suitable membranes are
commercially available from
Asahi Kasei of Tokyo, Japan; or from Membrane International of Glen Rock, NJ,
and USA.
[0088] In some embodiments, the cathode electrolyte 108, 108A, 108B is
operatively connected to a
waste gas treatment system (not illustrated) 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
publication no. US 2009-0169452A1 filed on December 24, 2008. 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 publication no. US 2009-0020044A1 filed on May
23,2008, supra. 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.
[0089] In some embodiments, the cathode and anode are also operatively
connected to an off-peak
electrical power-supply system 114 that supplies off-peak voltage to the
electrodes. 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.
[0090] In another embodiment, the system produces an acid, e.g., hydrochloric
acid 124 in the anode
electrolyte 104. In some embodiments, the anode compartment is operably
connected to a system for
dissolving minerals and/or waste materials comprising divalent cations to
produce a solution of
divalent cations, e.g., Ca++ and Mg++. In some embodiments, the divalent
cation solution is utilized
to precipitate hydroxides, carbonates and/or bicarbonates by contacting the
divalent cation solution
with the present
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CA 02696086 2014-02-12
=
alkaline solution and a source of carbon dioxide gas as described in US Patent
Application
publication no. US 2009-0169452A1 filed on December 24,2008, supra. In some
embodiments, the
precipitates are used as building materials e.g., cement and aggregates as
described in commonly
assigned U.S. Patent Application publication no. US 2009-0020044 Al.
[0091] With reference to Fig. 1, on applying a voltage across the anode 102
and cathode 106,
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:
H2 = 2H, + 2e- (anode, oxidation reaction)
2H20 + 2e- = H2 + 20H- (cathode, reduction reaction)
[0092] 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, 1AV, 1.3V, 1.2V, 1.1V, 1.0V, 0.9V, 0.8V, 0.7V, 0.6V, 0.5V, OAV, 0.3V,
0.2V, 0.1 V or less is
applied across the anode and cathode.
[0093] As discussed above, in the system, on applying a voltage across the
anode 102 and cathode
106, the positively charged protons formed at the anode will attempt to
migrate to the cathode
through the anode electrolyte 104, while the negatively charged hydroxide ions
formed at the cathode
will attempt to migrate to the anode through the cathode electrolyte 108,
108A, 108B. As is illustrated
in Fig. 1 and with reference to hydroxide ions in the cathode electrolyte 108,
108A, 108B, since the
first cation exchange membrane 116 will restrict the migration of anions from
the cathode electrolyte
108, 108A, 108B, and since the anion exchange membrane 120 will prevent the
migration of anions
from the anode electrolyte 104 to the salt solution 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.
[0094] In some embodiments, depending on the ionic species desired in cathode
electroyte 108,
108A, 108B and/or the anode electolyte 104 and/or the salt solution 118,
alternative reactants can be
utilized. Thus, for example, if a potassium salt such as potassium hydroxide
or potassium carbonate
is desired in the cathode elelctolyte 108, 108A, 108B, then a potassium salt
such as potassium
chloride can be utilized in the salt solution 118. Similarly, if sulfuric acid
is desired in the anode
electrolyte, then a sulfate such as sodium sulfate can be utilized in the salt
solution 118. 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
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CA 02696086 2014-10-20
. .
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.
[0095] With reference to Fig. 1 method 300 in some embodiments comprises
a step 302 of
applying a voltage across a cathode 106 and a gas diffusion anode 102 in an
electrochemical system 100,
wherein the cathode contacts a cathode electrolyte comprising dissolved carbon
dioxide. In some
embodiments, the method includes a step of providing hydrogen to the gas
diffusion anode 102; a step of
contacting the cathode 106 with a cathode electrolyte 108, 108A, 1086
comprising dissolved carbon
dioxide gas 107A; and a step of applying a voltage 114 across the anode and
cathode; a step whereby
protons are produced at the anode and hydroxide ions and hydrogen gas produced
at the cathode; a step
whereby a gas is not produced at the anode when the voltage is applied across
the anode and cathode; a
step wherein the voltage applied across the anode and cathode is less than 2V;
a step comprising
directing hydrogen gas from the cathode to the anode; a step comprising
whereby protons are migrated
from the anode to an anode electrolyte; a step comprising interposing an anion
exchange membrane
between the anode electrolyte and the salt solution; a step comprising
interposing a first cation exchange
membrane between the cathode electrolyte and the salt solution, wherein the
salt solution is contained
between the anion exchange membrane and the first cation exchange membrane; a
step comprising
whereby anions migrate from the salt solution to the anode electrolyte through
the anion exchange
membrane, and cations migrate from the salt solution to the cathode
electrolyte through the first cation
exchange membrane; a step comprising producing hydroxide ions and/or carbonate
ions and/or
bicarbonate ions in the cathode electrolyte; a step comprising producing an
acid in the anode electrolyte;
a step comprising producing sodium hydroxide and/or sodium carbonate and/or
sodium bicarbonate in the
cathode electrolyte; a step whereby hydrochloric acid is produced in the anode
electrolyte; a step
comprising contacting the cathode electrolyte with a divalent cation solution,
wherein the divalent cations
comprise calcium and magnesium ions; a step comprising producing partially
desalinated water from the
salt solution; a step comprising withdrawing a first portion of the cathode
electrolyte and contacting the
first portion of cathode electrolyte with carbon dioxide; and a step
comprising contacting the first portion of
cathode electrolyte with a divalent cation solution.
[0096] In some embodiments, hydroxide ions are formed at the cathode 106
and in the cathode
electrolyte 108, 108A, 1088 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 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
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CA 02696086 2010-03-24
other method know in the art, hydroxide ions can be produced in the cathode
electrolyte with the present
lower voltages.
[0097] In some embodiments, hydroxide ions, bicarbonate ions and
carbonate ions are produced in
the cathode electrolyte where the voltage applied across the anode and cathode
is less than 3.0V, 2.9V,
2.8V, 2.7V, 2.6V, 2.5V, 2.4V, 2.3V, 2.2V, 2.1V, 2.0V, 1.9V, 1.8V, 1.7V, 1.6V,
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, 0.1V or less without
forming a gas at the anode. In
some embodiments, the method is adapted to withdraw and replenish at least a
portion of the cathode
electrolyte and the acid in the anode electrolyte back into the system in
either a batch, semi-batch or
continuous mode of operation.
[0098] In an exemplarary embodiment, a system configured substantially as
illustrated in Figs. 1 and
2 was operated with a constant current density applied across the electrodes
at steady state conditions
while carbon dioxide gas was continuously dissolved into the cathode
electrolyte, at various temperatures
and voltages. In the system, a platinum catalyst, gas diffusion anode obtained
from E-TEK Corporation,
(USA) was used as the anode. A Raney nickel deposited onto a nickel gauze
substrate was used as the
cathode. In the system, the initial acid concentration in the anode
electrolyte was 1 M; the initial sodium
chloride salt solution was 5 M; and the initial concentration of the sodium
hydroxide solution in the
cathode compartment was 1 M. In the system, the pH of the cathode compartment
was maintained at
either 8 or 10 by regulating the amount of carbon dioxide dissolved in the
cathode electrolyte.
Table 1: Experimental Current Density, Temperature and Voltage Characteristics
of the System
T ( C) Potential (V) pH Current density
(mNcm2)
0.8 10 8.6
8 11.2
1.2 10 28.3
8 29.2
1.6 10 50.2
8 50.6
75 0.8 10 13.3
8 17.8
1.2 10 45.3
8 49.8
1.6 10 80.8
8 84.7
[0099] As is illustrated in Table 1, a range of current densities was
achieved across the electrode in
the system. As will be appreciated by one ordinarily skilled in the art, the
current density that can be
achieved with other configurations of the system may vary, depending on
several factors including the
cumulative electrical resistance losses in the cell, environmental test
conditions, the over-potential
associated with the anodic and cathodic reactions, and other factors.
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CA 02696086 2010-03-24
[00100] It will also be appreciated that the current densities achieved
in the present configuration and
as set forth in Table 1 are correlated with the production of hydroxide ions
at the cathode, and thus are
correlated with the production of sodium hydroxide and/or sodium carbonate
and/or sodium bicarbonate in
the cathode electrolyte, as follows. With reference to Table 1, at 75 C, 0.8 V
and a pH of 10, each cm2 of
electrode passed 13.3 mA of current, where current is a measure of charge
passed (Coulomb) per time
(second). Based on Faraday's Laws, the amount of product, e.g., hydroxide
ions, produced at an
electrode is proportional to the total electrical charge passed through the
electrode as follows:
n = (I *t) / (F * z)
where n is moles of product, I is a current, t is time, F is Faraday's
constant, and z is the electrons
transferred per product ionic species (or reagent ionic species). Thus, based
on the present example,
1.38x10-4 moles of hydroxide ions are produced per second per cm2 of
electrode, which is correlated with
the production of sodium hydroxide in the cathode electrolyte. In the system
the production rate of NaOH
dictates the production rate of NaHCO3 and Na2CO3 through Le Chatelier's
principle following the net
chemical equilibria equations of
H2CO3 + OH- = H20 + HCO3-
and HCO3- + OH- = H20 + C032-,
where an increase in concentration of one species in equilibria will change
the concentration of all species
so that the equilibrium product maintains the equilibrium constant. Thus, in
the system, the equilibrium
concentrations of H2CO3, HCO3-, and C032- vs. pH in the electrolyte will
follow the carbonate speciation
diagram as discussed above.
[00101] In the system as illustrated in Fig. 1 and as discussed with
reference to the carbonate
speciation graph, supra, 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 speciation 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.
[00102] In another embodiment, the present system and method are
integrated with a carbonate
and/or bicarbonate precipitation system (not illustrated) wherein a solution
of divalent cations, when
added to the present cathode electrolyte, causes formation of precipitates of
divalent carbonate and/or
bicarbonate compounds, e.g., calcium carbonate or magnesium carbonate and/or
their bicarbonates. In
some embodiments, the precipitated divalent carbonate and/or bicarbonate
compounds may be utilized as
building materials, e.g., cements and aggregates as described for example in
commonly assigned U.S.
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CA 02696086 2014-02-12
Patent Application publication no. US 2009-0020044 Al filed on May 23,2008.
[00103] In an alternative embodiment, the present system and method are
integrated with a mineral
and/or material dissolution and recovery system (not illustrated) wherein the
acidic anode electrolyte
solution 104 or the basic cathode electrolyte 108 is utilized to dissolve
calcium and/or
magnesium-rich minerals e.g., serpentine or olivine, or waste materials, e.g.,
fly ash, red mud and the
like, to form divalent cation solutions that may be utilized, e.g., to
precipitate carbonates and/or
bicarbonates as described herein. In some embodiments, the precipitated
divalent carbonate and/or
bicarbonate compounds may be utilized as building materials, e.g., cements and
aggregates as
described for example in commonly assigned U.S. Patent Application publication
no. US
2009-0020044 Al, filed on May 23,2008.
[00104] In an alternative embodiment, the present system and method are
integrated with an
industrial waste gas treatment system (not illustrated) for sequestering
carbon dioxide and other
constituents of industrial waste gases, e.g., sulfur gases, nitrogen oxide
gases, metal and
particulates, wherein by contacting the flue gas with a solution comprising
divalent cations and the
present cathode electrolyte comprising hydroxide, bicarbonate and/or carbonate
ions, divalent cation
carbonates and/or bicarbonates are precipitated as described in commonly
assigned U.S. Patent
Application publication no. US 2009-0169452 Al filed on December 24, 2008. The
precipitates,
comprising, e.g., calcium and/or magnesium 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 publication no. US 2009-0020044 Al filed on
May 23, 2008.
[00105] In another embodiment, the present system and method are integrated
with an aqueous
desalination system (not illustrated) wherein the partially desalinated water
of the third electrolyte of
the present system is used as feed-water for the desalination system, as
described in commonly
assigned U.S. Patent Application publication no. US 2009-0001020 Al filed on
June 27, 2008.
[00106] In an alternative embodiment, the present system and method are
integrated with a
carbonate and/or bicarbonate solution disposal system (not illustrated)
wherein, rather than producing
precipitates by contacting a solution of divalent cations with the first
electrolyte solution to form
precipitates, the system produces a solution, slurry or suspension comprising
carbonates and/or
bicarbonates. In some embodiments, the solution, slurry or suspension is
disposed of in a location
where it is held stable for an extended periods of time, e.g., the
solution/slurry/suspension is disposed
in an ocean at a depth where the temperature and pressure are sufficient to
keep the slurry stable
indefinitely, as described in U.S. Patent Application publication no. US 2009-
0169452 Al filed on
December 24,2008; or in a subterranean site.
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