Note: Descriptions are shown in the official language in which they were submitted.
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LOW-VOLTAGE ALKALINE PRODUCTION FROM BRINES
BACKGROUND
[00021 In many chemical processes an alkaline solution comprising, e.g.,
hydroxide ions and/or carbonate ions and/or bicarbonate ions is utilized 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. An alkaline solution can be produced by an
electrochemical system that converts an aqueous salt solution to the alkaline
solution and an acid as described in US Provisional patent application
61/151,470 filed February 10, 2009, available on USPTO Public PAIR.
However, as the process is very energy intensive, a large amount of electrical
energy is consumed; also, large amounts of salt and water are consumed.
Consequently, lowering the energy and material consumed are very desirable.
SUMMARY
[00031 This invention provides for a low-voltage, low-energy electrochemical
system and method of producing an alkaline solution, comprising reducing
water at the cathode to hydroxide ions and hydrogen gas, and allowing the
hydroxide ions to migrate into the cathode electrolyte to produce the alkaline
solution. By the system and method, at the anode, hydrogen gas is oxidized to
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protons without producing a gas at the anode, and the protons are allowed to
migrate into the anode electrolyte or an adjacent electrolyte to produce an
acid. In some embodiments, the alkaline solution further comprises
bicarbonate ions and/or carbonate ions produced by adding carbon dioxide to
the cathode electrolyte. In some embodiments, the alkaline solution is
produced by applying less than 3V across the anode and cathode. In some
embodiments, hydrogen gas produced at the cathode is recovered and
directed to the anode where it is reduced to protons.
[0004] In some embodiments, a brine, e.g., subterranean brine, is utilized as
1o a source of salt used in producing the alkaline solution; and, in some
embodiments, an ion-depleted brine is produced.
[0005] In one embodiment, the system comprises an electrochemistry unit
comprising a hydrogen-oxidizing anode in communication with a cathode
electrolyte; wherein the electrochemistry unit is operably connected to a
carbon sequestration system configured to sequester carbon dioxide with the
cathode electrolyte.
[0006] In another embodiment, the system comprises a hydrogen-oxidizing
anode in communication with a cathode electrolyte comprising bicarbonate
ions; and a brine production system configured to provide cations to the
cathode electrolyte.
[00071 In some embodiments of the system, the cathode electrolyte
comprises added carbon dioxide and, in some embodiments, the cathode
electrolyte comprises hydroxide ions and/or bicarbonate ions and/or carbonate
ions.
[0008] In some embodiments, the system comprises cation and anion
exchange membranes configured to separate cations and anions from the
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brine to produce an ion-depleted brine; in some embodiments, the ions
comprises sodium ions and chloride ions.
100091 In some embodiments, the system is configured to produce hydrogen
gas and hydroxide ions at a cathode in contact with the cathode electrolyte,
and oxidize hydrogen gas to protons at an anode in contact with an anode
electrolyte without producing a gas at the anode, when a voltage is applied
across the anode and cathode. In some embodiments, the voltage is less than
3V.
[0010 In some embodiments, the system is configured to produce an acid in
to the anode electrolyte; in some embodiments, the acid comprises hydrochloric
acid.
[00111 In some embodiments, the system comprises an acid dissolution
system configured to produce divalent cations with the acid; in some
embodiments, the divalent cations comprise calcium ions and/or magnesium
ions.
[00121 In some embodiments, the system comprises a carbon sequestration
system configured to sequester carbon dioxide with the cathode electrolyte; in
some embodiments, the carbon dioxide is contained in an industrial waste
gas. In some embodiments, the carbon dioxide is sequestered as carbonates
and/or bicarbonates; in some embodiments, the carbonates and/or
bicarbonates comprise divalent cations, for example, calcium ions and/or
magnesium ions.
[0013] In some embodiments, the system comprises a water treatment
system configured to produce water for use in generating hydrogen gas and
hydroxide ions at the cathode. In some embodiments, the water treatment
system is configured to adjust the pH of electrolytes and acids in the system;
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and, in some embodiments, the water treatment system is configured to adjust
the ionic concentration of electrolytes and acids in the system.
100141 In some embodiments, the system comprises a desalination system
configured to produce desalinated water from the depleted brine; in some
embodiments, the desalinated water is operatively connected to the water
treatment system.
[00151 In another embodiment, the method provides for a low-voltage, low
energy electrochemical method of producing an alkaline solution comprising,
oxidizing hydrogen gas to protons at a hydrogen-oxidizing anode in
io communication with a cathode electrolyte comprising bicarbonate ions; and
providing cations to the cathode electrolyte from a brine.
100161 In another embodiment, the method comprises oxidizing hydrogen to
protons at a hydrogen-oxidizing anode in communication with a cathode
electrolyte; and sequestering carbon dioxide with the cathode electrolyte
[00171 In some embodiments, the cations comprise sodium ions. In some
embodiments, the method comprises adding carbon dioxide to the cathode
electrolyte. In some embodiments, the method comprises producing hydrogen
gas and hydroxide ions at a cathode in contact with the cathode electrolyte
without producing a gas at the anode, by applying a voltage across the anode
and cathode. In some embodiments, the voltage is less than 3V.
100181 In some embodiments of the method, the cathode electrolyte
comprises hydroxide ions and/or carbonate ions and/or bicarbonate ions; and
in some embodiments, the method comprises separating cations and anions
from the brines to produce an ion-depleted brine.
100191 In some embodiments, the method comprises producing an acid in
the cathode electrolyte; in some embodiments, the acid comprises
hydrochloric acid.
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[00201 In some embodiments, the method comprises using the acid in an
acid dissolution system to dissolve material and produce divalent cations; in
some embodiments, the divalent cations comprise calcium ions and/or
magnesium ions.
[00211 In some embodiments, the method comprises configuring a carbon
sequestration system to sequester carbon dioxide with the cathode electrolyte.
In some embodiments, the carbon dioxide is contained in an industrial waste
gas; in some embodiments, the carbon dioxide is sequestered as carbonates
and/or bicarbonates; in some embodiments, the carbonates and/or
1o bicarbonates comprise divalent cations.
[00221 In some embodiments, the method comprises using a water
treatment system to dilute the cathode and anode electrolytes, the brine and
the acid; in some embodiments of the method, hydrogen gas and hydroxide
ions are generated at the cathode by reducing water at the cathode.
[0023] In some embodiments, the method comprises adjusting the pH of the
cathode and anode electrolytes, the brine and the acid with the water; in some
embodiments, the method comprises adjusting the ionic concentration in the
anode and cathode electrolytes, the brine and the acid with the water.
[0024] In some embodiment, the method comprises producing desalinated
water from the ion-depleted brine; in some embodiments, the desalinated
water is operatively connected for use in the water treatment system.
[00251 In various embodiments, the products comprise sodium hydroxide
and/or sodium bicarbonate, hydrochloric acid and an ion-depleted brine from
which certain cation and anions have been removed. In some embodiments,
the products are utilized to sequester carbon dioxide and other constituents
of
industrial waste gases, e.g., sulfur gases, nitrogen oxide gases and other
combustion gases, by contacting the waste gas with a solution comprising
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divalent cations and the hydroxide and/or bicarbonate and/or carbonate to
precipitate carbonates and/or bicarbonates as described in commonly
assigned U.S. Patent Application no. 12/344,019 filed on December 24, 2008,
U.S. Publication no. 2009/0169452. The precipitates, comprising, e.g., calcium
and/or magnesium carbonates and/or bicarbonates in various embodiments
are utilized as building materials, e.g., as cements and aggregates, as
described in commonly assigned U.S. Patent 7,735,274.
[00261 In another application, the ion-depleted brine from which certain
cation and anions have been removed, e.g., sodium and chloride ions, is used
io as feed water in a desalination system where the water is further processed
as described in commonly assigned U.S. Patent 7,744,761.
[00271 In another embodiment, the acid produced in the anode electrolyte
and/or the alkaline solution produced in the cathode electrolyte are utilized
to
dissolve minerals and waste materials comprising divalent cations, e.g., Ca++
and Mg++ to produce divalent cation solutions that are utilized in producing
divalent metal ion carbonate precipitates using the cathode electrolyte. In
various embodiments, the precipitates are used as building materials, e.g.,
cement and aggregates as described in commonly assigned U.S. Patent
7,735,274.
10028] 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 gas generated at the cathode is oxidized
to protons at the anode without producing a gas at the anode, a relatively low
energy is utilized to produce the alkaline solution. Also, by the system and
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method, since carbon dioxide from industrial waste gases is utilized to
produce the alkaline solution, the system and method is utilized to sequester
large amounts of carbon dioxide and thus reduce carbon dioxide emissions
into the atmosphere. Similarly, the acid produced is utilized in various ways
including dissolving materials, e.g., minerals and biomass to produce cations
for use in the system.
[0029]
BRIEF DESCRIPTION OF THE DRAWINGS
The following are brief descriptions of drawings that illustrate
to embodiments of the invention:
[0030] Fig. 1 is an illustration of an embodiment of the system.
[0031] Fig. 2 is an illustration of an embodiment of the anode system.
[0032] Fig. 3 is an illustration of an embodiment of the method.
[0033] Fig. 4 is an illustration of an embodiment of the system.
[0034] Fig. 5 is an illustration of carbonate ion/bicarbonate ion speciation
in
water.
[0035] Fig. 6 is an illustration of an effect of adding carbon dioxide to the
cathode electrolyte.
[0036] Fig. 7 is an illustration of an embodiment of the system.
[0037] Fig. 8 is a flow chart of an embodiment of the system.
[0038] Fig. 9 is an illustration of an embodiment of the brine system.
[0039] Fig. 10 is an illustration of an embodiment of the brine system.
[0040] Fig. 11 is an illustration of an embodiment of the brine system.
[0041] Fig. 12 is an illustration of an embodiment of the brine system.
[0042] Fig. 13 is an illustration of an embodiment of the brine system.
[0043] Fig. 14 is an illustration of an embodiment of the brine system.
[0044] Fig. 15 is an illustration of an embodiment of the brine system.
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DETAILED DESCRIPTION
[00451 This invention provides for a low-voltage/low-energy system and
method of producing an alkaline solution in an electrochemical system by
oxidizing hydrogen at the anode to protons, and reducing water at the cathode
to hydroxide ions and hydrogen at the cathode. In some embodiments, carbon
dioxide is added to the cathode electrolyte to produce carbonate ions and/or
bicarbonate ions in the cathode electrolyte; a gas is not produced at the
anode. In some embodiments, an alkaline solution comprising, e.g., sodium
1o hydroxide and/or sodium carbonate and/or sodium bicarbonate is produced in
the cathode electrolyte by applying a voltage across the anode and cathode.
In some embodiments, the volts is less than 3V. In some embodiments,
subterranean brine is utilized as a source of salt/cations/anions used in
producing the alkaline solution.
[00461 In some embodiments, an acid, e.g., hydrochloric acid, is produced in
the anode electrolyte from hydrogen ions, produced at the anode and
migrated from the anode into the anode, and cations in the cations in the
electrolyte, e.g., chloride ions.
[0047] In some embodiments, the acid is utilized to dissolve a material, e.g.,
a mineral, e.g., serpentine or olivine, to provide divalent cation solution,
e.g.,
calcium and magnesium ions, 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, sodium chloride solution is used as the anode
electrolyte.
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[00481 In some embodiments, on applying a voltage across the anode and
cathode, cations, e.g., sodium ions in the anode electrolyte, migrate from the
salt solution through a cation exchange membrane into the cathode electrolyte
to produce an alkaline solution comprising, e.g., sodium hydroxide and/or
sodium carbonate and/or sodium bicarbonate in the cathode electrolyte;
concurrently, anions in the salt solution, e.g., chloride ions, migrate into
the
anode electrolyte to produce an acid, e.g., hydrochloric acid, with in the
protons that form at the anode.
[00491 In some embodiments, hydrogen gas and hydroxide ions are
to 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.
[00501 As can be appreciated by one ordinarily skilled in the art, since the
embodiments herein can be configured with an alternative or equivalent salt,
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 alternative acid, e.g.,
sulfuric
acid in the anode electrolyte, by applying the voltage herein across the anode
and cathode, the invention is not limited to the exemplarary embodiments
described herein, but is useable with an equivalent salt, 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. Accordingly, to the extent that such
equivalents
are based on or are suggested by the embodiment herein, these equivalents
are within the scope of the appended claims.
[00511 In the following detailed description, embodiments of the system and
method are described with reference to the one or more illustrated Figures.
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However, it should be understood that this description is illustrative and is
not
restrictive since the invention is adaptable for use with other cell
configurations including a one-cell, a two-cell, three-cell and other multi-
cell
configurations, not described in detail herein but are reasonably
contemplated.
[00521 Similarly, it should be understood that although the invention is
described with particularity with use of a brine comprising sodium ions and
chloride ions, this description also is also illustrative and not restrictive
since
the invention is adaptable for use with equivalent aqueous salt, e.g.,
sulfates
and nitrates and like, e.g., potassium sulfate, as can be appreciated by those
ordinarily skilled in the art.
[00531 With reference to Figs. 1 - 15, in some embodiments, carbon dioxide
is added to 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.
[00541 The carbon dioxide added to the cathode electrolyte may be obtained
from various industrial sources that release 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
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vaporized materials.
[00551 In some embodiments, the system includes a gas treatment system
that removes constituents in the carbon dioxide gas stream before the carbon
dioxide 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
to 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.
100561 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.
[0057 Referring to Fig.1, 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 hydrogen 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
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than 2V is applied across the anode and the cathode. In the system, a gas is
not produced at the anode 102.
[0058] As is illustrated in Fig. 1, first cation exchange membrane 116 is
positioned between the cathode electrolyte 108, 108 A, 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 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
1o 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.
[00591 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.
[00601 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,
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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
to gas or vapor that may evolve from the cathode electrolyte, the partition
may
serve as a means to prevent mixing of the gases from 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.
[0061] Thus, 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, 108B, 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.
[00621 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
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electrolyte in the gas/liquid contactor before the cathode electrolyte is
returned
to the system.
[00631 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.
[00641 Fig. 2 illustrates a schematic of a suitable gas diffusion anode that
can be used in embodiments of the system described herein. In some
to 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.,
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t t
proton migration, from the anode to the anode electrolyte 116.
[00651 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
1o 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.
[00661 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, 108B
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,
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will block the migration of cations, e.g., protons from the anode electrolyte
104
to the salt solution 118.
[0067] 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 hydrogen gas is oxidized to protons and electrons; un-reacted
hydrogen gas is recovered and circulated 140 at the anode.
[00681 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.
[00691 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
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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.
100701 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
io 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,
is 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, e.g., an ion-depleted brine, from
salt
20 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 7,744,761; alternatively, the solution can be used in
industrial and agricultural applications where its salinity is acceptable.
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[0071] 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
to corrosion.
[00721 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 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.
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[0073] 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 regulated by regulating an
io amount of cathode electrolyte removed from the system through the carbon
dioxide gas/liquid contactor 128.
[0074 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
is comprises a salt solution, a brine 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
20 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
25 embodiments, the hydrogen delivery system is configured to deliver hydrogen
gas to the anode where oxidation of the gas is catalyzed to protons and
Docket No. CLRA-027 -20-
CA 02694978 2010-03-24
electrons. In some embodiments, un-reacted hydrogen gas in the system is
recovered and re-circulated to the anode.
100751 Referring to Fig. 4 wherein the salt solution, e.g., concentrated NaCl
solution, is added directly to the cathode electrolyte 108, 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
membranel 20 will block the passage of cations, the protons will accumulate in
1o 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 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.
[00761 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
Docket No. CLRA-027 -21-
CA 02694978 2010-03-24
and equilibrate to produce carbonic acid, protons, carbonate ions and/or
bicarbonate ions in the first cathode electrolyte compartment as follows:
CO2 + H2O <__> H2CO3 <==> H+ + HCO3 <==> H+ +C03 2-
In the 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
to 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.
(00771 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 reduction of water, as follows:
2H2O + 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
Docket No. CLRA-027 -22-
CA 02694978 2010-03-24
dependent on the pH of the electrolyte, the overall reaction in the cathode
electrolyte 104 is either:
Scenario 1: 2H20+ 2CO2 + 2e" = H2 + 2HC03 ; or
Scenario 2: H2O + CO2 + 2e = H2 + C032_
or a combination of both, depending on the pH of the cathode electrolyte. This
is illustrated in the carbonate speciation diagram in Fig. 5.
[0078] 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
to Or, at standard temperature and pressure conditions:
E cell = -AG /nF
where, Ecell 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
JNmol). The Ecell of each of these reactions is pH dependent based on the
Nernst equestion as is illustrated in Fig.6 ans as discussed below.
[00791 For either scenario, the overall cell potential can be determined
through the combination of Nernst equations for each half cell reaction:
E=E -RTIn(Q)/nF
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:
Etotal = 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,
Docket No. CLRA-027 -23-
CA 02694978 2010-03-24
where pHa is the pH of the anode electrolyte.
When water is reduced to hydroxide ions and hydrogen gas at the cathode as
follows:
2H2O + 2e = H2 + 20H-,
E is -0.83 V, n is 2, and Q is the square of the activity of 0H- so that:
Ecathode = -0.059 pHc,
where pHc is the pH of the cathode electrolyte.
100801 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
1o 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:
Etotai = -0.059 (pHa - pHc) = -0.059 ApH.
[00811 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.
[00821 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.
[00831 Thus, 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
Docket No. CLRA-027 -24-
CA 02694978 2010-03-24
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.
[00841 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 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.
[0085] 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.OV, or even
less than 0.8 V or 0.6V across the cathode and anode.
[00861 In some embodiments, hydroxide ions and/or 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. In some embodiments, the system can be configured
to operate in various production modes including batch mode, semi-batch
Docket No. CLRA-027 -25-
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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.
100871 In some embodiments, hydroxide ions and/or 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.OV or less, 1.9V or less, 1.8V or less,
l0 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.OV 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.
[00881 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.
[00891 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
Docket No. CLRA-027 -26-
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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 an 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
io 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 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.
10090 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.
Docket No. CLRA-027 -27-
CA 02694978 2011-03-01
[0091] 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
io available from Asahi Kasei of Tokyo, Japan; or from Membrane International
of Glen Rock, NJ, and USA.
[00921 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 no. 12/344,019 filed on
December 24, 2008 published as U.S. Publication no. 2009/0169452. 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 7,735,274. 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.
-28-
CA 02694978 2011-03-01
[0093] 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.
[0094] 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
1o 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
alkaline solution and a source of carbon dioxide gas as described in U.S.
Patent Application no. 12/344,019 filed on December 24, 2008, supra, U.S.
Publication no. 2009/0169452. In some embodiments, the precipitates are
used as building materials e.g., cement and aggregates as described in
commonly assigned U.S. Patent 7,735,274.
[0095] 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)
[0096] 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;
-29-
CA 02694978 2010-03-24
and since water in the cathode electrolyte is reduced to 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
to some embodiments, hydroxide ions are produced when less than 2.OV, 1.5V,
1.4V, 1.3V, 1.2V, 1.1 V, 1.OV, 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.
100971 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
Docket No. CLRA-027 -30-
CA 02694978 2010-03-24
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.
[00981 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 1108, 108A, 108B, then a potassium salt
such as potassium chloride can be utilized in the salt solution 118.
Similarly, if
io 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
vapors to produce a desired result. 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.
[00991 With reference to Figs 1 and 3, 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, 108B 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
Docket No. CLRA-027 -31-
CA 02694978 2010-03-24
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
to 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
is 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
20 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
25 electrolyte with a divalent cation solution.
[001001 In some embodiments, hydroxide ions are formed at the cathode 106
and in the cathode electrolyte 108, 108A, 108B by applying a voltage of less
Docket No. CLRA-027 -32-
CA 02694978 2010-03-24
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.OV 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.OV or less, 0.9V or less, 0.8V or less, 0.7V or less, 0.6V or
less, O.5V or less, 0.4V or less, 0.3V or less, 0.2V or less, or 0.1 V or
less,
io 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
is 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.
100101 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.OV, 2.9V, 2.8V, 2.7V,
20 2.6V, 2.5V, 2.4V, 2.3V, 2.2V, 2.1 V, 2.OV, 1.9V, 1.8V, 1.7V, 1.6V, 1.5V,
1.4V,
1.3V, 1.2V, 1.1 V, 1.OV, 0.9V, 0.8V, 0.7V, 0.6V, 0.5V, 0.4V, 0.3V, 0.2V, 0.1 V
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,
25 semi-batch or continuous mode of operation.
[001021 With reference to Figs. 7- 9, in one embodiment, the system 700
comprises a cathode 106 in contact with a cathode electrolyte 108 comprising
Docket No. CLRA-027 -33-
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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
s membrane 122 that is in contact with the anode 102.
[001031 In systems 700, 800, 900 as illustrated in Figs. 7-9, 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 - 9, on applying a relatively low voltage,
e.g.,
io 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
15 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.
20 [001041 In certain embodiments as illustrated in Figs. 7-9, 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
25 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. 7-9, under
the
applied voltage 114 across the anode 102 and cathode 106, hydrogen ions
Docket No. CLRA-027 -34-
CA 02694978 2010-03-24
produced at the anode 102 migrate from the anode 102 into the anode
electrolyte 104 to produce an acid, e.g., hydrochloric acid.
[001051 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.7-9, 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
to 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.
[001061 As is illustrated in Figs. 7-9, 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.
[001071 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.
[001081 With reference to Figs. 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 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,
Docket No. CLRA-027 -35-
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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.
[001091 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
io 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.
[00110] Also 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.
[00111] 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
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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.
[001121 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 co-pending and commonly assigned US Provisional
Patent Application no. 61/151,484, titled "Electro-catalyst Electrodes for Low-
voltage electrochemical Hydroxide System", filed February 10, 2009, available
on USPTO Public PAIR. 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.
[001131 With reference to Figs. 1 - 9 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
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CA 02694978 2011-03-01
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, SOx, NOX, as described in co-
pending and commonly assigned US Provisional Patent application no.
61/223,657, titled "Gas, Liquids, Solids Contacting Methods and Apparatus",
filed July 7, 2009 available on USPTO Public PAIR. 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.
1001141 Although carbon dioxide is present in ordinary ambient air, partly due
io to the very low concentration in air, 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 stream, 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
is and method, since the cathode electrolyte is contained in a 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.
20 1001151 In some embodiments, and with reference to Figs. 1 - 9, 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 reducing water in the
25 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
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CA 02694978 2010-03-24
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.
[001161 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
to 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 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.
Docket No. CLRA-027 -39-
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[001171 With reference to Figs. 1-15, in some embodiments, the anode
electrolyte 102 comprises a salt solution, e.g., a terrestrial brine, that
includes
sodium ions and chloride ions; the system 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 is configured to migrate
hydrogen ions from the anode into the anode electrolyte; the anode electrolyte
comprises an acid; the system is configured to produce bicarbonate ions
and/or carbonate ions in the cathode electrolyte 108; migrate hydroxide ions
io 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.
[001181 With reference to Figs. 1-15, 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 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, 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 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
Docket No. CLRA-027 -40-
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Fig. 8, 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.
[001191 In the embodiments, the mineral dissolution system is operatively
connected to nano-filtration system that is configured to separate sodium ions
and chloride ions from the mineral solution comprising, e.g., calcium ions,
1o magnesium ions, silica, hydrochloric acid and/or sodium hydroxide. In some
embodiments, the nano-filtration system is configured with a reverse osmosis
system that is capable of concentrating sodium ions and chloride ions into a
salt solution that is used as the anode electrolyte .
[00120] With reference to Figs. 1 - 15 the method in some embodiments
comprises a step 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 1 V across the cathode 106 and an anode 102 in contact with
the anode electrolyte without producing a gas at the anode.
[00121] In some embodiments of the method, 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 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.
Docket No. CLRA-027 -41-
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[001221 In some embodiments, ambient air is excluded the cathode
electrolyte 108; a pH of between and 7 and 14 or greater is 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
io 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.
[001231 In some embodiments, the method 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 and produce a mineral solution
comprising calcium ions and/or magnesium ions, wherein the minerals
comprises mafic minerals; filtering the mineral solution 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; utilizing the salt solution as the anode electrolyte 104;
precipitating a
carbonate and/or bicarbonate with the cathode electrolyte; wherein the
carbonate and/or bicarbonate comprises calcium and/or magnesium
Docket No. CLRA-027 -42-
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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 without environmental
acidification.
[001241 With reference to Figs. 1 - 15, the method in another embodiment
comprises a step of producing an acid in an electrochemical system, e.g.,
system 800, 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
io 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 the carbonate and/or bicarbonate comprises calcium and/or
Docket No. CLRA-027 -43-
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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.
[00125] With reference to Figs 1-15, the system and method produce an
alkaline solution 108 and an acid 124 by a redox reaction utilizing a salt
solution 130 and water 902. A suitable salt solution includes a synthetic
saltwater, e.g., a sodium chloride solution made by dissolving sodium chloride
salt in water; or a naturally occurring saltwater, e.g., brine 904.
[00126] In an embodiment of the system as illustrated in Figs. 9-15, the
system comprises an anode 122, e.g., a hydrogen-oxidizing anode in
communication with a cathode electrolyte 108 comprising bicarbonate ions;
and a brine production system 904 configured to provide cations, e.g., Na+, to
the cathode electrolyte 108. In another embodiment, the system comprises an
anode, e.g., an electrochemistry unit 100, 400, 700, 800 comprising
hydrogen-oxidizing anode122 in communication with a cathode electrolyte 108
in a cathode compartment 144 wherein the electrochemistry unit is operably
connected to a carbon sequestration system (not illustrated) configured to
sequester carbon dioxide 106 A, 107, 107A with the cathode electrolyte 108.
In some embodiment of the system, the brine production system 904
comprises subterranean brines; in some embodiments, the cathode electrolyte
108 comprises added carbon dioxide 107.
[00127] In some embodiments of the system, the cathode electrolyte
comprises hydroxide ions, bicarbonate ions and/or carbonate ions; ion
exchange membranes, e.g., cation exchange membrane 116, 122 and anion
exchange membrane 120 configured to separate cations and anions from the
salt 130, e.g., brine, to produce an ion-depleted salt 124, e.g., ion-depleted
Docket No. CLRA-027 -44-
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brine 125. In some embodiments, the cations comprises sodium ions; in some
embodiments, the system is configured to produce hydrogen gas 112 and
hydroxide ions at the cathode 106 in contact with the cathode electrolyte 108
and oxidize hydrogen to protons at the anode 122 in contact with the anode
electrolyte 104 without producing a gas at the anode, when a voltage 114 is
applied across the anode and cathode. In some embodiments, the voltage is
less than 3V. In some embodiments, the system is configured to produce an
acid 124, e.g., HCI in the anode electrolyte.
1001281 In some embodiments, the system comprises an acid dissolution
to system (not illustrated) configured to produce divalent cations with the
acid; in
some embodiments, the divalent cations comprise calcium ions and/or
magnesium ions.
[001291 In some embodiments, the system comprises a carbon sequestration
system (not illustrated) configured to sequester carbon dioxide with the
cathode electrolyte 108. In some embodiments, carbon dioxide is contained in
an industrial waste gas is used; in some embodiments the carbon dioxide is
sequestered as carbonate and/or bicarbonate, e.g., carbonate and/or
bicarbonate comprising divalent cations.
[001301 In some embodiments as illustrated in Figs. 9 - 15, the system
comprises a water treatment system 902, 1000, 1100, 1200, 1300, 1400, 1500
configured fro several uses, e.g., to dilute a solution, e.g., the brine 130,
the
acid 104, the cathode electrolyte 108 or the anode electrolyte 104. I n some
embodiments, the water treatment system is also configured to adjust the pH
of the electrolytes the acid, the electrolytes and the brine.
[001311 As is illustrated in Figs. 11 and 12, the water treatment system
includes one or more of the following unit processes and equipment: a
sedimentation or screen filter; an activation carbon filter; a reverse osmosis
Docket No. CLRA-027 -45-
CA 02694978 2010-03-24
system; an ultra-filtration system; a UV lamp; a chlorination process; a
hardness remover; a pH adjustment system; a flocculation system; an electro-
dialysis system. Such unit process may be conventionally; however, for some
applications, e.g., preparing the electrolytes, a customized unit or process
may be required as is know in the art.
[00132] Also as illustrated in Figs. 9-15, the system includes a brine
production and treatment system 904 comprising, in some embodiments, a
brine storage system; a brine saturation system; and a brine secondary
purification system. Such brine production and treatment system includes a
io conventional brine treatment system or and/or brine treatment system
customized for the present alkali production system and method.
1001331 In some embodiments, the system include a desalination system (not
illustrated) configured to produce desalinated water from the ion-depleted
brine 125. In some embodiments, the desalinated water is operatively
connected to the water treatment system.
[001341 With reference to Figs. 1-15, the method in various embodiments
comprise a step of oxidizing hydrogen to protons at a hydrogen-oxidizing
anode 122 in communication with a cathode electrolyte 108 comprising
bicarbonate ions; and a step of providing cations from a brine 130 to the
cathode electrolyte 108. In another embodiments, the method comprises
oxidizing hydrogen to protons at a hydrogen-oxidizing anode 122 in
communication with a cathode electrolyte 108; and sequestering carbon
dioxide with the cathode electrolyte 108.
[001351 In various embodiments, the method include a step of using a brine
comprising subterranean brines comprising sodium ions; a step of adding
carbon dioxide to the cathode electrolyte; a step of producing hydrogen gas
and hydroxide ions at a cathode in contact with the cathode electrolyte
Docket No. CLRA-027 -46-
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without producing a gas at the anode, by applying a voltage across the anode
and cathode; a step of applying a voltage is less than 3V across the anode
and cathode.
[001361 In some embodiments the method includes a step of producing
hydroxide ions and/or carbonate ions and/or bicarbonate ions in the cathode
electrolyte; a step of separating cations and anions from the brines to
produce
an ion-depleted brine; a step of producing an acid in the anode electrolyte,
e.g., hydrochloric acid; a step of configuring the acid in an acid dissolution
system to dissolve material and produce divalent cations, including divalent
io cations comprise calcium ions and/or magnesium ions; a step of configuring
a
carbon sequestration system to sequester carbon dioxide with the cathode
electrolyte, wherein the carbon dioxide is contained, e.g., in an industrial
waste gas, and wherein the carbon dioxide is sequestered as carbonate
and/or bicarbonate, e.g., divalent cation carbonates; a step of utilizing a
water
treatment system to dilute the cathode/anode electrolytes, the salt, e.g., the
brine, and the acid.
[001371 In some embodiments the method includes a step of generating
hydrogen gas and hydroxide ions by reducing water at the cathode; a step of
adjusting the pH of the cathode/anode electrolytes, brine and acid with the
water; a step of adjusting the ionic concentration in the anode/cathode
electrolytes, brine and acid with the water; a step of producing desalinated
water from the ion-depleted brine; a step of circulating the desalinated water
for further treatment in the water treatment system.
[001381 In an exemplarary embodiment, a system configured substantially as
illustrated in Figs. 1 -15 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
Docket No. CLRA-027 -47-
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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 pH Current density
(V) (mA/cm2)
0.8 10 8.6
25 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
Docket No. CLRA-027 -48-
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[001391 As is illustrated in Table 1, a range of current densities was
achieved
across the electrode in the system. As can be appreciated, 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.
[00140 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
to 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 +01-1- = H2O + HC03
and HC03 + OH- = H2O + C032-,
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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, HC03 , and C032- vs. pH in the electrolyte will follow the carbonate
speciation diagram as discussed above.
[001411 In the system as illustrated in Figs. 1 - 9 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
io 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.
Docket No. CLRA-027 -50-
CA 02694978 2011-03-01
[00142] In another embodiment, the 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. Patent 7,735,274.
[001431 In an alternative embodiment, the 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 7,735,274.
[00144] In an alternative embodiment, the 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
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CA 02694978 2011-03-01
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 no. 12/344,019 filed on
December 24, 2008, U.S. Publication no. 2009/0169452. 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 7,735,274.
[001451 In another embodiment, the system and method are integrated with
an aqueous desalination system (not illustrated) wherein the partially
io 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 7,744,761.
[001461 In an alternative embodiment, the 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 no. 12/344,019 filed on
December 24, 2008, U.S. Publication no. 2009/0169452; or in a subterranean
site.
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