U.S. patent application number 12/989781 was filed with the patent office on 2011-02-24 for low-energy electrochemical bicarbonate ion solution.
Invention is credited to Bryan Boggs, Valentin Decker, Ryan J. Gilliam.
Application Number | 20110042230 12/989781 |
Document ID | / |
Family ID | 42395872 |
Filed Date | 2011-02-24 |
United States Patent
Application |
20110042230 |
Kind Code |
A1 |
Gilliam; Ryan J. ; et
al. |
February 24, 2011 |
LOW-ENERGY ELECTROCHEMICAL BICARBONATE ION SOLUTION
Abstract
A low-energy electrochemical method and system of forming
bicarbonate ion solutions in an electrochemical cell utilizing
carbon dioxide in contact with an electrolyte contained between two
ion exchange membranes in an electrochemical cell. On applying a
low voltage across an anode and cathode in electrical contact with
the ion exchange membranes, bicarbonate ions form in the
electrolyte without forming a gas, e.g., chlorine or oxygen at the
electrodes.
Inventors: |
Gilliam; Ryan J.; (San Jose,
CA) ; Boggs; Bryan; (Campbell, CA) ; Decker;
Valentin; (San Jose, CA) |
Correspondence
Address: |
Calera Corporation;Eric Witt
14600 Winchester Blvd.
Los Gatos
CA
95032
US
|
Family ID: |
42395872 |
Appl. No.: |
12/989781 |
Filed: |
January 28, 2009 |
PCT Filed: |
January 28, 2009 |
PCT NO: |
PCT/US09/32301 |
371 Date: |
October 26, 2010 |
Current U.S.
Class: |
205/482 ;
204/242; 204/252; 205/480; 205/555 |
Current CPC
Class: |
B01D 61/44 20130101;
C25B 1/22 20130101; C25B 1/00 20130101; C25B 1/14 20130101 |
Class at
Publication: |
205/482 ;
204/242; 204/252; 205/555; 205/480 |
International
Class: |
C25B 1/14 20060101
C25B001/14; C25B 9/00 20060101 C25B009/00; C25B 1/00 20060101
C25B001/00; C25B 1/26 20060101 C25B001/26; C25B 1/18 20060101
C25B001/18 |
Claims
1. An electrochemical system comprising: an anode, a cathode and a
first electrolyte disposed between the anode and cathode, wherein
the system is configured to form bicarbonate ions in the first
electrolyte without forming a gas at the cathode or anode on
applying a voltage across the anode and cathode and contacting the
first electrolyte with carbon dioxide.
2. (canceled)
3. The system of claim 1 comprising: a first anion exchange
membrane and a cation exchange membrane between which is contained
the first electrolyte.
4. (canceled)
5. The system of claim 3, further comprising: a second electrolyte
contacting the first anion exchange membrane and the anode; a third
electrolyte contained between the cation exchange membrane and a
second anion exchange membrane; and a fourth electrolyte contacting
the second anion exchange membrane and the cathode.
6. (canceled)
7. (canceled)
8. The system of claim 5, further comprising: a fifth electrolyte
contained between the second cation exchange membrane and a second
anion exchange membrane, and wherein the second electrolyte
contacts the second anion exchange membrane and the anode.
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. The system of claim 8, wherein the first electrolyte comprises
sodium chloride and carbon dioxide.
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. The system of claim 1, configured to form sodium bicarbonate in
the first electrolyte.
24. The system of claim 13, configured to form hydrochloric acid in
the third electrolyte.
25. The system of claim 24, wherein the anode and cathode are
selected from tin, nickel, cobalt or copper.
26. The system of claim 25, configured to oxidize the anode to tin
ions in the second electrolyte and reducing tin ions to tin at the
cathode.
27. (canceled)
28. The system of claim 26, configured to form sodium bicarbonate
in the first electrolyte.
29. (canceled)
30. (canceled)
31. The system of claim 28, configured to form tin ions in the
electrolyte at the anode and reducing tin ions to tin from the
electrolyte at the cathode.
32. (canceled)
33. (canceled)
34. (canceled)
35. (canceled)
36. (canceled)
37. (canceled)
38. (canceled)
39. (canceled)
40. (canceled)
41. An electrochemical method comprising: applying a voltage across
an anode and a cathode through a first electrolyte comprising added
carbon dioxide to form bicarbonate ions in the first electrolyte
without forming a gas at the cathode or the anode, wherein the
first electrolyte is located between the anode and cathode.
42. (canceled)
43. The method of claim 41, wherein the first electrolyte is
contained between an anion exchange membrane and a cation exchange
membrane.
44. The method of claim 43, wherein the anion exchange membrane
contacts the anode through the second electrolyte; and the cation
exchange membrane contacts the cathode through a third
electrolyte.
45. (canceled)
46. The method of claim 44, wherein the first cation exchange
membrane separates the first electrolyte from the third
electrolyte; the second cation exchange membrane contacts the anode
through the second electrolyte; a first anion exchange membrane
separates the third electrolyte from the fourth electrolyte; and
the fourth electrolyte contacts the cathode.
47. The method of claim 44, wherein the first cation exchange
membrane separates the first electrolyte from the third
electrolyte; the first anion exchange membrane separates the third
electrolyte from the fourth electrolyte; the fourth electrolyte
contacts the cathode; a fifth electrolyte is contained between the
second cation exchange membrane and a second anion exchange
membrane; and the second anion exchange membrane contacts the anode
through the second electrolyte.
48. The method of claim 44, wherein the first electrolyte comprises
sodium chloride and carbon dioxide.
49. The method of claim 44, further comprising transferring anions
across the anion exchange membrane from the first electrolyte to
the second electrolyte.
50. (canceled)
51. The method of claim 44, further comprising transferring cations
across the cation exchange membrane from the first electrolyte to
the third electrolyte.
52. The method of claim 44, further comprising transferring protons
across the first cation ion exchange membrane from the first
electrolyte to the third electrolyte.
53. (canceled)
54. (canceled)
55. The method of claim 44, comprising precipitating alkaline metal
carbonates utilizing the first electrolyte.
56. (canceled)
57. The method of claim 44, comprising forming sodium bicarbonate
in the first electrolyte.
58. The method of claim 44, further comprising separating the
cathode from the third electrolyte utilizing second anion exchange
membrane whereby the cathode is electrically connected to second
anion exchange membrane through fourth electrolyte.
59. The method of claim 58, further comprising transferring
chloride ions across the second anion exchange membrane from the
fourth electrolyte to the third electrolyte.
60. (canceled)
61. The method of claim 59, comprising forming hydrochloric acid in
the third electrolyte.
62. (canceled)
63. (canceled)
64. (canceled)
65. (canceled)
66. The method of claim 44 comprising forming hydrochloric acid in
the third electrolyte.
67. (canceled)
68. (canceled)
69. (canceled)
70. (canceled)
71. (canceled)
72. (canceled)
73. (canceled)
74. (canceled)
75. (canceled)
Description
BACKGROUND
[0001] Bicarbonate ion solutions are used to regulate or achieve a
chemical reaction or buffer the pH of a solution. Conventionally,
bicarbonate ion solutions are obtained by dissolving bicarbonate
salts, e.g., sodium bicarbonate, in water. However, producing
bicarbonate salts conventionally is energy intensive and,
consequently, bicarbonate ion solutions are expensive.
SUMMARY
[0002] This invention pertains to a low energy system and method of
producing bicarbonate ions utilizing an electrolyte and carbon
dioxide in an electrochemical cell. In one embodiment, the system
comprises an anode, a cathode and an electrolyte contained between
ion exchange membranes in an electrochemical cell. On applying a
voltage across the anode and cathode while contacting the
electrolyte with carbon dioxide, the system is capable of forming
bicarbonate ions in the electrolyte without forming a gas at the
electrodes, e.g., without forming hydrogen at the cathode or
chlorine at the anode. The system is also capable of forming an
acid, e.g., hydrochloric acid in another electrolyte in contact
with an ion exchange membrane; and, in various embodiments, ions of
the anode can be recovered at the cathode by reusing the anode
electrolyte at the cathode.
[0003] In another embodiment, the system comprising an anode, a
cathode and an electrolyte contained between ion exchange
membranes, is capable of forming bicarbonate ions in the
electrolyte on applying a voltage of, e.g., less than 0.05 V across
the anode and cathode while contacting the electrolyte with carbon
dioxide. The system is also capable of forming an acid, e.g.,
hydrochloric acid in another electrolyte in contact with an ion
exchange membrane; and, in various embodiments, ions of the anode
can be recovered at the cathode by reusing the anode electrolyte at
the cathode.
[0004] In one embodiment, the method comprises applying a voltage
across an anode and a cathode in an electrochemical cell containing
an electrolyte comprising carbon dioxide and contained between ion
exchange membranes, to form bicarbonate ions in the electrolyte
without forming a gas at the electrodes, e.g., without forming
chlorine at the anode or hydrogen at the cathode. The method is
also capable of forming an acid, e.g., hydrochloric acid in another
electrolyte in contact with an ion exchange membrane; and, in
various embodiments, ions of the anode can be recovered at the
cathode by reusing the anode electrolyte at the cathode.
[0005] In another embodiment, the method comprises forming
bicarbonate ions in an electrolyte contained between ion exchange
membranes in an electrochemical cell by applying a voltage of less
than 2.0 V, less than 1.5 V, less than 1.0 V, less than 0.5 V, less
than 0.1 V or less than 0.05 V across the anode and cathode while
contacting the electrolyte with carbon dioxide. The system is also
capable of forming an acid, e.g., hydrochloric acid in another
electrolyte in contact with an ion exchange membrane; and, in
various embodiments, ions of the anode can be recovered at the
cathode by reusing the anode electrolyte at the cathode.
[0006] With the present system and method, carbon dioxide from any
convenient source can be used to contact the electrolyte between
the ion exchange membranes. Such sources include carbon dioxide
dissolved in a liquid, carbon dioxide in solid form, e.g., dry ice,
or gaseous carbon dioxide. In particular embodiments, carbon
dioxide in combustion gases of an industrial plant, e.g., the stack
gases of fossil fuel power-generating plants or cement plants can
be used.
[0007] In various embodiments, the present system and method are
adaptable for batch, semi-batch or continuous flows of
electrolytes, bicarbonate ions, carbon dioxide and acid in the
electrochemical cell. In various embodiments, the solution
comprising bicarbonates ions can be used to sequester carbon
dioxide by contacting the bicarbonate ion solution with an alkaline
earth metal ion solution in the presence of carbon dioxide to
precipitate carbonates, e.g., to precipitate calcium and magnesium
carbonates from saltwater as described in U.S. patent application
Ser. No. 12/126,776, filed on May 23, 2008, herein incorporated by
reference. The precipitated carbonates, in various embodiments, can
be used as building products, e.g., cements and other building
products as described in the United States Patent Applications
incorporated herein by reference.
[0008] In another embodiment, the system and method can be used to
precipitate carbonates from saltwater to produce desalinated water
as described in U.S. patent application Ser. No. 12/163,205, filed
on Jun. 27, 2008, herein incorporated by reference. In various
embodiments, the acids produced by the present method can be used
to dissolve alkaline earth metal minerals to obtain alkaline earth
metal cations for use in sequestering carbon dioxide as described
in the United States patent applications incorporated herein by
reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The following figures illustrate by way of examples and not
by limitation various embodiments of the present system and
method:
[0010] FIG. 1 illustrates an embodiment of the present system.
[0011] FIG. 2 illustrates an embodiment of the present system.
[0012] FIG. 3 illustrates an embodiment of the present system.
[0013] FIG. 4 illustrates an embodiment of the present system.
[0014] FIG. 5 is a flow chart of an embodiment of the present
method.
[0015] FIG. 6 is a flow chart of an embodiment of the present
method.
DETAILED DESCRIPTION
[0016] In the following detailed description of exemplary
embodiments of the system and method where a range of values is
specified, each intervening value in the range is encompassed by
the invention. Thus, values between the upper and lower limit of
the range and any other stated and intervening value in the range
are included unless the context clearly dictates otherwise. Also,
upper and lower limits of smaller ranges are included in smaller
ranges and are encompassed within the scope of the invention,
subject to any specifically excluded limit in the stated range.
[0017] Herein, numerical values may be preceded by the term
"about." The term "about" is used to provide literal support for
the exact number that it precedes, and/or as a number that is near
to or approximately the number that it precedes. In determining
whether a number is near to or approximately a specifically recited
number, the near and/or approximating unrecited number may be a
number that, in the context in which it is presented, provides the
substantial equivalent of a specifically recited number.
[0018] Herein, unless otherwise specified, all technical and
scientific terms have the same meaning as understood by one of
ordinary skill in the art to which this invention pertains.
Publications and patents incorporated by reference herein are fully
incorporated to disclose their contents as disclosed. A
publication, when cited, is cited for its disclosure on its
publication date and is not an admission that the present invention
is not entitled to antedate such publication by virtue of prior
invention. The date of a cited publication may differ from the
actual publication date and may need independent confirmation.
[0019] Herein, the singular forms "a," "an," and "the" encompass
plural forms unless the context clearly dictates otherwise. As will
be apparent to one ordinarily skilled in the art, each of the
embodiments described and illustrated herein comprises discrete
elements that may be separated from, or combined with, other
elements without departing from the scope of the claims, e.g., a
recited method may be performed in the order of events recited or
in another logical order without departing from the scope of the
claims.
[0020] Herein, the invention in various embodiments is described
for convenience in terms of producing sodium bicarbonate ions, and
optionally, hydrochloric acid. However, it will be appreciated by
one ordinarily skilled in the art that the present system and
method may produce other bicarbonate ions such as, e.g., potassium
and calcium bicarbonate ions and other acids such as sulfuric acid,
depending on the electrolytes used.
[0021] In various embodiments, the present invention is directed to
a low voltage system and method of forming bicarbonate ions by
contacting carbon dioxide with an electrolyte salt solution
positioned between ion exchange membranes in an electrochemical
cell. In one embodiment, on applying a low voltage across a cathode
and anode in the cell, bicarbonate ions form in the solution
without forming a gas at the electrodes, e.g., without forming
chlorine at the anode or hydrogen at the cathode. By the present
system and method, bicarbonate ions are formed in the solution on
applying a voltage across the anode and cathode of less than 2.8,
2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5,
1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or
0.1 V, and other low voltages as disclosed herein. In various
embodiments, an acid solution is also formed in another electrolyte
in contact with an ion exchange membrane, e.g., hydrochloric acid,
in the electrochemical cell. Optionally, in some embodiments, the
electrolyte in contact with the anode is reused as the electrolyte
at the cathode to recover anode material at the cathode.
[0022] Referring to FIG. 1, in one embodiment system 100 comprises
first electrolyte 102 and carbon dioxide 104 contained between
anion exchange membrane 106A and cation exchange membrane 108A in
an electrochemical cell 110. Electrochemical cell 100 includes
anode 112 and cathode 114; second electrolyte 116 contacting anion
exchange membrane 106A and anode 112; and third electrolyte 118
contacting cation exchange 108A membrane and cathode 114. On
applying a voltage across the anode and cathode, the system is
capable of forming bicarbonate ions 122 in first electrolyte 102
without forming a gas, e.g., hydrogen at cathode 114 or chlorine at
anode 112. In various embodiments the system is capable of forming
bicarbonate ions in first electrolyte 102 when a voltage of 0.2 V
or less, 0.3 V or less, 0.4 V or less, 0.5 V or less, 0.6 V or
less, 0.7 V or less, or 0.8 V or less is applied across the anode
and cathode.
[0023] In various embodiments and with reference to FIGS. 1-4, the
system also capable of forming an acid 124 in third electrolyte
solution 118 contacting cation exchange membrane 108A as a result
of transfer of protons across cation exchange membrane 108A from
first electrolyte 102. For example, as is illustrated in FIG. 1,
protons transferred from first electrolyte 102 to third electrolyte
118 will result in formation of an acid solution 124 in third
electrolyte 118; thus, where third electrolyte contains chloride
ions, hydrochloric acid 124 will form in third electrolyte 118.
[0024] Depending on whether a sacrificial anode is used, e.g., tin,
copper, iron, zinc, the system in various embodiments is capable of
oxidizing the anode to from cations in the electrolyte in contact
with the anode e.g., tin ions, in second electrolyte 116. Hence, as
is illustrated in FIG. 1, in various embodiments the system is
capable of forming a chloride solution in second electrolyte 116
contacting the anode, e.g., where a tin anode is used and tin ions
are present in the second electrolyte 116, stannous chloride will
form in second electrolyte 116 as a result of transfer of chloride
ions across anion exchange membrane 106A from first electrolyte
102. Similarly, as illustrated in FIGS. 2-4, where a tin anode is
used, stannous chloride solution will form in electrolyte 116 a
result of ions migrating to or from second electrolyte 116 across
the ion exchange membrane in contact with second electrolyte 116 as
discussed below. In various embodiments, optionally, the
electrolyte solution 116 in contact with anode 112 comprising anode
ions can be reused as electrolyte 118 in contact with cathode 114
to recover anode material at the cathode. As will be appreciated by
one ordinarily skilled in the art, tin and other sacrificial metal
can thus be recovered at the cathode, depending on the material
used as the sacrificial anode.
[0025] With reference to FIGS. 1-4, in various embodiments, system
100, system 200, system 300 and system 400 comprise inlet ports 126
A-E (where needed) for introducing substances in to the cell, e.g.,
for introducing fluids, gases, salts and the like into cells 110,
202, 302, 402; and outlet ports 130A-E (where needed) for removing
fluids from the cells. For example, with reference to FIG. 1,
system 100 comprises inlet port 1268 for introducing carbon dioxide
104 into first electrolyte 102, and inlet port 126C for introducing
sodium chloride solution 128 into first electrolyte 102. Similarly,
system 100 of FIG. 1 comprises outlet ports 130A for removing acid
124 from third compartment 136, and outlet port 130B for removing
bicarbonate ion solution from first compartment 132. As will be
appreciated by one ordinarily skilled in the art, the inlet and
outlet ports are adaptable for various flow protocols including
batch flow, semi-batch flow, or continuous flow. In various
embodiments, the system includes voltage regulator 120 for
regulating voltages across the electrodes and currents through the
electrolytes.
[0026] In an embodiment illustrated in FIG. 1, electrochemical cell
110 comprises first compartment 132, second compartment 134 and
third compartment 136 formed by positioning anion exchange membrane
106A and cation exchange membrane 108A in cell 110 such that first
electrolyte 102 is separated from second electrolyte 116 and third
electrolyte 118. As will be appreciated in the art, the ion
exchange membranes are positioned to contact the electrolytes on
opposite surfaces such that ions from one electrolyte will migrate
to another electrolyte through the ion exchange membrane without
mixing of the electrolytes.
[0027] In various embodiments as illustrated in FIGS. 1-4, the
system, depending on its configuration, is initially charged (where
appropriate) with first electrolyte 102, second electrolyte 116,
third electrolyte 118, fourth electrolyte 206 and fifth electrolyte
404 comprising an aqueous salt solution such as a saltwater, e.g.,
seawater, brine, brackish water, sodium chloride, conductive fresh
water and the like. In an embodiment that produced the results as
set forth in Table 1, the system was initially charged with first
electrolyte 102 and fifth electrolyte 404 comprising 2 M sodium
chloride solution; in another embodiment the system was initially
charged with first electrolyte 102 and fifth electrolyte 404
comprising 0.5 M sodium chloride solution. In other specific
embodiments the system can be charged initially with a salt
solution, e.g., sodium chloride, at a concentration from 0.1 to 4
M, e.g., 0.1 to 2.5 M, or 0.2 to 2.0 M, or 0.1 to 1.0 M, or 0.2 to
1.0 M, or 0.2 to 0.8 M, or 0.3 to 0.7 M, or 0.4 to 0.6 M, or 0.5 to
2.5 M, or 1.0 to 2.5 M, or 1.5 to 2.5 M, or 1.7 to 2.3 M.
[0028] With reference to FIGS. 1-4, anion exchange membranes 106A,
106B and cation exchange membranes 108A, 108B comprise ionic
membranes selectively permeable to one ion or one class of ions,
e.g., cation membranes selectively permeable to sodium ions only or
hydrogen ions only, or to cations generally; or anion membranes
selectively permeable to chloride ions only or to anions generally,
can be used. In various embodiments, anion exchange membranes 106A,
106B and cation exchange membranes 108A, 108B may comprise
membranes that will function in an acid and/or basic electrolytic
at pH from 1 to 14; also, the membranes may be selected to function
with electrolytes wherein the temperatures ranges from about
0.degree. C. to 100.degree. C. or higher. Such ion exchange
membranes are commercially available, e.g., PCA GmbH of Germany
supplies a suitable anion exchange membrane permeable to chloride
ions and identified as PCSA-250-250; and a cation exchange membrane
permeable to sodium ions and identified as PCSK 250-250.
[0029] With reference to FIGS. 1-4, in various embodiments anode
112 comprises a sacrificial anode, e.g., tin, copper, iron, zinc.
Where a sacrificial anode such as tin is used, cations such as
Sn.sup.2+ will form in second electrolyte 116 in contact with anode
112. Optionally, as will be appreciated by one ordinarily skilled
in the art, cations in electrolyte 116 in contact with anode 112
can be recovered by plating out the cations at the cathode 114,
e.g., using electrolyte 116 from the anode as the electrolyte at
the cathode. Thus, the anode material can be recovered at the
cathode by switching electrolyte 116 in contact anode 112 with the
electrolyte in contact with the cathode 114 when a sufficient
concentration of Sn.sup.2+ has accumulated in the electrolyte 116,
and allowing the cations to plate out at the cathode. It will also
be appreciated that when sacrificial anode 112 is diminished and
cathode 114 is augmented sufficiently, these electrodes may be
switched so that anode 112 is transferred to replace cathode 114
and vice versa.
[0030] As is illustrated in FIGS. 1-4, the voltage across anode 112
and cathode 114 can be regulated to form bicarbonate ions 122 in
first electrolyte 102 without forming a gas, e.g., chlorine at
anode 112 or hydrogen at cathode 114. In various embodiments,
bicarbonate ions 122 are formed when the voltage applied across
anode 112 and cathode 114 is less than 2.8, 2.7, 2.6, 2.5, 2.4,
2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1,
1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 V. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.8 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.7 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.6 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.5 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.4 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.3 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.2 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.1 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.05 V without forming a
gas at the electrodes.
[0031] In various embodiments as illustrated in FIGS. 1-4, a
protonated solution, e.g., hydrochloric acid 124 is formed in third
electrolyte 118. For example, with reference to FIG. 1, on transfer
of protons from first electrolyte 102 to third electrolyte 118
through cation exchange membrane 108A, the pH of the third
electrolyte 118 will adjust, e.g., become more acid if protons
accumulate in the electrolyte. The acid formed will depend on the
electrolytes used, e.g., as illustrated in FIG. 1, where third
electrolyte 118 comprises chloride ions, hydrochloric acid will
form in third electrolyte 118. With the accumulation of protons in
third electrolyte 118, the pH of this electrolyte will decrease; it
will be appreciated, however, that the pH of third electrolyte may
increase, decrease or remain constant depending on the rate of
removal of third electrolyte from the system.
[0032] Also as will be appreciated by one skilled in the art and as
is illustrated, e.g., in FIG. 1, where first electrolyte 102
initially comprises sodium chloride solution 128, sodium
bicarbonate 122 will form in first electrolyte 102 as a consequence
of the migration of protons and chloride ions from first
electrolyte 102. Further, as sodium bicarbonate is an amphoteric
salt that forms a mildly alkaline solution in water, with the
formation of sodium bicarbonate in first electrolyte 102 the pH of
the first electrolyte will increase (assuming that first
electrolyte 102 is not removed from the system) due to formation of
hydroxyl ions (OH.sup.-) in accordance with the following
reaction:
NaHCO.sub.3.sup.-+H.sub.2O.fwdarw.H.sub.2CO.sub.3+Na.sup.++OH.sup.-
[0033] In various embodiments of the invention as illustrated in
FIGS. 1-6, carbon dioxide 104 from any convenient source can be
used. Such sources include carbon dioxide dissolved in a liquid,
solid carbon dioxide, e.g., dry ice, or gaseous carbon dioxide. In
various embodiments, carbon dioxide in post-combustion effluent
stacks of industrial plants such as power plants, cement plants and
coal processing plants can be used. In various embodiments carbon
dioxide 104 may comprise substantially pure carbon dioxide or a
multi-component gaseous stream comprising carbon dioxide and one or
more additional gases. Additional gases and other components may
include CO, SO.sub.x (e.g., SO.sub.2), NO.sub.x, mercury and other
heavy metals and dust particles e.g., from calcining and combustion
processes. In various embodiments, one or more of these additional
components can be precipitated by contacting first electrolyte 102
with a solution of alkaline earth metal ions, e.g., where SO.sub.2
is contained in the gas stream, sulfates and sulfides of calcium
and magnesium can be precipitated.
[0034] Multi-component gaseous streams include reducing condition
streams, e.g., syngas, shifted syngas, natural gas, and hydrogen
and the like, and oxidizing condition streams, e.g., flue gases
from combustion. Such gaseous streams include oxygen-containing
flue gas, e.g., from a coal fired power plant, a cement plant, or a
natural gas power plant; turbo charged boiler product gas; coal
gasification product gas; shifted coal gasification product gas;
anaerobic digester product gas; wellhead natural gas; reformed
natural gas or methane hydrates; and the like. In various
embodiments, gases that are not absorbed in first electrolyte 102,
e.g., nitrogen, in one embodiment are vented from the system; in
other embodiments, the gases are collected for other uses.
[0035] As will be appreciated by one skilled in the art and with
reference to FIGS. 1-6, without being bound by any theory it is
believed that bicarbonate ions (HCO.sub.3.sup.-) form in first
electrolyte 102 as a result of carbon dioxide contacting water in
the first electrolyte 102, as follows:
CO.sub.2+H.sub.2O====>H.sup.++HCO.sub.3.sup.-.
Thus, in accordance with the present invention and with reference
to FIG. 1, where first electrolyte 102 comprise Na.sup.+ and
Cl.sup.- ions from added sodium chloride 128, by placing first
electrolyte 102 between cation exchange membrane 108A selective to
transferring H.sup.+ ions, and an anion exchange membrane 106A
selective to transferring of Cl.sup.- ions, and applying a voltage
across the electrodes, H.sup.+ will migrate through the cation
exchange membrane 108A to adjacent third electrolyte 118.
Similarly, Cl.sup.- will migrate from first electrolyte 102 through
the anion exchange membrane 106A to adjacent second electrolyte
116. Consequently, in first electrolyte 102, a solution comprising
sodium bicarbonate will form. Depending on the rate of introduction
and/or removal of first electrolyte from the system and the voltage
applied across electrodes 112, 114, the concentration of
bicarbonate ions in first electrolyte 102 will adjust, e.g.,
increase, decrease or will not change.
[0036] Also, with reference to FIG. 1, as H.sup.+ migrate from
first electrolyte 102 through cation exchange membrane 108A to
adjacent electrolyte 118, the pH of adjacent third electrolyte 118
will adjust depending on rate of introduction and/or removal of
first electrolyte 102 from the system. Similarly, as chloride ions
migrate from the first electrolyte to adjacent second electrolyte
114 across the anion exchange membrane 106A, the chloride in second
electrolyte 114 will adjust, e.g., increase, decrease or does not
change. Hence, as illustrated in FIGS. 1-6, in various embodiments
of the system and method, a solution of bicarbonate ions 122, e.g.,
sodium bicarbonate, is obtained in first electrolyte 102, an acid
solution 124, e.g., hydrochloric acid, is obtained in third
electrolyte 118, and a chloride solution is obtained in second
electrolyte 116.
[0037] In an embodiment of system 200 as illustrated in FIG. 2,
first electrolyte 102 and carbon dioxide 104 are contained between
first anion exchange membrane 106A and first cation exchange
membrane 108A in an electrochemical cell 202 comprising anode 112
and cathode 114. In the system, second electrolyte 116 contacts
first anion exchange membrane 106A and anode 112; third electrolyte
118 is contained between first cation exchange membrane 108A and
second anion exchange membrane 106B; and fourth electrolyte 206
contacts second anion exchange membrane 1068 and cathode 114,
wherein on applying a voltage 130 across cathode 114 and anode 112,
the system forms bicarbonate ions 122 in first electrolyte 102
without forming a gas at the cathode or anode. In various
embodiments, the system forms bicarbonate ions in first electrolyte
102 when a voltage of 0.4 V or less, or 0.6 V or less, or 0.8 V or
less is applied across the anode and cathode. In various
embodiments, bicarbonate ions 122 are formed when the voltage
applied across anode 112 and cathode 114 is less than 2.8, 2.7,
2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4,
1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1
V. In certain embodiments, bicarbonate ions are formed when the
voltage applied across the anode and cathode is less than 0.8 V
without forming a gas at the electrodes. In certain embodiments,
bicarbonate ions are formed when the voltage applied across the
anode and cathode is less than 0.7 V without forming a gas at the
electrodes. In certain embodiments, bicarbonate ions are formed
when the voltage applied across the anode and cathode is less than
0.6 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.5 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.4 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.3 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.2 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.1 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.05 V without forming a gas at the electrodes.
[0038] System 200 in various embodiments will form an acid, e.g.,
hydrochloric acid 124, depending on the electrolytes used. As is
illustrated in FIG. 2, the system will form a protonated solution
(acid solution) in third electrolyte 118, e.g., hydrochloric acid
as a result of transfer of protons across cation exchange membrane
108A from first electrolyte 102; and an ionic solution, e.g.,
stannous chloride will form in second electrolyte 116 as a result
of chloride ions transferring across anion exchange membrane 106
from first electrolyte 102, assuming tin ions are present in the
second electrolyte 116 from oxidation of anode 112 comprising tin.
In various embodiments, optionally, electrolyte 116 in contact with
anode 112 is reused as electrolyte 118 in contact with cathode 114
to recover anodic metal that may have oxidized into second
electrolyte 116 at anode 112. Likewise, electrolyte 206 in contact
with cathode 114 may be reused as electrolyte 116 in contact with
anode 112. It will be appreciated that when sacrificial anode 112
is diminished and cathode 114 is augmented sufficiently, these
electrodes may be switched so that anode 112 is transferred to
replace cathode 114 and vice versa.
[0039] As is illustrated in FIG. 2, system 200 includes inlet ports
126 A-E adapted for introducing materials into cell 202, e.g., for
introducing carbon dioxide 104, sodium chloride solution 126 and
other electrolytes into cell 202; and outlet ports 130 A-D for
removing materials from the cell, e.g., removing bicarbonate
solution 122 and acid 124 from the cell. As will be appreciated by
one ordinarily skilled in the art, the inlet and outlet ports are
adaptable for various flow protocols including batch flow,
semi-batch flow, or continuous flow. In various embodiments, the
system includes voltage/current regulator 120 for regulating
currents and voltages across the anode, cathode and the
electrolytes.
[0040] In the system illustrated in FIG. 2, electrochemical cell
202 comprises first compartment 132, second compartment 134, third
compartment 136 and fourth compartment 138 formed by positioning
first anion exchange membrane 106A and first cation exchange
membrane 108A to separate first electrolyte 102 from second
electrolyte 116 and third electrolyte 118, and by positioning
second anion exchange membrane 1068 to separate third electrolyte
118 from fourth electrolyte 206. As will be appreciated in the art,
the ion exchange membranes in various embodiments are positioned to
contact the electrolytes at opposite surfaces to allow movement of
ions from one electrolyte to another electrolyte through the ion
exchange membranes without mixing of the electrolytes.
[0041] As with the system of FIG. 1, in the system of FIG. 2, first
102, second 116 third 118 and fourth 206 electrolytes initially may
comprise an aqueous salt solution such as a saltwater, e.g.,
seawater, brine, brackish water, conductive fresh water and the
like. In results obtained from one embodiment as set forth in Table
1, first electrolyte 102 initially comprised 2 M sodium chloride
solution; in another embodiment first electrolyte 102 comprised 0.5
M sodium chloride solution. In specific embodiments the system may
be charged initially with a salt solution, e.g., sodium chloride,
at a concentration from 0.1 to 4 M, e.g., 0.1 to 2.5 M, or 0.2 to
2.0 M, or 0.1 to 1.0 M, or 0.2 to 1.0 M, or 0.2 to 0.8 M, or 0.3 to
0.7 M, or 0.4 to 0.6 M, or 0.5 to 2.5 M, or 1.0 to 2.5 M, or 1.5 to
2.5 M, or 1.7 to 2.3 M.
[0042] With reference to FIG. 2, the voltage across anode 112 and
cathode 114 can be regulated to form bicarbonate ions 122 in first
electrolyte 102 without forming a gas, e.g., chlorine at anode 112
or hydrogen at cathode 114. Similarly, by regulating a voltage
across cathode 114 and anode 112 as with the system of FIG. 1, a
protonated (acid) solution 124 is formed in third electrolyte 118
in contact with cation exchange membrane 108A by protons
transferred from first electrolyte 102. The acid solution formed
will depend on the electrolytes used, e.g., as illustrated in FIG.
2, where the first electrolyte 102 comprises sodium chloride, the
acid solution formed will comprise hydrochloric acid. An acid
solution is formed, in various embodiments, when the voltage
applied across anode 112 and cathode 114 is less than 2.8, 2.7,
2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4,
1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1
V. In certain embodiments, an acid solution is formed when the
voltage applied across the anode and cathode is less than 0.8 V
without forming a gas at the electrodes. In certain embodiments, an
acid solution is formed when the voltage applied across the anode
and cathode is less than 0.7 V without forming a gas at the
electrodes. In certain embodiments, an acid solution is formed when
the voltage applied across the anode and cathode is less than 0.6 V
without forming a gas at the electrodes. In certain embodiments, an
acid solution is formed when the voltage applied across the anode
and cathode is less than 0.5 V without forming a gas at the
electrodes. In certain embodiments, an acid solution is formed when
the voltage applied across the anode and cathode is less than 0.4 V
without forming a gas at the electrodes. In certain embodiments, an
acid solution is formed when the voltage applied across the anode
and cathode is less than 0.3 V without forming a gas at the
electrodes. In certain embodiments, an acid solution is formed when
the voltage applied across the anode and cathode is less than 0.2 V
without forming a gas at the electrodes. In certain embodiments, an
acid solution is formed when the voltage applied across the anode
and cathode is less than 0.1 V without forming a gas at the
electrodes. In certain embodiments, an acid solution is formed when
the voltage applied across the anode and cathode is less than 0.05
V without forming a gas at the electrodes.
[0043] In the system of FIG. 2 as with the system of FIG. 1,
without being bound by any theory, it is believed that bicarbonate
ions are formed in first electrolyte 102 by carbon dioxide
contacting water in the first electrolyte, as follows:
CO.sub.2+H.sub.2O====>H.sup.++HCO.sub.3.sup.-
Thus, in accordance with the present invention and with reference
to FIG. 2, where first electrolyte 102 comprise Na.sup.+ and
Cl.sup.- ions from added sodium chloride 128, by placing first
electrolyte 102 between cation exchange membrane 108A selective to
transferring H.sup.+ ions, and anion exchange membrane 106A
selective to transferring of Cl.sup.- ions, and applying a voltage
across the electrodes, H.sup.+ will migrate through cation exchange
membrane 108A to adjacent third electrolyte 118. Similarly,
Cl.sup.- will migrate from the first electrolyte through the anion
exchange membrane 106A to adjacent second electrolyte 116.
Consequently, in first electrolyte 102, a solution comprising
sodium bicarbonate 122 will form. Depending on the rate of
introduction and/or removal of first electrolyte from the cell and
the voltage applied across electrodes 112, 114, the concentration
of sodium bicarbonate 122 in first electrolyte 102 will be
adjusted, e.g., increase, decrease or does not change.
[0044] Also with reference to FIG. 2, as H.sup.+ migrate from first
electrolyte 102 through cation exchange membrane 108A to adjacent
third electrolyte 118, the acidity of adjacent third electrolyte
118 will adjust depending on rate of introduction and/or removal of
third electrolyte 118 from the system. Similarly, as chloride ions
migrate from fourth electrolyte 206 to adjacent third electrolyte
118 across second anion exchange membrane 106B the chloride ions
concentration in adjacent third electrolytes 118 and fourth
electrolyte 206 will adjust.
[0045] Hence, as illustrated in FIG. 2, in various embodiments a
solution of bicarbonate ions 122, e.g., sodium bicarbonate is
obtained in first electrolyte 102; an acid solution 124, e.g.,
hydrochloric acid is obtained in third electrolyte 118; a chloride
solution, e.g., tin chloride is obtained in second electrolyte 116
where a tin anode is used; and the fourth electrolyte 206 is
depleted of chloride ions and cations, e.g., the electrolyte is
depleted of Sn.sup.2+ where the fourth electrolyte was initially
charged with a tin salt, e.g., stannous chloride.
[0046] Referring to FIG. 3, system 300 comprises first electrolyte
102 contained between first cation exchange membrane 108A and
second cation exchange membrane 1088 and to which carbon dioxide
104 is added in an electrochemical cell 302 comprising anode 112
and cathode 114; second electrolyte 116 contacting second cation
exchange membrane 1088 and anode 112; third electrolyte 118
contained between first cation exchange membrane 108A and anion
exchange membrane 106B in electrochemical cell 302; and fourth
electrolyte 206 contacting anion exchange membrane 106B and cathode
114, wherein on applying a voltage 120 across the cathode and anode
the system is capable of forming bicarbonate ions 122 in first
electrolyte 102 without forming a gas at cathode 114 or anode
112.
[0047] In system 300 illustrated in FIG. 3, electrochemical cell
302 comprises first compartment 132, second compartment 134, third
compartment 136 and fourth compartment 138 formed by positioning
first cation exchange membrane 108A and second cation exchange
membrane 1088 to separate first electrolyte 102 from second
electrolyte 116 and from third electrolyte 118; and by positioning
second anion exchange membrane 1068 to separate third electrolyte
118 from fourth electrolyte 206. As will be appreciated, the ion
exchange membranes in various embodiments are positioned to contact
the electrolytes at opposite surfaces to allow for movement of ions
from one electrolyte to another electrolyte through the ion
exchange membranes without mixing of the electrolytes.
[0048] As with the system of FIGS. 1 and 2, in the system of FIG.
3, first 102, second 116 third 118 and fourth 206 electrolytes may
initially comprise an aqueous salt solution, e.g., seawater, brine,
brackish water, conductive fresh water and the like. With results
achieved in one embodiment as set forth in Table 1, first
electrolyte 102 initially comprised 2 M solution of sodium
chloride; in another embodiment the first electrolyte 102 initially
comprised 0.5 M solution of sodium chloride. In specific
embodiments, electrolytes in the system may be charged initially
with a salt solution, e.g., sodium chloride, at a concentration
from 0.1 to 4 M, e.g., 0.1 to 2.5 M, or 0.2 to 2.0 M, or 0.1 to 1.0
M, or 0.2 to 1.0 M, or 0.2 to 0.8 M, or 0.3 to 0.7 M, or 0.4 to 0.6
M, or 0.5 to 2.5 M, or 1.0 to 2.5 M, or 1.5 to 2.5 M, or 1.7 to 2.3
M.
[0049] With reference to FIG. 3, the voltage across the anode 112
and cathode 114 can be regulated to form bicarbonate ions 122 in
the first electrolyte 102 without forming a gas, e.g., chlorine at
anode 112 or hydrogen at cathode 114. In various embodiments,
bicarbonate ions 122 are formed in first electrolyte 102 when the
voltage applied across anode 112 and cathode 114 is less than 2.8,
2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5,
1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or
0.1 V. Similarly, on applying a voltage across the cathode and
anode acid solution 124 is formed in third electrolyte 118 in
contact with cation exchange membrane 108A as a result of protons
transferring from first electrolyte 102. The acid formed depends on
the electrolytes used, e.g., as illustrated in FIG. 3, where the
first electrolyte 102 comprises sodium chloride, the acid formed
comprises hydrochloric acid 124.
[0050] In certain embodiments, bicarbonate ions and the acid
solution are formed when the voltage applied across the anode and
cathode is less than 0.8 V without forming a gas at the electrodes.
In certain embodiments, bicarbonate ions and the acid solution are
formed when the voltage applied across the anode and cathode is
less than 0.7 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions and the acid solution are formed when
the voltage applied across the anode and cathode is less than 0.6 V
without forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.5 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.4 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.3 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.2 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.1 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.05 V without
forming a gas at the electrodes.
[0051] As is illustrated in FIG. 3, system 300 includes inlet ports
126 A-D adapted for introducing materials into cell 302, e.g., for
introducing carbon dioxide 104, sodium chloride solution 126 and
other electrolytes into cell 302; and outlet ports 130 A-D for
removing materials from the cell, e.g., removing bicarbonate
solution 122 and acid 124 from the cell. As will be appreciated by
one ordinarily skilled in the art, the inlet and outlet ports are
adaptable for various flow protocols including batch flow,
semi-batch flow, or continuous flow. In various embodiments, the
system includes voltage/current regulator 120 for regulating
voltages across the anode and cathode and currents through the
electrolytes.
[0052] In the system of FIG. 3, as with the systems of FIGS. 1 and
2, without being bound by any theory, it is believed that
bicarbonate ions (HCO.sub.3.sup.-) are formed in first electrolyte
102 by carbon dioxide contacting water in the first electrolyte, as
follows:
CO.sub.2+H.sub.2O====>H.sup.++HCO.sub.3.sup.-
Thus, in accordance with the present invention and with reference
to FIG. 3, where second electrolyte 116 comprise Na.sup.+ and
Cl.sup.- ions from added sodium chloride 128, by placing first
electrolyte 102 between cation exchange membrane 108A selective to
transferring H.sup.+ ions, and second cation exchange membrane 108B
selective to transferring of cations, e.g., Na.sup.+ ions, and on
applying a voltage across the electrodes, H.sup.+ will migrate
through first cation exchange membrane 108A to adjacent third
electrolyte 118. Similarly, Na.sup.+ will migrate from second
electrolyte 116 through second cation exchange membrane 1088 to
adjacent first electrolyte 102. Consequently, in first electrolyte
102, a solution comprising sodium bicarbonate 122 will form.
Depending on the rate of introduction and/or removal of first
electrolyte 102 from the cell and the voltage applied across the
electrodes 112, 114, the concentration of sodium bicarbonate in
first electrolyte 102 will adjust, e.g., increase, decrease or will
not change.
[0053] Also with reference to FIG. 3, as H.sup.+ migrate from first
electrolyte 102 through first cation exchange membrane 108A to
adjacent third electrolyte 118, the acidity of adjacent third
electrolyte 118 will adjust depending on the rate of introduction
and/or removal of first electrolyte 102 from the system. Similarly,
as chloride ions migrate from fourth electrolyte 206 to adjacent
third electrolyte 118 across second anion exchange membrane 106B
the chloride ion concentration in adjacent electrolytes 118 and 206
will adjust.
[0054] Hence, as illustrated in FIG. 3, in various embodiments a
solution of bicarbonate ions 122, e.g., sodium bicarbonate is
obtained in first electrolyte 102; an acid solution 124, e.g.,
hydrochloric acid is obtained in third electrolyte 118; a chloride
solution, e.g., tin chloride is obtained in second electrolyte 116
where a tin anode is used; fourth electrolyte 206 is depleted of
chloride ions due to chloride transfer across anion exchange
membrane 1068; and fourth electrolyte 204 is also depleted of
cations by a reduction reaction at the cathode, e.g., fourth
electrolyte 206 is depleted of Sn.sup.2+ where the fourth
electrolyte was initially charged with, e.g., stannous
chloride.
[0055] Optionally, as will be appreciated by one ordinarily skilled
in the art, cations in electrolyte 116 in contact with anode 112
can be recovered by plating out the cations at the cathode 114,
e.g., using electrolyte 116 from the anode as the electrolyte at
the cathode. Thus, the anode material can be recovered at the
cathode by switching electrolyte 116 in contact anode 112 with the
electrolyte in contact with the cathode 114 when a sufficient
concentration of Sn.sup.2+ has accumulated in the electrolyte 116,
and allowing the cations to plate out at the cathode. Similarly, it
will be appreciated that when sacrificial anode 112 is diminished
and cathode 114 is augmented sufficiently, these electrodes may be
switched so that anode 112 is transferred to replace cathode 114
and vice versa.
[0056] In an embodiment as illustrated in FIG. 4, system 400
comprises first electrolyte 102 contained between first cation
exchange membrane 108A and second cation exchange membrane 1088;
second electrolyte 116 contacting anode 112 and separated from
fifth electrolyte 404 by first anion exchange membrane 106A; third
electrolyte 118 contained between first cation exchange membrane
108A and second anion exchange membrane 1068; fourth electrolyte
206 contacting second anion exchange membrane 106B and cathode 114;
and fifth electrolyte 404 comprising an electrolyte containing,
e.g., sodium chloride solution 128, and contained between first
anion exchange membrane 106A and second cation exchange membrane
108B, wherein on applying a voltage across the cathode 114 and
anode 112 and adding carbon dioxide 104 to first electrolyte 102,
the system is capable of forming bicarbonate ions 122 in first
electrolyte 102 without forming a gas at cathode 114 and anode
112.
[0057] Referring to system 400 of FIG. 4, electrochemical cell 402
comprises first compartment 132, second compartment 134, third
compartment 136, fourth compartment 138, and fifth compartment 140
formed by positioning first cation exchange membrane 108A and
second cation exchange membrane 108B to separate first electrolyte
102 from fifth electrolyte 404 and from third electrolyte 118. In
the system, second anion exchange membrane 106B is positioned to
separate third electrolyte 118 from fourth electrolyte 206; and
first anion exchange membrane 106A is positioned to separate second
electrolyte 116 in contact with anode 112 from fifth electrolyte
404 comprising sodium chloride solution 128.
[0058] As is illustrated in FIG. 4, in various embodiments
initially sodium chloride 128 is added to fifth compartment 140 and
carbon dioxide is added to first electrolyte 102 in compartment
132. As will be appreciated in the art, the ion exchange membranes
in various embodiments are positioned to contact the electrolytes
at opposite surfaces to allow for transfer of ions from one
electrolyte to another electrolyte through the ion exchange
membranes without mixing of the electrolytes. In various
embodiments system 400 is capable of forming bicarbonate ions in
first electrolyte 102 when a voltage of 0.4 V or less, or 0.6 V or
less, or 0.8 V or less is applied across the anode 112 and cathode
114.
[0059] In the system of FIG. 4, first electrolyte 102, second
electrolyte 116 third electrolyte 118, and fourth electrolyte 206
initially may comprise an aqueous salt solution such as a
saltwater, e.g., sodium chloride, stannous chloride, seawater,
brine, brackish water, conductive fresh water and the like. As
indicated by the results achieved with one embodiment as set forth
in Table 1, initially a 2 M solution of sodium chloride sodium
chloride solution 128 was added to fourth compartment 140 to form
fifth electrolyte 404; in another embodiment, initially fifth
electrolyte 404 comprised 0.5 M solution of sodium chloride. In
specific embodiments, the fifth electrolyte 404 may be charged
initially with a salt solution, e.g., sodium chloride, at a
concentration from 0.1 to 4 M, e.g., 0.1 to 2.5 M, or 0.2 to 2.0 M,
or 0.1 to 1.0 M, or 0.2 to 1.0 M, or 0.2 to 0.8 M, or 0.3 to 0.7 M,
or 0.4 to 0.6 M, or 0.5 to 2.5 M, or 1.0 to 2.5 M, or 1.5 to 2.5 M,
or 1.7 to 2.3 M.
[0060] Referring to FIG. 4, the voltage across anode 112 and
cathode 114 can be regulated to form bicarbonate ions 122 in first
electrolyte 102 without forming a gas, e.g., chlorine at anode 112
or hydrogen at cathode 114. In various embodiments, bicarbonate
ions 122 are formed in first electrolyte 102 where the voltage
applied across anode 112 and cathode 114 is less than 2.8, 2.7,
2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4,
1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1
V. Similarly, on applying a voltage across the cathode 114 and
anode 112 an acid solution 124 is formed in third electrolyte 118
in contact with first cation exchange membrane 108A as a result of
protons transfer through first cation exchange membrane 108A from
first electrolyte 102. The acid formed depends on the electrolytes
used, e.g., as illustrated in FIG. 4, where first electrolyte 102
comprises sodium chloride, the acid formed in third electrolyte 118
comprises hydrochloric acid. In certain embodiments, bicarbonate
ions and the acid solution are formed when the voltage applied
across the anode and cathode is less than 0.8 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions and
the acid solution are formed when the voltage applied across the
anode and cathode is less than 0.7 V without forming a gas at the
electrodes. In certain embodiments, bicarbonate ions and the acid
solution are formed when the voltage applied across the anode and
cathode is less than 0.6 V without forming a gas at the electrodes.
In certain embodiments, bicarbonate ions and the acid solution are
formed when the voltage applied across the anode and cathode is
less than 0.5 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions and the acid solution are formed when
the voltage applied across the anode and cathode is less than 0.4 V
without forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.3 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.2 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.1 V without
forming a gas at the electrodes. In certain embodiments,
bicarbonate ions and the acid solution are formed when the voltage
applied across the anode and cathode is less than 0.05 V without
forming a gas at the electrodes.
[0061] As is illustrated in FIG. 4, system 400 includes inlet ports
126 A-E adapted for introducing substances into cell 402, e.g., for
introducing carbon dioxide 104, sodium chloride solution 128 and
other electrolytes into cell 402; and outlet ports 130 A-E for
removing substances from the cell, e.g., removing bicarbonate
solution 122 and acid 124 from the cell. As will be appreciated by
one ordinarily skilled in the art, the inlet and outlet ports are
adaptable for various flow protocols including batch flow,
semi-batch flow, or continuous flow. In various embodiments, the
system includes voltage regulator 120 for regulating voltages
across the anode and cathode and current through the
electrolytes.
[0062] In system 400 of FIG. 4, as with the systems of FIGS. 1, 2
and 3, without being bound by any theory, it is believed that
bicarbonate ions (HCO.sub.3.sup.-) are formed in first electrolyte
102 by carbon dioxide contacting water in the first electrolyte
102, as follows:
CO.sub.2+H.sub.2O====>H.sup.++HCO.sub.3.sup.-
Thus, in accordance with the present invention and with reference
to FIG. 4, where fifth electrolyte 404 comprise Na.sup.+ and
Cl.sup.- ions from added sodium chloride 128, by placing first
electrolyte 102 between cation exchange membrane 108A selective to
transferring H.sup.+ ions, and second cation exchange membrane 108B
selective to transferring of cations, e.g., Na.sup.+ ions, and on
applying a voltage across the electrodes, H.sup.+ will migrate
through first cation exchange membrane 108A to adjacent third
electrolyte 118. Similarly, Na.sup.+ will migrate from fifth
electrolyte 404 through second cation exchange membrane 108B to
first electrolyte 102. Consequently, in first electrolyte 102, a
solution comprising sodium bicarbonate 122 will form. Depending on
the rate of introduction and/or removal of first electrolyte from
the cell and the voltage applied across the electrodes 112, 114,
the concentration of sodium bicarbonate 122 in first electrolyte
102 will adjust, e.g., increase, decrease or will not change.
[0063] Also with reference to FIG. 4, as H.sup.+ migrate from first
electrolyte 102 through first cation exchange membrane 108A to
adjacent third electrolyte 118, the acidity of adjacent third
electrolyte 118 will adjust depending on the rate of introduction
and/or removal of hydrochloric acid 124 from the system. Similarly,
as chloride ions migrate from fourth electrolyte 206 to adjacent
third electrolyte 118 across second anion exchange membrane 108B,
the chloride ion concentration in adjacent electrolytes 118 and 206
will adjust. Additionally, as chloride ions migrate from sodium
chloride solution 128 in fifth electrolyte 404 to the second
electrolyte 116 across first anion exchange membrane 106A, fifth
electrolyte 404 will be depleted of chloride ions; consequently,
fifth electrolyte will be depleted of sodium chloride, and
correspondingly, the chloride ion content of the second electrolyte
116 will adjust, e.g., increase, decrease or remain constant
depending on the flow of second electrolyte 116 from the
system.
[0064] Hence, as illustrated in FIG. 4, in various embodiments a
solution of bicarbonate ions 122, e.g., sodium bicarbonate is
obtained in first electrolyte 102; an acid solution 124, e.g.,
hydrochloric acid is obtained in third electrolyte 118; a chloride
solution, e.g., stannous chloride, is obtained in second
electrolyte 116; fourth electrolyte 206 will be depleted of
chloride ions; and fifth electrolyte 404 initially comprising
sodium chloride solution 128 will be depleted of sodium and
chloride ions.
[0065] Optionally, as will be appreciated by one ordinarily skilled
in the art, cations in electrolyte 116 in contact with anode 112
can be recovered by plating out the cations at the cathode 114,
e.g., using electrolyte 116 from the anode as the electrolyte at
the cathode. Thus, the anode material can be recovered at the
cathode by switching electrolyte 116 in contact anode 112 with the
electrolyte in contact with the cathode 114 when a sufficient
concentration of Sn.sup.2+ has accumulated in the electrolyte 116,
and allowing the cations to plate out at the cathode. Similarly, it
will be appreciated that when sacrificial anode 112 is diminished
and cathode 114 is augmented sufficiently, these electrodes may be
switched so that anode 112 is transferred to replace cathode 114
and vice versa.
[0066] In an embodiment as illustrated in FIG. 5 and with reference
to FIGS. 1-4, present method 500 comprises step 502 of applying a
voltage 120 across an anode 112 and a cathode 114 through a first
electrolyte 102 comprising carbon dioxide 104 to form bicarbonate
ions 122 in the first electrolyte without forming a gas at the
cathode or the anode. In accordance with the method and with
reference to FIG. 1, first electrolyte 102 is contained between
first anion exchange membrane 106A and first cation exchange
membrane 108A in electrochemical cell 100; the anion exchange
membrane contacts the anode 112 through second electrolyte 116; and
the cation exchange membrane contacts cathode 112 through third
electrolyte 118. In various embodiments, the method forms
bicarbonate ions 122 in first electrolyte 102 when a voltage, e.g.,
0.4 V or less, or 0.6 V or less, or 0.8 V or less is applied across
the anode and cathode. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.8 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.7 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.6 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.5 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.4 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.3 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.2 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.1 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.05 V without forming a gas at the electrodes.
[0067] As described with reference to the systems of FIGS. 1-4
above, method 500 forms a protonated solution in third electrolyte
118, e.g., hydrochloric acid 124 as a result of transfer of protons
across first cation exchange membrane 108A from first electrolyte
102; and an ionic solution, e.g., stannous chloride in second
electrolyte 116, as a result of chloride ions transferring across
first anion exchange membrane 106A from first electrolyte 102, and
tin ions forming in second electrolyte 116 by oxidation of anode
112 comprising tin.
[0068] In various embodiments of method 500, optionally, where
anode 112 comprises a sacrificial anode, e.g., tin, copper, iron,
zinc, cations such as Sn.sup.2+ will form in second electrolyte 116
in contact with anode 112. Optionally, as described above with
reference to FIGS. 1-4, cations in electrolyte 116 in contact with
anode 112 can be recovered by plating out the cations at the
cathode 114, e.g., using electrolyte 116 from the anode as the
electrolyte at the cathode. Thus, anode material can be recovered
at the cathode 114 by switching electrolyte 116 in contact anode
112 with the electrolyte in contact with the cathode 114 when a
sufficient concentration of Sn.sup.2+ has accumulated in the
electrolyte 116, and allowing the cations to plate out at the
cathode.
[0069] In another embodiment and with reference to FIGS. 1-4,
method 600 comprises step 602 of applying a voltage 120 of less
than 2.0 V, less than 1.5 V, less than 1.0 V, less than 0.5 V, less
than 0.1 V or less than 0.05 V across an anode 112 and a cathode
114 through first electrolyte 102 comprising carbon dioxide 104 to
form bicarbonate ions 122 in the first electrolyte. In various
embodiments the method forms bicarbonate ions in first electrolyte
when a voltage, e.g., 0.4 V or less, or 0.6 V or less, or 0.8 V or
less is applied across the anode and cathode. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.8 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.7 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.6 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.5 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.4 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.3 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.2 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.1 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.05 V without forming a
gas at the electrodes.
[0070] In accordance with method 600, and with reference to FIG. 1,
first electrolyte 102 is contained between first anion exchange
membrane 106A and first cation exchange membrane 108A in
electrochemical cell 302; first anion exchange membrane 106A
contacts anode 112 through second electrolyte 116; and first cation
exchange membrane 108A contacts the cathode through third
electrolyte 118. In another embodiment of method 600, and with
reference to FIG. 3, first electrolyte 102 is contained between
first cation exchange membrane 108A and second cation exchange
membrane 108B in electrochemical cell 303; second cation exchange
membrane 1088 contacts anode 112 through second electrolyte 116;
first cation exchange membrane 108A separates first electrolyte 102
from third electrolyte 118; second anion exchange membrane 1068
separates third electrolyte 118 from fourth electrolyte 206; and
fourth electrolyte 206 is in contact with cathode 114. In various
embodiments, method 600 forms bicarbonate ions 122 in first
electrolyte when a voltage, e.g., 0.4 V or less, or 0.6 V or less,
or 0.8 V or less is applied across the anode and cathode.
[0071] As disclosed with reference to the system of FIGS. 1-4
above, method 600 forms an acid, e.g., hydrochloric acid 124,
depending on the electrolytes used. As is illustrated in FIG. 1,
the method forms a protonated solution in third electrolyte 118,
e.g., hydrochloric acid as a result of transfer of protons across
first cation exchange membrane 108A from first electrolyte 102; and
an ionic solution, e.g., stannous chloride in second electrolyte
116, as a result of chlorine ions transferring across first anion
exchange membrane 106A from first electrolyte 102, and tin ions
forming by oxidation of the anode 112.
[0072] In various embodiments of method 600, optionally, where
anode 112 comprises a sacrificial anode, e.g., tin, copper, iron,
zinc, cations such as Sn.sup.2+ will form in second electrolyte 116
in contact with anode 112. Optionally, as described above with
reference to FIGS. 1-4, cations in electrolyte 116 in contact with
anode 112 can be recovered by plating out the cations at the
cathode 114, e.g., using electrolyte 116 from the anode as the
electrolyte at the cathode. Thus, anode material can be recovered
at the cathode 114 by switching electrolyte 116 in contact anode
112 with the electrolyte in contact with the cathode 114 when a
sufficient concentration of Sn.sup.2+ has accumulated in the
electrolyte 116, and allowing the cations to plate out at the
cathode. Similarly, it will be appreciated that when sacrificial
anode 112 is diminished and cathode 114 is augmented sufficiently,
these electrodes may be switched so that anode 112 is transferred
to replace cathode 114 and vice versa.
[0073] Exemplary results achieved in one embodiment of the present
system and method are set forth in Table 1.
TABLE-US-00001 TABLE 1 LOW ENERGY ELECTROCHEMICAL BICARBONATE ION
SOLUTIONS Voltage across pH of electrolyte pH of Bicarbonate Anode
and solution in ion solution Cathode (V) Compartment 136 in
Compartment 132 0.4 Initial 6.163 4.229 pH Final 4.367 5.950 pH 0.6
Initial 5.846 4.447 pH Final 4.408 5.824 pH 0.8 Initial 8.502 4.306
pH Final 4.353 6.642 pH
[0074] In this example, based on system 100 of FIG. 1 and method
500 of FIG. 5 and method 600 of FIG. 6, first electrolyte 102,
contained in compartment 132, was charged with a 2 M sodium
chloride solution 128 to which carbon dioxide gas 104 was added.
Third electrolyte 118 comprising saltwater, e.g., stannous chloride
was contained in compartment 136. First anion exchange membrane
106A separated first electrolyte 102 from second electrolyte 116;
first cation exchange membrane 108A separated first electrolyte 102
from third electrolyte 118; anode 112 formed of tin foil were
placed in contact with second electrolyte 116, and cathode 114
formed of tin foil was placed in contact with third electrolyte
118. Voltages of 0.4 V, 0.6 V and 0.8 V were applied across anode
112 and cathode 114 in a batch mode operation for one hour. As set
forth in Table 1, the pH of first electrolyte 102 in compartment
132 increased (correlating to an increase of hydroxide ion
concentration in first electrolyte 102 as described above), while
the pH of third electrolyte 118 in compartment 136 decreased
(correlating to an increase in protons in third electrolyte 118 as
described above), without the formation of a gas, e.g., chlorine at
anode 112 or hydrogen at cathode 114.
[0075] As discussed above with reference to FIGS. 1-4, without
being bound by any theory it is believed that in first electrolyte
102 bicarbonate ions formed as a result of carbon dioxide
contacting water in first electrolyte 102, as follows:
CO.sub.2+H.sub.2O====>H.sup.++HCO.sub.3.sup.-.
In first electrolyte 102, Na.sup.+ and Cl.sup.- ions are present
from the sodium chloride 128. Thus, in accordance with the present
invention, by placing first electrolyte 102 between first cation
exchange membrane 108A selective to transferring H.sup.+ ions, and
first anion exchange membrane 106A selective to transferring of
Cl.sup.- ions, and on applying a voltage across the electrodes,
H.sup.+ migrated through cation exchange membrane 108A to adjacent
third electrolyte 118. Similarly, Cl.sup.- migrated from first
electrolyte 102 through anion 106A exchange membrane to adjacent
second electrolyte 116. Consequently, a solution comprising sodium
bicarbonate 122 formed in first electrolyte 102. With the formation
of sodium bicarbonate in first electrolyte 102 the pH of the first
electrolyte increased in accordance with the following
reaction:
NaHCO.sub.3.sup.-+H.sub.2O.fwdarw.H.sub.2CO.sub.3+Na.sup.++OH.sup.-
As discussed with reference to FIGS. 1-4, as H.sup.+ migrated from
the first electrolyte 102 through first cation exchange membrane
108A to adjacent third electrolyte 118 in third compartment 136,
the acidity of adjacent third electrolyte 118 increased as
indicated by the decrease in pH in third compartment 136 as set
forth in Table 1.
[0076] As will be appreciated by one ordinary skilled in the art,
the voltages may be adjusted up or down from these exemplary
voltages; a minimum theoretical voltages 0 V or very close to 0 V,
but to achieve a useful rate of production of bicarbonate ions, a
practical lower limit may be in some embodiments 0.001 V or 0.01 V,
or 0.1 V, depending on the desired time for bicarbonate ion
production and/or pH adjustment, volume of first electrolyte
solution 102, and other factors apparent to those of ordinary
skill; e.g., in some embodiments system 100, system 200, system 300
and system 400 and method 500 and method 600 are capable of
producing bicarbonate ions at voltages as low as 0.001 V, or 0.01
V, or 0.1V, and can also produce bicarbonate ions at higher
voltages if more rapid production is desired, e.g., at 0.2-2.0 V;
in various embodiments the bicarbonate ions are produced with no
gas formation at the anode or cathode, e.g., no formation of
hydrogen or chlorine at the electrodes.
[0077] In these examples, and in various embodiments of the
invention, a pH difference of more than 0.5, 1.0, 1.5, 2.0, 2.5,
3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5,
10.0, 10.5, 11.0, 11.5, or 12.0 pH units may be produced in a first
electrolyte solution 102 and in third electrolyte solution 118 when
a voltage of 1.0 V or less, or 0.9 V or less, or 0.8 V or less, or
0.7 V or less, or 0.6V or less, or 0.5 V or less, or 0.4 V or less,
or 0.3 V or less, or 0.2 V or less, or 0.1 V or less, or 0.05 V or
less is applied across the anode and cathode. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.8 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.7 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.6 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.5 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.4 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.3 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.2 V without forming a
gas at the electrodes. In certain embodiments, bicarbonate ions are
formed when the voltage applied across the anode and cathode is
less than 0.1 V without forming a gas at the electrodes. In certain
embodiments, bicarbonate ions are formed when the voltage applied
across the anode and cathode is less than 0.05 V without forming a
gas at the electrodes.
[0078] As will be appreciated, in particular embodiments, the
present invention provides a system and method capable of producing
a pH difference of more than 0.5 pH units in first electrolyte 102
and third electrolyte 118 when a voltage of 0.05 V or less is
applied across the anode and cathode. In some embodiments, the
invention provides a system and method capable of producing a pH
difference of more than 1.0 pH units between first electrolyte 102
and third electrolyte 118 when a voltage of 0.1V or less is applied
across the anode and cathode. In some embodiments, the invention
provides a system and method capable of producing a pH difference
of more than 2.0 pH units between a first electrolyte and third
electrolyte when a voltage of 0.2 V or less is applied across the
anode and cathode.
[0079] In some embodiments, the invention provides a system and
method capable of producing bicarbonate ions in first electrolyte
102 when a voltage of 0.4V or less is applied across the anode and
cathode. In some embodiments, the invention provides a system and
method capable of producing bicarbonates ions 122 when a voltage of
0.6V or less is applied across the anode and cathode. In some
embodiments, the invention provides a system and method capable of
producing bicarbonate ions 122 when a voltage of 0.8V or less is
applied across the anode and cathode. In particular embodiments,
the invention provides a system capable of producing bicarbonate
ions 122 when a voltage of 1.0 V or less is applied across the
anode and cathode. In some embodiments the invention provides a
system capable of producing bicarbonate ions 122 in first
electrolyte 102 when a voltage of 1.2 V or less is applied across
the anode and cathode.
[0080] It will be appreciated that the voltage need not be kept
constant and that the voltage applied across the anode and the
cathode may be very low, e.g., 0.05V or less and that the voltage
may be increased as needed as the concentration of bicarbonate ions
in the solution 102 increases. In this manner, a desired
bicarbonate ion concentration may be achieved with the minimum
average voltage, without generating a gas at the electrodes. Thus,
in some embodiments as described in the previous paragraph, the
average voltage may be less than 80%, 70%, 60%, or less than 50% of
the voltages noted in the previous paragraph for particular
embodiments.
[0081] In some embodiments, one or more of the initial electrolytes
charged into the system may be depleted of divalent cations, e.g.,
the electrolytes are depleted of magnesium or calcium ion as for
example where the electrolytes are taken form an ion exchange
process. Thus, in some embodiments the total concentration of
divalent cations in the electrolyte solutions in contact with the
ion exchange membrane or membranes is less than 0.06 mol/kg
solution, or less than 0.05 mol/kg solution, or less than 0.04
mol/kg solution, or less than 0.02 mol/kg solution, or less than
0.01 mol/kg solution, or less than 0.005 mol/kg solution, or less
than 0.001 mol/kg solution, or less than 0.0005 mol/kg solution, or
less than 0.0001 mol/kg solution, or less than 0.00005 mol/kg
solution.
[0082] As discussed in various embodiments herein, the carbon
dioxide that contacts first electrolyte 102 may initially form
bicarbonate ions 122 in the first electrolyte. As bicarbonate ions
are removed from first electrolyte 102 more carbon dioxide may
dissolve in the electrolyte to form bicarbonate and/or carbonate
ions. Depending on the pH of the first electrolyte, the balance is
shifted toward bicarbonate or toward carbonate formation, as is
well understood in the art. In these embodiments the pH of the
first electrolyte may decrease, remain the same, or increase,
depending on the rate of removal of bicarbonate and/or carbonate
ions compared to rate of introduction of carbon dioxide. It will be
appreciated that no bicarbonate ions need form in these
embodiments, or that bicarbonate ions may not form during one
period but form during another period.
[0083] Optionally, the present system is used to produce
bicarbonate ions 122, which, when included in a solution comprising
alkaline earth cations and hydroxide ions causes precipitation of
carbonate and/or bicarbonate compounds such as calcium carbonate or
magnesium carbonate and/or their bicarbonates. In various
embodiments, divalent cations such as magnesium and/or calcium are
present in the solutions used in the process, and/or are added. The
precipitated carbonate compound can be used as cements and other
building and construction material such as aggregates and the like
as described in U.S. patent application Ser. No. 12/126,776, filed
on May 23, 2008, incorporated herein by reference.
[0084] In an optional step, the acidified electrolyte solution 118
illustrated in FIGS. 1-4 is utilized to dissolve a calcium and/or
magnesium rich mineral, such as mafic mineral including serpentine
or olivine, to form a solution for precipitating carbonates and
bicarbonates as described in the United States patent applications
incorporated herein by reference. For example, acidified stream 118
can be used to dissolve calcium and/or magnesium rich minerals such
as serpentine and olivine to from an electrolyte solution that can
be charged with bicarbonate ions 122 and then made sufficiently
basic to precipitate carbonate compounds. Such precipitation
reactions and the use of the precipitates, e.g., as in cements are
described in the U.S. patent application Ser. No. 12/126,776, filed
on May 23, 2008 and incorporated herein by reference.
[0085] In an other optional embodiment, the bicarbonate ion
solutions of the present invention can be utilized to desalinate
saltwater by removing divalent cations as insoluble carbonates,
e.g., removing calcium and magnesium ions from a saltwater e.g.,
seawater based on the following reactions and as described in U.S.
patent application Ser. No. 12/163,205, filed on Jun. 27, 2008,
herein incorporated by reference:
HCO.sub.3.sup.+====>H++CO.sub.3.sup.- (bicarbonate ions
dissociate to carbonate ions)
Ca.sup.+++CO.sub.3.sup.-====>CaCO.sub.3 (carbonate ions
precipitate calcium carbonate)
Mg.sup.+++CO.sub.3.sup.-====>MgCO.sub.3 (carbonate ions
precipitate magnesium carbonate)
[0086] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it will be readily apparent to those of ordinary
skill in the art in light of the teachings of this invention that
certain changes and modifications may be made thereto without
departing from the spirit or scope of the appended claims.
[0087] Accordingly, the preceding merely illustrates the principles
of the invention. It will be appreciated that those skilled in the
art will be able to devise various arrangements, which, although
not explicitly described or shown herein, embody the principles of
the invention, and are included within its spirit and scope. Also,
examples and conditional language recited herein are principally
intended to aid the reader in understanding the principles of the
invention and the concepts contributed by the inventors to
furthering the art, and are to be construed as being without
limitation to such specifically recited examples and conditions.
Moreover, all statements herein reciting principles, aspects, and
embodiments of the invention as well as specific examples thereof,
are intended to encompass both structural and functional
equivalents thereof. Additionally, it is intended that such
equivalents include both currently known equivalents and
equivalents developed in the future, i.e., any elements developed
that perform the same function, regardless of structure. The scope
of the present invention, therefore, is not intended to be limited
to the exemplary embodiments shown and described herein. Rather,
the scope and spirit of present invention is embodied by the
appended claims.
* * * * *