RELATED APPLICATIONS

[001] This application claims benefit under 35 U.S.C. § 119(e) to U.S. provisional patent application no. 61/512,063, filed July 27, 2011 , the entire disclosure of which is herein incorporated by reference.

TECHNICAL FIELD

[002] The subject matter described herein relates to fuel cells and to electrochemical desalination and production of economically valuable chemical stocks.

BACKGROUND

[003] Desalination can be used in a variety of applications, including treatment of brine solutions produced by industrial processes, pre-disposal treatment of produced water (e.g. from oil and gas recovery operations) production of drinking water from seawater or brackish or otherwise non-potable water supplies, production of irrigation water, and other processes that reduce a total dissolved solids concentration of an input fluid. In general, desalination processes are energy intensive and therefore quite expensive. Additionally, desalination processes generally produce substantial quantities of concentrated brine that must be disposed of or treated so that it is suitable to be discharged or used. In the example of seawater desalination to produce drinking water, concerns about damage to marine life, various environmental regulations, and the like can dictate against directly discharging this brine back to the ocean without lowering its concentration. SUMMARY

[004] Implementations of the current subject matter can provide one or more advantages that can improve upon unfavorable aspects of conventional desalination processes, potentially including, but not limited to those mentioned above. As an example, water having a high concentration of total dissolved solids (e.g. a brine solution, produced water, etc.) can be desalinated or otherwise reduced in total dissolved solids in a process that can be driven by a combination of oxidation and reduction reactions occurring respectively at an anode and a cathode of an electrochemical desalination cell. The combination of oxidation and reduction reactions can be thermodynamically favorable (e.g. can have a Gibbs Free Energy of reaction that is less than zero), and can in some examples produce usable electricity. Carbon dioxide can optionally be sequestered as part of the process occurring at the cathode of an electrochemical desalination cell consistent with some implementations of the current subject matter. Some implementations of the current subject matter can use calcium carbonate as an input feed to provide some of the energy required for a desalination process. Calcium carbonate is widely available and relatively inexpensive. As discussed in greater detail below, implementations of the current subject matter can also optionally produce useful and valuable chemical feed stocks, which can be used or sold to further offset costs of operation or enhance revenue.

[005] In one aspect, a system includes an anion exchange membrane, a cation exchange membrane, an anode assembly, a cathode assembly, and an external circuit connecting the anode assembly to the cathode assembly. The anion exchange membrane allows passage of anions while restricting passage of cations, and the cation exchange membrane allows passage of cations while restricting passage of anions. The cation exchange membrane is disposed relative to the anion exchange membrane to form at least one desalination compartment between the cation exchange membrane and the anion exchange membrane. The anode assembly includes an anode electrode configured to contact an anode electrolyte solution at least partially contained between the anode electrode and the anion exchange membrane. The cathode assembly includes a cathode electrode configured to contact a cathode electrolyte solution at least partially contained between the cathode electrode and the cation exchange membrane. At least one oxidation reaction involving at least one anode reactant at the anode electrode causes creation of anodic cations in the anode electrolyte solution, and at least one reduction reaction involving at least one cathode reactant at the cathode causes creation of cathodic anions in the cathode electrolyte solution such that a full reaction including the at least one oxidation reaction and the at least one reduction reaction is thermodynamically favorable. The created anodic cations cause brine anions from a brine provided in the desalination compartment to pass through the anion exchange membrane into the anode electrolyte solution, and the created cathodic anions cause brine cations from the brine provided in the desalination compartment to pass through the cation exchange membrane into the cathode electrolyte solution such that the brine is reduced in concentration of the brine anions and the brine cations.

[006] In one aspect, a method includes providing an anode reactant at an anode assembly and a cathode reactant at a cathode assembly of an electrochemical desalination cell. The anode assembly includes an anode electrode, and the cathode assembly includes a cathode electrode. At least one first compound of the anode reactant is oxidized, for example in an oxidation reaction, at the anode assembly to produce anodic cations in an anode electrolyte solution, and at least one second compound of the cathode reactant is reduced at the cathode electrode, for example in a reduction reaction, to produce cathodic anions in a cathode electrolyte solution. The oxidizing and the reducing combine in a thermodynamically favorable full reaction. The method also includes providing a brine solution that is separated from the anode electrolyte solution by an anion exchange membrane and from the cathode electrolyte solution by a cation exchange membrane. A reduced concentration brine is produced by brine anions passing through the anion exchange membrane from the brine to the anode electrolyte solution and by brine cations passing through the cation exchange membrane from the brine to the cathode electrolyte solution.

[007] In some variations, one or more of the following can optionally be included in any feasible combination. The full reaction can optionally be sufficiently thermodynamically favorable that the reducing of the concentration of the brine occurs without application of an external electromotive potential across the external circuit. In addition, the full reaction can further optionally be sufficiently thermodynamically favorable to supply current to an electrical load on the external circuit in addition to reducing of the concentration of the brine. The oxidation reaction can optionally produce a positive charge concentration in the anode electrolyte, and the reduction reaction can optionally produce a negative charge concentration in the cathode electrolyte, thereby drawing brine anions into the anode electrolyte through the anion exchange membrane and brine cations into the cathode electrolyte through the cation exchange membrane. An anode compartment at least partially defined by the anion exchange membrane and the anode electrode can optionally be configured to be provided with the anode electrolyte. A cathode compartment at least partially defined by the cation exchange membrane and the cathode electrode can optionally be configured to be provided with the cathode electrolyte.

[008] The anode reactant can optionally include at least one of hydrogen gas, methane, methanol, ethanol, carbon monoxide, ammonia, water, and water vapor. The cathode reactant can optionally include at least one of oxygen, nitrogen, liquid water, water vapor, an oxide of nitrogen, an oxide of phosphorus, an oxide of sulfur, and an oxide of carbon. The anodic anions can optionally include hydrogen ions. The cathodic anions can optionally include at least one of hydroxide ions, carbonate ions, bicarbonate ions, phosphate ions, nitrate ions, and sulfate ions. The at least one anode reactant can optionally include a first gas-phase compound, and the at least one cathode reactant can optionally include a second gas-phase compound. The anode assembly can optionally include a first gas diffusion electrode for receiving the first gas phase compound, and the cathode assembly can optionally include a second gas diffusion electrode for receiving the second gas-phase compound. At least one of the anode electrode and the cathode electrode can optionally include at least one catalyst material for enhancing at least one of the oxidation reaction and the reduction reaction, respectively. The anode electrolyte solution can optionally include a suspension of a at least one of a solid carbonate salt and an acid-soluble solid compound.

[009] The passing of the brine anions from the brine provided in the desalination compartment through the anion exchange membrane into the anode electrolyte solution can optionally cause the anode electrolyte solution to become enriched to produce a higher concentration anode electrolyte containing at least one first product in solution. The at least one first product can optionally include the brine anions. A first product purification process or sub-system can optionally receive the higher concentration anode electrolyte and can optionally extract the first product in at least one of a first solid, crystalline form and a first purified, concentrated aqueous form. The first product purification process or sub-system can also optionally produce a lower concentration solution of the first product, which can optionally be returned to the anode compartment to serve as the anode electrolyte solution. [0010] The passing of the brine cations from the brine provided in the desalination compartment through the cation exchange membrane into the cathode electrolyte solution can optionally cause the cathode electrolyte solution to become enriched to produce a higher concentration cathode electrolyte containing at least one second product in solution. The at least one second product can optionally include the brine cations. A second product purification process or sub-system can optionally receive the higher concentration cathode electrolyte and can optionally extract the second product in at least one of a second solid, crystalline form and a second purified, concentrated aqueous form. The second product purification or sub-system can also optionally produce a lower concentration solution of the second product, which can optionally be returned to the cathode compartment to serve as the cathode electrolyte solution.

[0011] Systems and methods consistent with this approach are described as well as articles that comprise a tangibly embodied machine-readable medium operable to cause one or more machines (e.g., computers, etc.) to result in operations described herein. Similarly, computer systems are also described that may include a processor and a memory coupled to the processor. The memory may include one or more programs that cause the processor to perform one or more of the operations described herein. As a non-limiting example, at least one processor executing instructions can perform operations, which can optionally include operating or causing to be operated at least one device for providing the anode reactant at the anode, the cathode reactant at the cathode, and the brine in the desalination compartment.

[0012] The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principles associated with the disclosed implementations. In the drawings, [0014] FIG. 1 is a diagram illustrating aspects of a electrochemical desalination cell showing features consistent with implementations of the current subject matter;

[0015] FIG. 2 is a diagram illustrating aspects of an integrated processing system in which the electrochemical desalination cell of FIG. 1 is integrated with other processes or sub-systems;

[0016] FIG. 3A is a diagram illustrating additional details of a discharge processing process or sub-system;

[0017] FIG. 3B is a diagram illustrating additional details of a brine pre -treatment process or sub-system;

[0018] FIG. 4A is a diagram illustrating additional details of a first product concentration and crystallization process or sub-system;

[0019] FIG. 4B is a diagram illustrating additional details of a second product concentration and crystallization process or sub-system;

[0020] FIG. 5A is a diagram illustrating additional details of a first product post-processing process or sub-system;

[0021] FIG. 5B is a diagram illustrating additional details of an anode electrolyte recovery process or sub-system;

[0022] FIG. 6A is a diagram illustrating additional details of a second product post-processing process or sub-system;

[0023] FIG. 6B is a diagram illustrating additional details of a cathode electrolyte recovery process or sub-system;

[0024] FIG. 7 is a process flow diagram illustrating aspects of a method having one or more features consistent with implementations of the current subject matter;

[0025] FIG. 8 is a diagram illustrating aspects of a system in which calcium carbonate is added to the anode electrolyte solution and bicarbonate ion production is favored in the cathode compartment;

[0026] FIG. 9 is a diagram illustrating aspects of a system in which calcium carbonate is added to the anode electrolyte solution and carbonate ion production is favored in the cathode compartment; [0027] FIG. 10 is a diagram illustrating aspects of a system in which calcium carbonate is not added to the anode electrolyte solution and bicarbonate ion production is favored in the cathode compartment;

[0028] FIG. 11 is a diagram illustrating aspects of a system in which calcium carbonate is not added to the anode electrolyte solution and carbonate ion production is favored in the cathode compartment; and

[0029] FIG. 12 is a diagram illustrating how a system consistent with implementations of the current subject matter can be included in a process chain with additional treatment processes to achieve improved results.

[0030] When practical, similar reference numbers denote similar structures, features, or elements.

DETAILED DESCRIPTION

[0031] An electrochemical desalination cell (EDC) consistent with one or more implementations of the current disclosed subject matter can desalinate a brine solution while simultaneously generating electricity through the electromotive force created by reactions occurring at an anode and cathode of the EDC. The reactions at the anode and cathode can also synthesize compounds or parts of compounds that incorporate some set of ions from the brine solution, thereby allowing at least partial recovery of one or more waste products from another industrial process into a commercially valuable form.

[0032] FIG. 1 shows a diagram of a representative electrochemical desalination cell 100 consistent with one or more implementations of the current subject matter in which at least one desalination process occurs in concert with at least one oxidation-reduction reaction such that the overall cell reaction is thermodynamically favorable and that allows one or more fuel cell reactions to occur. In the system shown in FIG. 1, an anode assembly 102 and a cathode assembly 104 are arranged on opposite ends of a series of compartments that includes an anode compartment 106 and a cathode compartment 108 separated by a respective anion exchange membrane 1 10 and a cation exchange membrane 112 from a desalination compartment 114. The anion exchange membrane 110 can restrict the movement of cations between the desalination compartment 1 14 and the anode compartment 106 while allowing passage of anions according to the electrochemical potential existing across the anion exchange membrane 1 10. The cation exchange membrane 1 12 can restrict the movement of anions between the desalination compartment 1 14 and the cathode compartment 108 while allowing passage of cation according to the electrochemical potential existing across the cation exchange membrane 1 12.

[0033] An anode electrolyte solution 1 16 can be provided in the anode compartment 106 adjacent to or otherwise in contact with the anode assembly 102, and a cathode electrolyte solution 1 18 can be provided in a cathode compartment 108 adjacent to or otherwise in contact with the cathode assembly 104. The anode electrolyte solution 1 16 and the cathode electrolyte solution 1 18 can each include electrolytes that are initially present at a relatively low concentration. These electrolytes can ions generated at the anode assembly 102 and cathode assembly, respectively, as well as one or more compounds that can optionally be included for increasing conductivity, decreasing the incidence of scaling, and/or for other reasons. A brine 120 or other relatively highly concentrated solution containing one or more dissolved species in an undesirably elevated concentration can be provided in the desalination compartment 1 14. It will be understood that the term "brine" is used herein to refer generically to an aqueous solution of one or more salts. While some implementations of the current subject matter involve the use of brines at very high concentrations of total dissolved solids, for example potentially at or near the solubility limit, other concentrations, for example potentially including relatively dilute solutions at much lower concentrations, are also within the scope of the current subject matter.

[0034] The anode assembly 102 and the cathode assembly 103 can respectively also include an anode reactant chamber 122 and a cathode reactant chamber 124, an anode electrode 125 and a cathode electrode 126, and an anode current collector 127 and a cathode current collector 128. The anode electrode 125 can optionally include an anode catalytic layer, and the cathode electrode 126 can optionally include a cathode catalytic layer, both of which are discussed in more detail below.

[0035] One or both of an anode reactant 130 provided at the anode assembly 102 and a cathode reactant 132 provided at the cathode assembly 104 can optionally include a gas phase reactant, a liquid-phase reactant, a dissolved phase reactant, and a solid phase reactant consistent with one or more implementations of the current subject matter. Examples of compounds that can serve as an anode reactant 130 can include, but are not limited to hydrogen gas, methane, methanol, ethanol, carbon monoxide, ammonia, liquid water, and water vapor. Examples of compounds that can serve as an cathode reactant 132 can include, but are not limited to oxygen, nitrogen, liquid water, water vapor, an oxide of nitrogen, an oxide of phosphorus, an oxide of sulfur, and an oxide of carbon. If one or both of the anode reactant 130 and the cathode reactant 132 include at least one gas phase compound, the respective anode reactant chamber 122 and/or cathode reactant chamber 124 can include a gas diffusion electrode. In implementations of the current subject matter in which the anode reactant 130 includes a gas-phase anode reactant, the gas diffusion electrode of the anode assembly 102 can create a diffusion layer adjacent to the anode electrode 125 in the anode electrolyte 1 16 provided in the anode compartment 106. Similarly, in implementations of the current subject matter in which the cathode reactant 132 includes a gas- phase cathode reactant, the gas diffusion electrode of the cathode assembly 104 can create a diffusion layer adjacent to the cathode electrode collector 126 in the cathode electrolyte 1 18 provided in the cathode compartment 108.

[0036] An external circuit 134 can connect the anode assembly 102, specifically the anode current collector 127, and the cathode assembly 104, specifically the cathode current collector 128, via which electrons 136 can flow from the anode assembly 102 to the cathode, optionally across an external electrical load 138. Electrons 136 are generated at the anode assembly 102 through oxidation of one or more compounds in the anode reactant 130 to create one or more electrons 136 that travel to the cathode assembly via the external circuit and one or more anodic cations (CA ) 140 that are released into the anode electrolyte 1 16 in the anode compartment 106. The electrons 136 received at the cathode assembly 104 participate in one or more reduction reactions with one or more compounds in the cathode reactant 132 to produce one or more cathode anions (Ac- ) 142 that are released into the cathode electrolyte 1 18 in the cathode compartment 108.

[0037] A gas diffusion electrode as mentioned above for use in either or both of the anode assembly 102 and the cathode assembly 104 can, in some implementations of the current subject matter, include a gas diffusion layer, such as for example those commercially available for use in fuel cells. In some examples in which a catalyst is used at either or both of the anode assembly 102 and the cathode assembly 104, the respective gas diffusion layer can be coated with an electro-catalyst ink as discussed in greater detail below. Other electrode configurations are also within the scope of the current subject matter. Introduction of a gas at either or both of the anode assembly 102 and the cathode assembly 104 can additionally or alternatively be accomplished by bubbling of the gas through a diffuser or other functionally similar apparatus. If a desired reactant is in a liquid or a solid phase, that reactant can optionally be mixed into the anode electrolyte solution 1 16, thereby potentially eliminating the need for a gas diffusion electrode. In addition, either or both of the anode assembly 102 and anode compartment 106 and the cathode assembly 104 and cathode compartment 108 can optionally be integrated into a unitary composite structure.

[0038] Consistent with some implementations of the current subject matter, either or both of the anode compartment 106 and the cathode compartment 108 can include a structure that allows pressure to be exerted on the respective anion exchange membrane 1 10 or cation exchange membrane 1 12. Such a structure can optionally include one or more thin sheets of plastic or other material that have been etched or cut to allow for flow through. Other methods of constructing spacers of this kind to form an anode compartment 106 and/or cathode compartment 108 can include, but are not limited to, close integration with the associated electrode (e.g. the anode assembly 102 with the anode compartment 106 and the cathode assembly 104 with the cathode compartment 108), integration with the associated ion exchange membrane (e.g. the anion exchange membrane 1 10 with the anode compartment 106 and the cation exchange membrane 1 12 with the cathode compartment 108), construction using track etching of plastics or meshes, use of mesh, use of ion exchange materials, use of electrically conductive materials, and other approaches to reducing flow resistance and increasing performance while decreasing costs.

[0039] As noted above, either or both of the anode electrode 125 and a gas diffusion electrode of the anode assembly 102 can optionally include one or more catalyst materials that lower the activation energy or otherwise provide a kinetically superior reaction pathway for oxidation of the anode reactant 130 to release an electron 136 into the external circuit 138 and a positively charged anodic cation (CA ) 140 into the anode electrolyte solution 1 16 in the anode compartment 106. In some implementations of the current subject matter, a catalyst material for use in an anode assembly 102 can include, but is not limited to, fuel cell grade platinum dispersed on carbon black, other noble metals, non-noble metals, alloys, and mixture catalysts, non metal and hybrid catalysts, and the like. Selection of one or more suitable catalysts can depend on considerations such as cost, durability, resistance to fouling, and the like. Additionally, use of compounds in the anode reactant 130 other than those described herein is within the scope of the current subject matter. One or more reaction-specific catalyst materials can be used in addition to or instead of those mentioned above to enhance one or more oxidation reactions specific to the compounds present in a given anode reactant 130 and a given anode electrolyte solution 1 16. New generations of catalysts, such as for example those based on nano- materials as well as newly developed catalysts that can or might improve the rate of reactions consistent features described herein are also within the scope of the current subject matter.

[0040] Either or both of the cathode electrode 126 and a gas diffusion electrode of the cathode assembly 104 can also optionally include one or more catalyst materials that lower the activation energy or otherwise provide a kinetically superior reaction pathway for reduction of one or more compounds of the cathode reactant 132 to receive an electron 136 delivered by the external circuit 138 and release a cathodic anion (Ac ) 142 into the cathode electrolyte solution 1 18 in the cathode compartment 108. In some implementations of the current subject matter, a catalyst material for use in a cathode assembly 104 can include one or more of the catalyst materials discussed above for use in the anode assembly 102. Alternatively or in addition, one or more reaction-specific catalyst materials can be used to enhance one or more reactions specific to the compounds present in a given cathode reactant 132 and a given cathode electrolyte solution 1 18.

[0041] The anode reactant 130 can include one or more compounds that are dissociable at the anode assembly 102 to produce an electron (e ^— ) 136 and an anodic cation 140, for example through an oxidation reaction. In some implementations of the current subject matter, the anodic cations 140 produced at the anode assembly 102 can include hydrogen ions, which can also be referred to as protons (H ). The anodic cations 140 thus generated can pass into solution in the anode compartment 106. When the anodic cations 140 include hydrogen ions, once released into solution in the anode compartment 106, these hydrogen ions can associate with one or more water molecules to form a hydronium ion (H ₃ O ) or some other common form in which a free proton exists in an aqueous solution. For the purposes of this disclosure, the term hydrogen ion is intended to refer to any aqueous form of an aqueous, acidic form of dissociated hydrogen. Examples of compounds in the anode reactant 130 that can undergo this process can include, but are not limited to, hydrogen gas (H ₂ ), methanol, ethanol, carbon monoxide, water in either liquid or vapor forms, or other easily oxidized compounds. [0042] The cathode reactant 132 can include one or more compounds that can undergo a reduction reaction at the cathode assembly 104 to receive an electron (e ^— ) 140 and thereby produce a cathodic anion (Ac- ) 142 in solution in the cathode compartment 108. In some implementations of the current subject matter, the cathode gas can include carbon dioxide (C0 ₂ ) and oxygen (0 ₂ ), or other combinations of gases. The one or more compounds used in the anode reactant 130 can optionally be mixed in a required or desired proportion by a gas proportioner or other device and then introduced into a gas diffusion electrode of the anode assembly 102. Similarly, the one or more compounds used in the cathode reactant 132 can optionally be mixed in a required or desired proportion by a separate gas proportioner or other device and then introduced into a gas diffusion electrode of the cathode assembly 104. Other cathode reactants that are within the scope of the current subject matter include, but are not limited to, nitrogen, oxides of nitrogen, oxides of phosphorus, oxides of sulfur, oxides of carbon, and the like.

[0043] In the anode compartment 106, the anode electrolyte solution 116 can realize an increase in positively charged ions as a result of the production of the anodic cations 140 at the anode assembly 102. The anion exchange membrane 110 allows anions but not cations to pass through it. Accordingly, the charge imbalance in the anode compartment 106 can be remedied only by transfer of brine anions (A _B ^~~ ) 144 from the brine 120 in the desalination compartment 1 14 across the anion exchange membrane 110 and into the anode compartment 106. This process can reduce the concentration of brine anions (A _B ^~ ) 144 in the brine 120.

[0044] Similarly, the production of cathodic anions (Ac- ) 142 in the cathode compartment 108 by reduction reactions of one or more compounds in the cathode reactant 132 at the cathode assembly 104 can result in a surplus of negatively charged ions in the cathode compartment 106. The cation exchange membrane 112 dividing the cathode compartment 108 from the desalination compartment 114 allows cations but not anions to pass through it. Accordingly, the charge imbalance in the cathode compartment 108 can be remedied only by transfer of brine cations (C _B ) 146 from the brine 120 in the desalination compartment 1 14 across the cation exchange membrane 112 and into the cathode compartment 108. This process can reduce the concentration of brine cations (C _B ) 146 in the brine 120.

[0045] The end result of the transfer of brine anions (A _B ^~~ ) 144 across the anion exchange membrane 110 into the anode compartment 106 and brine cations (C _B ) 146 across the cation exchange membrane 1 12 in the cathode compartment 108 is a reduction in the concentration of the total ion concentration in solution in the brine 120. Accordingly, a reduced concentration brine 150 is produced. In addition, the transfer of brine anions (AB ^~ ) 144 into the anode electrolyte solution 1 16 can produce a concentrated solution of a first commercially useful product in the form of a higher concentration anode electrolyte solution 152. Similarly, the transfer of brine cations (Be ) 146 into the cathode electrolyte solution 1 18 can produce a concentrated solution of a second commercially useful product in the form of a higher concentration cathode electrolyte solution 154. In some implementations of the current subject matter, at least one of the first commercially useful product and the second commercially useful product can be recovered from the higher concentration anode electrolyte solution 152 or the higher concentration cathode electrolyte solution, respectively, for example using one or more recovery processes external to the electrochemical desalination cell 100. It can also be possible in some implementations of the current subject matter to directly produce at least one of the first commercially useful product and the second commercially useful product directly in the respective anode compartment 106 or cathode compartment.

[0046] In addition to the first commercially useful product and the second commercially useful product, which can each optionally include more than one chemical compound, the oxidation- reduction reactions occurring at the anode assembly 102 and cathode assembly 104 linked by the external circuit 134 can provide electrical power to serve the external electrical load 138, which can also provide a valuable product of the above-described process.

[0047] FIG. 2 shows a diagram of an integrated system 200 in which additional processes (which can be included as process sub-systems) are included to respectively address pre-treatment and post-treatment of materials provided to and recovered from a electrochemical desalination cell 100, such as that described above in reference to FIG 1. The reduced concentration brine 150 output from the desalination compartment 1 14 can be further treated by a discharge process or sub-system 300, details of which are discussed in further detail below in reference to FIG. 3A. The output of the discharge process or subsystem 300 can be a concentrated brine, which can be recycled to the inlet of the desalination compartment 1 14 as part of the brine 120. As also shown in FIG. 2, the brine 120 can be provided from a brine pre-treatment process or sub-system 350, details of which are discussed in further detail below in reference to FIG. 3B. With further reference to FIG. 2, the higher concentration anode electrolyte solution 152 output from the anode compartment 106 of the electrochemical desalination cell 100 can be directed to one or more first product refinement processes or sub-systems 400, details of which are discussed in further detail below in reference to FIG. 4A. The higher concentration cathode electrolyte solution 154 output from the cathode compartment 108 of the electrochemical desalination cell 100 can be directed to one or more second product refinement processes or sub-systems 450, details of which are discussed in further detail below in reference to FIG. 4B. Outputs of a first product concentration and crystallization process can be directed to one or both of a first product post-processing process or subsystem 500 and an anode electrolyte recovery process or subsystem 550, details of which are discussed in further detail below in reference to FIG. 5A and FIG. 5B, respectively. Similarly, outputs of a second product concentration and crystallization process can be directed to one or both of a second product post-processing process or subsystem 600 and a cathode electrolyte recovery process or sub-system 650, details of which are discussed in further detail below in reference to FIG. 6A and FIG. 6B, respectively.

[0048] FIG. 3A shows an example of a discharge process or subsystem 300, which can receive the reduced concentration brine 150 output from the desalination compartment 1 14 for further treatment. In one example, the reduced concentration brine 150 can be fed as the input process stream to a re-concentration and desalination process or subsystem 302, which can in some implementations of the current subject matter include one or more of a forward osmosis process, a reverse osmosis process, a thermal process, or the like. This re-concentration and desalination process or subsystem 302 can produce two output streams: a dilute solution 304, which can in some examples include less than 500 ppm of total dissolved solids, and a re-concentrated brine solution 120, which can optionally be recycled for re-treatment by an electrochemical desalination cell 100 such as that shown in FIG. 1 by delivery to the desalination compartment 1 14 of. The dilute solution 304 can optionally undergo additional processes such as testing and/or pH and salinity adjustments 310 before discharge 312, either as drinking water or as an environmentally safe "fresh water" discharge.

[0049] FIG. 3B shows an example of a brine pre -treatment process or sub-system 350, which can prepare a brine 120 suitable for being provided to the desalination compartment of an electrochemical desalination cell 100 such as that shown in FIG. 1. In an example in which the electrochemical desalination cell 100 is used to treat produced water from oil and/or gas 352, one or more brine pre -treatment processes or sub-systems 354 can be applied. Non-limiting examples of such pre -treatment processes can include, but are not limited to, one or more of skimming and fiocculation or other methods to remove organic material, remove of naturally occurring radioactive materials, pre-concentration to a pre-determined salinity (e.g. by forward osmosis or the like), softening or other processes or procedures to create a simpler brine (e.g. having an elevated concentration of fewer distinct salt compounds), and the like. The output from the brine pre -treatment processes or sub-systems 354 can be delivered as the brine 120 provided in the desalination compartment 1 14.

[0050] FIG. 4A shows an example of a brine pre -treatment process or sub-system first product refinement processes or sub-systems 400, which can, in some implementations of the current subject matter, include one or more concentration and crystallization operations that receive the higher concentration anode electrolyte solution 152 output from the anode compartment 106 of the electrochemical desalination cell 100. A first, pre-concentration process or sub-system 402, which can optionally include one or more of forward osmosis, reverse osmosis, thermal concentration, or the like, can produce two process streams: a lower concentration first product solution 404, and a higher concentration first product solution 406. The lower concentration first product solution 404 can be directed to an anode electrolyte recovery process or sub-system 550, details of which are described below in reference to FIG. 5B. The higher concentration first product solution 406 can be further processed, for example with a crystallization process or subsystem 410, which produces a refined first product 412. The refined first product 412 can optionally include the first product in a solid, crystalline form, a concentrated solution form, or the like. In one example discussed in more detail below, a first product can be calcium chloride.

[0051] FIG. 4B shows an example of a second product refinement processes or sub-system 450, which can, in some implementations of the current subject matter, include one or more concentration and crystallization operations that receive the higher concentration cathode electrolyte solution 154 output from the cathode compartment 108 of the electrochemical desalination cell 100. A first, pre-concentration process or sub-system 452, which can optionally include one or more of forward osmosis, reverse osmosis, thermal concentration, or the like, can produce two process streams: a lower concentration second product solution 454, and a higher concentration second product solution 456. The lower concentration second product solution 454 can be directed to a cathode electrolyte recovery process or sub-system 650, details of which are described below in reference to FIG. 6B. The higher concentration second product solution 456 can be further processed, for example with a crystallization process or sub-system 460, which produces a refined second product 462. The refined second product 462 can optionally include the second product in a solid, crystalline form, a concentrated solution form, or the like. In one example discussed in more detail below, a first product can be calcium chloride. In one example discussed in more detail below, a second product can be sodium bicarbonate (NaHC0 ₃ ) or sodium carbonate (Na ₂ C0 ₃ ), also referred to commercially as soda ash.

[0052] FIG. 5A shows an example of a first product post-processing process or subsystem 500 to which the produced solid first product 412 from the first product refinement process or subsystem 400 can be directed. A first product post-processing process or sub-system 502 can optionally include one or more of purity testing, further drying, packaging for shipment, and the like, and can produce a finished, commercially valuable form of the first product 504 (e.g. a crystalline, purified solid form of the first product, a concentrated solution of the first product, or the like).

[0053] FIG. 5B shows an example of an anode electrolyte recovery process or sub-system 550 to which the lower concentration first product solution 404 of a first product refinement process or sub-system 400 can be directed. A pH and/or concentration adjustment process or sub-system 552 can include increasing or decreasing the first product concentration and/or the pH of the lower concentration first product solution 404 to better match the anode electrolyte solution 1 16 provided in the anode compartment 106. An additive addition process or sub-system 554 can optionally include adding one or more dissolved anode reactants 130 or other additives prior to providing the anode electrolyte solution 1 16 to the anode compartment 106. In one example discussed in more detail below, an anode electrolyte additive can include calcium carbonate.

[0054] FIG. 6A shows an example of a second product post-processing process or subsystem 600 to which the produced solid second product 462 from the second product refinement process or sub-system 450 can be directed. A second product post-processing process or sub-system 602 can optionally include one or more of purity testing, further drying, packaging for shipment, and the like, and can produce a finished, solid, commercially valuable form of the second product 604 (e.g. a crystalline, purified solid form of the second product, a concentrated solution of the second product, or the like). [0055] FIG. 6B shows an example of an cathode electrolyte recovery process or sub-system 650 to which the lower concentration second product solution 454 of a second product refinement process or sub-system 450 can be directed. A pH and/or concentration adjustment process or sub-system 652 can include increasing or decreasing the second product concentration and/or the pH of the lower concentration second product solution 454 to better match the cathode electrolyte solution 1 18 provided in the cathode compartment 108. An additive addition process or sub-system 654 can optionally include adding one or more dissolved cathode reactants 132 or other additives prior to providing the cathode electrolyte solution 1 18 to the cathode compartment 108.

[0056] Also shown in FIG. 2 is a reactant treatment process or sub-system 250, which can prepare one or more of the compounds supplied to either or both of the anode assembly 102 and the cathode assembly 104. In an example in which the anode reactant 130 includes hydrogen gas and the cathode reactant includes carbon dioxide, the reactant treatment process or sub-system 250 can include a methane reforming process or sub-system, which can optionally receive methane gas and perform one or more treatment processes and/or gas purification processes on the methane. Such processes can include, but are not limited to steam or other auto-thermal reforming, carbon monoxide oxidation to carbon dioxide (e.g. if carbon monoxide is not used as part of the anode reactant 130), carbon dioxide separation from a hydrogen gas stream (e.g. if carbon dioxide is detrimental to a desired reaction at the anode assembly 102), capture of carbon dioxide from the anode electrolyte 1 16 for use as a cathode reactant 132 at the cathode assembly 104, or the like.

[0057] FIG. 7 shows a process flow chart 700 illustrating features of a method, at least some of which can appear in an implementation of the current subject matter. At 702, an anode reactant 130 is provided at an anode assembly 102 and a cathode reactant 132 is provided at a cathode assembly 104 of an electrochemical desalination cell 100. At 704, at least one first compound in the anode reactant 130 is oxidized at the anode assembly 102 to produce anodic cations 140 in an anode electrolyte solution 1 16, which can optionally be provided in an anode compartment 106 such that the anode electrolyte solution 1 16 is in electrical contact with the anode assembly 102. At 706, at least one second compound in the cathode reactant 132 is reduced at the cathode assembly 104 to produce cathodic anions 142 in a cathode electrolyte solution 1 18, which can optionally be provided in a cathode compartment 108 such that the cathode electrolyte solution 1 18 is in electrical contact with the cathode assembly 104. The oxidizing and the reducing combine to form a full reaction that is a thermodynamically favorable (e.g. the Gibbs Free Energy of the full reaction is less than zero). A brine 120 is provided at 710, optionally in a desalination compartment 1 14, and can be separated from the anode compartment 106 by an anion exchange membrane 1 10 and from the cathode compartment 108 by a cation exchange membrane 1 12. At 712, brine anions 144 pass through the anion membrane 108 from the brine 120 to the anode electrolyte solution 1 16 106 and brine cations 146 pass through the cation membrane 1 10 from the brine 120 to the cathode electrolyte solution 1 18 to produce a reduced concentration brine 150. Other products 152, 154 can optionally be produced, for example due to at least one of transport of the brine anions 144 into the anode electrolyte solution 1 16 and transport of the brine cations 146 into the cathode electrolyte solution 1 18.

[0058] Consistent with some implementations of the current subject matter, the anode electrolyte solution 1 16 can include one or more of a suspension of a solid compound and an aqueous compound whose solubility in aqueous solution is a strong function of the pH of the aqueous solution. In an example illustrated in the system 800 and system 900 of FIG. 8 and FIG. 9, respectively, a solid carbonate salt, such as for example calcium carbonate (CaC0 ₃ ), can advantageously be suspended in the anode electrolyte solution 1 16. While the following several examples illustrating features consistent with implementations of the current subject matter are discussed in reference to the use of calcium carbonate, it will be well understood that other carbonate salts, such as for example magnesium carbonate (MgC0 ₃ ), carbonate salts of other alkali earth metals (i.e. those in Group II on the periodic table of the elements), as well as other acid soluble compounds, can be used in place of or in addition to calcium carbonate in the following examples and in other implementations having one or more common features with these examples.

[0059] In the presence of hydrogen ions generated by oxidation reactions of the anode reactant 130 at the anode assembly 102, solid calcium carbonate undergoes dissolution as part of an equilibrium relationship between solid calcium carbonate, bicarbonate ion in solution (HC0 ₃ ), and carbonic acid (H ₂ C0 ₃ ). Carbonic acid in turn exists in equilibrium with carbon dioxide in the gas phase according to Dalton's Law of partial pressures and the pH of the solution according to the following chemical equilibrium equations: [0060] CaC0 ₃ (s) + H ^{+ →} Ca ²⁺ (aq) + HCO^aq) (1)

—

[0061] HC0 ₃ (aq) + H ^{+ →} H ₂ C0 ₃ (aq) (2)

—

[0062] H ₂ C0 ₃ (aq) ^→ H ₂ 0(1) + C0 ₂ (g) (3)

—

[0063] At a sufficiently low pH in the anode compartment 106, the equilibrium of reactions 1 , 2, and 3 is driven toward the production of gas-phase carbon dioxide, which, when extracted from the solution in the anode compartment 106, leaves positively charged calcium ions. The inclusion of calcium carbonate or some other compound, either in a solid suspension phase or in solution in the anode electrolyte solution 1 16 is optional. However, use of such a compound can, in some implementations of the current subject matter, provide one or more advantages, potentially including but not limited to increasing the pH in the anode electrolyte 120 in the anode compartment 106, decreasing the concentration of hydrogen ions in the anode electrolyte 120 in the anode compartment 106 and thereby decrease the overpotential necessary for oxidation of hydrogen ions at the anode assembly 102 and concomitant efficiency losses, and increasing overall possible cell working potential (for example if the entire reaction happens at the surface of the anode assembly 102).

[0064] In the example of calcium carbonate being used in the anode electrolyte solution 1 16, additional advantages can be realized due to the creation of an excess of calcium ions in the anode compartment 106. Like the hydrogen ions or other anodic cations 140, the calcium ions cannot move through the anion exchange membrane 1 10 separating the anode compartment 106 from the desalination compartment 1 14, the calcium ions instead draw brine anions (AB ) from the brine 120 provided in the desalination compartment 1 14. If the brine 120 contains a high concentration of sodium chloride (NaCl), the primary brine anion (AB ^~ ) 144 passing through the anion exchange membrane 1 10 is chloride ion (Cl ^— ). A solution of calcium chloride (CaCl ₂ ) can thereby be produced in the anode compartment 106. These ions can be kept in aqueous form by controlling the pH and electrolyte concentration in the anode compartment 106 such that the higher concentration anode electrolyte 152 is a solution of this compound in a controllable concentration. While the descriptions of the illustrative examples presented in FIG. 8, FIG. 9, FIG. 10, and FIG. 1 1 reference a brine 120 that includes sodium chloride, the scope of the current subject matter is not limited in any way to sodium chloride brines. Other dissolved salts can be present in a brine 120 and can be removed through application of one or more of the features described herein consistent with implementations of the current subject matter.

[0065] The overall reaction on the anode side of the system 800, 900 for these examples has a Gibbs Free Energy of reaction (AG) of approximately -56 kJ'moi ^"1 and can be represented as follows:

[0066] CaC0 ₃ (s) + H ₂ + 2C1 ^" -> H ₂ 0 + C0 ₂ (g) + CaCl ₂ (aq) + 2e ^" (4)

[0067] Continuing with the above example of a brine 120 containing sodium chloride, the cathode reactant 132 can include a controlled mixture of carbon dioxide and oxygen (the ratio of carbon dioxide to oxygen can be varied widely to control the reaction products) fed into the gas diffusion electrode at the cathode assembly 104. The cathode reactant 132 can react at the surface of a catalyst (e.g. one as described above or consistent with features described herein) at the cathode assembly 104 to produce carbonate ions (C0 ₃ ^2~ ) and/or bicarbonate ions (HCO ₃ ) depending on the gas ratio and pH in the cathode electrolyte solution 1 18 in the cathode compartment 108. When bicarbonate ions are produced, water can also be involved in the reaction. The catalyst, the ratio of gases in the cathode reactant 132, and the chemical composition of the cathode electrolyte solution 1 18 can affect which ions are produced and in what quantities. The generated cathodic anions 142, in this example some mixture of carbonate and bicarbonate, are released into the cathode electrolyte solution 1 18 provided in the cathode compartment 108. As noted above, these cathodic anions 142 are negatively charged and therefore cannot migrate across the cation exchange membrane 1 12 into the desalination compartment 1 14. Charge balance can be restored, both in the cathode compartment 108 and in the desalination compartment 1 14, by allowing positively charged brine cations (CB ) 146 to migrate through the cation exchange membrane 1 12.

[0068] In the example in which the brine 120 includes a high concentration of sodium chloride, the primary brine cations (CB ) 146 passing through the cation membrane 1 10 can be sodium ion ( a ⁺ ). A solution of sodium carbonate (Na ₂ C0 ₃ ) or sodium bicarbonate (NaHC0 ₃ ) can thereby be produced in the cathode compartment 108. These ions can be kept in aqueous form by controlling the pH and electrolyte concentration in the cathode compartment 108 such that the higher concentration cathode electrolyte 154 discharged from the cathode compartment 108 includes a solution of one or more of these compounds in a controllable concentration.

[0069] The overall reaction on the cathode side of the system 800, 900 for these examples has a Gibbs Free Energy of reaction (AG) of approximately -147 kJ'moi ^"1 if formation of the bicarbonate ion is favored as shown in FIG. 8 and can be represented as follows:

[0070] X0 ₂ (g) + H ₂ 0 + 2C0 ₂ (g) + 2e ^" + 2Na ⁺ → 2NaHC0 ₃ (aq) (5)

[0071] The overall reaction for the system 800 including the anode and cathode sides, which can involve an enthalpy (ΔΗ) of reaction of -325 kJ'moi ^"1 , a Gibbs Free Energy (AG) of -203.7 kJ'mol ^"1 , and a generated electrical potential of 1.06 V, can be represented as follows:

[0072] H ₂ + CaC0 ₃ (s) + ½0 ₂ (g) + 2NaCl + C0 ₂ (g) - CaCl ₂ + 2NaHC0 ₃ (aq) (6)

[0073] If formation of the carbonate ion is favored as shown in FIG. 9, the overall reaction on the cathode side of the system 900 for this example has a Gibbs Free Energy of reaction (AG™) of approximately -133.4 kJ'moi ^"1 and can be represented as follows:

[0074] ½0 ₂ (g) + C0 ₂ (g) + 2e ^" + 2Na ⁺ -> Na ₂ C0 ₃ (aq) (7)

[0075] The overall reaction for the system 900 including the anode and cathode sides, which can involve an enthalpy (ΔΗ) of reaction of -298.3 kJ'moi ^"1 , a Gibbs Free Energy (AG) of -189.3 kJ'mol ^"1 , and a generated electrical potential of 0.981 V, can be represented as follows:

[0076] H ₂ + CaC0 ₃ (s) + ½0 ₂ (g) + 2NaCl - H ₂ 0 + CaCl ₂ + Na ₂ C0 ₃ (aq) (8)

[0077] Carbon dioxide is produced in the reactions (see e.g. equation 4 above) occurring in the anode compartment 106. As such, in some implementations of the current subject matter, this generated carbon dioxide can be collected as it escapes from solution. The collected carbon dioxide can be delivered as part of the cathode reactant 132 to the cathode assembly 104 where it can be reduced to carbonate ion or bicarbonate ion depending on the pH of the cathode electrolyte solution 1 18 in the cathode compartment 108.

[0078] In some implementations of the current subject matter, the concentrations of the aqueous species produced in either or both of the anode compartment 106 and the cathode compartment 108 can be permitted to reach a sufficiently high concentration to cause precipitation of the one or more products from solution in the respective compartment rather than the first and/or second product being discharged in the form of a high concentration anode electrolyte 152 or a high concentration cathode electrolyte 154, respectively. However, doing so may not be advantageous depending on the specific configuration of a system 100 because precipitation of solids in the anode compartment 106 or cathode compartment 108 can cause fouling of one or both of the anode assembly 102 or cathode assembly 104 or of the anion exchange membrane 110 or the cation exchange membrane 112. Such high concentrations of electrolytes can also lessen the driving force for ion movement across either or both of the anion exchange membrane 110 and the cation exchange membrane 1 12 from the desalination compartment 114, because the concentration gradient of anions and/or cations generally also drives ion flow across the anion exchange and cation exchange membranes 1 10, 1 12.

[0079] FIG. 10 and FIG. 11 show two additional examples of systems 1000, 1100 in which calcium carbonate is not added to the anode electrolyte solution 116. In these examples, the overall reaction on the anode side of the system 100 for this example has a Gibbs Free Energy of reaction (AG) of 0 kJ'mol ^"1 by definition of the Gibbs Free Energy and can be represented as follows:

[0080] H ₂ + 2C1 -> 2HC1 + 2e (9)

[0081] The overall reaction on the cathode side of the system 1000, 1100 for these examples are the same as those shown above in reference to FIG. 8 and FIG. 9 and given in equations 5 and 7, respectively depending on whether bicarbonate ion or carbonate ion are favored.

[0082] The overall reaction for the system 1000 including the anode and cathode sides, which can involve an enthalpy (ΔΗ) of reaction of -31 1.2 kJ'mol ^"1 , a Gibbs Free Energy (AG) of -147.8 kJ'mol ^"1 , and a generated electrical potential of 0.766 V, can be represented as follows:

[0083] H ₂ + X0 ₂ (g) + H ₂ 0 + 2NaCl + 2C0 ₂ (g) -> 2HC1 + 2NaHC0 ₃ (aq) (10)

[0084] The overall reaction for the system 1100 including the anode and cathode sides, which can involve an enthalpy (ΔΗ) of reaction of -283.7 kJ'mol ^"1 , a Gibbs Free Energy (AG) of -133.4 kJ'mol ^"1 , and a generated electrical potential of 0.691 V, can be represented as follows:

[0085] H ₂ + 0 ₂ (g) + 2NaCl + C0 ₂ (g) -> 2HC1 + Na ₂ HC0 ₃ (aq) (11) [0086] In additional or alternative implementations of the current subject matter, the cathode reactant 132 can include oxides of nitrogen, which generally include nitric oxide (NO) and nitrogen dioxide (N0 ₂ ) and are commonly referred to as ΝΟχ. In some implementations of the current subject matter, such compounds can be added to or otherwise mixed with oxygen gas as part of the cathode reactant 132. Oxides of nitrogen are a common pollutant produced by combustion processes occurring at high temperature. In contact with a suitable catalyst and electrons 136 supplied through the external circuit 134, ΝΟχ can react to form nitrate or nitrite ions in solution within the cathode compartment 108, and in the presence of excess oxygen, nitrite in solution can generally react to form nitrate ions. Similar to the reactions discussed above that produce one or more of carbonate and bicarbonate ions and consistent with the teachings provided herein, a suitable set of reactants based on a reduction of ΝΟχ at the cathode or in the cathode compartment 108 can produce an electric potential across the cell that could be harvested for electricity production. Such features can offer a significant benefit over currently available technologies that release energy from exothermic reactions as heat. Harvesting even some of the resultant energy as electricity can provide advantages as electricity is generally a more useful and valuable form of energy than is heat.

[0087] In addition to the catalyst materials that can be used in association with one or both of an anode electrode 125 at the anode assembly 102 and a cathode electrode 126 at the cathode assembly 104, one or more reaction assisting components can be included to improve performance. In some implementations of the current subject matter, an electrocatalyst can be mixed with a hydrophobic component, such as for example a Teflon emulsion, and an ion conductive component, such as for example Nafion at the anode assembly 102 and one or more of several anionic ionomers at the cathode assembly 104, to form an ink that can be deposited on respective gas diffusion electrode surfaces or other anode electrode or cathode electrode surfaces as the catalytic layer. Other polymers, compounds, binders, and other additives can alternatively or additionally be added to help improve the efficiency of a electrochemical desalination system, for example by enabling better transport of ions to and from the catalyst surface (especially while enhancing or at least not harming the electron-conductive pathway), enabling effective transport of reactants in various phases to the catalyst surface and products away from it, preventing leakage out of the electrode, preventing certain species that might undergo unfavorable electrochemical reactions from reaching the electrode), controlling the local pH and reaction conditions to produce more efficient reactions, or the like. As a non-limiting example of such an approach, a Nafion coating, a membrane that is either pre-formed or formed in situ by one or more polymerization reactions, or the like on the anode can prevent anion (e.g, chloride ions in the examples shown in FIG.8, FIG. 9, FIG. 10, and FIG. 1 1) from reaching the anode, thereby preventing accidental production of an undesirable gas-phase compound (e.g. chlorine gas from chloride ions, bromine gas from bromide ions, etc.).

[0088] As noted above, calcium carbonate can be added to the anode electrolyte solution 1 16 to achieve potential advantages such as increasing the achievable working potential, decreasing the harshness of the potentially highly acidic conditions inside the anode compartment 106, and the like. The calcium carbonate can react with hydrogen ions generated at the anode assembly 102 through a normal carbonate pathway at low pH to bicarbonate and then carbon dioxide and water, which can be allowed to bubble off or be captured for use as at least part of the cathode reactant 132 provided at the cathode assembly 104. However, calcium carbonate is not necessary for the functioning of the current subject matter. If calcium carbonate is not added to the anode electrolyte solution 1 16, hydrochloric acid can be synthesized as shown in and discussed in reference to FIG. 10 and FIG. 1 1. The overall system in such an example can be somewhat less efficient from an energy standpoint, but production of a useful chemical feedstock such as hydrochloric acid can in some circumstances be a more economically favorable end product than electricity generation. Other alkaline earth salts can optionally be added to the anode electrolyte solution 1 16, as well as other acid soluble compounds that can allow control over which cations are predominant in the anode electrolyte solution 1 16 and therefore what compound or compounds is/are produced. Some other metal ions can be favored in certain conditions and can allow production of other more inorganic salts with different potential economic values.

[0089] At the cathode assembly 104, solutions containing specific ions that are favorable for reduction reactions to produce more favorable or valuable products can optionally be introduced to increase efficiency, to produce specific cathodic anions 142 at the cathode assembly 104, or the like. As a non-limiting example, a nitrite rich solution can be added to the cathode electrolyte solution 1 18 in the cathode compartment 108 to enhance production of nitrates. Other compounds can be added in some implementations of the current subject matter for pH control or other reasons. [0090] Other optional additives usable in conjunction with either or both of the anode assembly 102 and the cathode assembly 104 can include additives that can be added to the anode electrolyte solution 1 16 and/or the cathode electrolyte solution, respectively, to increase solution ion conductivity, such as for example ammonium carbonate or cesium carbonate or other solutions that can increase conductivity but that produce ions that are easy to remove through simple low energy processes, such as for example waste heat or large ions that can be removed through nanofiltration or other approaches. Compounds to increase efficiency of reactions at the electrodes, help catalyze reactions, and/or control pH or other reaction conditions can also be added.

[0091] The anion and/or cation exchange membranes 1 10, 1 12 can optionally include commercially available electrodialysis ion exchange membranes, such as for example those available from Asahi Glass Co. (Tokyo, Japan) or Membranes International (Ringwood, New Jersey). In some implementations of the current subject matter, ion exchange membranes with special coatings or structural features to allow for ion specific conduction can be used. Ion specificity can enhance or improve separation processes and thereby improve overall performance by reducing unwanted side reactions that can produce precipitates or other byproducts that can cause scaling or other problems at the electrodes and membranes. In addition or alternatively, membranes and materials that can be easily integrated with the anode and/or cathode compartments 106, 108 can improve ease of sealing, flow, ion transport, and cell assembly.

[0092] Consistent with some implementations of the current subject matter, the brine 120 can be a very highly saline brine produced as a byproduct of a desalination process, produced water from the oil and gas industry, or the like. Such brines can have salinities close to saturation (~10x that of seawater or more). In other implementations of the current subject matter, the brine 120 can be far less saline, for example at a lower salinity than seawater. In some examples, one or more additives can be added to the brine 120, for example to increase the conductivity of the brine 120. Increasing the brine conductivity can, consistent with some implementations of the current subject matter, facilitate or otherwise improve the efficiency of removal of other ions from the brine 120, for example if ions are added to the brine 120 that are not easily passed across one or the other or both of the anion exchange membrane 1 10 and the cation exchange membrane 1 12, but are readily removable from solution in a later post-processing operation. A system such as described herein can experience enhanced efficiency in treating more highly concentrated brines because of the presence of a driving force similar to that in a reverse electrodialysis cell for the ions to move from the concentrated brine 120 into the anode and cathode electrolyte solutions 1 16, 1 18, simply due to a concentration gradient.

[0093] In alternative or additional implementations of the current subject matter, a system including one or more features discussed herein can include more than one set of ion exchange membranes and anode and/or cathode compartments in a manner similar to an electrodialysis or reverse electrodialysis stack. The potential generated by oxidation and reduction reactions at the electrodes can be used to move more ions and further concentrate water in some compartments and dilute it in others (similar to electrodialysis). As an example, in reference to the electrochemical desalination cell 100 of FIG. 1 , the desalination compartment can optionally be separated into additional sub-compartments by the inclusion of one or more additional pairs of anion exchange and cation exchange membranes. In an illustrative example, a second cation exchange membrane can be disposed to form a first brine concentration compartment nearer to the anion exchange membrane 1 10 shown in FIG. 1. A second anion exchange membrane can be disposed to form a second brine concentration compartment nearer to the cation exchange membrane 1 12 shown in FIG. 1. The brine 120 can be provided in a central desalination compartment between the included second cation exchange membrane and the included second anion exchange membrane. The action of the anode assembly 102 and the cathode assembly 104 to respectively create excess charge concentrations in the anode compartment 106 and the cathode compartment 108 can cause depletion of the brine anion 144 and brine cation 146 concentrations respectively in the first brine concentration compartment and the second brine concentration compartment which is remedied by transport of the respective ions from the central desalination compartment across the included second cation exchange membrane and the included second anion exchange membrane. It will be readily understood from the descriptions herein that additional stacks of paired anion and cation exchange membranes can advantageously be used consistent with one or more implementations of the current subject matter.

[0094] In other implementations of the current subject matter, the concentration differences created by an electrochemical desalination cell 100 can be used to generate additional electrical potential (similar to reverse electrodialysis). Such systems can provide benefits particularly in combination with ion selective membranes. By using ion selective membranes, solutions of specific ions can be selectively concentrated or selectively depleted to generate solutions necessary for production of pure chemicals at the electrodes or in other processes. Such stacks could have one, two or several membranes and compartments stacked or otherwise arranged in series. The overall system can still generate electricity if the membranes and compartments are arranged and used similarly to a reverse electrodialysis system. If arranged in a traditional electrodialysis mode, the electrochemical potential of the reactions at the electrodes and the resistance of the membranes can provide an upper limit on the number of stacked cells that can be used in conjunction with an electrochemical desalination cell that is operated to generate electricity or at least to not require electrical currents inputs.

[0095] Consistent with one or more implementations of the current subject matter, an electrochemical desalination approach can be integrated with other technologies or systems to achieve improved outcomes. For example, unlike many desalination processes, the electrochemical desalination approach can work better with more highly concentrated brine while being less efficient at lower concentrations because the resistivity of the feed water (e.g. the brine 120) will lower the electricity generation efficiency. At lower salinities of the feed water, the feed water can act as a resistor in the middle of the circuit. Therefore it can be advantageous to integrate an electrochemical desalination approach with other desalination processes to allow both to operate at more efficient points. For example, an electrochemical desalination approach can be integrated with another desalination process, such as for example forward osmotic, reverse osmotic, thermal, electrodialytic, or the like, to take the brine from the other desalination process, remove some of the salt and then send the lower concentration output back into the desalination process. This process of exchanging brine solutions between an electrochemical desalination approach as described herein and another desalination process and the process can be arranged in a continuous process loop. Furthermore, use of ion selective membranes can allow selective removal of salts that are more difficult for a conventional desalination process to handle so that both processes can be more efficient. As a non-limiting example, smaller ions can be easier to move across an ion exchange membrane in an electrochemical desalination approach while they might be more difficult to block in an osmotic process.

[0096] In another example, by integrating an electrochemical desalination approach with a forward osmotic (FO) process, the brine from the FO process can be provided as the brine 120 input to an electrochemical desalination approach, where its concentration could be lowered significantly and valuable salts produced. The depleted concentration brine output from the electrochemical desalination approach can then be re-concentrated in the FO process before being passed through the electrochemical desalination approach again. In this manner, it can be possible to achieve a zero liquid discharge approach to desalination. As used herein, the term "zero liquid discharge" can refer to an approach that creates drinkable or clean water as the only discharge such that pollutants or other undesirable compounds are not discharged or disposed of in aqueous or liquid form. The efficiency of the overall process can also optionally be improved if the FO process makes use of waste heat to recover the draw solution and the electrochemical desalination approach is the source of the waste heat. An electrochemical desalination approach can also be integrated with FO and one or more other pretreatment processes for highly saline brines, in which case the process starts with a pretreatment process, then passes the pretreated brine to an electrochemical desalination approach form which the depleted concentration brine is passed to the FO process for reconcentration. The reconcentrated brine can either be disposed of or can be looped back into the electrochemical desalination approach to produce a truly zero liquid discharge solution.

[0097] FIG. 12 shows an example of a process train 1200 for handling produced water from the oil and gas industry. As shown the produced water 1202 can have a very high total dissolved solids concentration, for example as high as 230,000 ppm or more. A first treatment process 1204 can optionally include one or more of chemical precipitation, filtration, removal of organic compounds, hardness, naturally occurring radioactive materials (NORM), or the like. A brine 120, such as for example a NaCl brine, can be produced by the first treatment process 1204 and passed to an electrochemical desalination system 100 consistent with or having one or more features similar to the implementations of the current subject matter described herein. The electrochemical desalination system 100 can produce a depleted concentration brine 150, which can in some examples have a total dissolved solids concentration of 20,000 ppm or less. The electrochemical desalination system 100 can also generate electricity and/or produce one or more concentrated streams 152, 154 of economically valuable chemical products as discussed above. The output concentration of an electrochemical desalination system 100 can optionally be tunable. [0098] The depleted concentration brine 150 can be passed to another treatment system or process 1206, such as for example a forward osmosis process, which can reconcentrate the depleted concentration brine 150 into a reconcentrated brine 1210. The other treatment system or process 1206 can also use waste heat from the electrochemical desalination system 100 to in some examples reclaim 90% or more of the depleted concentration brine 150 for more beneficial uses. The reclaimed water 1212 produced by the her treatment system or process 1206 can in some examples have a total dissolved solids concentration of less than 500 ppm.

[0099] In addition to the ability to concentrate the incoming feed of brine 120 to an electrochemical desalination approach as described herein, a conventional desalination process can also work well to concentrate electrolytes from the anode compartment 106 and the cathode compartment 108. To harvest the chemical co-products produced at the anode assembly 102 and the cathode assembly 104, the anode and cathode electrolyte solutions 1 16, 1 18 can require concentration and/or partial or complete dewatering to produce economically valuable forms of the generated compounds. A conventional desalination process can concentrate such compounds either for sale in solution form or to reduce the energy necessary to remove the salts through thermal processing.

[00100] Production of the fuel (e.g. one or more compounds in the anode reactant 130, one or more compounds in the cathode reactant 132, etc.) for an electrochemical desalination approach and evaporation of water from the anode and cathode electrolyte solutions 1 16, 1 18 can be two other major processes performed in conjunction with the electrochemical desalination approach. A system as described herein can optionally be integrated with a natural gas reformer or other hydrogen source if hydrogen gas is used as at least part of the anode reactant 130. Such a reformer can optionally produce one or more of hydrogen, carbon monoxide, and carbon dioxide. Carbon dioxide produced in this manner can optionally be used as at least part of the cathode reactant 132 while hydrogen gas and/or carbon monoxide can optionally be used as at least part of the anode reactant 130. Excess heat produced by the reformer (especially if it is an autothermal reformer) can be used as an at least partial heat source for evaporation of water in a spray dryer or other machine that uses heat to evaporate water and produce solids from it. An electrochemical desalination approach can also be integrated with one or more desalination systems as mentioned above. In the case of FO, the waste heat can also be used to drive the recovery of the draw solution. The electrochemical desalination system can also be integrated with crystallizers or other items to accomplish such tasks.

[00101] As used herein, the term "provided in" as used in reference to a fluid such as a solution or a gas and a container or other at least partially defined volume such as a compartment, cell, passage, space, or the like indicates that the fluid is present in the container or other at least partially defined volume either as a non-flowing, static volume of the fluid, or as a flowing stream of the fluid. In other words, unless explicitly excluded in the foregoing description, a fluid described as being provided in a container or other at least partially defined volume can undergo one or more reactions consistent with implementations of the current subject matter that can be modeled in terms of a batch reactor, a semi-batch reactor, a plug flow reactor, a continuous flow stirred tank reactor, or any other kind of idealized or non-idealized reaction system.

[00102] One or more aspects or features of the subject matter described herein can be realized in digital electronic circuitry, integrated circuitry, specially designed application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) computer hardware, firmware, software, and/or combinations thereof. For example, various aspects or features can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. Control devices, including but not limited to flow controllers, valves, heaters, or the like can be controlled by one or more commands produced by such a programmable system. A programmable system can alternatively or in addition receive data from one or more monitoring devices such as pressure sensors, temperature sensors, concentration analyzers or sensors, or the like. Such data can be used in making one or more determinations related to operation of a system or method consistent with implementations of the current subject matter.

[00103] Computer programs such as those discussed above, which can also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor, and can be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/machine language. As used herein, the term "machine-readable medium" refers to any computer program product, apparatus and/or device, such as for example magnetic discs, optical disks, memory, and Programmable Logic Devices (PLDs), used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal used to provide machine instructions and/or data to a programmable processor. The machine-readable medium can store such machine instructions non-transitorily, such as for example as would a non-transient solid-state memory or a magnetic hard drive or any equivalent storage medium. The machine-readable medium can alternatively or additionally store such machine instructions in a transient manner, such as for example as would a processor cache or other random access memory associated with one or more physical processor cores.

[00104] To provide for interaction with a user, one or more aspects or features of the subject matter described herein can be implemented on a computer having a display device, such as for example a cathode ray tube (CRT) or a liquid crystal display (LCD) or a light emitting diode (LED) monitor for displaying information to the user and a keyboard and a pointing device, such as for example a mouse or a trackball, by which the user may provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well. For example, feedback provided to the user can be any form of sensory feedback, such as for example visual feedback, auditory feedback, or tactile feedback; and input from the user may be received in any form, including, but not limited to, acoustic, speech, or tactile input. Other possible input devices include, but are not limited to, touch screens or other touch-sensitive devices such as single or multi-point resistive or capacitive trackpads, voice recognition hardware and software, optical scanners, optical pointers, digital image capture devices and associated interpretation software, and the like. A computer remote from a system consistent with implementations of the current subject matter can be linked to the system over a wired or wireless network to enable data exchange between the system and the remote computer (e.g. receiving data at the remote computer from the system and transmitting information such as calibration data, operating parameters, software upgrades or updates, and the like) as well as remote control, diagnostics, etc. of the system.

[00105] The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail herein, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and sub-combinations of the disclosed features and/or combinations and sub-combinations of one or more features further to those disclosed herein. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. The scope of the following claims may include other implementations or embodiments.