ELECTROCHEMICAL PROCESSES FOR ACIDIFICATION OF A LIQUID STREAM WITH IMPROVED EFFICIENCY

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 (e) to U.S. Provisional Application Ser. No. 63/705,696, titled “ELECTROCHEMICAL PROCESSES FOR ACIDIFICATION OF A LIQUID STREAM WITH IMPROVED EFFICIENCY,” filed on Oct. 10, 2024, the subject matter of same being incorporated herein by reference in its entirety for all purposes.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under Contract No. N00014-21-C-1019 awarded by the Department of the Navy. The government has certain rights in the invention.

FIELD OF TECHNOLOGY

Aspects and embodiments disclosed herein relate to electrochemical devices for changing the pH of a fluid stream with improved efficiency. The device may be used, for example, to capture inorganic carbon from seawater. Further aspects and features disclosed herein pertain to electrolytic-cation exchange modules (E-CEM).

SUMMARY

In accordance with one aspect, there is provided an apparatus for generation of carbon dioxide, hydrogen, and oxygen from a saline water source. The apparatus comprises an anodic compartment having an inlet and an outlet, an anode disposed on a first side of the anodic compartment, a cathodic compartment having an inlet and an outlet, a cathode disposed on a first side of the cathodic compartment, a first cation permeable fluidic separator disposed on a second side of the anodic compartment, a second cation permeable fluidic separator disposed on a second side of the cathodic compartment, a first center compartment having an inlet and an outlet, and a second center compartment having an inlet and an outlet. The first center compartment is defined between the second center compartment and the second cation permeable fluidic separator. The second center compartment is defined between the first cation permeable fluidic separator and the first center compartment. The outlet of the first center compartment is one of fluidly connectable to or in fluid communication with the inlet of the second center compartment.

In some embodiments, the apparatus further comprises a third cation permeable fluidic separator disposed between the first center compartment and the second center compartment.

In some embodiments, the apparatus further comprises a source of anolyte including one of deionized water or an aqueous sodium sulfate solution that is one of fluidly connectable to or in fluid communication with the inlet of the anodic compartment.

In some embodiments, the apparatus further comprises a source of catholyte including one of deionized water or an aqueous sodium sulfate solution that is one of fluidly connectable to or in fluid communication with the inlet of the cathodic compartment.

In some embodiments, the saline water source is one of fluidly connectable to or in fluid communication with the inlet of the first center compartment.

In some embodiments, the saline water source is a source of seawater.

In some embodiments, the apparatus further comprises a controller configured to regulate power supplied across the anode and cathode and a flow rate of the saline water through the first center compartment that results in effluent exiting the outlet of the first center compartment having a second pH that is reduced relative to a first pH of the aqueous saline solution that is supplied to the inlet of the first center compartment.

In some embodiments, the controller is further configured to regulate power supplied across the anode and cathode and a flow rate of the effluent from the outlet of the first center compartment through the second center compartment that results in effluent exiting an outlet of the second center compartment having a third pH that is reduced relative to the second pH.

In some embodiments, the third pH is about 4 or less.

In some embodiments, the apparatus further comprises an additional fluid flow compartment having an inlet and an outlet, the additional fluid flow compartment being disposed between the first center compartment and the second center compartment.

In some embodiments, the apparatus further comprises a third cation permeable fluidic separator disposed between the additional fluid flow compartment and the first center compartment.

In some embodiments, the apparatus further comprises a fourth cation permeable fluidic separator disposed between the additional fluid flow compartment and the second center compartment.

In some embodiments, the outlet of the anodic compartment is one of fluidly connectable to or in fluid communication with the inlet of the additional fluid flow compartment.

In accordance with another aspect, there is provided a method of facilitating generation of hydrogen and carbon dioxide from seawater. The method comprises providing an electrolytic cell including an anodic compartment having an inlet and an outlet, an anode disposed on a first side of the anodic compartment, a cathodic compartment having an inlet and an outlet, a cathode disposed on a first side of the cathodic compartment, a first cation permeable fluidic separator disposed on a second side of the anodic compartment, a second cation permeable fluidic separator disposed on a second side of the cathodic compartment, a first center compartment having an inlet and an outlet, and a second center compartment having an inlet and an outlet, the first center compartment defined between the second center compartment and the second cation permeable fluidic separator, the second center compartment defined between the first cation permeable fluidic separator and the first center compartment. The method further comprises providing instructions to flow an anolyte through the anodic compartment, flow a catholyte through the cathodic compartment, flow the seawater through the first center compartment, flow effluent from the outlet of the first center compartment into the inlet of the second center compartment, and remove hydrogen and carbon dioxide from the cathodic compartment and the second center compartment, respectively.

In some embodiments, the method further comprises providing instructions to regulate power supplied across the anode and cathode and/or a flow rate of the seawater through the first center compartment that results in effluent exiting the outlet of the first center compartment having a second pH that is reduced relative to a first pH of the seawater that is supplied to an inlet of the first center compartment.

In some embodiments, the method further comprises providing instructions to regulate power supplied across the anode and cathode and/or a flow rate of effluent from the outlet of the first center compartment through the second center compartment that results in effluent exiting an outlet of the second center compartment having a third pH that is reduced relative to the second pH.

In some embodiments, the third pH is about 4 or less.

In some embodiments, the electrolytic cell further includes an additional fluid flow compartment disposed between the first center compartment and the second center compartment and the method further comprises providing instructions to flow effluent from the outlet of the anodic compartment through the additional fluid flow compartment.

In accordance with another aspect, there is provided a method of generating carbon dioxide and hydrogen from seawater. The method comprises providing an electrolytic-cation exchange module device including an anodic compartment having an inlet and an outlet, a cathodic compartment having an inlet and an outlet, a first center compartment having an inlet and an outlet and defined between the anodic compartment and cathodic compartment, and a second center compartment having an inlet and an outlet and defined between the first center compartment and the anodic compartment, flowing a catholyte through the cathodic compartment to form an effluent catholyte, introducing feed seawater into the inlet of the first center compartment, flowing a first effluent seawater from the outlet of the first center compartment to the inlet of the second center compartment, withdrawing a second effluent seawater from the outlet of the second center compartment, extracting carbon dioxide from the second effluent seawater, and extracting hydrogen from the effluent catholyte.

In some embodiments, the method further comprises flowing an anolyte through the anodic compartment to form an effluent anolyte.

In some embodiments, the method further comprises providing an additional fluid flow compartment having an inlet and an outlet, the additional fluid flow compartment defined between the first center compartment and the second center compartment.

In some embodiments, the method further comprises flowing the effluent anolyte from the outlet of the anodic compartment to the inlet of the additional fluid flow compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in the various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 is a schematic drawing of one example of an electrochemical cell;

FIG. 2 is a schematic drawing of another example of an electrochemical cell;

FIG. 3 is a diagram illustrating the equilibrium for inorganic carbonic species in seawater at 10° C.;

FIG. 4 is a schematic drawing of a portion of an E-CEM;

FIG. 5 is a graph illustrating seawater effluent pH versus run time in an example of an E-CEM device;

FIG. 6A is a graph showing results of a run of an E-CEM process using an E-CEM device with a first seawater compartment thickness;

FIG. 6B is a graph showing results of a run of an E-CEM process using an E-CEM device with a second seawater compartment thickness;

FIG. 7 is a graph showing current density versus the inverse of residence time in an example of an E-CEM device;

FIG. 8 is a graph showing the theoretical amount of H⁺ ions that would be used to reduce the pH in synthetic seawater in an example of an E-CEM device;

FIG. 9A is a graph showing expected versus calculated current density at different pH levels in an E-CEM device with a first seawater compartment thickness;

FIG. 9B is a graph showing expected versus calculated current density at different pH levels in an E-CEM device with a second seawater compartment thickness;

FIG. 10 is a graph showing results of calculations to estimate excess H⁺ ion production in an example of an E-CEM device as a function of residence time at different pH levels;

FIG. 11 is a schematic diagram of an example of an E-CEM device as disclosed herein; and

FIG. 12 is a schematic diagram of another example of an E-CEM device as disclosed herein.

DETAILED DESCRIPTION

The total carbon content of the world's oceans is approximately 38,000 gigatons (GT). Over 95% of this carbon is in the form of dissolved bicarbonate ion (HCO₃⁻). This bicarbonate ion, along with the carbonate ion (CO₃²⁻), is responsible for buffering and maintaining the pH of the ocean which is relatively constant below the first 100 meters of ocean depth. The dissolved bicarbonate and carbonate ions present in the ocean are effectively bound CO₂, and the sum of the concentrations of these species, along with dissolved gaseous CO₂, represents the total carbon dioxide concentration [CO₂]_T, of seawater.

At a typical ocean pH of 7.8, kept relatively constant by a complex bicarbonate-carbonate buffer system, [CO₂]_T is about 2000 μmoles/kg near the surface and about 2400 μmoles/kg at depths below 300 meters. This equates to approximately 100 mg/L of [CO₂]_T. Of the total CO₂ in the ocean, about 2-3% is dissolved gaseous CO₂, about 1% is present as the dissolved carbonate ion, and the remainder, about 96%, is present as the dissolved bicarbonate ion. It is known that the equilibrium form and concentration of water containing CO₂ and its various ionic forms is dependent on the pH of the water. For example, at a seawater pH of 4.5, 99% of all carbonate species in seawater exist as carbonic acid, H₂CO₃. Thus, to convert HCO₃⁻ to H₂CO₃, the pH of seawater may be lowered.

CO₂ dissolved in water is in equilibrium with H₂CO₃ as shown in equation 1:

The hydration equilibrium constant is 1.70×10⁻³. This indicates that H₂CO₃ is not stable in water at elevated concentrations and gaseous CO₂ readily dissociates at pH of 4.5, allowing CO₂ to be easily removed by degassing or stripping once the seawater has been acidified such that the unstable H₂CO₃ is deprotonated to the predominant carbonate species.

Electrochemical cells are used in marine, offshore, municipal, industrial, and commercial implementations. The design parameters of electrochemical cells, for example, inter-electrode spacing, thickness of electrodes and coating density, electrode areas, methods of electrical connections, etc., can be selected for different implementations. Aspects and embodiments disclosed herein are not limited to the number of electrodes, the space between electrodes, the electrode material, material of any spacers between electrodes, number of passes within the electrochemical cells, or electrode coating material.

An electrochemical device with ion exchange membranes can be designed to change the pH of a fluid stream while generating reaction products at the electrodes. FIGS. 1 and 2 show two variations of a device with three fluid streams separated by two ion exchange membranes of the same ionic selectivity. The electrode reactions depend on the composition of the electrolytes, electrode materials and operating conditions. Common reactions include:

In addition, chlorine gas evolution is possible at the anode if the anolyte contains chloride ions:

In FIG. 1, both membranes are cation exchange membranes (CEM), which preferentially pass cations. Under a DC voltage, H⁺ ions generated at the anode in the anode compartment 5 pass into the center compartment 10 and acidify the fluid stream by reacting with anions such as HCO₃⁻ or SO₄⁻². Excess H⁺ ions either continue into the cathode compartment 15, where they react with OH− ions to form water or are swept out of the center compartment by the fluid.

Conversely, in FIG. 2 both membranes are anion exchange membranes (AEM), which preferentially pass anions. OH⁻ ions generated at the cathode pass into the center compartment 10 and increases the pH of the fluid stream. Excess OH⁻ ions either continue into the anode compartment 5, where they react with OH⁻ ions to form water or are swept out of the center compartment 10 by the fluid.

One use of the device in FIG. 1 is the E-CEM process to reduce seawater pH and convert dissolved bicarbonate ions to CO₂ gas while simultaneously producing both oxygen, in the anode compartment 5 and hydrogen gas through electrolytic dissociation of water in the cathode compartment 15. The CO₂ and H₂ gas may be utilized as feedstock to a modified Fischer-Tropsch process to produce jet fuel, as detailed in, e.g., U.S. Pat. No. 9,303,323 B2, which is incorporated herein by reference. Furthermore, the oxygen gas may be utilized for a variety of applications in the industrial, environmental, medical, and/or energy sectors.

The main reactions in the center (seawater) compartment 10 are:

The pK₁ and pK₂ values are for seawater at 10° C. Other ions may react with the H⁺, such as conversion of borate to boric acid.

Seawater has a pH of ˜8. FIG. 3 shows the equilibrium diagram for inorganic carbonic species in seawater at 10° C. If the pH is reduced to less than ˜4, essentially all the carbonate and bicarbonate is converted to H₂CO₃.

The feeds to the anode and cathode compartments 5, 15 are conductive solutions, such as reverse osmosis (RO) product water with conductivity <200 μS/cm or sodium sulfate solution with conductivity of ˜200-3000 μS/cm.

FIG. 4 is a schematic of the E-CEM process. A fraction of the H⁺ ions generated at the anode lower the pH in the anolyte and exit the device in the effluent from the anode compartment 5. The remaining H⁺ ions enter the seawater compartment 10 through the first CEM. A fraction of these H⁺ ions react with HCO₃⁻ in the seawater to form H₂CO₃. The remaining H⁺ ions pass unreacted through the center compartment 10 and enter the cathode compartment 15 or are transported out the center compartment 10 with the seawater. The unreacted H⁺ ions can be considered “losses” in the E-CEM process that reduce its energy efficiency, i.e., it increases the kWh required per mol of H₂CO₃ in the seawater effluent.

The present disclosure proposes a method to acidify the seawater feed and effluent in an Electrolytic-Cation Exchange Module (E-CEM) device.

The E-CEM process was tested in the laboratory using a module with the following specifications:

• • Flow compartment width: 1.25 in (3.18 cm)
  • Flow compartment length: 7.0 in (17.8 cm)
  • Electrode compartment thickness: 0.06 in (0.15 cm)
  • Seawater compartment thickness: 0.375 in (0.95 cm) or 0.75 in (1.9 cm)
  • Active membrane area: 8.75 in² (56.45 cm²)
  • Electrodes: Platinum coated titanium plate
  • Membranes: Ionpure® heterogeneous CEM

Hereinafter, seawater compartment thickness of 0.375 inches will be referred to as “1× thickness” and thickness of 0.75 inches will be referred to as “2× thickness”. An example of a test run is shown in FIG. 5. After the DC voltage is applied at a range of 60V-80V, the pH in the seawater effluent decreases until it reaches a steady state value of about 4. The seawater compartment thickness was 0.375 in (0.95 cm).

The operating conditions were:

• • Seawater feed: synthetic Instant Ocean® seawater with conductivity of 49.05 mS/cm and HCO₃ concentration of 194 ppm (higher than typical seawater).
  • Anolyte and catholyte feed: 270 μS/cm Na₂SO₄ solution in deionized water
  • Current density: 317 A/m² (1.79 A)
  • Anolyte flow rate: 0.15 l/min (residence time T=3.4 sec)
  • Seawater flow rate: 0.30 l/min (residence time T=10.8 sec)
  • Catholyte flow rate: 0.15 l/min (residence time T=3.4 sec)

FIGS. 6A and 6B show the results for additional runs at different seawater compartment thickness; the steady pH in the seawater effluent is plotted vs. 1/residence time at different current densities.

From the regression equations, the current density utilized at different residence times (or vice versa) to achieve a given steady state pH can be calculated. FIG. 7 shows current density vs. inverse of residence time (1/sec) so that the data points can be fitted with linear curves.

FIG. 8 shows the theoretical amount of H⁺ ions used to reduce the pH in synthetic seawater, assuming the pK₁ and pK₂ values in Equations 3 and 4. Reactions of H⁺ ions with other ions in seawater are ignored for the following analysis.

From the applied current the amount of H⁺ ions generated at the anodes (in mol/s) can be estimated for the test runs using the Faraday constant. FIGS. 9A and 9B show that the amount of H⁺ ions generated exceed the theoretical amount necessary for titration in most of the tests (the ratios less than 1.0 may be due to inaccuracies in measurements).

The pH of the anolyte effluent varies from 2.6-3.0, averaging around 2.8. Based on the reduction in pH from the inlet to the outlet and the flow rate, the amount of H⁺ ions used to reduce the pH in the anolyte can be estimated.

Calculations were used to estimate the amount of excess H⁺ ions that are “wasted” in the seawater compartment. The results are shown in FIG. 10. Note that the percent of excess H⁺ ions in the seawater compartments increase as the residence time is decreased and can reach 25% to 30% at the lowest residence times.

The overall indication is that a significant percentage of the H⁺ ions generated is underutilized, particularly as the residence time decreases. Aspects and embodiments disclosed herein include modifications of E-CEM devices to increase the utilization rate and thereby reduce the energy consumption of the process in terms of kWh supplied from the DC power supply per mol of H₂CO₃ removed from seawater.

A first embodiment of an improved apparatus for generation of carbon dioxide and hydrogen from a saline water source (an E-CEM device) is illustrated generally at 100 in FIG. 11. The E-CEM device 100 includes an anodic compartment 110 having an inlet 110A and an outlet 110B and an anode 120 disposed on a first side of the anodic compartment 110. The anodic compartment inlet 110A is supplied with anolyte (anode feed) 165, for example, deionized water or an aqueous sodium sulfate solution. The E-CEM device 100 further includes a cathodic compartment 130 having an inlet 130A and an outlet 130B, and a cathode 140 disposed on a first side of the cathodic compartment 130. The cathodic compartment inlet 130A is supplied with catholyte (cathode feed) 170, for example, deionized water or an aqueous sodium sulfate solution. A first cation permeable fluidic separator CEM is disposed on a second side of the anodic compartment 110 and a second cation permeable fluidic separator CEM is disposed on a second side of the cathodic compartment 130. The second cation permeable fluidic separator CEM may be a monovalent cation selective membrane. Two center compartments (also referred to herein as seawater compartments) 150A, 150B are defined between the first cation permeable fluidic separator CEM and the second cation permeable fluidic separator CEM. The two center compartments 150A, 150B are separated from one another by a third cation permeable fluidic separator CEM. A fluid circulation loop is connected between an outlet of the first center compartment 150A and an inlet of the second center compartment 150B such that the outlet of the first center compartment 150A is one of fluidly connectable to or in fluid communication with the inlet of the second center compartment 150B.

In alternate embodiments, the anodic compartment 110 may be a membrane electrode assembly rather than a flow through compartment, especially when using deionized water as the anolyte. In some embodiments, a membrane electrode assembly may comprise a proton exchange membrane (PEM), which conducts protons (H) but blocks electrons and gases, thin layers of catalyst material (e.g., platinum-based) on either side of the membrane, and gas diffusion layers (GDLs) that allow gases (e.g., H₂, O₂) to reach the catalyst.

Seawater flows in series through the two center compartments 150A, 150B. Excess H⁺ ions from the second center compartment 150B (next to the anode 120) pass into the first center compartment 150A through the CEM separating the two center compartments 150A, 150B.

The seawater feed 175 entering the first center compartment 150A is pre-acidified by the excess H⁺ ions from the second center compartment 150B. In some embodiments, the flow rate and current are controlled so that the pH in the effluent from the first center compartment 150A is above 6.0, low enough to begin the titration of HCO₃⁻ to H₂CO₃, but high enough so that rate of migration on H⁺ ions into the cathode compartment 130 is much lower than that in the traditional E-CEM process.

As the seawater enters the second center compartment 150B, its pH is reduced further to reach a target effluent pH of 4.0 or below to accomplish complete (or substantially complete) conversion of HCO₃⁻ to H₂CO₃.

The E-CEM device 100 may include a controller, for example, a general purpose computer, ASIC, PLC or other form of controller known in the art, configured to regulate the flow rate of the fresh seawater 175 through the first center compartment 150A, the flow rate of the effluent seawater 180 from the first center compartment 150A through the second center compartment 150B, and/or power supplied across the anode and cathode 120, 140 to maintain predetermined pHs of the seawater effluents from the first and second center compartments 150A, 150B using one or more pumps or valves (not shown so as not to obscure the figure). In another embodiment, relative residence time of the seawater in the first center compartment and second center compartment can be varied by modifying intermembrane spacing relative to one another, which can alter the pH such that effluent from one compartment is more (or less) acidic than the other.

A pH sensor pH may be disposed at the outlet of the first center compartment 150A and in communication with the controller. Another pH sensor pH may be disposed at the outlet of the second center compartment 150B and in communication with the controller. The controller may utilize measurements of pH of the effluent from the outlet of the first center compartment 150A and/or measurements of the pH of the effluent from the outlet of the second center compartment 150B to determine how to regulate flow rates of liquid (e.g., seawater) through the first and second center compartments 150A, 150B and/or power supplied across the anode and cathode 120, 140.

In a second embodiment, indicated generally at 200 in FIG. 12, is similar to the E-CEM device 100, with like reference numbers indicating like features, except that the two center compartments 150A, 150B are stacked, separated by CEMs and an additional fluid flow compartment 115 similar in thickness to the anodic compartment 110. The seawater flows in series through the two center compartments 150A, 150B as in the embodiment 100 illustrated in FIG. 11. The effluent from the anodic compartment 110 flows in series through the additional fluid flow compartment 115 through a second fluid circulation loop providing fluid communication between the outlet of the anodic compartment 110 and an inlet of the additional fluid flow compartment 115.

The combined excess H⁺ ions in the effluent of the anodic compartment 110 and the excess H⁺ ions from the second center compartment 150B pass into the first center compartment 150A and pre-acidify the seawater feed 175. Again, ideally the pH in the first center compartment 150B should be controlled to above 6.0, with further reduction to the target effluent pH as the seawater flows through the second center compartment 150B.

A fraction of the cations such as Na⁺, Ca⁺² and Mg⁺² enter the additional fluid flow compartment 115 and exit the device 200 in the effluent from the additional fluid flow compartment 115.

In other embodiments, more center compartments, alternating with additional fluid flow compartments 115, can be added. While at least two center compartments are needed, more than two center compartments may be advantageous. By staging multiple center compartments fluidically and electrically in series, H⁺ can be conserved along the entire fluid path length. Additionally and/or alternatively, due to the increased path length within a device with more than two center compartments, higher seawater flow rates through the device could be realized.

In the E-CEM device 200, the controller is configured to regulate flow rates of liquid through any one or more of the first center compartment 150A, second center compartment 150B, anodic compartment 110, and/or additional fluid flow compartment 115 to produce the acidified seawater 180 and effluent from the second seawater compartment 150B with predetermined pHs, for example, based on readings from pH meter(s) on or within conduit(s) through which any one or more of the effluent from any one or more of the first center compartment 150A, second center compartment 150B, anodic compartment 110, and/or additional fluid flow compartment 115 pass.

Both E-CEM device embodiments 100, 200 benefit by reducing the total power consumption and reduced number of modules required for producing acidified seawater. This also lowers the footprint of the overall unit. Either of the E-CEM device embodiments 100, 200 may be operated with polarity reversal to, for example, reduce scaling on the anodes and/or cathodes. Additionally and/or alternatively, a monovalent selective membrane may be used adjacent the cathodic compartment 130 in order to prevent calcium and magnesium from entering the cathodic compartment 130, thereby reducing scaling potential of calcium or magnesium hydroxides or carbonates under elevated pH conditions in the catholyte.

The present disclosure also contemplates a method of facilitating generation of hydrogen and carbon dioxide from seawater. The method includes providing an electrolytic cell 100, 200 including an anodic compartment 110 having an inlet 110A and an outlet 110B, an anode 120 disposed on a first side of the anodic compartment 110, a cathodic compartment 130 having an inlet 130A and an outlet 130B, a cathode 140 disposed on a first side of the cathodic compartment 130, a first cation permeable fluidic separator CEM disposed on a second side of the anodic compartment 110, a second cation permeable fluidic separator CEM disposed on a second side of the cathodic compartment 130, a first center compartment 150A, and a second center compartment 150B, the first center compartment 150A defined between the second center compartment 150B and the second cation permeable fluidic separator CEM, the second center compartment 150B defined between the first cation permeable fluidic separator CEM and the first center compartment 150A. The method further comprises providing instructions to flow an anolyte through the anodic compartment, flow a catholyte through the cathodic compartment, flow the seawater through the first center compartment, flow effluent from an outlet of the first center compartment into an inlet of the second center compartment, and remove hydrogen and carbon dioxide from the cathodic compartment and the second center compartment, respectively.

The method may further comprise providing instructions to regulate power supplied across the anode and cathode and a flow rate of the seawater through the first center compartment that results in effluent exiting the outlet of the first center compartment having a second pH that is reduced relative to a first pH of the seawater that is supplied to an inlet of the The method may further comprise providing instructions to regulate power supplied across the anode and cathode and a flow rate of effluent from the outlet of the first center compartment through the second center compartment that results in effluent exiting an outlet of the second center compartment having a third pH that is reduced relative to the second pH.

The third pH may be about 4 or less.

The electrolytic cell may further includes an additional fluid flow compartment disposed between the first center compartment and the second center compartment and the method may further comprise providing instructions to flow effluent from the outlet of the anodic compartment through the additional fluid flow compartment.

The present disclosure further contemplates a method of generating carbon dioxide and hydrogen from a saline water source. The method includes providing an electrolytic-cation exchange module device including an anodic compartment having an inlet and an outlet, a cathodic compartment having an inlet and an outlet, a first center compartment defined between the anodic compartment and cathodic compartment, and a second center compartment defined between the first center compartment and the anodic compartment, flowing a catholyte through the cathodic compartment to form an effluent catholyte, introducing feed seawater into an inlet of the first center compartment, flowing a first effluent seawater from an outlet of the first center compartment to an inlet of the second center compartment, withdrawing a second effluent seawater from an outlet of the second center compartment, extracting carbon dioxide from the second effluent seawater, and extracting hydrogen from the effluent catholyte.

The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality” refers to two or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Having thus described several aspects of at least one embodiment, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Any feature described in any embodiment may be included in or substituted for any feature of any other embodiment. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the disclosed methods and materials are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments disclosed.