Acidification of catholyte feed in an electrolytic - cation exchange module (e-CEM) device

Abstract

An apparatus for generation of carbon dioxide and hydrogen a saline water source are disclosed. The apparatus may include 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 center compartment defined between the first cation permeable fluidic separator and the second cation permeable fluidic separator, and a source of acidic catholyte that is one of fluidly connectable to or in fluid communication with the inlet of the cathodic compartment. Methods of generating hydrogen, carbon dioxide, and oxygen from seawater using the apparatus are also disclosed.

Description

[0001] Attorney Docket No.: 202488109PPCT01

[0002] ACIDIFICATION OF CATHOLYTE FEED IN AN ELECTROLYTIC - CATION

[0003] EXCHANGE MODULE (E-CEM) DEVICE

[0004] CROSS-REFERENCE TO RELATED APPLICATIONS

[0005] This application claims priority to U.S. Provisional Application Serial No. 63 / 698,191, titled ‘ACIDIFICATION OF CATHOLYTE FEED IN AN ELECTROLYTIC - CATION EXCHANGE MODULE (E-CEM) DEVICE / ’ filed on September 24, 2024. the subject matter of same being incorporated herein by reference in its entirety for all purposes.

[0006] GOVERNMENT LICENSE RIGHTS

[0007] This invention was made with U.S. government support under Contract No. N00014- 21-C-1019 awarded by the Department of the Navy. The government has certain rights in the invention.

[0008] FIELD OF TECHNOLOGY

[0009] Aspects and embodiments disclosed herein relate to devices and methods for acidifying seawater to generate and capture carbon dioxide (CO2) and hydrogen (H2).

[0010] SUMMARY

[0011] In accordance with an aspect, there is provided an apparatus for generation of carbon dioxide and hydrogen 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 center compartment defined between the first cation permeable fluidic separator and the second cation permeable fluidic separator, and a source of acidic catholyte that is one of fluidly connectable to or in fluid communication with the inlet of the cathodic compartment.

[0012] In some embodiments, the source of acidic catholyte includes anolyte from the outlet of the anodic compartment that has been at least partially degassed.

[0013] 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. Attorney Docket No.: 202488109PPCT01

[0014] In some embodiments, the apparatus further comprises a source of 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.

[0015] In some embodiments, the apparatus further comprises a controller configured to regulate relative amounts of the at least partially degassed anolyte from the output of the anodic compartment and the one of the deionized water or the aqueous sodium sulfate solution that are mixed to form the acidic catholyte to maintain a predetermined pH of the acidic catholyte. The predetermined pH of the acidic catholyte may be in a range of from 2 to 4.

[0016] In some embodiments, the apparatus further comprises a pH sensor disposed at the outlet of the anodic compartment and in communication with the controller.

[0017] In some embodiments, the controller is further configured to regulate a flow rate of anolyte through the anodic compartment at a rate which maintains a pH of the anolyte from the outlet of the anodic compartment at a predetermined value. The predetermined pH value may be from 2 to 3.

[0018] In some embodiments, the source of acidic catholyte includes one of deionized water or an aqueous sodium sulfate solution that has been dosed with an acid.

[0019] In some embodiments, the acid is sulfuric acid provided from a source of sulfuric acid.

[0020] In some embodiments, the apparatus further comprises a controller configured to regulate relative amounts of the one of the deionized water or the aqueous sodium sulfate solution and the acid dosed into the one of the deionized water or the aqueous sodium sulfate solution to provide the source of acidic catholyte with a predetermined pH.

[0021] In some embodiments, the apparatus further comprises a source of saline water that is one of fluidly connectable to or in fluid communication with the center compartment.

[0022] In some embodiments, the source of acidic catholyte includes effluent from the center compartment.

[0023] In some embodiments, the apparatus further comprises a degasification sub-system configured to remove carbon dioxide from the effluent from the center compartment and form a degasified effluent that is utilized as the acidic catholyte.

[0024] In some embodiments, the apparatus further comprises one or more pH sensors disposed to monitor pH of one or both of the degasified effluent or effluent from the cathodic compartment, and a controller in communication with the one or more pH sensors and configured to control one or more operating parameters of the apparatus to maintain a Attorney Docket No.: 202488109PPCT01 predetermined pH level or levels in the one or both of the degasified effluent or effluent from the cathodic compartment.

[0025] 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, and a second cation permeable fluidic separator disposed on a second side of the cathodic compartment, a center compartment defined between the first cation permeable fluidic separator and the second cation permeable fluidic separator. The method further comprises providing instructions to flow the seawater through the center compartment, flow an anolyte through the anodic compartment, flow an acidic catholyte through the cathodic compartment, and remove hydrogen and carbon dioxide from the cathodic compartment and the center compartment, respectively.

[0026] In some embodiments, the method further comprises providing instructions to produce the acidic catholyte from anolyte from the outlet of the anodic compartment that has been at least partially degassed.

[0027] In some embodiments, the method further comprises providing instructions to fluidly connect a source of one of deionized water or an aqueous sodium sulfate solution to the inlet of the cathodic compartment.

[0028] In some embodiments, the method further comprises providing instructions to regulate relative amounts of the at least partially degassed anolyte from the output of the anodic compartment and the one of the deionized water or the aqueous sodium sulfate solution that are mixed to form the acidic catholyte to maintain a predetermined pH of the acidic catholyte.

[0029] In some embodiments, the method further comprises providing instructions to produce the acidic catholyte from one of deionized water or an aqueous sodium sulfate solution that has been dosed with an acid.

[0030] In some embodiments, the acid is sulfuric acid provided from a source of sulfuric acid.

[0031] In some embodiments, the method further comprises providing instructions to regulate relative amounts of the one of the deionized water or the aqueous sodium sulfate Attorney Docket No.: 202488109PPCT01 solution and the acid dosed into the one of the deionized water or the aqueous sodium sulfate solution to provide the source of acidic catholyte with a predetermined pH.

[0032] In accordance with another aspect, there is provided a method of retrofitting an apparatus for generation of carbon dioxide and hydrogen from a saline water source, the apparatus comprising an anodic compartment having an inlet and an outlet, a cathodic compartment having an inlet and an outlet, and a center compartment defined between the anodic compartment and cathodic compartment. The method comprises connecting a source of acidic catholyte to the inlet of the cathodic compartment.

[0033] In some embodiments, the method further comprises connecting a first fluid line from the outlet of the anodic compartment to a degasification sub-system and connecting a second fluid line from the degasification sub-system to the inlet of the cathodic compartment.

[0034] In some embodiments, the method further comprises providing a mixing vessel, connecting a first inlet of the mixing vessel to a source of one of deionized water or an aqueous sodium sulfate solution, connecting a second inlet of the mixing vessel to a source of an acid, and connecting an outlet of the mixing vessel to the inlet of the cathodic compartment.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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:

[0037] FIG. 1 is a schematic drawing of one example of an electrochemical cell;

[0038] FIG. 2 is a schematic drawing of another example of an electrochemical cell;

[0039] FIG. 3 is a diagram illustrating the equilibrium for inorganic carbonic species in seawater at 10 °C;

[0040] FIG. 4 is a schematic drawing of the E-CEM process;

[0041] FIG. 5 is a graph showing change in pH over time in the seawater compartment in a run of an E-CEM process;

[0042] 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;

[0043] 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; Attorney Docket No.: 202488109PPCT01

[0044] FIG. 7 is a graph showing current density versus the inverse of residence time in an example of an E-CEM device;

[0045] 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;

[0046] FIG. 9A is a graph illustrating experimental versus calculated current density at different pH levels in an E-CEM device with a first seawater compartment thickness;

[0047] FIG. 9B is a graph illustrating experimental versus calculated current density at different pH levels in an E-CEM device with a second seawater compartment thickness;

[0048] FIG. 10 is a graph illustrating 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;

[0049] FIG. 11 is a schematic diagram of an example of an E-CEM device as disclosed herein;

[0050] FIG. 12 is a schematic diagram of another example of an E-CEM device as disclosed herein; and

[0051] FIG. 13 is a schematic diagram of another example of an E-CEM device as disclosed herein.

[0052] DETAILED DESCRIPTION

[0053] 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 w ith dissolved gaseous CO2, represents the total carbon dioxide concentration [CCh]T, of seawater.

[0054] At a typical ocean pH of 7.8, kept relatively constant by a complex bicarbonatecarbonate buffer system, | CO2 | r is about 2000 pmoles / kg near the surface and about 2400 pmoles / kg at depths below 300 meters. This equates to approximately 100 mg / L of | CO2 | i . 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 know n 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 Attorney Docket No.: 202488109PPCT01 seawater pH of 4.5, 99% of all carbonate species in seawater exist as carbonic acid, H2CO3. Thus, to convert HCOs to H2CO3, the pH of seawater may be lowered.

[0055] CO2 dissolved in water is in equilibrium with H2CO3 as shown in equation 1 :

[0056] CO2 + H2O H2CO3 (1)

[0057] The hydration equilibrium constant is 1.70x KT3. This indicates that H2CO3 is not stable in water and gaseous CO2 readily dissociates at pH of 4.5, allowing CChto be easily removed by degassing or stripping once the seawater has been acidified to ensure that the unstable H2CO3 is deprotonated to the predominant carbonate species.

[0058] 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.

[0059] 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:

[0060] Anode: 2 H2O 4 H++ O2 (g) + 4e" (1)

[0061] Cathode: 2 H2O + 4e 2 OH’ + 2 H2(g) (2)

[0062] In addition, chlorine gas evolution is possible at the anode if the anolyte contains chloride ions:

[0063] 2 Cl" CI2 (g) + 2e"

[0064] In FIG. 1 , both membranes are cation exchange membranes (CEM), which preferentially pass cations. Under a DC voltage, H+ions generated at the anode pass into the center compartment and acidifies the fluid stream by reacting with anions such as HCOs" or Attorney Docket No.: 202488109PPCT01

[0065] SOT2Excess H+ions either continue into the cathode compartment, where they react with OH’ ions to form water or are swept out of the center compartment by the fluid.

[0066] 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 and increases the pH of the fluid stream. Excess OH’ ions either continue into the anode compartment, where they react with OH’ ions to form water or are swept out of the center compartment by the fluid.

[0067] 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 hydrogen gas through electrolytic dissociation of water in the cathode compartment. The CO2 and H2 gas may be utilized as feedstock to a modified Fischer-Tropsch process to produce jet fuel.

[0068] The main reactions in the center (seawater) compartment are:

[0069] H++ HCOs’ H2CO3 H2O + CO2(g) pKi = 6. 1 (3)

[0070] H++ CDs’ HCO3’ pK2= 9.3 (4)

[0071] The pKi and pK2 values are for seawater at 10 °C. Other ions may react with the H+, such as conversion of borate to boric acid.

[0072] 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 are converted to H2CO3.

[0073] The feeds to the anode and cathode compartments are conductive solutions, such as reverse osmosis (RO) product water with conductivity < 200 LiS / cm or sodium sulfate solution with conductivity7of - 200 - 3000 pS / cm.

[0074] 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 exits the device in the effluent from the anode compartment. The remaining H+ions enter the seawater compartment through the first CEM. A fraction of these H+ions react with HCOs’ in the seawater to form H2CO3. The remaining H+ions pass unreacted through the center compartment and enter the cathode compartment or is transported out the center compartment with the seawater. The unreacted H1ions 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. Attorney Docket No.: 202488109PPCT01

[0075] The present disclosure proposes a method to pre-acidify the catholyte feed using the anolyte effluent, acid, or seawater effluent in an Electrolytic - Cation Exchange Module (E- CEM) device.

[0076] The E-CEM process w as tested in the laboratory7using a module with the following specifications:

[0077] Flow compartment width: 1.25 in (3.18 cm)

[0078] Flow compartment length: 7.0 in (17.8 cm)

[0079] Electrode compartment thickness: 0.06 in (0. 15 cm)

[0080] Seawater compartment thickness: 0.375 in (0.95 cm) or 0.75 in (1.9 cm)

[0081] Active membrane area: 8.75 in2(56.45 cm2)

[0082] Electrodes: Platinum coated titanium plate

[0083] Membranes: lonpure® heterogeneous CEM

[0084] Hereinafter, seawater compartment thickness of 0.375 inches will be referred to as “IX thickness” and thickness of 0.75 inches will be referred to as “2X thickness”. An example of a test run is shown in FIG. 5. After the DC voltage is applied, 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).

[0085] The operating conditions were:

[0086] Seawater feed: synthetic Instant Ocean® seawater with conductivity' of 49.05 mS / cm and HCO3 concentration of 194 ppm (higher than typical seawater)

[0087] Anolyte and catholyte feed: 270 pS / cm Na2SO4 solution in deionized water

[0088] Current density7: 317 A / m2(1.79 A)

[0089] Anolyte flow rate: 0. 15 l / min (residence time T = 3.4 sec)

[0090] Seawater flow rate: 0.30 l / min (residence time T = 10.8 sec)

[0091] Catholyte flow rate: 0. 15 l / min (residence time T = 3.4 sec)

[0092] FIGS. 6 A and 6B show7the results for additional runs at different seaw7ater compartment thickness; the steady pH in the seawater effluent is plotted vs. 1 / residence time at different current densities. Attorney Docket No.: 202488109PPCT01

[0093] 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 cunent density vs. inverse of residence time (1 / sec) so that the data points can be fitted with linear curves.

[0094] FIG. 8 shows the theoretical amount of H+ions used to reduce the pH in synthetic seawater, assuming the pKi and pK2 values in Equations 3 and 4. Reactions of H+ions with other ions in seawater are ignored for the following analysis.

[0095] 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).

[0096] 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.

[0097] 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. Additional tests and analysis may be performed to improve the accuracy of the estimates.

[0098] The overall indication is that a significant percentage of the H1ions generated is underutilized, particularly as the residence time decreases. Aspects and embodiments disclosed herein include modifications of the 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.

[0099] 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 HOB and an anode 120 disposed on a first side of the anodic compartment 110. The E-CEM device 100 further includes a cathodic compartment 130 having an inlet 130 A and an outlet 130B, and a cathode 140 disposed on a first side of the cathodic compartment 130. 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. A center compartment 150 is defined between the first cation permeable fluidic separator CEM and the second cation permeable Attorney Docket No.: 202488109PPCT01 fluidic separator CEM. A source of acidic catholyte 155 is one of fluidly connectable to or in fluid communication with the inlet 130A of the cathodic compartment 130.

[0100] In the E-CEM device 100, O2 gas in the anolyte effluent 160 is removed by vacuum, by membrane degasification or by purging with air, by a degasification / deoxygenation system 165 as show n in FIG. 11. The effluent is then circulated as the catholyte feed. The source of acidic catholyte 155 thus includes anolyte from the outlet 110A of the anodic compartment 110 that has been at least partially degassed.

[0101] The E-CEM device 100 may be provided with a source of anolyte 175 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 110A of the anodic compartment 110.

[0102] The E-CEM device 100 may be provided with a source of fresh catholyte 170 including one of deionized water or an aqueous sodium sulfate solution that is also one of fluidly connectable to or in fluid communication with the inlet 130A of the cathodic compartment 130.

[0103] 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 relative amounts of the at least partially degassed anolyte from the output 110B of the anodic compartment 110 and the one of the deionized w ater or the aqueous sodium sulfate solution that are mixed to form the acidic catholyte 155 to maintain a predetermined pH of the acidic catholyte 155 using one or more pumps or valves (not shown so as not to obscure the figure). A desired pH range for catholyte entering the catholyte compartment is from 2 to 4.

[0104] A pH sensor pH may be disposed at the outlet 110A of the anodic compartment 110 and in communication with the controller. The controller may be configured to regulate a flow rate of anolyte 175 through the anodic compartment at a rate which maintains a pH of the anolyte from the outlet 110A of the anodic compartment 110 at a predetermined value. A desirable pH range of the anolyte at the outlet of the anodic compartment is from 2 to 3.

[0105] In a second embodiment, indicated generally at 200 in FIG. 12, the catholyte is acidified by addition of an acid, for example, sulfuric acid. Sufficient acid may be added to the catholyte to form an acidified catholyte with a pH of from 2 to 3. The E-CEM device 200 is substantially the same as the E-CEM device 100, with like reference numbers indicating like features, except that there is no recirculation of degassed anolyte 155 into the cathodic compartment 130. Rather the source of acidic catholyte 155’ includes fresh catholyte 170, for example, one of deionized water or an aqueous sodium sulfate solution, that has been dosed with an acid, indicated in FIG. 12 as being sulfuric acid although other suitable acids Attorney Docket No.: 202488109PPCT01 may be utilized. The fresh catholyte 170 and acid may be introduced into a mixing vessel 180 and mixed prior to being introduced into the inlet 130A of the cathodic chamber 130 as illustrated, or may be introduced separately into the cathodic chamber 130. In the E-CEM device 200, the controller is configured to regulate relative amounts of the one of the deionized water or the aqueous sodium sulfate solution 170 and the acid dosed into the one of the deionized water or the aqueous sodium sulfate solution to provide the source of acidic catholyte 155’ with a predetermined pH, for example, based on readings from a pH meter on or within a conduit through which the acidic catholyte 155’ passes or at or within the inlet 130A of the cathodic compartment 130.

[0106] In a third embodiment, indicated generally at 300 in FIG. 13, the pH of the seawater is reduced to preferably 4.0 or below after passing through the center compartment 150, resulting in complete conversion of HCOf to H2CO3. The dissolved CO2 in the seawater effluent is removed by a degasification process 165’ utilizing gas permeable membranes or vacuum. A fraction of the degasified seawater effluent is reused as feed to the cathode compartment ("‘seawater recycle” and “cathode feed” in FIG. 13), optionally supplemented by fresh catholyte 170 including one of deionized water or an aqueous sodium sulfate solution. The remainder of the degasified seawater effluent can be discharged or mixed with fresh seawater to pre-acidify the feed to the center compartment 150. pH sensors may be disposed on or within fluid conduits carrying the cathode compartment effluent and / or the degasified seawater effluent. A controller may monitor the pH of each of these fluid streams and control one or more operating parameters, for example, current across the anode 120 and cathode 140, or flow rate of fluid through any one or more of the compartments 110, 130, 150 to maintain the pH of these fluid streams at predetermined desired levels.

[0107] In some E-CEM processes the cathode compartment 130 is fed with reverse osmosis (RO) permeate with TDS typically in the range of 5 - 20 ppm or with tap water with TDS ty pically 100 - 300 ppm. The pH of the catholyte feed is such processes is ty pically between 6 and 8. As the catholyte flows through the cathode compartment 130, its pH increases due to OH' ions generated at the cathode 140. Simultaneously cations in the center compartment 150 migrate into the cathode compartment 130 under the DC field.

[0108] If the catholyte pH approaches and exceeds pH 10, the divalent ions from the seawater such as Ca+2and Mg+2may form precipitates that scale the surfaces of the CEM membranes and cathode 140. For example, HCO3 in the catholyte feed may be converted to CO?'2in the cathode compartment 130 which can then precipitate with Ca+2as CaCCh. Mg+2 Attorney Docket No.: 202488109PPCT01 and OH' ions may precipitate as Mg(OH)2. To prevent irreversible scaling in the cathode compartment 130, the polarity of the applied DC field can be periodically reversed. During reversal the DC output voltage is turned off, the polarity is reversed, and the voltage is then turned back on. When there is no applied DC current, seawater flowing through the center compartment 150 is not acidified, so the effluent is not directly usable. It can be temporarily diverted to discharge or mixed with previously acidified seawater effluent in a tank before degasification. The use of polarity reversal may reduce the productivity of the E-CEM process in terms of overall rate of HCOs' conversion to H2CO3.

[0109] RO permeate and tap water have lower conductivities compared to seawater. Calculations and experimental measurements have shown that most of the voltage drop in an E-CEM cell is in the anode and cathode compartments.

[0110] Reusing degasified seawater effluent with pH < 4 as catholyte feed can reduce the frequency of reversal and the voltage drop. The H+ions in the catholyte feed 155” would neutralize a fraction of the OH' ions generated at the cathode 140, so the catholyte effluent pH would be lower than in an E-CEM process utilizing RO permeate or tap water as feed. This may reduce the potential for precipitation or scaling. The catholyte effluent pH would depend on variables such as the current density, the flow rate, temperature, and feed pH.

[0111] The conductivity7of degassed seawater is approximately 50,000 pS / cm vs. 200 - 500 pS / cm for typical tap water. The electrical resistance in the catholyte would be reduced by more than 100X. The overall resistance of the cathode compartment 130 also includes the resistance in the boundary layers next to the CEM membranes and electrodes and the electrode potentials, so the overall resistance would be greatly reduced, but not by 100X.

[0112] Hypothetically all of the degassed seawater effluent can be fed to the cathode compartment; the cathode compartment thickness may be increased to at least that of the center compartment 150 to balance the pressure drops through the two compartments. The concentration of divalent ions in the seawater effluent would be lower than that in the seawater feed because a fraction of the cations w ould have been transferred to the cathode compartment. As the catholyte flows through the cathode compartment 130, it would regain the divalent ions for a net change of zero in concentrations.

[0113] In each of the E-CEM device embodiments 100, 200, 300 a source of saline water, indicated in FIGS. 11, 12, and 13 as being seaw ater, is one of fluidly connectable to or in fluid communication with the center compartment 150.

[0114] In each of the E-CEM device embodiments 100. 200, 300 the acidity of the feed will prevent scaling at the electrode surface and membrane. This will reduce the need for frequent Attorney Docket No.: 202488109PPCT01 polarity reversal with the possibility of eliminating the need for polarity reversal. Low pH also contributes to the feed's increased conductivity, reducing the overall cell voltage. Literature also indicates that hydrogen evolution reaction (HER) is faster in acidic conditions from improved electrode reaction kinetics. In the long run, this process may increase H2 generation efficiency .

[0115] The present disclosure also contemplates a method of facilitating generation of hydrogen and carbon dioxide from seawater. The method includes 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, and a second cation permeable fluidic separator disposed on a second side of the cathodic compartment, the center compartment defined between the first cation permeable fluidic separator and the second cation permeable fluidic separator. The method further includes providing instructions to flow the seawater through the center compartment, flow an anolyte through the anodic compartment, flow an acidic catholyte through the cathodic compartment, and remove hydrogen and carbon dioxide from the cathodic compartment and the center compartment, respectively.

[0116] The method may further include providing instructions to produce the acidic catholyte from anolyte from the output of the anodic compartment that has been at least partially degassed, and may further include providing instructions to fluidly connect a source of one of deionized water or an aqueous sodium sulfate solution to the inlet of the cathodic compartment. In some embodiments the method may further include providing instructions to regulate relative amounts of the at least partially degassed anolyte from the output of the anodic compartment and the one of the deionized water or the aqueous sodium sulfate solution that are mixed to form the acidic catholyte to maintain a predetermined pH of the acidic catholyte.

[0117] In some embodiments the method may further include providing instructions to produce the acidic catholyte from one of deionized water or an aqueous sodium sulfate solution that has been dosed with an acid, for example, sulfuric acid provided from a source of sulfuric acid.

[0118] In some embodiments the method may further include providing instructions to regulate relative amounts of the one of the deionized water or the aqueous sodium sulfate Attorney Docket No.: 202488109PPCT01 solution and the acid dosed into the one of the deionized water or the aqueous sodium sulfate solution to provide the source of acidic catholyte with a predetermined pH.

[0119] The present disclosure further contemplates a method of retrofitting an apparatus for generation of carbon dioxide and hydrogen from a saline water source, the apparatus comprising an anodic compartment having an inlet and an outlet, a cathodic compartment having an inlet and an outlet, and a center compartment defined between the anodic compartment and cathodic compartment. The method includes connecting a source of acidic catholyte to the inlet of the cathodic compartment. The method may further include connecting a first fluid line from the outlet of the anodic compartment to a degasification subsystem and connecting a second fluid line from the degasification sub-system to the inlet of the cathodic compartment and / or may further include providing a mixing vessel, connecting a first inlet of the mixing vessel to a source of one of deionized water or an aqueous sodium sulfate solution, connecting a second inlet of the mixing vessel to a source of an acid, and connecting an outlet of the mixing vessel to the inlet of the cathodic compartment.

[0120] 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’7refers 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.

[0121] Having thus described several aspects of at least one embodiment, it is to be appreciated 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. Attorney Docket No.: 202488109PPCT01

[0122] 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.

Claims

Attorney Docket No.: 202488109PPCT01CLAIMSWhat is claimed is:

1. An apparatus for generation of carbon dioxide and hydrogen from a saline water source, the apparatus comprising: 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 center compartment defined between the first cation permeable fluidic separator and the second cation permeable fluidic separator; and a source of acidic catholyte that is one of fluidly connectable to or in fluid communication with the inlet of the cathodic compartment.

2. The apparatus of claim 1, wherein the source of acidic catholyte includes anolyte from the outlet of the anodic compartment that has been at least partially degassed.

3. The apparatus of claim 2, further comprising 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.

4. The apparatus of claim 2, further comprising a source of one of deionized water or an aqueous sodium sulfate solution that is also one of fluidly connectable to or in fluid communication with the inlet of the cathodic compartment.

5. The apparatus of claim 4, further comprising a controller configured to regulate relative amounts of the at least partially degassed anolyte from the output of the anodic compartment and the one of the deionized water or the aqueous sodium sulfate solution that are mixed to form the acidic catholyte to maintain a predetermined pH of the acidic catholyte.Attorney Docket No.: 202488109PPCT017. The apparatus of claim 6, further comprising a pH sensor disposed at the outlet of the anodic compartment and in communication with the controller.

8. The apparatus of claim 7, wherein the controller is further configured to regulate a flow rate of anolyte through the anodic compartment at a rate which maintains a pH of the anolyte from the outlet of the anodic compartment at a predetermined value.

9. The apparatus of claim 1, wherein the source of acidic catholyte includes one of deionized water or an aqueous sodium sulfate solution that has been dosed with an acid.

10. The apparatus of claim 9, wherein the acid is sulfuric acid provided from a source of sulfuric acid.

11. The apparatus of claim 9, further comprising a controller configured to regulate relative amounts of the one of the deionized water or the aqueous sodium sulfate solution and the acid dosed into the one of the deionized water or the aqueous sodium sulfate solution to provide the source of acidic catholyte with a predetermined pH.

12. The apparatus of claim 1, further comprising a source of saline water that is one of fluidly connectable to or in fluid communication with the center compartment.

13. The apparatus of claim 1, wherein the source of acidic catholyte includes effluent from the center compartment.

14. The apparatus of claim 13, further comprising a degasification sub-system configured to remove carbon dioxide from the effluent from the center compartment and form a degasified effluent that is utilized as the acidic catholyte.

15. The apparatus of claim 14, further comprising: one or more pH sensors disposed to monitor pH of one or both of the degasified effluent or effluent from the cathodic compartment; and a controller in communication with the one or more pH sensors and configured to control one or more operating parameters of the apparatus to maintain a predetermined pHAttorney Docket No.: 202488109PPCT01 level or levels in the one or both of the degasified effluent or effluent from the cathodic compartment.

16. A method of facilitating generation of hydrogen and carbon dioxide from seawater, the method comprising: 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 center compartment defined between the first cation permeable fluidic separator and the second cation permeable fluidic separator; and providing instructions to: flow the seawater through the center compartment; flow an anolyte through the anodic compartment; flow an acidic catholy te through the cathodic compartment; and remove hydrogen and carbon dioxide from the cathodic compartment and the center compartment, respectively.

17. The method of claim 1 , further comprising providing instructions to produce the acidic catholyte from anolyte from the outlet of the anodic compartment that has been at least partially degassed.

18. The method of claim 17, further comprising providing instructions to fluidly connect a source of one of deionized water or an aqueous sodium sulfate solution to the inlet of the cathodic compartment.

19. The method of claim 18, further comprising providing instructions to regulate relative amounts of the at least partially degassed anolyte from the output of the anodic compartment and the one of the deionized water or the aqueous sodium sulfate solution that are mixed to form the acidic catholyte to maintain a predetermined pH of the acidic catholyte.Attorney Docket No.: 202488109PPCT0120. The method of claim 16, further comprising providing instructions to produce the acidic catholyte from one of deionized water or an aqueous sodium sulfate solution that has been dosed with an acid.

21. The method of claim 20, wherein the acid is sulfuric acid provided from a source of sulfuric acid.

22. The method of claim 20, further comprising providing instructions to regulate relative amounts of the one of the deionized water or the aqueous sodium sulfate solution and the acid dosed into the one of the deionized water or the aqueous sodium sulfate solution to provide the source of acidic catholyte with a predetermined pH.

23. A method of retrofitting an apparatus for generation of carbon dioxide and hydrogen from a saline water source, the apparatus comprising an anodic compartment having an inlet and an outlet, a cathodic compartment having an inlet and an outlet, and a center compartment defined between the anodic compartment and cathodic compartment, the method comprising: connecting a source of acidic catholyte to the inlet of the cathodic compartment.

24. The method of claim 23, further comprising connecting a first fluid line from the outlet of the anodic compartment to a degasification sub-system and connecting a second fluid line from the degasification sub-system to the inlet of the cathodic compartment.

25. The method of claim 23, further comprising: providing a mixing vessel; connecting a first inlet of the mixing vessel to a source of one of deionized water or an aqueous sodium sulfate solution; connecting a second inlet of the mixing vessel to a source of an acid; and connecting an outlet of the mixing vessel to the inlet of the cathodic compartment.

Images