Electrochemical cell

Abstract

This electrochemical cell comprises a first anode or an anode chamber for generating protons, a cathode chamber for generating hydroxide ions or a first cathode, and a plurality of electrolyte units provided between the first anode or the anode chamber and the first cathode or the cathode chamber. Each of the plurality of electrolyte units has: an electrolyte membrane; and a first liquid chamber disposed on the first-anode or anode-chamber side and a second liquid chamber disposed on the first-cathode or cathode-chamber side, with the electrolyte membrane interposed therebetween. The plurality of electrolyte units are disposed with a porous electroconductive layer interposed therebetween. A catalyst layer is provided to both sides of the porous electroconductive layer.

Description

electrochemical cell

[0001] The present invention relates to electrochemical cells.

[0002] Patent Document 1 discloses an electrodialysis device in which bipolar membranes and anion exchange membranes are alternately arranged between an anode and a cathode, and a plurality of acid chambers and alkaline chambers are arranged adjacent to each other with the anion exchange membranes sandwiched between the anode and the cathode.

[0003] Japanese Patent Application Laid-Open No. 2022-97062

[0004] In the electrodialysis device of Patent Document 1, multiple liquid chambers are stacked using bipolar membranes. A bipolar membrane is an ion exchange membrane having a structure in which a cation exchange layer and an anion exchange layer are laminated together. By applying a voltage equal to or greater than the theoretical splitting voltage of water to both sides of the ion exchange membrane, the water in the ion exchange membrane is split into protons and hydroxide ions. When multiple liquid chambers are stacked using bipolar membranes in an electrochemical cell, a large amount of electrical energy is required to dissociate water in the bipolar membrane.

[0005] An object of the present disclosure is to provide an electrochemical cell that can reduce the operating voltage.

[0006] An electrochemical cell according to one aspect of the present disclosure includes a first anode or anode chamber that generates protons, a first cathode or a cathode chamber that generates hydroxide ions, and a plurality of electrolyte units provided between the first anode or anode chamber and the first cathode or cathode chamber, each of the plurality of electrolyte units having an electrolyte membrane, a first liquid chamber disposed on the first anode or anode chamber side with the electrolyte membrane interposed therebetween, and a second liquid chamber disposed on the first cathode or cathode chamber side, and the plurality of electrolyte units are arranged with a porous conductive layer interposed therebetween, and the porous conductive layer has catalyst layers on both sides.

[0007] According to the present disclosure, an electrochemical cell capable of reducing the operating voltage can be provided.

[0008] It is a schematic diagram of a carbon compound production system. It is a cross-sectional view showing a configuration example of a concentration separation part. It is an explanatory diagram explaining the operation of a concentration separation device. It is a diagram showing a configuration example of an electrodialysis device to which an electrochemical cell is applied.

[0009] (1) An electrochemical cell according to one aspect of the present disclosure includes a first anode or anode chamber that generates protons, a first cathode or a cathode chamber that reduces protons and generates hydroxide ions, and a plurality of electrolyte units provided between the first anode or anode chamber and the first cathode or cathode chamber, each of the plurality of electrolyte units having an electrolyte membrane, a first liquid chamber disposed on the first anode or anode chamber side with the electrolyte membrane interposed therebetween, and a second liquid chamber disposed on the first cathode or cathode chamber side, and the plurality of electrolyte units are arranged with a porous conductive layer interposed therebetween, and the porous conductive layer has catalyst layers on both sides.

[0010] An electrochemical cell according to another aspect of the present disclosure includes a first anode or anode chamber that generates protons, a first cathode or a cathode chamber that generates hydroxide ions, and a plurality of electrolyte units disposed between the first anode or anode chamber and the first cathode or cathode chamber, each of the plurality of electrolyte units having an electrolyte membrane, a first liquid chamber disposed on the first anode or anode chamber side with the electrolyte membrane interposed therebetween, and a second liquid chamber disposed on the first cathode or cathode chamber side, the plurality of electrolyte units being disposed with a porous conductive layer interposed therebetween, the porous conductive layer having catalyst layers on both sides. Examples of the first cathode include a first cathode that reduces protons and a first cathode that reduces water.

[0011] In this specification, "stacking without using a bipolar membrane" means stacking at least two liquid chambers without using a bipolar membrane, and does not exclude the electrochemical cell from having a bipolar membrane.

[0012] According to the electrochemical cell described in (1) above, by stacking the electrolyte units using porous conductive layers each having a catalyst layer on both sides, the voltage required for hydrogen ions to pass between the electrolyte units can be reduced, which allows the voltage applied to the electrochemical cell to be lowered, thereby reducing energy consumption.

[0013] According to the above configuration, since a plurality of electrolyte units can be stacked without using a bipolar membrane, the voltage required for hydrogen ion permeation between the electrolyte units can be reduced compared to when a bipolar membrane is used. This is because when a bipolar membrane is used, at least water molecules are converted into protons (H + ) and hydroxyl groups (OH - ), but by using a porous conductive layer having the above-mentioned catalyst layer on both sides, the application of such a voltage becomes unnecessary. Specifically, the voltage required for the porous conductive layer having the above-mentioned catalyst layer on both sides is the sum of the voltages required for the reaction in which protons become hydrogen molecules and the reaction in which hydrogen molecules become protons, and this total voltage is significantly smaller than the voltage required to dissociate water. Note that in the bipolar membrane, water molecules are converted into protons (H + ) and hydroxyl groups (OH - The theoretical voltage for dissociating protons into hydrogen molecules and hydrogen molecules into protons in the porous conductive layer having the catalyst layers on both sides thereof is approximately 0.83 V, and the theoretical voltage for the reaction in which protons become hydrogen molecules and the reaction in which hydrogen molecules become protons in the porous conductive layer having the catalyst layers on both sides thereof is 0 V. In other words, by stacking multiple liquid chambers using porous conductive layers having catalyst layers on both sides thereof, the voltage applied to the electrochemical cell can be further reduced compared to when a similar stacking is performed using a bipolar membrane, and energy consumption can be reduced.

[0014] (2) In the electrochemical cell described in (1) above, the first anode may produce protons from hydrogen, and the first cathode may produce hydrogen from protons.

[0015] The electrochemical cell described in (2) above can be made to function as an electrochemical hydrogen pump. For example, the voltage applied to the electrochemical cell can be lowered compared to methods that utilize water electrolysis or water dissociation using a bipolar membrane, thereby further reducing energy consumption.

[0016] (3) In the electrochemical cell described in (1) or (2) above, a first electrolytic solution having carbon dioxide absorbed therein may be supplied to the first liquid chamber, and a second electrolytic solution may be supplied to the second liquid chamber.

[0017] According to the electrochemical cell described in (3) above, carbon dioxide can be generated, and therefore the electrochemical cell can be used as a carbon dioxide production device.

[0018] (4) In the electrochemical cell described in any one of (1) to (3) above, the anode chamber may include a second anode, an electrolyte, and a first bipolar membrane, and the cathode chamber may include a second cathode, an electrolyte, and a second bipolar membrane.

[0019] According to the electrochemical cell described in (4) above, protons and hydroxide ions are generated by dissociation of water in the bipolar membranes in the anode and cathode chambers, and a predetermined acid or alkali can be generated in the first and second liquid chambers. Therefore, the electrochemical cell can be used as an electrodialysis device.

[0020] (5) In the electrochemical cell described in (4) above, an electrolyte solution containing an inorganic salt, an organic acid salt, or an amino acid salt may be supplied to either the first liquid chamber or the second liquid chamber.

[0021] According to the electrochemical cell described in (5) above, it is possible to use the electrochemical cell to produce an acid or alkali from an inorganic salt, an organic acid or alkali from an organic acid salt, or an amino acid or alkali from an amino acid salt.

[0022] (6) In the electrochemical cell described in any one of (1) to (5) above, at least one of the porous conductive layer and the catalyst layers provided on both sides of the porous conductive layer may be subjected to a water-repellent treatment.

[0023] According to the electrochemical cell described in (6) above, at least one of the porous conductive layer and the catalyst layers provided on both sides thereof is provided with water repellency, thereby suppressing leakage of liquid from the first liquid chamber and the second liquid chamber into the layer. Furthermore, in the electrochemical cell of the present disclosure, while water penetrates into the porous conductive layer along with the movement of protons, according to the above configuration, the layer is provided with water repellency, which makes it easier for water to condense within the layer, thereby maintaining a space in which hydrogen gas can diffuse for a long period of time.

[0024] (7) In the electrochemical cell according to any one of (1) to (6) above, the catalyst layer may include catalyst particles supported on the surface of the porous conductive layer.

[0025] According to the electrochemical cell described in (7) above, the surface area of ​​the catalyst layer can be increased, and the reactivity of the catalyst can be enhanced.

[0026] (8) In the electrochemical cell described in (7) above, the porous conductive layer may have a liquid outlet.

[0027] According to the electrochemical cell described in (8) above, water present in the layer can be discharged. Protons passing through the layer move while carrying water with them as they flow through the interior of the layer. Discharging the water present in the layer through the outlet can improve the diffusibility of hydrogen.

[0028] (9) The electrochemical cell according to (8) above may further include a flow path through which the liquid discharged from the outlet flows, and a valve for opening and closing the flow path.

[0029] According to the electrochemical cell described in (9) above, the liquid flow path can be switched between open and closed, so that the liquid can be appropriately discharged and unnecessary leakage of other components within the layer can be suppressed.

[0030] The present disclosure will be specifically described with reference to the drawings showing embodiments thereof.

[0031] FIG. 1 is a schematic diagram of a carbon compound production system S. In this embodiment, as an example, an electrochemical cell is applied to the carbon compound production system S. The carbon compound production system S of this embodiment is a system that uses a carbon dioxide-containing gas containing a low concentration of carbon dioxide as a raw material gas, concentrates and recovers carbon dioxide from the raw material gas, and produces a carbon compound that becomes a valuable resource from the recovered carbon dioxide. The carbon compound production system S of this embodiment includes a concentration and separation device 1, an electrolytic reduction device 2, and a control device 3. The concentration and separation device 1 includes an absorption tower 10, a concentration and separation section 20, a recovery section 30, a gas-liquid separation section 40, and a hydrogen storage section 50. The concentration and separation device 1 is an example of a carbon dioxide production device.

[0032] The absorption tower 10 brings the carbon dioxide-containing gas into gas-liquid contact with the first electrolytic solution, causing the carbon dioxide to be absorbed into the first electrolytic solution. In this specification, "absorption" means that the carbon dioxide undergoes a chemical reaction to form predetermined ions and dissolves. The absorption tower 10 is an example of a gas-liquid contact section.

[0033] The carbon dioxide-containing gas is a gas containing a low concentration of carbon dioxide, such as the atmosphere or exhaust gas. The concentration of carbon dioxide in the carbon dioxide-containing gas is, for example, 0.01 vol % to 30 vol %. The carbon dioxide-containing gas may contain gases other than carbon dioxide, such as nitrogen, water vapor, carbon monoxide, hydrogen sulfide, carbonyl sulfide, sulfur dioxide, nitrogen dioxide, methane, and hydrogen.

[0034] The concentration / separation unit 20 desorbs and releases carbon dioxide from the liquid that has absorbed it, thereby producing concentrated carbon dioxide gas. The concentrated carbon dioxide gas contains a higher concentration of carbon dioxide than the carbon dioxide-containing gas. The carbon dioxide concentration in the concentrated carbon dioxide gas is typically 90 vol % to 100 vol %. The concentrated carbon dioxide gas produced in the concentration / separation unit 20 is supplied to the electrolytic reduction device 2.

[0035] The concentration / separation unit 20 constitutes an electrochemical cell including a first anode 22 and a first cathode 24. The concentration / separation unit 20 desorbs carbon dioxide from a liquid that has absorbed carbon dioxide using electrodialysis with hydrogen pumping. A hydrogen-containing gas containing hydrogen is supplied to the concentration / separation unit 20. Hydrogen gas at a higher pressure than the hydrogen-containing gas is generated by the hydrogen pressure boosting operation of the electrochemical hydrogen pump.

[0036] The hydrogen concentration of the hydrogen-containing gas is less than 99 vol% in the hydrogen-containing gas. The hydrogen concentration in the hydrogen-containing gas is preferably 50 vol% or less, more preferably 30 vol% or less, and even more preferably 10 vol% or less. The lower limit of the hydrogen concentration in the hydrogen-containing gas is not particularly limited, but may be, for example, 0.01 vol% or more. The hydrogen-containing gas may be a gas containing hydrogen as an impurity. When the hydrogen concentration in the gas is 100 vol%, it means a gas consisting only of hydrogen, i.e., pure hydrogen.

[0037] The hydrogen-containing gas may be a gas adjusted to have an overall hydrogen concentration of less than 99 vol% by mixing a gas having a hydrogen concentration of less than 99 vol% with a gas having a hydrogen concentration of 99 vol% or more.

[0038] In the concentration / separation unit 20, hydrogen contained in the hydrogen-containing gas is supplied to the first anode 22 of the electrochemical hydrogen pump, where it undergoes an oxidation reaction to generate protons. Components other than hydrogen contained in the hydrogen-containing gas remain unreacted. By supplying a mixed gas containing hydrogen and components other than hydrogen to the concentration / separation unit 20, it is possible to separate (remove) hydrogen from the mixed gas and discharge a gas containing components other than hydrogen. The gas containing components other than hydrogen is recovered in the recovery unit 30.

[0039] The concentration / separation apparatus 1 of this embodiment functions as a carbon dioxide production apparatus that produces high-concentration carbon dioxide, and also functions as a hydrogen separation apparatus that separates hydrogen from a hydrogen-containing gas.

[0040] The electrolytic reduction device 2 generates a gas containing carbon compounds by electrolytically reducing carbon dioxide in the concentrated carbon dioxide gas obtained in the concentration / separation section 20. The electrolytic reduction device 2 is an example of a reduction device. The electrolytic reduction device 2 generates a mixed gas containing carbon compounds such as hydrocarbons (e.g., methane, ethylene, etc.) and carbon monoxide, and hydrogen. The concentration of hydrogen in the mixed gas is, for example, less than 99 vol% in the mixed gas, preferably 50 vol% or less, more preferably 30 vol% or less, and even more preferably 10 vol% or less.

[0041] The mixed gas of carbon compounds and hydrogen produced in the electrolytic reduction device 2 is supplied to the concentration / separation unit 20. The concentration / separation unit 20 separates hydrogen from the mixed gas and discharges a gas containing carbon compounds. The gas containing carbon compounds can be used as a valuable resource.

[0042] The carbon compound production system S can realize carbon recycling, which converts carbon dioxide contained in the atmosphere or exhaust gases into various carbon compounds as a carbon resource and reuses them. The carbon compound production system S will be described in detail below.

[0043] The absorption tower 10 includes a main body 11 extending vertically, a gas inlet 12 provided at the bottom of the side wall of the main body 11, a liquid inlet 13 and a gas outlet 14 provided at the top of the main body 11, and a liquid outlet 15 provided at the bottom of the main body 11. The gas inlet 12 is connected to a carbon dioxide-containing gas supply source (not shown) via a first passage 601.

[0044] The carbon dioxide-containing gas is supplied into the tower from the gas inlet 12 via the first passage 601, flows through the tower, and is then discharged from the gas outlet 14.

[0045] The first electrolytic solution for absorbing carbon dioxide is supplied from a liquid inlet 13 and absorbs carbon dioxide by coming into contact with a carbon dioxide-containing gas in the tower. The first electrolytic solution that has absorbed carbon dioxide is supplied from a liquid outlet 15 to the concentration / separation section 20 via a second passage 602.

[0046] The method for contacting the carbon dioxide-containing gas with the first electrolytic solution is not particularly limited. Examples include a method of bubbling the carbon dioxide-containing gas into the first electrolytic solution, a method of dropping the first electrolytic solution in the form of mist into the carbon dioxide-containing gas by a spraying method, and a method of bringing high-pressure carbon dioxide-containing gas into countercurrent contact with the absorbing solution in an absorption tower 10 filled with a porcelain or metal mesh filler. This produces a first electrolytic solution that has absorbed carbon dioxide.

[0047] The first electrolytic solution of this embodiment is a mixed solution containing an absorbing solution that contributes to the absorption of carbon dioxide and an electrolyte solution that contributes to the oxidation-reduction reaction of hydrogen, which will be described later. The absorbing solution and the electrolyte solution contain the same cations (e.g., K + In this specification, the term "mixed liquid" means a liquid containing a component corresponding to the absorption liquid and a component corresponding to the electrolyte solution, and does not necessarily mean that the absorption liquid and the electrolyte solution are actually mixed separately.

[0048] The absorbing liquid contained in the first electrolytic solution is an alkaline aqueous solution. Examples of the alkaline aqueous solution include aqueous solutions of alkali metal compounds, alkaline earth metal compounds, and amine compounds, and an aqueous solution of an alkali metal compound is preferred.

[0049] Examples of alkali metal compounds and alkaline earth metal compounds include compounds of alkali metals such as sodium, lithium, and potassium, and alkaline earth metals such as calcium, magnesium, and barium. The alkali metal compounds and alkaline earth metal compounds are preferably hydroxides, oxides, and nitrates of alkali metals or alkaline earth metals, more preferably hydroxides. Specific examples of alkaline aqueous solutions include aqueous solutions of potassium hydroxide, sodium hydroxide, calcium hydroxide, and the like, with potassium hydroxide being preferred.

[0050] Examples of the amine compound include basic amines such as monoethanolamine, diethanolamine, diisopropanolamine, methyldiethanolamine, triethanolamine, etc. The aqueous alkaline solution may be used alone or in combination of two or more.

[0051] Examples of the electrolyte solution contained in the first electrolytic solution include an aqueous potassium chloride solution and an aqueous sodium chloride solution, and preferably an aqueous potassium chloride solution. The electrolyte solutions may be used alone or in combination of two or more.

[0052] FIG. 2 is a cross-sectional view showing an example of the configuration of the enrichment / separation unit 20. As shown in FIGS. 1 and 2 , the enrichment / separation unit 20 has a substantially rectangular cross section and a substantially rectangular parallelepiped shape overall. The enrichment / separation unit 20 further includes an anode plate 21 having an anode gas chamber (first gas chamber) 211, a first anode 22, a plurality of electrolyte units 23, a first cathode 24, a cathode plate 25 having a cathode gas chamber (second gas chamber) 251, and a power supply 26. The anode plate 21, the first anode 22, the plurality of electrolyte units 23, the first cathode 24, and the cathode plate 25 are arranged in this order and are fastened together by, for example, fastening members (not shown). Gaskets (not shown) may be disposed between the anode plate 21 and the first anode 22 and between the first cathode 24 and the cathode plate 25, respectively. For ease of explanation, two electrolyte units 23 are shown in FIG. 1, but the concentration / separation section 20 may include a large number of electrolyte units 23, for example, 50 or 100 units.

[0053] Each electrolyte unit 23 includes an anode fluid chamber (first fluid chamber) 231, an electrolyte membrane 232, and a cathode fluid chamber (second fluid chamber) 233. In each electrolyte unit 23, the anode fluid chamber 231 is disposed on the first anode 22 side, with the electrolyte membrane 232 interposed therebetween, and the cathode fluid chamber 233 is disposed on the first cathode 24 side. A plurality of electrolyte units 23 are stacked with intermediate layers 28 interposed therebetween to form a stack.

[0054] The anode plate 21 has an anode gas chamber 211 formed in a portion facing the first anode 22, through which a hydrogen-containing gas flows. The anode gas chamber 211 regulates the flow of the hydrogen-containing gas supplied to the first anode 22.

[0055] The anode gas chamber 211 includes an anode gas flow channel 212, a first supply port 213 connected to one end (inlet) of the anode gas flow channel 212, and a first exhaust port 214 connected to the other end (outlet) of the anode gas flow channel 212. As an example, the anode gas flow channel 212 is a groove-shaped flow channel formed on the surface of the anode plate 21. The anode gas flow channel 212 is a single flow channel that is arranged so as to turn back within a region of the surface of the anode plate 21 that faces the first anode 22. Alternatively, the anode gas flow channel 212 may include multiple flow channels or may include a branched channel. The hydrogen-containing gas supplied from the first supply port 213 flows through the anode gas flow channel 212 and is then discharged from the first exhaust port 214. In the area of ​​the surface of the anode plate 21 facing the first anode 22, the portion other than the portion where the anode gas flow path 212 is formed is in contact with the surface of the first anode 22, thereby allowing electrons to move between the anode plate 21 and the first anode 22.

[0056] The anode plate 21 may also be composed of multiple components each having a different function. The anode plate 21 may also be composed, for example, by stacking an end plate, a current collector plate, and a plate member having an anode gas flow channel 212 on one surface thereof in this order. The end plate fastens and integrates the components constituting the concentration / separation unit 20 in cooperation with the fastening members (not shown) and the cathode-side end plate. Electrons are transferred between the current collector plate and the first anode 22 via the plate member having the anode gas flow channel 212, and the plate member is connected to the power source 26 via wiring. The plate member having the anode gas flow channel 212 defines an anode gas chamber 211 via the flow channel and regulates the flow of hydrogen-containing gas supplied to the first anode 22.

[0057] 2, a first supply port 213 is provided at the bottom of the anode plate 21, and a first exhaust port 214 is provided at the top of the anode plate 21. When the anode plate 21 has a substantially rectangular parallelepiped shape extending vertically, the first supply port 213 and the first exhaust port 214 may be provided near the vertices of the diagonal corners or near the center of the short sides.

[0058] The first discharge port 214 is connected to the recovery unit 30 via a third passage 603. The first supply port 213 is connected to the electrolytic reduction device 2 via a fourth passage 604, the junction 70, and a fifth passage 605. The first supply port 213 is also connected to the hydrogen storage unit 50 via the fourth passage 604, the junction 70, and a sixth passage 606.

[0059] The cathode plate 25 has a cathode gas chamber 251 formed in a portion facing the first cathode 24, through which the hydrogen gas generated at the first cathode 24 flows. Hereinafter, the hydrogen gas generated at the first cathode 24 will also be referred to as high-pressure hydrogen gas.

[0060] The cathode gas chamber 251 includes a cathode gas flow channel 252 and a second outlet 253 connected to one end (outlet) of the cathode gas flow channel 252. As an example, the cathode gas flow channel 252 is a groove-shaped flow channel formed in the surface of the cathode plate 25. The cathode gas flow channel 252 is a single flow channel that is arranged so as to turn back in a region of the surface of the cathode plate 25 facing the first cathode 24. Alternatively, the cathode gas flow channel 252 may include multiple flow channels or may include a branched channel. High-pressure hydrogen gas supplied to the cathode gas flow channel 252 flows toward the second outlet 253. In the region of the surface of the cathode plate 25 facing the first cathode 24, the portion other than the portion where the cathode gas flow channel 252 is formed is in contact with the surface of the first cathode 24, thereby enabling the transfer of electrons between the cathode plate 25 and the first cathode 24. Like the anode plate 21, the cathode plate 25 can also be made up of a plurality of components each having a different function.

[0061] 2, a second exhaust port 253 is provided on the upper part of the cathode plate 25. The second exhaust port 253 is connected to the hydrogen storage unit 50 via an eleventh passage 611. The hydrogen storage unit 50 stores the high-pressure hydrogen gas discharged from the cathode gas chamber 251.

[0062] In the concentration / separation unit 20, the gas flow rate per unit time in the anode gas flow channel 212 is preferably greater than the gas flow rate per unit time in the cathode gas flow channel 252. For example, the flow channel cross-sectional area of ​​the anode gas flow channel 212 may be greater than the flow channel cross-sectional area of ​​the cathode gas flow channel 252, thereby making the gas flow rate per unit time in the anode gas flow channel 212 greater than the gas flow rate per unit time in the cathode gas flow channel 252. The flow rate of the hydrogen-containing gas supplied to the anode gas chamber 211 may be adjusted by the compressor 93b. With the above configuration, even when a hydrogen-containing gas containing a low concentration of hydrogen is used, a sufficient amount of gas can be supplied to the first anode 22, thereby preventing insufficient hydrogen oxidation reaction.

[0063] The gas flow rate per unit time in the anode gas flow channel 212 refers to the flow rate near the inlet of the anode gas flow channel 212. The gas flow rate per unit time in the anode gas flow channel 212 is the same as the flow rate per unit time of the hydrogen-containing gas supplied to the first supply port 213. The gas flow rate per unit time in the cathode gas flow channel 252 refers to the flow rate near the outlet of the cathode gas flow channel 252. The gas flow rate per unit time in the cathode gas flow channel 252 is the same as the flow rate per unit time of the high-pressure hydrogen gas discharged from the second discharge port 253.

[0064] The cross-sectional areas of the anode gas flow channel 212 and the cathode gas flow channel 252 refer to the cross-sectional areas of the respective channels cut along a plane perpendicular to the direction of fluid flow. When the cross-sectional areas are substantially uniform from the inlet to the outlet of the channel, the cross-sectional areas at any distance from the inlet are used as the cross-sectional areas. When the cross-sectional areas change with increasing distance from the inlet, the cross-sectional areas may be the average values ​​of the cross-sectional areas near the inlet and the outlet, or the average values ​​of the cross-sectional areas near the inlet, the outlet, and one or more positions within the channel. The one or more positions within the channel may be half the distance from the inlet to the outlet. In the case of the anode gas flow channel 212, the inlet and outlet refer to the inlet and outlet of the anode gas flow channel 212, and in the case of the cathode gas flow channel 252, the inlet and outlet refer to the inlet and outlet of the cathode gas flow channel 252.

[0065] The anode plate 21 is electrically connected to the first anode 22. The cathode plate 25 is electrically connected to the first cathode 24. The anode plate 21 and the cathode plate 25 are connected to a power source 26 via wiring. The concentration / separation unit 20 includes a current sensor 91 that detects the current flowing between the first anode 22 and the first cathode 24.

[0066] The power supply 26 applies a voltage to the first anode 22 and the first cathode 24 via the anode plate 21 and the cathode plate 25. The high-potential terminal of the power supply 26 is connected to the anode plate 21, and the low-potential terminal is connected to the cathode plate 25.

[0067] The first anode 22 is supplied with a hydrogen-containing gas and generates protons from hydrogen in the hydrogen-containing gas. The first anode 22 is a gas diffusion electrode and includes an anode catalyst layer 221 containing an anode catalyst and an anode gas diffusion layer 222. The anode catalyst layer 221 is provided on one surface of the anode gas diffusion layer 222. The anode liquid chamber 231 contacts the surface of the first anode 22 facing the anode catalyst layer 221, and the anode plate 21 (anode gas chamber 211) contacts the surface facing the anode gas diffusion layer 222. The anode catalyst layer 221 may be formed by supporting highly dispersed anode catalyst particles on the anode gas diffusion layer 222. Such an anode catalyst layer 221 can be manufactured, for example, by applying a mixture containing anode catalyst particles, a cation exchange resin, and a solvent to a predetermined substrate, drying the solvent, and transferring the dried mixture from the substrate to the surface of the anode gas diffusion layer 222. Alternatively, by using the anode gas diffusion layer 222 as the predetermined substrate, the anode catalyst layer 221 can be formed directly on the surface of the anode gas diffusion layer 222 and within a predetermined thickness from the surface.

[0068] Examples of anode catalysts include platinum, ruthenium, rhodium, palladium, and iridium. Anode catalysts may be used singly or in combination of two or more. When two or more types are combined, a combination containing at least platinum and ruthenium may be used. Anode catalysts using such a combination have improved durability against catalyst poisoning by carbon monoxide compared to, for example, a catalyst using platinum alone. The thickness of the anode catalyst layer 221 is, for example, 5 μm to 50 μm. When the thickness of the anode catalyst layer 221 is within the above range, protons can be generated effectively.

[0069] The anode gas diffusion layer 222 is made of a porous material and has electrical conductivity and gas diffusibility. The anode gas diffusion layer 222 uniformly diffuses the hydrogen-containing gas supplied from the fourth passage 604 through the anode gas flow channel 212 to the anode catalyst layer 221. Examples of the anode gas diffusion layer 222 include porous carbon fiber sheets such as carbon paper, carbon cloth, and carbon felt, and sintered bodies made from carbon particles, with carbon paper being preferred. The anode gas diffusion layer 222 may also be a sintered body of metal fibers made from titanium alloy, stainless steel, or the like, a sintered body of powdered metal, a metal mesh, or a foamed metal body. The thickness of the anode gas diffusion layer 222 is, for example, 100 μm to 1000 μm. A thickness of the anode gas diffusion layer 222 within the above range can improve gas diffusibility in the direction from the first anode 22 to the first cathode 24.

[0070] The first cathode 24 generates hydrogen from protons supplied from the first anode 22 side. The first cathode 24 is a gas diffusion electrode and includes a cathode catalyst layer 241 containing a cathode catalyst, and a cathode gas diffusion layer 242. The cathode catalyst layer 241 is provided on one surface of the cathode gas diffusion layer 242. The cathode liquid chamber 233 is in contact with the surface of the first cathode 24 facing the cathode catalyst layer 241, and the cathode plate 25 (cathode gas chamber 251) is in contact with the surface facing the cathode gas diffusion layer 242. The cathode catalyst layer 241 may be formed by supporting fine particles of the cathode catalyst in a highly dispersed manner on the cathode gas diffusion layer 242. The cathode catalyst layer 241 can be manufactured by a method similar to that for the anode catalyst layer 221, for example, by applying a mixture containing fine particles of the cathode catalyst, a cation exchange resin, and a solvent onto a predetermined substrate, and then drying the solvent.

[0071] The cathode catalyst may be the same as the anode catalyst described above, preferably platinum. The cathode catalyst may be used alone or in combination of two or more. The thickness of the cathode catalyst layer 241 is, for example, 5 μm to 50 μm. When the thickness of the cathode catalyst layer 241 is within the above range, hydrogen can be generated effectively.

[0072] The cathode gas diffusion layer 242 is made of a porous material and has electrical conductivity and gas diffusibility. Examples of materials for the cathode gas diffusion layer 242 include the same materials as those for the anode gas diffusion layer 222. The thickness of the cathode gas diffusion layer 242 is, for example, 100 μm to 1000 μm. When the thickness of the cathode gas diffusion layer 242 is within the above range, the diffusibility of hydrogen in the direction from the first anode 22 to the first cathode 24 can be improved.

[0073] The first anode 22 and the first cathode 24 are preferably treated to be water-repellent. The water-repellent treatment is performed, for example, by adding or laminating a water-repellent material such as polytetrafluoroethylene to the anode gas diffusion layer 222 and the cathode gas diffusion layer 242. The water-repellent properties can also be imparted to the first anode 22 and the first cathode 24 by performing a similar water-repellent treatment on the anode catalyst layer 221 and the cathode catalyst layer 241. By imparting water-repellent properties, leakage of liquid from the anode fluid chamber 231 to the first anode 22 and leakage of liquid from the cathode fluid chamber 233 to the first cathode 24 can be suppressed. In addition to the method of treating the first anode 22 and the first cathode 24 to be water-repellent, a polymer membrane having ion exchange groups may be provided between the first anode 22 and the anode fluid chamber 231 and between the first cathode 24 and the cathode fluid chamber 233. An example of a material for the polymer membrane having ion exchange groups is Nafion (registered trademark). By providing such a membrane, it is possible to prevent the liquid in the liquid chamber from migrating toward the electrode while maintaining the movement of charge.

[0074] The electrolyte unit 23 includes an electrolyte membrane 232, an anode fluid chamber 231 disposed on the first anode 22 side via the electrolyte membrane 232, and a cathode fluid chamber 233 disposed on the first cathode 24 side. Each electrolyte unit 23 has the same configuration. The electrolyte membrane 232 is a cation exchange membrane (CEM) and is made of an electrolyte material having cation conductivity. Examples of the electrolyte membrane 232 include fluorine-based cation exchange membranes such as perfluorosulfonic acid-based membranes. The thickness of the electrolyte membrane 232 is, for example, 2 μm to 500 μm.

[0075] The anode fluid chamber 231 is made of, for example, resin and has the shape of a vertically extending flat plate. The anode fluid chamber 231 includes a third supply port 234 provided in a lower portion, a third outlet 235 provided in an upper portion, and an anode fluid flow path 236 formed between the third supply port 234 and the third outlet 235. One end (inlet) of the anode fluid flow path 236 is connected to the third supply port 234, and the other end (outlet) of the anode fluid flow path 236 is connected to the third outlet 235. In the anode fluid flow path 236, the liquid flows from the inlet to the outlet.

[0076] The shape of the anode fluid chamber 231 and the positions of the third supply port 234 and the third discharge port 235 in the anode fluid chamber 231 are not limited to the above example. For example, the third supply port 234 may be provided on the upper part or side of the anode fluid chamber 231, and the third discharge port 235 may be provided on the lower part or side of the anode fluid chamber 231.

[0077] Concentrated carbon dioxide gas is released from the first electrolytic solution in the anolyte flow path 236. A gas-liquid mixture of the released concentrated carbon dioxide gas and the second electrolytic solution, which is the electrolytic solution after releasing the carbon dioxide, flows through the anolyte flow path 236 and is then discharged from the third outlet 235.

[0078] The anode fluid flow path 236 is a space defined between the anode catalyst layer 221 and the electrolyte membrane 232, and is separated from the outside by a frame made of resin or the like that defines the anode fluid chamber 231. The anode catalyst layer 221 is disposed so that the entire surface of one side of the anode catalyst layer 221 comes into contact with the electrolyte when the space is filled with the electrolyte. The anode fluid flow path 236 may be formed by using a mesh-shaped flow path forming member as a spacer, and by a space created by the flow path forming member crossing three-dimensionally. The spacer prevents the anode fluid flow path 236 from being blocked due to deformation of the anode catalyst layer 221 and the electrolyte membrane 232, for example.

[0079] The third supply port 234 of each anode fluid chamber 231 is connected to the absorber 10 via a second passage 602. The second passage 602 branches at a branch point 602a to connect to each anode fluid chamber 231. The third discharge port 235 of each anode fluid chamber 231 is connected to the gas-liquid separation unit 40 via a seventh passage 607. A plurality of seventh passages 607 are provided corresponding to each anode fluid chamber 231. The seventh passages 607 may be joined downstream.

[0080] The cathode fluid chamber 233 is made of, for example, resin and has a flat plate shape that extends vertically. The cathode fluid chamber 233 includes a fourth supply port 237 provided at an upper portion, a fourth discharge port 238 provided at a lower portion, and a cathode fluid flow path 239 formed between the fourth supply port 237 and the fourth discharge port 238. One end (inlet) of the cathode fluid flow path 239 is connected to the fourth supply port 237, and the other end (outlet) of the cathode fluid flow path 239 is connected to the fourth discharge port 238. In the cathode fluid flow path 239, liquid flows from the inlet to the outlet.

[0081] The cathode fluid flow path 239 is a space defined between the electrolyte membrane 232 and the cathode catalyst layer 241, and is separated from the outside by a frame made of resin or the like that defines the cathode fluid chamber 233. The cathode fluid flow path 239 is disposed so that one entire surface of the cathode catalyst layer 241 comes into contact with the electrolyte when the space is filled with the electrolyte. The cathode fluid flow path 239 may be provided with a spacer, similar to the anode fluid flow path 236.

[0082] In the cathode fluid chamber 233 , the second electrolytic solution is supplied through a fourth supply port 237 , and the first electrolytic solution from which the absorbed solution component has been regenerated is discharged from a fourth discharge port 238 .

[0083] The fourth supply port 237 of each cathode fluid chamber 233 is connected to the gas-liquid separation unit 40 via an eighth passage 608. A plurality of eighth passages 608 are provided corresponding to each cathode fluid chamber 233. The eighth passages 608 may be joined upstream. The fourth discharge port 238 of each cathode fluid chamber 233 is connected to the absorption tower 10 via a ninth passage 609. The ninth passage 609 branches out corresponding to each cathode fluid chamber 233 and joins at a joining point 609 a.

[0084] Each cathode fluid chamber 233 is provided with a liquid sensor 92. The liquid sensor 92 is, for example, a pH meter, and measures the pH of the liquid in the cathode fluid chamber 233. The liquid sensor 92 may be provided in the eighth passage 608 or the ninth passage 609.

[0085] In the concentration / separation section 20, adjacent electrolyte units 23 and the other electrolyte unit 23 are stacked in the same direction with an intermediate layer 28 interposed therebetween. One surface of the intermediate layer 28 contacts the cathode fluid chamber 233 of one electrolyte unit 23, and the other surface of the intermediate layer 28 contacts the anode fluid chamber 231 of the other electrolyte unit 23. The intermediate layer 28 supplies protons supplied from the cathode fluid chamber 233 of one electrolyte unit 23 to the anode fluid chamber 231 of the other adjacent electrolyte unit 23.

[0086] The intermediate layer 28 includes a catalyst layer 281 containing a catalyst and a gas diffusion layer 282. The catalyst layer 281 is formed on both surfaces of the gas diffusion layer 282. The catalyst layer 281 may be configured by supporting fine catalyst particles in a highly dispersed state on the surface of the gas diffusion layer 282.

[0087] Examples of catalysts include those similar to the anode catalyst described above, preferably platinum. The catalysts may be used alone or in combination of two or more. The catalyst is preferably used in the form of fine particles. Fine particles of a metal that functions as a catalyst, such as platinum, may be used. Alternatively, fine particles of the metal may be supported on the surface of an electronically conductive carrier, such as carbon black. Such catalyst layer 281 can be manufactured, for example, by applying a mixture containing fine catalyst particles, a cation exchange resin, and a solvent to a predetermined substrate, drying the solvent, and transferring the dried mixture from the substrate to the surface of the gas diffusion layer 282. Alternatively, by using the gas diffusion layer 282 as the predetermined substrate, the catalyst layer 281 can be formed directly on the surface of the gas diffusion layer 282 and within a predetermined thickness from the surface.

[0088] The thickness of the catalyst layer 281 is, for example, 5 μm to 50 μm. When the thickness of the catalyst layer 281 is 5 μm or more, the catalytic reactivity can be increased. When the thickness is 50 μm or less, the migration distance of protons can be shortened, and the operating voltage of the electrochemical cell can be further reduced.

[0089] The gas diffusion layer 282 is made of a porous material and has electrical conductivity and gas diffusibility. The gas diffusion layer 282 uniformly diffuses hydrogen molecules supplied from the catalyst layer 281 in contact with the cathode fluid chamber 233 to the catalyst layer 281 in contact with the anode fluid chamber 231. Materials constituting the gas diffusion layer 282 include the same materials as those used for the anode gas diffusion layer 222, and carbon paper is preferred. The thickness of the gas diffusion layer 282 is, for example, 100 μm to 1000 μm. When the thickness of the gas diffusion layer 282 is within the above range, the diffusibility of hydrogen in the direction from the first anode 22 to the first cathode 24 can be improved.

[0090] The intermediate layer 28 is preferably treated to be water-repellent. The water-repellent treatment is performed, for example, by adding or laminating a water-repellent material such as polytetrafluoroethylene to at least one of the pair of catalyst layer 281 and gas diffusion layer 282. By imparting water-repellent properties, leakage of liquid from the anode fluid chamber 231 and the cathode fluid chamber 233 into the intermediate layer 28 can be suppressed.

[0091] In addition to imparting water repellency to the intermediate layer 28, a method for suppressing such liquid leakage may be achieved by providing a polymer membrane having ion exchange groups between the cathode fluid chamber 233 and the catalyst layer 281 in contact with the cathode fluid chamber 233, or between the anode fluid chamber 231 and the catalyst layer 281 in contact with the anode fluid chamber 231. An example of a material for the polymer membrane having ion exchange groups is Nafion (registered trademark). By providing such a membrane, it is possible to suppress the liquid in the fluid chamber from migrating into the intermediate layer while maintaining charge transfer. In particular, when a polymer membrane having ion exchange groups is provided between the cathode fluid chamber 233 and the catalyst layer 281 in contact with the cathode fluid chamber 233, it is preferable to adhere the catalyst layer 281 and the polymer membrane having ion exchange groups to each other, or to bring them into contact with each other and then apply pressure to them so that they are in close contact with each other. By adopting such a configuration, it is possible to prevent the hydrogen gas generated in the catalyst layer 281 from migrating to the cathode liquid chamber 233 side, and it is possible to increase the proportion of hydrogen gas that moves to the gas diffusion layer 282 side.

[0092] Methods for bonding the catalyst layer 281 and the polymer membrane having ion exchange groups include a method in which a mixture containing a polymer having ion exchange groups and a solvent is applied to the surface of the catalyst layer 281 to a predetermined thickness and then dried to form a polymer membrane in an adhered state, and a method in which a polymer membrane having ion exchange groups is pressed against the surface of the catalyst layer 281 and heat-treated at a predetermined temperature, so-called hot pressing, for pressure bonding. Note that in the latter method, the heat treatment temperature is preferably equal to or higher than the glass transition temperature of the polymer membrane having ion exchange groups.

[0093] The intermediate layer 28 preferably further includes a sixth outlet 283 for discharging the liquid and a valve 284 for opening and closing the sixth outlet 283. The sixth outlet 283 may be provided in the lower part of the gas diffusion layer 282. The valve 284 may be provided at the outlet of the sixth outlet or in the middle of the flow path through which the liquid discharged from the sixth outlet flows. The sixth outlet 283 discharges water generated inside the gas diffusion layer 282 of the intermediate layer 28 as protons pass through to the outside. When protons pass through the catalyst layer 281 of the intermediate layer 28, they carry water (so-called hydration water) with them and remain inside the gas diffusion layer 282 as liquid water. Discharging this remaining water through the sixth outlet 283 improves the diffusibility of hydrogen inside the gas diffusion layer 282. Switching between opening and closing the valve 284 allows appropriate water discharge and suppresses hydrogen leakage.

[0094] The plurality of electrolyte units 23 is not limited to a configuration in which all of the electrolyte units 23 are stacked with the intermediate layer 28 interposed therebetween, but may be a configuration in which at least two electrolyte units 23 are stacked with the intermediate layer 28 interposed therebetween. The plurality of electrolyte units 23 may be stacked by using a combination of the intermediate layer 28 and a layer having a different configuration. The layer having a different configuration may be any layer that can supply protons from the cathode fluid chamber 233 to the anode fluid chamber 231, and may be, for example, a bipolar membrane formed by laminating a cation exchange membrane and an anion exchange membrane.

[0095] The gas-liquid separation unit 40 separates the concentrated carbon dioxide gas from the second electrolytic solution. The gas-liquid separation unit 40 performs gas-liquid separation by, for example, water displacement, gravity separation, or the like. The gas-liquid separation unit 40 receives the gas-liquid mixture discharged from each anode fluid chamber 231 via a seventh passage 607. The gas-liquid separation unit 40 supplies the second electrolytic solution, from which the concentrated carbon dioxide gas has been separated, to each cathode fluid chamber 233 via an eighth passage 608.

[0096] The gas-liquid separation unit 40 is connected to the electrolytic reduction device 2 via a tenth passage 610. The gas-liquid separation unit 40 supplies the separated concentrated carbon dioxide gas to the electrolytic reduction device 2 via the tenth passage 610.

[0097] The electrolytic reduction device 2 generates carbon compounds by electrolyzing carbon dioxide together with water. The configuration of the electrolytic reduction device 2 is not particularly limited, but may include, for example, an anode, a cathode, and an ion exchange membrane disposed between the anode and the cathode. The gas obtained by the electrolytic reduction device 2 is a mixed gas containing carbon compounds as reduced products and hydrogen as a by-product. The electrolytic reduction device 2 is connected to the confluence 70 via a fifth passage 605.

[0098] The confluence unit 70 combines the mixed gas sent from the electrolytic reduction device 2 as the first hydrogen source and the hydrogen gas sent from the hydrogen storage unit 50 as the second hydrogen source, as necessary, and supplies the combined gas to the concentration / separation unit 20. The confluence unit 70 may further be connected to a third hydrogen source. The third hydrogen source is, for example, a hydrogen tank pre-filled with pure hydrogen having a hydrogen concentration of 100 vol %. Hydrogen from the third hydrogen source may be supplied to the hydrogen storage unit 50.

[0099] 1 shows an example in which the confluence part 70 is provided outside the concentration and separation part 20. Alternatively, the confluence part 70 may be provided inside the concentration and separation part 20. When the confluence part 70 is provided inside the concentration and separation part 20, it may be configured as follows. The concentration and separation part 20 includes a first first supply port 213 connected to the fifth passage 605 and a second first supply port 213 connected to the sixth passage 606. The first first supply port 213 and the second first supply port 213 are both connected to the inlet of the anode gas flow path 212 via the confluence part 70 inside the concentration and separation part 20.

[0100] As described above, the carbon compound production system S includes the first passage 601 to the eleventh passage 611. The first passage 601 flows the carbon dioxide-containing gas from the carbon dioxide-containing gas supply source to the absorption tower 10. The first passage 601 includes a compressor 93a. The second passage 602 flows the first electrolytic solution from the absorption tower 10 to the anode fluid chamber 231. The second passage 602 includes a pump 94a, a control valve 95a, and a flow meter 96a. The third passage 603 flows the exhaust gas from which hydrogen has been separated from the anode gas chamber 211 to the recovery unit 30. The fourth passage 604 flows the hydrogen-containing gas containing the mixed gas and / or high-pressure hydrogen gas from the junction 70 to the anode gas chamber 211. The fourth passage 604 includes a compressor 93b. The fifth passage 605 flows the mixed gas from the electrolytic reduction device 2 to the junction 70. The fifth passage 605 includes a control valve 95b and a flow meter 96b. The sixth passage 606 allows high-pressure hydrogen gas to flow from the hydrogen storage section 50 to the junction section 70. The sixth passage 606 includes a control valve 95c and a flow meter 96c.

[0101] The seventh passage 607 allows the gas-liquid mixture to flow from the anode fluid chamber 231 to the gas-liquid separation unit 40. The seventh passage 607 is equipped with a flow meter 96d. The eighth passage 608 allows the second electrolytic solution to flow from the gas-liquid separation unit 40 to the cathode fluid chamber 233. The eighth passage 608 is equipped with a control valve 95e and a flow meter 96e. The ninth passage 609 allows the first electrolytic solution to flow from the cathode fluid chamber 233 to the absorption tower 10. The ninth passage 609 is equipped with a pump 94f, a control valve 95f, and a flow meter 96f. The tenth passage 610 allows the concentrated carbon dioxide gas to flow from the gas-liquid separation unit 40 to the electrolytic reduction device 2. The eleventh passage 611 allows the high-pressure hydrogen gas to flow from the cathode gas chamber 251 to the hydrogen storage unit 50.

[0102] The compressors 93a and 93b compress and deliver gas. The pumps 94a and 94f deliver fluid. The control valves 95a, 95b, 95c, 95e, and 95f control the volumetric flow rate or mass flow rate of the fluid flowing through the passages. The flow meters 96a, 96b, 96c, 96d, 96e, and 96f measure the volumetric flow rate or mass flow rate of the fluid flowing through the passages. The fourth passage 604 and the fifth passage 605 may be equipped with gas sensors that detect the concentration of gas. Hereinafter, the compressors 93a and 93b will also be collectively referred to as compressors 93. The pumps 94a and 94f will also be collectively referred to as pumps 94. The control valves 95a, 95b, 95c, 95e, and 95f will also be collectively referred to as control valves 95. The flow meters 96 a , 96 b , 96 c , 96 d , 96 e , and 96 f are also collectively referred to as flow meters 96 .

[0103] An electrolytic solution circulation system is configured by the absorption tower 10, the second passage 602, the concentration / separation section 20, the seventh passage 607, the gas-liquid separation section 40, the eighth passage 608, and the ninth passage 609. The electrolytic solution containing the absorbing liquid and the electrolyte solution is recycled by absorbing carbon dioxide in the absorption tower 10, releasing the carbon dioxide in the concentration / separation section 20, and then absorbing carbon dioxide again in the absorption tower 10.

[0104] The carbon compound production system S includes a first bypass passage 612 that allows the second electrolytic solution discharged from the anode fluid chamber 231 to bypass the cathode fluid chamber 233. The first bypass passage 612 allows the first electrolytic solution to flow from the gas-liquid separation unit 40 to the second passage 602, bypassing the cathode fluid chamber 233. One end of the first bypass passage 612 is connected to the second passage 602 upstream of the branch point 602a. Alternatively, the first bypass passage 612 may connect the second passage 602 and the eighth passage 608. The carbon compound production system S may further include a second bypass passage (not shown) that allows the first electrolytic solution discharged from the cathode fluid chamber 233 to bypass the absorption tower 10 and the anode fluid chamber 231. One end of the second bypass passage is connected to the ninth passage 609, and the other end is connected to the eighth passage 608.

[0105] The control device 3 is a computer and includes a processor such as a central processing unit (CPU) (not shown), a memory, an input / output interface, etc. The memory stores various computer programs and data referenced by the processor. The input / output interface is connected to the current sensor 91, the liquid sensor 92, the compressor 93, the pump 94, the control valve 95, and the flow meter 96. The control device 3 acquires measurement values ​​from the current sensor 91, the liquid sensor 92, and the flow meter 96. The control device 3 outputs control signals to the compressor 93, the pump 94, and the control valve 95 to control their operation. Details of the control performed by the control device 3 will be described later.

[0106] Fig. 3 is an explanatory diagram illustrating the operation of the concentration and separation device 1. The operation of the concentration and separation device 1 and the carbon compound production system S will be described using Fig. 3. For the sake of simplicity, Fig. 3 shows an example in which two electrolyte units 23 are stacked.

[0107] A carbon dioxide-containing gas containing a low concentration of carbon dioxide is supplied to the absorption tower 10, and a first electrolytic solution is also supplied. The carbon dioxide-containing gas is pressurized by a compressor 93a as needed and then supplied. The first electrolytic solution is supplied at a predetermined flow rate by driving a pump 94f. In this embodiment, the first electrolytic solution is a mixed solution (KOH-KCL solution) of an aqueous potassium hydroxide solution as an absorption solution and an aqueous potassium chloride solution as an electrolyte solution.

[0108] The absorption reaction of the carbon dioxide-containing gas in the absorption tower 10 is expressed by the following reaction formula (1): KOH + CO → KHCO (1)

[0109] The absorption reaction produces a first electrolytic solution (KHCO3-KCL solution) that has absorbed carbon dioxide. In the first electrolytic solution, the carbon dioxide becomes bicarbonate ions. The first electrolytic solution (KHCO3-KCL solution) that has absorbed carbon dioxide is supplied to the concentration / separation unit 20 at a predetermined flow rate via the second passage 602 by driving the pump 94a.

[0110] More specifically, the carbon dioxide absorption reactions represented by the following reaction formulas (1-1) and (1-2) proceed, thereby obtaining a first electrolytic solution (KHCO3-KCL solution) that has absorbed carbon dioxide: 2KOH + CO2 → K2CO3 + H2O (1-1) K2CO3 + H2O + CO2 → 2KHCO3 (1-2)

[0111] The first electrolytic solution may be an electrolytic solution in which potassium hydroxide (KOH) has completely reacted to potassium bicarbonate (KHCO3), or an electrolytic solution containing a portion of potassium carbonate (K2CO3), which is the product of the above reaction formula (1-1). The first electrolytic solution may be an electrolytic solution in which most of the carbon dioxide has reacted to potassium carbonate (K2CO3), which is obtained by stopping the carbon dioxide absorption reaction at the above reaction formula (1-1). In the first electrolytic solution, carbon dioxide is converted to bicarbonate ions (HCO3 - ) can be formed.

[0112] In the concentration / separation unit 20, a first electrolytic solution (KHCO3-KCL solution) that has absorbed carbon dioxide is supplied from the third supply port 234 of the anode fluid chamber 231, and a hydrogen-containing gas is supplied from the first supply port 213 of the anode gas chamber 211. A voltage is applied from a power source 26 to the first anode 22 and the first cathode 24. The hydrogen-containing gas may contain only the mixed gas from the electrolytic reduction device 2, or may contain a combined gas obtained by combining the mixed gas and high-pressure hydrogen gas from the hydrogen storage unit 50. The hydrogen-containing gas contains hydrogen and a carbon compound. The hydrogen-containing gas is pressurized by a compressor 93b as necessary and then supplied.

[0113] While the hydrogen-containing gas passes through the anode gas flow channel 212, the hydrogen-containing gas is supplied from the anode gas diffusion layer 222 to the anode catalyst layer 221. As represented by the following reaction formula (2), hydrogen molecules are converted into protons (H + ) and electrons. H2 → 2H + +2e - ... (2)

[0114] Of the components contained in the hydrogen-containing gas, hydrogen is consumed in the anode catalyst layer 221, while carbon compounds (components other than hydrogen) remain unreacted. The gas containing carbon compounds, i.e., the exhaust gas after hydrogen separation, is discharged from the first outlet 214. The recovery unit 30 recovers the discharged exhaust gas.

[0115] Protons (H + ) moves to the anolyte chamber 231 adjacent to the first anode 22. The protons (H + ), the pH of the KHCO3 solution in the anolyte chamber 231 decreases compared to before the oxidation reaction. The chemical equilibrium of the following reaction formula (3) shifts to the right, and carbon dioxide is produced. - +H + ⇔CO2+H2O...(3)

[0116] As carbon dioxide is released from the first electrolytic solution, the liquid in the anolyte flow path 236 becomes a second electrolytic solution (KCL solution) composed mainly of potassium chloride. The second electrolytic solution may contain a small amount of KHCO. The gas-liquid mixture of the generated concentrated carbon dioxide gas containing carbon dioxide and the second electrolytic solution (KCL solution) is supplied to the gas-liquid separation unit 40 via the third outlet 235 and the seventh passage 607.

[0117] The concentrated carbon dioxide gas and the second electrolytic solution (KCL solution) are separated from each other in the gas-liquid separation unit 40. The concentrated carbon dioxide gas is supplied to the electrolytic reduction device 2 via a tenth passage 610. The second electrolytic solution (KCL solution) is supplied to the cathode fluid chamber 233 via an eighth passage 608 and a fourth supply port 237.

[0118] In the electrolyte membrane 232, potassium ions (K + ) passes through the inside of the electrolyte membrane 232 and moves into the cathode fluid chamber 233.

[0119] Potassium ions (K + ) in the second electrolyte (KCL solution) in the cathode fluid chamber 233. + ) increases. Potassium ions (K +) increases, the proton (H + ) is supplied to the intermediate layer 28. + ) is consumed, the pH of the second electrolytic solution (KCL solution) increases. This causes the absorption solution (KOH) to be regenerated. By regenerating the absorption solution, the liquid in the cathode solution flow path 239 becomes a first electrolytic solution (KOH-KCL solution) containing the absorption solution and the electrolyte solution. The first electrolytic solution (KOH-KCL solution) is circulated and supplied to the absorption tower 10 via the fourth outlet 238 and the ninth passage 609.

[0120] Protons (H + ) are adsorbed by the catalyst layer 281 on the first anode 22 side and then supplied as hydrogen molecules to the gas diffusion layer 282. The hydrogen molecules pass through the inside of the gas diffusion layer 282 and are converted into protons (H + ) is converted to a proton (H + ) is supplied to the anolyte chamber 231 of the adjacent electrolyte unit 23.

[0121] Similar reactions occur in each electrolyte unit 23, resulting in the formation of protons (H + ) moves from the first anode 22 side to the first cathode 24 side and is supplied to the first cathode 24.

[0122] Protons (H + ) is adsorbed onto the cathode catalyst layer 241. As shown in the following reaction formula (4), hydrogen molecules are regenerated in the cathode catalyst layer 241 by a reduction reaction. + +2e - →H2...(4)

[0123] The hydrogen gas generated at the first cathode 24 may be hydrogen gas generated by a reduction reaction of water, as represented by the following reaction formula (5): 2H2O+2e - →H2 + 2OH - ...(5)

[0124] The hydrogen gas generated at the first cathode 24 can be at a higher pressure than the hydrogen-containing gas supplied to the first anode 22. The hydrogen gas generated at the first cathode 24 is a gas containing hydrogen and water, and hydrogen gas with a hydrogen concentration of 99 vol% or more can be obtained by removing the water. The hydrogen gas generated at the first cathode 24 is discharged from the second outlet 253 and stored in the hydrogen storage unit 50 in a water-removed state. Alternatively, the hydrogen gas generated at the first cathode 24 may be stored in the hydrogen storage unit 50 while still containing water.

[0125] In the electrolytic reduction device 2, the concentrated carbon dioxide gas is electrolyzed together with water to generate a mixed gas containing carbon compounds derived from the concentrated carbon dioxide gas and hydrogen.

[0126] The mixed gas is supplied to the concentration separation section 20 via the fifth passage 605, the junction section 70, and the fourth passage 604. In the concentration separation section 20, carbon compounds and hydrogen are separated, and an exhaust gas containing carbon compounds is discharged.

[0127] In the carbon compound production system S, the entire amount of the mixed gas produced in the electrolytic reduction device 2 is usually supplied to the concentration and separation device 1 as a hydrogen-containing gas. The flow rate of the mixed gas may be adjusted as appropriate by a control valve 95b. When the flow rate of the mixed gas discharged from the electrolytic reduction device 2 or the amount of mixed gas produced in the electrolytic reduction device 2 is less than a predetermined value, the amount of hydrogen in the hydrogen-containing gas is increased by adding high-pressure hydrogen gas to the hydrogen-containing gas. The ratio of the mixed gas and high-pressure hydrogen gas contained in the hydrogen-containing gas can be set based on the hydrogen concentrations of the mixed gas and high-pressure hydrogen gas and the flow rate of the mixed gas. At the start of operation, a hydrogen-containing gas containing only high-pressure hydrogen gas may be supplied to the concentration and separation device 1.

[0128] In the carbon compound production system S, the flow paths of the first electrolytic solution and the second electrolytic solution can be switched based on the pH value of the liquid flowing through the cathode fluid chamber 233. The pH value of the liquid may be, for example, the pH of the second electrolytic solution supplied to the cathode fluid chamber 233, or the pH of the first electrolytic solution discharged from the cathode fluid chamber 233. If the pH value is less than a predetermined value, it is considered that the reaction in the anode fluid chamber 231, which shifts the chemical equilibrium of the reaction formula (3) to the right, has not progressed sufficiently.

[0129] If the pH value is equal to or higher than a predetermined value, the second electrolytic solution discharged from the third outlet 235 of the anode fluid chamber 231 is supplied to the cathode fluid chamber 233 via the seventh passage 607, the gas-liquid separation unit 40, and the eighth passage 608. If the pH value is equal to or higher than a predetermined value, the first electrolytic solution discharged from the fourth outlet 238 of the cathode fluid chamber 233 is supplied to the absorption tower 10 via the ninth passage 609, so that the first electrolytic solution absorbs carbon dioxide again.

[0130] If the pH value is less than the predetermined value, the second electrolytic solution discharged from the third outlet 235 of the anode fluid chamber 231 is supplied again to the anode fluid chamber 231 as the first electrolytic solution via the first bypass passage 612 and the second passage 602. If the pH value is less than the predetermined value, the first electrolytic solution discharged from the fourth outlet 238 of the cathode fluid chamber 233 may be supplied again to the cathode fluid chamber 233 as the second electrolytic solution via the second bypass passage and the eighth passage 608 (not shown) in order to raise the pH value to at least the predetermined value.

[0131] The following describes the control processing executed by the control device 3. The control device 3 manages the operating status of the carbon compound production system S based on the measured values ​​of the current sensor 91, the liquid sensor 92, and the flow meter 96. The control device 3 estimates the amount of hydrogen consumed in the concentration / separation unit 20, the amount of carbon dioxide produced in the concentration / separation unit 20, the amount of mixed gas produced in the electrolytic reduction device 2, and the like, based on, for example, the current value of the DC power supply energizing the concentration / separation unit 20 detected by the current sensor 91 and the amount of electricity obtained by integrating the current value.

[0132] Based on the estimation result, the control device 3 may automatically control the operation of the compressor 93, the pump 94, and the control valve 95. Examples of the automatic control will be described below.

[0133] The control device 3 adjusts the content and supply amount of the hydrogen-containing gas supplied to the concentration / separation unit 20 based on the flow rate of the mixed gas discharged from the electrolytic reduction device 2 or the amount of mixed gas produced in the electrolytic reduction device 2. The content and supply amount of the hydrogen-containing gas may be adjusted by controlling the aperture of the control valves 95b and 95c. The content of the hydrogen-containing gas may be the mixing ratio of the mixed gas and hydrogen gas. When the flow rate of the mixed gas discharged from the electrolytic reduction device 2 is less than a predetermined flow rate value, the control device 3 adds high-pressure hydrogen gas from the hydrogen storage unit 50 to make up for the shortfall in the flow rate of the mixed gas.

[0134] The control device 3 switches the flow path for the first electrolytic solution discharged from the cathode fluid chamber 233 and the flow path for the second electrolytic solution discharged from the anode fluid chamber 231 based on the pH value of the liquid flowing through the cathode fluid chamber 233. If the pH value is equal to or greater than a predetermined value, the control device 3 controls the second electrolytic solution discharged from the anode fluid chamber 231 to be supplied to the cathode fluid chamber 233 without flowing through the first bypass passage 612. The control device 3 also controls the first electrolytic solution discharged from the cathode fluid chamber 233 to be supplied to the absorption tower 10. If the pH value is less than the predetermined value, the control device 3 controls the second electrolytic solution discharged from the anode fluid chamber 231 to be flowed through the first bypass passage 612 and supplied to the anode fluid chamber 231. The control device 3 also controls the first electrolytic solution discharged from the cathode fluid chamber 233 to be flowed through a second bypass passage (not shown) and supplied to the cathode fluid chamber 233.

[0135] In the above embodiment, the mixed gas is used as the hydrogen source. Alternatively, hydrogen gas may be supplied to the enrichment / separation unit 20 from a hydrogen source other than the mixed gas.

[0136] According to the above configuration, concentrated carbon dioxide gas can be produced by electrodialysis using hydrogen pumping with hydrogen-containing gas containing low concentrations of hydrogen in the concentration / separation unit 20. For example, the voltage applied to the concentration / separation unit 20 can be lower than in methods using water electrolysis, thereby reducing energy consumption. Because gas containing low concentrations of hydrogen is used as the hydrogen source, there is greater freedom in selecting the hydrogen source and greater freedom in system design.

[0137] Furthermore, with the above configuration, since the intermediate layer 83 is provided, the voltage required for the permeation of protons between the plurality of electrolyte units can be reduced compared to when a bipolar membrane is used. This is because, while a bipolar membrane requires the application of a voltage at least sufficient to dissociate water, the use of the intermediate layer 83 eliminates the need to apply such a voltage. Specifically, the voltage required in the intermediate layer 83 is the sum of the voltages required for the reaction in which protons become hydrogen molecules and the reaction in which hydrogen molecules become protons, and this total voltage is significantly smaller than the voltage required to dissociate water.

[0138] The hydrogen gas obtained by the concentration / separation unit 20 or a mixed gas derived from concentrated carbon dioxide gas can be used as the hydrogen source, allowing for efficient gas cycling within the system. Since the concentration / separation unit 20 produces carbon dioxide and separates hydrogen from the reduced product, there is no need to provide a separate hydrogen separation process, improving operating efficiency and further reducing energy consumption. There is no need to provide a separate carbon dioxide production device and separation device, simplifying the system configuration.

[0139] By circulating the mixed solution of the absorption liquid and the electrolyte liquid, the amount of energy required for absorbing and releasing carbon dioxide can be reduced, and operating efficiency can be improved. By stacking the electrolyte units 23 using intermediate layers 28 each having a gas diffusion layer 282 with a catalyst layer 281 supported on both sides, the voltage required for hydrogen ion permeation between the electrolyte units 23 can be reduced compared to when a bipolar membrane is used, for example.

[0140] The electrochemical cell can be used for purposes other than concentration and separation devices. For example, the electrochemical cell may be used in an electrodialysis device. Fig. 4 is a diagram showing an example of the configuration of an electrodialysis device 8 to which the electrochemical cell is applied.

[0141] The electrodialysis device 8 includes an anode chamber 81 that produces protons and a cathode chamber 82 that produces hydroxide ions, and includes a plurality of electrolyte units 84 stacked between the anode chamber 81 and the cathode chamber 82 with intermediate layers 83 interposed therebetween.

[0142] The anode chamber 81 includes a second anode 811 and a first bipolar membrane 812. The cathode chamber 82 includes a second cathode 821 and a second bipolar membrane 822. The anode chamber 81 and the cathode chamber 82 include an electrolyte solution such as a sodium hydroxide solution or a sodium sulfide solution. The first bipolar membrane 812 and the second bipolar membrane 822 are provided to generate protons and hydroxide ions by dissociation of water.

[0143] The intermediate layer 83 includes a gas diffusion layer 832 with catalyst layers 831 on both sides. The electrolyte unit 84 includes an electrolyte membrane 841, which is a cation exchange membrane, an acid chamber 842, and an alkaline chamber 843. The acid chamber 842 is disposed on the anode chamber 81 side, with the electrolyte membrane 841 interposed therebetween, and the alkaline chamber 843 is disposed on the cathode chamber 82 side. The acid chamber 842 may further include a deionization chamber disposed on the cathode chamber 82 side, with an anion exchange membrane interposed therebetween. An aqueous solution containing, for example, an inorganic salt, an organic acid salt, or an amino acid salt is supplied as an electrolyte to the acid chamber 842 or the deionization chamber. Water is supplied to the alkaline chamber 843.

[0144] When a voltage is applied to the electrodialysis device 8 from a power supply (not shown), an acid solution containing a predetermined acid is produced in the acid chamber 842, and an alkaline solution containing a predetermined alkali is produced in the alkaline chamber 843. When a voltage is applied to the electrodialysis device 8, protons are produced on the cation exchange layer side of the first bipolar membrane 812 in the anode chamber 81, and these protons migrate to the adjacent acid chamber 842. This proton migration lowers the pH of the acid chamber 842, and an organic acid is produced. In the electrolyte membrane 841, electrodialysis causes cations in the acid chamber 842 to migrate through the electrolyte membrane 841 to the alkaline chamber 843. This migration increases the number of cations in the alkaline chamber 843, and as this increase occurs, protons are supplied to the intermediate layer 83. An alkaline aqueous solution is produced in the alkaline chamber 843 in response to the consumption of protons.

[0145] The protons supplied to the intermediate layer 83 are reduced and converted to hydrogen molecules by the catalyst layer 831 on the anode chamber 81 side (catalyst layer 831 in contact with the alkaline chamber 843) using the mechanism described above. These hydrogen gases then diffuse through the gas diffusion layer 832 and are converted to protons by the catalyst layer 831 on the cathode chamber 82 side (catalyst layer 831 in contact with the acid chamber 842). These hydrogen gases are then supplied to the acid chamber 842 of the adjacent electrolyte unit 84. If a deionization compartment (not shown) is provided, an aqueous solution of an organic acid salt is supplied to this deionization compartment, and water is supplied to the acid chamber 842 and the alkaline chamber 843. In this case, when a voltage is applied to the electrodialysis device 8, cations of the aqueous solution of an organic acid salt in the deionization compartment pass through the electrolyte membrane 841 to the alkaline chamber 843, and anions pass through an anion exchange membrane (not shown) to the acid chamber 842. As a result, an acid solution is concentrated in the acid chamber 842, and an alkaline solution is concentrated in the alkaline chamber 843.

[0146] In the electrodialysis device 8, an anion exchange membrane can also be used as the electrolyte membrane 841 of the electrolyte unit 84. When an anion exchange membrane is used as the electrolyte membrane 841, an aqueous solution containing, for example, an inorganic salt, an organic acid salt, or an amino acid salt is supplied as an electrolyte to the alkaline chamber 843. Water is supplied to the acid chamber 842. In this case, when a voltage is applied to the electrodialysis device 8, protons are generated on the cation exchange layer side of the first bipolar membrane 812 in the anode chamber 81 and these protons migrate to the adjacent acid chamber 842. Hydroxide ions are generated on the anion exchange layer side of the second bipolar membrane 822 in the cathode chamber 82 and these hydroxide ions migrate to the adjacent alkaline chamber 843. In the intermediate layer 83, protons supplied from the adjacent alkaline chamber 843 are converted into hydrogen molecules in the catalyst layer 831 in contact with the alkaline chamber 843 by the same mechanism as described above, and then converted back into protons in the catalyst layer 831 in contact with the acid chamber 842, and supplied to the acid chamber 842 of the adjacent electrolyte unit 84. Then, by electrodialysis, anions in the alkaline chamber 843 pass through the inside of the electrolyte membrane 841 and move to the acid chamber 842. Due to these movements, an acidic aqueous solution is produced in the acid chamber, and an alkaline aqueous solution is produced in the alkaline chamber 843.

[0147] Furthermore, when the electrochemical cell of the present disclosure is applied to a carbon dioxide production apparatus that produces high-concentration carbon dioxide, the example of the concentration / separation unit 20 includes the first anode 22 and the first cathode 24, but an anode chamber that produces protons and a cathode chamber that produces hydroxide ions may be provided instead of the first anode 22 and the first cathode 24. Even in this embodiment, carbon dioxide can be desorbed from a liquid that has absorbed carbon dioxide.

[0148] Furthermore, when the electrochemical cell of the present disclosure is applied to an electrodialysis device, as explained using the electrodialysis device 8, it is configured to include the anode chamber 81 and the cathode chamber 82. However, instead of the anode chamber 81 and the cathode chamber 82, a first anode that generates protons and a first cathode that reduces the protons may be provided, respectively. Even in this embodiment, a liquid of the desired components can be produced in the acid chamber, alkaline chamber, or deionization chamber by electrodialysis.

[0149] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the scope of the claims and equivalents thereto. The sequences shown in each embodiment are not limited, and within the scope of no contradiction, each processing step may be executed in a different order, or multiple processes may be executed in parallel. The entity that performs each process is not limited, and within the scope of no contradiction, the process of each device may be executed by another device.

[0150] The matters described in each embodiment can be combined with each other. Furthermore, the independent claims and dependent claims described in the claims can be combined with each other in any and all combinations, regardless of the reference format. Furthermore, the claims use a format in which a claim references two or more other claims (multiple claim format), but this is not limited to this. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used.

[0151] REFERENCE SIGNS LIST Carbon compound production system 1 Concentration / separation device 2 Electrolytic reduction device 3 Control device 10 Absorption tower 20 Concentration section 21 Anode plate 211 Anode gas chamber 212 Anode gas flow path 213 First supply port 214 First outlet 22 First anode 221 Anode catalyst layer 222 Anode gas diffusion layer 23 Electrolyte unit 231 Anode liquid chamber 232 Electrolyte membrane 233 Cathode liquid chamber 24 First cathode 241 Cathode catalyst layer 242 Cathode gas diffusion layer 25 Cathode plate 251 Cathode gas chamber 252 Cathode gas flow path 253 Second outlet 26 Power source 28 Intermediate layer 281 Catalyst layer 282 Gas diffusion layer 283 Sixth outlet 284 Valve 30 Recovery section 40 Gas-liquid separation device 50 Hydrogen storage section 70 Confluence section

Claims

1. An electrochemical cell comprising: a first anode or anode chamber that generates protons; a first cathode or a cathode chamber that generates hydroxide ions; and a plurality of electrolyte units provided between the first anode or anode chamber and the first cathode or cathode chamber, each of the plurality of electrolyte units having an electrolyte membrane, a first liquid chamber disposed on the first anode or anode chamber side with the electrolyte membrane interposed therebetween, and a second liquid chamber disposed on the first cathode or cathode chamber side, the plurality of electrolyte units being arranged with a porous conductive layer interposed therebetween, and the porous conductive layer having catalyst layers on both sides.

2. The electrochemical cell of claim 1, wherein the first anode produces protons from hydrogen, and the first cathode produces hydrogen from protons.

3. An electrochemical cell according to claim 1 or claim 2, wherein a first electrolytic solution having carbon dioxide absorbed therein is supplied to the first liquid chamber, and a second electrolytic solution is supplied to the second liquid chamber.

4. An electrochemical cell according to claim 1 or 2, wherein the anode chamber comprises a second anode, an electrolyte and a first bipolar membrane, and the cathode chamber comprises a second cathode, an electrolyte and a second bipolar membrane.

5. The electrochemical cell according to claim 4, wherein an electrolyte containing an inorganic salt, an organic acid salt or an amino acid salt is supplied to either the first liquid chamber or the second liquid chamber.

6. An electrochemical cell according to claim 1 or 2, wherein at least one of the porous conductive layer and the catalyst layers provided on both sides of the porous conductive layer is treated to be water repellent.

7. The electrochemical cell according to claim 1 or claim 2, wherein the catalyst layer comprises catalyst particles supported on the surface of the porous conductive layer.

8. An electrochemical cell according to claim 1 or claim 2, wherein the porous conductive layer is provided with a liquid outlet.

9. The electrochemical cell according to claim 8, further comprising a flow path through which the liquid discharged from the outlet flows, and a valve for opening and closing the flow path.

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