Carbon dioxide concentration apparatus

Abstract

This carbon dioxide concentration apparatus comprises: an absorption unit that causes an electrolytic solution to absorb carbon dioxide; an electrochemical cell that generates carbon dioxide gas from the electrolytic solution; and a storage unit that stores the electrolytic solution. The electrochemical cell comprises an anode, an anolyte chamber, an electrolyte membrane, a catholyte chamber, and a cathode. The storage unit includes at least one of a first storage unit for storing the electrolytic solution that circulates to / from the absorption unit, a second storage unit for storing the electrolytic solution that circulates to / from the anolyte chamber, and a third storage unit for storing the electrolytic solution that circulates to / from the catholyte chamber.

Description

Carbon dioxide concentration device

[0001] This invention relates to a carbon dioxide concentration device.

[0002] One of the causes of global warming is the increase in emissions of greenhouse gases such as carbon dioxide. To reduce carbon dioxide emissions, technologies are being developed to separate and concentrate carbon dioxide from exhaust gases and the atmosphere.

[0003] Patent Document 1 discloses a carbon dioxide recovery system that includes a carbon dioxide release device and a carbon dioxide dissolving unit configured to dissolve carbon dioxide in exhaust gas in a first alkaline solution. The carbon dioxide release device is configured to fill the space between the anode electrode and a cation exchange membrane with the first alkaline solution in which carbon dioxide is dissolved, and to fill the space between the cation exchange membrane and the cathode electrode with a second alkaline solution, thereby supplying hydrogen to the anode electrode.

[0004] Japanese Patent Publication No. 2024-31641

[0005] In a device comprising an absorption unit that absorbs carbon dioxide into an electrolyte and an electrochemical cell that generates carbon dioxide, if the electrolyte is continuously flowed between the absorption unit and the electrochemical cell, there is a possibility that the electrolyte may flow out of the absorption unit and the electrochemical cell without having reacted sufficiently.

[0006] The purpose of this disclosure is to provide a technology that enables sufficient reaction of the electrolyte in the absorption section of a carbon dioxide concentrator, the anode liquid chamber, or the cathode liquid chamber of an electrochemical cell.

[0007] A carbon dioxide concentration apparatus according to one aspect of the present disclosure comprises an absorption unit for absorbing carbon dioxide into an electrolyte, an electrochemical cell for generating carbon dioxide gas from the electrolyte, and a storage unit for storing the electrolyte, wherein the electrochemical cell comprises an anode, an anode liquid chamber, an electrolyte membrane, a cathode liquid chamber, and a cathode, and the storage unit includes at least one of a first storage unit for storing the electrolyte circulating with the absorption unit, a second storage unit for storing the electrolyte circulating with the anode liquid chamber, and a third storage unit for storing the electrolyte circulating with the cathode liquid chamber.

[0008] According to this disclosure, the electrolyte can be sufficiently reacted in the absorption section of a carbon dioxide concentrator, the anode liquid chamber, or the cathode liquid chamber of an electrochemical cell.

[0009] This is a schematic diagram of the carbon dioxide concentrator 100 of this embodiment. This is a cross-sectional view showing an example of the configuration of the concentration unit 20. This is an explanatory diagram illustrating the operation of the carbon dioxide concentrator 100. This is a diagram illustrating the first state of the circulation system. This is a diagram illustrating the second state of the circulation system. This is a diagram illustrating the third state of the circulation system.

[0010] (1) A carbon dioxide concentrator according to one aspect of the present disclosure comprises an absorption unit for absorbing carbon dioxide into an electrolyte, an electrochemical cell for generating carbon dioxide gas from the electrolyte, and a storage unit for storing the electrolyte, wherein the electrochemical cell comprises an anode, an anode liquid chamber, an electrolyte membrane, a cathode liquid chamber, and a cathode, and the storage unit includes at least one of a first storage unit for storing the electrolyte circulating with the absorption unit, a second storage unit for storing the electrolyte circulating with the anode liquid chamber, and a third storage unit for storing the electrolyte circulating with the cathode liquid chamber.

[0011] In the carbon dioxide concentrator described in (1) above, the electrochemical cell may be an electrochemical hydrogen pump comprising an anode that generates protons from hydrogen and a cathode that generates hydrogen from protons. The anode liquid chamber may be a liquid chamber provided between the anode and the electrolyte membrane to which the electrolyte that has absorbed carbon dioxide is supplied. The cathode liquid chamber may be a liquid chamber provided between the electrolyte membrane and the cathode to which the electrolyte from which carbon dioxide has been removed is supplied.

[0012] In a carbon dioxide concentrator, the operating efficiency of the device can be improved by circulating the electrolyte between the absorption unit, which absorbs carbon dioxide into the electrolyte, and the anode and cathode chambers of an electrochemical cell that generates carbon dioxide from the electrolyte. When the electrolyte is continuously circulated between the absorption unit, anode chamber, and cathode chamber, the reaction of the electrolyte may be insufficient in one of the three chambers, and incompletely reacted electrolyte may flow out. Incompletely reacted electrolyte contains unreacted electrolyte. The flow of incompletely reacted electrolyte to the next circulation point leads to a reduction in the carbon dioxide concentration efficiency. In particular, the flow of incompletely reacted electrolyte from the anode chamber into the cathode chamber significantly reduces the carbon dioxide concentration efficiency.

[0013] One way to reduce unreacted electrolyte is to increase the utilization rate of the electrolyte, for example, by reducing the electrolyte flow rate. However, in response to a decrease in the electrolyte flow rate, the amount of carbon dioxide gas generated relative to the electrolyte flow rate increases, and the amount of carbon dioxide gas accumulating in the flow path increases. An increase in the amount of carbon dioxide gas accumulating in the flow path is undesirable because it leads to an increase in the voltage required for electrolysis in the electrochemical cell and an increase in energy consumption.

[0014] According to the carbon dioxide concentration apparatus described in (1) above, the electrolyte can be sufficiently circulated between the absorption section and the first storage section, between the anode liquid chamber and the second storage section, or between the cathode liquid chamber and the third storage section, thereby enabling the reaction of the electrolyte to proceed sufficiently.

[0015] (2) The carbon dioxide concentration apparatus described in (1) above may be equipped with a circulation system that can switch between a first state in which the electrolyte of the first storage unit is circulated between the first storage unit and the absorption unit, a second state in which the electrolyte of the first storage unit is circulated between the anode liquid chamber and at least one of a third state in which the electrolyte of the first storage unit is circulated between the cathode liquid chamber and at least one of these states.

[0016] According to the carbon dioxide concentrator described in (2) above, the destination of the electrolyte in the first storage section can be switched, so the electrolyte can be recycled within the carbon dioxide concentrator. By switching the destination of the electrolyte to the anode liquid chamber or cathode liquid chamber after a predetermined reaction has sufficiently progressed in the absorption section, it is possible to suppress the flow of electrolyte that has not yet fully reacted to the next destination, thereby improving the carbon dioxide concentration efficiency.

[0017] (3) The carbon dioxide concentrator according to (1) or (2) above may be equipped with a circulation system that can switch between a first state in which the electrolyte is circulated between the absorption unit and the first storage unit, between the anode liquid chamber and the second storage unit and between the cathode liquid chamber and the third storage unit; a second state in which the electrolyte is circulated between the absorption unit and the third storage unit, between the anode liquid chamber and the first storage unit and between the cathode liquid chamber and the second storage unit; and at least one third state in which the electrolyte is circulated between the absorption unit and the second storage unit, between the anode liquid chamber and the third storage unit and between the cathode liquid chamber and the first storage unit.

[0018] According to the carbon dioxide concentration apparatus described in (3) above, the circulation destination of the electrolyte stored in the first, second, and third storage sections can be switched. By switching the circulation system after the predetermined reactions in the absorption section, anode liquid chamber, and cathode liquid chamber have progressed sufficiently, it is possible to prevent electrolyte that has not yet reacted sufficiently from flowing to the next circulation destination. By switching the circulation system as appropriate, batch-type circulation of the electrolyte becomes possible. The state of the electrolyte can be appropriately adjusted for each batch, and the carbon dioxide concentration efficiency can be improved.

[0019] (4) In the carbon dioxide concentration apparatus described in (2) or (3) above, the circulation system may be switched based on the pH of the electrolyte.

[0020] According to the carbon dioxide concentration device described in (4) above, the circulation system can be switched while taking into account the pH which changes in accordance with the reaction rate of the electrolyte. The circulation system can be switched to the appropriate state at the appropriate timing in accordance with the reaction rate of the electrolyte.

[0021] (5) In any one of the carbon dioxide concentration devices (2) to (4) above, the circulation system may be switched in the order of the first state, the second state, and the third state.

[0022] According to the carbon dioxide concentration device of (5) above, the reaction of the electrolytic solution can be carried out in a series, that is, carbon dioxide is absorbed in the absorption part, carbon dioxide is desorbed from the electrolytic solution and a predetermined component is consumed in the anode liquid chamber, and a predetermined component of the electrolytic solution is regenerated in the cathode liquid chamber. By circulating the electrolytic solution sequentially to each circulation destination, the operating efficiency of the device can be improved.

[0023] (6) In the carbon dioxide concentration device of (5) above, after switching the circulation system to the third state, the circulation system may be switched back to the first state again.

[0024] According to the carbon dioxide concentration device of (6) above, the above series of reactions can be repeated.

[0025] (7) In any one of the carbon dioxide concentration devices (1) to (6) above, a sensor for measuring the pH of the electrolytic solution may be provided.

[0026] According to the carbon dioxide concentration device of (7) above, the pH of the electrolytic solution can be accurately grasped in real time by the sensor, so that the switching of the circulation system based on the pH can be accurately and promptly executed.

[0027] (8) In any one of the carbon dioxide concentration devices (1) to (7) above, the sensor may be provided inside at least one of the cathode liquid chamber, the first storage part, the second storage part, and the third storage part or near the inner side of the end of the passage connecting to at least one of the cathode liquid chamber, the first storage part, the second storage part, and the third storage part.

[0028] According to the carbon dioxide concentrator of (8) above, the pH of the electrolytic solution can be measured inside the cathode liquid chamber, the first storage section, the second storage section, and the third storage section, or near the end of the passage connecting them. In the anode liquid chamber to which the electrolytic solution that has absorbed carbon dioxide is supplied, hydrogen carbonate ions due to the dissolution of carbon dioxide are present in the electrolytic solution, and a buffering action occurs, so the change in pH accompanying the reaction of the electrolytic solution is reduced. In the cathode liquid chamber, the change in pH accompanying the reaction of the electrolytic solution is larger than in the anode liquid chamber where such a buffering action occurs. By measuring the pH of the electrolytic solution inside or near the cathode liquid chamber, the progress of the reaction in the electrochemical cell can be estimated more accurately. By measuring the pH inside or near the first storage section, the second storage section, and the third storage section, the progress of the reaction of the electrolytic solution circulating between each circulation destination can be estimated.

[0029] (9) In the carbon dioxide concentrator according to any one of (1) to (8) above, the flow rate of the electrolytic solution circulating between the absorption section and the flow rate of the electrolytic solution circulating between the anode liquid chamber or the flow rate of the electrolytic solution circulating between the cathode liquid chamber may be different.

[0030] According to the carbon dioxide concentrator of (9) above, the electrolytic solution can be circulated at different flow rates to the absorption section and the anode liquid chamber or the cathode liquid chamber. Since the liquid volume can be controlled independently in the absorption section and the electrochemical cell, even when the progress of the reaction of the electrolytic solution is different between the absorption section and the electrochemical cell, the reaction can proceed well in each of the absorption section and the electrochemical cell.

[0031] The present disclosure will be specifically described with reference to the drawings showing its embodiments.

[0032] FIG. 1 is a schematic diagram of a carbon dioxide concentrator 100 of the present embodiment. The carbon dioxide concentrator 100 is a device for concentrating and recovering carbon dioxide from a raw material gas using a gas G1 containing low-concentration carbon dioxide as the raw material gas. The carbon dioxide concentrator 100 includes an absorption tower 10, a concentration section 20, a storage tank 30, a gas-liquid separation section 40, and a control device 50.

[0033] The absorption tower 10 brings gas G1 and electrolyte S into gas-liquid contact to absorb carbon dioxide in gas G1 into electrolyte S. In this specification, "absorption" means dissolving into predetermined ions through a chemical reaction.

[0034] Gas G1 is a gas containing a low concentration of carbon dioxide, such as air or exhaust gas. The concentration of carbon dioxide in gas G1 is, for example, 0.01 vol% to 30 vol%. Gas G1 may also contain components other than carbon dioxide, such as nitrogen, water vapor, carbon monoxide, hydrogen sulfide, carbonyl sulfide, sulfur dioxide, nitrogen dioxide, methane, hydrogen, etc.

[0035] The absorption tower 10 comprises a main body 11 extending vertically, a gas supply port 12 provided at the lower part of the side wall of the main body 11, a liquid supply port 13 and a first gas discharge port 14 provided at the upper part of the main body 11, and a first liquid discharge port 15 provided at the bottom of the main body 11. The gas supply port 12 is connected to a carbon dioxide-containing gas supply source (not shown).

[0036] Gas G1 is supplied to the gas supply port 12. Gas G1 is supplied into the tower, flows through the tower, and is then discharged from the first gas discharge port 14. Electrolyte S for absorbing carbon dioxide is supplied to the liquid supply port 13. Electrolyte S absorbs carbon dioxide by coming into contact with carbon dioxide-containing gas in the tower. The electrolyte S, which has absorbed carbon dioxide, is discharged from the first liquid discharge port 15.

[0037] The method of bringing the gas G1 and the electrolyte S into contact is not particularly limited. For example, methods include bubbling the gas G1 into the electrolyte S, atomizing the electrolyte S into the gas G1 using a spray or atomizing method, or bringing high-pressure gas G1 and electrolyte S into countercurrent contact in an absorption tower 10 filled with a packing material made of porcelain or metal mesh.

[0038] The concentration unit 20 desorbs (releases) carbon dioxide from the electrolyte S that has absorbed carbon dioxide, generating gas G2 containing carbon dioxide. Gas G2 is a concentrated carbon dioxide gas containing a higher concentration of carbon dioxide than gas G1. The concentration of carbon dioxide in gas G2 is typically 90 vol% to 100 vol%.

[0039] The concentration unit 20 includes an electrochemical hydrogen pump (electrochemical cell) comprising an anode 22, an electrolyte unit 23, and a cathode 24. The electrolyte unit 23 includes an anode liquid chamber 231 (first liquid chamber), an electrolyte membrane 232, and a cathode liquid chamber 233 (second liquid chamber). Electrolyte S is supplied to the anode liquid chamber 231 and the cathode liquid chamber 233.

[0040] Although Figure 1 shows one electrolyte unit 23 for the sake of simplicity, the concentration unit 20 may include multiple electrolyte units 23, such as 50 or 100 units.

[0041] The concentration unit 20 uses an electrodialysis method by hydrogen pumping to remove carbon dioxide from the electrolyte S that has absorbed carbon dioxide, and regenerates the electrolyte of the electrolyte by moving predetermined ions through the electrolyte membrane 232. Gas G3 containing hydrogen is supplied to the anode 22 of the concentration unit 20. The cathode 24 generates gas G4, which is at a higher pressure than gas G3, by the hydrogen pressurization operation of the electrochemical hydrogen pump. Details of the concentration unit 20 will be described later.

[0042] The hydrogen concentration in gas G3 may be 100 vol% or less. The lower limit of the hydrogen concentration in gas G3 is not particularly limited, but may be, for example, 0.01 vol% or higher.

[0043] The storage tank 30 stores the electrolyte S supplied to the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233. The storage tank 30 includes a first tank 31, a second tank 32, and a third tank 33.

[0044] The first tank 31 comprises a main body 311 extending vertically, and a fifth supply port 312 and a fifth discharge port 313 provided at the lower part of the side wall of the main body 311. Electrolyte S is stored in the main body 311. The stored electrolyte S is discharged from the fifth discharge port 313 and supplied to one of the absorption tower 10, anode liquid chamber 231, or cathode liquid chamber 233, which are the circulation destinations. After flowing through the circulation destinations, the electrolyte S is discharged and then supplied back to the main body 311 through the fifth supply port 312.

[0045] The second tank 32 comprises a main body 321 extending vertically, and a sixth supply port 322 and a sixth discharge port 323 provided at the lower part of the side wall of the main body 321. The third tank 33 comprises a main body 331 extending vertically, and a seventh supply port 332 and a seventh discharge port 333 provided at the lower part of the side wall of the main body 331. The configurations of the second tank 32 and the third tank 33 are the same as those of the first tank 31, so a detailed explanation is omitted. The first tank 31 to the third tank 33 may each be composed of multiple tanks.

[0046] The gas-liquid separation unit 40 performs gas-liquid separation by, for example, a water displacement method or a gravity separation method. The gas-liquid separation unit 40 is supplied with a gas-liquid mixture of gas G2 discharged from the anode liquid chamber 231 and electrolyte S. The gas-liquid separation unit 40 separates the gas G2 and electrolyte S in the mixture from each other, and after separation, discharges the gas G2 from the second gas outlet 401 and the electrolyte S from the second liquid outlet 402.

[0047] Gas G2 is recovered in a carbon dioxide recovery unit (not shown). This yields high-concentration carbon dioxide gas. Alternatively, the gas-liquid separation unit 40 may be connected to another device (not shown), and the gas G2 discharged from the gas-liquid separation unit 40 may be supplied to the other device. An example of a device to which gas G2 is supplied is an electrolytic reduction device that produces hydrocarbons (e.g., methane, ethylene, etc.) and carbon compounds such as carbon monoxide by electrolytically reducing carbon dioxide.

[0048] The carbon dioxide concentrator 100 includes passages 6 that constitute the circulation system for the electrolyte S. The passages 6 include the first passage 61 to the seventh passage 67. The first tank 31, the second tank 32, and the third tank 33 are each connected by passages 6 to one of the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233, so that the electrolyte S can be circulated between them.

[0049] Figure 2 is a cross-sectional view showing an example of the configuration of the concentration unit 20. Figure 2 shows an example in which two electrolyte units 23 are stacked.

[0050] The concentration unit 20 has a substantially rectangular cross-section and an overall substantially rectangular parallelepiped shape. The concentration unit 20 comprises an anode plate 21 having an anode gas chamber 211, an anode 22, one or more electrolyte units 23, a cathode 24, a cathode plate 25 having a cathode gas chamber 251, and a power supply 26.

[0051] The anode plate 21, anode 22, one or more electrolyte units 23, cathode 24, and cathode plate 25 are arranged in this order and are fastened together, for example, by fastening members (not shown). Gaskets (not shown) may be placed between the anode plate 21 and the anode 22, and between the cathode 24 and the cathode plate 25.

[0052] The electrolyte unit 23 comprises an electrolyte membrane 232, an anode liquid chamber 231 located on the anode 22 side via the electrolyte membrane 232, and a cathode liquid chamber 233 located on the cathode 24 side.

[0053] The anode plate 21 includes an anode gas chamber 211 and a first supply port 212 into which hydrogen-containing gas G3 is supplied. The anode gas chamber 211 functions as a gas flow path for the gas G3. The anode gas chamber 211 is, for example, a groove-shaped flow path formed on the surface of the anode plate 21, and is arranged to fold back in the region of the surface of the anode plate 21 facing the anode 22. The gas G3 is supplied to the anode 22 as it passes through the anode gas chamber 211. The flow of gas G3 supplied to the anode 22 is restricted by the anode gas chamber 211. The anode plate 21 may also include a first discharge port 213 for discharging the gas G3 that has flowed through the anode gas chamber 211.

[0054] The configuration of the anode plate 21 is not limited, and for example, it may be constructed by stacking an end plate, a current collector plate, and a plate member having an anode gas chamber 211 on one side in that order.

[0055] The cathode plate 25 comprises a cathode gas chamber 251 and a second discharge port 252 for discharging hydrogen-containing gas G4. The cathode gas chamber 251 functions as a gas flow path for the gas G4. The cathode gas chamber 251 is, for example, a groove-shaped flow path formed on the surface of the cathode plate 25, and is arranged to fold back in the region of the surface of the cathode plate 25 facing the cathode 24. The gas G4 generated in the cathode 24 is discharged from the second discharge port 252 through the cathode gas chamber 251. The gas G4 discharged from the second discharge port 252 is recovered, for example, by a hydrogen recovery unit (not shown). Alternatively, the gas G4 discharged from the second discharge port 252 may be supplied to the anode 22 and used as gas G3.

[0056] The configuration of the cathode plate 25 is not limited, and for example, it may be constructed by stacking a plate member with a cathode gas chamber 251 on one side, a current collector plate, and an end plate in that order.

[0057] The anode plate 21 is electrically connected to the anode 22. The cathode plate 25 is electrically connected to the cathode 24. The anode plate 21 and the cathode plate 25 are connected to the power supply 26 via wiring.

[0058] The power supply 26 applies voltage to the anode 22 and cathode 24 via the anode plate 21 and 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.

[0059] The concentration unit 20 may be equipped with measuring instruments such as a current sensor for detecting the current flowing between the anode 22 and the cathode 24, and a voltage sensor for detecting the voltage.

[0060] The anode 22 is an electrode that generates protons from hydrogen in gas G3. The anode 22 is, for example, a gas diffusion electrode and comprises 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 is in contact with the surface of the anode 22 on the anode catalyst layer 221 side, and the anode plate 21 (anode gas chamber 211) is in contact with the surface on the anode gas diffusion layer 222 side. The anode catalyst layer 221 may be formed by supporting fine particles of the anode catalyst in a highly dispersed manner on the anode gas diffusion layer 222.

[0061] Examples of anode catalysts include platinum, ruthenium, rhodium, palladium, and iridium. Anode catalysts may be used individually or in combination of two or more. When using a combination of two or more, for example, a combination containing at least platinum and ruthenium can be used.

[0062] The anode gas diffusion layer 222 is made of a porous material and has conductivity and gas diffusivity. The anode gas diffusion layer 222 uniformly diffuses the gas G3 supplied through the anode gas chamber 211 into the anode catalyst layer 221. Examples of materials for the anode gas diffusion layer 222 include porous carbon fiber sheets such as carbon paper, carbon cloth, and carbon felt, and sintered bodies made of carbon particles, with carbon paper being preferred. The anode gas diffusion layer 222 may also be, for example, a sintered body of metal fibers, a sintered body of powdered metal, a metal mesh, or a foamed metal body. As the metal, for example, titanium alloy or stainless steel may be used.

[0063] The method for producing the anode 22 is not particularly limited. For example, it can be produced by applying a slurry of a liquid composition containing the anode catalyst to one surface of the anode gas diffusion layer 222 and drying it.

[0064] The cathode 24 is an electrode that generates hydrogen from protons supplied from the anode 22. The cathode 24 is, for example, 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 cathode 24 on the cathode catalyst layer 241 side, and the cathode plate 25 (cathode gas chamber 251) is in contact with the surface on the cathode gas diffusion layer 242 side. The cathode catalyst layer 241 may be formed by highly dispersedly supporting fine particles of the cathode catalyst on the cathode gas diffusion layer 242.

[0065] Examples of cathode catalysts include those similar to the anode catalyst described above, and platinum is preferred. The cathode catalyst may be used alone or in combination of two or more types.

[0066] The cathode gas diffusion layer 242 is composed of a porous material and has conductivity and gas diffusivity. The material for the cathode gas diffusion layer 242 is the same as that used for the anode gas diffusion layer 222.

[0067] The method for producing the cathode 24 is not particularly limited. For example, it can be produced by applying a slurry of a liquid composition containing a cathode catalyst to one surface of the cathode gas diffusion layer 242 and drying it.

[0068] A polymer membrane having ion exchange groups may be provided between the anode 22 and the anode liquid chamber 231, and between the cathode 24 and the cathode liquid chamber 233. Examples of materials for the polymer membrane having ion exchange groups include Nafion®. By providing such a membrane, it is possible to suppress the movement of the liquid in the liquid chamber toward the electrode while maintaining the transfer of charge.

[0069] The electrolyte unit 23 comprises an anode liquid chamber 231, an electrolyte membrane 232, and a cathode liquid chamber 233. When multiple electrolyte units 23 are provided, each electrolyte unit 23 has the same configuration.

[0070] The electrolyte membrane 232 is a cation exchange membrane (CEM) and is composed of an electrolyte material having cation conductivity. Examples of electrolyte membranes 232 include fluorine-based cation exchange membranes such as perfluorosulfonic acid-based membranes.

[0071] The anode liquid chamber 231 is composed of, for example, a roughly rectangular parallelepiped frame made of resin. The anode liquid chamber 231 includes a third supply port 234 provided at the bottom, a third discharge port 235 provided at the top, and an anode liquid flow path 236 formed between the third supply port 234 and the third discharge port 235.

[0072] The anode liquid channel 236 is a space formed between the anode catalyst layer 221 and the electrolyte membrane 232. The anode liquid channel 236 is separated from the outside by a frame that constitutes the anode liquid chamber 231. The anode catalyst layer 221 is arranged so that when the space is filled with electrolyte S, the entire surface of one side of the anode catalyst layer 221 is in contact with the electrolyte S. The anode liquid channel 236 may also be formed by a space created by the three-dimensional intersection of channel forming members, which are formed in a mesh-like manner. In the anode liquid channel 236, gas G2 and electrolyte S flow from the third supply port 234 (inlet) to the third discharge port 235 (outlet).

[0073] The electrolyte S, which has absorbed carbon dioxide, is supplied to the third supply port 234. The electrolyte S desorbs carbon dioxide as it flows through the anode liquid channel 236. The third discharge port 235 discharges a gas-liquid mixture of the gas G2 containing the desorbed carbon dioxide and the electrolyte S from which the carbon dioxide has been removed.

[0074] The shape of the anode liquid chamber 231 and the positions of the third supply port 234 and the third discharge port 235 can be set as appropriate.

[0075] The cathode liquid chamber 233 is composed of, for example, a roughly rectangular parallelepiped frame made of resin. The cathode liquid chamber 233 includes a fourth supply port 237 provided at the bottom, a fourth discharge port 238 provided at the top, and a cathode liquid flow path 239 formed between the fourth supply port 237 and the fourth discharge port 238.

[0076] The cathode liquid channel 239 is a space formed between the electrolyte membrane 232 and the cathode catalyst layer 241. The cathode liquid chamber 233 is separated from the outside by the frame that constitutes the cathode liquid channel 239. The cathode catalyst layer 241 is positioned so that when the space is filled with electrolyte S, the entire surface of one side of the cathode catalyst layer 241 is in contact with the electrolyte S. The cathode liquid channel 239 may also be equipped with spacers, similar to the anode liquid channel 236. In the cathode liquid channel 239, the electrolyte S flows from the fourth supply port 237 (inlet) to the fourth discharge port 238 (outlet).

[0077] The fourth supply port 237 is supplied with electrolyte S from which carbon dioxide has been removed. The fourth discharge port 238 discharges electrolyte S from which the absorbent solution described later has been regenerated.

[0078] When the concentration unit 20 comprises a plurality of electrolyte units 23, the plurality of electrolyte units 23 are stacked with an intermediate layer 28 in between, forming a laminate. In the concentration unit 20, adjacent electrolyte units 23 and other electrolyte units 23 are stacked in the same orientation with the intermediate layer 28 in between. One surface of the intermediate layer 28 contacts the cathode liquid chamber 233 of one electrolyte unit 23, and the other surface of the intermediate layer 28 contacts the anode liquid chamber 231 of the other electrolyte unit 23. The intermediate layer 28 supplies protons supplied from the cathode liquid chamber 233 of one electrolyte unit 23 to the anode liquid chamber 231 of the adjacent other electrolyte unit 23.

[0079] 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 also be constructed by supporting fine particles of the catalyst in a highly dispersed manner on the surface of the gas diffusion layer 282.

[0080] Examples of catalysts include those similar to the anode catalyst described above, and platinum is preferred. The catalyst may be used alone or in combination of two or more types.

[0081] The gas diffusion layer 282 is made of a porous material and has conductivity and gas diffusivity. The gas diffusion layer 282 uniformly diffuses hydrogen molecules supplied from the catalyst layer 281 in contact with the cathode liquid chamber 233 to the catalyst layer 281 in contact with the anode liquid chamber 231. The material constituting the gas diffusion layer 282 is the same as that of the anode gas diffusion layer 222, and is preferably carbon paper.

[0082] The method for producing the intermediate layer 28 is not particularly limited. For example, it can be produced by applying a slurry of a liquid composition containing a catalyst to the surface of the gas diffusion layer 282 and drying it.

[0083] The intermediate layer 28 may include a leakage suppression section (not shown) to suppress the leakage of liquid from the anode liquid chamber 231 and the cathode liquid chamber 233 to the intermediate layer 28. The leakage suppression section is formed, for example, by adding or laminating a water-repellent material such as polytetrafluoroethylene to at least one of the pair of catalyst layers 281 and gas diffusion layers 282.

[0084] Figure 2 shows a configuration in which electrolyte units 23 are stacked using an intermediate layer 28 having a gas diffusion layer 282 with catalyst layers 281 supported on both sides. The intermediate layer 28 only needs to be able to supply protons from the cathode liquid chamber 233 to the anode liquid chamber 231. The intermediate layer 28 may be, for example, a bipolar membrane formed by laminating a cation exchange membrane and an anion exchange membrane. When stacking three or more electrolyte units 23, an intermediate layer 28 using a gas diffusion layer and an intermediate layer 28 using a bipolar membrane may be used in combination.

[0085] The passage configuration in the carbon dioxide concentrator 100 will now be described. The carbon dioxide concentrator 100 includes a first passage 61 to a seventh passage 67. The first passage 61 to the seventh passage 67 are not particularly limited, and known piping or the like can be used as appropriate.

[0086] The first passage 61 flows the electrolyte S from the first tank 31 to the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233. The upstream end of the first passage 61 is connected to the fifth discharge port 313 of the first tank 31. Downstream of the first passage 61, the first to third branch passages 611 to 613 are provided. The first branch passage 611 is connected to the liquid supply port 13 of the absorption tower 10. The second branch passage 612 is connected to the third supply port 234 of the anode liquid chamber 231. The third branch passage 613 is connected to the fourth supply port 237 of the cathode liquid chamber 233.

[0087] The second passage 62 flows the electrolyte S from the second tank 32 to the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233. The upstream end of the second passage 62 is connected to the sixth discharge port 323 of the second tank 32. Downstream of the second passage 62, there are fourth to sixth branch passages 621 to 623. The fourth branch passage 621 is connected to the liquid supply port 13 of the absorption tower 10. The fifth branch passage 622 is connected to the third supply port 234 of the anode liquid chamber 231. The sixth branch passage 623 is connected to the fourth supply port 237 of the cathode liquid chamber 233.

[0088] The third passage 63 flows the electrolyte S from the third tank 33 to the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233. The upstream end of the third passage 63 is connected to the seventh discharge port 333 of the third tank 33. Downstream of the third passage 63, seventh to ninth branch passages 631 to ninth branch passages 633 are provided. The seventh branch passage 631 is connected to the liquid supply port 13 of the absorption tower 10. The eighth branch passage 632 is connected to the third supply port 234 of the anode liquid chamber 231. The ninth branch passage 633 is connected to the fourth supply port 237 of the cathode liquid chamber 233.

[0089] The fourth passage 64 allows the electrolyte S and gas G2 to flow from the anode liquid chamber 231 to the gas-liquid separation unit 40. The upstream end of the fourth passage 64 is connected to the third discharge port 235 of the anode liquid chamber 231. The downstream end of the fourth passage 64 is connected to the gas-liquid separation unit 40.

[0090] The fifth passage 65 allows the electrolyte S to flow from the absorption tower 10, the gas-liquid separation unit 40, and the cathode liquid chamber 233 to the first tank 31. The downstream end of the fifth passage 65 is connected to the fifth supply port 312 of the first tank 31. Upstream of the third passage 63, the tenth to twelfth branch passages 651 to 653 are provided. The tenth branch passage 651 is connected to the first liquid discharge port 15 of the absorption tower 10. The eleventh branch passage 652 is connected to the second liquid discharge port 402 of the gas-liquid separation unit 40. The twelfth branch passage 653 is connected to the fourth discharge port 238 of the cathode liquid chamber 233.

[0091] The sixth passage 66 allows the electrolyte S to flow from the absorption tower 10, the gas-liquid separation unit 40, and the cathode liquid chamber 233 to the second tank 32. The downstream end of the sixth passage 66 is connected to the sixth supply port 322 of the second tank 32. Upstream of the sixth passage 66, the thirteenth to fifteenth branch passages 661 to fifteenth branch passages 663 are provided. The thirteenth branch passage 661 is connected to the first liquid discharge port 15 of the absorption tower 10. The fourteenth branch passage 662 is connected to the second liquid discharge port 402 of the gas-liquid separation unit 40. The fifteenth branch passage 663 is connected to the fourth discharge port 238 of the cathode liquid chamber 233.

[0092] The seventh passage 67 allows the electrolyte S to flow from the absorption tower 10, the gas-liquid separation unit 40, and the cathode liquid chamber 233 to the third tank 33. The downstream end of the seventh passage 67 is connected to the seventh supply port 332 of the third tank 33. Upstream of the seventh passage 67, the sixteenth to eighteenth branch passages 671 to eighteenth branch passages 673 are provided. The sixteenth branch passage 671 is connected to the first liquid discharge port 15 of the absorption tower 10. The seventeenth branch passage 672 is connected to the second liquid discharge port 402 of the gas-liquid separation unit 40. The eighteenth branch passage 673 is connected to the fourth discharge port 238 of the cathode liquid chamber 233.

[0093] Each of the first to eighteenth branch lines 611 to 673 is provided with on-off valves V1 to V18. The on-off valves V1 to V18 are composed of known solenoid valves or the like. The on-off valves V1 to V18 can be opened and closed in response to signals from the control device 50, allowing the passage of fluid when open and restricting the passage of fluid when closed. The on-off valves V1 to V18 may also function as flow control valves that adjust the flow rate of the fluid passing through when they are open.

[0094] By controlling the open / close combinations of the on / off valves V1 to V3 provided in the first branch 611 to the third branch 613, and the on / off valves V10 to V12 provided in the tenth branch 651 to the twelfth branch 653, the electrolyte S can be circulated between the first tank 31 and any one of the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233.

[0095] By controlling the open / close combinations of the on-off valves V4 to V6 provided in the fourth branch 621 to the sixth branch 623, and the on-off valves V13 to V15 provided in the thirteenth branch 661 to the fifteenth branch 663, the electrolyte S can be circulated between the second tank 32 and any one of the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233.

[0096] By controlling the open / close combinations of the on-off valves V7 to V9 provided in the seventh branch 631 to the ninth branch 633, and the on-off valves V16 to V18 provided in the sixteenth branch 671 to the eighteenth branch 673, the electrolyte S can be circulated between the third tank 33 and any one of the absorption tower 10, the anode liquid chamber 231, and the cathode liquid chamber 233.

[0097] If the carbon dioxide concentrator 100 is equipped with a plurality of anode liquid chambers 231 and cathode liquid chambers 233, a plurality of first branch lines 611 to 18th branch lines 673 may be provided to correspond to each anode liquid chamber 231 and each cathode liquid chamber 233.

[0098] Pump P1 is installed between the upstream end of the first passage 61 and the branching point of the first branch 611 to the third branch 613. Pump P2 is installed between the upstream end of the second passage 62 and the branching point of the fourth branch 621 to the sixth branch 623. Pump P3 is installed between the upstream end of the third passage 63 and the branching point of the seventh branch 631 to the ninth branch 633. By driving pumps P1 to P3, the electrolyte S in each tank is discharged.

[0099] Each of the first to seventh passages 61 to 67 may be equipped with measuring instruments such as a flow meter for measuring the flow rate of the fluid flowing through the passage, and a gas sensor for detecting the concentration of the gas flowing through the passage. Each of the fourth to seventh passages 67 may be equipped with a pump for delivering fluid, a flow control valve for adjusting the flow rate of the fluid flowing through the passage, and so on.

[0100] The carbon dioxide concentrator 100 is equipped with a pH sensor 8 for measuring the pH of the electrolyte S. The pH sensor 8 measures the pH at predetermined time intervals.

[0101] Figures 1 and 2 show an example in which a pH sensor 8 is installed in the cathode liquid chamber 233. The pH sensor 8 is preferably installed near the fourth discharge port 238 so as to measure the pH of the electrolyte S as it is discharged from the cathode liquid chamber 233. Alternatively, the pH sensor 8 may be installed in the passages (the 12th branch passage 653, the 15th branch passage 663, and the 18th branch passage 673) connected to the fourth discharge port 238 (the outlet of the electrolyte S) of the cathode liquid chamber 233. The area near the end is, for example, the region from the end connected to the discharge port of each branch passage to the confluence point of each branch passage. Multiple pH sensors 8 may be installed.

[0102] The pH sensor 8 may be provided in at least one of the first to third tanks 31 to 33. The pH sensor 8 may be provided inside at least one of the first to third passages 63 connected to the fifth to seventh discharge ports 313 to 333 (outlets of the electrolyte S) of the first to third tanks 31 to 33. In the first to third passages 63, the pH sensor 8 may be provided inside near the ends connected to the fifth to seventh discharge ports 313 to 333. The area near the ends is, for example, the region from the end connected to the discharge port of each passage to the branching point of the branching path of each passage.

[0103] The control device 50 is a computer that controls the operation of the carbon dioxide concentration device 100. The control device 50 includes a processor such as a CPU (Central Processing Unit) (not shown), memory, a communication unit, and an input / output interface. The memory stores various computer programs and data referenced by the processor. The input / output interface is connected to the on-off valves V1 to V18, the power supply 26, the pH sensor 8, various control devices, and various measuring instruments. The control device 50 acquires measured values ​​from the pH sensor 8 and the various measuring instruments. Based on the acquired measured values, the control device 50 outputs control signals to the on-off valves V1 to V18, the power supply 26, and the various control devices to control their operation.

[0104] Figure 3 is an explanatory diagram illustrating the operation of the carbon dioxide concentrator 100. Figure 3 shows an example in which two electrolyte units 23 are stacked. The operation of the carbon dioxide concentrator 100 will be explained using Figure 3. Hereafter, in order to distinguish between electrolytes S according to their composition, the electrolytes S will be referred to as electrolyte S1, electrolyte S2, and electrolyte S3 for convenience.

[0105] A gas G1 containing a low concentration of carbon dioxide is supplied to the absorption tower 10, along with an electrolyte S1.

[0106] Electrolyte S1 is an alkaline electrolyte and is a mixture containing an absorbent solution that mainly contributes to the absorption of carbon dioxide and an electrolyte solution containing a predetermined electrolyte. The absorbent solution and the electrolyte solution are aqueous solutions containing the same cations. In this specification, "mixture" means a liquid containing the components corresponding to the absorbent solution and the components corresponding to the electrolyte solution, and does not require the actual mixing of separate absorbent solutions and electrolyte solutions.

[0107] The absorbent solution contained in the electrolyte S1 is an alkaline aqueous solution. Examples of alkaline aqueous solutions 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.

[0108] Examples of alkali metal compounds and alkaline earth metal compounds include alkali metal compounds such as sodium, lithium, and potassium, or alkaline earth metal compounds such as calcium, magnesium, and barium. Preferably, alkali metal compounds and alkaline earth metal compounds are hydroxides, oxides, or nitrates of alkali metals or alkaline earth metals, and more preferably hydroxides. Specific examples of alkaline aqueous solutions include aqueous solutions of potassium hydroxide, sodium hydroxide, and calcium hydroxide, and preferably aqueous solutions of potassium hydroxide.

[0109] Examples of amine compounds include basic amines such as monoethanolamine, diethanolamine, diisopropanolamine, methyldiethanolamine, and triethanolamine. The alkaline aqueous solution may be used individually or in combination of two or more types.

[0110] Examples of electrolyte solutions included in electrolyte solution S1 include aqueous potassium chloride solution and aqueous sodium chloride solution, with aqueous potassium chloride solution being preferred. The electrolyte solution may be used individually or in combination of two or more types.

[0111] In this embodiment, the electrolyte S1 is a mixture of an aqueous potassium hydroxide solution as an absorbent and an aqueous potassium chloride solution as an electrolyte solution (KOH-KCl solution).

[0112] In the absorption tower 10, the carbon dioxide absorption reaction represented by the following reaction equations (1) and (2) proceeds, and the electrolyte S2 (KHCO) absorbs carbon dioxide. 3 A KCl solution is obtained. In the electrolyte S2, carbon dioxide is converted into bicarbonate ions (HCO3). - ) can form 2KOH + CO 2 →K2CO 3 +H2O...(1) K2CO 3 +H2O+CO 2 →2KHCO 3 ... (2)

[0113] Electrolyte S2 (KHCO) that absorbed carbon dioxide 3 -KCL solution) may be an electrolyte solution in which KOH has completely reacted to KHCO 3 or may be an electrolyte solution containing a part of K2CO which is the product of the above reaction formula (1). 3

[0114] In the concentration section 20, a gas G3 containing hydrogen is supplied to the anode gas chamber 211, an electrolyte solution S2 (KHCO 3 -KCL solution) that has absorbed carbon dioxide is supplied to the anode liquid chamber 231, and an electrolyte solution S3 (KCL solution) from which carbon dioxide has been desorbed is supplied to the cathode liquid chamber 233. When a voltage is applied from the power source 26 to the anode 22 and the cathode 24, the following reaction occurs.

[0115] In the anode catalyst layer 221 of the anode 22, hydrogen molecules in the gas G3 supplied from the anode gas chamber 211 are separated into protons (H + ) and electrons by the reaction represented by the following reaction formula (3). Protons (H + ) move to the anode liquid chamber 231 adjacent to the anode 22. H 2 →2H + +2e - ...(3)

[0116] In the anode liquid chamber 231, corresponding to the movement of protons (H + ), the pH of the KHCO 3 solution in the electrolyte solution S2 decreases compared to before the oxidation reaction. Due to the decrease in pH, the chemical equilibrium of the following reaction formula (4) shifts to the right, and carbon dioxide is generated as a gaseous product. Potassium ions (K + ) in the electrolyte solution S2 move through the inside of the electrolyte membrane 232 to the cathode liquid chamber 233. HCO3 - +H + ⇔CO 2 +H2O...(4)

[0117] The electrolyte solution S2 flowing through the anode liquid chamber 231 becomes the electrolyte solution S3 from which carbon dioxide has been desorbed by the carbon dioxide desorption reaction of the above reaction formula (4) and is discharged from the anode liquid chamber 231. The electrolyte solution S3 from which carbon dioxide has been desorbed is a KCL solution mainly composed of potassium chloride. The electrolyte solution S3 from which carbon dioxide has been desorbed contains a slight amount of KHCO 3 ​It may include

[0118] The gas G4 containing carbon dioxide generated in the anode liquid chamber 231 and the electrolyte S3 from which the carbon dioxide has been removed are separated into gas and liquid in the gas-liquid separation unit 40. The gas G4 is recovered in the gas recovery unit.

[0119] In the cathode liquid chamber 233, potassium ions (K) in the KCl solution within the cathode liquid chamber 233 + As the number of protons increases, + ) is supplied to the intermediate layer 28. The electrolyte S3 flowing through the cathode liquid chamber 233 contains protons (H + As the pH rises in response to the consumption of the absorbent solution (KOH), the absorbent solution (KOH) is regenerated, resulting in a KOH-KCl solution containing the absorbent solution and electrolyte solution, i.e., electrolyte S1, which is discharged from the cathode liquid chamber 233.

[0120] Protons (H) supplied to the intermediate layer 28 + The hydrogen molecules are adsorbed onto the catalyst layer 281 on the anode 22 side and then supplied to the gas diffusion layer 282 as hydrogen molecules. The hydrogen molecules pass through the gas diffusion layer 282 and are converted into protons (H) in the catalyst layer 281 on the cathode 24 side. + It is converted to a proton (H + ) is supplied to the anode liquid chamber 231 of the adjacent electrolyte unit 23.

[0121] A similar reaction occurs in each electrolyte unit 23, resulting in protons (H) + The liquid moves from the anode 22 side to the cathode 24 side and is supplied to the cathode 24 from the cathode liquid chamber 233 adjacent to the cathode 24.

[0122] In the cathode catalyst layer 241 of cathode 24, hydrogen molecules are again generated by the reaction shown in the following reaction equation (5). The hydrogen generated in cathode 24 permeates through the cathode gas diffusion layer 242 and is discharged from the second discharge port 252 as gas G4 containing high-pressure hydrogen gas. Gas G4 has, for example, a hydrogen concentration of 99 vol% or more. 2H + +2e - →H 2 ... (5)

[0123] The hydrogen gas produced at cathode 24 may be hydrogen gas produced by the reduction reaction of water, as shown in the following reaction equation (6): Electrolyte S2 (KHCO 3 Hydrogen gas can be generated when water contained in the KCl solution or electrolyte S3 (KCl solution) is reduced in the cathode catalyst layer 241. 2H2O + 2e - →H2 + 2OH - ... (6)

[0124] In the carbon dioxide concentrator 100, the electrolyte S is circulated between one of the first to third tanks 33, which serve as storage destinations, and one of the absorption tower 10, anode liquid chamber 231, and cathode liquid chamber 233, which serve as circulation destinations. Before the start of circulation, one of the electrolytes S1, S2, or S3, each with a different composition, is stored in the first to third tanks 33. The circulation system of the carbon dioxide concentrator 100 can be switched between first to third states, in which the combination of storage destinations and circulation destinations differs from each other. Switching of the circulation system is performed by controlling the opening and closing of on / off valves V1 to V18.

[0125] Figure 4 illustrates the first state of the circulation system, Figure 5 illustrates the second state of the circulation system, and Figure 6 illustrates the third state of the circulation system. Table 1 shows the operation of the on-off valves V1 to V18, the circulation destinations of the electrolyte S stored in the first tank 31 to the third tank 33, and the types of reactions at the circulation destinations for the three states of the circulation system. The states of the circulation system will be explained using Figures 4 to 6 and Table 1. In Figures 4 to 6, the passages that serve as the flow paths for the electrolyte S are shown with thick lines.

[0126]

[0127] As shown in Figure 4 and Table 1, in the first state of the circulation system, valves V1, V5, V9, V10, V14, and V18 are in the open state, and the remaining 12 valves are controlled to be in the closed state. The electrolyte S can circulate between the first tank 31 and the absorption tower 10, between the second tank 32 and the anode liquid chamber 231, and between the third tank 33 and the cathode liquid chamber 233.

[0128] In the first state, electrolyte S1 (KOH-KCl solution) is initially stored in the first tank 31, and electrolyte S2 (KHCO2) is stored in the second tank 32. 3 A KCl solution is stored in the first tank 31, and electrolyte S3 (KCl solution) is stored in the third tank 33. Electrolyte S1 in the first tank 31 becomes electrolyte S2 as the carbon dioxide absorption reaction in the absorption tower 10 progresses. Electrolyte S2 in the second tank 32 becomes electrolyte S3 as the carbon dioxide desorption reaction in the anode liquid chamber 231 progresses. Electrolyte S3 in the third tank 33 becomes electrolyte S1 as the KOH regeneration reaction in the cathode liquid chamber 233 progresses.

[0129] As shown in Figure 5 and Table 1, in the second state, of the on-off valves V1 to V18, valves V2, V6, V7, V11, V15, and V16 are in the open state, and the remaining 12 on-off valves are controlled to be in the closed state. The electrolyte S can circulate between the first tank 31 and the anode liquid chamber 231, between the second tank 32 and the cathode liquid chamber 233, and between the third tank 33 and the absorption tower 10.

[0130] In the second state, initially, electrolyte S2 is stored in the first tank 31, electrolyte S3 is stored in the second tank 32, and electrolyte S1 is stored in the third tank 33. The electrolyte S2 in the first tank 31 becomes electrolyte S3 as the carbon dioxide desorption reaction in the anode liquid chamber 231 progresses. The electrolyte S3 in the second tank 32 becomes electrolyte S1 as the KOH regeneration reaction in the cathode liquid chamber 233 progresses. The electrolyte S1 in the third tank 33 becomes electrolyte S2 as the carbon dioxide absorption reaction in the absorption tower 10 progresses.

[0131] As shown in Figure 6 and Table 1, in the third state, of the on-off valves V1 to V18, valves V3, V4, V8, V12, V13 and V17 are in the open state, and the remaining 12 on-off valves are controlled to be in the closed state. The electrolyte S can circulate between the first tank 31 and the cathode liquid chamber 233, between the second tank 32 and the absorption tower 10, and between the third tank 33 and the anode liquid chamber 231.

[0132] In the third state, initially, electrolyte S3 is stored in the first tank 31, electrolyte S1 is stored in the second tank 32, and electrolyte S2 is stored in the third tank 33. The electrolyte S3 in the first tank 31 becomes electrolyte S1 as the KOH regeneration reaction in the cathode liquid chamber 233 progresses. The electrolyte S1 in the second tank 32 becomes electrolyte S2 as the carbon dioxide absorption reaction in the absorption tower 10 progresses. The electrolyte S2 in the third tank 33 becomes electrolyte S3 as the carbon dioxide desorption reaction in the anode liquid chamber 231 progresses.

[0133] In the carbon dioxide concentrator 100, after setting the circulation system to a specific state, the electrolyte S is circulated for a certain period of time to allow the reaction of the electrolyte S to proceed sufficiently. After the reaction of the electrolyte S has proceeded sufficiently, the state of the circulation system is switched. By switching the circulation system, a new reaction can be carried out in the electrolyte S after a certain reaction has occurred.

[0134] The circulation system is preferably switched in the order of first state, second state, and third state. By switching the circulation system in the above order, a series of reactions including carbon dioxide absorption, desorption, and regeneration of electrolyte S can be carried out continuously. After switching the circulation system to the third state, it may be switched back to the first state to repeatedly switch between the series of states from the first state to the third state.

[0135] The circulation system can be switched based on the pH value of the electrolyte S measured by the pH sensor 8. The pH value of the electrolyte S changes in accordance with the progress of the reaction in reaction equation (4) above. If the reaction in which the chemical equilibrium in reaction equation (4) shifts to the right has not progressed sufficiently, the pH value of the electrolyte S in the anode chamber 231 will be relatively high, and the pH value of the electrolyte S in the cathode chamber 233 will be relatively low. If the reaction in which the chemical equilibrium in reaction equation (4) shifts to the right has progressed sufficiently, the pH value of the electrolyte S in the anode chamber 231 will be relatively low, and the pH value of the electrolyte S in the cathode chamber 233 will be relatively high. The progress of the reaction can be estimated based on the pH value of the electrolyte S.

[0136] In particular, in the cathode liquid chamber 233, HCO3 -In contrast to the anode liquid chamber 231, where a buffering action occurs due to the absorption solution containing a large amount of , the pH value of the cathode liquid chamber 233 tends to fluctuate more easily in response to the degree of reaction. By measuring the pH value of the electrolyte S flowing into the cathode liquid chamber 233, the progress of the reaction can be grasped with greater accuracy.

[0137] In this embodiment, the control device 50 automatically switches the circulation system. The control device 50 stores in advance in its memory the pH threshold (described later), the switching sequence of the circulation system state, and the correspondence between the circulation system state and the open / closed state of each on-off valve V1 to V18.

[0138] During operation of the carbon dioxide concentrator 100, the control device 50 acquires the pH value of the electrolyte S in the cathode liquid chamber 233 via the pH sensor 8 at predetermined or appropriate time intervals. The control device 50 determines whether the acquired pH value is equal to or greater than a preset pH threshold. The pH threshold can be determined, for example, by considering the pH change of the electrolyte S associated with the regeneration of KOH.

[0139] If the control device 50 determines that the acquired pH value is equal to or greater than the pH threshold, it controls the on-off valves V1 to V18 to switch the state of the circulation system from the current state to the next state according to a preset switching sequence. The control device 50 switches, for example, from the first state to the second state, from the second state to the third state, or from the third state to the first state. The control device 50 refers to the correspondence between the state of the circulation system and the open / closed state of each on-off valve V1 to V18 and outputs a control signal to each on-off valve V1 to V18 instructing it to open / close according to the next state.

[0140] If the control device 50 determines that the acquired pH value is below the pH threshold, it does not switch the circulation system and maintains the current state. By continuing to circulate the electrolyte S until the pH value becomes equal to or above the pH threshold, the amount of unreacted electrolyte S can be reduced.

[0141] If the carbon dioxide concentrator 100 is equipped with multiple pH sensors 8 corresponding to multiple cathode liquid chambers 233, the control device 50 may determine whether the measured values ​​of all pH sensors 8 are equal to or greater than the pH threshold, or it may determine whether the measured values ​​of a predetermined number or more pH sensors 8 are equal to or greater than the pH threshold. The control device 50 may perform the above determination using the measured value of any one representative pH sensor 8 among the multiple pH sensors 8.

[0142] If the pH sensor 8 is installed inside the first to third tanks 31 to 33 or near their outlets, the control device 50 may perform the above determination using the measured value of the pH sensor 8 corresponding to the tank whose current circulation destination is the cathode liquid chamber 233. The current circulation destination of each tank can be identified based on the current switching state of the circulation system. Alternatively, the above determination may be performed using the measured value of each pH concentration sensor 8 corresponding to each tank. Different pH thresholds may be set for each circulation destination so that the above determination is performed considering the circulation destination of the electrolyte S of each tank.

[0143] The pH can be any value detected from the electrolyte S flowing through the carbon dioxide concentrator 100, or it can be a value detected from the electrolyte S flowing in a part other than the cathode liquid chamber 233. When the pH of the electrolyte S flowing through the anode liquid chamber 231 is measured by the pH sensor 8, the threshold determination described above is reversed. If the control device 50 determines that the pH value of the electrolyte S in the anode liquid chamber 231 is less than the pH threshold, it switches the state of the circulation system from the current state to the next state. If the control device 50 determines that the pH value of the electrolyte S in the anode liquid chamber 231 is equal to or greater than the pH threshold, it does not switch the circulation system and maintains the current state.

[0144] The switching of the circulation system may be performed manually. The control device 50 may, for example, receive a switching instruction from an operator that includes at least one of the switching timing or the state of the circulation system to be switched, and control the on / off valves V1 to V18 in accordance with the received switching instruction.

[0145] In the carbon dioxide concentrator 100, the flow rate per unit time of the electrolyte S circulating between the absorption tower 10 and the 100 may be different from the flow rate per unit time of the electrolyte S circulating between the anode liquid chamber 231 and the electrolyte S circulating between the cathode liquid chamber 233, or one or both. For example, in the first state of the circulation system, the flow rate per unit time of the electrolyte S circulating between the first tank 31 and the absorption tower 10 may be different from the flow rate per unit time of the electrolyte S circulating between the second tank 32 and the anode liquid chamber 231 and the electrolyte S circulating between the third tank 33 and the cathode liquid chamber 233, or one or both. The same applies in the second or third state of the circulation system.

[0146] The flow rate of the electrolyte S per unit time can be adjusted, for example, by varying the flow rates of pumps P1 to P3 and thereby varying the flow rate of the electrolyte S discharged from the first tank 31 to the third tank 33. The flow rate of the electrolyte S per unit time may also be adjusted by adjusting the opening degree of each on-off valve provided on the circulation path.

[0147] The passage configuration of the carbon dioxide concentrator 100 can be any appropriate passage configuration as long as the flow path of the electrolyte S can be switched so that the storage destination and the circulation destination of the electrolyte S are different from each other, as described above. For example, each passage 61-63, 65-67 may be equipped with a switching valve that can switch the flow path of the electrolyte S in multiple directions, and the flow path of the electrolyte S may be switched by controlling the switching direction of the switching valve. The absorption tower 10, anode liquid chamber 231, and cathode liquid chamber 233 may each have a passage whose upstream end is connected to a discharge port and whose downstream end branches to correspond to the first tank 31 to the third tank 33, respectively. The absorption tower 10, anode liquid chamber 231, and cathode liquid chamber 233 may each have a passage whose downstream end is connected to a supply port and whose upstream end branches to correspond to the first tank 31 to the third tank 33, respectively.

[0148] Switching the electrolyte S circulation system can also be done by replacing (changing) the tank 3 that stores the electrolyte S supplied to the circulation destination. For example, first, the first tank 31 is connected to the absorption tower 10, the second tank 32 is connected to the anode liquid chamber 231, and the third tank 33 is connected to the cathode liquid chamber 233, and the electrolyte S is circulated in each tank while it is connected. Then, the tanks are changed. For example, the third tank 33 is connected to the absorption tower 10, the first tank 31 is connected to the anode liquid chamber 231, and the third tank 33 is connected to the cathode liquid chamber 233. The circulation system is switched by circulating the electrolyte S in each tank while it is connected.

[0149] In this embodiment, the carbon dioxide concentrator 100 is configured to have three tanks corresponding to three circulation destinations, and to circulate and supply electrolyte S separately to each circulation destination. Alternatively, the carbon dioxide concentrator 100 may supply electrolyte S in a circulating manner between at least one tank and one circulation destination, and supply electrolyte S in a non-circulating manner between the other tanks and other circulation destinations. The carbon dioxide concentrator 100 may have one or two tanks corresponding to one or two circulation destinations. If it has one or two tanks, electrolyte S discharged from other circulation destinations may be supplied to circulation destinations that do not receive electrolyte S from a tank.

[0150] In each embodiment, a conductivity meter may be used instead of the pH sensor 8 to switch the circulation system. The circulation system can be switched by considering the electrical conductivity, which changes in accordance with the degree of reaction of the electrolyte. The electrical conductivity of the electrolyte flowing through the anode liquid chamber 231 and the cathode liquid chamber 233 changes in accordance with the degree of reaction of the electrolyte in the liquid chambers. By measuring the electrical conductivity, the degree of reaction of the electrolyte in the liquid chambers can be estimated. By using electrical conductivity, which shows a linear change in accordance with the degree of reaction of the electrolyte, the degree of reaction can be estimated easily and accurately.

[0151] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. 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 claims and equivalents thereof. The sequences shown in each embodiment are not limiting, and within a consistent scope, each processing step may be performed in a different order, and multiple processes may be performed in parallel. The processing entities for each process are not limiting, and within a consistent scope, the processing of each device may be performed by other devices.

[0152] The matters described in each embodiment can be combined with each other. Furthermore, the independent and dependent claims described in the claims can be combined with each other in any combination, regardless of the form of reference. In addition, the claims use a form in which claims referencing two or more other claims (multi-claim form), but are not limited to this. A form in which multi-claims referencing at least one multi-claim (multi-multi-claim) may also be used.

[0153] 100 Carbon dioxide concentrator 10 Absorption tower (absorption section) 20 Concentration section 22 Anode 231 Anode liquid chamber 232 Electrolyte membrane 233 Cathode liquid chamber 24 Cathode 3 Storage section 31 First tank (first storage section) 32 Second tank (second storage section) 33 Third tank (third storage section) 40 Gas-liquid separation section 50 Control device 6 Passage 8 pH sensor

Claims

1. A carbon dioxide concentration apparatus comprising: an absorption unit for absorbing carbon dioxide into an electrolyte; an electrochemical cell for generating carbon dioxide gas from the electrolyte; and a storage unit for storing the electrolyte, wherein the electrochemical cell comprises an anode, an anode liquid chamber, an electrolyte membrane, a cathode liquid chamber, and a cathode, and the storage unit includes at least one of a first storage unit for storing the electrolyte circulating with the absorption unit, a second storage unit for storing the electrolyte circulating with the anode liquid chamber, and a third storage unit for storing the electrolyte circulating with the cathode liquid chamber.

2. The carbon dioxide concentration apparatus according to claim 1, comprising a circulation system that can switch between a first state in which the electrolyte of the first storage unit is circulated between the absorption unit and the first storage unit, a second state in which the electrolyte of the first storage unit is circulated between the anode liquid chamber and the first storage unit and at least one third state in which the electrolyte of the first storage unit is circulated between the cathode liquid chamber and the first storage unit.

3. A carbon dioxide concentration apparatus according to claim 1 or 2, comprising a circulation system that can switch between a first state in which the electrolyte is circulated between the absorption unit and the first storage unit, between the anode liquid chamber and the second storage unit, and between the cathode liquid chamber and the third storage unit; a second state in which the electrolyte is circulated between the absorption unit and the third storage unit, between the anode liquid chamber and the first storage unit, and between the cathode liquid chamber and the second storage unit; and at least one third state in which the electrolyte is circulated between the absorption unit and the second storage unit, between the anode liquid chamber and the third storage unit, and between the cathode liquid chamber and the first storage unit.

4. The carbon dioxide concentration apparatus according to claim 2, wherein the circulation system is switched based on the pH of the electrolyte.

5. The carbon dioxide concentration apparatus according to claim 2, wherein the circulation system is switched in the order of the first state, the second state, and the third state.

6. The carbon dioxide concentration apparatus according to claim 5, wherein after switching the circulation system to the third state, the circulation system is switched back to the first state.

7. The carbon dioxide concentration apparatus according to claim 1 or claim 2, further comprising a sensor for measuring the pH of the electrolyte.

8. The carbon dioxide concentration apparatus according to claim 7, wherein the sensor is provided inside at least one of the cathode liquid chamber, the first storage section, the second storage section, and the third storage section, or on the inside near the end of a passage connected to at least one of the cathode liquid chamber, the first storage section, the second storage section, and the third storage section.

9. The carbon dioxide concentration apparatus according to claim 1 or claim 2, wherein the flow rate of the electrolyte circulating with the absorption section is different from the flow rate of the electrolyte circulating with the anode liquid chamber or the cathode liquid chamber.

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