Method and apparatus for releasing carbon dioxide dissolved in alkaline solution, and method and system for recovering carbon dioxide from exhaust gas

Abstract

Disclosed is a method for releasing carbon dioxide dissolved in a first alkaline solution, the method including: a step of preparing an anode electrode, a cathode electrode, and a cation exchange membrane that is disposed between the anode electrode and the cathode electrode, wherein the anode electrode includes a first catalyst and a first gas diffusion layer, and the cathode electrode includes a second catalyst, a second gas diffusion layer, and a water repellent layer; a step of filling the first alkaline solution, in which carbon dioxide is dissolved, between the anode electrode and the cation exchange membrane; a step of filling a second alkaline solution between the cation exchange membrane and the cathode electrode; a step of supplying a hydrogen-containing gas to the anode electrode at a flow rate of more than 0 cm / minute per electrode area of 1 cm2; and a step of supplying an oxygen-containing gas to the carbon dioxide at a flow rate of more than 0 cm / minute per electrode area of 1 cm2.

Description

Method and apparatus for releasing carbon dioxide dissolved in alkaline solution, and method and system for recovering carbon dioxide from exhaust gas

[0001] The present disclosure relates to a method and apparatus for releasing carbon dioxide dissolved in an alkaline solution, and a method and system for recovering carbon dioxide from flue gas.

[0002] The steel industry has set a goal of virtually eliminating carbon dioxide emissions from the steelmaking process by 2050. Therefore, a technology capable of highly efficient carbon dioxide capture from flue gas is essential. The most promising technology is the chemical absorption method using an amine absorbent, and demonstration studies are being conducted at power plants and other facilities. This method selectively dissolves carbon dioxide from flue gas into a solvent, and the solvent is heated in a capture tower, for example, to release the carbon dioxide (the released carbon dioxide can be stored or effectively utilized, for example). However, the capture tower requires a large amount of thermal energy, and the materials inside the tower are exposed to high-temperature, highly alkaline amine vapor, which poses a major problem of corrosion.

[0003] As an alternative to the chemical absorption method, electrodialysis using electrical energy, as described in Non-Patent Document 1, is being considered. With this method, carbon dioxide dissolved in an alkaline solution can be electrochemically released, and the equipment used is not exposed to high-temperature, strongly alkaline vapor, for example. However, on the anode electrode side, oxygen (gas bubbles) are generated along with hydrogen ions in the water electrolysis reaction shown in the following formula (1), which results in high electrical resistance and a significant increase in power consumption, as well as the possibility of physical electrode destruction. H ２ O → 2H ＋ +1 / 2O ２ +2e － ...(1)

[0004] Patent Document 1 discloses a method for suppressing the generation of oxygen bubbles as described above. According to this method, the generation of oxygen bubbles is suppressed by supplying hydrogen to the anode electrode, thereby replacing the reaction shown in formula (1) above with the reaction shown in formula (2) below. ２ →2H＋ +2e － ...(2)

[0005] JP 2024-31641 A

[0006] Ikuo Taniguchi, "Innovative Energy-Saving CO2 Separation and Capture Method Using Electrodialysis Technology," Journal of the Society of Seawater Science and Technology of Japan, 2015, Vol. 69, No. 6, pp. 363-372

[0007] The inventors have conducted research and found that even with the method disclosed in Patent Document 1, depending on the required level, the reduction in power consumption for recovering carbon dioxide may not be sufficient, and there is room for improvement.

[0008] The present invention has been made in view of the above circumstances, and one of its objects is to provide a method for releasing carbon dioxide dissolved in an alkaline solution, which method can reduce power consumption compared to conventional methods, an apparatus therefor, and a method for recovering carbon dioxide from exhaust gas and a system therefor.

[0009] Aspect 1 of the present invention provides a method for producing a cation exchange membrane comprising the steps of: preparing an anode electrode, a cathode electrode, and a cation exchange membrane disposed between the anode electrode and the cathode electrode, wherein the anode electrode includes a first catalyst and a first gas diffusion layer; and the cathode electrode includes a second catalyst, a second gas diffusion layer, and a water-repellent layer; filling a first alkaline liquid having carbon dioxide dissolved therein between the anode electrode and the cation exchange membrane; filling a second alkaline liquid between the cation exchange membrane and the cathode electrode; and filling a second alkaline liquid between the anode electrode and the cation exchange membrane with an electrode area of ​​1 cm. ２ supplying a hydrogen-containing gas at a flow rate of more than 0 cm / min per electrode area of ​​1 cm to the cathode electrode; ２ supplying an oxygen-containing gas at a flow rate of more than 0 cm / min per unit volume of the first alkaline liquid.

[0010] Aspect 2 of the present invention is the method according to aspect 1, further comprising the step of applying a voltage between the anode electrode and the cathode electrode.

[0011] Aspect 3 of the present invention is the method according to aspect 1 or 2, wherein the cathode electrode includes a plurality of water-repellent layers.

[0012] A fourth aspect of the present invention is a method for recovering carbon dioxide from flue gas, comprising: dissolving carbon dioxide in flue gas in a first alkaline liquid; and releasing the carbon dioxide dissolved in the first alkaline liquid by the method according to any one of the first to third aspects.

[0013] Aspect 5 of the present invention provides a fuel cell comprising an anode electrode, a cathode electrode, and a cation exchange membrane disposed between the anode electrode and the cathode electrode, wherein the anode electrode comprises a first catalyst and a first gas diffusion layer, and the cathode electrode comprises a second catalyst, a second gas diffusion layer, and a water-repellent layer, a first filling section capable of filling a first alkaline liquid having carbon dioxide dissolved therein between the anode electrode and the cation exchange membrane, a second filling section capable of filling a second alkaline liquid between the cation exchange membrane and the cathode electrode, and a 1 cm thick electrode layer on the anode electrode. ２ a hydrogen-containing gas supply unit capable of supplying a hydrogen-containing gas at a flow rate of more than 0 cm / min per electrode; ２ an oxygen-containing gas supply unit capable of supplying an oxygen-containing gas at a flow rate exceeding 0 cm / min per unit volume.

[0014] A sixth aspect of the present invention is the device according to the fifth aspect, further comprising a power supply capable of applying a voltage between the anode electrode and the cathode electrode.

[0015] Aspect 7 of the present invention is the device according to aspect 5 or 6, wherein the cathode electrode includes a plurality of water-repellent layers.

[0016] Aspect 8 of the present invention is a system for recovering carbon dioxide from exhaust gas, comprising: a carbon dioxide dissolving section that can be filled with a first alkaline liquid and that can dissolve carbon dioxide in exhaust gas into the first alkaline liquid; and the device according to any one of Aspects 5 to 7, wherein the first alkaline liquid in which carbon dioxide has been dissolved in the device can be supplied from the carbon dioxide dissolving section.

[0017] According to an embodiment of the present invention, it is possible to provide a method for releasing carbon dioxide dissolved in an alkaline solution, which can reduce power consumption compared to conventional methods, an apparatus therefor, and a method for recovering carbon dioxide from exhaust gas and a system therefor.

[0018] 1 is an example of an apparatus 1 (schematic diagram) for releasing carbon dioxide dissolved in an alkaline solution according to an embodiment of the present invention; FIG. 2 is an example of a system 100 (schematic diagram) for recovering carbon dioxide from flue gas according to an embodiment of the present invention; FIG. 3 is a flowchart of an example of a method for recovering carbon dioxide from flue gas according to an embodiment of the present invention; and FIG. 4 shows the change in voltage before and after oxygen supply in Test No. 1.

[0019] The inventors have investigated the effect of carbon dioxide (CO ) dissolved in an alkaline solution. ２ ) that can reduce power consumption compared to conventional methods. Patent Document 1 discloses that the reaction of the following formula (3) can occur on the cathode electrode side: ＋ +2e － →H ２ ...(3)

[0020] The present inventors have developed a cathode electrode with an electrode area of ​​1 cm , in order to promote the reaction represented by the following formula (4), which is more reactive than the reaction represented by the formula (3). ２ By supplying an oxygen-containing gas at a flow rate of more than 0 cm / min per ２ It was thought that the power consumption when emitting the ２ +2H ＋ +2e － →H ２ O... (4)

[0021] However, as a result of investigations by the present inventors, it was found that simply supplying an oxygen-containing gas to a cathode electrode including a catalyst and a gas diffusion layer does not sufficiently promote the reaction of the above formula (4). This is thought to be because water generated on the right side of formula (4) fills the inside of the cathode electrode (gas diffusion layer, etc.) and inhibits further reaction. Therefore, the present inventors considered providing a water-repellent layer that is more hydrophobic than the gas diffusion layer on the cathode electrode in order to remove the water. This prevents the water from filling the inside of the cathode electrode, thereby promoting the reaction of the above formula (4) and producing more CO than before. ２ Furthermore, the power consumption when emitting the ２ By optimizing the oxygen flow rate, current value, device structure, etc., it has become possible to extract electricity (i.e., generate electricity) without applying voltage. Note that the above mechanism does not limit the technical scope of the embodiments of the present invention.

[0022] The following provides details of each requirement stipulated by the embodiment of the present invention.

[0023] FIG. 1 shows a graph of carbon dioxide (CO ) dissolved in an alkaline solution according to an embodiment of the present invention. ２ 1 shows an example of an apparatus 1 (hereinafter also referred to as "carbon dioxide releasing apparatus 1") for releasing carbon dioxide. As shown in FIG. 1, the carbon dioxide releasing apparatus 1 includes an anode electrode 2, a cathode electrode 3, a cation exchange membrane 4 disposed between the anode electrode 2 and the cathode electrode 3, and a power supply 5 capable of applying a voltage between the anode electrode 2 and the cathode electrode 3 as needed. Furthermore, if the power supply 5 is not provided, for example, the anode electrode 2 and the cathode electrode 3 may be electrically connected directly at the power supply 5, or other electronic components such as an electric resistor may be inserted instead of the power supply 5.

[0024] The anode 2 includes a first catalyst and a first gas diffusion layer 2a. As an example of the anode 2, as shown in FIG. 1, it may include a first catalyst layer 2b including the first catalyst and a first gas diffusion layer 2a. As another example of the anode 2, instead of the first catalyst layer 2b / first gas diffusion layer 2a shown in FIG. 1, a configuration in which the first catalyst is supported in the first gas diffusion layer 2a may be used. Furthermore, as shown in FIG. 1, the anode 2 may include a proton exchange membrane 2c.

[0025] The cathode electrode 3 includes a second catalyst, a second gas diffusion layer 3a, and a water-repellent layer 3c. As shown in FIG. 1 , one example of the cathode electrode 3 may include a second catalyst layer 3b including the second catalyst, a water-repellent layer 3c, and a second gas diffusion layer 3a. Another example of the cathode electrode 3 may include, from the cation exchange membrane 4 side, a water-repellent layer 3c and a layer in which the second catalyst is supported in the second gas diffusion layer 3a, instead of the second catalyst layer 3b / water-repellent layer 3c / second gas diffusion layer 3a shown in FIG. 1 . Another example of the cathode electrode 3 may include, from the cation exchange membrane 4 side, a layer in which the second catalyst is supported in the water-repellent layer 3c and a second gas diffusion layer 3a, instead of the second catalyst layer 3b / water-repellent layer 3c / second gas diffusion layer 3a shown in FIG. 1 . 1 , the cathode electrode 3 may include, from the cation exchange membrane 4 side, a layer in which a second catalyst is supported in the second gas diffusion layer 3a, and a water-repellent layer 3c. Alternatively, the cathode electrode 3 may include an appropriate combination of layers included in these configurations.

[0026] The carbon dioxide release device 1 comprises a first filling section 10 capable of filling a first alkaline solution 6 containing dissolved carbon dioxide between the anode electrode 2 and the cation exchange membrane 4, a second filling section 11 capable of filling a second alkaline solution 7 between the cation exchange membrane 4 and the cathode electrode 3, and a second filling section 12 capable of filling a second alkaline solution 7 between the anode electrode 2 and the cation exchange membrane 4 with an electrode area of ​​1 cm. ２ a hydrogen-containing gas supply unit 8 capable of supplying a hydrogen-containing gas 8a at a flow rate exceeding 0 cm / min per unit area; and a cathode electrode 3 having an electrode area of ​​1 cm. ２and an oxygen-containing gas supply unit 9 capable of supplying an oxygen-containing gas 9a at a flow rate exceeding 0 cm / min per unit volume. The hydrogen-containing gas supply unit 8 may include, for example, a hydrogen-containing gas filling unit (not shown) and a first mass flow controller (not shown) capable of controlling the hydrogen-containing gas flow rate. The oxygen-containing gas supply unit 9 may include an oxygen-containing gas filling unit (not shown) and a second mass flow controller (not shown) capable of controlling the oxygen-containing gas flow rate.

[0027] The method for releasing carbon dioxide dissolved in an alkaline solution according to an embodiment of the present invention can be carried out using the device 1. The method includes the steps of (a) preparing an anode electrode 2, a cathode electrode 3, and a cation exchange membrane 4 disposed between the anode electrode 2 and the cathode electrode 3, (b) filling a first alkaline solution 6 having carbon dioxide dissolved therein between the anode electrode 2 and the cation exchange membrane 4, (c) filling a second alkaline solution 7 between the cation exchange membrane 4 and the cathode electrode 3, and (d) disposing a 1 cm2 electrode on the anode electrode 2. ２ (e) supplying a hydrogen-containing gas 8a to the cathode 3 at a flow rate of more than 0 cm / min per electrode area of ​​1 cm ２ The method includes a step of supplying an oxygen-containing gas 9a at a flow rate of more than 0 cm / min per saturation gas, and, if necessary, a step (f) of applying a voltage between the anode electrode 2 and the cathode electrode 3. In step (a), the anode electrode 2 includes a first catalyst and a first gas diffusion layer 2a, and the cathode electrode 3 includes a second catalyst, a second gas diffusion layer 3a, and a water-repellent layer 3c. The above method makes it possible to reduce power consumption compared to conventional methods when releasing carbon dioxide dissolved in an alkaline solution. Each step will be described in detail below.

[0028] <(a) Step of Preparing the Anode 2, the Cathode 3, and the Cation Exchange Membrane 4 Disposed Between the Anode 2 and the Cathode 3> The anode 2 includes a first catalyst and a first gas diffusion layer 2a. As an example of the anode 2, as shown in FIG. 1 , the anode 2 may include a first catalyst layer 2b containing the first catalyst and a first gas diffusion layer 2a. In this case, the first gas diffusion layer 2a and the first catalyst layer 2b do not need to be in contact with each other, for example, by having another layer therebetween. However, contact between the first gas diffusion layer 2a and the first catalyst layer 2b is preferable because it makes it easier for the hydrogen-containing gas 8a to reach the first catalyst layer 2b.

[0029] The first gas diffusion layer 2a is a layer that is electrically conductive and can efficiently diffuse the hydrogen-containing gas 8a into the first catalyst (or the first catalyst layer 2b containing the first catalyst). The first gas diffusion layer 2a can be formed, for example, of a known gas diffusion layer used in fuel cells. For example, the material forming the first gas diffusion layer 2a is preferably a conductive porous membrane, and can be, for example, a conductive porous carbon material such as carbon paper, carbon cloth, or carbon felt, or a porous metal material. At least a portion of the first gas diffusion layer 2a may be imparted with water repellency. The water repellency treatment can be performed using, for example, a fluorine-based resin (e.g., polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, or polyvinylidene fluoride). The first gas diffusion layer 2a to which water repellency has been imparted may be the same as or different from the water-repellent layer 3c described below.

[0030] The first catalyst (or the first catalyst layer 2b containing the first catalyst) is a catalyst that promotes the reaction of the following formula (2), that is, promotes the ionization of hydrogen: ２ →2H ＋ +2e － ...(2) The first catalyst can be a noble metal catalyst such as gold, silver, platinum, iridium, osmium, palladium, rhodium, or ruthenium. Alternatively, a non-noble metal catalyst such as iron, cobalt, nickel, titanium, manganese, copper, aluminum, chromium, vanadium, molybdenum, tungsten, gallium, or lead, or an alloy of these metals, or an oxide of these metals or alloys, can also be used.

[0031] The first catalyst may be supported on a conductive support, which may be conductive carbon particles such as carbon black (e.g., acetylene black, furnace black, etc.), graphite, activated carbon, carbon fiber, carbon nanotubes, carbon nanowires, etc.

[0032] The first catalyst layer 2b may contain an ionomer that functions as a binder for the first catalyst (and the conductive support) and also as a proton conduction path. The ionomer may be a perfluoroalkyl sulfonic acid resin such as Nafion (registered trademark) manufactured by DuPont.

[0033] The ratio of the catalyst and the conductive carrier in the first catalytic layer 2b is preferably 10 to 90 mass %, more preferably 30 to 70 mass %. The amount of the first catalyst supported is 0.1 mg / cm ２ The upper limit is not particularly limited, but is preferably 2.0 mg / cm ２ It can be the following:

[0034] As another example of the anode 2, a configuration in which a first catalyst is supported in the first gas diffusion layer 2a (hereinafter also referred to as a "first catalyst-containing gas diffusion layer") may be used instead of the first catalyst layer 2b / first gas diffusion layer 2a shown in Fig. 1. The proportion of the first catalyst in the first catalyst-containing gas diffusion layer is preferably 10 to 90 mass%, more preferably 30 to 70 mass%.

[0035] The anode electrode 2 may include a proton exchange membrane 2c as shown in FIG. 1. The anode electrode 2 may include, from the cation exchange membrane 4 side as shown in FIG. 1, a proton exchange membrane 2c, a first catalyst layer 2b, and a first diffusion layer 2a, in this order. Alternatively, the anode electrode 2 may include a proton exchange membrane 2c and a first catalyst-containing gas diffusion layer, in this order. By bringing the first catalyst into contact with the first alkaline liquid 6 via the proton exchange membrane 2c, for example, hydrogen ions generated at the first catalyst can react with carbonate ions at a location farther away from the first catalyst, thereby releasing carbon dioxide as shown in the following formula (5): CO ３ ２－ +2H＋ →H ２ O+CO ２ ...(5) As the proton exchange membrane 2c, a known material can be used, for example, a perfluoroalkyl sulfonic acid resin such as Nafion (registered trademark) manufactured by DuPont.

[0036] The cathode electrode 3 includes a second catalyst, a second gas diffusion layer 3a, and a water-repellent layer 3c. As shown in Fig. 1, one example of the cathode electrode 3 may include a second catalyst layer 3b including the second catalyst, a water-repellent layer 3c, and a second gas diffusion layer 3a. In this case, the second catalyst layer 3b, the water-repellent layer 3c, and the second gas diffusion layer 3a do not need to be in contact with each other, for example, by providing another layer therebetween. However, it is preferable that they are in contact with each other, because this makes it easier for the oxygen-containing gas 9a to reach the second catalyst layer 3b.

[0037] The second gas diffusion layer 3a is a layer that is electrically conductive and can efficiently diffuse the oxygen-containing gas 9a into the second catalyst (or the second catalyst layer 3b containing the second catalyst). The second gas diffusion layer 3a can be formed of, for example, a known gas diffusion layer used in fuel cells. For example, the material forming the second gas diffusion layer 3a is preferably a conductive porous membrane, and can be, for example, a conductive porous carbon material such as carbon paper, carbon cloth, or carbon felt, or a porous metal material.

[0038] The second catalyst (or the second catalyst layer 3b containing it) is a catalyst that promotes the reaction of the following formula (4), that is, promotes the fuel cell reaction (or the water production reaction): ２ +2H ＋ +2e － →H ２ O (4) As the second catalyst, those described above for the first catalyst can be mentioned.

[0039] The second catalyst may be supported on a conductive support, such as the conductive support on which the first catalyst can be supported.

[0040] The second catalyst layer 3b may contain an ionomer that functions as a binder for the second catalyst (and the conductive carrier) and also as a proton conduction path. The ionomer may be a perfluoroalkyl sulfonic acid resin such as Nafion (registered trademark) manufactured by DuPont.

[0041] The ratio of the second catalyst and the conductive carrier in the second catalyst layer 3b is preferably 10 to 90 mass %, more preferably 30 to 70 mass %. The amount of the second catalyst supported is 0.1 mg / cm. ２ The upper limit is not particularly limited, but is preferably 2.0 mg / cm ２ It can be the following:

[0042] The water-repellent layer 3c is a layer having higher hydrophobicity (water repellency) than the second gas diffusion layer 3a. This allows water generated on the right side of the above formula (4) to be effectively transferred, for example, to the second alkaline liquid 7, thereby suppressing adverse effects on the electrode reaction. Whether the water-repellent layer 3c is more hydrophobic than the second gas diffusion layer 3a can be confirmed, for example, by measuring the water contact angle. The water contact angle of the water-repellent layer 3c is preferably greater than 90°, more preferably 100° or greater, even more preferably 110° or greater, and even more preferably 120° or greater. The water-repellent layer 3c can be formed, for example, from a known water-repellent layer (water-repellent microporous layer) used in fuel cells. For example, a conductive porous membrane that has been subjected to a water-repellent treatment is preferred as the material for the water-repellent layer 3c. The conductive porous membrane can be, for example, a conductive porous carbon material such as carbon paper, carbon cloth, or carbon felt, or a porous metal material. The water-repellent treatment can be performed using, for example, a fluorine-based resin (e.g., polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride). The amount of the fluorine-based resin is preferably 1 to 50 mass % with respect to the total mass of the water-repellent layer 3c. The pore size of the water-repellent layer 3c is preferably smaller than that of the second gas diffusion layer 3a. This makes it easier to prevent a large amount of water from penetrating into the cathode electrode 3.

[0043] The cation exchange membrane 4 is disposed between the anode electrode 2 and the cathode electrode 3. The cation exchange membrane 4 is capable of transferring excess cations 6d in the first alkaline solution 6 into the second alkaline solution 7. The cation exchange membrane 4 may be made of a known material, such as a known resin to which anionic functional groups such as sulfonic acid groups, carboxylic acid groups, or phosphate groups have been introduced. Commercially available products that can be used include Nafion (registered trademark) manufactured by DuPont and NeoSepta (registered trademark) manufactured by Astom Corporation.

[0044] The means for preparing the anode electrode 2, the cathode electrode 3, and the cation exchange membrane 4 disposed between the anode electrode 2 and the cathode electrode 3 is not particularly limited, and for example, a commercially available general-purpose product may be used, or other products may be used.

[0045] <(b) Step of Filling the First Alkaline Liquid 6 Having Dissolved Carbon Dioxide Between the Anode Electrode 2 and the Cation Exchange Membrane 4> In step (e) or (f) described below, the first alkaline liquid 6 having dissolved carbon dioxide is filled between the anode Electrode 2 and the cation exchange membrane 4 (first filling section 10) so as to enable the reaction of the above formula (5) on the anode Electrode 2 side. As a filling method, for example, the first alkaline liquid 6 may be supplied by a pump or the like so as to fill at least a part of the first filling section 10. Note that the carbon dioxide dissolved in the first alkaline liquid 6 converts into carbonate ions (CO ３ ２－ ) can be formed. The first alkaline liquid 6 before carbon dioxide dissolution (i.e., first alkaline liquid 6a described later) is not particularly limited, but may be, for example, an aqueous solution of an alkali metal hydroxide (MOH: M is an alkali metal), or an aqueous solution of NaOH or KOH. The concentration of the solute (e.g., MOH) of the first alkaline liquid 6 is not particularly limited, but may be, for example, 0.1 to 10 mol / L. For example, when the solute is MOH, the first alkaline liquid 6 in which carbon dioxide is dissolved (i.e., first alkaline liquid 6b described later) will be MHCO ３ and / or M ２ CO ３ The solution may be an aqueous solution of

[0046] <(c) Step of Filling the Second Alkaline Liquid 7 Between the Cation Exchange Membrane 4 and the Cathode Electrode 3> In step (e) or (f) described below, the second alkaline liquid 7 is filled between the cation exchange membrane 4 and the cathode Electrode 3 (second filled section 11) so as to transfer excess cations 6d in the first alkaline liquid 6 to the second alkaline liquid 7 through the cation exchange membrane 4. For example, the second alkaline liquid 7 may be supplied using a pump or the like so as to fill at least a portion of the second filled section 11. The second alkaline liquid 7 is not particularly limited, but like the first alkaline liquid 6, it may be, for example, an aqueous solution of an alkali metal hydroxide (MOH, where M is an alkali metal), such as an aqueous solution of NaOH or KOH. The solute of the second alkaline liquid 7 may be the same as or different from the solute of the first alkaline liquid 6; however, it is preferable that the solutes are the same from the viewpoints of ease of material procurement and management, etc. Furthermore, the concentration of the solute (e.g., MOH) in the second alkaline liquid 7 is preferably lower than the concentration of the solute in the first alkaline liquid 6. This can promote the migration of excess cations 6d in the first alkaline liquid 6 to the second alkaline liquid 7. The carbon dioxide concentration (carbonate ion concentration) in the second alkaline liquid 7 can be lower than that in the first alkaline liquid 6, and for example, the concentration in the second alkaline liquid 7 can be approximately zero. For example, the first alkaline liquid 6 after carbon dioxide release (i.e., the first alkaline liquid 6c described below) may be used as the second alkaline liquid 7.

[0047] <(d) Step of Supplying Hydrogen-Containing Gas 8a to Anode Electrode 2> In step (e) or (f) described below, a hydrogen-containing gas 8a is supplied to the anode electrode 2 with an electrode area of ​​1 cm 2 so as to enable the reaction of the above formula (2). ２The hydrogen-containing gas 8a is supplied at a flow rate of more than 0 cm / min per sieve. The flow rate of the hydrogen-containing gas 8a is preferably 0.1 cm / min or more, more preferably 0.5 cm / min or more, and even more preferably 1.0 cm / min or more. The upper limit is not particularly limited, but may be, for example, 20 cm / min or less. The hydrogen gas content in the hydrogen-containing gas 8a may be, for example, 1 vol% or more, 10 vol% or more, 20 vol% or more, or 50 vol% or more. The hydrogen-containing gas 8a may be a gas consisting of hydrogen (and an impurity gas), or may be a mixed gas of hydrogen with an inert gas and / or air.

[0048] <(e) Step of Supplying Oxygen-Containing Gas 9a to Cathode Electrode 3> In this step or in step (f) described later, the cathode electrode 3 is supplied with an oxygen-containing gas 9a having an electrode area of ​​1 cm 2 so as to enable the reaction of the above formula (4). ２ The oxygen-containing gas 9a is supplied at a flow rate of more than 0 cm / min per CO 2 . The flow rate of the oxygen-containing gas 9a is preferably 0.1 cm / min or more, more preferably 0.5 cm / min or more, and even more preferably 1.0 cm / min or more. ２ The power consumption when discharging the oxygen can be further reduced. The upper limit is not particularly limited, but may be, for example, 20 cm / min or less. The oxygen gas content in the oxygen-containing gas 9a may be, for example, 1 vol% or more, 10 vol% or more, 20 vol% or more, or 50 vol% or more. The oxygen-containing gas 9a may be a gas containing oxygen (and an impurity gas), a mixed gas of oxygen and an inert gas, air, or the like.

[0049] <Optional (f) Step of applying a voltage between the anode electrode 2 and the cathode electrode 3> If necessary, a voltage is applied between the anode electrode 2 and the cathode electrode 3 by the power supply 5. The voltage value can be adjusted appropriately according to the desired amount of carbon dioxide recovered (current value). As in the examples described later, ２ By optimizing the oxygen flow rate, current value, device structure, etc., it is possible to extract electricity (i.e., generate electricity) without applying voltage.

[0050] The carbon dioxide release method according to the embodiment of the present invention may include other steps within the scope of achieving its object. Furthermore, the carbon dioxide release device 1 according to the embodiment of the present invention may include other configurations within the scope of achieving its object.

[0051] A method for recovering carbon dioxide from exhaust gas according to an embodiment of the present invention includes the method for releasing carbon dioxide dissolved in an alkaline solution according to the embodiment of the present invention described above, and specifically includes the steps of dissolving carbon dioxide from exhaust gas in a first alkaline solution and releasing the carbon dioxide dissolved in the first alkaline solution by the above-described method. The recovery method will be described in detail below.

[0052] FIG. 2 shows an example of a system 100 for recovering carbon dioxide from flue gas (hereinafter also referred to as the "carbon dioxide recovery system 100") according to an embodiment of the present invention. As shown in FIG. 2, the carbon dioxide recovery system 100 includes a carbon dioxide release device 1 and a carbon dioxide dissolver 13 capable of dissolving carbon dioxide in flue gas 12 in a first alkaline liquid 6 (hereinafter, the first alkaline liquid 6 before dissolving carbon dioxide will be referred to as the "first alkaline liquid 6a," the first alkaline liquid 6b after dissolving carbon dioxide will be referred to as the "first alkaline liquid 6b," and the first alkaline liquid 6c after releasing carbon dioxide). Furthermore, the carbon dioxide recovery system 100 can supply the first alkaline liquid 6b, in which carbon dioxide has been dissolved by the carbon dioxide dissolver 13, between the anode electrode 2 and the cation exchange membrane 4, for example, by a pump. The carbon dioxide recovery system 100 can dissolve carbon dioxide in the flue gas 12 in the alkaline liquid and release the carbon dioxide using the carbon dioxide release device 1, thereby recovering carbon dioxide from the flue gas and further reducing power consumption during carbon dioxide release.

[0053] The carbon dioxide capture system 100 shown in FIG. 2 is capable of repeatedly capturing carbon dioxide from exhaust gas. The carbon dioxide capture system 100 will be described in more detail below. The carbon dioxide capture system 100 includes a carbon dioxide separation unit 14 that separates and captures carbon dioxide 12a from a gas-liquid mixture containing a first alkaline liquid 6c after carbon dioxide release and the released carbon dioxide 12a, and an alkaline liquid regeneration unit 15 that can regenerate the first alkaline liquid 6c after carbon dioxide release as a second alkaline liquid 7, for example, by adding a solute 7a of the second alkaline liquid. The carbon dioxide capture system 100 can also supply the second alkaline liquid 7 regenerated in the alkaline liquid regeneration unit 15 between the cation exchange membrane 4 and the cathode electrode 3, for example, by a pump. The second alkaline liquid 7 filled between the cation exchange membrane 4 and the cathode electrode 3 can be adjusted to the first alkaline liquid 6a, for example, by adding an appropriate solute (not shown), and then supplied to the carbon dioxide dissolution unit 13.

[0054] 3 shows a flowchart of an example of a method for recovering carbon dioxide from flue gas using the carbon dioxide recovery system 100. First, in step S1, the carbon dioxide dissolver 13 dissolves carbon dioxide in the flue gas 12 in the first alkaline liquid 6a.

[0055] In step S2, a first alkaline liquid 6b having carbon dioxide dissolved therein is filled between the anode electrode 2 and the cation exchange membrane 4 of the device 1. In step S3, a second alkaline liquid 7 is supplied from the alkaline liquid regenerating unit 15, thereby filling the second alkaline liquid 7 between the cathode electrode 3 and the cation exchange membrane 4 of the device 1. For convenience, step S3 is described after step S2, but step S3 may be performed before step S2 or simultaneously with step S2.

[0056] In step S4, for example, a hydrogen-containing gas supply unit 8 of the device 1 supplies a hydrogen-containing gas having an electrode area of ​​1 cm to the anode electrode 2. ２ supplying a hydrogen-containing gas 8a at a flow rate exceeding 0 cm / min per

[0057] In step S5, for example, an oxygen-containing gas supply unit 9 of the device 1 supplies an oxygen-containing gas having an electrode area of ​​1 cm to the cathode electrode 3.２ The oxygen-containing gas 9a is supplied at a flow rate of more than 0 cm / min per saturation gas. Although step S5 is described after step S4 for convenience, step S5 may be performed before step S4 or simultaneously with step S4. Furthermore, although steps S4 and / or S5 are described after steps S2 and S3 for convenience, they may be performed before steps S2 and / or S3 or simultaneously with steps S2 and / or S3.

[0058] If necessary, in step S6, a voltage is applied between the anode electrode 2 and the cathode electrode 3. In step S6, the reactions of the above formulas (2), (4), and (5) may occur. Furthermore, cations 6d in the first alkaline liquid 6b may migrate to the second alkaline liquid 7 through the cation exchange membrane 4. Note that in an embodiment in which no voltage is applied (i.e., step S6 is not performed), the reactions of the above formulas (2), (4), and (5), as well as the migration of cations 6d, may occur, for example, in step S5. In the carbon dioxide recovery system 100, the second alkaline liquid 7 after the migration (concentration) of cations 6d can be adjusted as the first alkaline liquid 6a by adding additional solute as necessary, and can be used as the first alkaline liquid 6a in step S1.

[0059] In step S7, the carbon dioxide 12a is separated in the carbon dioxide separation unit 14 from the gas-liquid mixture containing the first alkaline liquid 6c after the carbon dioxide has been released (and the cations 6d have been moved) and the released carbon dioxide 12a. This allows the carbon dioxide 12a to be recovered. Here, the first alkaline liquid 6c after the carbon dioxide has been released contains carbonate ions (CO ３ ２－ ) is consumed as carbon dioxide and cations 6d are transferred, so the liquid may have a low concentration of each ion (for example, close to water).

[0060] In step S8, the alkaline liquid regenerating unit 15 appropriately adds the solute 7a of the second alkaline liquid 7 to the first alkaline liquid 6c, thereby regenerating the second alkaline liquid 7. In the carbon dioxide recovery system 100, this regenerated second alkaline liquid 7 can be used as the second alkaline liquid 7 in step S3.

[0061] The method for capturing carbon dioxide from flue gas according to the embodiment of the present invention may include other steps as long as the object is achieved. Furthermore, the carbon dioxide capture system 100 according to the embodiment of the present invention may include other configurations as long as the object is achieved.

[0062] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0063] Example 1 A carbon dioxide release test was conducted using a carbon dioxide release device 1 as shown in Figure 1. The anode electrode 2 (first gas diffusion layer 2a / first catalyst layer 2b) of the device 1 was an anode electrode (gas diffusion layer / catalyst layer) of a JARI standard cell for a polymer electrolyte fuel cell (PEFC). Furthermore, a proton exchange membrane 2c (Nafion (registered trademark) NRE212, manufactured by Du Pont) was disposed (press-bonded) on the first catalyst layer 2b side of the anode electrode 2. The cathode electrode 3 (second catalyst layer 3b / water-repellent layer 3c / second gas diffusion layer 3a) of the device 1 was either SIGRACET (registered trademark) GDL Grade 28BC manufactured by SGL CARBON GmbH alone or with the addition of a water-repellent layer 3c / second gas diffusion layer 3a (the layer configuration, from the cation exchange membrane 4 side, was second catalyst layer 3b / water-repellent layer 3c / second gas diffusion layer 3a / water-repellent layer 3c / second gas diffusion layer 3a). The cation exchange membrane 4 of the device 1 was a cation exchange membrane (Neosepta (registered trademark) CMB manufactured by Astom Corporation). The distance between the anode electrode 2 and the cation exchange membrane 4 (first filling section 10) and the distance between the cation exchange membrane 4 and the cathode electrode 3 (second filling section 11) were both 2 mm. The first alkaline solution 6 in which carbon dioxide was dissolved was K ２ CO ３ An aqueous solution (1 mol / L) was used and supplied to the first filling section 10. A KOH aqueous solution (0.1 mol / L) was used as the second alkaline liquid 7 and supplied to the second filling section 11. The first alkaline liquid 6 and the second alkaline liquid 7 were each circulated at a flow rate of 0.9 mL / min using a liquid feed pump.

[0064] Using a mass flow controller, anode electrode 2 (electrode area 25 cm ２ ) and hydrogen gas (manufactured by Air Water, purity: 99.999% by volume or more) as the hydrogen-containing gas 8a was supplied at a rate of 50 mL / min (electrode area: 1 cm ２ First, the voltage was measured when a constant current shown in Table 1 was applied without supplying the oxygen-containing gas 9a to the cathode electrode 3 (electrode area 25 cm). ２ ) as the oxygen-containing gas 9a (manufactured by Air Water Corporation, purity: 99.999% by volume or more), and ２ The oxygen flow rate (cm / min) shown in Table 1 was measured at an oxygen flow rate of 1 cm per electrode area. ２ The actual oxygen flow rate (cm ３ / min) with an electrode area of ​​25 cm ２ The voltage is calculated by dividing the voltage by the oxygen supply voltage (V) by the voltage (V). During the constant current flow, gas was generated from the first alkaline solution 6, and the generation of carbon dioxide was confirmed. As an example, FIG. 4 shows the change in voltage before and after oxygen supply in Test No. 1, with the dashed line indicating the time point at which oxygen supply began. As shown in FIG. 4, it was found that the voltage dropped dramatically after oxygen supply. This is thought to be due to the fact that, before oxygen supply, the reaction of formula (3) above was occurring on the cathode electrode 3 side, but the oxygen supply caused the reaction of formula (4) above to occur. The results are summarized in Table 1. In Table 1, "Voltage (before oxygen supply)" refers to the voltage value immediately before oxygen supply, and "Voltage (after oxygen supply)" refers to the voltage value 100 seconds after oxygen supply.

[0065]

[0066] The results in Table 1 reveal the following. Tests 1 to 6 all met all of the requirements defined in this embodiment, and the voltage after oxygen supply was reduced compared to before oxygen supply, thereby enabling a reduction in power consumption compared to the prior art (i.e., the conditions before oxygen supply) disclosed in Patent Document 1. Furthermore, Tests 1 to 3 and 5 were able to further reduce power consumption by including multiple water-repellent layers. Furthermore, when compared with the same cathode electrode configuration, Test No. 4 had a higher oxygen flow rate than Test No. 6 (or Test No. 2 than Test No. 5), thereby enabling a further reduction in power consumption.

[0067] (Example 2) A test was conducted in the same manner as in Example 1, except that the cathode electrode layer configuration, constant current value, and oxygen flow rate were changed as shown in Table 2, and the distance between the anode electrode 2 and the cation exchange membrane 4 (first filled portion 10) and the distance between the cation exchange membrane 4 and the cathode electrode 3 (second filled portion 11) were each changed to half (1 mm). The results are summarized in Table 2. However, in Table 2, the oxygen flow rate was appropriately adjusted so that the voltage after oxygen supply was lower. In some cases, the voltage in Table 2 may be further lowered by further fine-tuning the oxygen flow rate. Furthermore, although the voltage before oxygen supply was not measured in Table 2, it is believed that, as in Example 1, the voltage was higher than after oxygen supply.

[0068]

[0069] The results in Table 2 reveal the following. Tests Nos. 7 to 12 all met all of the requirements defined in this embodiment, and, like Example 1, were considered to have reduced power consumption compared to the prior art. Note that Test No. 9 of Example 2 had a lower voltage after oxygen supply than Test No. 4 of Example 1. This is thought to be due to the reduced distance between the first filled section 10 and the second filled section 11, reducing solution resistance, and other factors. Furthermore, in Tests Nos. 7 and 8, the voltage after oxygen supply was negative, meaning that it was possible to extract (generate) electricity. Through Example 2, the inventors discovered that there is an appropriate oxygen flow rate. That is, if the oxygen flow rate is too high, the solution will have difficulty reaching the catalyst on the cathode electrode surface, and if it is too low, the oxygen will have difficulty reaching the catalyst. It is thought that the appropriate oxygen flow rate may vary depending on the amount of water produced. Test No. In Examples 7 to 12, increasing the constant current value can increase the amount of water produced, and accordingly, it was necessary to increase the oxygen flow rate so as to further reduce power consumption (and further enable power to be extracted). Those skilled in the art who have read this specification (particularly this example) will understand that increasing the electrode area to 1 cm can further reduce power consumption (and further enable power to be extracted). ２ The oxygen flow rate per unit area, current value, device structure (distance of the alkaline solution filling section (solution resistance), etc.) can be optimized as appropriate.

[0070] This application claims priority from Japanese Patent Application No. 2024-086549, filed May 28, 2024. Japanese Patent Application No. 2024-086549 is incorporated herein by reference.

[0071] DESCRIPTION OF SYMBOLS 1 Carbon dioxide release device 2 Anode electrode 2a First gas diffusion layer 2b First catalyst layer 2c Proton exchange membrane 3 Cathode electrode 3a Second gas diffusion layer 3b Second catalyst layer 3c Water-repellent layer 4 Cation exchange membrane 5 Power source 6 First alkaline liquid 6a First alkaline liquid before carbon dioxide dissolution 6b First alkaline liquid after carbon dioxide dissolution 6c First alkaline liquid after carbon dioxide release 6d Cations of first alkaline liquid 7 Second alkaline liquid 7a Solute of second alkaline liquid 8 Hydrogen-containing gas supply unit 8a Hydrogen-containing gas 9 Oxygen-containing gas supply unit 9a Oxygen-containing gas 10 First filling unit 11 Second filling unit 12 Exhaust gas 12a Carbon dioxide 13 Carbon dioxide dissolution unit 14 Carbon dioxide separation unit 15 Alkaline liquid regeneration unit 100 Carbon dioxide recovery system

Claims

1. A process of preparing an anode electrode, a cathode electrode, and a cation exchange membrane disposed between the anode electrode and the cathode electrode, wherein the anode electrode includes a first catalyst and a first gas diffusion layer, and the cathode electrode includes a second catalyst, a second gas diffusion layer, and a water-repellent layer; a process of filling a first alkaline liquid having carbon dioxide dissolved therein between the anode electrode and the cation exchange membrane; a process of filling a second alkaline liquid between the cation exchange membrane and the cathode electrode; and a process of filling a second alkaline liquid between the anode electrode and the cation exchange membrane with an electrode area of ​​1 cm. ２ supplying a hydrogen-containing gas at a flow rate of more than 0 cm / min per electrode area of ​​1 cm to the cathode electrode; ２ supplying an oxygen-containing gas at a flow rate of more than 0 cm / min per minute.

2. The method of claim 1, further comprising the step of applying a voltage between said anode electrode and said cathode electrode.

3. The method of claim 1 or 2, wherein the cathode electrode comprises a plurality of water-repellent layers.

4. A method for recovering carbon dioxide from exhaust gas, comprising: a step of dissolving carbon dioxide in exhaust gas in a first alkaline liquid; and a step of releasing the carbon dioxide dissolved in the first alkaline liquid by the method according to claim 1 or 2.

5. A fuel cell comprising an anode electrode, a cathode electrode, and a cation exchange membrane disposed between the anode electrode and the cathode electrode, wherein the anode electrode comprises a first catalyst and a first gas diffusion layer, and the cathode electrode comprises a second catalyst, a second gas diffusion layer, and a water-repellent layer, wherein a first filling section can be filled between the anode electrode and the cation exchange membrane with a first alkaline liquid having carbon dioxide dissolved therein, and a second filling section can be filled between the cation exchange membrane and the cathode electrode, and wherein the anode electrode is provided with an electrode surface area of ​​1 cm. ２ a hydrogen-containing gas supply unit capable of supplying a hydrogen-containing gas at a flow rate of more than 0 cm / min per electrode; ２ an oxygen-containing gas supply unit capable of supplying an oxygen-containing gas at a flow rate per unit volume exceeding 0 cm / min.

6. The apparatus of claim 5, further comprising a power supply capable of applying a voltage between said anode electrode and said cathode electrode.

7. The device according to claim 5 or 6, wherein the cathode electrode comprises a plurality of water-repellent layers.

8. A system for recovering carbon dioxide from exhaust gas, comprising: a carbon dioxide dissolving section that can be filled with a first alkaline liquid and that can dissolve carbon dioxide in exhaust gas in the first alkaline liquid; and the device according to claim 5 or 6, wherein the first alkaline liquid in which carbon dioxide has been dissolved in the device can be supplied from the carbon dioxide dissolving section.

Images