Carbon dioxide capture system

Abstract

To provide a carbon dioxide recovery system where the reduction with time of the CO2 adsorption amount of an electrochemical cell can be suppressed.SOLUTION: In a carbon dioxide recovery system separating CO2 from a CO2-containing gas containing CO2 by an electrochemical reaction, an electrochemical cell 101 where an action electrode 102 including a CO2 adsorbent 102b and a counter electrode 103 are disposed so as to sandwich an electrolyte 106 is provided. An electron is supplied from the counter electrode to the action electrode by applying voltage between the action electrode and the counter electrode. The CO2 adsorbent adsorbs CO2 involved in the supply of the electron. A material satisfying at least one of a condition that an oxygen dissolution amount is 0.2 cm3 / cm3 or less and a condition that oxygen diffusion coefficient is 5×10-7 cm2 / s or less is used as the electrolyte.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This invention relates to a carbon dioxide capture system for recovering CO2 from CO2-containing gases. [Background technology]

[0002] Patent Document 1 proposes an apparatus for separating CO2 from a CO2-containing gas by an electrochemical reaction. In the gas separation system of Patent Document 1, a CO2 adsorbent capable of adsorbing CO2 is provided at the working electrode of the electrochemical cell. The CO2 adsorbent is an electroactive species, and by changing the potential difference between the working electrode and the counter electrode, the adsorption and release of CO2 by the CO2 adsorbent can be switched. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2018-533470 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The inventors of this invention have found that when a CO2 adsorbent that does not have an active site is used at the working electrode of an electrochemical cell, the amount of CO2 adsorbed decreases for the following reasons.

[0005] In other words, when using a CO2 adsorbent that does not have an active site, reactive oxygen species (O2) are generated from the O2 contained in the CO2-containing gas. - This contributes to CO2 adsorption at the working electrode. On the other hand, when reactive oxygen species generated at the working electrode diffuse to the counter electrode, the counter electrode active material is oxidatively decomposed by the reactive oxygen species, reducing the amount of electrons supplied from the counter electrode to the working electrode. As a result, the amount of CO2 adsorbed at the working electrode decreases.

[0006] In view of the above points, the present invention aims to provide a carbon dioxide capture system that can suppress the decrease in the amount of CO2 adsorbed by an electrochemical cell.

Means for Solving the Problem

[0007] To achieve the above object, the carbon dioxide recovery system according to claims 1, 6, and 9 includes an electrochemical cell (101) in which a working electrode (102) containing a CO2 adsorbent (102b) and a counter electrode (103) are provided with an electrolyte (106) interposed therebetween.

[0008] According to the invention described in claim 1, when a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO2 adsorbent adsorbs CO2 as electrons are supplied. As the electrolyte, a material satisfying at least one of the following conditions is used: the amount of dissolved oxygen is 0.2 cm 3 / cm 3 or less, and the oxygen diffusion coefficient is 5×10 -7 cm 2 / s or less.

[0009] Also, according to the invention described in claim 7, when a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO2 adsorbent adsorbs CO2 as electrons are supplied. A counter electrode active material is provided on the counter electrode, and an antioxidant that reacts preferentially with active oxygen rather than the counter electrode active material is added to the counter electrode active material.

[0010] Also, according to the invention described in claim 11, no active material is provided on the counter electrode. By applying a voltage between the working electrode and the counter electrode so that the potential difference obtained by subtracting the potential of the counter electrode from the potential of the working electrode is not more than a predetermined value, electrons are supplied from the counter electrode to the working electrode, and the CO2 adsorbent adsorbs CO2 as electrons are supplied.

[0011] According to the inventions described in claims 1, 7, and 9, it is possible to suppress a decrease in the amount of electrons supplied from the counter electrode to the working electrode, and to suppress a decrease in the CO2 adsorption amount of the working electrode.

[0012] Note that the reference numerals in parentheses for the above respective components indicate the correspondence with the specific means described in the embodiments described later.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram showing the carbon dioxide recovery system of the first embodiment. [Figure 2] It is a diagram showing the CO2 recovery device. [Figure 3] It is a cross-sectional view of the electrochemical cell of the first embodiment. [Figure 4] It is a diagram for explaining the CO2 recovery mode and the CO2 release mode of the CO2 recovery device. [Figure 5] It is a diagram showing the change in the amount of electron supply in the electrochemical cell of the first embodiment. [Figure 6] It is a diagram showing the change in the amount of CO2 adsorption in the electrochemical cell of the first embodiment. [Figure 7] It is a cross-sectional view of the electrochemical cell of the third embodiment.

Mode for Carrying Out the Invention

[0014] Hereinafter, a plurality of modes for implementing the present disclosure will be described with reference to the drawings. In each mode, the same reference numerals may be given to the parts corresponding to the matters described in the preceding mode, and duplicate explanations may be omitted. When only a part of the configuration is described in each mode, other modes previously described can be applied to other parts of the configuration. Not only combinations of parts explicitly shown to be combinable in each embodiment, but also partial combinations of embodiments are possible without particular problems in combination, even if not explicitly stated.

[0015] (First Embodiment) Hereinafter, the first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the carbon dioxide recovery system 10 of the present embodiment is provided with a compressor 11, a CO2 recovery device 100, a flow path switching valve 12, a CO2 utilization device 13, and a control device 14.

[0016] The compressor 11 pumps the CO2-containing gas to the CO2 recovery device 100. The CO2-containing gas is a mixed gas containing CO2 and other gases, such as air. The CO2-containing gas contains at least O2 as the gas other than CO2.

[0017] The CO2 recovery device 100 is a device that separates and recovers CO2 from a CO2-containing gas. The CO2 recovery device 100 discharges the CO2-removed gas, or the CO2 recovered from the CO2-containing gas, after the CO2 has been recovered from the gas. The configuration of the CO2 recovery device 100 will be described in detail later.

[0018] The flow path switching valve 12 is a three-way valve that switches the flow path of the exhaust gas from the CO2 recovery device 100. When CO2 removal gas is discharged from the CO2 recovery device 100, the flow path switching valve 12 switches the exhaust gas flow path to the atmosphere side, and when CO2 is discharged from the CO2 recovery device 100, it switches the exhaust gas flow path to the CO2 utilization device 13 side.

[0019] The CO2 utilization device 13 is a device that utilizes CO2. The CO2 utilization device 13 can include, for example, a storage tank for storing CO2 or a conversion device for converting CO2 into fuel. The conversion device can be one that converts CO2 into a hydrocarbon fuel such as methane. The hydrocarbon fuel may be a gaseous fuel at room temperature and pressure, or a liquid fuel at room temperature and pressure.

[0020] The control device 14 consists of a well-known microcomputer including a CPU, ROM, and RAM, and its peripheral circuits. The control device 14 performs various calculations and processes based on a control program stored in the ROM, and controls the operation of various controlled devices. In this embodiment, the control device 14 performs operation control of the compressor 11, operation control of the CO2 recovery device 100, flow path switching control of the flow path switching valve 12, and the like.

[0021] Next, the CO2 recovery device 100 will be described using Figure 2. As shown in Figure 2, the CO2 recovery device 100 is equipped with an electrochemical cell 101. The electrochemical cell 101 has a working electrode 102, a counter electrode 103, and an insulating layer 104. In the example shown in Figure 2, the working electrode 102, the counter electrode 103, and the insulating layer 104 are each configured in a plate shape. Note that in Figure 2, the working electrode 102, the counter electrode 103, and the insulating layer 104 are shown with gaps between them, but in reality, these components are arranged to be in contact with each other.

[0022] The electrochemical cell 101 may be housed in a container (not shown). The container may be provided with a gas inlet for introducing CO2-containing gas into the container and a gas outlet for releasing CO2 removal gas or CO2 from the container.

[0023] The CO2 recovery device 100 separates and recovers CO2 from a CO2-containing gas by adsorption and desorption of CO2 through electrochemical reactions. The CO2 recovery device 100 is equipped with a power supply 105 that applies a predetermined voltage to the working electrode 102 and the counter electrode 103, and the potential difference between the working electrode 102 and the counter electrode 103 can be changed. The working electrode 102 is the negative electrode, and the counter electrode 103 is the positive electrode.

[0024] The electrochemical cell 101 can operate by switching between a CO2 recovery mode, in which CO2 is recovered at the working electrode 102, and a CO2 release mode, in which CO2 is released from the working electrode 102, by changing the potential difference between the working electrode 102 and the counter electrode 103. The CO2 recovery mode is a charging mode that charges the electrochemical cell 101, and the CO2 release mode is a discharge mode that discharges the electrochemical cell 101.

[0025] In CO2 recovery mode, a first voltage V1 is applied between the working electrode 102 and the counter electrode 103, and electrons are supplied from the counter electrode 103 to the working electrode 102. At the first voltage V1, the working electrode potential is less than the counter electrode potential. If the first voltage V1 is defined as the potential difference obtained by subtracting the potential of the counter electrode 103 from the potential of the working electrode 102, it can be set to a range of, for example, -0.5 to -2.0 V.

[0026] In CO2 emission mode, a low second voltage V2 is applied between the working electrode 102 and the counter electrode 103, supplying electrons from the working electrode 102 to the counter electrode 103. The second voltage V2 only needs to be lower than the first voltage V1, and the relative magnitudes of the working electrode potential and the counter electrode potential are not limited. In other words, in CO2 emission mode, the working electrode potential may be less than the counter electrode potential, the working electrode potential may be equal to the counter electrode potential, or the working electrode potential may be greater than the counter electrode potential.

[0027] As shown in Figure 3, the working electrode 102 is provided with a working electrode current collector 102a and a CO2 adsorbent 102b.

[0028] The working electrode current collector 102a is a porous conductive material having pores through which a CO2-containing gas can pass. For example, a carbonaceous material or a porous metal can be used as the working electrode current collector 102a. As the carbonaceous material constituting the working electrode current collector 102a, for example, carbon paper, carbon cloth, nonwoven carbon mat, porous gas diffusion layer (GDL), etc. can be used. As the porous metal constituting the working electrode current collector 102a, for example, a metal mesh made of metal (e.g., Al, Ni, etc.) can be used.

[0029] The CO2 adsorbent 102b adsorbs CO2 by accepting electrons and desorbs the adsorbed CO2 by releasing electrons. The CO2 adsorbent 102b is a material that does not undergo a structural change in its chemical skeleton when adsorbing CO2.

[0030] In this embodiment, the CO2 adsorbent 102b is a material that can transfer electrons without changing the structure of its chemical skeleton by applying a negative potential to the counter electrode 103. The CO2 adsorbent 102b is a material in which, when electrons are supplied from the counter electrode 103, the charge is delocalized throughout the entire material without charge concentration on specific elements in the chemical structure. In other words, the CO2 adsorbent 102b does not have a chemical structure that serves as an active site for adsorbing CO2.

[0031] When a first voltage V1 is applied between the working electrode 102 and the counter electrode 103, electrons are supplied from the counter electrode 103 to the working electrode 102, and the CO2 adsorbent 102b takes in electrons and adsorbs CO2. When a second voltage V2 is applied between the working electrode 102 and the counter electrode 103, electrons are supplied from the working electrode 102 to the counter electrode 103, and the CO2 adsorbent 102b releases electrons and desorbs CO2.

[0032] The CO2 adsorbent 102b of the present embodiment is a highly conductive high specific surface area material. As the high specific surface area material constituting the CO2 adsorbent 102b, for example, materials that can be used as carbon electrodes such as carbon black, graphene, carbon nanotubes, activated carbon, ketjen black, and mesoporous carbon can be used.

[0033] In the CO2 recovery mode, an oxygen reduction reaction represented by the following reaction formula (1) and a carbonate ion generation reaction represented by the reaction formula (2) proceed at the working electrode 102, and CO2 is adsorbed on the working electrode 102. That is, the oxygen reduction reaction triggers the CO2 adsorption at the working electrode 102.

[0034] O2 + 2e - → O2 - ···(1) O2 - + CO2 → 1 / 2O2 + CO3 2- ···(2) At the working electrode 102, O2 contained in the CO2-containing gas receives electrons and is reduced, and an oxygen reduction reaction occurs in which superoxide O2 - which is a kind of active oxygen is generated. The active oxygen O2 - generated by the oxygen reduction reaction is highly reactive, and a carbonate ion generation reaction occurs in which CO2 is oxidized to carbonate ion CO3 2- which is an oxide ion of CO2 is generated. At the working electrode, CO2 is adsorbed on the working electrode 102 in the state of carbonate ions containing CO3 2- . That is, at the working electrode 102, the active oxygen O2 - generated by the oxygen reduction reaction contributes to CO2 adsorption.

[0035] A binder is added to the CO2 adsorbent 102b. The binder is provided to hold the CO2 adsorbent 102b to the working electrode current collector 102a. The binder has adhesive properties and is placed between the CO2 adsorbent 102b and the working electrode current collector 102a.

[0036] A conductive resin can be used as the binder. Examples of conductive resins include epoxy resins containing Ag (silver) as a conductive filler, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and other fluororesins.

[0037] The binder, like the conductive material, can be brought into contact with the working electrode current collector 102a containing the CO2 adsorbent 102b using an organic solvent. Alternatively, the binder raw materials and the CO2 adsorbent 102b may be dispersed and mixed using a homogenizer or the like, the mixture may be formed, and then pressed onto the working electrode current collector 102a, or the mixture of the binder and the CO2 adsorbent 102b may be spray-coated onto the working electrode current collector 102a.

[0038] As shown in Figure 3, the counter electrode 103 has the same configuration as the working electrode 102, and is provided with a counter electrode current collector 103a and a counter electrode active material 103b.

[0039] The counter electrode current collector 103a may be made of the same conductive material as the working electrode current collector 102a, or it may be made of a different material.

[0040] The counter electrode active material 103b is an auxiliary electroactive species that transfers electrons with the CO2 adsorbent 102b through a redox reaction. As the counter electrode active material 103b, for example, a metal complex that enables electron transfer by changing the valence of a metal ion can be used. Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickerosene, and cobaltocene, or porphyrin metal complexes. In this embodiment, the following polyvinylferrocene is used as the counter electrode active material 103b.

[0041] [ka] The counter electrode active material 103b is doped with a conductive material and a binder. The conductive material forms a conductive path to the counter electrode active material 103b. The binder can be any material that can hold the counter electrode active material 103b to the counter electrode current collector 103a and is conductive. The conductive material of the counter electrode 103 can be a carbon material such as carbon nanotubes, carbon black, or graphene. The binder of the counter electrode 103 may be the same material as that used for the working electrode 102, or a different material may be used.

[0042] The insulating layer 104 is positioned between the working electrode 102 and the counter electrode 103, acting as a separator that separates the working electrode 102 and the counter electrode 103. The insulating layer 104 prevents physical contact between the working electrode 102 and the counter electrode 103, and electrically insulates the working electrode 102 and the counter electrode 103.

[0043] The insulating layer 104 is ion-permeable. In this embodiment, a porous material is used as the insulating layer 104. The material of the insulating layer 104 can be a cellulose film, a polymer, a polymer-ceramic composite material, or the like.

[0044] The electrochemical cell 101 is provided with a working electrode 102 and a counter electrode 103 sandwiching an electrolyte 106. The electrolyte 106 is an ion-conducting material provided between the working electrode 102 and the counter electrode 103. The electrolyte 106 is separated into the working electrode 102 side and the counter electrode 103 side by an insulating layer 104.

[0045] The electrolyte 106 is in contact with the CO2 adsorbent 102b. The ions contained in the electrolyte 106 promote electron withdrawal of the CO2 adsorbent 102b when it adsorbs CO2.

[0046] The electrolyte 106 can be, for example, an ionic liquid. An ionic liquid is a salt of a liquid that is non-volatile at room temperature and pressure. When using an ionic liquid as the electrolyte 106, the ionic liquid may be gelled to prevent elution from the electrochemical cell 101.

[0047] In CO2 recovery mode, when the O2 contained in the CO2-containing gas dissolves in the electrolyte 106 and comes into contact with the CO2 adsorbent 102b, the O2 is converted into reactive oxygen species O2. - Reactive oxygen species are generated, and the reactive oxygen species generated at the working electrode 102 diffuse to the counter electrode 103. Therefore, in order to prevent O2 from coming into contact with the CO2 adsorbent 102b via the electrolyte 106 and to suppress the diffusion of reactive oxygen species from the working electrode 102 to the counter electrode 103, it is desirable to use a material with a low oxygen solubility and a small oxygen diffusion coefficient as the electrolyte 106. In this embodiment, the electrolyte 106 has an oxygen solubility of 0.2 cm³. 3 / cm 3 The following conditions must be met, and the oxygen diffusion coefficient must be 5 × 10 -7 cm 2 The material used satisfies at least one of the following conditions: / s or less.

[0048] On the other hand, in the CO2 recovery mode, the CO2 contained in the CO2-containing gas dissolves in the electrolyte 106 and comes into contact with the CO2 adsorbent 102b, and the CO2 adsorbent 102b binds with the CO2. For this reason, in order to promote the contact of CO2 with the CO2 adsorbent 102b via the electrolyte 106, it is desirable to use a material as the electrolyte 106 that has a large carbon dioxide dissolution rate and a large carbon dioxide diffusion coefficient. In this embodiment, the electrolyte 106 has a carbon dioxide dissolution rate of 1 × 10⁻⁶ -3 cm 3 / cm 3 The above is true, and the carbon dioxide diffusion coefficient is 1 × 10⁻⁶. -7 cm 2 Materials with a temperature of / s or higher are used.

[0049] The diffusion coefficients of oxygen and carbon dioxide can be measured by NMR spectroscopy. NMR diffusion is performed using a pulsed magnetic field gradient (PFG) system. Molecular diffusion is a phenomenon where molecules move their positions through translational motion. By applying a pulsed magnetic field gradient to each position, positional information can be imprinted on the phase of the nuclear spin of the atomic nuclei. Then, by analyzing the history of the magnetic field gradient before and after diffusion, the diffusion coefficient of the diffusing substance can be calculated.

[0050] The amounts of dissolved oxygen and carbon dioxide can be measured by the volumetric method using a gas burette and a mercury pressure gauge. In the volumetric method using a gas burette and a mercury pressure gauge, the amount of gas dissolved in the electrolyte 106 can be measured by measuring the volume and pressure of the gas in the gas burette when the electrolyte 106 and the gas reach dissolution equilibrium.

[0051] As the electrolyte 106 that satisfies the above-mentioned conditions for oxygen solubility, oxygen diffusion coefficient, carbon dioxide solubility, and carbon dioxide diffusion coefficient, at least one of the following ionic liquids, [TMPA][TFSI] and [P14][TFSI], can be used.

[0052] [ka]

[0053] [ka] [TMPA][TFSI] and [P14][TFSI] may be used individually as electrolyte 106, or they may be used as a mixture of electrolyte 106. In other words, the ionic liquid used as electrolyte 106 contains at least one of [TMPA] and [P14] as cations and [TFSI] as an anion.

[0054] Next, the operation of the carbon dioxide capture system 10 of this embodiment will be described. As shown in Figure 4, the carbon dioxide capture system 10 operates by alternately switching between a CO2 capture mode and a CO2 release mode. The operation of the carbon dioxide capture system 10 is controlled by the control device 14.

[0055] First, let's explain the CO2 recovery mode. In CO2 recovery mode, the compressor 11 operates and supplies CO2-containing gas to the CO2 recovery device 100. In the CO2 recovery device 100, the voltage applied between the working electrode 102 and the counter electrode 103 is called the first voltage V1. This allows for the simultaneous donation of electrons by the counter electrode active material 103b of the counter electrode 103 and the withdrawal of electrons by the CO2 adsorbent 102b of the working electrode 102. The counter electrode active material 103b of the counter electrode 103 releases electrons and enters an oxidized state, supplying electrons from the counter electrode 103 to the working electrode 102.

[0056] At the working electrode 102, reactive oxygen species (O2) are generated from the O2 contained in the CO2-containing gas. - The oxygen reduction reaction that generates reactive oxygen species O2 - The CO2 contained in the CO2-containing gas is oxidized to carbonate ions (CO3). 2- The carbonate ion generation reaction proceeds. The CO2 contained in the CO2-containing gas is adsorbed onto the CO2 adsorbent 102b. As a result, the CO2 recovery device 100 can recover CO2 from the CO2-containing gas.

[0057] In CO2 recovery mode, when O2 contained in the CO2-containing gas receives electrons at the working electrode 102, reactive oxygen species O2 are produced. - This is generated. In this embodiment, an electrolyte 106 with a small oxygen solubility and a small oxygen diffusion coefficient is used. Therefore, reactive oxygen species O2 contribute to CO2 adsorption at the working electrode 102. - This allows for the generation of reactive oxygen species while suppressing their diffusion to the counter electrode 103.

[0058] After the CO2 is recovered from the CO2-containing gas by the CO2 recovery device 100, the CO2-free CO2-removed gas is discharged from the CO2 recovery device 100. The flow path switching valve 12 switches the gas flow path to the atmosphere, and the CO2-removed gas discharged from the CO2 recovery device 100 is discharged into the atmosphere.

[0059] Next, the CO2 release mode will be described. In the CO2 release mode, the compressor 11 stops operating, and the supply of CO2-containing gas to the CO2 recovery device 100 is stopped. In the CO2 recovery device 100, the voltage applied between the working electrode 102 and the counter electrode 103 is set to the second voltage V2. This allows for the simultaneous donation of electrons to the CO2 adsorbent 102b of the working electrode 102 and the withdrawal of electrons to the counter electrode active material 103b of the counter electrode 103. The counter electrode active material 103b of the counter electrode 103 accepts electrons and enters a reduced state.

[0060] The CO2 adsorbent 102b of the working electrode 102 releases electrons. The CO2 adsorbent 102b removes CO2 by releasing electrons.

[0061] The CO2 released from the CO2 adsorbent 102b is discharged from the CO2 recovery device 100. The flow path switching valve 12 switches the gas flow path to the CO2 utilization device 13 side, and the CO2 discharged from the CO2 recovery device 100 is supplied to the CO2 utilization device 13.

[0062] Here, the electron supply amount and CO2 adsorption amount of the electrochemical cell 101 of this embodiment will be described. Figure 5 shows the change in the electron supply amount from the counter electrode 103 to the working electrode 102 when the CO2 recovery mode is repeatedly performed in the electrochemical cell 101 of this embodiment. Figure 6 shows the change in the CO2 adsorption amount of the working electrode 102 when the CO2 recovery mode is repeatedly performed in the electrochemical cell 101 of this embodiment.

[0063] Figures 5 and 6 show the electron supply and CO2 adsorption amount of an electrochemical cell 101 using [TMPA] and [TFSI] as the electrolyte 106 in this embodiment. Furthermore, Figures 5 and 6 show the electron supply and CO2 adsorption amount of an electrochemical cell using [BMIM] and [TFSI], which are conventionally used, as a comparative example.

[0064] The horizontal axis in Figures 5 and 6 represents the number of times the CO2 recovery mode has been executed in electrochemical cell 101. The vertical axis in Figure 5 represents the electron supply ratio, which is the rate of change in electron supply when the electron supply amount for the first CO2 recovery is set to 1.0 (100%). The vertical axis in Figure 6 represents the CO2 adsorption ratio, which is the rate of change when the CO2 adsorbed amount for the first CO2 recovery is set to 1.0 (100%).

[0065] As shown in Figure 5, when the CO2 recovery mode is repeated, the electron supply decreases in both this embodiment and the comparative example. When the number of CO2 recovery cycles exceeds 5, the rate of decrease in electron supply is smaller in this embodiment than in the comparative example. In other words, it can be seen that the electrochemical cell 101 of this embodiment is able to suppress the decrease in electron supply more effectively than the comparative example.

[0066] As shown in Figure 6, when the CO2 recovery mode is repeated, the amount of CO2 adsorbed decreases in both this embodiment and the comparative example. When the number of CO2 recovery cycles exceeds 11, the rate of decrease in the amount of CO2 adsorbed in this embodiment is smaller than that of the comparative example. In other words, it can be seen that the electrochemical cell 101 of this embodiment is able to suppress the decrease in the amount of CO2 adsorbed more effectively than the comparative example.

[0067] In the CO2 recovery device 100 of this embodiment described above, an electrolyte 106 with a small oxygen solubility and a small oxygen diffusion coefficient is used. Therefore, when using a CO2 adsorbent 102b that does not have active sites, it is possible to allow the generation of reactive oxygen species that contribute to CO2 adsorption while suppressing the diffusion of reactive oxygen species generated at the working electrode 102 to the counter electrode 103. As a result, oxidation and decomposition of the counter electrode active material 103b by reactive oxygen species can be suppressed, a decrease in the amount of electrons supplied from the counter electrode 103 to the working electrode 102 can be suppressed, and a decrease in the amount of CO2 adsorbed by the working electrode 102 can be suppressed.

[0068] Furthermore, in this embodiment, at least one of [TMPA][TFSI] and [P14][TFSI] is used as the electrolyte 106. These ionic liquids have a low oxygen solubility and a low oxygen diffusion coefficient, and can effectively suppress the diffusion of reactive oxygen species generated at the working electrode 102 to the counter electrode 103.

[0069] (Second Embodiment) Next, a second embodiment of the present invention will be described. Hereinafter, only the parts that differ from the first embodiment will be described.

[0070] In this second embodiment, the counter electrode active material 103b is supplemented with an antioxidant to prevent oxidation of the counter electrode active material 103b. The antioxidant is a substance that reacts preferentially with reactive oxygen species than the counter electrode active material 103b. In this embodiment, phenols having a hydroxyl group on an aromatic substituent are used as the antioxidant.

[0071] As such a phenolic antioxidant, BASF Japan Ltd.'s product name Irganox1010 can be used. Irganox1010 has the molecular formula C 73 H 108 O 12 It is pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionic acid], and has the following structural formula.

[0072] [ka] In this second embodiment, the counter electrode active material 103b and the antioxidant are mixed in a mass ratio of 1:1. That is, the mixture of the counter electrode active material 103b and the antioxidant contains 50 wt% of the antioxidant.

[0073] According to this second embodiment, by adding an antioxidant to the counter electrode active material 103b, even if reactive oxygen species generated at the working electrode 102 diffuse to the counter electrode 103, the antioxidant preferentially reacts with the reactive oxygen species. Therefore, the reaction between reactive oxygen species and the counter electrode active material 103b can be suppressed, the oxidative decomposition of the counter electrode active material 103b can be suppressed, the decrease in the amount of electrons supplied from the counter electrode 103 to the working electrode 102 can be suppressed, and the decrease in the amount of CO2 adsorbed by the working electrode 102 can be suppressed.

[0074] Furthermore, the configuration of adding an antioxidant to the counter electrode active material 103b in this second embodiment is not limited to configurations using an electrolyte 106 with low oxygen solubility and a low oxygen diffusion coefficient, but can also be applied to configurations using conventional electrolytes.

[0075] (Third embodiment) Next, a third embodiment of the present invention will be described. Only the parts that differ from the above embodiments will be described below.

[0076] In this third embodiment, the pore size of the insulating layer 104, which is made of a porous material, is set to a size that ensures ion permeability while preventing decomposition products of the counter electrode active material 103b from passing through. In other words, the pore size of the insulating layer 104 is smaller than the size of the decomposition products generated by the oxidative decomposition of the counter electrode active material 103b by reactive oxygen species. Specifically, the pore size of the insulating layer 104 is set to 1 μm or less.

[0077] According to this third embodiment, when reactive oxygen species generated at the working electrode 102 reach the counter electrode 103 and decomposition products of the counter electrode active material 103b are generated by the reactive oxygen species, the decomposition products do not permeate the insulating layer 104. Therefore, it is possible to prevent the decomposition products of the counter electrode active material 103b from permeating the insulating layer 104 and diffusing from the counter electrode 103 to the working electrode 102 side, and the decomposition products of the counter electrode active material 103b can be contained only in the electrolyte 106 on the counter electrode 103 side separated by the insulating layer 104. As a result, the electrolyte 106 on the counter electrode 103 side separated by the insulating layer 104 can be saturated with decomposition products, further decomposition of the counter electrode active material 103b can be suppressed, and the decrease in the amount of CO2 adsorbed by the working electrode 102 can be suppressed.

[0078] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. Only the parts that differ from the above embodiments will be described below.

[0079] As shown in Figure 7, in this fourth embodiment, the counter electrode 103 is not provided with the counter electrode active material 103b. The counter electrode active material 103b is an electroactive species that transfers electrons through oxidation-reduction reactions. In this fourth embodiment, a carbonaceous material or a porous metal is used as the counter electrode current collector 103a that constitutes the counter electrode 103. Note that the counter electrode active material 103b corresponds to the active material of the present invention.

[0080] In the electrochemical cell 101, when a voltage is applied between the working electrode 102 and the counter electrode 103, electrons and ions contained in the electrolyte 106 form an electrical double layer. In CO2 recovery mode, cations of the electrolyte 106 move to the surface of the working electrode 102, and anions of the electrolyte 106 move to the surface of the counter electrode 103. A potential difference is formed near each surface, and electrons are supplied from the counter electrode 103 to the working electrode 102. In CO2 release mode, anions of the electrolyte 106 move to the surface of the working electrode 102, and cations of the electrolyte 106 move to the surface of the counter electrode 103, and electrons are supplied from the working electrode 102 to the counter electrode 103.

[0081] In this fourth embodiment, in which the counter electrode active material 103b is not provided, the voltage applied between the working electrode 102 and the counter electrode 103 in the CO2 adsorption mode is increased compared to the above embodiments in which the counter electrode active material 103b is provided. In other words, in the CO2 adsorption mode, the potential difference between the working electrode potential and the counter electrode potential with respect to the counter electrode potential is increased to the negative side, so that the potential difference obtained by subtracting the potential of the counter electrode 103 from the potential of the working electrode 102 is less than or equal to a predetermined value (for example, -2.0V or less).

[0082] According to this fourth embodiment, when using CO2 adsorbent 102b that does not have active sites, the generation of reactive oxygen species that contribute to CO2 adsorption is permitted, and even if reactive oxygen species reach the counter electrode 103, the counter electrode active material will not undergo oxidative decomposition. Therefore, it is possible to suppress the decrease in the amount of CO2 adsorbed due to oxidative decomposition of the counter electrode active material.

[0083] Furthermore, if a carbonaceous material is used as the counter electrode current collector 103a in this fourth embodiment, the carbonaceous material may be oxidized by reactive oxygen species, potentially reducing the amount of electrons supplied from the counter electrode 103 to the working electrode 102. Therefore, by using an electrolyte 106 with a low oxygen solubility and a small oxygen diffusion coefficient, the diffusion of reactive oxygen species from the working electrode 102 to the counter electrode 103 can be suppressed, thereby suppressing the oxidation of the carbonaceous material constituting the counter electrode current collector 103a.

[0084] (Other embodiments) The present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of the invention. Furthermore, the means disclosed in each of the above embodiments may be combined as appropriate to the extent that they are feasible.

[0085] The features of the carbon dioxide capture system disclosed herein are as follows:

[0086] (Item 1) A carbon dioxide recovery system that separates CO2 from a CO2-containing gas by an electrochemical reaction, The electrochemical cell (101) comprises a working electrode (102) containing a CO2 adsorbent (102b) and a counter electrode (103) arranged so as to sandwich an electrolyte (106). When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO2 adsorbent combines with CO2 as electrons are supplied. As the aforementioned electrolyte, the oxygen solubility is 0.2 cm³. 3 / cm 3 The following conditions must be met, and the oxygen diffusion coefficient must be 5 × 10 -7 cm 2A carbon dioxide capture system that uses materials that satisfy at least one of the following conditions: / s or less.

[0087] (Item 2) The aforementioned electrolyte has a carbon dioxide dissolution rate of 1 × 10⁻⁶ -3 cm 3 / cm 3 The carbon dioxide capture system described in item 1 above.

[0088] (Item 3) The aforementioned electrolyte has a carbon dioxide diffusion coefficient of 1 × 10⁻⁶ -7 cm 2 A carbon dioxide capture system as described in item 1 or 2, which is 1 / s or more.

[0089] (Item 4) The carbon dioxide capture system according to any one of items 1 to 3, wherein the electrolyte is at least one of [TMPA][TFSI] and [P14][TFSI].

[0090] (Item 5) The counter electrode is provided with a counter electrode active material. The carbon dioxide recovery system according to any one of items 1 to 4, wherein the counter electrode active material is further enriched with an antioxidant that reacts preferentially with reactive oxygen species than the counter electrode active material.

[0091] (Item 6) A carbon dioxide recovery system that separates CO2 from a CO2-containing gas by an electrochemical reaction, The electrochemical cell (101) comprises a working electrode (102) containing a CO2 adsorbent (102b) and a counter electrode (103) arranged so as to sandwich an electrolyte (106). When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO2 adsorbent combines with CO2 as electrons are supplied. The counter electrode is provided with a counter electrode active material. The carbon dioxide recovery system is characterized in that the counter electrode active material is supplemented with an antioxidant that reacts preferentially with reactive oxygen species than the counter electrode active material.

[0092] (Item 7) The carbon dioxide recovery system according to item 5 or 6, wherein the antioxidant is a phenol.

[0093] (Item 8) The carbon dioxide recovery system according to item 7, wherein the antioxidant is pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionic acid].

[0094] (Item 9) An insulating layer (104) is provided between the working electrode and the counter electrode to electrically insulate the working electrode and the counter electrode, The carbon dioxide recovery system according to any one of items 5 to 8, wherein the insulating layer is a porous material whose pore size is smaller than the size of the decomposition products generated when the counter electrode active material is decomposed by the active oxygen.

[0095] (Item 10) The aforementioned counter electrode does not have an active material provided. A carbon dioxide capture system according to any one of items 1 to 4, wherein a voltage is applied between the working electrode and the counter electrode such that the potential difference obtained by subtracting the potential of the counter electrode from the potential of the working electrode is less than or equal to a predetermined value, thereby supplying electrons from the counter electrode to the working electrode, and the CO2 adsorbent combines with CO2 as a result of the supply of electrons.

[0096] (Item 11) A carbon dioxide recovery system that separates CO2 from a CO2-containing gas by an electrochemical reaction, The electrochemical cell (101) comprises a working electrode (102) containing a CO2 adsorbent (102b) and a counter electrode (103) arranged so as to sandwich an electrolyte (106). The aforementioned counter electrode does not have an active material provided. A carbon dioxide capture system in which a voltage is applied between the working electrode and the counter electrode such that the potential difference obtained by subtracting the potential of the counter electrode from the potential of the working electrode is less than or equal to a predetermined value, thereby supplying electrons from the counter electrode to the working electrode, and the CO2 adsorbent combines with CO2 as electrons are supplied. [Explanation of symbols]

[0097] 101 Electrochemical cell 102 Working electrode 102b CO2 adsorbent 103 Opposite 103b Counter electrode active material (active material) 104 Insulating layer 106 Electrolytes

Claims

1. CO 2 Contains CO 2 CO from the contained gas 2 A carbon dioxide capture system that separates, CO 2 The electrochemical cell (101) comprises a working electrode (102) containing an adsorbent (102b) and a counter electrode (103) arranged so as to sandwich an electrolyte (106). When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO 2 As electrons are supplied to the adsorbent CO 2 It adsorbs, As the electrolyte, a material that satisfies at least one of the following conditions is used: the dissolved oxygen amount is 0.2 cm 3 / cm 3 or less, and the oxygen diffusion coefficient is 5×10 -7 cm 2 / s or less. A carbon dioxide recovery system using such a material.

2. The aforementioned electrolyte has a carbon dioxide dissolution rate of 1 × 10⁻⁶ -3 cm 3 / cm 3 The carbon dioxide recovery system according to claim 1, as described above.

3. The aforementioned electrolyte has a carbon dioxide diffusion coefficient of 1 × 10⁻⁶ -7 cm 2 The carbon dioxide recovery system according to claim 1, wherein the rate is 1 / s or more.

4. The carbon dioxide recovery system according to claim 1, wherein the electrolyte is at least one of [TMPA] [TFSI] and [P14] [TFSI].

5. The aforementioned counter electrode does not have an active material provided. A voltage is applied between the working electrode and the counter electrode such that the potential difference obtained by subtracting the potential of the counter electrode from the potential of the working electrode is less than or equal to a predetermined value, thereby supplying electrons from the counter electrode to the working electrode, and the CO 2 As electrons are supplied to the adsorbent CO 2 A carbon dioxide recovery system according to any one of claims 1 to 4, which adsorbs carbon dioxide.

6. The counter electrode is provided with a counter electrode active material (103b), The carbon dioxide recovery system according to claim 1, wherein the counter electrode active material is further enriched with an antioxidant that reacts preferentially with reactive oxygen species than the counter electrode active material.

7. CO 2 Contains CO 2 CO from the contained gas 2 A carbon dioxide capture system that separates, CO 2 The electrochemical cell (101) comprises a working electrode (102) containing an adsorbent (102b) and a counter electrode (103) arranged so as to sandwich an electrolyte (106). When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO 2 As electrons are supplied to the adsorbent CO 2 It adsorbs, The counter electrode is provided with a counter electrode active material (103b), The carbon dioxide recovery system is characterized in that the counter electrode active material is supplemented with an antioxidant that reacts preferentially with reactive oxygen species than the counter electrode active material.

8. The carbon dioxide recovery system according to claim 6 or 7, wherein the antioxidant is a phenol.

9. The carbon dioxide recovery system according to claim 8, wherein the antioxidant is pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionic acid].

10. An insulating layer (104) is provided between the working electrode and the counter electrode to electrically insulate the working electrode and the counter electrode, The carbon dioxide recovery system according to claim 6 or 7, wherein the insulating layer is a porous material, and the pore size is smaller than the size of the decomposition products generated by the oxidative decomposition of the counter electrode active material by the reactive oxygen species.

11. CO 2 Contains CO 2 CO from the contained gas 2 A carbon dioxide capture system that separates, CO 2 The electrochemical cell (101) comprises a working electrode (102) containing an adsorbent (102b) and a counter electrode (103) arranged so as to sandwich an electrolyte (106). When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO 2 As electrons are supplied to the adsorbent CO 2 It adsorbs, The aforementioned counter electrode does not have an active material provided. A voltage is applied between the working electrode and the counter electrode such that the potential difference obtained by subtracting the potential of the counter electrode from the potential of the working electrode is less than or equal to a predetermined value, thereby supplying electrons from the counter electrode to the working electrode, and the CO 2 As electrons are supplied to the adsorbent CO 2 A carbon dioxide capture system that adsorbs carbon dioxide.

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