Carbon dioxide capture system

Abstract

To provide a carbon dioxide recovery system for recovering CO2 from CO2-containing gas by electrochemical reaction which improves CO2 recovery efficiency.SOLUTION: A carbon dioxide recovery system for separating CO2 from CO2-containing gas containing CO2 by electrochemical reaction includes an electrochemical cell 101 which is provided so as to sandwich an electrolytic solution 106 between an action electrode 102 containing a CO2 adsorbent 102b, and a counter electrode 103. Electrons are supplied to the action electrode from the counter electrode by applying a voltage between the action electrode and the counter electrode, and the CO2 adsorbent adsorbs CO2. The CO2 adsorbent is a porous body having a pore having a pore size more than the ion diameter of the electrolytic solution.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 a method for separating CO2 from a CO2-containing gas by electrochemical reaction. In this method, a potential difference is applied between the cathode and anode of an electrochemical cell, and the CO2-containing gas is supplied to the cathode, thereby separating CO2 from CO3. 2- The electrochemical reaction that produces CO3 2- An electrochemical reaction takes place in which CO2 is produced. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-33340 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, if the working electrode material of an electrochemical cell has few voids, CO2-containing gases and electrolyte ions do not diffuse sufficiently into the working electrode material. As a result, the proportion of effective active sites capable of adsorbing CO2 in the working electrode material decreases, and the CO2 recovery efficiency decreases.

[0005] In view of the above, the present invention aims to improve the CO2 recovery efficiency in a carbon dioxide recovery system that recovers CO2 from a CO2-containing gas by electrochemical reaction. [Means for solving the problem]

[0006] To achieve the above objective, Claim 1 、2、4、6The invention described herein is a carbon dioxide recovery system for separating CO2 from a CO2-containing gas by an electrochemical reaction, comprising an electrochemical cell (101) in which a working electrode (102) containing a CO2 adsorbent (102b) and a counter electrode (103) are 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 adsorbs CO2. The CO2 adsorbent exceeds the ionic diameter of the electrolyte. Furthermore, the ion size is less than 100 times the ion diameter of the electrolyte. It is a porous material having pores (200) with a pore diameter of [specified value]. The invention described in claim 1 is CO 2 The adsorbent is mesoporous carbon. The invention described in claim 2 is CO 2 The adsorbent is a porous carbon material with a metal-organic structure as a precursor. The invention described in claim 4 is CO 2 The adsorbent is a porous inorganic material with a metal-organic structure as a precursor. The invention described in claim 6 is CO 2 The adsorbent is a porous carbon material whose precursor is a composite in which a metal oxide is coated with a carbon material.

[0007] This allows O2, CO2, and electrolyte ions to sufficiently diffuse into the pores of the CO2 adsorbent. As a result, the proportion of effective active sites in the CO2 adsorbent can be increased, improving the CO2 recovery efficiency.

[0008] The symbols in parentheses for each of the above components indicate their correspondence to the specific means described in the embodiments described later. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing a carbon dioxide capture system according to the first embodiment. [Figure 2] This is a diagram showing a CO2 capture device. [Figure 3] This is a cross-sectional view of an electrochemical cell. [Figure 4] This diagram shows cations and anions in ionic liquids used as electrolytes. [Figure 5] This figure shows the pore size distribution of the CO2 adsorbent. [Figure 6] This diagram schematically shows the pore structure of a CO2 adsorbent. [Figure 7] This is a diagram for explaining the CO2 recovery mode and the CO2 release mode of the CO2 recovery device.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, a plurality of embodiments for implementing the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to those described in the preceding embodiment may be denoted by the same reference numerals, and redundant descriptions may be omitted. When only a part of the configuration is described in each embodiment, other embodiments described previously 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 hindrance to the combination, even if not explicitly stated.

[0011] (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.

[0012] 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 a gas other than CO2, and for example, air can be used. The CO2-containing gas contains at least O2 as a gas other than CO2.

[0013] The CO2 recovery device 100 is a device that separates and recovers CO2 from the CO2-containing gas. The CO2 recovery device 100 discharges the CO2-removed gas after CO2 has been recovered from the CO2-containing gas, or the CO2 recovered from the CO2-containing gas. The configuration of the CO2 recovery device 100 will be described in detail later.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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. 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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. The first voltage V1 can be, for example, in the range of 0.5 to 2.0 V.

[0022] 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.

[0023] As shown in Figure 3, the working electrode 102 is provided with a working electrode current collector 102a and a CO2 adsorbent 102b.

[0024] 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.

[0025] The CO2 adsorbent 102b will be explained in detail later.

[0026] 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.

[0027] 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.

[0028] The binder can be brought into contact with the working electrode current collector 102a containing the CO2 adsorbent 102b using an organic solvent such as NMP (N-methylpyrrolidone). 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.

[0029] 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.

[0030] 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.

[0031] The counter electrode active material 103b is an electroactive species that transfers electrons through oxidation-reduction. 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 polyvinylferrocene shown below is used as the counter electrode active material 103b.

[0032] [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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 an ionic liquid is used as the electrolyte 106, the ionic liquid may be gelled to prevent elution from the electrochemical cell 101.

[0037] Figure 4 illustrates the cations and anions of the ionic liquid used in the electrolyte 106 of this embodiment. The ionic liquid used as the electrolyte 106 contains a cation selected from at least one of Emin, Bmin, TMPA, P14, N4441, and P4441, and an anion selected from at least one of B(CN)4 and TFSI.

[0038] Here, we will explain the CO2 adsorbent 102b of the working electrode 102. 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. In other words, the CO2 adsorbent 102b itself does not possess a chemical structure that serves as an active site for adsorbing CO2.

[0039] 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.

[0040] 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.

[0041] In the CO2 recovery mode, an oxygen reduction reaction represented by the following reaction formula (1) and a carbonate ion generation reaction represented by 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.

[0042] 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 to generate superoxide O2 - which is a kind of active oxygen. The active oxygen O2 - generated by the oxygen reduction reaction is highly reactive and oxidizes CO2 to generate carbonate ion CO3 2- which is an oxide ion of CO2, and a carbonate ion generation reaction occurs, and CO2 is adsorbed on the CO2 adsorbent 102b. That is, the active oxygen O2 - generated by the oxygen reduction reaction contributes to the CO2 adsorption at the working electrode 102.

[0043] The CO2 adsorbent 102b is a highly specific surface area material having conductivity. The highly specific surface area material is a porous body having a large number of pores. The pores of the highly specific surface area material are not limited to those having a circular opening shape or cross-sectional shape.

[0044] In high-specific-surface-area materials, the areas where O2, CO2, and electrolyte 106 ions come into contact become effective active sites, which then become CO2 adsorption sites. In order to increase the proportion of effective active sites in high-specific-surface-area materials and improve the CO2 adsorption efficiency of CO2 adsorbent 102b, it is necessary for O2, CO2, and electrolyte 106 ions to sufficiently diffuse into the pores of the high-specific-surface-area material.

[0045] Therefore, in this embodiment, a high specific surface area material is used as the CO2 adsorbent 102b, having a pore diameter that exceeds the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106. Since the ionic diameter of the electrolyte 106 is larger than the molecular diameters of O2 and CO2, the high specific surface area material used as the CO2 adsorbent 102b only needs to have a pore diameter that exceeds the ionic diameter of the electrolyte 106.

[0046] If the electrolyte 106 contains multiple types of ions of different sizes, the "ionic diameter of the electrolyte" shall refer to the ionic diameter of the largest ion. The pore diameter of a high specific surface area material can be measured, for example, by the gas adsorption method. In the gas adsorption method, the pore diameter distribution can be measured from the relationship between pressure and adsorption amount by measuring the amount of adsorption of an inert gas (such as N2) while changing the pressure.

[0047] The molecular diameter of O2 is 0.34 nm, and the molecular diameter of CO2 is 0.46 nm. The ionic diameters of the cations and anions in the ionic liquid shown in Figure 4 are approximately 1 to 3 nm. Therefore, in this embodiment, a high specific surface area material with a pore diameter larger than 3 nm is used as the CO2 adsorbent 102b. It is desirable that as many pores as possible in the high specific surface area material exceed the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106, and most preferably all pores exceed the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106.

[0048] Furthermore, if the pore diameter of the high specific surface area material is too large, the specific surface area will decrease, and the CO2 adsorption efficiency will decline. For this reason, it is desirable that the pore diameter of the high specific surface area material used as the CO2 adsorbent 102b is less than approximately 100 times the ion diameter of the electrolyte 106.

[0049] Figure 5 shows an example of the pore size distribution of a high specific surface area material used as the CO2 adsorbent 102b. The shaded area in Figure 5 corresponds to the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the ionic liquid used as the CO2 adsorbent 102b. In the example shown in Figure 5, most of the pore sizes of the high specific surface area material are larger than the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106.

[0050] The pore size of the high specific surface area material used as the CO2 adsorbent 102b is preferably within a predetermined range that exceeds the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106. In the example shown in Figure 5, most of the pore size of the high specific surface area material falls within the predetermined range (e.g., 5 to 12 nm).

[0051] In this embodiment, mesoporous carbon is used as the high specific surface area material constituting the CO2 adsorbent 102b. Mesoporous carbon is a mesoporous material having a pore size of 2 to 50 nm.

[0052] Figure 6 schematically shows a magnified view of the pores 200 of the CO2 adsorbent 102b, with cations of the electrolyte 106 indicated by "+" and anions by "-". In Figure 6, the solid lines represent the walls of the pores 200, and each area enclosed by the solid lines represents a pore 200. In Figure 6, areas that are shaded are specifically labeled and exemplified as pores 200. As shown in Figure 6, in the CO2 adsorbent 102b of this embodiment, ions contained in O2, CO2, and the electrolyte 106 can easily enter and diffuse into the pores.

[0053] Next, the operation of the carbon dioxide capture system 10 of this embodiment will be described. As shown in Figure 7, 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.

[0054] First, let's explain the CO2 recovery mode. In CO2 recovery mode, the compressor 11 operates and CO2-containing gas is supplied 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 defined as the first voltage V1. As a result, the counter electrode active material 103b of the counter electrode 103 releases electrons and enters an oxidized state, and electrons are supplied from the counter electrode 103 to the working electrode 102.

[0055] 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 reaction to produce carbonate ions proceeds.

[0056] The CO2 adsorbent 102b of this embodiment has pore diameters that exceed the molecular diameters of O2, CO2, and the ionic diameter of the electrolyte 106, allowing ions of O2, CO2, and the electrolyte 106 to diffuse sufficiently into the pores of the CO2 adsorbent 102b. This increases the proportion of effective active sites in the CO2 adsorbent 102b, thereby accelerating the progress of the oxygen reduction reaction and the carbonate ion generation reaction.

[0057] The CO2 contained in the CO2-containing gas is efficiently adsorbed by the CO2 adsorbent 102b. As a result, the CO2 recovery device 100 can recover CO2 from the CO2-containing gas.

[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. By releasing electrons, the CO2 adsorbent 102b desorbs the adsorbed CO2. In the CO2 release mode, the carbonate ions CO3 adsorbed on the CO2 adsorbent 102b at the working electrode 102 are released. 2- As the carbonate ion dissociation reaction proceeds, in which CO2 is dissociated into CO2, CO2 is removed from the CO2 adsorbent 102b.

[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] In the embodiment described above, a porous material is used as the CO2 adsorbent 102b, having a pore diameter that exceeds the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106. Therefore, in the CO2 adsorption mode, ions of O2, CO2, and the electrolyte 106 can sufficiently diffuse into the pores of the CO2 adsorbent 102b. This increases the proportion of effective active sites in the CO2 adsorbent 102b, thereby improving the CO2 recovery efficiency.

[0063] (Second Embodiment) Next, a second embodiment of the present invention will be described. The following describes the differences from the first embodiment described above.

[0064] In this second embodiment, at least one of a porous carbon material with a metal-organic structure as a precursor and a porous inorganic material with a metal-organic structure as a precursor is used as the high specific surface area material constituting the CO2 adsorbent 102b. A metal-organic structure is a porous three-dimensional structure in which an organic ligand is coordinately bonded to a metal element. In the following description, the metal-organic structure will be referred to as "MOF," the porous carbon material with a metal-organic structure as a precursor will be referred to as "MOF precursor carbon material," and the porous inorganic material with a metal-organic structure as a precursor will be referred to as "MOF precursor inorganic material."

[0065] For MOF precursor carbon materials, the materials described in "Fabrication of symmetric supercapacitors based on MOF-derived nanoporous carbons", J. Mater. Chem. A2 (2014) 19848-19854 can be used. For MOF precursor inorganic materials, the materials described in "Porous Co3O4 materials prepared by solid-state thermolysis of a novel Co-MOF crystal and their superior energy storage performances for supercapacitors", J. Mater. Chem. A1 (2013) 7235-7241 can be used.

[0066] The MOF used as a precursor for the MOF precursor carbon material can be at least one of the following: ZIF-8, MOF-5, MOF-2, Zn-BTC, ZIF-69, Mg-BDC, HKUST-1, Al-PCP, or IRMOF-3. The MOF precursor carbon material has the carbon elements contained in the precursor MOF as its basic framework. The MOF precursor carbon material is a nanoporous carbon with nano-sized pores.

[0067] MOF precursor carbon materials can be obtained by thermally decomposing a precursor MOF under an inert gas atmosphere such as Ar or N2. For example, when using ZIF-8, the thermal decomposition temperature can be set to 1000°C.

[0068] The MOF precursor inorganic material can be any of the following: Co-MOF, Co-BDC, MIL-101(Cr), Ce-BTC, MOF-100, ZIF-67, or Ni-BDC. The MOF precursor inorganic material has a metal oxide (e.g., Co3O4), which is an oxide of the metal element contained in the MOF, as its basic framework.

[0069] By calcining a precursor MOF in air, an inorganic material that serves as a precursor to an MOF can be obtained. For example, when using a Co-MOF, the heating temperature can be set to 450°C and the heating time to 2 hours.

[0070] MOF precursor carbon materials and MOF precursor inorganic materials are porous bodies with a uniform pore size distribution and possess high electrical conductivity. MOF precursor carbon materials have a high specific surface area, and MOF precursor inorganic materials have high structural stability.

[0071] MOF precursor carbon materials and MOF precursor inorganic materials have a uniform pore size distribution corresponding to the three-dimensional structure of the precursor MOF. The pore size of the MOF precursor carbon materials and MOF precursor inorganic materials is approximately the same as that of the precursor MOF. For example, the pore size of ZIF-8 is approximately 0.7 nm, and the pore size of Co-MOF is approximately 1 nm. By selecting the MOF used as a precursor based on its pore size, the pore size of the MOF precursor carbon materials and MOF precursor inorganic materials can be adjusted.

[0072] In the second embodiment described above, at least one of an MOF precursor carbon material and an MOF precursor inorganic material, with MOF as the precursor, is used as the CO2 adsorbent 102b. This makes it possible to make the pore diameter of the CO2 adsorbent 102b uniform. As a result, the CO2 adsorbent 102b can be made so as not to contain pores smaller than the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106, thereby increasing the proportion of effective active sites. Furthermore, the CO2 adsorbent 102b can be made so as not to contain pores that are too large relative to the ionic diameter of the electrolyte 106, thereby ensuring a high specific surface area.

[0073] (Third embodiment) Next, a third embodiment of the present invention will be described. The following describes the parts that differ from the above embodiments.

[0074] In this third embodiment, a porous carbon material is used as the high specific surface area material constituting the CO2 adsorbent 102b, with a composite material in which a metal oxide is coated with a carbon material as the precursor. In the following description, the porous carbon material with a metal oxide as the precursor will be referred to as the "metal oxide precursor carbon material". The metal oxide precursor carbon material can be the material described in "Porous Structure and Applications of MgO-Template Carbon", Carbon 2010, No. 242, 60-68.

[0075] Metal oxide precursor carbon materials can be obtained by a mold carbonization method using a metal oxide as a template. In this method, a composite material in which a metal oxide is coated with a carbon material is acid-washed, dissolving and removing the metal oxide that served as the template, resulting in a porous carbon material with a hollow template. Low-concentration sulfuric acid can be used for acid washing. For example, MgO can be used as the metal oxide included in the precursor. A specific example of a metal oxide precursor carbon material is Knobel®, manufactured by Toyo Tanso Co., Ltd.

[0076] Metal oxide precursor carbon materials are porous bodies with a uniform pore size distribution, high conductivity, and a high specific surface area. The metal oxide precursor carbon material has a uniform pore size distribution corresponding to the particle size of the metal oxide used as a precursor. The pore size of the metal oxide precursor carbon material is approximately the same as the particle size of the metal oxide. For example, MgO particles have a particle size of about 10-100 nm. By selecting the particle size of the metal oxide used as a precursor, the pore size of the metal oxide precursor carbon material can be adjusted.

[0077] In the third embodiment described above, a metal oxide precursor carbon material is used as the CO2 adsorbent 102b. This makes it possible to make the pore diameter of the CO2 adsorbent 102b uniform. As a result, the CO2 adsorbent 102b does not contain pores smaller than the molecular diameter of O2, the molecular diameter of CO2, and the ionic diameter of the electrolyte 106, thereby increasing the proportion of effective active sites. Furthermore, the CO2 adsorbent 102b does not contain pores that are too large relative to the ionic diameter of the electrolyte 106, thereby ensuring a high specific surface area.

[0078] (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.

[0079] For example, in the configurations of each of the embodiments described above, an example was given in which a high specific surface area material was used as the CO2 adsorbent 102b, which does not have a chemical structure that serves as an active site for adsorbing CO2 in the material itself. However, such a high specific surface area material and a material that has a chemical structure that serves as an active site (for example, polyanthraquinone) may be used simultaneously. [Explanation of symbols]

[0080] 101 Electrochemical cell 102 Working electrode 102b CO2 adsorbent 103 Opposite 106 Electrolyte 200 pores

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 The adsorbent is CO ２ It adsorbs, The aforementioned CO ２ The adsorbent is a porous body having pores (200) with a pore diameter that is greater than the ion diameter of the electrolyte and less than 100 times the ion diameter of the electrolyte. The CO2 adsorbent is a mesoporous carbon carbon dioxide capture system.

2. A carbon dioxide recovery system for separating CO from a CO-containing gas containing CO by an electrochemical reaction, ２ where the CO-containing gas contains CO, ２ and the system separates CO from the CO-containing gas, ２ is provided. 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 The adsorbent is CO ２ It adsorbs, The aforementioned CO ２ The adsorbent is a porous body having pores (200) with a pore diameter that is greater than the ion diameter of the electrolyte and less than 100 times the ion diameter of the electrolyte. The CO2 adsorbent is a porous carbon material with a metal-organic structure as a precursor in this carbon dioxide recovery system.

3. The carbon dioxide recovery system according to claim 2, wherein the metal-organic structure is at least one of ZIF-8, MOF-5, MOF-2, Zn-BTC, ZIF-69, Mg-BDC, HKUST-1, Al-PCP, and IRMOF-3.

4. 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 The adsorbent is CO ２ It adsorbs, The aforementioned CO ２ The adsorbent is a porous body having pores (200) with a pore diameter that is greater than the ion diameter of the electrolyte and less than 100 times the ion diameter of the electrolyte. The CO2 adsorbent is a porous inorganic material with a metal-organic structure as a precursor in this carbon dioxide recovery system.

5. The carbon dioxide recovery system according to claim 4, wherein the metal-organic structure is at least one of Co-MOF, Co-BDC, MIL-101(Cr), Ce-BTC, MOF-100, ZIF-67, and Ni-BDC.

6. 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 The adsorbent is CO ２ It adsorbs, The aforementioned CO ２ The adsorbent is a porous body having pores (200) with a pore diameter that is greater than the ion diameter of the electrolyte and less than 100 times the ion diameter of the electrolyte. The CO2 adsorbent is a porous carbon material having a composite material in which a metal oxide is coated with a carbon material as a precursor, and the carbon dioxide recovery system has a uniform pore size distribution corresponding to the particle size of the metal oxide.

7. The carbon dioxide recovery system according to claim 6, wherein the metal oxide is MgO.

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