Carbon dioxide recovery system

Abstract

To provide an electric field adsorption / desorption type carbon dioxide recovery system using an electrochemical cell which suppresses reduction in CO2 recovery efficiency.SOLUTION: A carbon dioxide recovery system for separating CO2 from CO2-containing gas containing CO2 by electrochemical reaction includes: an action pole 102 including a CO2 adsorbent 102b; and an electrochemical cell 101 having a counter electrode 103. By applying a first voltage between the action pole and the counter electrode, electrons are supplied to the action pole from the counter electrode, and the CO2 adsorbent takes in the electrons and adsorbs CO2 by a Coulomb force of the electrons without coupling that shares an electron orbit with CO2. By applying a second voltage different from the first voltage between the action pole and the counter electrode, the electrons are supplied to the counter electrode from the action pole, and the CO2 adsorbent emits the electrons and desorbs CO2.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a carbon dioxide recovery system for recovering CO2 from a CO2-containing gas.

Background Art

[0002] As CO2 recovery methods, a thermal adsorption and desorption method in which CO2 is adsorbed and desorbed by temperature fluctuations, a pressure adsorption and desorption method in which CO2 is adsorbed and desorbed by pressure fluctuations, and an electric field adsorption and desorption method in which CO2 is electrochemically adsorbed and desorbed are known. The electric field adsorption and desorption method has the advantage that the amount of CO2 adsorbed can be greatly changed by turning the electric field on and off, and the input energy is not released without contributing to CO2 adsorption and desorption, and is more efficient than the thermal adsorption and desorption method and the pressure adsorption and desorption method.

[0003] Patent Document 1 discloses a gas separation device that separates a reaction gas (for example, CO2) from a gaseous mixture by an electric field adsorption and desorption method. This device includes a porous anode impregnated with an adsorptive compound and a porous cathode impregnated with a conductive liquid. Then, by supplying power from a power supply device to the anode and the cathode, the reaction gas is adsorbed and desorbed by the adsorptive compound.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the device of Patent Document 1, an acid-base reaction is used for adsorption and desorption of the reaction gas, and the reaction gas is adsorbed by chemical bonding with a specific element. For this reason, the reaction for adsorbing and desorbing the reaction gas takes time, and the CO2 recovery efficiency is lowered.

[0006] In view of the above points, an object of the present invention is to suppress a decrease in CO2 recovery efficiency in an electrostatic adsorption type carbon dioxide recovery system using an electrochemical cell.

Means for Solving the Problems

[0007] To achieve the above object, in the invention described in claim 1 、3、5 There is provided a carbon dioxide recovery system for separating CO2 from a CO2-containing gas by an electrochemical reaction, comprising an electrochemical cell (100) having a working electrode (102) including a CO2 adsorbent (102a) and a counter electrode (103). When a first 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 takes in electrons and adsorbs CO2 by the Coulomb force of the electrons without involving a bond sharing an electron orbit with CO2. When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO2 adsorbent releases electrons and desorbs CO2. In the invention according to claim 1, CO 2 The adsorbent takes in electrons when a first voltage is applied between the working electrode and the counter electrode, and emits electrons when a second voltage is applied between the working electrode and the counter electrode. The CO 2 adsorption site, and the CO 2 adsorbent, when taking in electrons, the CO 2 electrons are unevenly distributed among a plurality of elements contained in the adsorption site. In the invention according to claim 3, the CO 2 adsorbent is an organic compound, and the organic compound is an aromatic compound having at least one of the elements N and S in the aromatic ring. In the invention according to claim 5, the CO 2 adsorbent is an inorganic compound capable of electron transfer due to a change in the valence of the contained metal element. Thus, since the CO2 adsorbent adsorbs CO2 by the Coulomb force of electrons, CO2 is more likely to desorb than a material that adsorbs CO2 by a chemical bond with a specific element (i.e., a bond sharing an electron orbit with CO2). Therefore, it is possible to suppress a decrease in the CO2 adsorption capacity and a decrease in the CO2 recovery efficiency.

[0008] 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

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0010] (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.

[0011] 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 or the exhaust gas of an internal combustion engine can be used.

[0012] 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 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.

[0013] The flow path switching valve 12 is a three-way valve that switches the flow path of the exhaust gas of the CO2 recovery device 100. When the CO2-removed gas is discharged from the CO2 recovery device 100, the flow path switching valve 12 switches the flow path of the exhaust gas to the atmosphere side, and when CO2 is discharged from the CO2 recovery device 100, the flow path switching valve 12 switches the flow path of the exhaust gas to the CO2 utilization device 13 side.

[0014] The CO2 utilization device 13 is a device that utilizes CO2. As the CO2 utilization device 13, for example, a storage tank that stores CO2 or a conversion device that converts CO2 into fuel can be used. The conversion device can use a device that converts CO2 into a hydrocarbon fuel such as methane. The hydrocarbon fuel may be a gaseous fuel at normal temperature and pressure or a liquid fuel at normal temperature and pressure.

[0015] The control device 14 is composed of a well-known microcomputer including a CPU, ROM, RAM, etc. and its peripheral circuits. The control device 14 performs various calculations and processes based on the control program stored in the ROM and controls the operations of various controlled devices. The control device 14 of the present embodiment 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, etc.

[0016] Next, the CO₂ recovery device 100 will be described with reference to FIG. 2. As shown in FIG. 2, the CO₂ recovery device 100 is provided with an electrochemically adsorbing and desorbing electrostatic adsorption type electrochemical cell 101 that adsorbs and desorbs CO₂ through an electrochemical reaction. The electrochemical cell 101 has a working electrode 102, a counter electrode 103, and an insulating layer 104. In the example shown in FIG. 2, the working electrode 102, the counter electrode 103, and the insulating layer 104 are each configured in a plate shape. Note that in FIG. 2, the working electrode 102, the counter electrode 103, and the insulating layer 104 are each shown with a gap therebetween, but in reality, these components are arranged in contact with each other.

[0017] The electrochemical cell 101 may be housed in a container (not shown). The container can be provided with a gas inlet for allowing a CO₂-containing gas to flow into the container and a gas outlet for allowing a CO₂-removed gas or CO₂ to flow out of the container.

[0018] The CO₂ recovery device 100 adsorbs and desorbs CO₂ through the electrochemical reaction of the electrochemical cell 101, and separates and recovers CO₂ from the CO₂-containing gas. The CO₂ recovery device 100 is provided with a power source 105 that applies a predetermined voltage to the working electrode 102 and the counter electrode 103, and can change the potential difference between the working electrode 102 and the counter electrode 103. The working electrode 102 is the negative electrode, and the counter electrode 103 is the positive electrode.

[0019] 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 for charging the electrochemical cell 101, and the CO₂ release mode is a discharging mode for discharging the electrochemical cell 101.

[0020] In the 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 < the counter electrode potential. The first voltage V1 can be, for example, in the range of 0.5 to 2.0 V.

[0021] In the CO₂ emission mode, a second voltage V2 is applied between the working electrode 102 and the counter electrode 103, and electrons are supplied from the working electrode 102 to the counter electrode 103. The second voltage V2 is a voltage different from the first voltage V1. The second voltage V2 may be a voltage lower than the first voltage V1, and the magnitude relationship between the working electrode potential and the counter electrode potential is not limited. That is, in the CO₂ emission mode, the working electrode potential < the counter electrode potential may be satisfied, the working electrode potential = the counter electrode potential may be satisfied, or the working electrode potential > the counter electrode potential may be satisfied.

[0022] As shown in FIG. 3, the working electrode 102 is provided with a working electrode side base material 102a, a CO₂ adsorbent 102b, a working electrode side conductive substance 102c, and a working electrode side binder 102d. In FIG. 3, for the sake of convenience, the CO₂ adsorbent 102b, the working electrode side conductive substance 102c, and the working electrode side binder 102d are illustrated as being located at different positions from the working electrode side base material 102a, but actually, the CO₂ adsorbent 102b, the working electrode side conductive substance 102c, and the working electrode side binder 102d are provided inside the porous working electrode side base material 102a.

[0023] The working electrode side base material 102a is a porous conductive material having pores through which a gas containing CO₂ can pass. As the working electrode side base material 102a, for example, a carbonaceous material or a metal material can be used. As the carbonaceous material constituting the working electrode side base material 102a, for example, carbon paper, carbon cloth, non-woven carbon mat, porous gas diffusion layer (GDL), etc. can be used. As the metal material constituting the working electrode side base material 102a, for example, a metal mesh formed by making a metal (e.g., Al, Ni, etc.) into a mesh shape can be used.

[0024] The CO₂ adsorbent 102b adsorbs CO₂ by receiving electrons and desorbs the adsorbed CO₂ by releasing electrons. The CO₂ adsorbent 102b will be described in detail later.

[0025] The working electrode side conductive material 102c forms a conduction path to the CO2 adsorbent 102b. As the working electrode side conductive material 102c, for example, carbon materials such as carbon nanotubes, carbon black, and graphene can be used. In the present embodiment, the CO2 adsorbent 102b and the working electrode side conductive material 102c are used in a mixed state.

[0026] For the mixing of the CO2 adsorbent 102b and the working electrode side conductive material 102c, for example, the working electrode side conductive material 102c can be dissolved in an organic solvent such as NMP (N-methylpyrrolidone), and the working electrode side conductive material 102c dispersed in the organic solvent can be brought into contact with the CO2 adsorbent 102b. The contact between the working electrode side conductive material 102c and the CO2 adsorbent 102b can be carried out by, for example, immersing the working electrode side base material 102a containing the CO2 adsorbent 102b in the solvent in which the working electrode side conductive material 102c is dispersed and performing dip coating. Thereby, the working electrode side conductive material 102c can be uniformly brought into contact with the CO2 adsorbent 102b.

[0027] The working electrode side binder 102d is provided to hold the CO2 adsorbent 102b on the working electrode side base material 102a. The working electrode side binder 102d has an adhesive force and is provided between the CO2 adsorbent 102b and the working electrode side base material 102a.

[0028] In the present embodiment, the CO2 adsorbent 102b, the working electrode side conductive material 102c, and the working electrode side binder 102d are used in a mixed state. A mixture of the CO2 adsorbent 102b, the working electrode side conductive material 102c, and the working electrode side binder 102d is formed, and this mixture is adhered to the working electrode side base material 102a.

[0029] As the working electrode side binder 102d, a conductive resin can be used. As the conductive resin, an epoxy resin containing Ag or the like as a conductive filler, a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), or the like can be used.

[0030] The working electrode side binder 102d can be brought into contact with the working electrode side base material 102a containing the CO2 adsorbent 102b using an organic solvent, similar to the working electrode side conductive material 102c. Alternatively, the raw material of the working electrode side binder 102d and the CO2 adsorbent 102b can be dispersed and mixed using a homogenizer or the like, and then the mixture can be molded and pressure-bonded to the working electrode side base material 102a. Or, the mixture of the working electrode side binder 102d and the CO2 adsorbent 102b may be spray-coated on the working electrode side base material 102a.

[0031] The counter electrode 103 has the same configuration as the working electrode 102, and is provided with a counter electrode side base material 103a, an electroactive auxiliary material 103b, a counter electrode side conductive material 103c, and a counter electrode side binder 103d.

[0032] The electroactive auxiliary material 103b is an auxiliary electroactive species that exchanges electrons with the CO2 adsorbent 102b. As the electroactive auxiliary material 103b, for example, a metal complex that enables electron exchange by changing the valence of metal ions can be used. Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickelocene, and cobaltocene, or porphyrin metal complexes. These metal complexes may be polymers or monomers.

[0033] Also, as the electroactive auxiliary material 103b, organic compounds such as phenothiazine, inorganic compounds such as RuO2, MnO2, and MoS2, and carbon materials such as carbon black and activated carbon can be used.

[0034] In this embodiment, polyvinylferrocene shown below is used as the electroactive auxiliary material 103b. Ferrocene exchanges electrons by changing the valence of Fe between divalent and trivalent.

[0035]

Chemical formula

[0036] As the insulating layer 104, a separator or a gas layer such as air can be used. In this embodiment, a porous separator is used as the insulating layer 104. As the material of the separator, a separator made of a cellulose membrane, a polymer, a composite material of a polymer and a ceramic, or the like can be used.

[0037] An electrolyte material 106 having ion conductivity is provided between the working electrode 102 and the counter electrode 103. The electrolyte material 106 is provided between the working electrode 102 and the counter electrode 103 via the insulating layer 104. The electrolyte material 106 is provided so as to cover the working electrode 102, the counter electrode 103, and the insulating layer 104.

[0038] The electrolyte material 106 is in contact with the CO2 adsorbent 102b. The ions contained in the electrolyte material 106 promote the electron-withdrawing of the CO2 adsorbent 102b when the CO2 adsorbent 102b binds to CO2. The ions contained in the electrolyte material 106 do not directly react with the CO2 adsorption site of the CO2 adsorbent 102b that adsorbs CO2.

[0039] As the electrolyte material 106, an ionic liquid, a solid electrolyte, or the like can be used. An ionic liquid is a liquid salt that is non-volatile under normal temperature and pressure. When an ionic liquid is used as the electrolyte material 106, the ionic liquid may be gelled in order to prevent elution from the electrochemical cell 101. When a solid electrolyte is used as the electrolyte material 106, it is desirable to use an ionomer made of a polymer electrolyte or the like in order to increase the contact area with the CO2 adsorbent 102b.

[0040] As the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][Tf2N]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][Tf2N]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-ethyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, etc. can be used.

[0041] Alternatively, as the electrolyte material 106, H2SO4, Na2SO4, KOH, etc. can be used.

[0042] Here, the CO2 adsorbent 102b of the present embodiment will be described. The CO2 adsorbent 102b is a material that does not involve a structural change in the chemical skeleton when adsorbing CO2. In the present embodiment, as the CO2 adsorbent 102b, a material that can exchange electrons without a structural change in the chemical skeleton is used 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 material without charge concentration on specific elements in the chemical structure.

[0043] By applying a first voltage V1 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 by the Coulomb force of the electrons. By applying a second voltage V2 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.

[0044] When the CO₂ adsorbent 102b adsorbs CO₂, electrons taken into the CO₂ adsorbent 102b and ions contained in the electrolyte material 106 form an electric double layer. By forming the electric double layer during CO₂ adsorption in this way, electrons can be stably retained on the surface of the CO₂ adsorbent 102b. For this reason, it becomes possible to adsorb CO₂ that has diffused and reached the vicinity of the surface of the CO₂ adsorbent 102b by the Coulomb force of the electrons.

[0045] The CO₂ adsorbent 102b of the present embodiment has a CO₂ adsorption site that takes in electrons when a first voltage V1 is applied between the working electrode 102 and the counter electrode 103, and releases electrons when a second voltage V2 is applied between the working electrode 102 and the counter electrode 103. By having a CO₂ adsorption site in which the CO₂ adsorbent 102b can take in electrons in this way, the capacitance of the electric double layer can be increased.

[0046] As shown in FIG. 4, the CO₂ adsorbent 102b of the present embodiment adsorbs CO₂ contained in the CO₂-containing gas. In FIG. 4, illustration of the working electrode side conductive material 102c and the working electrode side binder 102d is omitted.

[0047] In the CO₂ adsorbent 102b of the present embodiment, electrons are unevenly distributed among a plurality of elements contained in the CO₂ adsorption site when taking in electrons, and electrons are not localized in a specific element of the CO₂ adsorption site. Also, as described above, the CO₂ adsorbent 102b takes in electrons and adsorbs CO₂ by the Coulomb force of the electrons, and does not involve a bond that shares the electron orbit with CO₂ during CO₂ adsorption. That is, the CO₂ adsorbent 102b adsorbs CO₂ not by a chemical bond with a specific site where charges are localized, but by the Coulomb force of delocalized electrons unevenly distributed among a plurality of elements.

[0048] By taking in electrons at the CO₂ adsorption sites contained in the CO₂ adsorbent 102b, an electric double layer can be formed between the CO₂ adsorption sites with electron bias and the ions contained in the electrolyte material 106, and the capacitance of the electric double layer can be further increased. In the CO₂ adsorbent 102b, since electrons are delocalized at the CO₂ adsorption sites, the formation of the electric double layer with the ions of the electrolyte material 106 and the CO₂ adsorption by the Coulomb force of the electrons can be switched at high speed and alternately. Therefore, both an increase in the capacitance of the electric double layer and an increase in the CO₂ adsorption capacity can be achieved.

[0049] As the CO₂ adsorbent 102b, any material capable of donating and accepting electrons without accompanying a structural change in the chemical skeleton may be used. The CO₂ adsorbent 102b is a material that can receive charges when a negative potential is applied with respect to the natural potential, does not change its chemical skeleton during charge transfer, and does not concentrate charges on specific elements.

[0050] In the present embodiment, an organic compound is used as the CO₂ adsorbent 102b. As the organic compound, for example, an aromatic compound can be used. It is desirable that the aromatic compound contains at least one of the elements N and S in the aromatic ring. N and S are elements with high electronegativity. In the organic compound, these elements with high electronegativity become the CO₂ adsorption sites.

[0051] As the organic compound, for example, at least one of benzothiadiazole, polyvinylbenzothiadiazole, and polydiaza phthalimide can be used.

[0052] Benzothiadiazole has the structure shown below, and N and S contained in the aromatic ring become the CO₂ adsorption sites. When benzothiadiazole receives electrons, the electrons are unevenly distributed to N and S, and the electrons are delocalized.

[0053]

Chemical formula

[0054]

Chemical formula

[0055] As shown in FIG. 5, the carbon dioxide recovery system 10 operates by alternately switching between the CO2 recovery mode and the CO2 release mode. The operation of the carbon dioxide recovery system 10 is controlled by the control device 14.

[0056] First, the CO2 recovery mode will be described. In the CO2 recovery mode, the compressor 11 operates to supply the 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 set as the first voltage V1. Thereby, the electron donation of the electroactive auxiliary material 103b of the counter electrode 103 and the electron withdrawal of the CO2 adsorbent 102b of the working electrode 102 can be realized simultaneously. The electroactive auxiliary material 103b of the counter electrode 103 releases electrons and becomes in an oxidized state, and electrons are supplied from the counter electrode 103 to the working electrode 102.

[0057] As shown in FIG. 6, the electrons supplied to the working electrode 102 move to the CO2 adsorbent 102b through the working electrode side conductive substance 102c. The CO2 adsorbent 102b made of an organic compound receives electrons by being reduced. When electrons are taken into the CO2 adsorption site of the CO2 adsorbent 102b, an electric double layer is formed between the CO2 adsorption site with electron bias and the cation 106a of the electrolyte material 106.

[0058] As shown below, the CO2 adsorbent 102b made of an organic compound becomes strongly polarized by accepting electrons at the CO2 adsorption site. The portion enclosed by the dashed line in benzothiadiazole indicates the bias of negative charge.

[0059] [Chemical formula] The C contained in CO2 has a δ+ charge, and CO2 is attracted to the CO2 adsorption site of the CO2 adsorbent 102b by electrostatic interaction. As a result, CO2 is adsorbed by the CO2 adsorbent 102b, and the CO2 recovery device 100 can recover CO2 from the CO2-containing gas.

[0060] After the CO2-containing gas has CO2 recovered by the CO2 recovery device 100, it is discharged from the CO2 recovery device 100 as a CO2-free CO2-removed gas. The flow path switching valve 12 switches the gas flow path to the atmosphere side, and the CO2-removed gas discharged from the CO2 recovery device 100 is discharged to the atmosphere.

[0061] Next, the CO2 release mode will be described. In the CO2 release mode, the compressor 11 stops operating, and the supply of the CO2-containing gas to the CO2 recovery device 100 stops.

[0062] As shown in FIG. 5, in the CO2 recovery device 100, the voltage applied between the working electrode 102 and the counter electrode 103 is set as the second voltage V2. Thereby, it is possible to simultaneously realize the electron donation of the CO2 adsorbent 102b of the working electrode 102 and the electron withdrawal of the electrochemically active auxiliary material 103b of the counter electrode 103. The electrochemically active auxiliary material 103b of the counter electrode 103 accepts electrons and becomes a reduced state.

[0063] As shown in FIG. 7, the CO2 adsorbent 102b releases electrons. By releasing electrons, the CO2 adsorbent 102b desorbs the adsorbed CO2 by electrostatic interaction.

[0064] The CO2 released from the CO2 adsorbent 102b is discharged from the CO2 recovery device 100. The flow path switching valve 12 has switched 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.

[0065] According to the present embodiment described above, as the CO2 adsorbent 102b of the working electrode 102, a material that can transfer electrons without accompanying a structural change in the chemical skeleton and in which charges are delocalized is used. When a first voltage 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 takes in electrons and adsorbs CO2 by the Coulomb force of the electrons without involving a bond that shares an electron orbit with CO2. Then, when a second voltage 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 releases electrons and desorbs CO2.

[0066] Since the CO2 adsorbent 102b of the present embodiment adsorbs CO2 by the Coulomb force of delocalized electrons, CO2 is more likely to desorb than a material that adsorbs CO2 by a chemical bond with a specific element (that is, a bond that shares an electron orbit with CO2). Therefore, according to the CO2 adsorbent 102b of the present embodiment, it is possible to suppress a decrease in the CO2 adsorption capacity and to suppress a decrease in the CO2 recovery efficiency.

[0067] Further, in the carbon dioxide recovery system of the present embodiment, when the CO2 adsorbent adsorbs CO2, the electrons taken into the CO2 adsorbent and the ions contained in the electrolyte material 106 form an electric double layer. As a result, electrons can be stably retained on the surface of the CO2 adsorbent 102b, and it becomes possible to adsorb CO2 that has diffused and reached the vicinity of the surface of the CO2 adsorbent 102b by the Coulomb force of the electrons.

[0068] In addition, when a first voltage V1 is applied between the working electrode 102 and the counter electrode 103, the CO2 adsorbent 102b of the present embodiment takes in electrons, and when a second voltage V2 is applied between the working electrode 102 and the counter electrode 103, it has a CO2 adsorption site that releases electrons. Thereby, the capacitance of the electric double layer formed by the electrons taken into the CO2 adsorbent and the ions contained in the electrolyte material 106 can be increased.

[0069] When the CO2 adsorbent 102b takes in electrons, electrons are unevenly distributed among a plurality of elements contained in the CO2 adsorption site, and electrons are not localized in a specific element. Therefore, in the CO2 adsorbent 102b, the formation of the electric double layer and CO2 adsorption can be switched at high speed and alternately, and both an increase in the capacitance of the electric double layer and an increase in the CO2 adsorption capacity can be achieved.

[0070] (Second Embodiment) Next, a second embodiment of the present invention will be described. Hereinafter, only the parts different from the first embodiment will be described.

[0071] In the second embodiment, an inorganic compound is used as the CO2 adsorbent 102b. When an inorganic compound is used as the CO2 adsorbent 102b, the CO2 adsorbent 102b and the working electrode side conductive substance 102c can be used in combination.

[0072] The inorganic compound used as the CO2 adsorbent 102b is a material capable of donating and accepting electrons due to a change in the valence of the contained metal element, and at least one of inorganic oxides, inorganic nitrides, inorganic chalcogenide-based materials, etc. can be used. Inorganic chalcogenide-based materials include sulfides, selenides, and tellurides.

[0073] The inorganic compound desirably contains a typical element with a high electronegativity that can interact with CO2. The inorganic compound desirably contains at least one of the elements O, N, S, Se, and Te. In the inorganic compound, these elements with high electronegativity become the CO2 adsorption sites.

[0074] As the inorganic oxide, for example, RuO2 and MnO2 can be used. The inorganic chalcogenide-based material is a compound of a metal element and S, Se, or Te, and for example, MoS2 can be used.

[0075] FIG. 8 shows CO2 adsorption when an inorganic compound is used as the CO2 adsorbent 102b. FIG. 8 shows an example in which RuO2 is used as the CO2 adsorbent 102b, and the CO2 adsorbent 102b also serves as the working electrode side conductive substance 102c.

[0076] As shown in FIG. 8, when electrons are supplied from the counter electrode 103 to the working electrode 102, a part of the CO2 adsorbent 102b receives electrons by being reduced by a redox reaction. In FIG. 8, the reduced state of the CO2 adsorbent 102b is shown by hatching.

[0077] The CO2 adsorbent 102b made of an inorganic compound takes in electrons at the CO2 adsorption site composed of a typical element (O in the case of RuO2), and forms an electric double layer between the CO2 adsorption site and the cation 106a of the electrolyte material 106.

[0078] The CO2 adsorbent 102b made of an inorganic compound adsorbs CO2 by electrostatic interaction with respect to the CO2 adsorption site (O in the case of RuO2).

[0079] As shown in the following reaction formula, a part of RuO2 changes the valence of Ru from tetravalent to trivalent with the acceptance of electrons, and changes the valence of Ru from trivalent to tetravalent with the release of electrons.

[0080] Ru(IV)O2 + x[EMIM] + + xe - ←→Ru(IV)Ru(III) 1-x O2[EMIM] x + Note that [EMIM] + is the cation 106a of the ionic liquid used as the electrolyte material 106.

[0081] In the second embodiment described above, an inorganic compound is used as the CO2 adsorbent 102b. Also in the configuration of this second embodiment, the same effects as those of the first embodiment can be obtained, and a decrease in the CO2 recovery efficiency of the CO2 adsorbent 102b can be suppressed.

[0082] (Third Embodiment) Next, a third embodiment of the present invention will be described. Hereinafter, only the parts different from the above embodiments will be described.

[0083] In this third embodiment, a porous material is used as the CO2 adsorbent 102b. In this third embodiment, a carbon material is used as the porous material constituting the CO2 adsorbent 102b.

[0084] The carbon material is a porous body and has conductivity. When a carbon material is used as the CO2 adsorbent 102b, the CO2 adsorbent 102b can also serve as the working electrode side conductive substance 102c. As the carbon material, for example, at least one of graphite, carbon black, carbon nanotubes, graphene, and activated carbon can be used.

[0085] FIG. 9 shows CO2 adsorption when a carbon material is used as the CO2 adsorbent 102b. In the example shown in FIG. 9, the CO2 adsorbent 102b also serves as the working electrode side conductive substance 102c.

[0086] As shown in FIG. 9, when electrons are supplied from the counter electrode 103 to the working electrode 102, the electrons can conduct to the surface of the CO2 adsorbent 102b. The CO2 adsorbent 102b takes in electrons and forms an electric double layer with the cations 106a of the electrolyte material 106.

[0087] The CO2 adsorbent 102 made of a carbon material has a large contact area with the electrolyte material 106, so the capacitance of the electric double layer increases. Therefore, the amount of CO2 adsorbed and the adsorption efficiency by the CO2 adsorbent 102 can be increased.

[0088] In the third embodiment described above, a carbon material is used as the CO₂ adsorbent 102b. Also in the configuration of this third embodiment, the same effects as those of the first embodiment can be obtained, and it is possible to suppress a decrease in the CO₂ recovery efficiency of the CO₂ adsorbent 102b.

[0089] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. Hereinafter, only the parts different from the above embodiments will be described.

[0090] In this fourth embodiment, a porous material is used as the CO₂ adsorbent 102b. In this fourth embodiment, a metal-organic complex is used as the porous material constituting the CO₂ adsorbent 102b. When a metal-organic complex is used as the CO₂ adsorbent 102b, it is desirable to mix and use a working electrode side conductive material 102c made of a carbon material.

[0091] A metal-organic complex is a metal-organic framework (MOF) having a porous structure in which organic ligands are coordinately bonded to metal ions. As the organometallic complex, for example, at least one of CAU-8, HKUST-1 (MOF-199), MOF-801, and MOF-867 can be used.

[0092] CAU-8 contains Al ions as metal ions and is an organometallic structure containing benzophenone dicarboxylate as an organic ligand. HKUST-1 (MOF-199) contains Cu ions as metal ions and is an organometallic structure containing 1,3,5-benzenetricarboxylate as an organic ligand. MOF-801 and MOF-867 are organometallic structures containing Zr ions as metal ions.

[0093] The CO₂ adsorbent 102b forms an electric double layer with the cations 106a of the electrolyte material 106 by taking in electrons. Since the CO₂ adsorbent 102 made of an organometallic complex has a large contact area with the electrolyte material 106, the capacitance of the electric double layer increases. Therefore, the amount of CO₂ adsorbed and the adsorption efficiency by the CO₂ adsorbent 102 can be increased.

[0094] In the fourth embodiment described above, an organometallic complex is used as the CO2 adsorbent 102b. Also in the configuration of this fourth embodiment, the same effects as those of the first embodiment can be obtained, and it is possible to suppress a decrease in the CO2 recovery efficiency of the CO2 adsorbent 102b.

[0095] (Example) Next, examples of each of the above embodiments will be described with reference to FIG. 10. The current efficiency when CO2 is adsorbed by the CO2 adsorbent 102b will be described using examples and comparative examples. The current efficiency indicates the ratio of the number of CO2 molecules adsorbed by the CO2 adsorbent 102b to the number of electrons flowing through the CO2 adsorbent 102b.

[0096] As the CO2 adsorbent 102b, benzothiadiazole is used in Example 1, polyvinylbenzothiadiazole is used in Example 2, carbon black is used in Example 3, polydiaza phthalimide is used in Example 4, RuO2 is used in Example 5, MoS2 is used in Example 6, and MnO2 is used in Example 7. As the CO2 adsorbent 102b, anthraquinone is used in Comparative Example 1 and fluorenone is used in Comparative Example 2.

[0097] As shown in FIG. 6, the current efficiency of Example 1 was 93%, the current efficiency of Example 2 was 95%, the current efficiency of Example 3 was 96%, the current efficiency of Example 4 was 93%, the current efficiency of Example 5 was 102%, the current efficiency of Example 6 was 92%, and the current efficiency of Example 7 was 105%. The current efficiency of Comparative Example 1 was 60% and the current efficiency of Comparative Example 2 was 40%. Thus, with the materials of Examples 1 to 7, a significantly higher current efficiency was obtained than with the materials of Comparative Examples 1 and 2, and the materials of Examples 1 to 7 have a superior CO2 adsorption ability than the materials of Comparative Examples 1 and 2.

[0098] (Other Embodiments) The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. Also, the means disclosed in the above embodiments may be appropriately combined within the range where they can be implemented.

[0099] For example, in each of the above embodiments, an example in which an organic compound, an inorganic compound, a carbon material, and an organometallic complex are each used alone as the CO2 adsorbent 102b has been described, but these may be used in appropriate combinations.

[0100] Also, in each of the above embodiments, the working electrode side binder 102d for holding the CO2 adsorbent 102b on the working electrode side base material 102a is provided, but the present invention is not limited thereto, and the working electrode side binder 102d may be omitted.

Description of Reference Numerals

[0101] 101 Electrochemical cell 102 Working electrode 102b CO2 adsorbent 103 Counter electrode 104 Insulating layer 106 Electrolyte material

Claims

1. A carbon dioxide recovery system for separating CO from a CO-containing gas by an electrochemical reaction, comprising: ２ a working electrode (102) containing a CO adsorbent (102b) and a counter electrode (103); ２ When a first 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 adsorbent takes in electrons and adsorbs CO by the Coulomb force of the electrons without involving a bond sharing an electron orbit with CO; ２ When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO adsorbent releases electrons and desorbs CO; The CO adsorbent has a CO2 adsorption site that takes in electrons when the first voltage is applied between the working electrode and the counter electrode and releases electrons when the second voltage is applied between the working electrode and the counter electrode; ２ The CO adsorbent is an organic compound, and the organic compound is an aromatic compound having at least one of the elements N and S in an aromatic ring. When a first 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 adsorbent takes in electrons and adsorbs CO by the Coulomb force of the electrons without involving a bond sharing an electron orbit with CO; ２ When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO adsorbent releases electrons and desorbs CO; ２ The CO2 adsorbent has a CO2 adsorption site that takes in electrons when the first voltage is applied between the working electrode and the counter electrode and releases electrons when the second voltage is applied between the working electrode and the counter electrode; ２ The CO2 adsorbent is a carbon dioxide recovery system in which electrons are unevenly distributed among a plurality of elements contained in the CO2 adsorption site when taking in electrons. When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO adsorbent releases electrons and desorbs CO; ２ The CO adsorbent releases electrons and desorbs CO; ２ The CO2 adsorbent has a CO2 adsorption site that takes in electrons when the first voltage is applied between the working electrode and the counter electrode and releases electrons when the second voltage is applied between the working electrode and the counter electrode; The CO2 adsorbent has a CO2 adsorption site that takes in electrons when the first voltage is applied between the working electrode and the counter electrode and releases electrons when the second voltage is applied between the working electrode and the counter electrode; The CO2 adsorbent is a carbon dioxide recovery system in which electrons are unevenly distributed among a plurality of elements contained in the CO2 adsorption site when taking in electrons.

2. The CO adsorbent is an organic compound, and the organic compound is an aromatic compound having at least one of the elements N and S in an aromatic ring. ２ The CO adsorbent is an organic compound, and the organic compound is an aromatic compound having at least one of the elements N and S in an aromatic ring. The carbon dioxide recovery system according to claim 1, wherein the organic compound is an aromatic compound having at least one of the elements N and S in an aromatic ring.

3. A carbon dioxide recovery system for separating CO from a CO-containing gas by an electrochemical reaction, comprising: ２ a working electrode (102) containing a CO adsorbent (102b) and a counter electrode (103); ２ When a first 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 adsorbent takes in electrons and adsorbs CO by the Coulomb force of the electrons without involving a bond sharing an electron orbit with CO; ２ When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO adsorbent releases electrons and desorbs CO; The CO adsorbent has a CO2 adsorption site that takes in electrons when the first voltage is applied between the working electrode and the counter electrode and releases electrons when the second voltage is applied between the working electrode and the counter electrode; ２ The CO adsorbent is an organic compound, and the organic compound is an aromatic compound having at least one of the elements N and S in an aromatic ring. When a first 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 adsorbent takes in electrons and CO ２ is adsorbed by the Coulomb force of electrons without involving a bond sharing an electron orbit with CO ２ and When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO ２ adsorbent releases electrons and CO ２ is desorbed. The CO₂ adsorbent is an organic compound, and the organic compound is a carbon dioxide recovery system that is an aromatic compound having at least one of the elements N and S in an aromatic ring.

4. The carbon dioxide recovery system according to claim 2 or 3, wherein the organic compound contains at least one of benzothiadiazole, polyvinylbenzothiadiazole, and polydiaza phthalimide.

5. A carbon dioxide recovery system for separating CO ２ from a CO ２ containing gas containing CO ２ by an electrochemical reaction, comprising: an electrochemical cell (101) having a working electrode (102) including a CO ２ adsorbent (102b) and a counter electrode (103), When a first 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 adsorbent takes in electrons and CO ２ is adsorbed by the Coulomb force of electrons without involving a bond sharing an electron orbit with CO ２ and When a second voltage different from the first voltage is applied between the working electrode and the counter electrode, electrons are supplied from the working electrode to the counter electrode, and the CO ２ adsorbent releases electrons and CO ２ is desorbed. The CO₂ adsorbent is an inorganic compound capable of electron transfer due to the valence change of the contained metal element, and it is a carbon dioxide recovery system.

6. The carbon dioxide recovery system according to claim 5, wherein the inorganic compound contains at least one of inorganic oxides, inorganic nitrides, or inorganic chalcogenide-based materials.

7. The inorganic compound is RuO ２ , MnO ２ , MoS ２ The carbon dioxide recovery system according to claim 5 or 6, which contains at least one of them.

8. The electrochemical cell has an insulating layer (104) provided between the working electrode and the counter electrode, and an electrolyte material (106) covering the working electrode, the counter electrode, and the insulating layer. When the CO ２ adsorbent adsorbs CO ２ , electrons taken into the CO ２ adsorbent and ions contained in the electrolyte material form an electric double layer. The carbon dioxide recovery system according to any one of claims 1 to 7.

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