Acid gas recovery system

Abstract

To provide an acid gas recovery system having an electrochemical cell which suppresses an influence of active oxygen produced in an electrochemical reaction, and suppresses performance deterioration of the electrochemical cell.SOLUTION: A carbon dioxide recovery system 10 as an acid gas recovery system has: an electrochemical cell 101 having an action electrode 102 and a counter electrode 103; and an electrolytic solution 108 containing water as a reducer for reducing at least active oxygen. When a first voltage V1 is applied between the action electrode 102 and the counter electrode 103, the carbon dioxide recovery system 10 adsorbs CO2 in an adsorption object accompanying supply of an electron to the action electrode 102 from the counter electrode 103, and recovers acidic gas.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an acid gas recovery system that recovers acid gas from a mixed gas containing acid gas by an electrochemical reaction using an electrochemical cell. [Background technology]

[0002] Conventionally, various techniques have been developed for an acid gas recovery system that recovers an acid gas from a mixed gas containing the acid gas by an electrochemical reaction in an electrochemical cell. For example, a technique described in Patent Document 1 is known as a technique for an acid gas recovery system.

[0003] The carbon dioxide recovery system described in Patent Document 1 is an acid gas recovery system that targets carbon dioxide gas as an acid gas. Patent Document 1 is configured to adsorb CO2 as it is without transferring charge to CO2 by concentrating an electric field on the electrode surface without using a redox-active organic substance (e.g., anthraquinone). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-177883 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when an electrochemical cell is operated in the presence of O2, such as from the atmosphere, charge transfer occurs relative to O2, generating active oxygen. It is expected that the generation of active oxygen will reduce the current efficiency, which indicates the amount of CO2 adsorbed per electron. Furthermore, the highly reactive active oxygen will cause the decomposition of the electrode materials that make up the electrochemical cell, which is thought to be one of the factors shortening the life of the electrochemical cell in the acid gas recovery system.

[0006] In view of the above, the present disclosure aims to provide an acid gas recovery system having an electrochemical cell, which suppresses the effects of active oxygen generated during an electrochemical reaction and inhibits deterioration in the performance of the electrochemical cell. [Means for solving the problem]

[0007] An acid gas recovery system according to one embodiment of the present disclosure is an acid gas recovery system that separates acid gas from an acid gas-containing gas that contains acid gas and oxygen by electrochemical reaction, and includes an electrochemical cell (101) and an electrolyte (108). The electrochemical cell includes a working electrode (102) and a counter electrode (103), and electrons are exchanged by applying a voltage between the working electrode and the counter electrode. The electrolyte contains a reducing agent that reduces at least active oxygen between the working electrode and the counter electrode. When a predetermined first voltage (V1) is applied between the working electrode and the counter electrode, the acid gas recovery system causes the adsorption target to adsorb the acid gas contained in the acid gas-containing gas with the supply of electrons from the counter electrode to the working electrode, thereby recovering the acid gas.

[0008] Therefore, according to the acid gas recovery system according to one embodiment of the present disclosure, acid gas can be recovered from an acid gas-containing gas by an electrochemical reaction using an electrochemical cell having an electrolyte solution containing a reducing agent. Even if active oxygen is generated by the operation of the electrochemical cell, the reducing agent constituting the electrolyte has a function of decomposing (reducing) the active oxygen, so that the effect of the active oxygen on the life and performance of the electrochemical cell can be suppressed to a small extent.

[0009] In addition, the reference numerals in parentheses for each means described in this section and in the claims indicate the correspondence with the specific means described in the embodiments described later. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a carbon dioxide capture system according to one embodiment. [Diagram 2]FIG. 1 is a configuration diagram of a carbon dioxide capture device according to an embodiment. [Diagram 3] FIG. 1 is a cross-sectional view of an electrochemical cell according to one embodiment. [Figure 4] FIG. 2 is an explanatory diagram regarding the operation of the carbon dioxide capture device in a CO2 capture mode and a CO2 release mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present disclosure will be described with reference to Figures 1 to 4. In this embodiment, an acid gas recovery system according to the present disclosure is realized as a carbon dioxide recovery system 10 that recovers carbon dioxide (CO2), which is a type of acid gas. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated descriptions are omitted.

[0012] As shown in FIG. 1, a carbon dioxide capture system 10 of this embodiment includes a compressor 11, a carbon dioxide capture device 100, a flow path switching valve 12, a carbon dioxide utilization device 13, and a control device .

[0013] The compressor 11 pressure-feeds the CO2-containing gas to the carbon dioxide capture device 100. The CO2-containing gas is a mixed gas containing CO2 and gases other than CO2, and may be, for example, the atmosphere or exhaust gas from an internal combustion engine. The CO2-containing gas contains O2 as a gas other than CO2.

[0014] The carbon dioxide capture device 100 is a device that separates and captures CO2 from a CO2-containing gas. The carbon dioxide capture device 100 discharges a CO2-removed gas after CO2 is captured from the CO2-containing gas, or the CO2 captured from the CO2-containing gas. The configuration of the carbon dioxide capture device 100 will be described in detail later.

[0015] The flow path switching valve 12 is a three-way valve that switches the flow path of the exhaust gas of the carbon dioxide capture device 100. When a CO2 removed gas is discharged from the carbon dioxide capture 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 carbon dioxide capture device 100, the flow path switching valve 12 switches the flow path of the exhaust gas to the carbon dioxide utilization device 13 side.

[0016] The carbon dioxide utilization device 13 is a device that utilizes CO2. For example, a storage tank that stores CO2 or a conversion device that converts CO2 into fuel can be used as the carbon dioxide utilization device 13. For the conversion device, a device that converts CO2 into a hydrocarbon fuel such as methane can be used. The hydrocarbon fuel may be a gas fuel at normal temperature and pressure, or may be a liquid fuel at normal temperature and pressure.

[0017] 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 processing based on a control program stored in the ROM, and controls the operation of various controlled devices. The control device 14 of this embodiment controls the operation of the compressor 11, the operation of the carbon dioxide capture device 100, and the flow path switching control of the flow path switching valve 12, etc.

[0018] Next, the carbon dioxide capture device 100 will be described with reference to Fig. 2. As shown in Fig. 2, the carbon dioxide capture device 100 has an electrochemical cell 101 of an electric field adsorption / desorption type that adsorbs and desorbs CO2 by an electrochemical reaction. The electrochemical cell 101 has a working electrode 102, a counter electrode 103, and an insulating layer 106. In the example shown in Fig. 2, the working electrode 102, the counter electrode 103, and the insulating layer 106 are each configured in a plate shape. Note that, although Fig. 2 illustrates the working electrode 102, the counter electrode 103, and the insulating layer 106 with a gap therebetween, in reality, these components are arranged so as to be in contact with each other.

[0019] Here, the electrochemical cell 101 may be accommodated in a container (not shown). The container may be provided with a gas inlet for introducing the CO2-containing gas into the container, and a gas outlet for discharging the CO2-removed gas and CO2 from the container.

[0020] The carbon dioxide capture device 100 adsorbs and desorbs CO2 by electrochemical reactions in an electrochemical cell 101, and separates and captures CO2 from a CO2-containing gas. The carbon dioxide capture device 100 is provided with a power source 107 that applies a predetermined voltage to a working electrode 102 and a counter electrode 103, and is capable of changing the potential difference between the working electrode 102 and the counter electrode 103. The working electrode 102 is a negative electrode, and the counter electrode 103 is a positive electrode.

[0021] By changing the potential difference between the working electrode 102 and the counter electrode 103, the electrochemical cell 101 can be switched between a CO2 capture mode in which CO2 is captured from a CO2-containing gas and a CO2 release mode in which the captured CO2 is released to the outside from the electrochemical cell 101. The CO2 capture mode is a charge mode in which the electrochemical cell 101 is charged, and the CO2 release mode is a discharge mode in which the electrochemical cell 101 is discharged.

[0022] In the CO2 capture 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 smaller than the counter electrode potential. The first voltage V1 can be set within a range of, for example, 0.2 to 3.0 V, preferably 0.5 to 2.0 V.

[0023] In addition, in the CO2 capture mode, it is preferable that the potential of the working electrode 102 is set to be equal to or lower than the equilibrium potential of the water electrolysis reaction and equal to or higher than the equilibrium potential of the oxygen + water reaction, because this makes it possible to suppress side reactions such as hydrogen generation among the electrochemical reactions in the CO2 capture mode.

[0024] In the CO2 release 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 release 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.

[0025] In the electrochemical cell 101 of this embodiment, when a voltage is applied between the working electrode 102 and the counter electrode 103, an electric double layer is formed by electrons and ions contained in the electrolyte solution 108. In the CO2 capture mode, when cations of the electrolyte solution 108 move near the working electrode 102 and anions of the electrolyte solution 108 move near the counter electrode 103, a potential difference is formed near the respective surfaces, and electrons are supplied from the counter electrode 103 to the working electrode 102.

[0026] The supply of electrons at the working electrode 102 promotes an electrochemical reaction between the water in the electrolyte 108 and the O2 contained in the CO2-containing gas, resulting in the formation of OH - The water in the electrolyte 108 is an example of a reducing agent. - The electrochemical reaction of the CO2 contained in the CO2-containing gas produces carbonate ions (CO3 2- ) or bicarbonate ion (HCO3 - ) is produced. In addition, O2, which is active oxygen, is also produced. - Even if generated, it is decomposed by the water constituting the electrolyte 108.

[0027] Since the CO2 in the CO2-containing gas is used in the reaction to produce carbonate ions or bicarbonate ions, the CO2 in the CO2-containing gas is adsorbed and removed as carbonate ions or bicarbonate ions are produced, and CO2 is recovered from the CO2-containing gas.

[0028] In addition, the CO2 adsorption in the CO2 capture mode can also be performed in a mode in which an adsorbent is used in combination. The adsorbent is a material that does not undergo structural changes in its chemical skeleton when it adsorbs acidic gases. As the adsorbent, a material is used that can donate and receive electrons without structural changes in its chemical skeleton by applying a negative potential to the counter electrode 103, and when electrons are supplied from the counter electrode 103, the charge is not concentrated on a specific element in the chemical structure, and the charge is delocalized throughout the material.

[0029] Specifically, an organic compound is used as the adsorbent, and for example, an aromatic compound can be used. The aromatic compound preferably contains at least one of N and S elements in the aromatic ring. N and S are elements with high electronegativity. In the organic compound, these elements with high electronegativity become the adsorption sites for the acid gas. For example, at least one of benzothiadiazole, polyvinylbenzothiadiazole, and polydiazaphthalimide can be used as the organic compound.

[0030] In the CO 2 release mode, anions in the electrolyte 108 move to the vicinity of the working electrode 102 , cations in the electrolyte 108 move to the vicinity of the counter electrode 103 , and electrons are supplied from the working electrode 102 to the counter electrode 103 .

[0031] As electrons are supplied from the counter electrode 103 to the working electrode 102, carbonate ions (CO3 2- ) or bicarbonate ion (HCO3 - ) to OH - As a result, in the CO2 capture mode, the CO2 adsorbed in the electrolyte 108 is released and can be captured from the electrochemical cell 101.

[0032] The working electrode 102 of the electrochemical cell 101 according to this embodiment is preferably made of a gas-permeable conductive material, since CO2-containing gas is the target for CO2 capture. Furthermore, the working electrode 102 according to this embodiment converts water contained in the electrolyte 108 and O2 in the CO2-containing gas into OH. -It is preferable that the catalyst has a function of catalyzing a reaction to produce

[0033] The working electrode 102 is made of a conductive porous material in order to realize a conductive material with gas permeability, and in this embodiment, a metal electrode made of a porous material is used. The metal electrode in this embodiment has holes through which the CO2-containing gas can pass. As the metal porous body constituting the working electrode 102, a foamed mesh made of a metal in a mesh shape can be used.

[0034] This increases the specific surface area of ​​the working electrode 102 and ensures electrical conductivity. The increase in the electrode interface and the gas-liquid interface allows the water and O2 in the electrolyte 108 to be converted into OH. - This can promote the reaction in producing

[0035] Note that porous materials including mesh and felt and sintered bodies thereof can be used as the porous material constituting the working electrode 102. In addition, it is also possible to adopt porous carbon materials such as activated carbon, acetylene black, carbon nanotubes, and graphene as the porous material.

[0036] The working electrode 102 according to this embodiment is made of a material active in the adsorption reaction. Specifically, the working electrode 102 can be made of platinum (Pt), stainless steel (SUS), nickel (Ni), or the like. By using a material active in the adsorption reaction as the constituent material of the working electrode 102, it is possible to reduce overvoltage during the electrochemical reaction, and to improve the energy efficiency of the operation of the carbon dioxide capture system 10.

[0037] The counter electrode 103 of the electrochemical cell 101 according to this embodiment is configured by an electrode having a substance that can donate electrons by changing the valence of an element in a molecule or crystal when a potential is applied, and has a counter electrode substrate 104 and a counter electrode active material 105 as shown in FIG. 3. The counter electrode substrate 104 is a conductive material. For example, a carbonaceous material or a metal material can be used as the counter electrode substrate 104. For example, a carbonaceous material constituting the counter electrode substrate 104 can be carbon paper, carbon cloth, a nonwoven carbon mat, a porous gas diffusion layer (GDL), or the like.

[0038] As the counter electrode active material 105, for example, a metal complex that can transfer electrons by changing the valence of the metal ion can be used. Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickelocene, and cobaltocene, and porphyrin metal complexes. These metal complexes may be polymers or monomers. In this embodiment, polyvinylferrocene is used as the counter electrode active material 105. Ferrocene transfers electrons by changing the valence of Fe between divalent and trivalent.

[0039] Alternatively, the counter electrode active material 105 may be a supplementary electroactive species that transfers electrons between the working electrode 102 and the counter electrode active material 105. When a potential is applied, the valence of an element in the molecule or crystal changes, and the counter electrode active material 105 may be a substance that can donate electrons. For example, an oxide of a transition metal from Group 5 to Group 11 of the periodic table may be used as the counter electrode active material 105. As the transition metal, an oxide of Cr, Mn, Fe, Co, Ni, Cu, Ru, Mo, Pd, or Ag may preferably be used, and more preferably, an oxide of Cr, Mn, Fe, or Ru may be used.

[0040] The counter electrode active material 105 may have a property of taking in ions (e.g., electrolyte ions) in the electrolyte solution 108 during an electrochemical reaction, and not releasing protons into the electrolyte solution 108 during electron transfer. Since protons are not released during electron transfer in an electrochemical reaction, OH - This does not inhibit the generation of OH in the electrolyte 108. - CO2 capture, O2- Therefore, it is possible to reliably reduce the effects of the above.

[0041] 3, the insulating layer 106 of the electrochemical cell 101 according to this embodiment is disposed between the working electrode 102 and the counter electrode 103, and separates the working electrode 102 from the counter electrode 103. The insulating layer 106 is an insulating ion-permeable membrane that prevents physical contact between the working electrode 102 and the counter electrode 103 to suppress electrical short circuits and allows ions to pass therethrough.

[0042] A separator or a gas layer such as air can be used as the insulating layer 106. In this embodiment, a porous separator is used as the insulating layer 106. The separator may be made of a cellulose film, a polymer, a composite material of polymer and ceramic, or the like.

[0043] An electrolyte 108 having ion conductivity is provided between the working electrode 102 and the counter electrode 103. The electrolyte 108 is provided between the working electrode 102 and the counter electrode 103 via an insulating layer 106. The electrolyte 108 is provided so as to cover the working electrode 102, the counter electrode 103, and the insulating layer 106.

[0044] The electrolyte 108 of the electrochemical cell 101 according to this embodiment contains water as a solvent. The water also functions as a reducing agent. As a solute of the electrolyte 108, a salt species consisting of a single or multiple substances that ionize in a solvent is adopted. The salt species adopted as the solute is a salt having a cation with an ionic potential smaller than that of lithium (Li). Specifically, as the solute, for example, sodium bis(fluorosulfonyl)imide (NaTFO), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium perchlorate (NaClO4), etc. can be used.

[0045] The water in the electrolytic solution 108 is not limited to the form in which it is previously contained in the electrolytic solution 108. For example, water may be added to the electrolytic solution 108 in such a manner that moisture contained in the CO2-containing gas is taken into the electrolytic solution 108. Furthermore, the timing of adding water to the electrolytic solution 108 is not limited to the operating state of the electrochemical cell 101.

[0046] In the electrolyte solution 108, by dissolving a salt species such as NaTFO as a solute in the solvent, it is possible to increase the boiling point of the electrolyte solution 108. This makes it possible to suppress evaporation of the solvent in the electrolyte solution 108.

[0047] In addition, by using a salt having a cation with an ion potential smaller than that of lithium (Li) as the solute of the electrolyte 108, it is possible to make the electrolyte 108 in a state in which it is difficult to stabilize by salification. This makes it possible to realize adsorption and desorption of CO2 by swinging the voltage in the electrochemical cell 101.

[0048] Next, the operation of the carbon dioxide capture system 10 of this embodiment will be described. As shown in Fig. 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 a control device 14.

[0049] First, the CO2 capture mode will be described. In the CO2 capture mode, the compressor 11 operates to supply CO2-containing gas to the carbon dioxide capture device 100. In the carbon dioxide capture device 100, a voltage applied between the working electrode 102 and the counter electrode 103 is set to a first voltage V1. This allows the counter electrode active material 105 of the counter electrode 103 to donate electrons and the working electrode 102 to withdraw electrons at the same time. The counter electrode active material 105 of the counter electrode 103 emits electrons and becomes oxidized, and electrons are supplied from the counter electrode 103 to the working electrode 102.

[0050] On the working electrode 102 side in the CO2 capture mode, as shown in reaction formula (1), in response to the supply of electrons from the counter electrode 103, OH is converted to CO2 by using water in the electrolyte 108 and O2 in the CO2-containing gas.- is generated.

[0051] 2H2O+O2+4e - →4OH - (1) As shown in reaction formula (2), OH generated on the working electrode 102 side - reacts with the CO2 contained in the CO2-containing gas to generate bicarbonate ions. At this time, the CO2 in the CO2-containing gas is used to generate bicarbonate ions, so the CO2 is adsorbed and removed from the CO2-containing gas.

[0052] OH - +CO2→HCO3 - (2) In addition to the above-mentioned adsorption method, it is also possible to adopt an adsorption method using an adsorbent in the CO2 capture mode.

[0053] After the CO2-containing gas has had its CO2 captured by the carbon dioxide capture device 100, it is discharged from the carbon dioxide capture device 100 as a CO2-removed gas that does not contain CO2. The flow path switching valve 12 switches the gas flow path to the atmosphere side, and the CO2-removed gas discharged from the carbon dioxide capture device 100 is discharged to the atmosphere.

[0054] Here, when the electrochemical cell 101 is operated in the carbon dioxide capture device 100, charge transfer occurs to O2, and superoxide O2, a type of active oxygen, is generated. - It is assumed that superoxide O2 is generated. - When this occurs, O2 - The high reaction activity of the catalyst causes decomposition of the electrode materials constituting the electrochemical cell, which is thought to be one of the factors shortening the life of the electrochemical cell in the carbon dioxide capture system.

[0055] In this regard, in the carbon dioxide capture device 100 according to the present embodiment, the solvent of the electrolyte 108 of the electrochemical cell 101 contains water, so that the operation of the electrochemical cell 101 produces O2 -Even if active oxygen is generated, the active oxygen is decomposed by the water constituting the electrolyte 108. That is, the carbon dioxide recovery system 10 is - This can suppress the influence on the electrode material caused by the heat generated by the heat generation, and thus suppress the shortening of the life span of the electrochemical cell 101.

[0056] 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 carbon dioxide capture device 100 stops. In the carbon dioxide capture device 100, the voltage applied between the working electrode 102 and the counter electrode 103 is set to a second voltage V2. This allows the working electrode 102 to donate electrons and the counter electrode active material 105 of the counter electrode 103 to withdraw electrons at the same time. The counter electrode active material 105 of the counter electrode 103 receives electrons and becomes in a reduced state.

[0057] When electrons are supplied from the working electrode 102 to the counter electrode 103, the OH - These electrons are used to generate water and O2 in the electrolyte 108, as shown in reaction formula (3).

[0058] 4OH - →O2+H2O+4e - (3) As electrons are supplied from the working electrode 102 to the counter electrode 103, the hydrogen carbonate ions in the electrolyte 108 are converted to OH as shown in reaction formula (4). - That is, the CO2 adsorbed in the CO2 capture mode is desorbed from the bicarbonate ions and released from the electrolyte 108.

[0059] CO3 - →OH - +CO2···(4) The CO2 released from the electrolyte 108 of the electrochemical cell 101 is discharged from the carbon dioxide capture device 100. Since the flow path switching valve 12 switches the gas flow path to the carbon dioxide utilization device 13 side, the CO2 discharged from the carbon dioxide capture device 100 is supplied to the carbon dioxide utilization device 13.

[0060] In this way, the carbon dioxide capture system 10 can alternately switch between a CO2 capture mode and a CO2 release mode to capture CO2 from a CO2-containing gas and release the captured CO2 to the carbon dioxide utilization device 13.

[0061] As described above, the carbon dioxide capture system 10 according to this embodiment includes the electrochemical cell 101 including the working electrode 102 and the counter electrode 103, and the electrolyte solution 108 including at least water.

[0062] In the CO2 capture mode, when a first voltage V1 is applied between the working electrode 102 and the counter electrode 103, a reaction shown in reaction formula (1) occurs with the supply of electrons from the counter electrode 103 to the working electrode 102, and OH is converted from water contained as a solvent and a reducing agent in the electrolyte 108. - As shown in reaction formula (2), the generated OH - and hydrogen carbonate ions and the like are generated by an electrochemical reaction using the CO2 contained in the CO2-containing gas. Since the CO2 contained in the CO2-containing gas is used to generate the hydrogen carbonate ions and the like, or the carbonate ions are generated, the CO2 can be adsorbed and removed from the CO2-containing gas in the electrolyte 108 of the electrochemical cell 101, and the recovery of CO2 can be realized.

[0063] In addition, as the electrochemical cell 101 operates, active oxygen, superoxide O2 - Even if O2 occurs, in this embodiment, the solvent of the electrolyte 108 contains water as a reducing agent. - by reaction with water - That is, the carbon dioxide capture system 10 can be used to generate O2 - Even if this occurs, O2 - This can suppress the influence on the electrode material caused by the heat generated by the heat generation, and thus suppress the shortening of the life span of the electrochemical cell 101.

[0064] In the CO2 release mode, when a second voltage V2 is applied between the working electrode 102 and the counter electrode 103, as shown in reaction formula (4), hydrogen carbonate ions in the electrolyte 108 are converted to OH as electrons are supplied to the counter electrode 103. - This dissociates CO2.

[0065] This allows the carbon dioxide capture system to capture the CO2 adsorbed in the electrolyte 108 outside the electrochemical cell 101. In addition, since the CO2 capture mode and the CO2 release mode can be switched by changing the voltage applied between the working electrode 102 and the counter electrode 103, the two modes can be realized without major system modifications.

[0066] In addition, the reducing agent reacts with active oxygen to produce OH. - Since the reducing agent has a property of generating CO2 and is a protic solvent, the energy required for adsorption and removal of CO2, which is an acidic gas, can be reduced. In addition, since the reducing agent is added to the electrolyte via the mist or gas form contained in the acidic gas-containing gas, it is sufficient that the reducing agent is contained in the electrolyte 108 during the electrochemical reaction, and the recovery of the acidic gas can be realized.

[0067] Since the acid gas is CO2, the carbon dioxide capture system 10 makes it possible to utilize the CO2 captured from the acid gas-containing gas in the carbon dioxide utilization device 13 or the like.

[0068] The electrolyte 108 in this embodiment contains water as a solvent and is composed of salt species consisting of a single or multiple substances that ionize in the solvent. By adding salt species to the solvent to form the electrolyte 108, the boiling point of the electrolyte 108 can be increased and evaporation of the solvent of the electrolyte 108 can be suppressed.

[0069] In addition, a salt having a cation with an ion potential smaller than Li is used as the salt species of the electrolyte solution 108 according to this embodiment. By using a salt having a cation with an ion potential smaller than lithium (Li), the electrolyte solution 108 can be made into a state in which it is difficult to stabilize by salification. This makes it possible to realize adsorption and desorption of CO2 by swinging the voltage in the electrochemical cell 101.

[0070] The counter electrode 103 of the electrochemical cell 101 according to this embodiment is composed of an electrode having a material that can donate electrons by changing the valence of elements in the molecule or crystal when a potential is applied. This allows the carbon dioxide capture system 10 to improve the electron donation ability of the counter electrode 103 of the electrochemical cell 101. In addition, it is desirable for the active material in the counter electrode 103 to have the property of incorporating electrolyte ions in the electrolyte 108 into the active material and not releasing protons into the electrolyte 108 when transferring electrons. By suppressing the release of protons on the counter electrode 103 side, it is possible to prevent OH - This is because inhibition of the production of

[0071] The working electrode 102 of the electrochemical cell 101 according to this embodiment is made of a conductive porous material. This makes it possible to increase the specific surface area while ensuring the conductivity of the working electrode 102 of the electrochemical cell 101, thereby increasing the electrode interface and the gas-liquid interface in the working electrode 102 and increasing the amount of OH. - This can promote the reaction of producing

[0072] Moreover, the working electrode 102 of the electrochemical cell 101 according to this embodiment is made of a material active in the adsorption reaction, such as stainless steel, platinum, etc. By configuring the working electrode 102 in this way, it is possible to reduce the reaction overvoltage in the electrochemical cell 101, and to improve the energy efficiency of the carbon dioxide capture system 10 in the CO2 capture mode and the CO2 release mode. (Other embodiments) The present disclosure is not limited to the above-described embodiment, and various modifications can be made as follows without departing from the spirit and scope of the present disclosure.

[0073] (a) In the above-described embodiment, the working electrode 102 does not have a CO2 adsorbent, but the present invention is not limited to this embodiment. As long as the electrolyte 108 of the electrochemical cell 101 contains water, the working electrode 102 of the electrochemical cell 101 may have a CO2 adsorbent. Even when the working electrode 102 having a CO2 adsorbent is used, since the electrolyte 108 contains water, the OH in the electrolyte 108 is not absorbed by the working electrode 102, as in the above-described embodiment. - By O2 - To reduce the impact of (b) In the above-described embodiment, in the CO2 capture mode, the potential of the working electrode 102 is equal to or lower than the equilibrium potential of the electrolysis reaction of water and equal to or higher than the equilibrium potential of the reaction of oxygen + water. This makes it possible to suppress the occurrence of side reactions such as hydrogen generation in the CO2 capture mode, and improve the efficiency of CO2 capture from the CO2-containing gas.

[0074] (c) In the above-described embodiment, the electrolytic solution 108 contains water, but is not limited to this. For example, the electrolytic solution 108 may contain alcohols, phenols, ionic liquids, or glymes. The electrolytic solution 108 may be in the form of a gel or solution, or may be a solid electrolyte that partially contains water.

[0075] (d) In the above-described embodiment, the water as a reducing agent is contained in the electrolyte 108, but the present invention is not limited to this embodiment. It is also possible to adopt an embodiment in which the working electrode 102 or the counter electrode 103 contains water as a reducing agent, or an embodiment in which water is contained as a reducing agent in each combination further including the electrolyte 108.

[0076] (e) In the above embodiment, the adsorption target is CO2 as an acidic gas, but the present invention is not limited to this embodiment. For example, other acidic gases such as SOx and NOx may be used as the target of adsorption in the acidic gas recovery system.

[0077] (f) In the above embodiment, the electrolyte 108 contains water as a solvent and a reducing agent, but the present invention is not limited to this embodiment. It is also possible to add moisture contained in the acidic gas-containing gas in the form of mist or gas to the electrolyte 108 of the electrochemical cell 101.

[0078] The features of the acid gas recovery system disclosed herein are as follows: (Item 1) An acid gas recovery system for separating an acid gas from an acid gas-containing gas containing an acid gas and oxygen by an electrochemical reaction, comprising: an electrochemical cell (101) having a working electrode (102) and a counter electrode (103), in which electrons are exchanged between the working electrode and the counter electrode by application of a voltage; and an electrolyte (108) between the working electrode and the counter electrode, the electrolyte (108) including a reducing agent that reduces at least active oxygen; When a predetermined first voltage (V1) is applied between the working electrode and the counter electrode, An acid gas recovery system that recovers the acid gas by adsorbing the acid gas contained in the acid gas-containing gas to an adsorption target in accordance with the supply of electrons from the counter electrode to the working electrode. (Item 2) When a second voltage (V2) different from the first voltage is applied between the working electrode (102) and the counter electrode (103), 2. The acidic gas recovery system according to item 1, wherein the acidic gas adsorbed from the adsorption target is dissociated with the supply of electrons to the counter electrode, thereby recovering the acidic gas. (Item 3) The reducing agent reacts with the active oxygen to form OH - 3. The acid gas recovery system according to item 1 or 2, (Item 4) 4. The acid gas recovery system according to any one of items 1 to 3, wherein the reducing agent is a protic solvent. (Item 5) 5. The acid gas recovery system according to any one of items 1 to 4, wherein the reducing agent is water. (Item 6) 6. The acidic gas recovery system according to any one of items 1 to 5, wherein the reducing agent is added to the electrolyte in the form of a mist or gas contained in the acidic gas-containing gas. (Item 7) 7. The acid gas recovery system according to any one of items 1 to 6, wherein the acid gas is CO2. (Item 8) 8. The acid gas recovery system according to any one of items 1 to 7, wherein the electrolyte (108) is composed of water as a solvent and the reducing agent, and a salt species consisting of a single or multiple substances that ionize in water. (Item 9) 9. The acidic gas recovery system according to any one of items 1 to 8, wherein a salt having a cation with an ionic potential smaller than Li is used as the salt species of the electrolyte (108). [Explanation of symbols]

[0079] 10 Carbon dioxide capture system 100 Carbon dioxide capture device 101 Electrochemical Cell 102 Working electrode 103 Opposite 108 Electrolyte

Claims

1. An acid gas recovery system for separating an acid gas from an acid gas-containing gas containing an acid gas and oxygen by an electrochemical reaction, comprising: An electrochemical cell (101) having a working electrode (102) and a counter electrode (103), in which electrons are exchanged by applying a voltage between the working electrode and the counter electrode; and an electrolyte (108) between the working electrode and the counter electrode, the electrolyte (108) including a reducing agent that reduces at least active oxygen; When a predetermined first voltage (V1) is applied between the working electrode and the counter electrode, An acid gas recovery system that recovers the acid gas by adsorbing the acid gas contained in the acid gas-containing gas to an adsorption target in accordance with the supply of electrons from the counter electrode to the working electrode.

2. When a second voltage (V2) different from the first voltage is applied between the working electrode (102) and the counter electrode (103), 2. The acid gas recovery system according to claim 1, wherein the acid gas adsorbed from the adsorption target is dissociated in association with the supply of electrons to the counter electrode, thereby recovering the acid gas.

3. The reducing agent reacts with the active oxygen to form OH － 3. The acid gas recovery system according to claim 1 or 2,

4. 3. The acid gas recovery system of claim 1, wherein the reducing agent is a protic solvent.

5. 5. The acid gas recovery system of claim 4, wherein the reducing agent is water.

6. 3. The acidic gas recovery system according to claim 1, wherein the reducing agent is added to the electrolyte in the form of a mist or gas contained in the acidic gas-containing gas.

7. The acid gas is CO ２ 3. The acidic gas recovery system according to claim 1 or 2,

8. The acid gas recovery system according to claim 1 or 2, wherein the electrolyte (108) is composed of water as a solvent and the reducing agent, and a salt species consisting of a single or multiple substances that ionize in water.

9. 3. The acidic gas recovery system according to claim 1, wherein the salt species of the electrolyte (108) is a salt having a cation with an ionic potential smaller than that of Li.

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