Carbon dioxide recycling system

Abstract

To provide a carbon dioxide recycling system capable of generating a CO2 reduction product although a process for obtaining a high-concentration CO2 gas by recovering and concentrating CO2 is not necessary.SOLUTION: A carbon dioxide recycling system 1 is configured to: have an electrochemical CO2 reduction device 10 comprising a reduction reaction electrode 11, an oxidation reaction electrode 12, and a first ion-exchange membrane 13 arranged between the reduction reaction electrode 11 and the oxidation reaction electrode 12; introduce an aqueous carbonate solution CAS where CO2 is dissolved in a first half cell HC1 configured by including the reduction reaction electrode 11 and the first ion-exchange membrane 13 as a catholyte; and have CO2 gasification means 80 for gasifying CO2 in the catholyte immediately before the reduction reaction electrode 11 reduces CO2 in the catholyte.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a carbon dioxide resource recovery system. [Background technology]

[0002] In order to solve environmental problems such as global warming, it is necessary to reduce carbon dioxide (CO2) emissions. In addition, there are high expectations for direct air capture (DAC) technology, which artificially captures CO2 from the atmosphere, and carbon dioxide capture and utilization (CCU) technology, which reduces the captured CO2 to useful chemical products and reuses it.

[0003] Toward the realization of such a CO2 resource recovery and circulation system, artificial photosynthesis technology is being developed to synthesize fuels and organic matter such as hydrogen and hydrocarbons using water (proton source) and CO2 (carbon source) as raw materials. Among artificial photosynthesis technologies, electrochemical CO2 reduction devices are devices that produce organic matter such as polycarbon compounds by electrochemically reducing CO2 at room temperature and atmospheric pressure. If this electrochemical CO2 reduction device is operated using renewable energy such as wind power or solar power, and the raw carbon source is also recovered from atmospheric CO2, it will become a carbon-negative CO2 resource recovery device that contributes to solving environmental and energy problems.

[0004] FIG. 11 shows an example of the conventional electrochemical CO2 reduction device 200. As shown in FIG. 11, the electrochemical CO2 reduction device 200 is composed of a cathode chamber 201, which is a half cell that reduces CO2 to produce carbon compounds, an anode chamber 202, which is a half cell that oxidizes water to produce oxygen, and an ion exchange membrane 203 that separates the cathode chamber 201 and the anode chamber 202. In this device, the cathode 204 provided in the cathode chamber 201 is, for example, a cathode gas diffusion electrode (GDE) (cathode GDE 204c) in which a CO2 reduction reaction catalyst (cathode catalyst 204b) is provided on a gas diffusion layer (GDL) with a micro porous layer (MPL) (GDL 204a with MPL). The anode 205 provided in the anode chamber 202 is, for example, an anode GDE 205b provided with an oxygen evolution reaction (OER) catalyst (OER catalyst 205a). The ion exchange membrane 203 is an anion-exchange membrane (AFM). In the cathode chamber 201 and the anode chamber 202, a neutral to alkaline aqueous solution is used as an electrolyte.

[0005] If catholyte and anolyte are alkaline electrolytes, the CO2 gas will become carbonate and dissolve (be consumed). AEM, which is used in an alkaline environment, is - As well as carbonate (HCO3 - , CO3 2- ) also passes through the cathode 204, crossing over from the anode 205 side, and even if an excess of CO2 gas is supplied to the cathode 204, the CO2 utilization rate is quite low. For this reason, in conventional devices, the CO2 reduction reaction is established in an alkaline environment by supplying an excess of CO2 gas. Note that even if catholyte and anolyte are neutral electrolytes, H2O will be converted to H + (proton) source, so local OH - The alkalinity that occurs as a result of this formation and the associated formation of carbonates is unavoidable.

[0006] In the above-mentioned device, CO2, which is a carbon source for electrolytic reduction, is supplied as CO2 gas to the cathode catalyst 204b of the cathode GDE 204c. The CO2 reduction reaction in the cathode chamber 201 proceeds at the three-phase interface between CO2 (gas), aqueous electrolyte (liquid), and cathode catalyst 204b (solid) as a reaction field. Therefore, in order to improve the utilization rate of CO2 and further to increase the production rate of the CO2 reduction product, it is necessary to supply CO2 as a gas to the catalyst (solid) surface in the electrolyte (liquid) as described above. The CO2 reduction product includes carbon compounds with one or more carbon atoms (C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, C210, C222, C23, C24, C25, C36, C37, C38, C39, C41, C42, C43, C54, C55, C66, C67, C78, ​​C79, C81, C91, C92, C93, C94, C95, C96, C102, C113, C123, C134, C145, C151, C165, C176, C186, C197, C198, C199, C223, C245, C251, C266, C277, C287, C299, C399, C43, C44, C55, C67, C78, ​​C81, C93, C104, C115, C125, C135, C145, C155, C166, C177, C18 2+ ) are included. C1, C2 generated by the electrochemical CO2 reduction device 200 2+ The unreacted CO2 and O2 generated by the electrochemical CO2 reduction device 200 are discharged from the anode GDE 205b. Note that the crossover CO2 refers to the CO2 supplied to the cathode 204 side that is converted to carbonate (HCO3 - , CO3 2- ) passes through the ion exchange membrane 203 and reaches the anode 205 side, and H generated locally from HO on the anode 205 side + This refers to the CO2 produced by directly reacting with

[0007] In the conventional electrochemical CO2 reduction device 200, high-concentration CO2 gas is supplied to the cathode chamber 201 of the CO2 reduction cell, and in order to improve the reaction efficiency, the use of a gas diffusion electrode (GDE) as described above has been considered. In places where high-concentration CO2 gas cannot be secured, the efficiency of the electrochemical CO2 reduction device 200 decreases because excessive CO2 gas cannot be supplied.

[0008] In order to obtain the high-concentration CO2 gas mentioned above, a DAC process is required to capture and concentrate dilute CO2 in the atmosphere. Current DAC processes, which use chemical adsorption methods using aqueous amine solutions or physical adsorption methods using porous solid adsorbents, require a large amount of energy to concentrate CO2. In addition, the process of desorbing the CO2 captured from the atmosphere as CO2 gas again also requires a large amount of energy, which is one of the factors that increases the cost.

[0009] An example of such a conventional electrochemical CO2 reduction device is a carbon dioxide reaction device described in Patent Document 1. This carbon dioxide reaction device includes an electrochemical reaction cell, a first supply unit, a second supply unit, and a first carbon dioxide separation unit. The electrochemical reaction cell includes a first storage unit, a second storage unit, a diaphragm, a cathode, and an anode. The first storage unit stores a gas containing carbon dioxide or a first electrolytic solution containing carbon dioxide. The second storage unit stores a second electrolytic solution containing water. The diaphragm is provided between the first storage unit and the second storage unit. The cathode is disposed so as to be in contact with the gas or the first electrolytic solution, and reduces carbon dioxide to generate a carbon compound. The anode is disposed so as to be in contact with the second electrolytic solution, and oxidizes water to generate oxygen. The first supply unit supplies the gas or the first electrolytic solution to the first storage unit. The second supply unit supplies the second electrolytic solution to the second storage unit. The first carbon dioxide separation unit is connected to an exhaust unit that exhausts an exhaust containing oxygen and carbon dioxide from the second storage unit, and separates the carbon dioxide from gas components in the exhaust. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2021-147679 A Summary of the Invention [Problem to be solved by the invention]

[0011] In the conventional electrochemical CO2 reduction device 200 including the carbon dioxide reaction device described in the above-mentioned Patent Document 1, as described above, in order to secure high-concentration CO2 gas, a DAC process is required to capture and concentrate dilute CO2 in the atmosphere. In addition, a process is also required to desorb the CO2 captured from the atmosphere as CO2 gas again. Therefore, the conventional device could not solve the problem that these processes require a large amount of energy and are expensive.

[0012] The above problem can be solved by developing an electrochemical CO2 reduction device (carbon dioxide resource recovery system) that does not require the process of capturing and concentrating CO2 to obtain highly concentrated CO2 gas, which is expected to enable low-cost CO2 resource recovery and circulation.

[0013] The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide a carbon dioxide resource recovery system capable of generating CO2 reduction products without the need for a process of capturing and concentrating CO2 to obtain high-concentration CO2 gas. [Means for solving the problem]

[0014] The carbon dioxide resource conversion system of the present invention which solves the above-mentioned problems comprises an electrochemical CO2 reduction device provided with a reduction reaction electrode, an oxidation reaction electrode, and a first ion exchange membrane disposed between the reduction reaction electrode and the oxidation reaction electrode, and comprises CO2 gasification means for introducing an aqueous carbonate solution in which CO2 is dissolved as catholyte into a first half-cell comprising the reduction reaction electrode and the first ion exchange membrane, and gasifying the CO2 in the catholyte immediately before reducing the CO2 in the catholyte with the reduction reaction electrode. Effect of the Invention

[0015] According to the present invention, it is possible to provide a carbon dioxide resource recovery system capable of generating CO2 reduction products while eliminating the need for a process of recovering and concentrating CO2 to obtain highly concentrated CO2 gas. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram illustrating the overall configuration of a carbon dioxide resource recovery system 1 according to one embodiment. [Diagram 2] FIG. 1 is a schematic diagram illustrating an electrochemical CO 2 reduction device 10 in a carbon dioxide resource recovery system 1 according to one embodiment. [Diagram 3] 1 is a graph (Bjerrum plot) showing the relationship between the solubility of CO2 in water and pH. [Figure 4] FIG. 1 is a schematic diagram showing an example of an electrochemical CO2 gasification device 81 as one embodiment of a CO2 gasification means 80. [Diagram 5] FIG. 1 is a schematic diagram showing an electrochemical CO2 gasification device 86 according to a first modified example, as one embodiment of the CO2 gasification means 80. [Figure 6] FIG. 1 is a schematic diagram showing an electrochemical CO2 gasification device 89 according to a second modified example, as one embodiment of the CO2 gasification means 80. [Figure 7] FIG. 13 is a schematic diagram showing an electrochemical CO2 gasification device 90 according to a third modified example, as another embodiment of the CO2 gasification means 80. [Figure 8] FIG. 13 is a schematic diagram showing an electrochemical CO2 gasification device 91 according to a fourth modified example, as another embodiment of the CO2 gasification means 80. [Figure 9] FIG. 1 is a schematic diagram showing an electrochemical CO2 reduction device 14 according to another embodiment of the CO2 gasification means 80. [Figure 10] FIG. 1 is a configuration diagram showing an example of a CO2 reuse mechanism 100. [Figure 11] FIG. 1 is a configuration diagram showing an example of a conventional electrochemical CO2 reduction device 200. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A carbon dioxide resource recovery system 1 according to one embodiment of the present invention (hereinafter, sometimes simply referred to as the present system 1) will be described in detail below with appropriate reference to the drawings. In the description of each embodiment, substantially the same or similar configurations are denoted by the same reference numerals, and where a description is redundant, the description may be omitted.

[0018] [Carbon dioxide resource recovery system 1] FIG. 1 is a schematic diagram illustrating the overall configuration of a carbon dioxide resource recovery system 1 according to one embodiment. As shown in Fig. 1, the system 1 includes an electrochemical CO2 reduction device 10, a gas-liquid separation device (cathode side) 20, a gas separation device (cathode side) 30, a liquid extraction device (cathode side) 40, a gas-liquid separation device (anode side) 50, a gas separation device (anode side) 60, and a liquid extraction device (anode side) 70. The operation of these devices is controlled by a control device CD such as a computer. In addition, a voltage is applied from a power source PS to the electrodes (cathode, anode) of the electrochemical CO2 reduction device 10, the gas separation device (cathode side) 30, and the gas separation device (anode side) 60.

[0019] The present system 1 supplies only an aqueous solution in which CO2 is dissolved (CO2-dissolved aqueous solution) to the electrochemical CO2 reduction device 10 (i.e., does not supply high-concentration CO2 gas) to generate CO2 reduction products. The CO2 reduction products include carbon compounds with one or more carbon atoms (C1, C 2+ ), that is, organic compounds such as hydrocarbons. The electrochemical CO2 reduction device 10 will be described later.

[0020] Examples of the aqueous solution include a CO2 recovery liquid (neutral to alkaline), an aqueous potassium carbonate solution, carbonated water, and seawater. Examples of the CO2 recovery liquid include a water-soluble amine recovery liquid in which CO2 is dissolved. In this embodiment, the CO2-dissolved aqueous solution and the CO2 recovery liquid are sometimes collectively referred to as a carbonate aqueous solution (CAS).

[0021] Also, C1, C 2+ Examples of gases include, but are not limited to, carbon monoxide (CO), methane (CH4), ethane (C2H6), ethylene (C2H4), and formaldehyde (CHO), and liquids such as methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), formic acid (CH2O2), and acetaldehyde (CH3CHO).

[0022] In the present system 1, the carbonate aqueous solution CAS is supplied to the cathode side (first half-cell HC1) (see FIG. 2) of the electrochemical CO2 reduction device 10, and CO2 is electrolytically reduced in the device 10 to generate a CO2 reduction product, as described above. The fact that CO2 in the carbonate aqueous solution CAS is electrolytically reduced in the first half-cell HC1 will be described later.

[0023] The CO2 reduction product generated in the electrochemical CO2 reduction device 10 is either gas or liquid, and is therefore separated into gas and liquid by the gas-liquid separator (cathode side) 20. The liquid separated by the gas-liquid separator (cathode side) 20 is sent to the liquid extractor (cathode side) 40, where it is extracted into chemical species such as C2H5OH and C3H7OH. This extraction can be performed by a known method that utilizes differences in boiling points, etc.

[0024] On the other hand, the gas separated in the gas-liquid separator (cathode side) 20 is sent to the gas separator (cathode side) 30, where it is separated into chemical species such as C2H6, CH4, carbon monoxide (CO), hydrogen (H2), etc. This separation can be performed by a known method that utilizes a gas separation membrane or the adsorption and desorption action of an adsorbent.

[0025] On the anode side (second half-cell HC2) (see FIG. 2) of the electrochemical CO2 reduction device 10, O2, crossover CO2, hydrogen peroxide (H2O2), and the like are generated. These are sent to the gas-liquid separator (anode side) 50, where they are separated into gas and liquid. The liquid (e.g., H2O2) separated in the gas-liquid separator (anode side) 50 is sent to the liquid extractor (anode side) 70, where it is separated from water. This separation can be performed, for example, by distillation, but is not limited to this.

[0026] On the other hand, the gas separated in the gas-liquid separator (anode side) 50 is sent to the gas separator (anode side) 60, where it is separated into O2 and crossover CO2. This separation can be performed by a known method such as a chemical absorption method, a physical absorption method, a solid absorption method, or a membrane separation method.

[0027] In addition, in the gas separation device (cathode side) 30 and the gas separation device (anode side) 60, an electrochemical pH swing device using a known proton-coupled electron transfer (PCET) organic material can be used or used in combination. By using an electrochemical pH swing device, it is possible to recover only CO2 gas from the mixed gas components. If only CO2 gas can be recovered, it is very advantageous for reusing the carbonate aqueous solution CAS.

[0028] That is, in this embodiment, it is preferable to provide a recycling mechanism 100 (see FIG. 10) that recovers at least one of the gas containing unreacted CO2 discharged from the first half-cell HC1 and the gas containing crossover CO2 discharged from the second half-cell HC2, dissolves it in the carbonate aqueous solution CAS, and reuses it as the catholyte in the first half-cell HC1. In this way, the unreacted CO2 and the crossover CO2 can be reused, improving the utilization efficiency of CO2.

[0029] The recycling mechanism 100 can utilize electrochemical pH swing by proton-coupled electron transfer (PCET). As described above, the recycling mechanism 100 utilizes the fact that the ionization and dissolution of CO2 depends on pH, and selectively actively transports only CO2 from the cathode side to the anode side with a pH gradient to concentrate CO2. In this way, CO2 can be selectively concentrated. In addition, since O2, which does not ionize and dissolve, is not actively transported, the desorption process for desorbing only CO2 can be eliminated.

[0030] [Electrochemical CO2 reduction device] Next, the electrochemical CO2 reduction device 10 in the present system 1 will be described in detail. FIG. 2 is a schematic diagram illustrating an electrochemical CO 2 reduction device 10 in a carbon dioxide resource recovery system 1 according to one embodiment. As shown in FIG. 2, the electrochemical CO2 reduction device 10 includes a reduction reaction electrode 11 (cathode), an oxidation reaction electrode 12 (anode), and a first ion exchange membrane 13 disposed between the reduction reaction electrode 11 and the oxidation reaction electrode 12.

[0031] In the electrochemical CO2 reduction device 10 in this system 1, a carbonate aqueous solution CAS in which CO2 is dissolved as catholyte is introduced into a first half-cell HC1 including a reduction reaction electrode 11 and a first ion exchange membrane 13. In addition, in the electrochemical CO2 reduction device 10, the same carbonate aqueous solution CAS as above is also introduced as anolyte into the second half-cell HC2 comprising the oxidation reaction electrode 12 and the first ion exchange membrane 13. The electrochemical CO2 reduction device 10 has a CO2 gasification means 80 (see Figs. 4 to 9) that gasifies the CO2 in the catholyte immediately before the reduction of the CO2 in the catholyte by the reduction reaction electrode 11. The CO2 gasification means 80 will be described later.

[0032] The reduction reaction electrode 11 is, for example, a cathode gas diffusion electrode (GDE) in which a CO2 reduction reaction catalyst (cathode catalyst) is provided on a gas diffusion layer (GDL) with a hydrophobic microporous layer (MPL). The MPL can be formed of a water-repellent resin such as polytetrafluoroethylene (PTFE) or fluorinated ethylene propylene (FEP) and carbon. Examples of the cathode catalyst include metal materials such as copper (Cu), silver (Ag), gold (Au), zinc (Zn), lead (Pb), indium (In), tin (Sn), cadmium (Cd), nickel (Ni), iron (Fe), platinum (Pt), and titanium (Ti), metal oxides thereof, and alloys containing these metals. The cathode catalyst is not limited to these, and may be an organometallic complex such as ruthenium (Ru) or rhenium (Re) known as a CO2 reduction catalyst, or a carbon material such as graphene or carbon nanotubes. The cathode catalyst can be provided by coating the surface of the GDL with MPL. 2+ For this purpose, specifically, a CuO-NPs GDE in which CuO nanoparticles are coated and supported on the surface of a GDL with an MPL can be used.

[0033] The oxidation reaction electrode 12 may be, for example, an anode GDE provided with an oxygen evolution reaction (OER) catalyst. The anode GDE may be, for example, a porous body made of a metal material such as platinum (Pt), gold (Au), nickel (Ni), cobalt (Co), palladium (Pd), iridium (Ir), manganese (Mn), iron (Fe), ruthenium (Ru), or titanium (Ti), or a metal oxide, metal hydroxide, alloy containing the metal, or metal complex thereof. In addition, the oxidation reaction electrode 12 may be made of a wide variety of materials known as oxidation catalysts capable of oxidizing water (H2O) to generate oxygen (O2) or hydrogen peroxide (H2O2). Examples of the oxidation reaction electrode 12 include carbon materials such as carbon black, activated carbon, carbon nanotubes, graphene, and diamond, transparent conductive oxides such as indium tin oxide (ITO), zinc oxide (ZnO), and fluorine-doped tin oxide (FTO), and further oxide semiconductors (TiO2, SrTiO3, WO3, Fe2O3, etc.) and mixed anion semiconductors (oxysulfide Y2Ti2O5S2, oxyhalides Bi4NbO8Cl, oxyfluorides Pb2Ti2O 5.4 F 1.2 As the oxidation reaction electrode 12, specifically, IrO2-supported porous Ti felt, Ni foam, Pt mesh, etc. can be used in order to increase the electrode reaction area so that OER does not become the reaction rate limiting.

[0034] The first ion exchange membrane 13 is preferably, for example, a bipolar membrane (BPM), but a cation exchange membrane (CEM), an anion exchange membrane (AEM), or the like can also be used. The BPM is an ion exchange membrane having a structure in which a CEM and an AEM are laminated. When a voltage equal to or greater than the theoretical decomposition voltage of water (0.83 V) is applied to both sides of the BPM, the water in the membrane becomes H. + and OH - Decomposed into catholyte and H + is supplied, and the anolyte is OH - is supplied.

[0035] Here, when a CEM is used as the first ion exchange membrane 13 (H + The cathodic and anodic reactions in the case of using AEM (OH - The cathodic and anodic reactions of the electrolyte (transport of electrolyte) are shown in Tables 1 and 2, respectively. When BPM is used as the first ion exchange membrane 13, even if there is a pH difference between the catholyte and the anolyte, the pH of each electrolyte can be stably maintained.

[0036] [Table 1]

[0037] [Table 2]

[0038] As described above, the present system 1 is supplied with only the aqueous carbonate solution CAS, without being supplied with high-concentration CO2 gas, by the electrochemical CO2 reduction device 10, and produces a CO2 reduction product. Here, in electrochemical CO2 reduction, the CO2 is dissolved, i.e., HCO3 - or CO3 2- In this state, the CO2 reduction reaction at the reduction reaction electrode 11 does not occur. However, if the dissolved CO2 can be converted to CO2 gas near the cathode catalyst of the reduction reaction electrode 11 in the first half-cell HC1 or just before the cathode catalyst, a three-phase interface reaction field of CO2 (gas)-water (liquid)-catalyst (solid) can be formed, and the CO2 reduction reaction can be realized.

[0039] As shown in Fig. 3, the solubility of CO2 in water depends on pH, which is utilized in the present system 1. Fig. 3 is a graph (Bjerrum plot) showing the relationship between the solubility of CO2 in water and pH. In the figure, the horizontal axis indicates pH, and the vertical axis indicates dissolved inorganic carbon (DIC).

[0040] As shown in Figure 3, the total concentration of dissolved inorganic carbon in carbonic acid changes with the change in pH of the aqueous solution (carbonate equilibrium). For example, pKa1 is around pH 6, and on the acidic side (pH 6 or less), there is more CO2 gas (g), and on the neutral side (pH 6-9), there is more HCO3 - In addition, pKa2 is around pH 9, and on the alkaline side (pH 9 or higher), CO3 2- The following equilibrium reactions take place at pKa1 and pKa2, respectively: (pKa1) H2CO3+OH - ⇔HCO3 - +H2O (pKa2) HCO3 - +OH - ⇔CO3 2- +H2O For H2O, H2O⇔H + +OH - may occur.

[0041] As mentioned above, when the body becomes acidic, CO2(g) escapes, and when the body becomes alkaline, CO2(g) is absorbed, increasing DIC. DIC = [H2CO3 * ]+[HCO3 - ]+[CO3 2- ]

[0042] As shown in Figure 3, CO2 is converted to HCO3 in neutral to alkaline conditions. - or CO3 2- However, in an acidic environment, it becomes CO2 gas. Therefore, this characteristic is utilized in the present system 1 to acidify the carbonate aqueous solution CAS near the cathode catalyst or just before the cathode catalyst, and the carbonate dissolved in the carbonate aqueous solution CAS is supplied to the cathode catalyst as CO2 gas.

[0043] As one embodiment of the present system 1, an electrochemical CO2 reduction device 10 having a CO2 gasification means 80 for acidifying an aqueous carbonate solution CAS can be used, thereby ensuring high-concentration CO2 gas and realizing a CO2 reduction reaction without excessive supply.

[0044] The CO2 gasification means 80 can be realized by acidifying the aqueous carbonate solution CAS immediately before introducing the aqueous carbonate solution CAS into the first half-cell HC1, or by acidifying the aqueous carbonate solution CAS in situ near the cathode catalyst. For example, the CO2 gasification means 80 can be as follows.

[0045] [One embodiment of CO2 gasification means] (An example of an electrochemical CO2 gasification device) 4 is a schematic diagram showing an example of an electrochemical CO2 gasification device 81 as one embodiment of the CO2 gasification means 80. FIG. 4 shows the electrochemical CO2 reduction device 10 and the electrochemical CO2 gasification device 81. As shown in FIG. 4, an example electrochemical CO2 gasification apparatus 81 includes a cathode 82 and an anode 83, a second ion exchange membrane 84 disposed between the cathode 82 and the anode 83, and a power supply 85 connected to the cathode 82 and the anode 83 and applying a voltage thereto.

[0046] This electrochemical CO2 gasification device 81 has a third half-cell HC3 including a cathode 82 and a second ion exchange membrane 84, and a fourth half-cell HC4 including an anode 83 and the second ion exchange membrane 84. Note that, for example, AEM is preferable as the second ion exchange membrane 84. An aqueous carbonate solution CAS (neutral to alkaline) is introduced into each of the third half-cell HC3 and the fourth half-cell HC4.

[0047] In this electrochemical CO2 gasification apparatus 81, H is introduced into the carbonate aqueous solution CAS by the cathode 82 in the third half-cell HC3 to which a voltage is applied. + The electrochemical CO2 gasification device 81 then introduces the carbonate aqueous solution CAS containing the gasified CO2 as catholyte into the first half-cell HC1 of the electrochemical CO2 reduction device 10. In this way, according to the electrochemical CO2 gasification device 81, the carbonate aqueous solution CAS containing gasified CO2 can be introduced into the first half-cell HC1 of the electrochemical CO2 reduction device 10 stably and reliably.

[0048] In this electrochemical CO2 gasification apparatus 81, the carbonate aqueous solution CAS (neutral to alkaline) introduced into the third half-cell HC3 is converted into OH by the AEM. - is supplied, and OH is supplied by the anode 83. - The aqueous carbonate solution CAS with a higher pH is introduced into the second half-cell HC2 of the electrochemical CO2 reduction device 10.

[0049] (First modified example of electrochemical CO2 gasification device) Fig. 5 is a schematic diagram showing an electrochemical CO2 gasification apparatus 86 according to a first modified example, as one embodiment of the CO2 gasification means 80. Fig. 5 shows only the electrochemical CO2 gasification apparatus 86. 5, in an electrochemical CO2 gasifier 86 according to a first modification, a third half-cell HC3 has a first cation exchange membrane 87 between a cathode 82 and a second ion exchange membrane 84. In addition, this electrochemical CO2 gasifier 86 has a first redox medium RM1 between the cathode 82 and the first cation exchange membrane 87, and an aqueous carbonate solution CAS is introduced between the first cation exchange membrane 87 and the second ion exchange membrane 84.

[0050] Furthermore, in the electrochemical CO2 gasifier 86 according to the first modification, the fourth half-cell HC4 has a second cation exchange membrane 88 between the anode 83 and the second ion exchange membrane 84. Also, this electrochemical CO2 gasifier 86 has a second redox medium RM2 between the anode 83 and the second cation exchange membrane 88, and an aqueous carbonate solution CAS is introduced between the second cation exchange membrane 88 and the second ion exchange membrane 84.

[0051] The first redox medium RM1 and the second redox medium RM2 form a redox pair. The redox ions of the first redox medium RM1 and the second redox medium RM2 are, for example, K3[Fe(CN)6] 3- / K4[Fe(CN)6] 4- , IO3 - / I - , Fe 3+ / Fe 2+ For example, the redox ion is K3[Fe(CN)6] 3- / K4[Fe(CN)6] 4- When using the above-mentioned 1,000 volts of hydrogen, the following reactions occur at the cathode 82 and the anode 83, respectively: Cathode: [Fe(CN)6] 3- +e - →[Fe(CN)6] 4- Anode: [Fe(CN)6] 4- →[Fe(CN)6] 3- +e -

[0052] In addition, the electrochemical CO2 gasification apparatus 86 according to the first modification is provided so that the first redox medium RM1 and the second redox medium RM2 circulate. In this way, it is possible to suppress the concentration polarization of redox ions caused by the oxidation-reduction reaction at the electrodes.

[0053] In the case of the electrochemical CO2 gasification apparatus 86 according to the first modification, the second ion exchange membrane 84 uses BPM. The first cation exchange membrane 87 of the third half-cell HC3 and the second cation exchange membrane 88 of the fourth half-cell HC4 may both be CEM. The first cation exchange membrane 87 and the second cation exchange membrane 88 are preferably of the same type, but may be of different types. CEM does not allow redox ions to pass through but allows counter ions to pass through.

[0054] The electrochemical CO2 gasification apparatus 86 shown in FIG. 5 uses H + CO2 gasification is produced in the catholyte that is acidified by the supply of CO2, and OH gasification is produced in the fourth half-cell HC4.- The bicarbonate ions or carbonate ions remain in the anolyte which is then alkalized. The catholyte is fed to a first half-cell HC1 of the electrochemical CO2 reduction device 10, and the anolyte is fed to a second half-cell HC2 of the electrochemical CO2 reduction device 10.

[0055] In this electrochemical CO2 gasification device 86, a voltage is applied to the cathode 82 and the anode 83 via a conductor to generate H in the BPM (second ion exchange membrane 84). + , O.H. - By carrying out both the production and the oxidation-reduction reactions of redox ions at the anode 83 and the cathode 82, a continuous catholyte acidification of an aqueous carbonate solution CAS and CO2 gasification can be carried out.

[0056] (Second modified example of electrochemical CO2 gasification device) Fig. 6 is a schematic diagram showing an electrochemical CO2 gasification apparatus 89 according to a second modified example, as one embodiment of the CO2 gasification means 80. Fig. 6 shows only the electrochemical CO2 gasification apparatus 89 according to the second modified example. As shown in FIG. 6, an electrochemical CO2 gasification apparatus 89 according to the second modified example differs from the electrochemical CO2 gasification apparatus 86 according to the first modified example shown in FIG. 5 in that a temperature difference is applied between the cathode 82 and the anode 83, but is otherwise similar. Therefore, the difference here is that a temperature difference is provided between the cathode 82 and the anode 83.

[0057] In this embodiment, based on the principle of thermochemical battery (temperature difference power generation), by applying a temperature difference between the cathode 82 and the anode 83, power can be generated by thermoelectromotive force (Equation 1 below), and operation can be achieved without an external power source. For example, in the case of N-type redox, the high temperature side T hot In the low temperature side, the oxidized form (Ox) becomes the reduced form (Red), and the low temperature side, T cold Then Red becomes Ox (equation 2 below).

[0058]

number

[0059]

number

[0060] In an electrochemical CO2 gasification apparatus 89 according to a second modified example shown in Fig. 6, a heat source (high temperature side) 82h is provided on the cathode 82, and a heat source (low temperature side) 83c is provided on the anode 83. These heat sources are sufficient as long as a temperature difference occurs between the cathode 82 and the anode 83, and only one of them may be provided. As described above, these heat sources can be provided without an external power source, but they can also be heated or cooled using an external power source. When there is no external power source, heat or cold generated by an external device can be used.

[0061] (Third modified example of electrochemical CO2 gasification device) Fig. 7 is a schematic diagram showing an electrochemical CO2 gasification apparatus 90 according to a third modified example, as another embodiment of the CO2 gasification means 80. Fig. 7 shows the electrochemical CO2 reduction device 10 and the electrochemical CO2 gasification apparatus 90 according to the third modified example. As shown in FIG. 7, in an electrochemical CO 2 gasification apparatus 90 according to a third modification, a third half-cell HC3 of the apparatus 90 is connected to a first half-cell HC1 and a second half-cell HC2 of the electrochemical CO 2 reduction apparatus 10. In the electrochemical CO2 gasification apparatus 90 according to the third modified example, the carbonate aqueous solution CAS containing CO2 gasified in the third half-cell HC3 is introduced as catholyte into the first half-cell HC1, and is also introduced as anolyte into the second half-cell HC2 comprising the oxidation reaction electrode 12 and the first ion exchange membrane 13.

[0062] The catholyte introduced into the first half-cell HC1 of the electrochemical CO2 reduction device 10 is acidified in the third half-cell HC3 of the electrochemical CO2 gasification device 90 according to the third modification, and the CO2 is gasified. Therefore, as described above, the reduction reaction electrode 11 is used to convert the CO2 reduction products (C1, C 2+) can be generated.

[0063] On the other hand, the anolyte introduced into the second half-cell HC2 of the electrochemical CO2 reduction device 10 is acidified in the third half-cell HC3 of the electrochemical CO2 gasification device 90 according to the third modification, but the OH - is supplied, the atmosphere becomes neutral to alkaline. Therefore, the gasified CO2 turns back into carbonate (HCO3 - , CO3 2- ) and dissolves in the carbonate aqueous solution CAS. Since this carbonate aqueous solution CAS is neutral to alkaline, the unreacted CO2 gas in the first half-cell HC1 of the electrochemical CO2 reduction device 10 can be contacted with the carbonate aqueous solution CAS to redissolve the unreacted CO2 gas in the carbonate aqueous solution CAS. In this embodiment, the carbonate aqueous solution CAS in which the unreacted CO2 gas in the first half-cell HC1 of the electrochemical CO2 reduction device 10 is redissolved may be referred to as a recovered electrolyte. That is, in this embodiment, the recovered electrolyte is reused as the carbonate aqueous solution CAS, so that a CO2 reduction product can be generated. In this way, the utilization efficiency of CO2 is improved.

[0064] The recovered electrolyte can be further supplied to the fourth half-cell HC4 of the electrochemical CO2 gasification apparatus 90, and then supplied again to the third half-cell HC3. - Since the pH is increased, the CO2 gas can be dissolved more reliably.

[0065] (Fourth modified example of electrochemical CO2 gasification device) Fig. 8 is a schematic diagram showing an electrochemical CO2 gasification apparatus 91 according to a fourth modified example, as another embodiment of the CO2 gasification means 80. Fig. 8 shows only the electrochemical CO2 gasification apparatus 91 according to the fourth modified example. As shown in Fig. 8, the electrochemical CO2 gasification apparatus 91 according to the fourth modification has a cathode 82 and an anode 83 as PCET electrodes that perform a proton-coupled electron transfer (PCET) reaction. The following reaction proceeds at the cathode 82 and the anode 83 in the electrochemical CO2 gasification apparatus 91. In the following formula, X(s) represents the PCET electrode. X(s)+nH + +ne - ⇔XHn(s) In other words, in this device 91, protons H are generated at the PCET electrode by an electrochemical reaction. + can be reversibly inserted and removed.

[0066] The PCET electrode may be made of a metal oxide such as, but not limited to, MnO2, CoO2, or NiO2. The method using the PCET electrode can be applied to aqueous solutions, unlike the method using the PCET organic molecules, which can only be applied to aprotic solvents (organic solvents, ionic liquids). In this modification, the second ion exchange membrane 84 is an AEM. Any known AEM can be used.

[0067] In the electrochemical CO gasification apparatus 91 according to the fourth modification having such a configuration, H is released into the aqueous solution from the PCET electrode that functions as the anode 83, which is the positive electrode, by applying a positive potential. + is supplied to the PCET electrode, which functions as the cathode 82, and H + is supplied to the PCET electrode, the pH increases. + and HCO3 - The reaction produces CO2 gas. This acidified aqueous solution is introduced into the first half-cell HC1 of the electrochemical CO2 reduction device 10 as catholyte from which CO2 has been gasified. On the other hand, a low pH recovered electrolyte is introduced into the fourth half-cell HC4 of the electrochemical CO2 gasification apparatus 91 according to the fourth modification. -As the AEM is permeated, the low pH becomes higher. Therefore, the recovered electrolyte converts CO2 into bicarbonate ions (HCO3 - ) and carbonate ions (CO3 2- ) can be regenerated as a carbonate aqueous solution CAS.

[0068] In the electrochemical CO2 gasification apparatus 91 according to the fourth modification, the periodic potential switching (polarity reversal) of the PCET electrode is synchronized with the switching of the supply flow path of the aqueous carbonate solution CAS (i.e., catholyte) to at least the first half-cell HC1. By doing so in this embodiment, a continuous CO2 reduction reaction can be performed.

[0069] [Other aspects of CO2 gasification means] FIG. 9 is a schematic diagram showing an electrochemical CO2 reduction device 14 according to another embodiment, for explaining a CO2 gasification means 80 according to the other embodiment. As shown in FIG. 9, in the CO2 gasification means 80A in the electrochemical CO2 reduction device 14 according to another embodiment, the first ion exchange membrane 13 is preferably a BPM, and H + The catholyte is locally acidified (in situ) in the vicinity of the reduction reaction electrode 11 by the above-mentioned reaction, whereby the CO2 in the catholyte is gasified. The reduction reaction electrode 11 is a GDE with a CO2 reduction reaction catalyst, and the oxidation reaction electrode 12 is a GDE with an OER catalyst.

[0070] As chemical reactions in the electrochemical CO2 reduction device 14 having such a configuration, for example, reactions α, β, γ, and δ shown in FIG. 9 occur. (Reaction α) 4OH - →O2+2H2O+e - (Reaction β) 4H2O→4H + +4OH - (Reaction γ) 2CO3 2- +4H + →2CO2(g)+2H2O (Reaction δ) CO2(g)+e - +H2O→C x H y O z +OH -

[0071] In this other embodiment, catholyte is supplied together with anolyte as a neutral to alkaline carbonate aqueous solution CAS. However, as described above, catholyte is supplied in the form of H supplied from BPM. + Since the aqueous solution of carbonate CAS containing dissolved carbonate is supplied to the first half-cell HC1, CO2 gas can be generated near the cathode three-phase interface reaction field and reduced to produce CO2 reduction products.

[0072] (An example of a CO2 recycling mechanism) One embodiment of the reuse mechanism has been described above. Here, another specific embodiment of the reuse mechanism described above will be described. Fig. 10 is a configuration diagram showing an example of a CO2 reuse mechanism 100. As shown in Fig. 10, the CO2 recycling mechanism 100 is composed of a cathode GDE 101, an anode GDE 102, and a quinone solution layer 103 containing a quinone compound, which is a PCET organic material, between the cathode GDE 101 and the anode GDE 102. In other words, the recycling mechanism 100 shown in Fig. 10 is an electrochemical pH swing device using a PCET organic material.

[0073] The gas introduced into the CO2 recycling mechanism 100 does not contain any liquid because it is the gas after gas-liquid separation of the CO2 reduction product from the electrochemical CO2 reduction device 10 or after gas-liquid separation of the crossover CO2. This gas is a mixed gas containing a relatively low concentration of CO2, including unreacted CO2, gases generated by the reaction (O2, etc.), and crossover CO2.

[0074] In this recycling mechanism 100, gas is introduced from the cathode GDE 101 into the quinone solution layer 103 to carry out a PCET reaction, thereby increasing the CO2 concentration and recovering it from the anode GDE 102. Incidentally, with respect to the gas introduced from the cathode GDE 101 side, CO2 dissolves in the quinone solution layer 103, but other gases (e.g., N2, O2, etc.) do not dissolve. Most of the CO2 is selectively dissolved and then concentrated. The CO2 recovered from the anode GDE 102 is highly concentrated because it is selectively actively transported by the pH gradient. It is preferable to recover CO2 by sweeping with a gas. Examples of the gas to be used for sweeping include an inert gas such as Ar and H2O. The quinone solution layer 103 is preferably a solution in which a quinone compound is dissolved in an aprotic solvent (organic solvent, ionic liquid), but is not limited thereto. For example, quinone solution layer 103 may be a quinone solution retaining separator containing 1M or less NaHCO3 in water.

[0075] The following reaction takes place in the cathode GDE 101 and anode GDE 102 of the recycling mechanism 100. Due to the reaction, the pH becomes higher on the cathode GDE 101 side of the recycling mechanism 100 and lower on the anode GDE 102 side. In the following formula, Q represents quinone. Q functions as Ox (oxidant) and QH2 functions as Red (reductant). (Cathode) Q+2e - +2H + →QH2 (Anode) QH2→Q+2e - +2H + HCO3 - +H + →CO2+H2O The overall reaction of the anode GDE 102 is as follows: (Anode total reaction) 2HCO3 - +QH2→Q+2CO2+2H2O

[0076] [Other preferred aspects] In the carbon dioxide resource recovery system 1 according to this embodiment, the catholyte is K +and Na + In this way, K is formed on the surface of the cathode catalyst of the reduction reaction electrode 11. + OrNa + By adsorption of H + This can suppress the adsorption of hydrogen, which is advantageous in an acidic environment.

[0077] Regarding the preferred embodiment, + and Na + is preferably added to catholyte as KCl or NaCl at a concentration of 0.5 to 3 M. In this way, HER, which is advantageous in an acidic environment, can be more reliably suppressed.

[0078] In the above embodiment, it has been described that a cathode GDE in which a CO2 reduction reaction catalyst is provided on an MPL-attached GDL is used as the reduction reaction electrode 11 of the electrochemical CO2 reduction device 10, but this embodiment is not limited to this. Also, in the above embodiment, it has been described that an anode GDE in which an OER catalyst is provided is used as the oxidation reaction electrode 12 of the electrochemical CO2 reduction device 10, but this embodiment is not limited to this. In this embodiment, the electrode structures of the reduction reaction electrode 11 and the oxidation reaction electrode 12 may be thin film, lattice, particle, wire or porous, and are not limited to those described above. The reduction reaction electrode 11 and the oxidation reaction electrode 12 having these electrode structures can perform the reduction reaction of CO2 gas and the oxygen generation reaction from H2O described above.

[0079] Although the carbon dioxide resource recovery system 1 according to the present invention has been described in detail above by way of an embodiment, the present invention is not limited to the above-described embodiment and includes various modified examples. For example, the above-described embodiment has been described in detail to easily explain the present invention, and is not necessarily limited to having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0080] 1 Carbon dioxide resource recovery system (this system) 10 Electrochemical CO2 reduction device 11 Reduction reaction electrode 12 Oxidation reaction electrode 13 First ion exchange membrane 14 Electrochemical CO2 reduction device 80, 80A CO2 gasification means 81, 86, 89-91 Electrochemical CO2 gasification equipment 82 Cathode 83 Anode 84 Second ion exchange membrane 85 Power supply 87 First Cation Exchange Membrane 88 Second cation exchange membrane 100 Reuse mechanism 101 Cathodic GDE 102 Anode GDE 103 Quinone solution layer CD control unit CAS Carbonate solution HC1 First half cell HC2 2nd half cell HC3 3rd half cell HC4 4th half cell PS power supply RM1 1st Redox Medium RM2 Second Redox Medium

Claims

1. An electrochemical CO2 analyzer comprising a reduction reaction electrode, an oxidation reaction electrode, and a first ion exchange membrane disposed between the reduction reaction electrode and the oxidation reaction electrode. ２ A reduction device is provided. A first half cell comprising the reduction reaction electrode and the first ion exchange membrane was charged with CO as a catholyte. ２ A carbonate aqueous solution containing The CO in the catholyte is ２ CO in the catholyte immediately before carrying out the reduction of ２ CO ２ Has gasification means A carbon dioxide resource recovery system.

2. The carbon dioxide resource recovery system according to claim 1, The CO ２ The gasification means is electrochemical CO ２ It is a gasification device, The electrochemical CO ２ The gasifier is a cathode and an anode; a second ion exchange membrane disposed between the cathode and the anode; a power supply connected to the cathode and the anode for applying a voltage thereto; Including, the carbonate aqueous solution is introduced into a third half-cell comprising the cathode and the second ion exchange membrane, and into a fourth half-cell comprising the anode and the second ion exchange membrane, In the third half-cell to which the voltage is applied, the CO in the carbonate aqueous solution is ２ and gasifying the gasified CO ２ and introducing an aqueous carbonate solution containing the compound as the catholyte into the first half-cell. A carbon dioxide resource recovery system.

3. The carbon dioxide resource recovery system according to claim 2, the third half-cell has a first cation exchange membrane between the cathode and the second ion exchange membrane, and a first redox medium between the cathode and the first cation exchange membrane, and the aqueous carbonate solution is introduced between the first cation exchange membrane and the second ion exchange membrane; the fourth half-cell has a second cation exchange membrane between the anode and the second ion exchange membrane, and a second redox medium between the anode and the second cation exchange membrane, and the aqueous carbonate solution is introduced between the second cation exchange membrane and the second ion exchange membrane; The first redox medium and the second redox medium are provided so as to circulate. A carbon dioxide resource recovery system.

4. The carbon dioxide resource recovery system according to claim 3, A temperature difference is applied between the cathode and the anode. A carbon dioxide resource recovery system.

5. The carbon dioxide resource recovery system according to claim 2, The gasified CO ２ introducing an aqueous carbonate solution containing the above as catholyte into the first half-cell and as anolyte into a second half-cell comprising the above oxidation reaction electrode and the above first ion exchange membrane; The carbonate aqueous solution introduced into the fourth half-cell contains unreacted CO ２ The carbonate solution contains A carbon dioxide resource recovery system.

6. The carbon dioxide resource recovery system according to claim 2, The cathode and the anode are both PCET electrodes that undergo proton-coupled electron transfer reactions; the second ion exchange membrane is an anion exchange membrane, Synchronizing periodic potential switching of the PCET electrode with switching of a supply flow path of the carbonate aqueous solution to at least the first half-cell. A carbon dioxide resource recovery system.

7. The carbon dioxide resource recovery system according to claim 1, The CO ２ The gasification means is the first ion exchange membrane is a bipolar membrane; H supplied from the bipolar membrane ＋ The catholyte is locally acidified in the vicinity of the reduction reaction electrode by ２ Gasify the A carbon dioxide resource recovery system.

8. The carbon dioxide resource recovery system according to claim 1, a second half-cell including the oxidation reaction electrode and the first ion exchange membrane; Unreacted CO discharged from the first half-cell ２ and crossover CO exhausted from the second half-cell. ２ and a recycling mechanism for recovering at least one of the gases containing A carbon dioxide resource recovery system.

9. The carbon dioxide resource recovery system according to claim 8, The recycling mechanism is configured to collect the CO ２ By utilizing the fact that the ionization and dissolution of depends on pH, CO ２ Only CO is actively transported selectively through a pH gradient. ２ To enrich A carbon dioxide resource recovery system.

10. The carbon dioxide resource recovery system according to claim 8, the recycling mechanism includes a quinone solution layer disposed between a cathode and an anode; The gas is introduced from the cathode into the quinone solution to carry out a proton-coupled electron transfer reaction, thereby producing CO ２ The concentration is increased and recovered from the anode. A carbon dioxide resource recovery system.

11. The carbon dioxide resource recovery system according to claim 1, The catholyte is K ＋ and Na ＋ Contains at least one of A carbon dioxide resource recovery system.

12. The carbon dioxide resource recovery system according to claim 11, The above K ＋ and the Na ＋ was added to the catholyte as KCl or NaCl at a concentration of 0.5 to 3M. A carbon dioxide resource recovery system.

13. The carbon dioxide resource recovery system according to claim 1, The first ion exchange membrane is a cation exchange membrane or an anion exchange membrane. A carbon dioxide resource recovery system.

14. The carbon dioxide resource recovery system according to claim 1, The electrode structure of the reduction reaction electrode and the oxidation reaction electrode is a thin film, a lattice, a particle, a wire, or a porous structure. A carbon dioxide resource recovery system.

15. The carbon dioxide resource recovery system according to claim 1, The carbonate aqueous solution is ２ is dissolved in a water-soluble amine recovery solution, an aqueous potassium carbonate solution, carbonated water or seawater. A carbon dioxide resource recovery system.

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