Carbon dioxide processing device, carbon dioxide processing method, and method for producing carbon compounds

Abstract

The present invention provides a carbon dioxide treatment device, a carbon dioxide treatment method, and a carbon compound production method that have high energy efficiency for carbon dioxide recovery and reduction and high carbon dioxide loss reduction effects. The carbon dioxide treatment device (100) includes a recovery device (1) for recovering carbon dioxide, an electrochemical reaction device (2) for electrochemically reducing carbon dioxide, and a pH adjuster (52). The pH of the cathode-side electrolyte becomes higher than that of the anode-side electrolyte. Carbon dioxide gas is supplied from a concentrating section (11) to a gas flow path on the opposite side of the cathode (21) from the anode (22), and the carbon dioxide gas is reduced at the cathode (21).

Description

Technical Field

[0001] The present invention relates to a carbon dioxide processing device, a carbon dioxide processing method and a method for producing carbon compounds. Background Art

[0002] The technology of recovering carbon dioxide from exhaust gases and the atmosphere and electrochemically reducing it to valuable products holds great promise for achieving carbon neutrality, but economic viability remains a major challenge. To improve economic viability, it is crucial to increase energy efficiency and minimize carbon dioxide losses during carbon dioxide recovery and reduction.

[0003] As a technology for recovering carbon dioxide, the following is known: after physically or chemically adsorbing carbon dioxide in a gas onto a solid or liquid adsorbent, it is removed by energy such as heat for utilization. Furthermore, as a technology for electrochemically reducing carbon dioxide, the following is known: a cathode having a catalyst layer formed using a carbon dioxide reduction catalyst on the side of the gas diffusion layer that contacts the electrolyte is used, and carbon dioxide gas is supplied from the side of the gas diffusion layer opposite the catalyst layer to perform electrochemical reduction (Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2018 / 232515 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Carbon dioxide reduction is a promising technology that has the potential to achieve carbon neutrality, but economic efficiency is the biggest challenge. To improve economic efficiency, it is important to recover carbon dioxide with high energy efficiency and perform conversion without loss.

[0009] One of the causes of energy loss in carbon dioxide electrolysis is hydrogen generation due to water electrolysis, a side reaction unrelated to the target carbon dioxide reduction reaction. Depending on the degradation state of the cathode and anode catalysts, simply controlling the voltage is not enough to suppress hydrogen generation.

[0010] An object of the present invention is to provide a carbon dioxide treatment apparatus, a carbon dioxide treatment method, and a method for producing a carbon compound, which have high energy efficiency for recovery and reduction of carbon dioxide and high carbon dioxide loss reduction effect.

[0011] Means for solving problems

[0012] The present invention adopts the following scheme.

[0013] (1) A carbon dioxide treatment device according to one embodiment of the present invention (e.g., the carbon dioxide treatment device 100 of the embodiment) comprises: a recovery device (e.g., the recovery device 1 of the embodiment) which recovers carbon dioxide; an electrochemical reaction device (e.g., the electrochemical reaction device 2 of the embodiment) which electrochemically reduces carbon dioxide; and a pH adjuster (e.g., the pH adjuster 52 of the embodiment), wherein the recovery device comprises: an absorption unit (e.g., the absorption unit 12 of the embodiment) which brings an anode-side electrolyte composed of a strongly alkaline aqueous solution into contact with carbon dioxide gas, so that carbon dioxide is dissolved and absorbed in the anode-side electrolyte; and a concentration unit (e.g., the concentration units 11 and 13 of the embodiment) which concentrates carbon dioxide, wherein the electrochemical reaction device comprises: an anode (e.g., the anode 22 of the embodiment); a cathode (e.g., the pH adjuster 52 of the embodiment). a cathode 21); an anion exchange membrane provided between the anode and the cathode (for example, the anion exchange membrane 23 of the embodiment); a liquid flow path provided between the anode and the anion exchange membrane and for the flow of the anode-side electrolyte that has absorbed carbon dioxide using the absorption section (for example, the liquid flow path 29a of the embodiment); and a liquid flow path provided between the cathode and the anion exchange membrane and for the flow of a cathode-side electrolyte composed of a strong alkaline aqueous solution whose pH has been adjusted using the pH adjuster (for example, the liquid flow path 28a of the embodiment), the pH of the cathode-side electrolyte being higher than that of the anode-side electrolyte, and carbon dioxide gas being supplied from the concentrating section to a gas flow path on the opposite side of the cathode from the anode (for example, the gas flow path 24a of the embodiment), where the carbon dioxide gas is reduced at the cathode.

[0014] (2) Alternatively, the carbon dioxide treatment device of one embodiment of the present invention may further include a power storage device (for example, the power storage device 3 of the embodiment) for supplying electric power to the electrochemical reaction device, and the power storage device may include a conversion unit (for example, the conversion unit 31 of the embodiment) for converting renewable energy into electric energy and a storage unit (for example, the storage unit 32 of the embodiment) for storing the electric energy converted by the conversion unit.

[0015] (3) Alternatively, the storage unit is a nickel-hydrogen battery, comprising a positive electrode (e.g., the positive electrode 33 of the embodiment), a negative electrode (e.g., the negative electrode 34 of the embodiment), a separator disposed between the positive electrode and the negative electrode (e.g., the separator 37 of the embodiment), a positive electrode side flow path disposed between the positive electrode and the separator (e.g., the positive electrode side flow path 36 of the embodiment), and a negative electrode side flow path disposed between the negative electrode and the separator (e.g., the negative electrode side flow path 35 of the embodiment), wherein during discharge of the nickel-hydrogen battery, the anode side electrolyte circulates in the order of the absorption unit, the negative electrode side flow path, the electrochemical reaction device, and the absorption unit, and during charge of the nickel-hydrogen battery, the anode side electrolyte circulates in the order of the absorption unit, the negative electrode side flow path, the electrochemical reaction device, the positive electrode side flow path, and the absorption unit.

[0016] (4) The pH adjuster may bring the cathode-side electrolyte into contact with carbon dioxide gas.

[0017] (5) Alternatively, the carbon dioxide treatment apparatus of one embodiment of the present invention may further include a carbon addition reaction apparatus (e.g., the carbon addition reaction apparatus 4 of the embodiment) that performs carbon addition by polymerizing ethylene generated by reducing carbon dioxide by the electrochemical reaction apparatus.

[0018] (6) Alternatively, the carbon dioxide treatment device of one embodiment of the present invention further comprises: a heat medium that is heated by the heat generated by the reaction in the carburizing reaction device; and a heat exchanger (for example, the heat exchanger 43 of the embodiment) that heats the anode side electrolyte by performing heat exchange between the heat exchanger and the anode side electrolyte.

[0019] (7) A carbon dioxide treatment method according to one embodiment of the present invention includes the following steps: bringing carbon dioxide gas into contact with an anode-side electrolyte composed of a strongly alkaline aqueous solution, so that carbon dioxide is dissolved and absorbed in the anode-side electrolyte; adjusting the pH of the cathode-side electrolyte to be higher than the pH of the anode-side electrolyte; and supplying the cathode-side electrolyte between the cathode and the anion exchange membrane, supplying the anode-side electrolyte between the anode and the anion exchange membrane, and supplying carbon dioxide gas to the side of the cathode opposite to the anode, thereby electrochemically reducing the carbon dioxide gas to produce carbon compounds and hydrogen.

[0020] (8) In the step of adjusting the pH of the cathode electrolyte, the cathode electrolyte and carbon dioxide may be brought into contact to dissolve the carbon dioxide in the cathode electrolyte.

[0021] (9) A method for producing a carbon compound according to one embodiment of the present invention uses the carbon dioxide treatment method described in (7) or (8) to produce a carbon compound obtained by reducing carbon dioxide.

[0022] (10) The method for producing a carbon compound according to one embodiment of the present invention may further include a step of polymerizing ethylene produced by reducing the dissolved carbon dioxide.

[0023] Effects of the Invention

[0024] According to the aspects (1) to (10), it is possible to provide a carbon dioxide treatment apparatus, a carbon dioxide treatment method, and a carbon compound production method that have high energy efficiency for recovery and reduction of carbon dioxide and high carbon dioxide loss reduction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a block diagram showing a carbon dioxide treatment apparatus according to an embodiment.

[0026] Figure 2 This is a schematic cross-sectional view showing an example of an electrolytic cell of an electrochemical reaction device.

[0027] Figure 3 is a schematic diagram showing the electrochemical reactions produced by the electrolysis cell.

[0028] Figure 4 This is a schematic cross-sectional view showing a nickel-hydrogen battery as an example of a storage unit.

[0029] Figure 5 It is a graph showing the electrolysis test results of Examples and Comparative Examples.

[0030] Description of Reference Numerals

[0031] 1... Recovery device, 2... Electrochemical reactor, 3... Power storage device, 4... Recarburization reactor, 6... Carbon number, 11... Concentrator, 12... Absorber, 13... Concentrator, 21... Cathode, 22... Anode, 23... Anion exchange membrane, 23a... Liquid flow path, 24... Gas flow path structure, 24a... Gas flow path, 25... Gas flow path structure, 25a... Gas flow path, 26... Power supply, 27... Power supply, 28... Liquid flow path structure, 28a... Liquid flow path, 29... Liquid flow path structure, 29a... Liquid flow path, 31... Converter, 32... Storage unit, 33... Positive electrode, 34... Negative electrode, 35... Negative electrode side flow path, 36... Positive electrode side flow path, 37... Separator, 41... Reactor, 42... Gas-liquid separator, 43... Heat exchanger, 50... Cooler, 51... pH measurement 52…pH adjuster, 53…pH measuring device, 62…liquid flow path, 63…liquid flow path, 64…liquid flow path, 65…liquid flow path, 66…liquid flow path, 66a…liquid flow path, 66b…liquid flow path, 69…circulation flow path, 70…gas flow path, 71…gas flow path, 72…gas flow path, 73…gas flow path, 74…gas flow path, 75…gas flow path, 76…gas flow path, 77…gas flow path, 84…reactor, 100…carbon dioxide treatment device, A…anode side electrolyte, B…anode side electrolyte, C…cathode side electrolyte, D…cathode side electrolyte, E…ethylene gas, F…produced gas, G1…gas, G2…concentrated gas, G3…separated gas, G4…concentrated gas, G5…concentrated gas, J1…olefin liquid, J2…olefin gas, K…heat medium DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the dimensions and the like in the drawings shown in the following description are merely examples, and the present invention is not necessarily limited thereto and can be implemented with appropriate modifications within the scope of the present invention.

[0033] [Carbon dioxide treatment device]

[0034] like Figure 1 As shown, a carbon dioxide treatment apparatus 100 according to one embodiment of the present invention includes a recovery unit 1, an electrochemical reactor 2, a power storage unit 3, a recarburization reactor 4, a heat exchanger 43, and a pH adjuster 52. The recovery unit 1 includes a concentration unit 11, an absorption unit 12, and a concentration unit 13. The power storage unit 3 includes a conversion unit 31 and a storage unit 32 electrically connected to the conversion unit 31. The recarburization reactor 4 includes a reactor 41 and a gas-liquid separator 42.

[0035] In the carbon dioxide treatment apparatus 100, the concentrating section 11 and the absorption section 12 are connected by a gas flow path 75. The concentrating section 11 and the concentrating section 13 are connected by a gas flow path 77. The absorption section 12 and the storage section 32 are connected by a liquid flow path 62. The electrochemical reactor 2 and the storage section 32 are connected by a liquid flow path 65. The electrochemical reactor 2 and the absorption section 12 are connected by a liquid flow path 66. The electrochemical reactor 2 and the reactor 41 are connected by a gas flow path 74. The reactor 41 and the gas-liquid separator 42 are connected by gas flow paths 72 and 73. A heat medium circulation flow path 69 is provided between the reactor 41 and the heat exchanger 43. The concentrating sections 11 and 13 are connected to the gas-liquid separator 42 by a gas flow path 71. The concentrating section 13 and the electrochemical reactor 2 are connected by a gas flow path 76. The pH adjuster 52 and the electrochemical reactor 2 are connected by liquid flow paths 63 and 64.

[0036] These flow paths are not particularly limited, and known pipes can be used as appropriate. In the gas flow paths 71 to 77, gas supply units such as compressors, pressure reducing valves, and measuring devices such as pressure gauges can be appropriately provided. Figure 1 In the embodiment, a cooler 50 is provided in the gas flow path 71. In addition, a liquid delivery unit such as a pump, a measuring device such as a flow meter, etc. can be appropriately provided in the liquid flow paths 62 to 66. Figure 1 In the embodiment, the pH measuring device 51 is provided in the liquid flow path 66 , and the pH measuring device 53 is provided in the liquid flow path 63 .

[0037] The recovery device 1 is a device for recovering carbon dioxide.

[0038] A gas G1 containing carbon dioxide, such as atmospheric air or exhaust gas, is supplied to the concentrating section 11 and the concentrating section 13. The carbon dioxide in the gas G1 is concentrated in the concentrating section 11 and the concentrating section 13. Concentrating sections 11 and 13 can be any known concentrating device, as long as they can concentrate carbon dioxide. For example, membrane separation devices utilizing different permeation rates through a membrane, or adsorption separation devices utilizing chemical or physical adsorption and desorption, can be used. Of these, adsorption utilizing chemical adsorption, particularly temperature swing adsorption, is preferred due to its superior separation performance.

[0039] Concentrated gas G2 in which carbon dioxide is concentrated by concentrating unit 11 is sent to absorber 12 through gas flow path 75. Separated gas G3 separated from concentrated gas G2 is sent to gas-liquid separator 42 through gas flow path 71.

[0040] Concentrated gas G4 in which carbon dioxide is concentrated by concentrating unit 13 is fed to electrochemical reactor 2 through gas flow path 75. Separated gas separated from concentrated gas G4 is fed to gas-liquid separator 42 through gas flow path 71 together with separated gas G3.

[0041] In the absorption section 12, the carbon dioxide gas in the concentrated gas G2 supplied from the concentrating section 11 comes into contact with the anode-side electrolyte A, and the carbon dioxide is dissolved and absorbed in the anode-side electrolyte A. The method for bringing the carbon dioxide gas into contact with the anode-side electrolyte A is not particularly limited, and an example thereof is a method of blowing the concentrated gas G2 into the anode-side electrolyte A to cause bubbling.

[0042] In the absorption section 12, an anode side electrolyte A composed of a strong alkaline aqueous solution is used as an absorption liquid for absorbing carbon dioxide. In carbon dioxide, since oxygen atoms strongly attract electrons, carbon atoms have a positive charge (δ+). Therefore, in a strong alkaline aqueous solution containing a large amount of hydroxide ions, carbon dioxide is easily converted from a water-soluble state to HCO3 - And to CO3 2- Until the dissolution reaction is carried out to become CO3 2- The carbon dioxide concentration in the concentrated gas G2 is high. This allows the carbon dioxide to dissolve more readily in a strongly alkaline aqueous solution than other gases such as nitrogen, hydrogen, and oxygen. In the absorption section 12, the carbon dioxide in the concentrated gas G2 is selectively absorbed into the anode-side electrolyte A. Thus, using the anode-side electrolyte A in the absorption section 12 assists in the concentration of carbon dioxide. Consequently, it is no longer necessary to concentrate the carbon dioxide to a high concentration in the concentration section 11, reducing the energy required for concentration in the concentration section 11.

[0043] The anode-side electrolyte B obtained by absorbing carbon dioxide in the absorption section 12 is transported to the electrochemical reactor 2 via the liquid flow path 62, the storage section 32, and the liquid flow path 65. Furthermore, the anode-side electrolyte A flowing out of the electrochemical reactor 2 is transported to the absorption section 12 via the liquid flow path 66. Thus, in the carbon dioxide treatment apparatus 100, the anode-side electrolyte circulates and is shared among the absorption section 12, the storage section 32, and the electrochemical reactor 2.

[0044] Examples of the strongly alkaline aqueous solution used in the anode-side electrolyte A include potassium hydroxide aqueous solution and sodium hydroxide aqueous solution. Of these, potassium hydroxide aqueous solution is preferred because it has excellent solubility of carbon dioxide in the absorption unit 12 and promotes reduction of carbon dioxide in the electrochemical reactor 2 .

[0045] The electrochemical reaction device 2 is a device for electrochemically reducing carbon dioxide. Figure 2 As shown, the electrochemical reaction device 2 includes a cathode 21, an anode 22, an anion exchange membrane 23, a liquid flow path structure 28 for forming a liquid flow path 28a, a liquid flow path structure 29 for forming a liquid flow path 29a, a gas flow path structure 24 for forming a gas flow path 24a, a gas flow path structure 25 for forming a gas flow path 25a, a power supply 26 and a power supply 27.

[0046] In the electrochemical reactor 2, a power supply 26, a gas flow path structure 24, a cathode 21, a liquid flow path structure 28, an anion exchange membrane 23, a liquid flow path structure 29, an anode 22, a gas flow path structure 25, and a power supply 27 are stacked in this order. Slits are formed in the liquid flow path structures 28 and 29. The areas within the slits surrounded by the cathode 21, anode 22, and the liquid flow path structures 28 and 29 serve as liquid flow paths 28a and 29a, respectively. A groove is formed on the cathode 21 side of the gas flow path structure 24. The portion of this groove surrounded by the gas flow path structure 24 and the cathode 21 serves as the gas flow path 24a. A groove is formed on the anode 22 side of the gas flow path structure 25. The portion of this groove surrounded by the gas flow path structure 25 and the anode 22 serves as the gas flow path 25a.

[0047] Thus, in the electrochemical reactor 2, a liquid flow path 28a is formed between the cathode 21 and the anion exchange membrane 23, a liquid flow path 29a is formed between the anode 22 and the anion exchange membrane 23, a gas flow path 24a is formed between the cathode 21 and the power supply 26, and a gas flow path 25a is formed between the anode 22 and the power supply 27. The power supply 26 and the power supply 27 are electrically connected to the storage unit 32 of the power storage device 3. Furthermore, the gas flow path structure 24 and the gas flow path structure 25 are conductive bodies, and can apply a voltage between the cathode 21 and the anode 22 using the power supplied from the storage unit 32.

[0048] The cathode 21 is an electrode that reduces carbon dioxide to produce carbon compounds and water to produce hydrogen. Any cathode 21 can be used as long as it can electrochemically reduce carbon dioxide and allow the generated gaseous carbon compounds and hydrogen to permeate the gas flow path 24a. For example, an electrode having a cathode catalyst layer formed on the liquid flow path 23a side of the gas diffusion layer can be used. A portion of the cathode catalyst layer may be embedded in the gas diffusion layer. A porous layer denser than the gas diffusion layer may be disposed between the gas diffusion layer and the cathode catalyst layer.

[0049] As the cathode catalyst forming the cathode catalyst layer, a known catalyst that promotes the reduction of carbon dioxide can be used. As a specific example of the cathode catalyst, metals such as gold, silver, copper, platinum, palladium, nickel, cobalt, iron, manganese, titanium, cadmium, zinc, indium, gallium, lead, tin, their alloys, intermetallic compounds, ruthenium complexes, rhenium complexes and other metal complexes can be illustrated. Among them, from the aspect of promoting the reduction of carbon dioxide, preferably copper, silver, more preferably copper. As the cathode catalyst, one can be used alone, or two or more can be used in combination.

[0050] As the cathode catalyst, a supported catalyst in which metal particles are supported on a carbon material (carbon particles, carbon nanotubes, graphene, etc.) may be used.

[0051] The gas diffusion layer of the cathode 21 is not particularly limited, and examples thereof include carbon paper and carbon cloth.

[0052] The method for producing the cathode 21 is not particularly limited, and an example thereof is a method in which a liquid composition containing a cathode catalyst is applied to the surface of the gas diffusion layer that will become the liquid flow path 23 a and then dried.

[0053] The anode 22 is an electrode for oxidizing hydroxide ions to generate oxygen. Any anode 22 can be used as long as it can electrochemically oxidize hydroxide ions and allow the generated oxygen to permeate the gas flow path 25a. For example, an electrode having an anode catalyst layer formed on the liquid flow path 23a side of the gas diffusion layer can be used.

[0054] The anode catalyst forming the anode catalyst layer is not particularly limited, and known anode catalysts can be used. Specifically, for example, metals such as platinum, palladium, and nickel, their alloys, intermetallic compounds, metal oxides such as manganese oxide, iridium oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, ruthenium oxide, lithium oxide, and lanthanum oxide, and metal complexes such as ruthenium complexes and rhenium complexes can be exemplified. As the anode catalyst, one type can be used alone, or two or more types can be used in combination.

[0055] Examples of the gas diffusion layer of the anode 22 include carbon paper and carbon cloth. Alternatively, a porous material such as a mesh, a punched material, a porous body, or a sintered metal fiber body may be used as the gas diffusion layer. Examples of the material of the porous body include metals such as titanium, nickel, and iron, and alloys thereof (e.g., SUS).

[0056] Examples of the material of the liquid flow channel structures 28 and 29 include fluororesins such as polytetrafluoroethylene.

[0057] Examples of the material of the gas flow path structures 24 and 25 include metals such as titanium and SUS, and carbon.

[0058] Examples of materials for the power supply bodies 26 and 27 include metals such as copper, gold, titanium, and SUS, and carbon. The power supply bodies 26 and 27 may be formed by plating a copper substrate with a surface treated with gold or the like.

[0059] The anion exchange membrane 23 is not particularly limited, and a conventionally known anion exchange membrane can be used.

[0060] The electrochemical reaction device 2 is a flow cell in which the anode-side electrolyte B supplied from the absorption unit 12 flows in the liquid flow path 29a, the cathode-side electrolyte D supplied from the pH adjuster 52 flows in the liquid flow path 28a, and the concentrated gas G4 supplied from the concentration unit 13 flows in the gas flow path 24a. Furthermore, by applying voltage to the cathode 21 and the anode 22, the carbon dioxide in the concentrated gas G4 flowing in the gas flow path 24a is reduced to generate carbon compounds and hydrogen. The electrochemical reaction in the electrochemical unit of the electrochemical reaction device 2 is carried out in Figure 3 CO3 is consumed at the cathode 2- , so the pH of the cathode side electrolyte becomes higher on the outlet side than on the inlet side of the liquid flow path 28a. The anode consumes hydroxide ions, but an equal amount of hydroxide ions is supplied from the cathode side, so the pH of the anode side electrolyte does not change on the inlet and outlet sides of the liquid flow path 29a. The pH of the cathode side electrolyte C is adjusted in the pH adjuster 52 to generate the cathode side electrolyte D. However, for the adjustment of the pH, an alkali such as KOH or an alkali aqueous solution can be used to increase the pH, or carbon dioxide gas can be used to lower the pH. The carbon dioxide supplied to the pH adjuster 52 can be, for example, carbon dioxide in the concentrated gas generated by the concentrator 11 or the concentrator 13.

[0061] Examples of carbon compounds generated by reducing carbon dioxide at the cathode 21 include carbon monoxide, ethylene, and ethanol. Figure 3 As shown, carbon monoxide and ethylene are generated as gaseous products in the following reactions. Hydrogen is also generated in the following reactions at the cathode 21. The generated gaseous carbon compounds and hydrogen permeate the gas diffusion layer of the cathode 21 and flow out from the gas flow path 24a.

[0062] CO2+H2O→CO+2OH -

[0063] 2CO+8H2O→C2H4+8OH - +2H2O

[0064] 2H2O→H2+2OH -

[0065] The hydroxide ions generated at the cathode 21 move toward the anode 22 in the anode electrolyte B and are oxidized in the following reaction to generate oxygen. The generated oxygen permeates the gas diffusion layer of the anode 22 and is discharged from the gas flow path 25a.

[0066] 4OH - →O2+2H2O

[0067] The generation of H 2 due to water electrolysis as a side reaction unrelated to the target CO 2 reduction reaction in the cathode 21 becomes one cause of energy loss in CO 2 electrolysis.

[0068] In order to suppress the production of H2 at the cathode in an embodiment, the balance of the catalytic activity of the anode and the cathode is very important. For example, when the anode is highly active and the cathode is less active, O2 is produced actively at the anode, and a reaction with the same number of electrons is also necessarily produced at the cathode. However, if the CO2 electrolysis reaction rate in the cathode is not sufficiently obtained, a water electrolysis H2 generation reaction will occur as a side reaction. Moreover, for this matter, the optimal solution for reaction rate management will also change according to the level and balance of degradation of the catalysts at the two poles in the operation of the carbon dioxide treatment device. Therefore, if there is a means for flexibly managing the reaction rate at the two poles, it is useful. In an embodiment, the pH of the electrolyte is used as a means for flexibly managing the reaction rate. In more detail, the pH of the anode side electrolyte is set to be lower than the pH of the cathode side electrolyte. As a unit for adjusting the pH of the electrolyte, alkali aqueous solutions such as KOH or KOH aqueous solutions are added to the electrolyte (pH increases), and carbon dioxide is dissolved in the electrolyte as an alkaline aqueous solution (pH decreases). Typically, the pH is lowered by blowing carbon dioxide into the electrolyte, which is a strongly alkaline aqueous solution, to dissolve it. Therefore, the pH can be adjusted by controlling the amount of carbon dioxide dissolved in the electrolyte, which is a strongly alkaline aqueous solution. In addition, the product is usually a gas. By sensing the gas flow rate, H2 concentration, and target concentration at the outlet of the carbon dioxide treatment device 100, the generation rate of the target carbon compound and the byproduct H2 can be quantified. Based on the quantitative results, by using [maximizing the target product generation rate] and [minimizing the byproduct H2 generation rate] as target variables and feeding back [the amount of CO2 dissolved in the cathode side electrolyte] and [the amount of CO2 dissolved in the anode side electrolyte], the optimal reaction rate at that time can be obtained under any catalyst degradation conditions.

[0069] Specific examples of pH include setting the pH of the anode-side electrolyte to 14 or less, for example, in the range of 8 to 14, and setting the pH of the cathode-side electrolyte to above 14.

[0070] In the carbon dioxide treatment apparatus 100, the pH of the cathode-side electrolyte used in the electrochemical reactor 2 is set higher than the pH of the anode-side electrolyte, thereby suppressing hydrogen generation at the cathode 21. This reduces the energy required for carbon dioxide desorption, improves energy efficiency, and reduces carbon dioxide loss, compared to, for example, a case where carbon dioxide is adsorbed on an adsorbent and then desorbed and reduced by heating.

[0071] The power storage device 3 is a device that supplies electric power to the electrochemical reaction device 2 .

[0072] In conversion unit 31, renewable energy is converted into electrical energy. Conversion unit 31 is not particularly limited; examples thereof include a wind turbine, a solar generator, and a geothermal generator. Power storage device 3 may include one, or two or more conversion units 31.

[0073] The storage unit 32 stores the electric energy converted by the conversion unit 31. By storing the converted electric energy in the storage unit 32, electric power can be stably supplied to the electrochemical reactor 2 even during periods when the conversion unit is not generating electricity. Furthermore, when utilizing renewable energy, voltage fluctuations generally tend to become significant. However, by temporarily storing the energy in the storage unit 32, electric power can be supplied to the electrochemical reactor 2 at a stable voltage.

[0074] The storage unit 32 in this example is a nickel-metal hydride battery. Note that the storage unit 32 only needs to be chargeable and dischargeable, and may be, for example, a lithium-ion secondary battery.

[0075] like Figure 4 As shown in (A), the storage unit 32 is a nickel-metal hydride battery including a positive electrode 33, a negative electrode 34, a separator 37 provided between the positive electrode 33 and the negative electrode 34, a positive electrode side flow path 36 formed between the positive electrode 33 and the separator 37, and a negative electrode side flow path 35 formed between the negative electrode 34 and the separator 37. The positive electrode side flow path 36 and the negative electrode side flow path 35 can be formed using, for example, a liquid flow path structure similar to the liquid flow path 28a (29a) of the electrochemical reaction device 2.

[0076] As the positive electrode 33 , for example, one obtained by coating a positive electrode active material on the positive electrode side flow path 36 side of a positive electrode current collector can be exemplified.

[0077] The positive electrode current collector is not particularly limited, and examples thereof include nickel foil and nickel-plated metal foil.

[0078] The positive electrode active material is not particularly limited, and examples thereof include nickel hydroxide and nickel oxyhydroxide.

[0079] The negative electrode 34 may be, for example, one obtained by coating a negative electrode active material on the negative electrode side flow path 35 of a negative electrode current collector.

[0080] The negative electrode current collector is not particularly limited, and an example thereof can be a nickel mesh.

[0081] The negative electrode active material is not particularly limited, and examples thereof include known hydrogen storage alloys.

[0082] The separator 37 is not particularly limited, and an ion exchange membrane can be exemplified, for example.

[0083] The nickel-metal hydride battery in the reservoir 32 is a flow cell in which electrolyte flows through the positive electrode-side flow path 36 on the positive electrode 33 side of the separator 37 and the negative electrode-side flow path 35 on the negative electrode 34 side of the separator 37. In the carbon dioxide treatment apparatus 100, the anode-side electrolyte B supplied from the absorption section 12 via the liquid flow path 62 and the anode-side electrolyte A supplied from the electrochemical reaction device 2 via the liquid flow path 66a flow into the negative electrode-side flow path 35 and the positive electrode-side flow path 36, respectively. Furthermore, the connection of the liquid flow paths 62 and 65 to the reservoir 32 can be switched between being connected to the negative electrode-side flow path 35 and being connected to the positive electrode-side flow path 36, respectively. Similarly, the connection of the liquid flow paths 66a and 66b to the reservoir 32 can be switched between being connected to the positive electrode-side flow path 36 and being connected to the negative electrode-side flow path 35, respectively.

[0084] During discharge of a nickel-metal hydride battery, hydroxide ions are generated from water molecules at the positive electrode, and the hydroxide ions moving to the negative electrode receive hydrogen ions from the hydrogen storage alloy to generate water molecules. Therefore, from the perspective of discharge efficiency, it is advantageous for the electrolyte flowing in the positive electrode side flow path 36 to be in a strong alkaline state, and it is advantageous for the electrolyte flowing in the negative electrode side flow path 35 to be in a weak alkaline state. Therefore, if Figure 4 As shown in (A), during discharge, it is preferable that liquid flow paths 62 and 65 are connected to the negative electrode side flow path 35, and liquid flow paths 66a and 66b are connected to the positive electrode side flow path 36, so that the anode side electrolyte B (weak base) supplied from the absorption section 12 flows in the negative electrode side flow path 35, and the anode side electrolyte A (strong base) supplied from the electrochemical reaction device 2 flows in the positive electrode side flow path 36. That is, during discharge, it is preferable that the electrolyte circulates in the order of the absorption section 12, the negative electrode side flow path 35 of the storage section 32, the electrochemical reaction device 2, the positive electrode side flow path 36 of the storage section 32, and the absorption section 12.

[0085] Furthermore, when charging a nickel-hydrogen battery, water molecules are generated from hydroxide ions at the positive electrode, and at the negative electrode, the water molecules are decomposed into hydrogen atoms and hydroxide ions, with the hydrogen atoms being absorbed into the hydrogen storage alloy. Therefore, from the perspective of charging efficiency, it is advantageous for the electrolyte flowing in the positive electrode side flow path 36 to be in a weak alkaline state, and it is advantageous for the electrolyte flowing in the negative electrode side flow path 35 to be in a strong alkaline state. Therefore, during charging, as Figure 4As shown in (B), it is preferable that liquid flow paths 62 and 65 are connected to the positive electrode side flow path 36, and liquid flow paths 66a and 66b are connected to the negative electrode side flow path 35, so that the anode side electrolyte B (weak base) supplied from the absorption section 12 flows in the positive electrode side flow path 36, and the anode side electrolyte A (strong base) supplied from the electrochemical reaction device 2 flows in the negative electrode side flow path 35. That is, during charging, the electrolyte preferably circulates in the order of the absorption section 12, the positive electrode side flow path 36 of the storage section 32, the electrochemical reaction device 2, the negative electrode side flow path 35 of the storage section 32, and the absorption section 12.

[0086] Generally speaking, when a secondary battery is incorporated into a device, the overall energy efficiency tends to decrease by the amount of charge and discharge efficiency. However, as described above, by utilizing the pH gradient of the anode-side electrolyte A and the anode-side electrolyte B before and after the electrochemical reactor 2, the electrolyte flowing into the positive electrode-side flow path 36 and the negative electrode-side flow path 35 of the reservoir 32 is appropriately replaced, thereby improving the charge and discharge efficiency by the amount of the "concentration overvoltage" of the electrode reaction expressed by Nemst's equation.

[0087] The recarburization reaction device 4 is a device that performs recarburization by polymerizing ethylene generated by reducing carbon dioxide in the electrochemical reaction device 2 .

[0088] Ethylene gas E generated by reduction at cathode 21 of electrochemical reactor 2 is transported to reactor 41 via gas flow path 74. In reactor 41, ethylene polymerization proceeds in the presence of an olefin polymerization catalyst. This allows the production of carbon-enriched olefins such as 1-butene, 1-hexene, and 1-octene.

[0089] The olefin polymerization catalyst is not particularly limited, and a known catalyst used in polymerization reaction can be used. Examples thereof include solid acid catalysts using silica alumina or zeolite as a support, and transition metal complex compounds.

[0090] In the carburization reactor 4 of this example, the post-polymerization reaction product gas F flowing out of the reactor 41 is conveyed to the gas-liquid separator 42 via the gas flow path 72. Olefins with a carbon number of 6 or greater are liquid at room temperature. Therefore, for example, when olefins with a carbon number of 6 or greater are the target carbon compound, setting the temperature of the gas-liquid separator 42 to approximately 30°C facilitates gas-liquid separation of the olefins with a carbon number of 6 or greater (olefin liquid J1) and the olefins with a carbon number of less than 6 (olefin gas J2). Furthermore, increasing the temperature of the gas-liquid separator 42 increases the carbon number of the resulting olefin liquid J1.

[0091] If the gas G1 supplied to the concentrator 11 of the recovery device 1 is atmospheric air, the separated gas G3 supplied from the concentrator 11 via the gas flow path 71 can also be used to cool the produced gas D in the gas-liquid separator 42. For example, a gas-liquid separator 42 equipped with a cooling pipe can be used. The separated gas G3 is passed through the cooling pipe, while the produced gas F is passed outside the cooling pipe, where it condenses on the surface of the cooling pipe to form the olefin liquid J1. Furthermore, the olefin gas J2 separated by the gas-liquid separator 42 contains unreacted components such as ethylene and olefins with a carbon number lower than the target olefin. Therefore, it can be returned to the reactor 41 via the gas flow path 73 and reused in the polymerization reaction.

[0092] The polymerization reaction of ethylene in the reactor 41 is an exothermic reaction in which the enthalpy of the feed material is higher than that of the generated material, and the reaction enthalpy becomes negative. In the carbon dioxide treatment device 100, the reaction heat generated by the reactor 41 of the carburizing reaction device 4 can also be used to heat the heat medium K, and the heat medium K is circulated to the heat exchanger 43 through the circulation flow path 69, and heat exchange is performed between the heat medium K and the anode side electrolyte B in the heat exchanger 43. In this case, the anode side electrolyte B supplied to the electrochemical reaction device 2 is heated. In the anode side electrolyte B using a strong alkaline aqueous solution, it is difficult to separate carbon dioxide as a gas even if it is heated and dissolved. As the temperature of the anode side electrolyte B increases, the redox reaction rate in the electrochemical reaction device 2 increases.

[0093] The carburizing reactor 4 may further include a reactor for performing a hydrogenation reaction of olefins obtained by polymerizing ethylene using the hydrogen generated by the electrochemical reactor 2 and a reactor for performing an anisotropy reaction of olefins and paraffins.

[0094] [Carbon dioxide treatment method]

[0095] A carbon dioxide treatment method according to one embodiment of the present invention comprises the following steps (a) and (b). The carbon dioxide treatment method of the present invention can be used in a method for producing carbon compounds. Specifically, the carbon dioxide treatment method of the present invention can be used to produce carbon compounds obtained by reducing carbon dioxide, or carbon compounds obtained using carbon compounds obtained by reducing carbon dioxide as raw materials.

[0096] Step (a): Carbon dioxide gas is brought into contact with an anode-side electrolyte solution composed of a strong alkaline aqueous solution, and carbon dioxide is dissolved and absorbed in the anode-side electrolyte solution.

[0097] Step (b): The pH of the cathode-side electrolyte is adjusted to be higher than the pH of the anode-side electrolyte.

[0098] Step (c): supplying the cathode side electrolyte between the cathode and the anion exchange membrane, supplying the anode side electrolyte between the anode and the anion exchange membrane, supplying carbon dioxide gas to the cathode side opposite to the anode, and electrochemically reducing the carbon dioxide gas to produce carbon compounds and hydrogen.

[0099] When a carbon dioxide treatment apparatus equipped with a carburizing reaction device is used, such as the carbon dioxide treatment apparatus 100, the carbon dioxide treatment method includes, in addition to steps (a) to (c), the following step (d). The following describes an example of a carbon dioxide treatment method using the carbon dioxide treatment apparatus 100.

[0100] Step (d): polymerizing ethylene produced by reducing carbon dioxide.

[0101] In the carbon dioxide treatment method using the carbon dioxide treatment apparatus 100, exhaust gas, atmospheric air, or the like is first supplied as gas G1 to the concentrator 11, where the carbon dioxide is concentrated to form concentrated gas G2. As described above, the absorption of carbon dioxide into the anode-side electrolyte A by the absorption unit 12 assists in the concentration, eliminating the need to concentrate the carbon dioxide to a high concentration in the concentrator 11. The carbon dioxide concentration of the concentrated gas G2 can be appropriately set, for example, to 25 to 85% by volume.

[0102] In step (a), the concentrated gas G2 is supplied from the concentrating section 11 to the absorbing section 12, where it contacts the anode electrolyte A, dissolving the carbon dioxide in the concentrated gas G2 and absorbing it into the anode electrolyte A. The anode electrolyte B in which the carbon dioxide is dissolved becomes weakly alkaline. Alternatively, the anode electrolyte B may be supplied from the absorbing section 12 via the storage section 32 to the heat exchanger 43, where the anode electrolyte B, heated by heat exchange with the heat medium K, is supplied to the electrochemical reactor 2. The temperature of the anode electrolyte B supplied to the electrochemical reactor 2 can be appropriately set, for example, to 65 to 105°C.

[0103] In step (b), the pH of the cathode electrolyte is adjusted to be higher than the pH of the anode electrolyte. The pH of the cathode electrolyte can be adjusted by adding an alkali or an alkaline aqueous solution (pH increase), contact with carbon dioxide (pH decrease), and the like. For example, the pH of the cathode electrolyte is set to be above 14, and the pH of the anode electrolyte is set to be below 14, specifically within the range of 8 to 14.

[0104] In step (c), the anode-side electrolyte B flows through the liquid flow path 29a of the electrochemical reactor 2, the cathode-side electrolyte D flows through the liquid flow path 28a, and the concentrated gas G4 generated by the enrichment unit 13 flows through the gas flow path 24a. Electricity is supplied from the power supply storage device 3 to the electrochemical reactor 2, and a voltage is applied between the cathode 21 and the anode 22. The carbon dioxide gas contained in the concentrated gas G4 is electrochemically reduced to produce carbon compounds, and water is reduced to produce hydrogen. At this time, the hydroxide ions in the anode-side electrolyte B are oxidized in the anode 22 to produce oxygen. The amount of dissolved carbon dioxide in the anode-side electrolyte B decreases as the reduction progresses, and the strongly alkaline anode-side electrolyte A flows out of the outlet of the liquid flow path 29a. The gaseous carbon compounds and hydrogen generated by the reduction of carbon dioxide pass through the gas diffusion layer of the cathode 21, flow out of the electrochemical reactor 2 through the gas flow path 24a, and are transported to the carburization reactor 4.

[0105] In step (d), ethylene gas E generated by the reduction of carbon dioxide is fed to reactor 41 and brought into contact with an olefin polymerization catalyst in the gas phase within reactor 41 to polymerize ethylene. This produces olefins obtained by polymerizing ethylene. For example, when an olefin having 6 or more carbon atoms is the target carbon compound, the generated gas F produced from reactor 41 is fed to gas-liquid separator 42 and cooled to approximately 30°C. This liquefies the target olefin having 6 or more carbon atoms (e.g., 1-hexene), while the olefin having less than 6 carbon atoms remains in a gaseous state. This allows for easy separation of the olefin liquid J1 (target carbon compound) and the olefin gas J2. The carbon numbers of the olefin liquid J1 and the olefin gas J2 undergoing gas-liquid separation can be adjusted by adjusting the temperature of the gas-liquid separation.

[0106] After gas-liquid separation, the olefin gas J2 can be returned to the reactor 41 and reused in the polymerization reaction. In this manner, when circulating olefins with a carbon number lower than the target olefin between the reactor 41 and the gas-liquid separator 42, it is preferable to adjust the contact time between the feed gas (a mixed gas of ethylene gas E and olefin gas J2) and the catalyst in the reactor 41 to achieve conditions that allow each molecule to undergo an average of one polymerization reaction. This prevents the carbon number of the olefins produced in the reactor 41 from unintentionally increasing, allowing the olefins with the target carbon number (olefin liquid J1) to be selectively separated in the gas-liquid separator 42.

[0107] This method can efficiently and selectively produce valuable products from renewable carbon sources, eliminating the need for large-scale purification equipment such as distillation columns required in conventional petrochemical processes using Fischer-Tropsch (FT) synthesis and the MtG process, resulting in an overall economic advantage.

[0108] The reaction temperature of the polymerization reaction is preferably 200 to 350°C.

[0109] From the viewpoint of suppressing excessive polymerization reaction and improving the selectivity of the target carbon compound, the polymerization reaction time, that is, the contact time of the raw material gas with the olefin polymerization catalyst, is preferably 10 to 250 g·min. / mol in terms of W / F.

[0110] Alternatively, the selectivity of the produced carbon compound may be improved by circulating an olefin having a carbon number smaller than that of the target olefin between the reactor 41 and the gas-liquid separator 42 and adjusting the contact time between the raw gas and the catalyst.

[0111] Furthermore, in the case of hydrogenating olefins obtained by polymerizing ethylene to obtain alkanes, the alkanes may be further anisotropically modified.

[0112] As the hydrogenation reaction of olefins, a known method can be adopted, and for example, a method of performing a hydrogenation reaction using a solid acid catalyst such as silica alumina or zeolite can be exemplified.

[0113] As the anisotropy reaction, a known method can be adopted, and for example, a method of performing anisotropy reaction using a solid acid catalyst such as silica alumina or zeolite can be exemplified.

[0114] The reaction temperature of the reactor 84 is preferably 200 to 350°C.

[0115] As described above, in one embodiment of the present invention, an electrolyte composed of a strongly alkaline aqueous solution is used. The electrolyte, in which carbon dioxide is dissolved by a recovery device, is supplied between the cathode and the anode, where the dissolved carbon dioxide in the electrolyte is electrochemically reduced. Consequently, the energy efficiency of carbon dioxide recovery and reduction is increased, and carbon dioxide losses are reduced.

[0116] It should be noted that the present invention is not limited to the above-described embodiment.

[0117] Furthermore, the carbon dioxide treatment apparatus of the embodiment may not include all of the carbon addition reactor, heat exchanger, and pH regulator. For example, ethylene may be produced using a carbon dioxide treatment method using this carbon dioxide treatment apparatus.

[0118] In the carbon dioxide treatment apparatus of the embodiment, the electrochemical reaction device and the power storage device may not share the electrolyte, and the electrolyte may be circulated only between the absorption section of the recovery device and the electrochemical reaction device.

[0119] In addition, components in the above-described embodiments may be appropriately replaced with well-known components without departing from the spirit of the present invention, and the above-described modifications may be appropriately combined.

[0120] [Example]

[0121] exist Figure 1 In the carbon dioxide treatment device 100 shown in FIG. 1 , a CO2 electrolysis test was conducted by changing the combination of potassium hydroxide concentrations (molar concentrations) of the cathode side electrolyte and the anode side electrolyte. The results of the CO2 electrolysis test (Faraday efficiency (%) of ethylene, carbon monoxide, methane, and hydrogen) are shown in FIG. Figure 5 is shown in the diagram.

[0122] <Example 1>

[0123] The KOH concentration of the cathode-side electrolyte was set to 7M, and the KOH concentration of the anode-side electrolyte was set to 1M.

[0124] <Comparative Example 1>

[0125] The KOH concentration of both the cathode-side electrolyte and the anode-side electrolyte was set to 1M.

[0126] <Comparative Example 2>

[0127] The KOH concentration of both the cathode-side electrolyte and the anode-side electrolyte was set to 7M.

[0128] <Comparative Example 3>

[0129] The KOH concentration of both the cathode-side electrolyte and the anode-side electrolyte was set to 10M.

[0130] <Results>

[0131] Example 1 shows the highest Faradaic efficiency for ethylene. This shows that by setting the pH of the electrolyte to a higher value on the cathode side than on the anode side, i.e., creating a hydrogen ion concentration gradient, the CO2 electrolysis efficiency can be improved.

[0132] In Example 1, it is believed that by setting the KOH concentration of the anode-side electrolyte to 1 M, oxygen generation became milder than when the KOH concentration was 7 M, and the reaction rate balance between the two electrodes improved. As a result, it is believed that charge compensation can be carried out without problems at the cathode, and CO2 electrolysis becomes the main reaction.

[0133] In Comparative Example 2, oxygen generation is favored and the cathode becomes rate-limiting. Therefore, it is thought that in order to compensate for the charge at the cathode, an overvoltage is applied locally in the region where electrons are easily supplied, shifting the potential to a region where hydrogen generation is favorable.

Claims

1. A carbon dioxide treatment device, wherein: The carbon dioxide treatment device comprises: a recovery device that recovers carbon dioxide; an electrochemical reaction device that electrochemically reduces carbon dioxide; and a pH adjuster. The recovery device comprises: an absorption section for contacting an anode-side electrolyte composed of a strong alkaline aqueous solution with carbon dioxide gas to dissolve and absorb carbon dioxide in the anode-side electrolyte; and a concentration section for concentrating carbon dioxide. The electrochemical reaction device comprises: an anode; a cathode; an anion exchange membrane provided between the anode and the cathode; a liquid flow path provided between the anode and the anion exchange membrane and through which the anode-side electrolyte having absorbed carbon dioxide by the absorption unit flows; and a liquid flow path provided between the cathode and the anion exchange membrane and through which flows a cathode-side electrolyte composed of a strongly alkaline aqueous solution whose pH has been adjusted by the pH adjuster, wherein the pH of the cathode-side electrolyte is higher than that of the anode-side electrolyte. Carbon dioxide gas is supplied from the concentrating section to a gas flow path on the cathode side opposite to the anode, and the carbon dioxide gas is reduced at the cathode.

2. The carbon dioxide treatment device according to claim 1, wherein: The carbon dioxide treatment device further includes a power supply storage device for supplying electric power to the electrochemical reaction device. The power supply storage device includes a conversion unit capable of converting renewable energy into electric energy and a storage unit for storing the electric energy converted by the conversion unit.

3. The carbon dioxide treatment device according to claim 2, wherein: The storage unit is a nickel-hydrogen battery, The nickel-hydrogen battery comprises a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, a positive electrode side flow path provided between the positive electrode and the separator, and a negative electrode side flow path provided between the negative electrode and the separator. During discharge of the nickel-hydrogen battery, the anode-side electrolyte circulates in the order of the absorption unit, the negative electrode-side flow path, the electrochemical reaction device, and the absorption unit. During charging of the nickel-hydrogen battery, the anode-side electrolyte circulates in the order of the absorption section, the negative-electrode-side flow path, the electrochemical reaction device, the positive-electrode-side flow path, and the absorption section.

4. The carbon dioxide treatment device according to any one of claims 1 to 3, wherein: The pH adjuster brings the cathode-side electrolyte into contact with carbon dioxide gas.

5. The carbon dioxide treatment device according to any one of claims 1 to 3, wherein: The carbon dioxide treatment device further includes a carbon addition reaction device that performs carbon addition by polymerizing ethylene generated by reducing carbon dioxide in the electrochemical reaction device.

6. The carbon dioxide treatment device according to claim 5, wherein: The carbon dioxide treatment device further includes a heat exchanger that heats the anode-side electrolyte by exchanging heat between a heat medium heated by heat generated by a reaction in the carburization reactor and the anode-side electrolyte.

7. A method for treating carbon dioxide, wherein: The carbon dioxide treatment method comprises the following steps: allowing carbon dioxide gas to contact an anode-side electrolyte composed of a strong alkaline aqueous solution, so that the carbon dioxide is dissolved and absorbed in the anode-side electrolyte; The pH of the cathode electrolyte is adjusted to be higher than that of the anode electrolyte; as well as The cathode side electrolyte is supplied between the cathode and the anion exchange membrane, the anode side electrolyte is supplied between the anode and the anion exchange membrane, carbon dioxide gas is supplied to the cathode side opposite to the anode, and the carbon dioxide gas is electrochemically reduced to produce carbon compounds and hydrogen.

8. The method for treating carbon dioxide according to claim 7, wherein: In the step of adjusting the pH of the cathode electrolyte, the cathode electrolyte and carbon dioxide are brought into contact to dissolve the carbon dioxide in the cathode electrolyte.

9. A method for producing a carbon compound, wherein: The carbon dioxide treatment method according to claim 7 or 8 is used to produce carbon compounds obtained by reducing carbon dioxide.

10. The method for producing a carbon compound according to claim 9, wherein The method further includes a step of polymerizing ethylene generated by reducing the carbon dioxide.

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