Carbon dioxide treatment device, treatment method, and method for producing carbon compound

Abstract

In a carbon dioxide treatment device for recovering carbon dioxide and performing electrochemical reduction, compared with the prior art, the carbon dioxide treatment device, the treatment method and the manufacturing method of the carbon compound can improve the absorption speed and the decomposition efficiency of the carbon dioxide. This carbon dioxide treatment device is provided with: a recovery device (1) provided with a carbon dioxide absorption unit (12) for dissolving and absorbing carbon dioxide in a strong base electrolyte solution; an electrochemical reaction device (2) that is supplied with an electrolyte solution in which carbon dioxide is dissolved in the carbon dioxide absorption unit and that electrochemically reduces carbon dioxide; an anion exchange type fuel cell (8) that supplies electric energy to the electrochemical reaction device; a carbon dioxide concentrated gas supply path (72) for supplying the carbon dioxide concentrated gas generated in the fuel cell to the electrolyte solution before being discharged from the recovery device and being supplied to the electrochemical reaction device; and a hydrogen supply path (73) that supplies hydrogen generated by the electrochemical reaction device to the fuel cell.

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] Efforts to mitigate or reduce the impact of climate change have been ongoing, and research and development related to reducing carbon dioxide emissions has been underway to achieve this goal. For example, technologies are known that recover carbon dioxide from waste gases and the atmosphere and electrochemically reduce it to produce valuable products. This technology holds promise for achieving carbon neutrality, but its economic viability remains a major challenge. To improve economic efficiency, it is important to increase energy efficiency and reduce 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, the adsorbed carbon dioxide is desorbed and utilized using energy such as heat. Furthermore, as a technology for electrochemically reducing carbon dioxide, the following is known: electrochemically reducing carbon dioxide by supplying carbon dioxide gas from the side of the gas diffusion layer opposite the catalyst layer to 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 (for example, see International Publication No. 2018 / 232515). Summary of the Invention

[0004] However, in the past, technologies for recovering carbon dioxide and electrochemically reducing carbon dioxide have been researched and developed separately. Therefore, the overall energy efficiency and carbon dioxide loss reduction effect of combining these technologies can be determined by multiplying the efficiencies of each technology, but there is room for further improvement. Thus, improving energy efficiency and carbon dioxide loss reduction effects from a comprehensive perspective by combining carbon dioxide recovery and electrochemical reduction technologies is profoundly significant.

[0005] In addition, it is known that in a carbon dioxide processing device having a recovery device for recovering carbon dioxide, when the pH of the electrolyte in which carbon dioxide is dissolved is high, the amount of hydrogen produced during the electrochemical reduction of carbon dioxide increases, while the decomposition efficiency of carbon dioxide deteriorates. On the other hand, in a carbon dioxide recovery device, a high pH of the electrolyte is advantageous from the perspective of the absorption rate of carbon dioxide. The fact that there are differences in the optimal pH conditions of the respective electrolytes for the recovery and electrolysis of carbon dioxide can be said to be a major issue in carbon dioxide processing devices.

[0006] As described above, in order to improve the conversion efficiency of carbon dioxide, it is necessary to improve both the recovery efficiency of carbon dioxide and the electrolysis efficiency.

[0007] The present invention aims to provide a technology that, in a carbon dioxide treatment device that recovers and electrochemically reduces carbon dioxide, can improve the absorption rate and decomposition efficiency of carbon dioxide compared to conventional methods. Furthermore, the present invention contributes to mitigating or alleviating the impacts of climate change.

[0008] The carbon dioxide treatment device involved in the first scheme of the present invention comprises: a recovery device, which is equipped with a carbon dioxide absorption section that dissolves carbon dioxide in a strong alkaline electrolyte and absorbs carbon dioxide; an electrochemical reaction device, which is supplied with the electrolyte in which the carbon dioxide is dissolved in the carbon dioxide absorption section and electrochemically reduces the carbon dioxide; an anion exchange fuel cell that supplies electric energy to the electrochemical reaction device; a carbon dioxide concentrated gas supply path that supplies the carbon dioxide concentrated gas generated in the fuel cell to the electrolyte before it is discharged from the recovery device and supplied to the electrochemical reaction device; and a hydrogen supply path that supplies the hydrogen generated in the electrochemical reaction device to the fuel cell.

[0009] According to the carbon dioxide treatment device of the first embodiment, the carbon dioxide concentrated gas generated in the fuel cell can be supplied to the electrolyte before being electrolyzed via the carbon dioxide concentrated gas supply path. As a result, the electrolysis of water and the generation of hydrogen in the electrochemical reaction device can be suppressed, thereby improving the efficiency of the electrolysis reaction of carbon dioxide. In addition, according to the carbon dioxide treatment device of the first embodiment, the hydrogen generated in the electrochemical reaction device can be used to generate electrical energy and supply it to the electrochemical reaction device. Therefore, according to the carbon dioxide treatment device of the first embodiment, the efficiency of the electrolysis reaction of carbon dioxide can be improved, and energy efficiency can be improved.

[0010] The second option may be, based on the carbon dioxide treatment device of the first option, that the electrochemical reaction device comprises: a cathode; an anode; an electrolyte membrane, which is arranged between the cathode and the anode; a cathode side liquid flow path, which is arranged adjacent to the cathode and supplies the electrolyte flow; an anode side liquid flow path, which is arranged adjacent to the anode and supplies the electrolyte flow; and a first liquid supply path, which supplies the electrolyte flowing through the cathode side liquid flow path to the anode side liquid flow path.

[0011] The third option may be that, based on the carbon dioxide treatment device of the first or second option, the carbon dioxide treatment device further includes an electric energy storage device for supplying electric energy to the electrochemical reaction device, the electric energy storage device includes: a conversion unit that converts renewable energy into electric energy; and an electric energy storage unit that includes a nickel-hydrogen battery for storing the electric energy converted by the conversion unit, and the electrochemical reaction device further includes a second liquid supply path that supplies the electrolyte flowing through the anode side liquid flow path to the nickel-hydrogen battery.

[0012] A fourth embodiment is the carbon dioxide treatment apparatus of any one of the first to third embodiments, wherein the carbon dioxide treatment apparatus further comprises a carbon addition reaction device for polymerizing ethylene generated by reducing carbon dioxide in the electrochemical reaction device to add carbon dioxide.

[0013] The fifth embodiment of the present invention relates to a carbon dioxide treatment method, which electrochemically reduces carbon dioxide, wherein the carbon dioxide treatment method comprises the following steps: dissolving carbon dioxide in an electrolyte; reducing the carbon dioxide dissolved in the electrolyte; supplying hydrogen generated during the reduction of the carbon dioxide to an anion exchange fuel cell to generate electricity; and supplying carbon dioxide concentrated gas generated during the power generation to the electrolyte after the dissolution of the carbon dioxide and before the reduction of the carbon dioxide to lower the pH of the electrolyte.

[0014] A method for producing a carbon compound according to a sixth aspect of the present invention includes a process for reducing carbon dioxide using the carbon dioxide treatment method according to the fifth aspect to produce a carbon compound.

[0015] According to the aspects of the present invention, in a carbon dioxide treatment apparatus that recovers and electrochemically reduces carbon dioxide, it is possible to increase the absorption rate and decomposition efficiency of carbon dioxide compared to conventional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a block diagram showing a carbon dioxide treatment apparatus according to an embodiment of the present invention.

[0017] Figure 2 This is a schematic cross-sectional view showing an example of an electrolytic cell in an electrochemical reaction section.

[0018] Figure 3A This is a diagram showing the electric energy storage portion of a nickel-metal hydride battery during discharge.

[0019] Figure 3B This is a diagram showing a nickel-metal hydride battery serving as an energy storage unit during charging. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0021] [Carbon dioxide treatment equipment]

[0022] Figure 1 It is a block diagram showing a carbon dioxide treatment apparatus 100 according to an embodiment of the present invention.

[0023] like Figure 1 As shown, the carbon dioxide treatment apparatus 100 according to this embodiment includes a recovery device 1, an electrochemical reaction unit 2 (electrochemical reaction unit), an electrical energy storage device 3, a recarburization reaction unit 4, a heat exchange unit 5, an anion exchange fuel cell 8, a carbon dioxide concentrated gas supply line 72, and a hydrogen supply line 73. The recovery device 1 includes a CO2 concentration unit 11 and a CO2 absorption unit 12 (carbon dioxide absorption unit). The electrochemical reaction unit 2 includes an electrolysis unit. The electrical energy storage device 3 includes a conversion unit 31 and an electrical energy storage unit 32. The recarburization reaction unit 4 includes a thermal reaction unit 41 and a gas-liquid separation unit 42.

[0024] In the carbon dioxide treatment device 100, the CO2 concentration unit 11 and the CO2 absorption unit 12 are connected by a gas flow path 61. The CO2 absorption unit 12 and the electric energy storage unit 32 are connected by liquid flow paths 62 and 66. The electric energy storage unit 32 and the heat exchange unit 5 are connected by a liquid flow path 63. The heat exchange unit 5 and the electrochemical reaction unit 2 are connected by a liquid flow path 64. The electrochemical reaction unit 2 and the electric energy storage unit 32 are connected by a second liquid supply path 65 serving as a liquid flow path. The electrochemical reaction unit 2 and the thermal reaction unit 41 are connected by a gas flow path 67. The thermal reaction unit 41 and the gas-liquid separation unit 42 are connected by a gas flow path 68 and a gas flow path 70. A heat medium circulation flow path 69 is provided between the thermal reaction unit 41 and the heat exchange unit 5. The CO2 concentration unit 11 and the gas-liquid separation unit 42 are connected by a gas flow path 71. The fuel cell 8 is connected to the liquid flow path (i.e., one or more of the liquid flow path 62, the liquid flow path 63, and the liquid flow path 64) that supplies the electrolyte B from the CO2 absorption unit 12 to the electrochemical reaction unit 2 via a carbon dioxide concentrated gas supply path 72. The fuel cell 8 is connected to the electrochemical reaction unit 2 via a hydrogen supply path 73.

[0025] The above-mentioned flow paths are not particularly limited, and known piping can be used as appropriate. Gas flow paths 61, 67, 68, 70, and 71, carbon dioxide concentrated gas supply path 72, and hydrogen supply path 73 can be appropriately provided with gas supply mechanisms such as compressors, valves, and measuring devices such as flow meters.

[0026] Furthermore, liquid delivery mechanisms such as pumps, valves, and measuring devices such as flow meters may be appropriately provided in the liquid flow paths 62 to 66 .

[0027] (Recovery device)

[0028] The recovery device 1 recovers carbon dioxide. A gas G1 containing carbon dioxide, such as atmospheric air or exhaust gas, is supplied to the CO2 concentrator 11. The CO2 concentrator 11 concentrates the carbon dioxide in the gas G1. As the CO2 concentrator 11, any known concentrator can be used as long as it can concentrate carbon dioxide. As the CO2 concentrator 11, for example, a membrane separation device utilizing a difference in permeation rate relative to a membrane, or an adsorption separation device utilizing chemical or physical adsorption and desorption can be used. From the viewpoint of excellent separation performance, adsorption utilizing chemical adsorption, particularly temperature swing adsorption, is preferred.

[0029] The concentrated gas G2 obtained by concentrating carbon dioxide in the CO2 concentrator 11 is supplied to the CO2 absorber 12 through the gas flow path 61. The separated gas G3 separated from the concentrated gas G2 is supplied to the gas-liquid separator 42 through the gas flow path 71.

[0030] In the CO2 absorption section 12, the carbon dioxide gas in the concentrated gas G2 supplied from the CO2 concentration section 11 comes into contact with the electrolyte A, and the carbon dioxide dissolves in the electrolyte A and is absorbed. The method for bringing the carbon dioxide gas into contact with the electrolyte A is not particularly limited, and an example thereof is a method of blowing the concentrated gas G2 into the electrolyte A to generate bubbles.

[0031] In the CO2 absorption section 12, an electrolyte A composed of a strong alkaline aqueous solution is used as an absorption liquid for absorbing carbon dioxide. In carbon dioxide, the oxygen atoms strongly attract electrons, so the carbon atoms have a positive charge (δ+). Therefore, in a strong alkaline aqueous solution containing a large amount of hydroxide ions, the dissolution reaction of carbon dioxide is easy to proceed from the hydrated state to HCO3 - Progress to CO3 2- , becoming CO3 2- This creates an equilibrium state with a high concentration ratio of carbon dioxide. As a result, carbon dioxide dissolves more readily in a strong alkaline aqueous solution than other gases such as nitrogen, hydrogen, and oxygen. In the CO2 absorption section 12, carbon dioxide in the concentrated gas G2 is selectively absorbed by the electrolyte A. Thus, using the electrolyte A in the CO2 absorption section 12 promotes the concentration of carbon dioxide. Consequently, the CO2 concentration section 11 does not need to concentrate carbon dioxide to a high concentration, reducing the energy required for concentration in the CO2 concentration section 11.

[0032] The electrolyte B that has absorbed carbon dioxide in the CO2 absorption unit 12 is transported to the electrochemical reaction unit 2 via the liquid flow path 62, the electric energy storage unit 32, the liquid flow path 63, the heat exchange unit 5, and the liquid flow path 64. Furthermore, the electrolyte A that has flowed out of the electrochemical reaction unit 2 is transported to the CO2 absorption unit 12 via the second liquid supply path 65, the electric energy storage unit 32, and the liquid flow path 66. In this manner, in the carbon dioxide treatment apparatus 100, the electrolyte circulates between the CO2 absorption unit 12, the electric energy storage unit 32, and the electrochemical reaction unit 2.

[0033] Examples of strong alkali aqueous solutions used in the electrolyte A include potassium hydroxide aqueous solutions and sodium hydroxide aqueous solutions. Among these, potassium hydroxide aqueous solutions are preferably used from the viewpoint of excellent solubility of carbon dioxide in the CO 2 absorption unit 12 and promotion of reduction of carbon dioxide in the electrochemical reaction unit 2 .

[0034] (Electrochemical reaction unit)

[0035] Figure 2 2 is a schematic cross-sectional view showing an example of an electrolytic unit 2a of the electrochemical reaction unit 2. The electrochemical reaction unit 2 uses the electrolytic unit 2a to electrochemically reduce carbon dioxide. Figure 2 As shown, the electrolysis unit 2a of the electrochemical reaction section 2 includes a cathode 21, an anode 22, an anion exchange membrane 23 (electrolyte membrane), a cathode side liquid flow path structure 24 forming a cathode side liquid flow path 24a, an anode side liquid flow path structure 26 forming an anode side liquid flow path 26a, a power supply 27, and a power supply 28. Figure 2 In FIG. 1 , one electrolytic cell 2 a is shown, but the electrochemical reaction section 2 may preferably include an electrolytic cell stack formed by stacking a plurality of electrolytic cells 2 a.

[0036] In the electrolysis unit 2a of the electrochemical reaction section 2, the power supply 27, the cathode side liquid flow path structure 24, the cathode 21, the anion exchange membrane 23, the anode 22, the anode side liquid flow path structure 26, and the power supply 28 are stacked in sequence. In addition, a cathode side liquid flow path 24a is formed between the cathode 21 and the cathode side liquid flow path structure 24. An anode side liquid flow path 26a is formed between the anode 22 and the anode side liquid flow path structure 26. The above-mentioned cathode side liquid flow path 24a and anode side liquid flow path 26a are arranged at positions opposite to each other with the cathode 21, the anion exchange membrane 23 and the anode 22 sandwiched therebetween. It is preferred that a plurality of the above-mentioned cathode side liquid flow paths 24a and anode side liquid flow paths 26a are respectively provided. The shapes of the cathode side liquid flow paths 24a and anode side liquid flow paths 26a can be not only straight but also zigzag.

[0037] Power supply 27 and power supply 28 are electrically connected to power storage section 32 of power storage device 3. Furthermore, cathode-side liquid flow path structure 24 and anode-side liquid flow path structure 26 are both conductive bodies, and can apply a voltage between cathode 21 and anode 22 using the power supplied from power storage section 32.

[0038] The cathode 21 is an electrode that reduces carbon dioxide to produce carbon compounds and water to produce hydrogen. Examples of the cathode 21 include an electrode including a gas diffusion layer and a cathode catalyst layer formed on the cathode-side liquid flow path 24a side of the gas diffusion layer.

[0039] The cathode catalyst layer may be arranged so that a portion thereof penetrates the gas diffusion layer. In addition, a porous layer denser than the gas diffusion layer may be arranged between the gas diffusion layer and the cathode catalyst layer.

[0040] 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, and their alloys, intermetallic compounds, ruthenium complexes, rhenium complexes and other metal complexes can be illustrated. Among them, from the viewpoint of promoting the reduction of carbon dioxide, copper and silver are preferably used, and copper is more preferably used. As the cathode catalyst, one can be used alone, or two or more can be used in combination. As the cathode catalyst, a supported catalyst in which metal particles are supported on a carbon material (carbon particles, carbon nanotubes, graphene, etc.) can also be used.

[0041] The gas diffusion layer of the cathode 21 is not particularly limited, and examples thereof include carbon paper and carbon cloth. The method for manufacturing the cathode 21 is not particularly limited, and examples thereof include a method in which a slurry containing a liquid composition of a cathode catalyst is applied to the surface of the gas diffusion layer that will become the cathode-side liquid flow path 24a and then dried.

[0042] The anode 22 is an electrode that oxidizes hydroxide ions to generate oxygen. Examples of the anode 22 include an electrode comprising a gas diffusion layer and an anode catalyst layer formed on the anode-side liquid flow path 26a side of the gas diffusion layer. The anode catalyst layer may be configured so that a portion of the anode catalyst layer penetrates the gas diffusion layer. Furthermore, a porous layer denser than the gas diffusion layer may be disposed between the gas diffusion layer and the anode catalyst layer.

[0043] 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, and alloys thereof, 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 species can be used alone, or two or more species can be used in combination.

[0044] Examples of the gas diffusion layer of the anode 22 include carbon paper and carbon cloth. Alternatively, a porous material such as a mesh material, a perforated material, a porous body, or a sintered metal fiber body may be used as the gas diffusion layer. Examples of materials for the porous body include metals such as titanium, nickel, and iron, and alloys thereof (e.g., SUS).

[0045] Examples of the material of the cathode-side liquid flow path structure 24 and the anode-side liquid flow path structure 26 include metals such as titanium and SUS, and carbon.

[0046] Examples of materials for the power supply bodies 27 and 28 include metals such as copper, gold, titanium, and SUS, and carbon. The power supply bodies 27 and 28 may be formed by plating a copper substrate with gold or other plating treatment.

[0047] The electrolysis unit 2a of the electrochemical reaction unit 2 is a flow unit for the electrolyte B supplied from the CO2 absorption unit 12 and transported through the power storage unit 32 and the heat exchange unit 5 to flow into the cathode side liquid flow path 24a. Moreover, by applying voltage to the cathode 21 and the anode 22, the dissolved carbon dioxide in the electrolyte B flowing in the cathode side liquid flow path 24a is electrochemically reduced at the cathode 21 to produce carbon compounds and hydrogen. The electrolyte B at the inlet of the cathode side liquid flow path 24a becomes CO3 due to the dissolved carbon dioxide. 2- On the other hand, as the electrolyte flows in the cathode side liquid flow path 24a and the reduction progresses, the amount of dissolved carbon dioxide, that is, the CO3 in the electrolyte 2- The amount of electrolyte decreases, and thus the electrolyte becomes electrolyte A in a strong alkaline state at the outlet of the cathode side liquid flow path 24a.

[0048] Examples of carbon compounds generated by reducing carbon dioxide at the cathode 21 include carbon monoxide and ethylene. For example, the following reactions progress to generate carbon monoxide and ethylene as gaseous products. Hydrogen is also generated at the cathode 21 through the following reactions. The generated gaseous carbon compounds and hydrogen flow out of the outlet of the cathode-side liquid flow path 24a. Mechanisms such as membrane separation can be used to separate the carbon compounds and hydrogen. Hydrogen is supplied to the anion exchange fuel cell 8 described later via the hydrogen supply path 73.

[0049] CO2+H2O→CO+2OH -

[0050] 2CO+8H2O→C2H4+8OH - +2H2O

[0051] 2H2O→H2+2OH -

[0052] The hydroxide ions generated at the cathode 21 pass through the anion exchange membrane 23 and migrate to the anode 22, where they are oxidized by the following reaction to generate oxygen. The generated oxygen passes through the gas diffusion layer of the anode 22, flows into the anode liquid flow path 26a, and flows out from the outlet of the anode liquid flow path 26a.

[0053] 4OH - →O2+2H2O

[0054] In this manner, in the carbon dioxide treatment apparatus 100, the electrolyte used for the electrochemical reaction section 2 is shared with the absorption liquid of the CO2 absorption section 12, and carbon dioxide is supplied to the electrochemical reaction section 2 while being dissolved in the electrolyte B, thereby performing electrochemical reduction. This reduces the energy required for desorption of carbon dioxide, compared to, for example, the case where carbon dioxide is adsorbed on an adsorbent and then desorbed by heating for reduction, thereby improving energy efficiency.

[0055] Here, the carbon dioxide reduction reaction progressing at cathode 21 generates byproducts in addition to the target carbon compounds such as ethylene. Specifically, byproducts such as methanol, ethanol, acetic acid, and formic acid are generated. These byproducts dissolve in the electrolyte and are difficult to separate. This results in carbon dioxide loss, and it is desirable to reduce this loss.

[0056] Specifically, the following carbon dioxide reduction reaction progresses at the cathode 21, thereby producing methanol, ethanol, acetic acid, and formic acid. Therefore, the electrolyte A flowing in the cathode-side liquid flow path 24a contains byproducts such as methanol, ethanol, acetic acid, and formic acid.

[0057] 2CO3 2- +12H2O+12e - →2CH3OH+16OH - 2CO3 2- +11H2O+12e - →C2H5OH+16OH - 2CO3 2- +8H2O+8e - →CH3COOH+12OH - 2CO3 2- +6H2O+4e -→2HCOOH+8OH -

[0058] In contrast, the electrolysis unit 2a of the electrochemical reaction section 2 according to this embodiment includes a first liquid supply path 20 for supplying the electrolyte A flowing through the cathode-side liquid flow path 24a to the anode-side liquid flow path 26a. The first liquid supply path 20 supplies the electrolyte A, which flows out of the outlet of the cathode-side liquid flow path 24a and contains byproducts such as methanol, ethanol, acetic acid, and formic acid, from the inlet of the anode-side liquid flow path 26a to the anode-side liquid flow path 26a. Thus, byproducts such as methanol, ethanol, acetic acid, and formic acid are oxidized by the oxidation reaction proceeding at the anode 22 to form carbon dioxide (CO3 2- ) and electronics (e - ) are recycled.

[0059] Specifically, at the anode 22, the oxidation reaction of by-products such as methanol, ethanol, acetic acid, and formic acid proceeds as follows, whereby these by-products are converted into carbon dioxide (CO3 2- ) and electronics (e - ) in the form of. The by-products are converted into carbon dioxide (CO3 2- ) and electronics (e - ) is supplied through the second liquid supply path 65 to the nickel-hydrogen battery constituting the electric energy storage unit 32 described later. In this way, in the electrolysis unit 2a of the electrochemical reaction unit 2 of this embodiment, carbon dioxide can be recovered and recycled, thereby reducing carbon dioxide loss and improving energy efficiency.

[0060] 2CH3OH+16OH - →2CO3 2- +12H2O+12e - C2H5OH+16OH - →2CO3 2- +11H2O+12e - CH3COOH+12OH - →2CO3 2- +8H2O+8e - 2HCOOH+8OH - →2CO3 2- +6H2O+4e -

[0061] (Fuel Cell)

[0062] return Figure 1The fuel cell 8 is a device that generates electrical energy from hydrogen and oxygen. Here, the fuel cell 8 is an anion exchange fuel cell. Anion exchange fuel cells are also called hydroxide exchange membrane fuel cells (HEMFC). An anion exchange fuel cell equipped with a short-circuit membrane that conducts both anions and electrons operates as an electrochemically driven CO2 separator (EDCS) that removes CO2 from the air supply. It can remove most of the CO2 contained in the intake air on the cathode side and concentrate it into the exhaust gas on the anode side (for example, Lin Shi, et al., "A short-circuit membrane electrochemical cell powered by hydrogen to remove CO2 from the air feed of hydroxide exchange membrane fuel cells." Nature Energy, 2022, vol. 7, pages 238-247).

[0063] The fuel cell 8 and the electrochemical reaction unit 2 are connected via a hydrogen supply path 73. The hydrogen generated in the electrochemical reaction unit 2 is supplied to the fuel cell 8. The fuel cell 8 generates electrical energy using the hydrogen. The electrical energy is supplied to the electrochemical reaction unit 2.

[0064] Hydrogen is generated by the water electrolysis reaction in the cathode 21 of the electrochemical reaction unit 2. The water electrolysis reaction consumes electrical energy, thereby reducing the efficiency of carbon dioxide electrolysis.

[0065] However, the carbon dioxide treatment apparatus 100 of this embodiment recovers hydrogen, converts the hydrogen into electrical energy using the fuel cell 8, and supplies the electrical energy to the electrochemical reaction unit 2. The fuel cell 8 can partially compensate for the electrical energy consumed by the electrolysis of water.

[0066] Furthermore, the fuel cell 8 is connected to the liquid flow path for supplying the electrolyte B from the CO2 absorption unit 12 to the electrochemical reaction unit 2 via a carbon dioxide concentrated gas supply path 72. The carbon dioxide concentrated gas supply path 72 supplies the carbon dioxide concentrated gas generated by the fuel cell 8 to the electrolyte B before being discharged from the recovery device 1 and supplied to the electrochemical reaction unit 2.

[0067] Here, in Figure 1In the illustrated carbon dioxide treatment device 100, a liquid flow path 62 connecting the CO2 absorption unit 12 and the electric energy storage unit 32, a liquid flow path 63 connecting the electric energy storage unit 32 and the heat exchange unit 5, and a liquid flow path 64 connecting the heat exchange unit 5 and the electrochemical reaction unit 2 are provided between the CO2 absorption unit 12 and the electrochemical reaction unit 2. Figure 1 In the illustrated carbon dioxide treatment apparatus 100 , the carbon dioxide concentrated gas supply path 72 connects the fuel cell 8 to the liquid flow path 62 . However, the carbon dioxide concentrated gas supply path 72 may connect the fuel cell 8 to the liquid flow path 63 or the liquid flow path 64 .

[0068] The carbon dioxide concentrated gas supply path 72 supplies carbon dioxide concentrated gas to the electrolyte B to lower the pH of the electrolyte B. Lowering the pH of the electrolyte B can reduce the amount of hydrogen generated in the electrochemical reaction unit 2 and further improve the carbon dioxide decomposition efficiency.

[0069] The pH of the electrolyte A supplied from the electrochemical reaction section 2 to the CO2 absorption section 12 can preferably be set to slightly less than 14. In the conventional carbon dioxide treatment apparatus 100, when the pH of the electrolyte A is raised to slightly less than 14, the carbon dioxide decomposition efficiency in the electrochemical reaction section 2 decreases. However, according to the research of the inventors of the present invention, by supplying a carbon dioxide-concentrated gas to the electrolyte B discharged from the CO2 absorption section 12, the pH of the electrolyte B can be lowered to slightly less than 12, which is a value suitable for the electrochemical reaction section 2.

[0070] (Electric energy storage device)

[0071] return Figure 1 The electrical energy storage device 3 supplies electricity to the electrochemical reaction unit 2. The conversion unit 31 converts renewable energy into electrical energy. The conversion unit 31 is not particularly limited; examples include a wind turbine, a solar generator, and a geothermal generator. The electrical energy storage device 3 may include one or more conversion units 31.

[0072] The electric energy storage unit 32 is electrically connected to the conversion unit 31. The electric energy converted by the conversion unit 31 is stored in the electric energy storage unit 32. By storing the converted electric energy in the electric energy storage unit 32, a stable supply of electric power can be provided to the electrochemical reaction unit 2 even during periods when the conversion unit 31 is not generating electricity. Furthermore, when utilizing renewable energy, voltage fluctuations generally tend to become significant. However, by temporarily storing the converted electric energy in the electric energy storage unit 32, electric power can be supplied to the electrochemical reaction unit 2 at a stable voltage.

[0073] The electric energy storage unit 32 of this embodiment is composed of a nickel-hydrogen battery. However, the electric energy storage unit 32 may be composed of, for example, a lithium-ion secondary battery, as long as it is chargeable and dischargeable.

[0074] Here, Figure 3A FIG. 1 is a diagram showing the nickel-hydrogen battery of the electric energy storage unit 32 during discharge. Figure 3B This is a diagram showing the nickel-hydrogen battery of the power storage unit 32 during charging. The power storage unit 32 is as described above. Figure 3A and Figure 3B As shown, the nickel-metal hydride battery includes a positive electrode 33, a negative electrode 34, a separator 35 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 35, and a negative electrode side flow path 37 formed between the negative electrode 34 and the separator 35. The positive electrode side flow path 36 and the negative electrode side flow path 37 can be formed using, for example, the same liquid flow path structure as the cathode side liquid flow path 24a and the anode side liquid flow path 26a of the electrochemical reaction unit 2.

[0075] The positive electrode 33 may be constructed, for example, by coating a positive electrode active material on the positive electrode side of the flow path 36 of the positive electrode current collector. The positive electrode current collector is not particularly limited, and examples thereof include nickel foil or nickel-plated metal foil. The positive electrode active material is not particularly limited, and examples thereof include nickel hydroxide or nickel oxyhydroxide.

[0076] The negative electrode 34 may be constructed, for example, by coating a negative electrode active material on the negative electrode side of the negative electrode current collector. The negative electrode current collector is not particularly limited, and an example thereof may be a nickel mesh. The negative electrode active material is not particularly limited, and an example thereof may be a known hydrogen storage alloy.

[0077] The separator 35 is not particularly limited, and an ion exchange membrane can be exemplified, for example.

[0078] The nickel-metal hydride battery in the electric energy storage unit 32 is a flow unit in which the electrolyte flows through the positive electrode side flow path 36 on the positive electrode 33 side of the separator 35 and the negative electrode side flow path 37 on the negative electrode 34 side of the separator 35. In the carbon dioxide treatment apparatus 100 of this embodiment, the electrolyte B supplied from the CO2 absorption unit 12 through the liquid flow path 62 and the electrolyte A supplied from the electrochemical reaction unit 2 through the second liquid supply path 65 are supplied and flowed into the positive electrode side flow path 36 and the negative electrode side flow path 37, respectively.

[0079] Furthermore, the connection of the liquid flow path 62 and the liquid flow path 63 to the electric energy storage unit 32 is switched between a state of being connected to the positive electrode side flow path 36 and a state of being connected to the negative electrode side flow path 37, respectively, by, for example, a switching valve. Similarly, the connection of the second liquid supply path 65 and the liquid flow path 66 to the electric energy storage unit 32 is switched between a state of being connected to the positive electrode side flow path 36 and a state of being connected to the negative electrode side flow path 37, respectively, by, for example, a switching valve.

[0080] When the nickel-metal hydride battery is discharged, hydroxide ions are generated from water molecules at the positive electrode 33, and the hydroxide ions moving to the negative electrode 34 take 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 weak alkaline state, and it is advantageous for the electrolyte flowing in the negative electrode side flow path 37 to be in a strong alkaline state. Therefore, during discharge, it is preferable to Figure 3A As shown, the liquid flow path 62 and the liquid flow path 63 are connected to the positive electrode side flow path 36, and the second liquid supply path 65 and the liquid flow path 66 are connected to the negative electrode side flow path 37, so that the weakly alkaline electrolyte B supplied from the CO2 absorption section 12 flows through the positive electrode side flow path 36, and the strongly alkaline electrolyte A supplied from the electrochemical reaction section 2 flows through the negative electrode side flow path 37. That is, during discharge, it is preferable that the electrolyte can be circulated in the order of the CO2 absorption section 12, the positive electrode side flow path 36 of the electric energy storage section 32, the electrochemical reaction section 2, the negative electrode side flow path 37 of the electric energy storage section 32, and the CO2 absorption section 12.

[0081] In addition, when the nickel-hydrogen battery is charged, water molecules are generated from hydroxide ions at the positive electrode 33, and the water molecules are decomposed into hydrogen atoms and hydroxide ions at the negative electrode 34, and the hydrogen atoms are 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 strong alkaline state, and it is advantageous for the electrolyte flowing in the negative electrode side flow path 37 to be in a weak alkaline state. Therefore, when charging, it is preferable to Figure 3B As shown, the liquid flow path 62 and the liquid flow path 63 are connected to the negative electrode side flow path 37, and the second liquid supply path 65 and the liquid flow path 66 are connected to the positive electrode side flow path 36, so that the weakly alkaline electrolyte B supplied from the CO2 absorption section 12 flows through the negative electrode side flow path 37, and the strongly alkaline electrolyte A supplied from the electrochemical reaction section 2 flows through the positive electrode side flow path 36. That is, during charging, it is preferable that the electrolyte can be circulated in the order of the CO2 absorption section 12, the negative electrode side flow path 37 of the electric energy storage section 32, the electrochemical reaction section 2, the positive electrode side flow path 36 of the electric energy storage section 32, and the CO2 absorption section 12.

[0082] Generally speaking, when a secondary battery is incorporated into a device, the overall energy efficiency tends to decrease by an amount corresponding to the charge-discharge efficiency. However, in this embodiment, as described above, the pH gradient of electrolyte A and electrolyte B before and after the electrochemical reaction unit 2 is utilized to appropriately exchange the electrolytes flowing in the positive electrode side flow path 36 and the negative electrode side flow path 37 of the energy storage unit 32. This improves the charge-discharge efficiency by an amount corresponding to the "concentration overvoltage" of the electrode reaction expressed by the Nernst equation.

[0083] return Figure 1 The recarburization reaction device 4 is a device that recarburizes ethylene generated by reducing carbon dioxide in the electrochemical reaction unit 2 by polymerizing it. Ethylene gas C generated by reduction at the cathode 21 of the electrochemical reaction unit 2 is transported to the thermal reaction unit 41 via a gas flow path 67. In the thermal reaction unit 41, an ethylene polymerization reaction proceeds in the presence of an olefin polymerization catalyst. This allows the production of recarburized olefins such as 1-butene, 1-hexene, and 1-octene.

[0084] The olefin polymerization catalyst is not particularly limited, and a known catalyst used for polymerization reaction can be used. Examples thereof include solid acid catalysts using silica alumina or zeolite as a support, and transition metal complexes.

[0085] In the carburization reactor 4 of this embodiment, the post-polymerization reaction product gas D flowing out of the thermal reaction section 41 is transported to the gas-liquid separation section 42 via the gas flow path 68. Olefins with a carbon number of 6 or greater are liquid at room temperature. Therefore, if, for example, olefins with a carbon number of 6 or greater are the target carbon compound, setting the temperature of the gas-liquid separation section 42 to approximately 30°C facilitates gas-liquid separation of the olefins with a carbon number of 6 or greater (olefin liquid E1) from the olefins with a carbon number of less than 6 (olefin gas E2). Furthermore, by increasing the temperature of the gas-liquid separation section 42, the carbon number of the resulting olefin liquid E1 can be increased.

[0086] If the gas G1 supplied to the CO2 concentrator 11 of the recovery unit 1 is atmospheric air, the separated gas G3 supplied from the CO2 concentrator 11 via the gas flow path 71 can also be utilized to cool the produced gas D in the gas-liquid separator 42. Using a gas-liquid separator 42 equipped with, for example, a cooling pipe, the separated gas G3 is passed through the cooling pipe, while the produced gas D is passed outside the cooling pipe, thereby condensing the olefin liquid E1 on the surface of the cooling pipe. Furthermore, the olefin gas E2 separated in the gas-liquid separator 42 contains unreacted components such as ethylene and olefins with a carbon number lower than that of the target olefin. Therefore, it can be returned to the thermal reactor 41 via the gas flow path 70 and reused in the polymerization reaction.

[0087] As for the polymerization reaction of ethylene at the thermal reaction section 41, the enthalpy of the supplied substance is higher than the enthalpy of the generated substance, and it is an exothermic reaction with a negative reaction enthalpy. In the carbon dioxide treatment device 100, the heat medium F is heated by utilizing the reaction heat generated in the thermal reaction section 41 of the carburizing reaction device 4, and the heat medium F is circulated to the heat exchange section 5 through the circulation flow path 69, and heat exchange is performed between the heat medium F and the electrolyte B in the heat exchange section 5. Thus, the electrolyte B supplied to the electrochemical reaction section 2 is heated. In the electrolyte B using a strong alkaline aqueous solution, even if the temperature is increased, it is difficult for dissolved carbon dioxide to separate as a gas. By increasing the temperature of the electrolyte B, the redox reaction rate at the electrochemical reaction section 2 is increased.

[0088] The carburizing reactor 4 may further include a reaction section for performing a hydrogenation reaction of olefins obtained by polymerizing ethylene using hydrogen generated in the electrochemical reaction section 2 , and a reaction section for performing an isomerization reaction of olefins and paraffin wax.

[0089] [Carbon dioxide treatment method]

[0090] The carbon dioxide treatment method according to one embodiment of the present invention is performed by using, for example, the above-mentioned carbon dioxide treatment device 100. Specifically, the carbon dioxide treatment method according to this embodiment may preferably include: a step (a) of dissolving carbon dioxide in an electrolyte; a step (b) of reducing the carbon dioxide dissolved in the electrolyte; a step (c) of supplying hydrogen generated during the reduction of carbon dioxide to a fuel cell to generate electricity; and a step (d) of supplying carbon dioxide concentrated gas generated during power generation to the electrolyte after the carbon dioxide is dissolved and before the carbon dioxide is reduced, thereby lowering the pH of the electrolyte. The carbon dioxide treatment method according to this embodiment can be used in a method for producing carbon compounds. That is, using the carbon dioxide treatment method according to this embodiment, carbon compounds obtained by reducing carbon dioxide and carbon compounds that can be obtained using carbon compounds obtained by reducing carbon dioxide as raw materials can be produced.

[0091] Furthermore, the carbon dioxide treatment method of this embodiment is characterized in that, in the electrochemical reduction of carbon dioxide as in the above-mentioned step (b), the electrolyte A flowing through the cathode-side liquid flow path 24a provided adjacent to the cathode 21 is supplied to the anode-side liquid flow path 26a provided adjacent to the anode 22. Thus, by-products such as methanol, ethanol, acetic acid, and formic acid generated by the reduction reaction at the cathode 21 can be oxidized by the oxidation reaction progressing at the anode 22 to form carbon dioxide (CO3 2- ) and electronics (e - ) can be recovered and recycled in the form of , which can reduce the loss of carbon dioxide and improve energy efficiency.

[0092] In addition, in the carbon dioxide treatment method of this embodiment, as in the case of using a carbon dioxide treatment apparatus equipped with a carburizing reaction apparatus 4 as in the above-mentioned carbon dioxide treatment apparatus 100, in addition to steps (a) to (d), it is preferred that a step (e) of polymerizing ethylene generated by reducing dissolved carbon dioxide may be further included.

[0093] It should be noted that the present disclosure is not limited to the above-described embodiments, and modifications and improvements within the scope that can achieve the object of the present disclosure are included in the present disclosure.

[0094] Alternatively, for example, a branch liquid flow path connected to the CO2 absorption unit 12 may be provided in the first liquid supply path 20 of the above embodiment via a switching valve such as a three-way valve. Thus, by switching the switching valve, the electrolyte A can be supplied directly to the CO2 absorption unit 12 via the branch liquid flow path.

[0095] In addition, in the carbon dioxide treatment device 100 of the above embodiment, a structure including a recovery device 1, an electric energy storage device 3, a carburization reaction device 4 and a heat exchange unit 5 is adopted, but it is not limited to this, and a structure without all or part of them can also be adopted.

Claims

1. A carbon dioxide treatment device comprising: A recovery device including a carbon dioxide absorption section for dissolving carbon dioxide in a strong alkaline electrolyte to absorb the carbon dioxide; an electrochemical reaction device that is supplied with the electrolyte in which the carbon dioxide is dissolved in the carbon dioxide absorption unit and electrochemically reduces the carbon dioxide; an anion exchange fuel cell that supplies electrical energy to the electrochemical reaction device; a carbon dioxide concentrated gas supply path for supplying the carbon dioxide concentrated gas generated in the fuel cell to the electrolyte before being discharged from the recovery device and supplied to the electrochemical reaction device; and A hydrogen supply path supplies hydrogen generated in the electrochemical reaction device to the fuel cell.

2. The carbon dioxide treatment device according to claim 1, wherein: The electrochemical reaction device comprises: cathode; anode; an electrolyte membrane disposed between the cathode and the anode; a cathode-side liquid flow path, disposed adjacent to the cathode and for the electrolyte to flow; an anode-side liquid flow path, which is disposed adjacent to the anode and through which the electrolyte flows; as well as The first liquid supply path supplies the electrolyte solution flowing through the cathode-side liquid flow path to the anode-side liquid flow path.

3. The carbon dioxide treatment device according to claim 1 or 2, wherein: The carbon dioxide treatment device further comprises an electric energy storage device for supplying electric energy to the electrochemical reaction device. The electric energy storage device comprises: a conversion unit that converts renewable energy into electric energy; and an electric energy storage unit including a nickel-hydrogen battery for storing the electric energy converted by the conversion unit, The electrochemical reaction device further includes a second liquid supply path that supplies the electrolyte solution flowing through the anode-side liquid flow path to the nickel-hydrogen battery.

4. The carbon dioxide treatment device according to claim 1 or 2, wherein: The carbon dioxide treatment device further includes a carbon addition reaction device that polymerizes ethylene generated by reducing carbon dioxide in the electrochemical reaction device to add carbon.

5. A method for treating carbon dioxide, wherein carbon dioxide is electrochemically reduced, wherein: The carbon dioxide treatment method comprises the following steps: Dissolving carbon dioxide in the electrolyte; reducing carbon dioxide dissolved in the electrolyte; supplying hydrogen generated during the reduction of the carbon dioxide to an anion exchange fuel cell to generate electricity; as well as The carbon dioxide concentrated gas generated during the power generation is supplied to the electrolyte after the carbon dioxide is dissolved and before the carbon dioxide is reduced, thereby lowering the pH of the electrolyte.

6. A method for producing a carbon compound, comprising: Carbon dioxide is reduced to produce carbon compounds using the carbon dioxide treatment method according to claim 5.

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