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

Abstract

To provide a technology capable of enhancing both the absorption rate and decomposition efficiency of carbon dioxide in a carbon dioxide treatment apparatus that recovers carbon dioxide and reduces it electrochemically, thereby surpassing conventional methods.SOLUTION: There is provided a carbon dioxide treatment apparatus 100 comprising: a recovery device 1 recovering carbon dioxide; an electrochemical reaction section 2 electrochemically reducing carbon dioxide; and an electrical energy storage device 3, wherein the recovery device 1 comprises a CO2 absorption section 12, wherein the electrical energy storage device 3 comprises an electrical energy storage section 32 composed of nickel-metal hydride batteries, and wherein the electrolyte circulates in the following sequence: the CO2 absorption section 12, the negative electrode side flow path 37 of the electrical energy storage section 32, the electrochemical reaction section 2, the positive electrode side flow path 36 of the electrical energy storage section 32, and the CO2 absorption section 12 during discharge, and the electrolyte circulates in the following sequence: the CO2 absorption section 12, the cathode-side flow path 36, the electrochemical reaction section 2, the anode-side flow path 37, and the CO2 absorption section 12 during charging.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide treatment device, a carbon dioxide treatment method, and a carbon compound production method. [Background technology]

[0002] Efforts aimed at mitigating or reducing the impact of climate change have been ongoing, and research and development into reducing carbon dioxide emissions has been conducted to achieve this. For example, one known technology for reducing carbon dioxide emissions involves capturing carbon dioxide from exhaust gases or the atmosphere and electrochemically reducing it to obtain valuable materials. This technology is promising for achieving carbon neutrality, but its biggest challenge is its economic viability. To improve economic viability, it is important to increase energy efficiency and reduce carbon dioxide loss in the capture and reduction of carbon dioxide.

[0003] Known carbon dioxide recovery techniques include physically or chemically adsorbing the carbon dioxide in a gas onto a solid or liquid adsorbent, and then desorbing it using energy such as heat for use. Also known as a technique for electrochemically reducing carbon dioxide is a technique in which carbon dioxide gas is supplied to a cathode having a catalyst layer formed with a carbon dioxide reduction catalyst on the side of the gas diffusion layer that comes into contact with the electrolyte, from the side opposite the catalyst layer of the gas diffusion layer, and then electrochemically reduced (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 232515 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventionally, carbon dioxide capture technology and carbon dioxide electrochemical reduction technology have been researched and developed separately. Therefore, although the overall energy efficiency and carbon dioxide loss reduction effect when the respective technologies are combined can be determined exponentially from the efficiency of each technology, there is room for further improvement. In this way, it can be said that it is significant to improve energy efficiency and carbon dioxide loss reduction effect from a comprehensive perspective by combining carbon dioxide capture technology and carbon dioxide electrochemical reduction technology.

[0006] Furthermore, in carbon dioxide treatment devices that have a capture device for capturing carbon dioxide, it is known that if the pH of the electrolyte in which carbon dioxide is dissolved is high, the amount of hydrogen generated during the electrochemical reduction of carbon dioxide increases, and the efficiency of carbon dioxide decomposition deteriorates. On the other hand, in carbon dioxide recovery devices, a high pH of the electrolyte is advantageous from the perspective of the carbon dioxide absorption rate. The discrepancy between the optimal pH conditions for the electrolyte in carbon dioxide capture and electrolysis can be said to be a major issue in carbon dioxide treatment devices.

[0007] As described above, in order to improve the carbon dioxide conversion efficiency, it is necessary to increase both the carbon dioxide capture efficiency and the electrolysis efficiency. The present invention has been made in view of the above, and aims to provide a technology that can improve the carbon dioxide absorption rate and decomposition efficiency compared to conventional carbon dioxide treatment devices that capture carbon dioxide and electrochemically reduce it. This will ultimately contribute to mitigating or reducing the impact of climate change. [Means for solving the problem]

[0008] (1) The present invention provides a recovery device (for example, recovery device 1 described below) that recovers carbon dioxide, an electrochemical reaction device (for example, electrochemical reaction unit 2 described below) that electrochemically reduces the carbon dioxide recovered by the recovery device, and an electric energy storage device (for example, electric energy storage device 3 described below) that supplies electric energy to the electrochemical reaction device, wherein the recovery device includes a carbon dioxide absorption unit (for example, CO2 absorption unit 12 described below) that dissolves the carbon dioxide in a strong alkaline electrolyte and absorbs it, and the electrochemical reaction device is supplied with the carbon dioxide dissolved in the electrolyte by the carbon dioxide absorption unit, and the electric energy storage device includes an electric energy storage unit (for example, electric energy storage unit 32 described below) made of a nickel-metal hydride battery that stores electric energy, and the electric energy storage unit includes a positive electrode (for example, positive electrode 33 described below), a negative electrode (for example, negative electrode 34 described below), and the The carbon dioxide treatment device (for example, a carbon dioxide treatment device 100 described later) includes a separator (for example, a separator 35 described later) provided between the positive electrode and the negative electrode, a positive electrode-side flow path (for example, a positive electrode-side flow path 36 described later) formed between the positive electrode and the separator, and a negative electrode-side flow path (for example, a negative electrode-side flow path 37 described later) formed between the negative electrode and the separator, wherein, when the electric energy storage unit is discharged, the electrolyte is circulated in the order of the carbon dioxide absorption unit, the negative electrode-side flow path of the electric energy storage unit, the electrochemical reaction device, the positive electrode-side flow path of the electric energy storage unit, and the carbon dioxide absorption unit, and when the electric energy storage unit is charged, the electrolyte is circulated in the order of the carbon dioxide absorption unit, the positive electrode-side flow path of the electric energy storage unit, the electrochemical reaction device, the negative electrode-side flow path of the electric energy storage unit, and the carbon dioxide absorption unit.

[0009] The carbon dioxide treatment device (1) flows the electrolyte from the carbon dioxide absorption unit to the negative electrode side flow path when discharging the nickel-metal hydride battery and to the positive electrode side flow path when charging. This allows the nickel-metal hydride battery to reduce the OH of the electrolyte. -This causes the electrolyte to have a low pH. When this electrolyte is passed through an electrochemical reactor, the CO2 conversion efficiency of the electrochemical reactor increases. Furthermore, the carbon dioxide treatment device (1) passes the electrolyte from the electrochemical reactor to the negative electrode flow path when charging the nickel-metal hydride battery, and to the positive electrode flow path when discharging. This allows the nickel-metal hydride battery to convert OH from the electrolyte to - This desorbs CO2, raising the pH of the electrolyte. If this electrolyte is passed through the carbon dioxide absorption section, the CO2 absorption efficiency of the carbon dioxide absorption section increases. Therefore, the carbon dioxide treatment device (1) dramatically improves the carbon dioxide treatment efficiency of the entire system.

[0010] (2) In the carbon dioxide treatment device of (1), the electrochemical reaction device may include a cathode (for example, the cathode 21 described below), an anode (for example, the anode 22 described below), an electrolyte membrane (for example, the anion exchange membrane 23 described below) provided between the cathode and the anode, a cathode-side liquid flow path (for example, the cathode-side liquid flow path 24a described below) provided adjacent to the cathode and through which the electrolytic solution flows, an anode-side liquid flow path (for example, the anode-side liquid flow path 26a described below) provided adjacent to the anode and through which the electrolytic solution flows, and a first liquid supply path (for example, the first liquid supply path 20 described below) that supplies the electrolytic solution that has flowed through the cathode-side liquid flow path to the anode-side liquid flow path.

[0011] (3) In the carbon dioxide treatment device of (1) or (2), the electric energy storage device may further include a conversion unit (for example, a conversion unit 31 described later) that converts renewable energy into electric energy.

[0012] (4) Any of the carbon dioxide treatment devices (1) to (3) may further include a carbon dioxide increasing reaction device (for example, the carbon dioxide increasing reaction device 4 described below) that polymerizes ethylene produced by the reduction of carbon dioxide in the electrochemical reaction device to increase carbon dioxide.

[0013] (5) The present invention also provides a carbon dioxide treatment method for electrochemically reducing carbon dioxide, the method including: a step of dissolving carbon dioxide in an electrolyte in a carbon dioxide absorption unit (for example, a CO2 absorption unit 12 described later); a step of discharging a nickel-metal hydride battery including a positive electrode (for example, a positive electrode 33 described later), a negative electrode (for example, a negative electrode 34 described later), a separator (for example, a separator 35 described later) provided between the positive electrode and the negative electrode, a positive-electrode-side flow path (for example, a positive-electrode-side flow path 36 described later) formed between the positive electrode and the separator, and a negative-electrode-side flow path (for example, a negative-electrode-side flow path 37 described later) formed between the negative electrode and the separator; a step of charging the nickel-metal hydride battery; and a step of dissolving carbon dioxide in an electrolyte in a carbon dioxide absorption unit (for example, a CO2 absorption unit 12 described later). a step of reducing the carbon dioxide dissolved in the electrolyte in an electrochemical reaction unit 2) described below using electrical energy from the nickel-metal hydride battery; a step of circulating the electrolyte through the carbon dioxide absorption unit, the negative electrode side flow path of the nickel-metal hydride battery, the electrochemical reaction device, the positive electrode side flow path of the nickel-metal hydride battery, and the carbon dioxide absorption unit in this order when the nickel-metal hydride battery is discharged; and a step of circulating the electrolyte through the carbon dioxide absorption unit, the positive electrode side flow path of the nickel-metal hydride battery, the electrochemical reaction device, the negative electrode side flow path of the nickel-metal hydride battery, and the carbon dioxide absorption unit in this order when the nickel-metal hydride battery is charged.

[0014] (6) The present invention also provides a method for producing a carbon compound, which comprises reducing carbon dioxide by the carbon dioxide treatment method of (5) to produce a carbon compound. [Effects of the Invention]

[0015] According to the present invention, in a carbon dioxide treatment device that recovers carbon dioxide and electrochemically reduces it, it is possible to improve the absorption rate and decomposition efficiency of carbon dioxide compared to conventional methods. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram illustrating a carbon dioxide treatment device according to an embodiment of the present invention. [Figure 2]FIG. 2 is a schematic cross-sectional view showing an example of an electrolysis cell of an electrochemical reaction section. [Figure 3A] FIG. 2 is a diagram showing a nickel-metal hydride battery of an electric energy storage unit during charging. [Figure 3B] FIG. 10 is a diagram showing a nickel-metal hydride battery of the electrical energy storage unit during discharging. [Figure 4] FIG. 2 is a block diagram showing the circulation path of the electrolyte during charging and discharging. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018] [Carbon dioxide treatment device] Fig. 1 is a block diagram showing a carbon dioxide treatment apparatus 100 according to an embodiment of the present invention. As shown in Fig. 1, the carbon dioxide treatment apparatus 100 according to this embodiment includes a recovery device 1, an electrochemical reaction unit 2, an electric energy storage device 3, a carbon dioxide enrichment reaction device 4, and a heat exchange unit 5. The recovery device 1 includes a CO2 concentration unit 11 and a CO2 absorption unit 12. The electrochemical reaction unit 2 includes an electrolysis cell. The electric energy storage device 3 includes a conversion unit 31 and an electric energy storage unit 32. The carbon dioxide enrichment reaction device 4 includes a thermal reaction unit 41 and a gas-liquid separation unit 42.

[0019] In the carbon dioxide treatment device 100, the CO2 concentrating unit 11 and the CO2 absorbing unit 12 are connected by a gas flow path 61. The CO2 absorbing 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, which is 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 gas flow paths 68 and 70. A heat medium circulation flow path 69 is provided between the thermal reaction unit 41 and the heat exchange unit 5. The CO2 concentrating unit 11 and the gas-liquid separation unit 42 are connected by a gas flow path 71.

[0020] The above-mentioned flow paths are not particularly limited, and known piping, etc. can be used as appropriate. Gas supply means such as compressors, valves, flow meters, and other measuring instruments can be installed as appropriate in the gas flow paths 61, 67, 68, 70, and 71. Liquid supply means such as pumps, valves, flow meters, and other measuring instruments can be installed as appropriate in the liquid flow paths 62 to 66.

[0021] (Recovery device) The recovery device 1 recovers carbon dioxide. A gas G1 containing carbon dioxide, such as the atmosphere or exhaust gas, is supplied to the CO2 concentration section 11. The CO2 concentration section 11 concentrates the carbon dioxide in the gas G1. Any known concentration device capable of concentrating carbon dioxide can be used as the CO2 concentration section 11, such as a membrane separation device that utilizes differences in permeation speed through a membrane, or an adsorption separation device that utilizes chemical or physical adsorption and desorption. From the viewpoint of excellent separation performance, adsorption that utilizes chemical adsorption, particularly temperature swing adsorption, is preferred.

[0022] The concentrated gas G2 in which carbon dioxide is concentrated in the CO2 concentration section 11 is supplied to the CO2 absorption section 12 through the gas flow path 61. The separated gas G3 separated from the concentrated gas G2 is supplied to the gas-liquid separation section 42 through the gas flow path 71.

[0023] In the CO2 absorption unit 12, the carbon dioxide gas in the concentrated gas G2 supplied from the CO2 concentration unit 11 comes into contact with the electrolytic solution A, and the carbon dioxide is dissolved and absorbed in the electrolytic solution A. The method for bringing the carbon dioxide gas into contact with the electrolytic solution A is not particularly limited, and an example thereof is a method of blowing the concentrated gas G2 into the electrolytic solution A and bubbling it.

[0024] In the CO2 absorption unit 12, an electrolyte A made of a strong alkaline aqueous solution is used as an absorption solution for absorbing carbon dioxide. Carbon dioxide has a positive charge (δ+) on the carbon atoms because the oxygen atoms strongly attract electrons. Therefore, in a strong alkaline aqueous solution containing a large amount of hydroxide ions, carbon dioxide changes from a hydrated state to HCO3 - CO3 2- The dissolution reaction proceeds easily up to CO3 2- The equilibrium state is reached where the abundance ratio of carbon dioxide is high. For this reason, carbon dioxide is more easily dissolved in a strong alkaline aqueous solution than other gases such as nitrogen, hydrogen, and oxygen, and carbon dioxide in the concentrated gas G2 is selectively absorbed by the electrolyte A in the CO2 absorption unit 12. In this way, by using the electrolyte A in the CO2 absorption unit 12, the concentration of carbon dioxide can be promoted. Therefore, in the CO2 concentration unit 11, it is not necessary to concentrate carbon dioxide to a high concentration, and the energy required for concentration in the CO2 concentration unit 11 can be reduced.

[0025] Electrolyte B, in which carbon dioxide has been absorbed in the CO2 absorption unit 12, is sent to the electrochemical reaction unit 2 through 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, electrolyte A, which has flowed out of the electrochemical reaction unit 2, is sent to the CO2 absorption unit 12 through the second liquid supply path 65, the electric energy storage unit 32, and the liquid flow path 66. In this way, in the carbon dioxide treatment device 100, the electrolyte is circulated between the CO2 absorption unit 12, the electric energy storage unit 32, and the electrochemical reaction unit 2.

[0026] Examples of strong alkaline aqueous solutions used in the electrolytic solution A include a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution. Among these, a potassium hydroxide aqueous solution is preferably used from the viewpoint of excellent solubility of carbon dioxide in the CO2 absorption section 12 and promotion of reduction of carbon dioxide in the electrochemical reaction section 2.

[0027] (Electrochemical reaction section) FIG. 2 is a schematic cross-sectional view showing an example of an electrolytic cell 2a of the electrochemical reaction unit 2. The electrochemical reaction unit 2 electrochemically reduces carbon dioxide using the electrolytic cell 2a. As shown in FIG. 2, the electrolytic cell 2a of the electrochemical reaction unit 2 includes a cathode 21, an anode 22, an anion exchange membrane 23, a cathode-side liquid flow path structure 24 that forms a cathode-side liquid flow path 24a, an anode-side liquid flow path structure 26 that forms an anode-side liquid flow path 26a, a power supply 27, and a power supply 28. Although FIG. 2 shows one electrolytic cell 2a, the electrochemical reaction unit 2 preferably includes an electrolytic cell stack configured by stacking a plurality of electrolytic cells 2a.

[0028] In the electrolysis cell 2a of the electrochemical reaction section 2, a power supply element 27, a cathode-side liquid flow path structure 24, a cathode 21, an anion exchange membrane 23, an anode 22, an anode-side liquid flow path structure 26, and a power supply element 28 are stacked in this order. A cathode-side liquid flow path 24a is formed between the cathode 21 and the cathode-side liquid flow path structure 24, and an anode-side liquid flow path 26a is formed between the anode 22 and the anode-side liquid flow path structure 26. The cathode-side liquid flow path 24a and the anode-side liquid flow path 26a are provided at positions facing each other with the cathode 21, the anion exchange membrane 23, and the anode 22 sandwiched therebetween. It is preferable to provide a plurality of each of the cathode-side liquid flow paths 24a and the anode-side liquid flow paths 26a, and the shapes thereof may be linear or zigzag.

[0029] The power supply members 27 and 28 are electrically connected to the electric energy storage unit 32 of the electric energy storage device 3. In addition, the cathode-side liquid flow path structure 24 and the anode-side liquid flow path structure 26 are both conductors, and a voltage can be applied between the cathode 21 and the anode 22 by power supplied from the electric energy storage unit 32.

[0030] The cathode 21 is an electrode that reduces carbon dioxide to produce carbon compounds and reduces water to produce hydrogen. The cathode 21 can be, for example, 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. The cathode catalyst layer may be disposed so that a portion of it penetrates into the gas diffusion layer. A porous layer that is denser than the gas diffusion layer may be disposed between the gas diffusion layer and the cathode catalyst layer.

[0031] As the cathode catalyst forming the cathode catalyst layer, a known catalyst that promotes the reduction of carbon dioxide can be used. Specific examples of the cathode catalyst include metals such as gold, silver, copper, platinum, palladium, nickel, cobalt, iron, manganese, titanium, cadmium, zinc, indium, gallium, lead, and tin, as well as alloys and intermetallic compounds thereof, and metal complexes such as ruthenium complexes and rhenium complexes. Among these, copper and silver are preferred, and copper is more preferred, from the viewpoint of promoting the reduction of carbon dioxide. As the cathode catalyst, one type may be used alone, or two or more types may 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.) may be used.

[0032] 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 of a liquid composition containing a cathode catalyst is applied to the surface of the gas diffusion layer that faces the cathode-side liquid flow path 24a, and then dried.

[0033] The anode 22 is an electrode that oxidizes hydroxide ions to produce oxygen. The anode 22 may be, for example, an electrode including 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 disposed so that a portion of the anode catalyst layer penetrates into the gas diffusion layer. Alternatively, a porous layer that is denser than the gas diffusion layer may be disposed between the gas diffusion layer and the anode catalyst layer.

[0034] The anode catalyst forming the anode catalyst layer is not particularly limited, and known anode catalysts can be used. Specific examples include metals such as platinum, palladium, and nickel, alloys and intermetallic compounds thereof, 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. One anode catalyst may be used alone, or two or more may be used in combination.

[0035] Examples of the gas diffusion layer of the anode 22 include carbon paper and carbon cloth. Alternatively, the gas diffusion layer may be made of a porous material such as a mesh material, a punched material, a porous material, or a sintered metal fiber material. Examples of the material for the porous material include metals such as titanium, nickel, and iron, and alloys thereof (e.g., SUS).

[0036] Examples of materials for 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.

[0037] Examples of materials for the power feeders 27 and 28 include metals such as copper, gold, titanium, and SUS, and carbon. The power feeders 27 and 28 may be copper bases whose surfaces are plated with gold or other plating.

[0038] The electrolytic cell 2a of the electrochemical reaction unit 2 is a flow cell in which the electrolyte B, supplied from the CO2 absorption unit 12 and delivered via the electric energy storage unit 32 and the heat exchange unit 5, flows into the cathode-side liquid flow path 24a. When a voltage is applied to the cathode 21 and the anode 22, the dissolved carbon dioxide in the electrolyte B flowing through the cathode-side liquid flow path 24a is electrochemically reduced at the cathode 21 to produce carbon compounds and hydrogen. Since the electrolyte B at the inlet of the cathode-side liquid flow path 24a contains dissolved carbon dioxide, the CO3 2- On the other hand, as the electrolyte flows through the cathode-side liquid flow path 24a and the reduction proceeds, the amount of dissolved carbon dioxide, i.e., the amount of CO3 in the electrolyte, decreases. 2- As the amount decreases, the electrolyte A becomes strongly alkaline at the outlet of the cathode-side liquid flow path 24a.

[0039] Examples of carbon compounds produced by the reduction of carbon dioxide at the cathode 21 include carbon monoxide and ethylene. For example, the following reaction proceeds to produce carbon monoxide and ethylene as gaseous products. At the cathode 21, hydrogen is also produced by the following reaction. The produced gaseous carbon compounds and hydrogen flow out from the outlet of the cathode-side liquid flow path 24a. CO2+H2O→CO+2OH - 2CO+8H2O→C2H4+8OH - +2H2O 2H2O → H2 + 2OH -

[0040] The hydroxide ions produced at the cathode 21 permeate the anion exchange membrane 23 and move to the anode 22, where they are oxidized to produce oxygen through the following reaction: The produced oxygen permeates the gas diffusion layer of the anode 22, flows into the anode-side liquid flow path 26a, and flows out from the outlet of the anode-side liquid flow path 26a. 4OH - →O2+2H2O

[0041] In this way, in the carbon dioxide treatment device 100, the electrolyte used in the electrochemical reaction unit 2 is also used as the absorption liquid for the CO2 absorption unit 12, and carbon dioxide is supplied to the electrochemical reaction unit 2 while still dissolved in the electrolyte B, and is electrochemically reduced. This reduces the energy required to desorb carbon dioxide, and improves energy efficiency, compared to, for example, when carbon dioxide is adsorbed onto an adsorbent and then desorbed by heating for reduction.

[0042] Here, the reduction reaction of carbon dioxide that proceeds at the cathode 21 generates by-products in addition to the target carbon compounds such as ethylene. Specifically, by-products such as methanol, ethanol, acetic acid, and formic acid are generated, and these by-products dissolve in the electrolyte solution and are difficult to separate. This results in a loss of carbon dioxide, and it is desirable to reduce this loss.

[0043] Specifically, methanol, ethanol, acetic acid, and formic acid are produced in the cathode 21 as a result of the following reduction reaction of carbon dioxide: Therefore, the electrolyte A that has flowed through the cathode-side liquid flow path 24a contains by-products such as methanol, ethanol, acetic acid, and formic acid. 2CO3 2- +12H2O+12e - →2CH3OH+16OH - 2CO3 2- +11H2O+12e - →C2H5OH+16OH - 2CO3 2- +8H2O+8e - →CH3COOH+12OH - 2CO3 2- +6H2O+4e - →2HCOOH+8OH -

[0044] In contrast, the electrolysis cell 2a of the electrochemical reaction unit 2 according to this embodiment may include a first liquid supply channel 20 that supplies the electrolyte solution A that has flowed through the cathode-side liquid flow channel 24a to the anode-side liquid flow channel 26a. The first liquid supply channel 20 supplies the electrolyte solution A, which flows out from the outlet of the cathode-side liquid flow channel 24a and contains by-products such as methanol, ethanol, acetic acid, and formic acid, from the inlet of the anode-side liquid flow channel 26a into the anode-side liquid flow channel 26a. As a result, by-products such as methanol, ethanol, acetic acid, and formic acid are oxidized by an oxidation reaction that proceeds in the anode 22, and carbon dioxide (CO3 2- ) and electrons (e - ) is collected.

[0045] Specifically, at the anode 22, the following oxidation reaction of by-products such as methanol, ethanol, acetic acid, and formic acid proceeds, and these by-products are converted into carbon dioxide (CO 2- ) and electrons (e - The by-product is converted into carbon dioxide (CO3 2- ) and electrons (e - ) is supplied to a nickel-metal hydride battery constituting the electric energy storage unit 32 described below via the second liquid supply path 65. In this way, in the electrolytic cell 2a of the electrochemical reaction unit 2 according to this embodiment, carbon dioxide can be recovered and recycled, thereby reducing carbon dioxide loss and improving energy efficiency. 2CH3OH+16OH - →2CO3 2- +12H2O+12e - C2H5OH+16OH - →2CO3 2- +11H2O+12e - CH3COOH+12OH - →2CO3 2- +8H2O+8e - 2HCOOH+8OH - →2CO3 2- +6H2O+4e -

[0046] (Electrical Energy Storage Device) Returning to FIG. 1 , the electric energy storage device 3 is a device that supplies power to the electrochemical reaction unit 2. Renewable energy is converted into electric energy in the conversion unit 31. The conversion unit 31 is not particularly limited, and examples thereof include a wind power generator, a solar power generator, and a geothermal power generator. The electric energy storage device 3 may be provided with one or more conversion units 31.

[0047] 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. Storing the converted electric energy in the electric energy storage unit 32 allows a stable supply of electric power to the electrochemical reaction unit 2 even during times when the conversion unit 31 is not generating electric power. Furthermore, when renewable energy is used, voltage fluctuations are generally prone to increase, but by temporarily storing the electric energy in the electric energy storage unit 32, electric power can be supplied to the electrochemical reaction unit 2 at a stable voltage.

[0048] The electric energy storage unit 32 in this embodiment is composed of a nickel-metal hydride battery.

[0049] 3A is a diagram showing the nickel-metal hydride battery of the electric energy storage unit 32 during charging. FIG. 3B is a diagram showing the nickel-metal hydride battery of the electric energy storage unit 32 during discharging. As shown in FIGS. 3A and 3B, the electric energy storage unit 32 is a nickel-metal hydride battery including 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, a liquid flow path structure similar to the cathode-side liquid flow path 24a and the anode-side liquid flow path 26a of the electrochemical reaction unit 2.

[0050] The positive electrode 33 may be, for example, a positive electrode current collector coated with a positive electrode active material on the side of the positive electrode flow path 36. The positive electrode current collector is not particularly limited, and examples thereof include nickel foil and nickel-plated metal foil. The positive electrode active material is not particularly limited, and examples thereof include nickel hydroxide and nickel oxyhydroxide.

[0051] The negative electrode 34 may be, for example, a negative electrode current collector coated with a negative electrode active material on the negative electrode flow path 37 side. The negative electrode current collector is not particularly limited, and may be, for example, a nickel mesh. The negative electrode active material is not particularly limited, and may be, for example, a known hydrogen storage alloy.

[0052] The separator 35 is not particularly limited, and may be, for example, an ion exchange membrane.

[0053] The nickel-metal hydride battery of the electric energy storage unit 32 is a flow cell in which an electrolyte flows through a positive electrode-side flow path 36 on the positive electrode 33 side of the separator 35, and through a negative electrode-side flow path 37 on the negative electrode 34 side of the separator 35. In the carbon dioxide treatment device 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 to and flow through the positive electrode-side flow path 36 and the negative electrode-side flow path 37, respectively.

[0054] Furthermore, the connection of the liquid flow paths 62 and 63 to the electric energy storage unit 32 can be switched between a state where they are connected to the positive electrode side flow path 36 and a state where they are connected to the negative electrode side flow path 37, for example, by a switching valve or the like. Similarly, the connection of the second liquid supply path 65 and the liquid flow path 66 to the electric energy storage unit 32 can be switched between a state where they are connected to the positive electrode side flow path 36 and a state where they are connected to the negative electrode side flow path 37, for example, by a switching valve or the like. The carbon dioxide treatment device 100 may be provided with a control unit that controls the flow path switching means. The control unit can control the switching means in accordance with the charge / discharge state of the nickel-metal hydride battery of the electric energy storage device 3, as will be described later.

[0055] As shown in FIG. 4, when the nickel-metal hydride battery is discharged, the following chemical reaction occurs in the positive electrode 33. NiOOH+H2O+e - →Ni(OH)2+OH - Furthermore, when the nickel-metal hydride battery is discharged, the following chemical reaction occurs in the negative electrode 34: MH+OH - →M+H2O+e - That is, when the nickel-metal hydride battery is discharged, hydroxide ions are generated from water molecules at the positive electrode 33, and the hydroxide ions that move to the negative electrode 34 receive hydrogen ions from the hydrogen storage alloy, generating water molecules. Then, the pH of the electrolyte in the positive electrode side flow path 36 becomes high, and the pH of the electrolyte in the negative electrode side flow path 37 becomes low.

[0056] This chemical reaction is utilized to optimize the pH of the electrolyte in the CO2 absorption unit 12 and the electrochemical reaction unit 2. In the electrochemical reaction unit 2, lowering the pH of the electrolyte reduces the amount of hydrogen generated during the electrochemical reduction of carbon dioxide, thereby increasing the efficiency of carbon dioxide decomposition. In the CO2 absorption unit 12, increasing the pH of the electrolyte increases the carbon dioxide absorption rate. Therefore, during discharge, as shown in FIG. 3B, the liquid flow paths 62 and 63 are connected to the anode-side flow path 37, and the second liquid supply path 65 and liquid flow path 66 are connected to the cathode-side flow path 36. Then, electrolyte B supplied from the CO2 absorption unit 12 flows through the anode-side flow path 37, and electrolyte A supplied from the electrochemical reaction unit 2 flows through the cathode-side flow path 36. As a result, as shown in the lower part of Figure 4, during discharge, the electrolyte is circulated in the following order: CO2 absorption section 12, negative electrode side flow path 37 of electrical energy storage section 32, electrochemical reaction section 2, positive electrode side flow path 36 of electrical energy storage section 32, and CO2 absorption section 12.

[0057] As shown in FIG. 4, when the nickel-metal hydride battery is being charged, the following chemical reaction occurs in the positive electrode 33: Ni(OH)2+OH - →NiOOH+H2O+e - When the nickel-metal hydride battery is being charged, the following chemical reactions occur in the negative electrode 34: M+H2O+e - →MH+OH - That is, when the nickel-metal hydride battery is charged, water molecules are generated from hydroxide ions at the positive electrode 33, 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.

[0058] This chemical reaction is also utilized to optimize the pH of the electrolyte in the CO2 absorption unit 12 and the electrochemical reaction unit 2. During charging, as shown in FIG. 3A, the liquid flow paths 62 and 63 are connected to the positive electrode side flow path 36, and the second liquid supply path 65 and liquid flow path 66 are connected to the negative electrode side flow path 37. Then, electrolyte B supplied from the CO2 absorption unit 12 flows through the positive electrode side flow path 36, and electrolyte A supplied from the electrochemical reaction unit 2 flows through the negative electrode side flow path 37. As a result, during charging, the electrolyte is circulated in the following order: the CO2 absorption unit 12, the positive electrode side flow path 36 of the electric energy storage unit 32, the electrochemical reaction unit 2, the negative electrode side flow path 37 of the electric energy storage unit 32, and the CO2 absorption unit 12, as shown in the upper part of FIG. 4.

[0059] In this embodiment, the pH of the electrolyte in the electrochemical reaction unit 2 is lowered and the pH of the electrolyte in the CO2 absorption unit 12 is increased by appropriately switching the electrolytes flowing through the positive electrode flow path 36 and the negative electrode flow path 37 of the electric energy storage unit 32. This significantly improves the carbon dioxide absorption and reduction efficiencies. The pH of the electrolyte is not particularly limited. For example, in the liquid flow path 62 that supplies electrolyte solution B from the CO2 absorption unit 12 to the electric energy storage unit 32, the pH of the electrolyte B may be set within a range of 13.0±1.0. In the liquid flow paths 63 and 64 that supply electrolyte solution B from the electric energy storage unit 32 to the electrochemical reaction unit 2, the pH of the electrolyte B may be set within a range of 11.5±1.0. In the liquid flow path 65 that supplies electrolyte solution A from the electrochemical reaction unit 2 to the electric energy storage unit 32, the pH of the electrolyte A may be set within a range of 12.0±1.0. In the liquid flow path 66 that supplies the electrolytic solution A from the electric energy storage unit 32 to the CO2 absorbing unit 12, the pH of the electrolytic solution A may be set within the range of 13.5±1.0, thereby further improving the carbon dioxide conversion efficiency.

[0060] The number of electric energy storage units 32 may be two or more. In this case, it is preferable to appropriately change the circulation path of the electrolyte. For example, a carbon dioxide treatment device having a solar power generator as the conversion unit 31 and nickel-metal hydride batteries A, B, C, and D as the electric energy storage units 32 can be operated as shown in Table 1 below.

[0061] [Table 1]

[0062] During the period from midnight to 8:00 on the first day, the amount of electricity generated by the conversion unit 31 is zero. During this period, electrical energy is supplied from battery B to the electrochemical reaction unit 2. During this period, the electrolyte is circulated through the CO2 absorption unit 12, the anode flow path 37 of battery B, the electrochemical reaction unit 2, the cathode flow path 36 of battery B, and the CO2 absorption unit 12, in this order. Battery A, battery C, and battery D are not charged or discharged. Electrochemical reactions do not progress in the cathode flow path 36 and the anode flow path 37 of battery A, battery C, and battery D, respectively. Therefore, during this period, it is not necessary to circulate the electrolyte through the cathode flow path 36 and the anode flow path 37 of battery A, battery C, and battery D, respectively. On the other hand, if the amount of electrolyte circulated is insufficient when the electrolyte is circulated only through battery B, batteries A, battery C, and battery D may be used simply as electrolyte flow paths to ensure sufficient circulation.

[0063] During the period from 8:00 to 16:00 on the first day, power is generated in the conversion unit 31. During this period, batteries A, B, and D are charged. Also during this period, electrical energy is supplied from battery C to the electrochemical reaction unit 2. During this period, the electrolyte is circulated for battery C, which is being discharged, as shown in the lower part of FIG. 4. Furthermore, the electrolyte is circulated for batteries A, B, and D, which are being charged, as shown in the upper part of FIG. 4.

[0064] During the period from 4:00 PM to midnight on the first day, the amount of power generated in the conversion unit 31 is zero. During this period, electrical energy is supplied from battery D to the electrochemical reaction unit 2. During this period, the electrolyte is circulated in the order of the CO2 absorption unit 12, the anode flow path 37 of battery B, the electrochemical reaction unit 2, the cathode flow path 36 of battery D, and the CO2 absorption unit 12. Neither charging nor discharging is performed in batteries A, B, and C. Therefore, during this period, the electrolyte does not need to be circulated through the cathode flow path 36 and the anode flow path 37 of batteries A, B, and C, respectively, and these batteries may be used simply as electrolyte flow paths.

[0065] From the second day onwards, charging and discharging of batteries A to D can be carried out as appropriate depending on the remaining amount of electrical energy. By appropriately switching the circulation path of the electrolyte in the multiple batteries depending on their charge / discharge states, the efficiency of carbon dioxide absorption and reduction can be further improved.

[0066] As explained above, the solar power generator generates electricity for only about one-third of the time in a day. However, when the solar power generator is used as the conversion unit 31, the electric energy storage unit 32 can store the OH - It not only functions as a means for adjusting the concentration of carbon dioxide, but also functions as an electricity storage device that extends the operating time of the electrochemical reaction section 2, thereby contributing to improving the efficiency of carbon dioxide treatment.

[0067] (Carbonization reactor) Returning to FIG. 1 , the carbon-enriched reactor 4 is a device that polymerizes ethylene produced by the reduction of carbon dioxide in the electrochemical reaction section 2 to increase carbon dioxide. Ethylene gas C produced by reduction at the cathode 21 of the electrochemical reaction section 2 is sent to the thermal reaction section 41 through a gas flow path 67. In the thermal reaction section 41, an ethylene polymerization reaction is carried out in the presence of an olefin polymerization catalyst. This makes it possible to produce carbon-enriched olefins such as 1-butene, 1-hexene, and 1-octene.

[0068] The olefin polymerisation catalyst is not particularly limited, and any known catalyst used in polymerisation reactions can be used, such as a solid acid catalyst using silica alumina or zeolite as a support, or a transition metal complex compound.

[0069] In the carbon-enrichment reaction apparatus 4 of this embodiment, the product gas D after the polymerization reaction flowing out from the thermal reaction section 41 is sent to the gas-liquid separation section 42 through the gas flow path 68. Olefins having 6 or more carbon atoms are liquid at room temperature. Therefore, when olefins having 6 or more carbon atoms are the target carbon compounds, for example, gas-liquid separation can be easily performed into olefins having 6 or more carbon atoms (olefin liquid E1) and olefins having less than 6 carbon atoms (olefin gas E2) by setting the temperature of the gas-liquid separation section 42 to about 30°C. Furthermore, the carbon number of the resulting olefin liquid E1 can be increased by increasing the temperature of the gas-liquid separation section 42.

[0070] If the gas G1 supplied to the CO2 concentration section 11 of the recovery device 1 is atmospheric air, the separated gas G3 sent from the CO2 concentration section 11 through the gas flow path 71 may be used to cool the produced gas D in the gas-liquid separation section 42. For example, a gas-liquid separation section 42 equipped with a cooling pipe may be used, with the separated gas G3 passing through the cooling pipe and the produced gas D passing outside the cooling pipe, causing it to condense on the surface of the cooling pipe to form an olefin liquid E1. Furthermore, the olefin gas E2 separated in the gas-liquid separation section 42 contains unreacted components such as ethylene and olefins with a smaller carbon number than the target olefin, and therefore can be returned to the thermal reaction section 41 through the gas flow path 70 and reused in the polymerization reaction.

[0071] The ethylene oligomerization reaction in the thermal reaction section 41 is an exothermic reaction in which the enthalpy of the feed material is higher than that of the product material, resulting in a negative reaction enthalpy. In the carbon dioxide treatment device 100, the heat transfer medium F is heated using the reaction heat generated in the thermal reaction section 41 of the carbon-enrichment reaction device 4, and the heat transfer medium F is circulated to the heat exchange section 5 through the circulation flow path 69, where heat exchange occurs between the heat transfer medium F and the electrolytic solution B. This heats the electrolytic solution B supplied to the electrochemical reaction section 2. In the electrolytic solution B containing a strong alkaline aqueous solution, dissolved carbon dioxide is unlikely to separate as a gas even when heated, and the increase in the temperature of the electrolytic solution B improves the oxidation-reduction reaction rate in the electrochemical reaction section 2.

[0072] The carbon-enrichment reaction device 4 may further include a reaction section that uses the hydrogen generated in the electrochemical reaction section 2 to perform a hydrogenation reaction of olefins obtained by polymerizing ethylene, or a reaction section that performs an isomerization reaction of olefins or paraffins.

[0073] [Carbon dioxide treatment method] A carbon dioxide treatment method according to one embodiment of the present invention is carried out, for example, by using the above-mentioned carbon dioxide treatment device 100. Specifically, the carbon dioxide treatment method of this embodiment preferably includes the steps of: (a) dissolving carbon dioxide in an electrolyte; (b) discharging a nickel-metal hydride battery including a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, a positive electrode-side flow path formed between the positive electrode and the separator, and a negative electrode-side flow path formed between the negative electrode and the separator; (c) charging the nickel-metal hydride battery; (d) reducing the carbon dioxide dissolved in the electrolyte using the electrical energy of the nickel-metal hydride battery; (e) circulating the electrolyte through the carbon dioxide absorption unit, the negative electrode-side flow path of the nickel-metal hydride battery, an electrochemical reaction device, the positive electrode-side flow path of the nickel-metal hydride battery, and the carbon dioxide absorption unit in this order when discharging the nickel-metal hydride battery; and (f) circulating the electrolyte through the carbon dioxide absorption unit, the positive electrode-side flow path of the nickel-metal hydride battery, the electrochemical reaction device, the negative electrode-side flow path of the nickel-metal hydride battery, and the carbon dioxide absorption unit in this order when charging the nickel-metal hydride battery. The carbon dioxide treatment method of this embodiment can be used in a method for producing a carbon compound. That is, by using the carbon dioxide treatment method of this embodiment, it is possible to produce a carbon compound obtained by reducing carbon dioxide, or a carbon compound obtained from a carbon compound obtained by reducing carbon dioxide as a raw material.

[0074] In the carbon dioxide treatment method of this embodiment, in the electrochemical reduction of carbon dioxide as in the above-mentioned step (d), the electrolyte A that has flowed through the cathode-side liquid flow path 24a provided adjacent to the cathode 21 may be supplied to the anode-side liquid flow path 26a provided adjacent to the anode 22. In this way, the oxidation reaction that proceeds at the anode 22 oxidizes by-products such as methanol, ethanol, acetic acid, and formic acid that are generated in the reduction reaction at the cathode 21 to produce carbon dioxide (CO3 2- ) and electrons (e- ) can be recovered and recycled, reducing carbon dioxide loss and improving energy efficiency.

[0075] Furthermore, in addition to steps (a) to (f), the carbon dioxide treatment method of this embodiment preferably further includes step (g) of polymerizing ethylene produced by reduction of dissolved carbon dioxide, as in the case of using a carbon dioxide treatment device equipped with a carbon-enrichment reaction device 4, such as the above-mentioned carbon dioxide treatment device 100.

[0076] The present disclosure is not limited to the above-described embodiments, and includes modifications and improvements within the scope of achieving the object of the present disclosure.

[0077] Furthermore, for example, the first liquid supply path 20 of the above embodiment may be provided with a branched liquid flow path connected to the CO2 absorbing unit 12 via a switching valve such as a three-way valve. This allows the electrolyte A to be supplied directly to the CO2 absorbing unit 12 via the branched liquid flow path by switching the switching valve.

[0078] Furthermore, the carbon dioxide treatment device 100 of the above embodiment is configured to include a recovery device 1, an electric energy storage device 3, a carbon-enrichment reaction device 4, and a heat exchange section 5, but is not limited to this, and may be configured to not include all or some of these. [Explanation of symbols]

[0079] 1. Recovery device 2. Electrochemical reaction section (electrochemical reaction device) 3 Electrical energy storage devices 4. Carbonization reactor 12 CO2 absorption section 20 1st liquid supply path 21 Cathode 22 Anode 23 Anion exchange membrane (electrolyte membrane) 24a Cathode side liquid flow path 26a Anode side liquid flow path 31 Conversion unit 32 Electrical Energy Storage Unit 33 Positive electrode 34 Negative electrode 35 Separator 36 Positive electrode flow path 37 Negative electrode side flow path 65 2nd liquid supply path 100 Carbon dioxide treatment device

Claims

1. a capture device for capturing carbon dioxide; an electrochemical reaction device that electrochemically reduces the carbon dioxide recovered by the recovery device; an electrical energy storage device that supplies electrical energy to the electrochemical reactor; Equipped with the recovery device includes a carbon dioxide absorption unit that dissolves and absorbs the carbon dioxide in a strong alkaline electrolyte, The carbon dioxide dissolved in the electrolytic solution in the carbon dioxide absorption unit is supplied to the electrochemical reaction device, the electric energy storage device includes an electric energy storage unit formed of a nickel-metal hydride battery that stores electric energy; The electrical energy storage unit A positive electrode and a negative electrode; a separator provided between the positive electrode and the negative electrode; a positive electrode side flow path formed between the positive electrode and the separator; a negative electrode-side flow path formed between the negative electrode and the separator; Equipped with When the electric energy storage unit is discharged, the electrolyte is circulated in the order of the carbon dioxide absorption unit, the negative electrode side flow path of the electric energy storage unit, the electrochemical reaction device, the positive electrode side flow path of the electric energy storage unit, and the carbon dioxide absorption unit, and when the electric energy storage unit is charged, the electrolyte is circulated in the order of the carbon dioxide absorption unit, the positive electrode side flow path of the electric energy storage unit, the electrochemical reaction device, the negative electrode side flow path of the electric energy storage unit, and the carbon dioxide absorption unit. Carbon dioxide treatment equipment.

2. The electrochemical reaction device is a cathode; an anode; an electrolyte membrane provided between the cathode and the anode; a cathode-side liquid flow path provided adjacent to the cathode and through which the electrolytic solution flows; an anode-side liquid flow path provided adjacent to the anode and through which the electrolytic solution flows; 2. The carbon dioxide treatment device according to claim 1, further comprising: a first liquid supply passage that supplies the electrolytic solution that has flowed through the cathode-side liquid flow passage to the anode-side liquid flow passage.

3. The electric energy storage device further includes a conversion unit that converts renewable energy into electric energy, The carbon dioxide treatment device according to claim 1 or 2, wherein the electric energy storage unit stores the electric energy converted by the conversion unit.

4. The carbon dioxide treatment device according to claim 1 , further comprising a carbon dioxide increasing reaction device that increases carbon dioxide by polymerizing ethylene produced by reduction of the carbon dioxide in the electrochemical reaction device.

5. A carbon dioxide treatment method for electrochemically reducing carbon dioxide, comprising: a step of dissolving carbon dioxide in the electrolytic solution in the carbon dioxide absorption section; discharging a nickel-metal hydride battery including a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, a positive electrode-side flow path formed between the positive electrode and the separator, and a negative electrode-side flow path formed between the negative electrode and the separator; charging the nickel-metal hydride battery; reducing the carbon dioxide dissolved in the electrolytic solution in an electrochemical reaction device using electrical energy from the nickel-metal hydride battery; a step of circulating the electrolytic solution through the carbon dioxide absorption unit, the negative electrode side flow path of the nickel-metal hydride battery, the electrochemical reaction device, the positive electrode side flow path of the nickel-metal hydride battery, and the carbon dioxide absorption unit in this order during discharge of the nickel-metal hydride battery; a step of circulating the electrolytic solution through the carbon dioxide absorption unit, the positive electrode side flow path of the nickel-metal hydride battery, the electrochemical reaction device, the negative electrode side flow path of the nickel-metal hydride battery, and the carbon dioxide absorption unit in this order during charging of the nickel-metal hydride battery; A carbon dioxide treatment method comprising:

6. A method for producing a carbon compound, comprising reducing carbon dioxide to produce a carbon compound by the carbon dioxide treatment method according to claim 5.

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