Carbon dioxide treatment apparatus, carbon dioxide treatment method

Abstract

To reduce energy consumption in the recovery of carbon dioxide and to improve the reaction efficiency in the electrochemical reduction of carbon dioxide.SOLUTION: A carbon dioxide treatment device 100 comprising an absorber 2 that absorbs carbon dioxide, a removal device 3 that removes an air component from an electrolyte containing the carbon dioxide absorbed by the absorber 2, an electrochemical reaction part 4 that has an electrochemical cell 41 that electrochemically reduces the carbon dioxide absorbed by the absorber 2 to carbon monoxide, and a photovoltaic generation device 5 that supplies power to the electrochemical reaction part 4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carbon dioxide treatment apparatus and a carbon dioxide treatment method.

Background Art

[0002] Conventionally, a technology for recovering carbon dioxide in exhaust gas or the atmosphere and electrochemically reducing it to obtain valuable substances is known. This technology is a promising technology capable of achieving carbon neutrality, but the biggest issue is its economic viability. To improve the economic viability, it is important to increase the energy efficiency and reduce the loss of carbon dioxide in the recovery and reduction of carbon dioxide.

[0003] As a technology for recovering carbon dioxide, a technology is known in which carbon dioxide in a gas is physically or chemically adsorbed onto a solid or liquid adsorbent and then desorbed by energy such as heat for utilization. Further, as a technology for electrochemically reducing carbon dioxide, a technology is known in which carbon dioxide gas is supplied from the side opposite to the catalyst layer of a gas diffusion layer to a cathode having a catalyst layer formed by using a carbon dioxide reduction catalyst on the side in contact with the electrolytic solution of the gas diffusion layer, and electrochemically reduced (see, for example, Patent Document 1).

[0004] Conventionally, the technology for recovering carbon dioxide and the technology for electrochemically reducing carbon dioxide have been separately researched and developed. Therefore, although the overall energy efficiency and the carbon dioxide loss reduction effect when combining each technology can be multiplicatively determined from the efficiency of each technology, there is still room for further improvement. Thus, it can be said that it is meaningful to enhance the energy efficiency and the carbon dioxide loss reduction effect from an overall perspective of combining the technology for recovering carbon dioxide and the technology for electrochemically reducing carbon dioxide.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in the technology of electrochemically reducing carbon dioxide, there are many technologies in which a large amount of energy is input when collecting carbon dioxide to obtain high-concentration carbon dioxide, and reducing the energy consumption is a major issue. In addition, when the electrolytic solution supplied for the electrochemical reduction of carbon dioxide contains air components (nitrogen, oxygen), there is a problem that the reaction efficiency decreases when electrochemically reducing carbon dioxide.

[0007] The present application aims to reduce the energy consumption when collecting carbon dioxide and improve the reaction efficiency when electrochemically reducing carbon dioxide in order to solve the above problems. And, by extension, it contributes to the energy efficiency improvement.

Means for Solving the Problems

[0008] [1] A carbon dioxide treatment apparatus comprising: an absorption device that absorbs carbon dioxide; a removal device that removes air components from an electrolytic solution containing carbon dioxide absorbed by the absorption device; an electrochemical reaction unit having an electrolytic cell that electrochemically reduces carbon dioxide absorbed by the absorption device to carbon monoxide; and a solar power generation device that supplies power to the electrochemical reaction unit.

[0009] Since the carbon dioxide treatment apparatus of the present invention is provided with a removal device that removes air components from an electrolytic solution containing carbon dioxide absorbed by the absorption device, the reaction efficiency when electrochemically reducing carbon dioxide can be improved. In addition, since the apparatus is provided with a solar power generation device that supplies power to the electrochemical reaction unit, it is possible to supply the power required for the electrochemical reduction of carbon dioxide in the electrolytic cell during the day from the solar power generation device, and as a result, the energy consumption when collecting carbon dioxide can be reduced.

[0010] [2] The absorption device includes a carbon dioxide absorption unit that dissolves and absorbs carbon dioxide in a strongly alkaline electrolytic solution. The carbon dioxide treatment apparatus according to [1], wherein carbon dioxide dissolved in the electrolytic solution in the carbon dioxide absorption unit is supplied to the electrochemical reaction unit.

[0011] The carbon dioxide treatment apparatus of the present invention includes a carbon dioxide absorption unit, and since carbon dioxide dissolved in the electrolytic solution in the carbon dioxide absorption unit is supplied to the first electrochemical reaction unit, the concentration of carbon dioxide can be promoted.

[0012] [3] The electrolytic cell includes a cathode, an anode, an ion exchange membrane provided between the cathode and the anode, a cathode-side liquid flow path provided adjacent to the cathode through which an electrolytic solution in which carbon dioxide is dissolved flows, and an anode-side liquid flow path provided adjacent to the anode through which an electrolytic solution flows, and the carbon dioxide treatment apparatus according to [1] or [2].

[0013] The carbon dioxide treatment apparatus of the present invention can electrochemically reduce carbon dioxide to carbon monoxide by an electrolytic cell.

[0014] [4] A carbon dioxide treatment method for electrochemically reducing carbon dioxide, a first step of constantly recovering carbon dioxide using the power transmitted from a power plant including night-time power; a second step of bringing the carbon dioxide recovered in the first step into contact with an electrolytic solution composed of a strong alkaline aqueous solution to dissolve and absorb the carbon dioxide in the electrolytic solution; a third step of removing air components contained in the electrolytic solution containing the carbon dioxide absorbed in the second step; and a fourth step of electrochemically reducing carbon dioxide to carbon monoxide by an electrolytic cell using daytime power and the power generated by a solar power generation device, the carbon dioxide treatment method.

[0015] The carbon dioxide treatment method of the present invention can always recover carbon dioxide using the power transmitted from a power plant including nighttime power, so the time for recovering carbon dioxide is long and the recovery amount can be increased. In addition, by using the daytime power and the power generated by the solar power generation device to electrochemically reduce carbon dioxide to carbon monoxide by an electrolytic cell, the energy consumption when reducing carbon dioxide can be reduced. Further, in order to remove the air components contained in the electrolytic solution containing the carbon dioxide recovered in the first step, the reaction efficiency when electrochemically reducing carbon dioxide can be improved.

Effects of the Invention

[0016] According to the present invention, it is possible to reduce the energy consumption when recovering carbon dioxide and improve the reaction efficiency when electrochemically reducing carbon dioxide.

Brief Description of the Drawings

[0017]

Figure 1

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] [Carbon Dioxide Treatment Apparatus] FIG. 1 is a schematic 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 the present embodiment includes a CO2 recovery facility 1, an absorption device 2, a removal device 3, an electrochemical reaction unit 4, a solar power generation device 5, a gas-liquid separation unit 6, and an oxygen separation unit 7.

[0020] The absorption device 2 includes a CO2 absorption unit 21. The removal device 3 includes a negative pressure chamber 31 and a pressure reducing device 32. The electrochemical reaction unit 4 includes an electrolytic cell 41.

[0021] In the carbon dioxide treatment apparatus 100, the CO2 recovery facility 1 and the CO2 absorption section 21 are connected by a gas flow path 101. The CO2 absorption section 21 and the negative pressure chamber 31 are connected by a liquid flow path 102. The negative pressure chamber 31 and the electrochemical reaction section 4 are connected by a liquid flow path 103. The electrochemical reaction section 4 and the gas-liquid separation section 6 are connected by a liquid flow path 104. The gas-liquid separation section 6 and the CO2 absorption section 21 are connected by a liquid flow path 105. The electrochemical reaction section 4 and the oxygen separation section 7 are connected by liquid flow paths 106 and 107. The negative pressure chamber 3 and the pressure reduction device 32 are connected by a gas flow path 108. The electrochemical reaction section 4 and the solar power generation device 5 are connected by a power transmission line 109.

[0022] Each of the above-mentioned flow paths is not particularly limited, and known piping or the like can be appropriately used. In the gas flow paths 101 and 108, air supply means such as a compressor, valves, measuring instruments such as a flow meter, etc. can be appropriately installed. Also, in the liquid flow paths 102, 103, 104, 105, 106, and 107, liquid supply means such as a pump, valves, measuring instruments such as a flow meter, etc. can be appropriately installed.

[0023] The CO2 recovery facility (Air Contacto) 1 recovers carbon dioxide in the atmosphere.

[0024] The absorption device 2 absorbs the carbon dioxide sent from the CO2 recovery facility 1. The CO2 absorption section 21 is supplied with a gas containing carbon dioxide such as air or exhaust gas. In the CO2 absorption section 21, the carbon dioxide gas in the gas comes into contact with the electrolytic solution, and the carbon dioxide is dissolved and absorbed in the electrolytic solution. The method of bringing the carbon dioxide gas into contact with the electrolytic solution is not particularly limited, and for example, a method of bubbling the gas into the electrolytic solution can be exemplified. The carbon dioxide recovered by the CO2 recovery facility 1 is sent to the CO2 absorption section 21 through the gas flow path 101.

[0025] In the CO2 absorption unit 21, an electrolytic solution composed of a strong alkaline aqueous solution is used as the absorption liquid for absorbing carbon dioxide. Since oxygen atoms strongly attract electrons, the carbon atom in carbon dioxide carries a positive charge (δ+). Therefore, in a strong alkaline aqueous solution with a large amount of hydroxide ions, carbon dioxide easily undergoes a dissolution reaction from the hydrated state to HCO3 - and proceeds to CO3 2- until the dissolution reaction readily progresses, reaching an equilibrium state with a high abundance ratio of CO3 2- . From this, carbon dioxide is more soluble in a strong alkaline aqueous solution compared to other gases such as nitrogen, hydrogen, and oxygen. In the CO2 absorption unit 21, carbon dioxide in the gas is selectively absorbed by the electrolytic solution. Thus, by using the electrolytic solution in the CO2 absorption unit 21, the concentration of carbon dioxide can be promoted.

[0026] The electrolytic solution in which carbon dioxide is absorbed in the CO2 absorption unit 21 is sent to the electrochemical reaction unit 4 through the liquid flow path 102 and the negative pressure chamber 31.

[0027] Examples of the strong alkaline aqueous solution used for the electrolytic solution include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution. Among them, an aqueous potassium hydroxide solution is preferably used from the viewpoint of excellent solubility of carbon dioxide in the CO2 absorption unit 21 and promotion of the reduction of carbon dioxide in the electrochemical reaction unit 4.

[0028] The electrochemical reaction unit 4 includes an electrolytic cell 41 as an electrolytic cell. The electrochemical reaction unit 4 electrochemically reduces carbon dioxide by means of the electrolytic cell 41. More specifically, in the reaction path where ethylene is the target product by the electrochemical reduction reaction of carbon dioxide, the electrochemical reaction unit 4 executes the reduction reaction of carbon dioxide to carbon monoxide. In FIG. 1, one electrolytic cell is shown, but preferably, the electrochemical reaction unit includes an electrolytic cell stack formed by laminating a plurality of electrolytic cells each including the electrolytic cell 41.

[0029] As shown in FIG. 1, the electrolytic cell 41 includes a cathode 411, an anode 412, an ion exchange membrane 413, a cathode-side liquid flow path structure 414 that forms a cathode-side liquid flow path, and an anode-side liquid flow path structure 415 that forms an anode-side liquid flow path.

[0030] In the electrolytic cell 41, the cathode-side liquid flow path structure 414, the cathode 411, the ion exchange membrane 413, the anode 412, and the anode-side liquid flow path structure 415 are laminated in this order. Also, a cathode-side liquid flow path is formed between the cathode 411 and the cathode-side liquid flow path structure 414, and an anode-side liquid flow path is formed between the anode 412 and the anode-side liquid flow path structure 415. These cathode-side liquid flow path and anode-side liquid flow path are provided at positions facing each other with the cathode 411, the ion exchange membrane 413, and the anode 412 interposed therebetween. It is preferable that a plurality of these cathode-side liquid flow paths and anode-side liquid flow paths are provided, and their shapes may be linear or zigzag. Further, a power supply body is provided on the surface of the cathode-side liquid flow path structure 414 opposite to the cathode 411. Furthermore, a power supply body is provided on the surface of the anode-side liquid flow path structure 415 opposite to the anode 412.

[0031] The power supply body is electrically connected to an electrical energy storage unit (not shown). Also, both the cathode-side liquid flow path structure 414 and the anode-side liquid flow path structure 415 are conductors, and a voltage can be applied between the cathode 411 and the anode 412 by the electric power supplied from the electrical energy storage unit.

[0032] The cathode 411 is an electrode that reduces carbon dioxide. More specifically, the cathode 411 of the electrolytic cell 41 mainly reduces carbon dioxide to carbon monoxide. However, a part of the generated carbon monoxide may be reduced to ethylene.

[0033] As the cathode 411, for example, an electrode including a gas diffusion layer and a cathode catalyst layer formed on the cathode-side liquid flow path side of the gas diffusion layer can be exemplified. A part of the cathode catalyst layer may be arranged to penetrate into the gas diffusion layer. Further, a porous layer denser than the gas diffusion layer may be arranged between the gas diffusion layer and the cathode catalyst layer.

[0034] As the cathode catalyst for forming the cathode catalyst layer, a known catalyst used for the reduction reaction 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, tin, etc., alloys and intermetallic compounds thereof, and metal complexes such as ruthenium complexes and rhenium complexes. Among them, silver, gold, and zinc are mentioned as cathode catalysts preferable for the reduction reaction from carbon dioxide to carbon monoxide. As the cathode catalyst, one kind may be used alone, or two or more kinds 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.

[0035] The gas diffusion layer of the cathode 411 is not particularly limited, and for example, carbon paper and carbon cloth can be exemplified. The manufacturing method of the cathode 411 is not particularly limited, and for example, a method of applying and drying a slurry of a liquid composition containing a cathode catalyst on the surface of the gas diffusion layer on the cathode-side liquid flow path side can be exemplified.

[0036] The anode 412 is an electrode that oxidizes hydroxide ions to generate oxygen. As the anode 412, for example, an electrode including a gas diffusion layer and an anode catalyst layer formed on the anode-side liquid flow path side of the gas diffusion layer can be exemplified. A part of the anode catalyst layer may be arranged to penetrate into the gas diffusion layer. Further, a porous layer denser than the gas diffusion layer may be arranged between the gas diffusion layer and the anode catalyst layer.

[0037] The anode catalyst for forming the anode catalyst layer is not particularly limited, and known anode catalysts can be used. Specifically, for example, metals such as platinum, palladium, and nickel, their alloys and 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, metal complexes such as ruthenium complexes and rhenium complexes can be exemplified. As the anode catalyst, one kind may be used alone, or two or more kinds may be used in combination.

[0038] Examples of the gas diffusion layer of the anode 412 include carbon paper and carbon cloth. Further, as the gas diffusion layer, a porous body such as a mesh material, a punching material, a porous body, or a sintered metal fiber body may be used. Examples of the material of the porous body include metals such as titanium, nickel, and iron, and their alloys (for example, SUS).

[0039] Examples of the material of the cathode side liquid flow path structure 414 and the anode side liquid flow path structure 415 include metals such as titanium and SUS, and carbon.

[0040] The negative pressure chamber 31 has a space for temporarily storing the electrolytic solution containing carbon dioxide sent through the CO2 absorption unit 21 liquid flow path 102. The decompression device 32 decompresses (negative pressure) the inside of the negative pressure chamber 31 to remove air components (nitrogen, oxygen) other than carbon dioxide contained in the electrolytic solution temporarily stored in the negative pressure chamber 31. As the decompression device 32, for example, a vacuum pump is used.

[0041] The solar power generation device 5 includes a solar cell that receives sunlight and generates electricity. The electric power obtained by the solar power generation device 5 is supplied for electrochemically reducing carbon dioxide to carbon monoxide in the electrolytic cell 41.

[0042] The gas-liquid separation unit 6 separates carbon monoxide from the electrolytic solution containing carbon monoxide generated in the electrolytic cell 41 of the electrochemical reaction unit 4 and recovers carbon monoxide.

[0043] The oxygen separation unit 7 separates oxygen from the electrolytic solution containing oxygen generated in the electrolytic cell 41 of the electrochemical reaction unit 4 and recovers the oxygen.

[0044] The reduction reaction of carbon dioxide by the electrolytic cell 41 will be described.

[0045] The electrolytic cell 41 is a flow cell into which the electrolytic solution supplied from the CO2 absorption unit 21 and sent through the liquid flow path 102, the negative pressure chamber 3, and the liquid flow path 103 flows into the cathode side liquid flow path. When a voltage is applied to the cathode 411 and the anode 412, the dissolved carbon dioxide in the electrolytic solution flowing through the cathode side liquid flow path is electrochemically reduced at the cathode 411. The electrolytic solution at the inlet of the cathode side liquid flow path is in a weakly alkaline state with a high abundance ratio of CO3 2- Since carbon dioxide is dissolved, it is in a weakly alkaline state with a high abundance ratio of CO3. On the other hand, as the reduction progresses while flowing through the cathode side liquid flow path, the amount of dissolved carbon dioxide, that is, the amount of CO3 2- in the electrolytic solution decreases, so that the electrolytic solution at the outlet of the cathode side liquid flow path becomes a strongly alkaline electrolytic solution.

[0046] As described above, at the cathode 411 of the electrolytic cell 41, the product generated by the reduction of carbon dioxide is mainly carbon monoxide. Specifically, at the cathode 411, carbon monoxide is generated as a gaseous product by the progress of the reaction represented by the following cathode half-reaction formula. The generated gaseous carbon monoxide flows out from the outlet of the cathode side liquid flow path. [Cathode half-reaction formula] 2CO3 2- + 4H2O → 2CO + 8OH -

[0047] The hydroxide ions generated at the cathode 411 of the electrolytic cell 41 permeate the ion exchange membrane 413 and move to the anode 412, where they are oxidized in the reaction represented by the following anode half-reaction formula to generate oxygen. The generated oxygen permeates the gas diffusion layer of the anode 412 and flows into the anode side liquid flow path, and flows out from the outlet of the anode side liquid flow path. [Anode half-reaction formula] 4OH -→O2 + 2H2O

[0048] Therefore, in the electrolysis cell 41, as a whole, the reaction represented by the following overall reaction formula proceeds. [Overall reaction formula] 2CO3 2- + 2H2O → 2CO + O2 + 4OH -

[0049] Thus, in the carbon dioxide treatment apparatus 100 of the present embodiment, the electrolytic solution used in the electrochemical reaction unit 4 is shared as the absorption liquid of the CO2 absorption unit 21, and carbon dioxide is supplied to the electrochemical reaction unit 4 while dissolved in the electrolytic solution and electrochemically reduced. As a result, for example, compared with the case where carbon dioxide is adsorbed by an adsorbent and desorbed by heating for reduction, the energy required for desorption of carbon dioxide is reduced, and the energy efficiency can be increased.

[0050] Here, as described above, since carbon dioxide is dissolved in the electrolytic solution at the inlet of the cathode-side liquid flow path, the ratio of the presence of CO3 2- is high and it is in a relatively weakly alkaline state. On the other hand, in the reduction reaction of carbon dioxide, since the selective production reaction of ethylene hardly proceeds under weak alkalinity, there is a problem that the production efficiency of the target ethylene is poor. For this reason, as described above, the gas flowing out from the outlet of the cathode-side liquid flow path of the electrolysis cell 41 is mainly carbon monoxide.

[0051] On the other hand, in the carbon dioxide treatment apparatus 100 of the present embodiment, the gas mainly composed of carbon monoxide flowing out from the outlet of the cathode-side liquid flow path of the electrolysis cell 41 is recovered by the gas-liquid separation unit 6. The recovered gas mainly composed of carbon monoxide is supplied for the production of ethylene.

[0052] According to the carbon dioxide treatment apparatus of the present embodiment, since the removal device 3 for removing the air components from the electrolytic solution containing carbon dioxide absorbed by the absorption device 2 is provided, the reaction efficiency when electrochemically reducing carbon dioxide can be improved. Further, since the solar power generation device 5 for supplying power to the electrochemical reaction unit is provided, the solar power generation device 5 can supply the power required for the electrochemical reduction of carbon dioxide in the electrolytic cell 41 during the day, and as a result, the energy consumption when recovering carbon dioxide can be reduced.

[0053] [Carbon Dioxide Treatment Method] The carbon dioxide treatment method according to the embodiment of the present invention is, for example, executed by using the above-described carbon dioxide treatment apparatus 100. Specifically, the carbon dioxide treatment method of the present embodiment includes a step (a) of constantly recovering carbon dioxide using the power transmitted from the power plant including the night power by the CO2 recovery facility 1, a step (b) of bringing carbon dioxide gas into contact with an electrolytic solution composed of a strong alkaline aqueous solution in the CO2 absorption unit 21 and dissolving and absorbing the carbon dioxide in the electrolytic solution, a step (c) of removing the air components contained in the electrolytic solution containing carbon dioxide absorbed by the CO2 absorption unit 21 by the removal device 3, and a step (d) of electrochemically reducing carbon dioxide to carbon monoxide by the electrolytic cell 41 using the daytime power and the power generated by the solar power generation device 5. The carbon dioxide treatment method of the present embodiment can be used in a method for producing ethylene.

[0054] Note that the present invention is not limited to the above-described aspects, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

Explanation of Reference Numerals

[0055] 1 CO2 recovery facility 2 Absorption device 3 Removal device 4 Electrochemical reaction unit 5 Solar power generation device 6 Gas-liquid separation unit 7 Oxygen separation unit 5 Second gas-liquid separation unit 21 CO2 absorption unit 31 Negative pressure chamber 32 Pressure reducing device 41 Electrolytic cell 100 Carbon dioxide treatment device

Claims

1. An absorption device for absorbing carbon dioxide, a removal device for removing nitrogen and oxygen from an electrolytic solution containing carbon dioxide absorbed by the absorption device, an electrochemical reaction section having an electrolytic cell for electrochemically reducing the carbon dioxide absorbed by the absorption device to carbon monoxide, a solar power generation device for supplying power to the electrochemical reaction section, and a gas-liquid separation section for separating carbon monoxide from the electrolytic solution containing carbon monoxide generated in the electrolytic cell of the electrochemical reaction section and recovering carbon monoxide. A carbon dioxide treatment device, wherein the gas mainly composed of carbon monoxide recovered by the gas-liquid separation section is supplied for the production of ethylene, and the electrolytic solution separated from the gas mainly composed of carbon monoxide by the gas-liquid separation section is returned to the absorption device.

2. The absorption device includes a carbon dioxide absorption section for dissolving and absorbing carbon dioxide in a strongly alkaline electrolytic solution. The carbon dioxide treatment device according to claim 1, wherein carbon dioxide dissolved in the electrolytic solution by the carbon dioxide absorption section is supplied to the electrochemical reaction section.

3. The electrolytic cell includes a cathode, an anode, an ion exchange membrane provided between the cathode and the anode, a cathode-side liquid flow path provided adjacent to the cathode through which an electrolytic solution in which carbon dioxide is dissolved flows, and an anode-side liquid flow path provided adjacent to the anode through which an electrolytic solution flows. The carbon dioxide treatment device according to claim 1.

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