Method for reducing carbon dioxide

Abstract

A voltage is applied, in a hydrothermal reaction field having a temperature within the range of 100-300°C and a pressure within the range of 10-50 MPa, to a reaction liquid in which at least carbon dioxide is dissolved in water, whereby the carbon dioxide is reduced.

Description

Carbon dioxide reduction method

[0001] The present invention relates to a method for reducing carbon dioxide in a hydrothermal reaction field. This application claims priority to Japanese Patent Application No. 2024-082226, filed on May 20, 2024, the contents of which are incorporated herein by reference.

[0002] Currently, carbon dioxide (CO ) is considered to be the cause of climate change worldwide. ２ Zero emissions, which essentially eliminates CO emissions, are being promoted. ２ It has been proposed to reductively decompose CO ２ It is disclosed that carbon monoxide (CO) is produced by electrochemically reducing

[0003] Ma, Sichao, and Paul JA Kenis. "Electrochemical conversion of CO2 to useful chemicals: current status, remaining challenges, and future opportunities." Current Opinion in Chemical Engineering 2, no. 2 (2013): 191-199.

[0004] However, conventionally known CO ２ The electrochemical reduction decomposition of CO has had the problem of low energy efficiency. Specifically, the formation of the reaction intermediate, i.e., the excited state, requires a large amount of energy, and the CO relative to water ２ This is believed to be due to the low solubility and diffusion coefficient of , which requires a large amount of energy to resolve.

[0005] The present invention has been proposed in view of the above-mentioned problems, and has an object to provide a method for reducing carbon dioxide that can efficiently reduce carbon dioxide with a simple configuration.

[0006] In order to solve the above problems, a method for reducing carbon dioxide according to one embodiment of the present invention proposes the following means: (1) A method for reducing carbon dioxide according to aspect 1 of the present invention reduces carbon dioxide by applying a voltage to a reaction solution in which at least carbon dioxide is dissolved in water in a hydrothermal reaction field at a temperature in the range of 100°C to 300°C and a pressure in the range of 10 MPa to 50 MPa.

[0007] (2) Aspect 2 of the present invention is the method for reducing carbon dioxide according to Aspect 1, wherein the electrodes for applying the voltage to the reaction solution are made of a conductive porous material.

[0008] (3) Aspect 3 of the present invention is the method for reducing carbon dioxide according to aspect 2, wherein the porous material has a nanoporous structure having nano-sized cavities.

[0009] (4) A fourth aspect of the present invention is the method for reducing carbon dioxide according to the second aspect, wherein the average pore diameter of the porous material is in the range of 1 nm or more and 1000 nm or less.

[0010] (5) Aspect 5 of the present invention is the method for reducing carbon dioxide according to any one of aspects 1 to 4, wherein the voltage is in the range of 1 V or more and 6 V or less.

[0011] (6) A sixth aspect of the present invention is the method for reducing carbon dioxide according to any one of the first to fifth aspects, wherein carbon monoxide is produced by reducing the carbon dioxide.

[0012] According to the present invention, CO ２ It is therefore possible to provide a method for reducing carbon dioxide that can efficiently reduce carbon dioxide with a simple configuration.

[0013] 1 is a schematic diagram showing a reduction device used in a carbon dioxide reduction method according to an embodiment of the present invention. ２ 1 is a graph showing the change in current density corresponding to the change in temperature of the dissolved water. ２ 1 is a graph showing the solubility of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,

[0014] Hereinafter, a carbon dioxide reduction method according to one embodiment of the present invention will be described with reference to the drawings. Note that the embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0015] In the following embodiments, when the term "nano-size" is used without any particular numerical range limitation, it refers to a range of 1 nm to 1000 nm.

[0016] (Carbon dioxide reduction device) First, a configuration example of a carbon dioxide reduction device suitable for the carbon dioxide reduction method of one embodiment of the present invention will be described. Fig. 1 is a schematic configuration diagram showing an example of a carbon dioxide reduction device used in the carbon dioxide reduction method of one embodiment of the present invention.

[0017] The carbon dioxide reduction device 10 used in the carbon dioxide reduction method of this embodiment includes a dissolution tank 11, an electrolysis tank 12, a water supply source 13 and a carbon dioxide supply source 14 connected to the dissolution tank 11, a pressure gauge 15 and a thermometer 16 connected to the dissolution tank 11, and a heating device 17 provided in the dissolution tank 11.

[0018] The dissolution tank 11 receives CO 2 supplied from a carbon dioxide supply source 14 via a pump 24. ２ The gas is mixed with water (H ２ The pressure-resistant water tank may be, for example, a metal pressure vessel.

[0019] Inside the dissolution tank 11, CO ２ In order to increase the solubility of the gas, the pressure is increased by the pump 24 to a range of 10 MPa to 50 MPa, in this embodiment to 10 MPa. The pressure is also increased by the heating device 17 to a range of 100°C to 300°C, in this embodiment to 150°C. By this pressure and heating, the CO ２The gas solubility can be increased to a maximum of about 7.5 (mol / kg).

[0020] The electrolytic cell 12 is connected to the dissolution tank 11 by a pressure pipe. The electrolytic cell 12 is made up of a pressure-resistant water tank, just like the dissolution tank 11, and is used to purify high-temperature, high-pressure CO 2 supplied from the dissolution tank 11. ２ Dissolved water, for example, CO with a liquid pressure of 10 MPa and a liquid temperature of 150°C ２ Dissolved water is stored.

[0021] A partition wall 21 is formed inside the electrolytic cell 12, dividing the internal space of the electrolytic cell 12 into two regions E1 and E2. The partition wall 21 prevents the generated gas from moving between the regions. The partition wall 21 is made of, for example, a ceramic plate or H ＋ The membrane may be made of a proton exchange membrane or the like that selectively allows the passage of

[0022] A cathode electrode 22 is formed in the region E1 of the electrolytic cell 12. An anode electrode 23 is formed in the region E2 of the electrolytic cell 12.

[0023] The cathode electrode 22 is made of a conductor such as a metal. In particular, an Au electrode is preferable from the viewpoint of corrosion resistance. When an Au electrode is used as the cathode electrode 22, a plate-shaped electrode or an electrode with a porous structure can be used.

[0024] In this embodiment, a nanoporous Au electrode having numerous nano-sized cavities is used as the cathode electrode 22. The use of such a nanoporous Au electrode significantly increases the surface area compared to a plate-shaped Au electrode, and the current density can be improved by several times or more.

[0025] The anode electrode 23 is made of a conductor such as a metal. In particular, from the viewpoint of corrosion resistance, Pt, IrO ２ As the anode electrode 23, a plate-shaped electrode or an electrode having a porous structure can be used, similar to the cathode electrode 22.

[0026] The gas-liquid separator 24a separates, for example, CO gas and H generated in the region E1 (cathode electrode 22 side) of the electrolytic cell 12. ２The gas-liquid separation means 24b may be configured with a filter device or the like that separates gas and water. ２ It may be configured with a filter device that separates gas from water.

[0027] The carbon dioxide reduction device 10 configured as described above uses high-temperature, high-pressure CO supplied from the dissolution tank 11. ２ In a hydrothermal reaction field formed inside the electrolytic cell 12 using dissolved water, a reduction voltage of, for example, 1 V or more and 6 V or less is applied between the cathode electrode 22 and the anode electrode 23, thereby efficiently generating CO ２ is reduced to CO and H ２ can be obtained.

[0028] In this embodiment, CO ２ CO is shown as an example of the reduction product of ２ The reduction products of CO vary depending on the shape of the cathode electrode 22. For example, when a nanoporous Au electrode is used, CO ２ As a reduction product of CO, formic acid (CH ３ Therefore, in the present invention, CO ２ The reduction product of is not limited to CO.

[0029] (Method for reducing carbon dioxide) A method for reducing carbon dioxide according to this embodiment using the carbon dioxide reduction device described above will be described. ２ When reducing, for example, high-temperature, high-pressure CO 2 in the electrolytic cell 12 is used, for example, with a liquid pressure in the range of 10 MPa to 50 MPa and a liquid temperature in the range of 100°C to 300°C. ２ Dissolved water (CO at a liquid pressure of 10 MPa and a liquid temperature of 150°C) ２ CO in dissolved water ２ A hydrothermal reaction field is formed by storing CO ２ A reduction voltage in the range of, for example, 1 V or more and 6 V or less is applied to the dissolution water.

[0030] As a result, the following reactions (1) and (2) occur at the cathode electrode 22: ２+2H ＋ +2e － →CO+H ２ O...(1) 2H ＋ +2e － →H ２ ...(2) Due to this reaction, CO gas and H ２ Gas is generated.

[0031] At the anode electrode 23, the following reaction (3) occurs: ２ O → 1 / 2O ２ +2H ＋ +2e － ...(3) Due to this reaction, O ２ Gas is generated.

[0032] In such a hydrothermal reaction field, CO ２ It is preferable to use an electrode with a porous structure as the cathode electrode 22 used in the reduction reaction of CO. In particular, if a nanoporous Au electrode with excellent corrosion resistance and a large number of nano-sized cavities is used as the cathode electrode 22, the current density can be greatly improved and the CO ２ The reduction reaction (see reaction formula (1) above) can be efficiently carried out.

[0033] Thereafter, CO gas and H gas generated at the cathode electrode 22 and the anode electrode 23 ２ Gas, O ２ If the gas is separated from the water by the gas-liquid separation means 24a and 24b, the greenhouse gas CO ２ From the gas, CO gas, which is useful as a raw material for various organic materials, and H gas, which is useful as a fuel for power generation, etc. ２ Gas, O ２ Gases and other substances can be generated efficiently and at low cost.

[0034] As described above, according to the carbon dioxide reduction method of the present embodiment, CO 2 , which has low solubility in water at room temperature and normal pressure, can be reduced. ２ High concentration CO gas is dissolved in water at high temperature and pressure. ２ Dissolved water can form. And at these high concentrations of CO ２ A hydrothermal reaction field is formed using dissolved water, and a reduction voltage is applied to generate CO ２By reducing CO ２ and industrially useful CO gas, H ２ Gas, O ２ Gas can be obtained.

[0035] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims.

[0036] Below is the actual CO ２ A hydrothermal reaction field is formed using dissolved water, and CO ２ First, we investigated the characteristics of CO reduction at a liquid pressure of 10 MPa. ２ The dissolution water was heated to liquid temperatures of 50°C, 100°C, 150°C, and 200°C, and the reduction voltage was changed from 0 V to 4 V, and the change in current density was measured. The results are shown in the graph in Figure 2.

[0037] 2, it was confirmed that the current density increases as the liquid temperature and voltage increase. In other words, it was confirmed that if the liquid temperature is increased under a high-pressure environment, such as a liquid pressure of 10 MPa, the reaction rate can be increased even at a low reduction voltage.

[0038] For reference, the CO2 emissions when the liquid pressure is increased stepwise from 0 to 50 MPa for water at temperatures of 25°C, 100°C, 200°C, and 250°C are ２ The change in the solubility of CO is shown in the graph in Figure 3. According to Figure 3, by simply increasing the liquid pressure to about 3 MPa, the solubility of CO ２ It can be seen that the solubility of

[0039] Next, gold was used as the cathode material to fabricate a flat Au plate electrode and a nanoporous Au electrode with numerous nano-sized cavities. Figure 4 shows a schematic diagram and SEM photographs of the nanoporous Au electrode. The current density was measured using each of these Au electrodes as the reduction voltage was varied from 0 V to 4 V. The results are shown in the graph of Figure 5.

[0040] According to the results shown in Figure 5, it was confirmed that by applying a nanostructure to the electrode, in a hydrothermal reaction field with excellent material transport, the increased surface area resulted in a current density more than twice that of a plate Au electrode, for example, at a reduction voltage of 4 V.

[0041] The carbon dioxide reduction method of the present invention is characterized by the fact that CO 2 has low solubility in water at room temperature and atmospheric pressure. ２ High concentration CO gas is dissolved in water at high temperature and pressure. ２ By forming a hydrothermal reaction field using dissolved water and applying a reduction voltage to it, CO can be produced efficiently at low cost. ２ Therefore, CO ２ This method efficiently reduces CO2 emissions at low cost, contributing to the achievement of zero emissions. Therefore, it has industrial applicability.

[0042] REFERENCE SIGNS LIST 10 Carbon dioxide reduction device 11 Dissolution tank 12 Electrolytic cell 13 Water supply source 14 Carbon dioxide supply source 15 Pressure gauge 16 Thermometer 17 Heating device 24a, 24b Gas-liquid separation means 22 Cathode electrode 23 Anode electrode

Claims

1. A method for reducing carbon dioxide, in which a voltage is applied to a reaction solution in which at least carbon dioxide is dissolved in water in a hydrothermal reaction field at a temperature in the range of 100°C to 300°C and a pressure in the range of 10 MPa to 50 MPa, thereby reducing the carbon dioxide.

2. The method for reducing carbon dioxide according to claim 1, wherein the electrodes for applying the voltage to the reaction solution are made of a conductive porous material.

3. The method for reducing carbon dioxide according to claim 2, wherein the porous material has a nanoporous structure having nano-sized cavities.

4. The method for reducing carbon dioxide according to claim 2, wherein the average pore diameter of the porous material is in the range of 1 nm to 1000 nm.

5. A method for reducing carbon dioxide according to claim 1 or 2, wherein the voltage is in the range of 1 V or more and 6 V or less.

6. A method for reducing carbon dioxide according to claim 1 or 2, wherein carbon dioxide is reduced to produce carbon monoxide.

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