Carbon dioxide reduction system

Abstract

A carbon dioxide reduction system 1 comprises an oxidation tank 101 including an oxidation electrode 102, a reduction tank 104 which is adjacent to the oxidation tank 101 and to which impurity-containing carbon dioxide is supplied, and an electrolyte membrane 106 disposed between the oxidation tank 101 and the reduction tank 104. A reduction electrode 105 is layered on the reduction-tank 104 side of the electrolyte membrane 106. The reduction electrode 105 is provided with a carbon dioxide reduction device 10 that is connected to the oxidation electrode 102 by an electroconductive wire and performs a reduction reaction with carbon dioxide by using a current flowing through the electroconductive wire, and a poisoning recovery device 20 for removing impurities adhering to the metal surface of the reduction electrode 105.

Description

Carbon Dioxide Reduction System

[0001] The present disclosure relates to carbon dioxide reduction systems.

[0002] The carbon dioxide reduction device used in artificial photosynthesis technology is composed of an oxidation electrode, a reduction electrode, an electrolyte, and an electrolyte membrane (see Patent Document 1). An inert gas such as helium is flowed into an oxidation tank containing an oxidation electrode, and carbon dioxide is flowed into a reduction tank containing a reduction electrode.

[0003] When light is irradiated onto the oxidation electrode, electron-hole pairs are generated and separated at the oxidation electrode, resulting in the oxidation reaction of water, which generates oxygen and protons. At the reduction electrode, protons and electrons combine to generate hydrogen. The protons, electrons, and carbon dioxide then combine to produce a reduction reaction of carbon dioxide.

[0004] In recent years, attention has been focused on a gas phase reduction method aimed at improving the efficiency of the carbon dioxide reduction reaction at a reduction electrode (see Patent Document 2).

[0005] International Publication No. 2022 / 113277 International Publication No. 2020 / 121556

[0006] In such a carbon dioxide reduction device, it is conceivable that exhaust gas containing carbon dioxide is introduced into the reduction tank.

[0007] Generally, exhaust gas mainly contains nitrogen, oxygen, carbon dioxide, carbon monoxide, methane, numerous hydrocarbon compounds, and other ionic components. When a reaction gas containing many impurities is supplied to a carbon dioxide reduction device as a carbon dioxide source, the impurities may be adsorbed onto the metal surface of the reduction electrode, resulting in poisoning that reduces reaction activity.

[0008] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a technology that can suppress a decrease in reaction activity in a carbon dioxide reduction device that is supplied with carbon dioxide containing impurities.

[0009] A carbon dioxide reduction system according to one aspect of the present disclosure comprises an oxidation tank including an oxidation electrode, a reduction tank adjacent to the oxidation tank and supplied with carbon dioxide containing impurities, and an electrolyte membrane arranged between the oxidation tank and the reduction tank, wherein the electrolyte membrane has a reduction electrode stacked on the reduction tank side, and the reduction electrode is connected to the oxidation electrode by a conductor, and the carbon dioxide reduction system comprises a carbon dioxide reduction device that performs a reduction reaction with the carbon dioxide by a current flowing through the conductor, and further comprises a poisoning recovery device that removes the impurities adhering to the metal surface of the reduction electrode.

[0010] According to the present disclosure, it is possible to provide a technology capable of suppressing a decrease in reaction activity in a carbon dioxide reduction device to which carbon dioxide containing impurities is supplied.

[0011] Fig. 1 is a diagram illustrating the system configuration of a carbon dioxide reduction system according to the present disclosure. Fig. 2 is a diagram illustrating a carbon dioxide reduction system according to a first embodiment. Fig. 3 is a diagram illustrating a carbon dioxide reduction system according to a second embodiment. Fig. 4 is a diagram illustrating a carbon dioxide reduction system according to a third embodiment. Fig. 5 is a flowchart illustrating an example of the operation of a poisoning recovery device of a carbon dioxide reduction system.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0013] (Carbon Dioxide Reduction System) As shown in FIG. 1 , a carbon dioxide reduction system 1 according to the present disclosure includes a carbon dioxide reduction device 10, a poisoning recovery device 20, and a reactive gas generation device 30.

[0014] The carbon dioxide reduction device 10 irradiates the oxidation electrode 102 with light, causing a carbon dioxide reduction reaction at the reduction electrode 105. The carbon dioxide reduction device 10 will be described in detail later.

[0015] The poisoning recovery device 20 is a means for removing impurities attached to the reduction electrode 105. When the amount of product produced in the carbon dioxide reduction device 10 decreases, the poisoning recovery device 20 removes impurities attached to the metal surface of the reduction electrode 105 of the carbon dioxide reduction device 10 to recover from poisoning. There is concern that impurities attached to the metal surface of the reduction electrode 105 may cause poisoning, which reduces reaction activity. By removing impurities, the poisoning recovery device 20 can recover the reduced reaction activity in the carbon dioxide reduction device 10.

[0016] The reactive gas generator 30 generates a reactive gas such as an exhaust gas. The reactive gas is carbon dioxide containing impurities. The reactive gas generator 30 may be a gas cylinder filled with the reactive gas, or may be a device that discharges the reactive gas as an exhaust gas. The reactive gas generator 30 supplies the generated reactive gas to the carbon dioxide reduction device 10.

[0017] In the carbon dioxide reduction system 1 according to the present disclosure, the poisoning recovery device 20 has at least one of the configurations of Examples 1 to 3.

[0018] First Example A carbon dioxide reduction system 1a according to a first example will be described with reference to Fig. 2. In the first example, the poisoning recovery device 20 applies an inert gas to the reduction electrode 105.

[0019] The carbon dioxide reduction system 1a includes a carbon dioxide reduction device 10, an aerotube 21, a temperature and pressure adjusting device 22, a gas cylinder 23, and a reactive gas generating device 30. The poisoning recovery device 20 according to the first embodiment includes the aerotube 21, the temperature and pressure adjusting device 22, and the gas cylinder 23.

[0020] The carbon dioxide reduction device 10 includes an oxidation tank 101 , a reduction tank 104 , a light source 110 , and a measurement device 141 .

[0021] The oxidation basin 101 includes an oxidation electrode 102 and an aqueous solution 103. The oxidation basin 101 is a liquid phase basin filled with the aqueous solution 103. A window 101a made of a material that transmits light emitted by the light source 110 is provided on the wall of the oxidation basin 101.

[0022] The oxidation electrode 102 is a semiconductor photocatalyst that exhibits photoactivity or redox activity, such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex. The oxidation electrode 102 is immersed in an aqueous solution 103. The aqueous solution 103 is an aqueous solution of an alkali metal hydroxide compound, such as a sodium hydroxide solution, a potassium hydroxide solution, a potassium bicarbonate solution, a sodium bicarbonate solution, a potassium chloride solution, or a sodium chloride solution.

[0023] A carrier gas is supplied to the oxidation vessel 101 from a carrier gas generator 121 via a pipe. The carrier gas is an inert gas such as nitrogen or helium.

[0024] The reduction tank 104 includes a reduction electrode 105 and an electrolyte membrane 106. The reduction tank 104 is adjacent to the oxidation tank 101 via the electrolyte membrane 106. The reduction tank 104 is a gas phase tank filled with carbon dioxide containing impurities, which is supplied from the reactive gas generator 30.

[0025] The reduction electrode 105 is copper, platinum, gold, indium, tungsten (VI) oxide, copper (II) oxide, or a porous metal complex having metal ions and anionic ligands.

[0026] The electrolyte membrane 106 is a Nafion (registered trademark) membrane or the like. The electrolyte membrane 106 is disposed between the oxidation chamber 101 and the reduction chamber 104. The reduction electrode 105 is laminated on the electrolyte membrane 106 on the reduction chamber 104 side.

[0027] The light source 110 irradiates the oxidation electrode 102 with light through a window 101a provided in the wall of the oxidation tank 101. The light source 110 may be an optical device or a source of natural light.

[0028] The reactive gas generator 30 supplies a reactive gas such as carbon dioxide containing impurities to the reduction tank 104 via a pipe.

[0029] The measuring device 141 measures the product of the oxidation-reduction reaction in the carbon dioxide reduction device 10 and quantitatively evaluates the amount of production. The measuring device 141 is, for example, a gas chromatograph. When the product is a liquid, the measuring device 141 is, for example, a liquid chromatograph.

[0030] In this carbon dioxide reduction device 10, the reduction electrode 105 is connected to the oxidation electrode 102 by a conductor, and undergoes a reduction reaction with carbon dioxide due to the current flowing through the conductor. Using holes and electrons generated by irradiating the oxidation electrode 102 with light from the light source 110, oxygen is produced by a water oxidation reaction in the oxidation tank 101, and hydrogen is produced by a proton reduction reaction in the reduction tank 104. Carbon monoxide, methane, ethylene, methanol, ethanol, formic acid, etc. are produced by this carbon dioxide reduction reaction.

[0031] In the present disclosure, when the amount of production measured by the measuring device 141 exceeds a predetermined threshold, the carbon dioxide reduction system 1 controls the poisoning recovery device 20 to operate.

[0032] In the first embodiment, the poisoning recovery device 20 applies an inert gas to the reduction electrode 105 using an aerotube 21 or the like. In the carbon dioxide reduction system 1a shown in FIG. 2, a gas cylinder 23 is filled with an inert gas. The inert gas is applied to the reduction electrode by the aerotube 21. This method is suitable when impurities are physically attached to the surface of the reduction electrode 105.

[0033] When a decrease in the production amount is detected, the poisoning recovery device 20 stops the supply of the reaction gas containing impurities. When the poisoning recovery device 20 uses an aerotube 21 to blow an inert gas onto the reduction electrode 105, impurities on the surface of the reduction electrode 105 are removed. The flow rate of the inert gas blown onto the reduction electrode 105 may be adjusted by a temperature and pressure adjustment device 22.

[0034] For example, when a decrease in the production amount is detected, the poisoning recovery device 20 switches the gas supplied to the reduction tank 104 from the reactive gas, specifically carbon dioxide containing impurities, to the inert gas filled in the gas cylinder 23. The poisoning recovery device 20 increases the flow rate of the inert gas using the temperature and pressure adjustment device 22, and supplies the inert gas to the reduction tank 104 for a certain period of time.

[0035] When using the aerotube 21 , it is preferable to apply an inert gas to the vicinity of the surface of the reduction electrode 105 at a pressure within the range allowed by the strength of the electrolyte membrane 106 .

[0036] Second Example A carbon dioxide reduction system 1b according to a second example will be described with reference to Fig. 3. In the second example, the poisoning recovery device 20 is a heating device 24 or a valve such as a pressure reducing valve or an automatic valve that can reduce the flow rate of the reaction gas. The poisoning recovery device 20 heats or reduces the pressure inside the reduction tank 104. The poisoning recovery device 20 releases the bond between the metal surface of the reduction electrode 105 and the impurities by heating or reducing the pressure inside the reduction tank 104. This method is suitable when the impurities are physically adsorbed to the surface of the reduction electrode 105 due to an interaction between the impurities and the reduction electrode 105.

[0037] In the second embodiment, the poisoning recovery device 20 heats the inside of the reduction tank 104 in order to break the bonds between the metal surface of the reduction electrode 105 and impurities that have been formed by van der Waals forces. The poisoning recovery device 20 is, for example, a heating device 24 that heats the gas to be supplied to the reduction tank 104. The heating device 24 raises the temperature of the gas to be supplied to the reduction tank 104 within a range not exceeding the temperature resistance of the electrolyte membrane 106, and supplies the gas for a certain period of time. The maximum temperature at which the electrolyte membrane 106 can be used is generally 70-80°C.

[0038] Alternatively, the poisoning recovery device 20 reduces the pressure in the reduction tank 104 for a certain period of time within a range not exceeding the mechanical strength of the electrolyte membrane 106. For example, the flow rate of the reactant gas into the reduction tank 104 is reduced by adjusting a pressure reducing valve, an automatic valve, or the like that can reduce the flow rate of the reactant gas, thereby reducing the pressure in the reduction tank 104.

[0039] The poisoning recovery device 20 may perform either one of heating and depressurizing the reduction tank 104, or may perform both. When both heating and depressurizing are performed, the order of these operations does not matter.

[0040] (Third Example) A carbon dioxide reduction system 1c according to a third example will be described with reference to Fig. 4. In the third example, the poisoning recovery device 20 oxidatively decomposes impurities adhering to the metal surface of the reduction electrode 105. This method is suitable for the case where the impurities are chemically adsorbed to the surface of the reduction electrode 105 due to chemical bonds acting between the impurities and the reduction electrode 105.

[0041] The poisoning recovery device 20 oxidizes and decomposes the impurities chemically adsorbed on the surface of the reduction electrode 105 by manipulating the potential, etc. As a result, the impurities are detached and removed from the surface of the reduction electrode 105.

[0042] In the third embodiment, the poisoning recovery device 20 is, for example, an electrochemical measurement device 25. The electrochemical measurement device 25 is connected to a conductor connecting the oxidation electrode 102 and the reduction electrode 105, and applies a voltage. By changing the potential difference between the oxidation electrode 102 and the reduction electrode 105, impurities are oxidized and released.

[0043] 2, the poisoning recovery device 20 fills a gas cylinder 23, which supplies gas to the reduction tank 104, with a highly oxidizing gas such as ozone. By supplying the highly oxidizing gas to the reduction tank 104, impurities attached to the reduction electrode 105 are oxidized and desorbed.

[0044] (Example) The carbon dioxide reduction system 1 according to the present disclosure may implement only one of the functions of the poisoning recovery device 20 described in the first to third examples, or may implement two or three of the functions.

[0045] When multiple functions are implemented, the poisoning recovery device 20 executes each function in order of weakest interaction, where the weakest interaction is the first embodiment, followed by the second and third embodiments, in that order.

[0046] In a case where the three functions are implemented, when the reaction activity of the carbon dioxide reduction device 10 becomes equal to or lower than the threshold, the poisoning recovery device 20 applies an inert gas to the reduction electrode 105, as will be described in the first embodiment. If the reaction activity is equal to or lower than the threshold after applying the inert gas, the poisoning recovery device 20 heats or reduces the pressure inside the reduction tank 104, as will be described in the second embodiment. If the reaction activity is equal to or lower than the threshold after heating or reducing the pressure inside the reduction tank 104, the poisoning recovery device 20 oxidizes and decomposes impurities adhering to the metal surface of the reduction electrode 105, as will be described in the third embodiment.

[0047] The process of the poison recovery device 20 will be described with reference to FIG.

[0048] When the poisoning recovery device 20 detects a decrease in reaction efficiency in step S1, the process proceeds to step S2. The decrease in reaction efficiency means that the amount of product produced measured by the measuring device 141 falls below a predetermined threshold.

[0049] In step S2, the poisoning recovery device 20 stops the supply of reactive gas to the reduction tank 104 and starts supplying inert gas. After a predetermined time has elapsed, in step S3, the poisoning recovery device 20 determines whether the decrease in reaction efficiency has been resolved. If the decrease has been resolved, the process ends.

[0050] If the decrease in reaction efficiency continues, in step S4, the poisoning recovery device 20 heats or depressurizes the inside of the reduction tank 104. After a predetermined time has elapsed, in step S5, the poisoning recovery device 20 determines whether the decrease in reaction efficiency has been resolved. If the decrease in reaction efficiency has been resolved, the process ends.

[0051] If the decrease in reaction efficiency continues, in step S6, the poisoning recovery device 20 oxidatively decomposes the impurities and ends the process. Here, the poisoning recovery device 20 may confirm that the decrease in reaction efficiency has been resolved, specifically, that the amount of product produced measured by the measurement device 141 has exceeded a predetermined threshold. When the decrease in reaction efficiency has been resolved, the carbon dioxide reduction system 1 resumes the oxidation-reduction reaction by the carbon dioxide reduction device 10.

[0052] According to the method shown in FIG. 5, recovery from poisoning is attempted in order of decreasing interaction, so that the carbon dioxide reduction device 10 is not significantly affected and the poisoning can be recovered efficiently.

[0053] The carbon dioxide reduction system 1 according to the present disclosure can suppress a decrease in reaction activity in a carbon dioxide reduction device to which carbon dioxide containing impurities is supplied, which is expected to improve the durability of the carbon dioxide reduction system 1.

[0054] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0055] REFERENCE SIGNS LIST 1 Carbon dioxide reduction system 10 Carbon dioxide reduction device 20 Poisoning recovery device 21 Aerotube 22 Temperature and pressure adjustment device 23 Gas cylinder 25 Electrochemical measurement device 30 Reaction gas generator 101 Oxidation tank 101a Window 102 Oxidation electrode 103 Aqueous solution 104 Reduction tank 105 Reduction electrode 106 Electrolyte membrane 110 Light source 121 Carrier gas generation unit 141 Measuring device

Claims

1. A carbon dioxide reduction system comprising: an oxidation vessel including an oxidation electrode; a reduction vessel adjacent to the oxidation vessel and supplied with carbon dioxide containing impurities; and an electrolyte membrane arranged between the oxidation vessel and the reduction vessel, wherein the electrolyte membrane has a reduction electrode laminated on the reduction vessel side, the reduction electrode being connected to the oxidation electrode by a conductor, and comprising a carbon dioxide reduction device that performs a reduction reaction with the carbon dioxide by a current flowing through the conductor; and a poisoning recovery device that removes the impurities adhering to the metal surface of the reduction electrode.

2. The carbon dioxide reduction system according to claim 1, wherein the poisoning recovery device applies an inert gas to the reduction electrode.

3. The carbon dioxide reduction system according to claim 1, wherein the poisoning recovery device heats or depressurizes the inside of the reduction tank.

4. The carbon dioxide reduction system according to claim 1, wherein the poisoning recovery device oxidizes and decomposes the impurities.

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