Methods used to recover fluorine from fuel cells

Abstract

This technology provides a method for recovering fluorine contained in fuel cells according to the purpose of treatment. [Solution] A method used to recover fluorine from a fuel cell comprises a first step of treating a fuel cell component containing fluorine with a supercritical medium using iron as a catalyst, or a second step of treating the fuel cell component with a supercritical medium without using iron as a catalyst. The first step is performed when the fluorine contained in the fuel cell component is to be recovered in the form of a harmless compound, and the second step is performed when the fluorine contained in the fuel cell component is to be reused.

Description

Technical Field

[0001] The present disclosure relates to a method used for recovering fluorine from a fuel cell.

Background Art

[0002] Patent Document 1 discloses a recycling method of a fuel cell component, in which a fluorine-containing component contained in the fuel cell component is separated from a noble metal-containing component by treating the fuel cell component in a supercritical medium. In this recycling method, the fluorine-containing component is separated in a state dissolved in the supercritical medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a need for a technology that can recover fluorine contained in a fuel cell according to the purpose of treatment.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms.

[0006] According to one aspect of the present disclosure, there is provided a method used for recovering fluorine from a fuel cell. This method includes a first step of treating a fuel cell component containing fluorine, which is a component of the fuel cell, with a medium in a supercritical state using iron as a catalyst, or a second step of treating the fuel cell component with a medium in a supercritical state without using iron as a catalyst. The first step is executed when recovering fluorine contained in the fuel cell component in a state of a harmless compound, and the second step is executed when reusing fluorine contained in the fuel cell component. According to the method used to recover fluorine from this type of fuel cell, the fluorine contained in the fuel cell can be recovered according to the purpose of treatment. [Brief explanation of the drawing]

[0007] [Figure 1] A diagram illustrating the schematic configuration of a fluorine recovery system for recovering fluorine from fuel cells. [Figure 2] A diagram showing the schematic configuration of a single cell in a fuel cell. [Figure 3] A flowchart illustrating a method used to recover fluorine from fuel cells. [Modes for carrying out the invention]

[0008] A. First Embodiment: Figure 1 shows a schematic configuration of a fluorine recovery system 100 for recovering fluorine from a fuel cell. The fluorine recovery system 100 recovers fluorine contained in fuel cell components by processing the fuel cell components, which are components of the fuel cell and contain fluorine, in a supercritical medium. The fluorine recovery system 100 comprises a waste tank 110, a reaction vessel 120, a water tank 130, a filter 140, and a treated water tank 150. The fuel cell components before processing are placed in the waste tank 110. The reaction vessel 120 is a container for processing the fuel cell components with a supercritical medium, and is, for example, a tank with pressure resistance and heat resistance. The products generated by the processing with the supercritical medium are recovered in the treated water tank 150.

[0009] Figure 2 shows a schematic configuration of a single cell 10 of the fuel cell. The fuel cell has a stack structure in which multiple single cells 10 are stacked. The fuel cell in this embodiment is a polymer electrolyte fuel cell that generates electricity through the reaction of a reaction gas. The reaction gas is, for example, hydrogen gas as a fuel gas and air as an oxidizing gas. Note that the fuel cell may be of other types, such as a solid oxide fuel cell.

[0010] The single cell 10 comprises an electrolyte membrane 20, a cathode catalyst layer 31, an anode catalyst layer 32, water-repellent layers 41 and 42, gas diffusion layers 51 and 52, and separators 61 and 62. Hereafter, the side with the cathode catalyst layer 31 will also be referred to as the "cathode side," and the side with the anode catalyst layer 32 will be referred to as the "anode side." When referring to the cathode catalyst layer 31 and the anode catalyst layer 32 without distinction, they will simply be called catalyst layers.

[0011] The electrolyte membrane 20 transports protons generated on the anode side to the cathode side. In this embodiment, the electrolyte membrane 20 is a proton-conducting ion exchange membrane formed of a fluororesin containing perfluorocarbon sulfonic acid.

[0012] The catalyst layer is formed by coating conductive particles, such as carbon particles, that support a catalyst, such as platinum or a platinum alloy, with a proton-conducting polymer electrolyte. In this embodiment, a fluorine-based resin such as a perfluorosulfonic acid polymer is used as the polymer electrolyte. The cathode catalyst layer 31 is laminated on one side of the electrolyte membrane 20. The anode catalyst layer 32 is laminated on the other side of the electrolyte membrane 20.

[0013] The water-repellent layers 41 and 42 are laminated on the surfaces of the cathode catalyst layer 31 and the anode catalyst layer 32 opposite to the surface in contact with the electrolyte membrane 20, respectively. In this embodiment, the water-repellent layers 41 and 42 are formed from carbon particles and a fluororesin such as polytetrafluoroethylene (PTFE) as a water-repellent substance.

[0014] The gas diffusion layers 51 and 52 are made of a gas-permeable and conductive material such as carbon cloth or carbon paper. The gas diffusion layer 51 is located on the outer surface of the water-repellent layer 41, and the gas diffusion layer 52 is located on the outer surface of the water-repellent layer 42. Hereinafter, the laminate consisting of the electrolyte membrane 20, the catalyst layer, and the gas diffusion layers 51 and 52 will be referred to as a Membrane Electrode Gas Diffusion Layer Assembly (MEGA) 90. In this embodiment, the Membrane Electrode Gas Diffusion Layer Assembly 90 includes the water-repellent layers 41 and 42.

[0015] The separators 61 and 62 are made of materials that have gas barrier properties and electrical conductivity. For example, they are made of carbon materials such as dense carbon, which is made by compressing carbon particles to make it gas-impermeable, or metal materials such as press-formed stainless steel or titanium steel. Separator 61 is placed on the outer surface of the gas diffusion layer 51, and separator 62 is placed on the outer surface of the gas diffusion layer 52. Separators 61 and 62 each have an oxidizer gas passage 71 through which oxidizer gas flows and a fuel gas passage 72 through which fuel gas flows.

[0016] Figure 3 is a flowchart illustrating a method used to recover fluorine from a fuel cell. First, in step S10, fuel cell components containing fluorine are prepared. In this embodiment, the fuel cell components containing fluorine are an electrolyte membrane 20, a catalyst layer, and water-repellent layers 41 and 42. In step S10, the fuel cell is disassembled into individual single cells 10, and a membrane electrode gas diffusion layer assembly 90 is removed from each single cell 10. The membrane electrode gas diffusion layer assembly 90 is then put into a waste tank 110 shown in Figure 1. That is, the fuel cell components are put into the waste tank 110. It is preferable that the membrane electrode gas diffusion layer assembly 90 put into the waste tank 110 is finely crushed.

[0017] After step S10 is performed, either step S21 or step S22 is performed. Step S21 is performed when fluorine contained in the fuel cell components is to be recovered in the form of a harmless compound. Step S22 is performed when fluorine contained in the fuel cell components is to be reused.

[0018] In step S21, the fluorine recovery system 100 treats the fuel cell components with a supercritical medium using iron as a catalyst. In this embodiment, the medium is water. The above treatment is carried out in the reaction vessel 120 shown in Figure 1. The membrane electrode gas diffusion layer assembly 90 and water are supplied to the reaction vessel 120 from the waste tank 110 and the water tank 130, respectively. Iron powder, which is the catalyst, is also supplied to the reaction vessel 120. The treatment of the membrane electrode gas diffusion layer assembly 90 with supercritical water is carried out, for example, under conditions of 400°C and 23.3 MPa. Through the above treatment, the membrane electrode gas diffusion layer assembly 90 is decomposed, and most of the fluorine atoms contained in the fuel cell components are changed into gaseous fluorides such as CHF3 and C2HF5. In other words, the fluorine contained in the fuel cell components is gasified and becomes a harmless compound. The catalyst metals such as platinum, and the carbon materials such as carbon particles and gas diffusion layers 51 and 52 contained in the membrane electrode gas diffusion layer assembly 90 remain in the supercritical water as solid components. In addition, the decomposition of the membrane electrode gas diffusion layer assembly 90 by the above-described process generates gases such as hydrogen and carbon dioxide. Step S21 is also called the first step.

[0019] In step S31, the solid components containing catalyst metals and carbon materials generated by the supercritical water treatment are separated from the gaseous and liquid components. These solid components are separated from the gaseous and liquid components by filtering through the filter 140 shown in Figure 1 and recovered. The catalyst metal contained in the recovered solid components is separated from components other than the catalyst metal by known methods and reused.

[0020] In step S41, fluorine contained in the fuel cell component is recovered. Specifically, the gaseous and liquid components of the products generated by the treatment with supercritical water are transferred to the treated water tank 150, so that the gasified fluorine is recovered in the treated water tank 150.

[0021] The fluorine contained in the fluoride gas such as CHF3 and C2HF5 recovered in the treated water tank 150 may then be converted into fluorite by decomposing the fluoride gas into hydrogen fluoride and reacting it with calcium carbonate. Thus, the fluorine contained in the fuel cell component may be recovered as fluorite.

[0022] In step S22, the fluorine recovery system 100 treats the fuel cell component with a medium in a supercritical state without using iron as a catalyst. In the present embodiment, the medium is water. The above treatment is performed in the reaction vessel 120. In the reaction vessel 120, the membrane electrode gas diffusion layer bonded body 90 and water are supplied from the waste tank 110 and the water tank 130, respectively. The treatment of the membrane electrode gas diffusion layer bonded body 90 with supercritical water is performed, for example, under the conditions of 400°C and 23.3 MPa. By the above treatment, the membrane electrode gas diffusion layer bonded body 90 is decomposed, and most of the fluorine atoms contained in the fuel cell component are dissolved in the supercritical water as fluoride ions. That is, the fluorine contained in the fuel cell component is liquefied. The catalyst metal such as platinum and the carbon materials such as carbon particles and gas diffusion layers contained in the membrane electrode gas diffusion layer bonded body 90 remain in the supercritical water as solid components. In addition, by decomposing the membrane electrode gas diffusion layer bonded body 90 by the above treatment, gases such as hydrogen are generated. Step S22 is also referred to as the second step.

[0023] In step S32, the solid components including the catalyst metal and carbon materials generated by the supercritical treatment are separated from the gaseous and liquid components. Since the treatment executed in step S32 is the same as the treatment executed in step S31, the description thereof will be omitted.

[0024] In step S42, fluorine contained in the fuel cell components is recovered. Specifically, the gaseous and liquid components of the products generated by the supercritical water treatment are transferred to the treated water tank 150, and the liquefied fluorine is recovered in the treated water tank 150.

[0025] The liquefied fluorine recovered in the treated water tank 150 may be reused as a fuel cell component. For example, the fluoride ions recovered in the treated water tank 150 may be polymerized to form an electrolyte membrane 20, which is a fuel cell component, and the formed electrolyte membrane 20 may be reused in the manufacture of a fuel cell. The original fuel cell component that contained the recovered fluorine and the fuel cell component formed by reuse may be the same material or different material. Furthermore, the liquefied fluorine recovered in the treated water tank 150 may be reused for the manufacture of products other than fuel cell components.

[0026] The method used to recover fluorine from fuel cells as described above comprises either a first step of treating fluorine-containing fuel cell components with a supercritical medium using iron as a catalyst, or a second step of treating fluorine-containing fuel cell components with a supercritical medium without using iron as a catalyst. The first step is performed when recovering fluorine contained in the fuel cell components in the form of a harmless compound, and the second step is performed when reusing fluorine contained in the fuel cell components. Therefore, fluorine contained in fuel cells can be recovered according to the purpose of treatment.

[0027] B. Other embodiments: (B-1) In the above embodiment, the fuel cell components are treated with water in a supercritical state. Alternatively, the fuel cell components may be treated with carbon dioxide, nitrogen, ammonia, etc., in a supercritical state.

[0028] (B-2) In the above embodiment, the single cell 10 is provided with a water-repellent layer 41. In contrast, the single cell 10 does not need to be provided with a water-repellent layer 41.

[0029] (B-3) In the above embodiment, the fuel cell components containing fluorine are the electrolyte membrane 20, the catalyst layer, and the water-repellent layers 41 and 42. However, the fuel cell components containing fluorine are not limited to the example described above.

[0030] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of symbols]

[0031] 10...Single cell, 20...Electrolyte membrane, 31...Cathode catalyst layer, 32...Anode catalyst layer, 41...Water-repellent layer, 42...Water-repellent layer, 51...Gas diffusion layer, 52...Gas diffusion layer, 61...Separator, 62...Separator, 71...Oxidizer gas flow path, 72...Fuel gas flow path, 90...Membrane electrode gas diffusion layer assembly, 100...Fluorine recovery system, 110...Waste tank, 120...Reaction vessel, 130...Water tank, 140...Filter, 150...Treated water tank

Claims

[Claim 1] A method used for recovering fluorine from fuel cells, The fuel cell comprises a first step of treating a fuel cell component containing fluorine with a medium in a supercritical state using iron as a catalyst, or a second step of treating the fuel cell component with a medium in a supercritical state without using iron as a catalyst. The first step is performed when the fluorine contained in the fuel cell component is recovered in the form of a harmless compound, and the second step is performed when the fluorine contained in the fuel cell component is to be reused. method.

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