Process for recycling fluoropolymers

Abstract

Provided is a recovery method of a fluorine-containing polymer that is not easily swelled by a recovered fluorine-containing polymer. The recovery method of a fluorine-containing polymer of the present invention is a recovery method of a fluorine-containing polymer of a fluorine-containing polymer recovered from a membrane electrode assembly, the membrane electrode assembly including: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, the anode and the cathode having: a catalyst layer including a catalyst and a fluorine-containing polymer having a sulfonic acid group, the electrolyte membrane including a fluorine-containing polymer having a sulfonic acid group, in the method, a first solution selected from a solution A consisting only of water and a solution B including water and an alcohol is brought into contact with the membrane electrode assembly, and then, the membrane electrode assembly is mixed with a second solution including water and an alcohol to obtain a mixed solution including: a fluorine-containing polymer, the second solution, and an insoluble substance, the insoluble substance included in the mixed solution is removed, and a fluorine-containing polymer included in the mixed solution from which the insoluble substance is removed is recovered.

Description

Technical Field

[0001] This invention relates to a method for recycling fluoropolymers. Background Technology

[0002] A membrane electrode assembly for use in a water electrolysis device and a fuel cell comprises: an anode having a catalyst layer; a cathode having a catalyst layer; and an electrolyte membrane disposed between the anode and the cathode.

[0003] In recent years, research has been conducted on the reuse of materials constituting membrane electrode assemblies (MEAs) to reduce environmental impact. For example, Patent Document 1 discloses a method for recovering fluoropolymers by using MEAs taken from a fuel cell and performing processes such as dissolving fluoropolymers from the electrolyte membrane into a solvent.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-171921 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] When recovering fluorinated polymers with sulfonic acid groups from membrane electrode assemblies, and then reusing the recovered fluorinated polymers as polymers for manufacturing electrolyte membranes and catalyst layers, it is required that the recovered fluorinated polymers do not easily swell due to moisture or other factors.

[0009] Referring to the method for recovering fluoropolymers described in Patent Document 1, the inventors attempted to recover fluoropolymers containing sulfonic acid groups from the electrolyte membrane by dissolving them in a solution containing alcohol. The results showed that the swelling of the recovered fluoropolymers was not sufficiently suppressed, and there was room for improvement.

[0010] The present invention was made in view of the above-mentioned problems, and the problem is to provide a method for recovering fluoropolymers that are not easily swollen.

[0011] Solution for solving the problem

[0012] The inventors conducted in-depth research on the above-mentioned issues and found that when a first solution is brought into contact with a membrane electrode assembly, an electrolyte membrane, or an electrode (at least one of an anode and a cathode), wherein the first solution is selected from a solution A consisting only of water and a solution B containing water and alcohol but with a low alcohol content, and then a second solution containing water and alcohol but with a high alcohol content is mixed with the membrane electrode assembly, electrolyte membrane, or electrode that has been in contact with the first solution, the desired effect can be obtained, thereby completing the present invention.

[0013] That is, the inventors have discovered that the above-mentioned problems can be solved by the following configuration. [1]

[0015] A method for recovering a fluoropolymer, characterized in that the fluoropolymer is recovered from a membrane electrode assembly comprising: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode; the anode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups; the cathode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups; and the electrolyte membrane comprising a fluoropolymer having sulfonic acid groups. In this method,

[0016] The first solution is brought into contact with the membrane electrode assembly. The first solution is selected from solution A, which consists only of water, and solution B, which contains water and alcohol, wherein the content of alcohol is less than 10 parts by mass relative to 100 parts by mass of water. Then,

[0017] The membrane electrode assembly that has been in contact with the first solution, and a second solution comprising water and an alcohol, wherein the alcohol content is 30 parts by mass or more relative to 100 parts by mass of water, are mixed to obtain a mixed solution comprising: the fluoropolymer, the second solution, and an insoluble substance containing the catalyst.

[0018] The insoluble matter contained in the mixed solution is removed, and the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is recovered. [2]

[0020] According to the fluoropolymer recovery method described in [1], the contact between the first solution and the membrane electrode assembly is the contact between solution A and the membrane electrode assembly, and the heated solution A is used. [3]

[0022] According to the method for recovering fluoropolymers as described in [1] or [2], wherein the first solution is heated when it is brought into contact with the membrane electrode assembly.

[0023] The temperature of the first solution is lower than the temperature of the second solution. [4]

[0025] The method for recycling fluoropolymers according to any one of [1] to [3], wherein the weight-average molecular weight of the recycled fluoropolymer is 10,000 to 1,000,000. [5]

[0027] According to the fluoropolymer recycling method described in [3], the temperature difference between the first solution and the second solution is above 5°C and below 115°C. [6]

[0029] A method for recovering fluoropolymers, characterized in that the fluoropolymer contained in an electrolyte membrane is recovered from a membrane electrode assembly comprising: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode; the anode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups; the cathode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups; and the electrolyte membrane containing a fluoropolymer having sulfonic acid groups. In this method,

[0030] Separate the electrolyte membrane from the membrane electrode assembly.

[0031] The first solution is brought into contact with the separated electrolyte membrane. The first solution is selected from solution A, which consists only of water, and solution B, which contains water and alcohol, wherein the content of alcohol is less than 10 parts by mass relative to 100 parts by mass of water. Then,

[0032] The electrolyte membrane, which has been in contact with the first solution, and a second solution comprising water and alcohol, wherein the alcohol content is 30 parts by mass or more relative to 100 parts by mass of water, are mixed to obtain a mixed solution comprising the fluoropolymer, the second solution, and insoluble matter.

[0033] The insoluble matter contained in the mixed solution is removed, and the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is recovered. [7]

[0035] According to the method for recovering fluoropolymers described in [6], the contact between the first solution and the electrolyte membrane is the contact between solution A and the electrolyte membrane, and the heated solution A is used. [8]

[0037] According to the method for recovering fluoropolymers as described in [6] or [7], wherein the first solution is heated when it is brought into contact with the electrolyte membrane.

[0038] The temperature of the first solution is lower than the temperature of the second solution. [9]

[0040] The method for recycling fluoropolymers according to any one of [6] to [8], wherein the weight-average molecular weight of the recycled fluoropolymer is 10,000 to 1,000,000.

[10]

[0042] According to the fluoropolymer recovery method described in [8], the temperature difference between the first solution and the second solution is above 5°C and below 115°C.

[11]

[0044] A method for recovering fluoropolymers, characterized in that at least one of a fluoropolymer contained in a catalyst layer of an anode and a fluoropolymer contained in a catalyst layer of a cathode is recovered from a membrane electrode assembly, wherein the membrane electrode assembly comprises: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, the anode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, the cathode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, and the electrolyte membrane comprising a fluoropolymer having sulfonic acid groups, wherein in the method,

[0045] Separate at least one of the anode and the cathode from the membrane electrode assembly.

[0046] The first solution is brought into contact with at least one of the separated anode and cathode. The first solution is selected from solution A, which consists only of water, and solution B, which contains water and alcohol, wherein the alcohol content is less than 10 parts by mass relative to 100 parts by mass of water.

[0047] At least one of the anode and the cathode, which has been in contact with the first solution, and a second solution comprising water and an alcohol, wherein the alcohol content is 30 parts by mass or more relative to 100 parts by mass of water, are mixed to obtain a mixed solution comprising the fluoropolymer, the second solution, and an insoluble substance.

[0048] The insoluble matter contained in the mixed solution is removed, and the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is recovered.

[12]

[0050] According to the method for recycling fluoropolymers as described in

[11] , the contact between the first solution and at least one of the anode and the cathode is the contact between solution A and the anode and the cathode, and the heated solution A is used.

[13]

[0052] According to the method for recycling fluoropolymers as described in

[11] or

[12] , wherein a heated first solution is used when the first solution is contacted with at least one of the anode and the cathode.

[0053] The temperature of the first solution is lower than the temperature of the second solution.

[14]

[0055] The method for recycling fluoropolymers according to any one of

[11] to

[13] , wherein the weight-average molecular weight of the recycled fluoropolymer is 10,000 to 1,000,000.

[15]

[0057] According to the fluoropolymer recovery method described in

[13] , the temperature difference between the first solution and the second solution is above 5°C and below 115°C.

[0058] The effects of the invention

[0059] According to the present invention, a method for recovering fluoropolymers that are not easily swollen can be provided. Attached Figure Description

[0060] Figure 1 This is a cross-sectional view showing an example of a membrane electrode assembly. Detailed Implementation

[0061] Unless otherwise specified, the following definitions of terms generally apply to this specification and the claims.

[0062] In polymers, a "unit" refers to an atomic group derived from a single molecule of a monomer, formed through monomer polymerization. A unit can be a atomic group formed directly through the polymerization reaction, or it can be formed by processing the polymer obtained through the polymerization reaction, transforming a portion of the atomic group into a different structural group. It should be noted that sometimes structural units derived from individual monomers are referred to by the name of their respective monomers, labeled "unit".

[0063] The numerical range indicated by "~" refers to the range of values ​​recorded before and after "~" as the lower and upper limits. In the numerical ranges described in this specification, the upper or lower limit recorded in a certain numerical range can be replaced with the upper or lower limit of other numerical ranges described in different stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit recorded in a certain numerical range can also be replaced with the values ​​shown in the embodiments.

[0064] Hereinafter, after describing the materials used in the method for recycling fluoropolymers of the present invention, the method for recycling fluoropolymers of the present invention will be described according to each embodiment.

[0065] [Membrane electrode assembly]

[0066] The membrane electrode assembly used in the fluoropolymer recycling method of the present invention comprises: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, wherein the anode has: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, the cathode has: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, and the electrolyte membrane comprises a fluoropolymer having sulfonic acid groups.

[0067] In the following description, unless otherwise specified, "fluoropolymers with sulfonic acid groups" will be referred to as "specific fluoropolymers".

[0068] An example of a membrane electrode assembly is described in detail with reference to the accompanying drawings.

[0069] Figure 1 This is a cross-sectional view showing an example of the membrane electrode assembly used in the embodiments described later. The membrane electrode assembly 10 includes: an anode 13 having a catalyst layer 11A and a gas diffusion layer 12A; a cathode 14 having a catalyst layer 11C and a gas diffusion layer 12C; and a solid polymer electrolyte membrane 15 disposed between the anode 13 and the cathode 14 in contact with the catalyst layer 11A and the catalyst layer 11C.

[0070] The membrane electrode assembly 10 is preferably a membrane electrode assembly recovered from a fuel cell (solid polymer fuel cell) or a water electrolysis device. There are no particular limitations on the method for recovering the membrane electrode assembly 10 from these devices; known methods can be used.

[0071] <Electrolyte membrane>

[0072] The solid polymer electrolyte membrane 15 contains a specific fluoropolymer and can use known solid polymer electrolyte membranes.

[0073] The specific fluoropolymer contained in the solid polymer electrolyte membrane 15 is not particularly limited, but preferably includes units based on fluoroolefins and units having sulfonic acid groups and fluorine atoms.

[0074] Examples of fluorinated olefins include fluoroolefins with 2 to 3 carbon atoms having one or more fluorine atoms in their molecule. Specific examples of fluoroolefins include tetrafluoroethylene (hereinafter also referred to as "TFE"), trifluorochloroethylene, vinylidene fluoride, fluoroethylene, and hexafluoropropylene, among which TFE is preferred.

[0075] The preferred unit is the one with a sulfonic acid group and a fluorine atom.

[0076] Equation (1) -[CF2-CF(-L-(SO3H)] n )]-

[0077] L is an optional perfluorocarbon group with an n+1 valence containing an ether-type oxygen atom.

[0078] The oxygen atom in an ether can be located at the end of a perfluorocarbon group or between carbon atoms.

[0079] The number of carbons in the n+1 valence perfluorocarbon group is preferably 1 or more, particularly preferably 2 or more, more preferably 20 or less, and especially preferably 10 or less.

[0080] As L, preferably, it is a perfluoroaliphatic hydrocarbon group with an n+1 valence containing an ether oxygen atom, and particularly preferably, it is a perfluoroalkylene group with a divalent valence containing an ether oxygen atom as n=1, or a perfluoroaliphatic hydrocarbon group with a trivalent valence containing an ether oxygen atom as n=2.

[0081] The aforementioned divalent perfluoroalkylene groups can be either linear or branched.

[0082] n is 1 or 2.

[0083] As the unit shown in formula (1), it is preferably the unit shown in formula (1-1), the unit shown in formula (1-2), the unit shown in formula (1-3), or the unit shown in formula (1-4).

[0084] Equation (1-1) -[CF2-CF(-OR) f1 -SO3H)]-

[0085] Equation (1-2) -[CF2-CF(-R) f1 -SO3H)]-

[0086]

[0087]

[0088] R f1 The perfluoroalkylene group may optionally contain an ether-like oxygen atom. The number of carbon atoms in the aforementioned perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, more preferably 20 or less, and particularly preferably 10 or less.

[0089] R f2 It is a perfluoroalkylene group with a single bond or optionally containing an ether-like oxygen atom. The number of carbon atoms in the aforementioned perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, more preferably 20 or less, and particularly preferably 10 or less.

[0090] R f3 It is a perfluoroalkylene group with a single bond or optionally containing an ether-like oxygen atom. The number of carbon atoms in the aforementioned perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, more preferably 20 or less, and particularly preferably 10 or less.

[0091] The oxygen atom in an ether can be located at the end of a perfluoroalkyl group or between carbon atoms.

[0092] r is 0 or 1.

[0093] m is 0 or 1.

[0094] The solid polymer electrolyte membrane 15 can also be reinforced by reinforcing materials. Examples of reinforcing materials include porous materials, fibers, woven fabrics, and nonwoven fabrics. Examples of materials that can be used as reinforcing materials include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, polyphenylene sulfide, polyethersulfone, and polyetheretherketone.

[0095] To further improve durability, the solid polymer electrolyte membrane 15 may contain one or more atoms selected from the group consisting of cerium and manganese. Cerium and manganese are capable of decomposing hydrogen peroxide, a substance that causes degradation of the solid polymer electrolyte membrane 15. Cerium and manganese are preferably present in the solid polymer electrolyte membrane 15 in ionic form, but if present in ionic form, they can exist in any state within the solid polymer electrolyte membrane 15.

[0096] The solid polymer electrolyte membrane 15 may contain silica and heteropoly acids (zirconium phosphate, phosphomolybdic acid, phosphotungstic acid, etc.) as water-retaining agents to prevent drying.

[0097] In order to consume the hydrogen that permeates through the membrane, the solid polymer electrolyte membrane 15 may also contain platinum atoms.

[0098] <Cathode>

[0099] The catalyst layer 11C of the cathode 14 contains a catalyst and a specific fluoropolymer, and can use a known catalyst layer for cathodes.

[0100] The specific fluoropolymer contained in catalyst layer 11C is not particularly limited, but preferably includes units having sulfonic acid groups and fluorine atoms, and includes at least one of units based on fluorinated olefins and units having cyclic ether structures.

[0101] Specific examples of units having sulfonic acid groups and fluorine atoms, as well as units based on fluorinated olefins, are the same as the units that may be contained in the specific fluorinated polymer in the solid polymer electrolyte membrane 15 described above.

[0102] As a specific example of a unit having a cyclic ether structure, one can cite the unit having a cyclic ether structure described in International Publication No. 2020 / 145287.

[0103] The catalyst contained in catalyst layer 11C is not particularly limited. Examples include supported catalysts on a carbon support or a support formed of metal oxide that contain platinum, platinum alloys, or platinum with a core-shell structure; iridium oxide catalysts; alloys containing iridium oxide; and catalysts containing iridium oxide with a core-shell structure. Carbon black powder can be used as a carbon support. Oxides of elemental or composite metals such as aluminum, tin, zinc, nickel, cobalt, iron, titanium, cerium, zirconium, palladium, lanthanum, niobium, tantalum, and antimony can be used as supports. Alternatively, non-metallic catalysts with electrode catalytic activity, such as carbon alloy catalysts, can also be used.

[0104] The gas diffusion layer 12C has the functions of uniformly diffusing gas or water into the catalyst layer 11C, discharging gas generated from the catalyst layer 11C, and acting as a current collector.

[0105] Examples of materials that can serve as the gas diffusion layer 12C include carbon paper, carbon cloth, carbon felt, and porous titanium. When the gas diffusion layer 12C is formed of carbon, it is preferable to use polytetrafluoroethylene (PTFE) or similar materials for water-repellent treatment. When it is a porous titanium material, it is preferable to have its surface coated with platinum.

[0106] It should be noted that, in Figure 1 The membrane electrode assembly 10 includes a gas diffusion layer 12C, but the gas diffusion layer is an arbitrary component and may not be included in the membrane electrode assembly.

[0107] <Anode>

[0108] The catalyst layer 11A of the anode 13 contains a catalyst and a specific fluoropolymer, and can use a known catalyst layer for anodes.

[0109] The specific fluoropolymer contained in the catalyst layer 11A is not particularly limited, but preferably includes units having sulfonic acid groups and fluorine atoms, as well as units based on fluorinated olefins. Specific examples of units having sulfonic acid groups and fluorine atoms, as well as units based on fluorinated olefins, are the same as the units that may be contained in the specific fluoropolymer in the solid polymer electrolyte membrane 15 described above.

[0110] The catalyst contained in catalyst layer 11A is not particularly limited; for example, a catalyst comprising a porous support and a metal supported on the porous support can be cited. Specific examples of the porous support and metal are the same as those in catalyst layer 11C described above.

[0111] The specific example of the gas diffusion layer 12A of the anode 13 is the same as the specific example of the gas diffusion layer 12C described above. The gas diffusion layer 12A and the gas diffusion layer 12C are also arbitrary components.

[0112] <Other Components>

[0113] The membrane electrode assembly 10 may also have a carbon layer (not shown) between the catalyst layer and the gas diffusion layer.

[0114] The carbon layer may comprise, for example, carbon and a nonionic fluoropolymer. A specific example of carbon is preferably carbon nanofibers with a diameter of 1-1000 nm and a length of 1000 μm or less. A specific example of a nonionic fluoropolymer is polytetrafluoroethylene (PTFE).

[0115] [First Solution]

[0116] The first solution is a solution selected from solution A and solution B, and is used in the embodiments described later.

[0117] <Solution A>

[0118] Solution A consists of only water.

[0119] Solution B

[0120] Solution B contains water and alcohol.

[0121] Specific examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoro-1-propanol, 2,2,3,3-tetrafluoro-1-propanol, 4,4,5,5,5-pentafluoro-1-pentanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 3,3,3-trifluoro-1-propanol, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol, and 3,3,4,4,5,5,6,6,7,7,8,8,8-tetrafluoro-1-octanol. From the viewpoint of superior efficacy of the present invention, ethanol and 1-propanol are preferred. One alcohol may be used alone, or two or more may be used in combination.

[0122] The alcohol content in solution B is 10 parts by mass or less compared to 100 parts by mass of water in solution B. From the viewpoint of achieving better results in this invention, it is preferably 9 parts by mass or less, and more preferably 8 parts by mass or less.

[0123] The alcohol content in solution B is more than 0 parts by mass relative to 100 parts by mass of water, preferably 1 part by mass or more, and more preferably 2 parts by mass or more.

[0124] [Second solution]

[0125] The second solution is the solution used in the embodiments described later, which contains water and alcohol.

[0126] The specific examples of alcohols are the same as those contained in solution B described above. Alcohols can be used alone or in combination of two or more.

[0127] The alcohol content in the second solution is 30 parts by mass or more than 100 parts by mass of water in the second solution. From the viewpoint that the solubility of the specific fluoropolymer is superior, it is preferably 35 parts by mass or more, and more preferably 40 parts by mass or more.

[0128] The alcohol content in the second solution is preferably 400 parts by mass or less, more preferably 360 parts by mass or less, and even more preferably 350 parts by mass or less, relative to 100 parts by mass of water in the second solution.

[0129] [First Implementation Method]

[0130] The recovery method of a specific fluoropolymer according to the first embodiment of the present invention (hereinafter also referred to as the "recovery method of the first embodiment") is a recovery method of a specific fluoropolymer from the above-described membrane electrode assembly.

[0131] In addition, the recovery method of the first embodiment includes a step of contacting the first solution with the membrane electrode assembly (hereinafter also referred to as "step 1-1").

[0132] In addition, the recovery method of the first embodiment includes a step (hereinafter also referred to as "step 1-2") after step 1-1, in which the membrane electrode assembly that has been in contact with the first solution and the second solution are mixed to obtain a mixed solution containing the specific fluoropolymer, the second solution and an insoluble substance containing the catalyst.

[0133] In addition, the recovery method of the first embodiment includes a step after step 1-2, removing the insoluble matter contained in the above mixed solution and recovering the specific fluoropolymer contained in the above mixed solution after the removal of the insoluble matter (hereinafter also referred to as "step 1-3").

[0134] According to the recycling method of the first embodiment, the specific fluoropolymer recovered is not prone to swelling. The details of the reason are not yet clear, but it is speculated to be based on the following reasons.

[0135] In cases where the membrane electrode assembly deteriorates after operation of a water electrolysis device or fuel cell containing the membrane electrode assembly, or when the specified service life has expired, the used membrane electrode assembly is recycled and replaced with a new one.

[0136] The recovered membrane electrode assembly's electrodes (at least one of the anode and cathode) sometimes contain, along with the catalyst layer and electrolyte membrane, at least one of low-molecular-weight compounds and oligomers as decomposition products of the specific fluoropolymer. It is assumed that such low-molecular-weight compounds and oligomers are generated by the decomposition of the specific fluoropolymer during operation of the aforementioned apparatus. It should be noted that, in this specification, such low-molecular-weight compounds and oligomers are sometimes simply referred to as "polymer decomposition products."

[0137] When a specific fluoropolymer contained in a membrane electrode assembly is dissolved and recovered using a solution with a high alcohol content, polymer decomposition products are also recovered along with the specific fluoropolymer. If polymer decomposition products are mixed with the specific fluoropolymer in the recovered product, they become the main cause of swelling of the specific fluoropolymer, and sometimes reduce the performance (e.g., power generation performance, durability) of the aforementioned devices that include membrane electrode assemblies formed using the recovered product.

[0138] To address this problem, based on the recovery method of the first embodiment, it is speculated that by performing step 1-1 before step 1-2, the polymer decomposition products contained in the membrane electrode assembly dissolve into the first solution, and the polymer decomposition products are removed or reduced from the membrane electrode assembly, resulting in the aforementioned excellent effect.

[0139] <Process 1-1>

[0140] Step 1-1 is the step of bringing the first solution into contact with the membrane electrode assembly.

[0141] Through this process, the catalyst layer of the anode, the catalyst layer of the cathode, and the polymer decomposition products contained in the electrolyte membrane in the membrane electrode assembly dissolve into the first solution, thus obtaining a membrane electrode assembly in which the polymer decomposition products have been removed or reduced.

[0142] It should be noted that in step 1-1, a solution A that is completely free of alcohol or a solution B with a low alcohol content is used as the first solution, thus the dissolution of the specific fluoropolymer into the first solution is suppressed.

[0143] Specific examples of methods for contacting the first solution with the membrane electrode assembly include immersing the membrane electrode assembly in the first solution and spraying the first solution onto the surface of the membrane electrode assembly using a spraying device such as a sprayer. From the viewpoint that polymer decomposition products dissolve more readily into the first solution, immersion is preferred. Furthermore, stirring the solution during immersion further facilitates the dissolution of polymer decomposition products into the first solution, which is also preferable.

[0144] The first solution may or may not be heated, but from the viewpoint of promoting the dissolution of polymer decomposition products and being able to further remove or reduce polymer decomposition products from the membrane electrode assembly, it is preferred to be heated.

[0145] The temperature of the first solution is preferably 5°C or higher, and from the viewpoint of further enhancing the above-mentioned effects, it is more preferably 35°C or higher, and even more preferably 75°C or higher.

[0146] From the viewpoint of being able to suppress the dissolution of specific fluoropolymers in the first solution and to further improve the recovery rate of specific fluoropolymers in steps 1-3, the temperature of the first solution is preferably 160°C or less, more preferably 140°C or less, and even more preferably 130°C or less.

[0147] When the first solution is heated, from the viewpoint of achieving better polymer recovery, the temperature of the first solution is preferably lower than the temperature of the second solution used in steps 1-2 described later.

[0148] From the viewpoint of achieving better results in the present invention, when the temperature of the first solution is lower than that of the second solution, the temperature difference ((temperature of the second solution) - (temperature of the first solution)) is preferably 5°C or more, more preferably 10°C or more, even more preferably 20°C or more, and preferably 120°C or less, more preferably 115°C or less, and even more preferably 100°C or less.

[0149] There is no particular limitation on the contact time between the first solution and the membrane electrode assembly, but it is preferably 1 minute or more, more preferably 5 minutes or more, and preferably 24 hours or less, more preferably 16 hours or less.

[0150] From the viewpoint of achieving better results with the present invention, the amount of the first solution used relative to 100 parts by mass of the membrane electrode assembly is preferably 200 parts by mass or more, more preferably 500 parts by mass or more. Furthermore, from the viewpoint of suppressing the amount of waste liquid, it is preferably 1,000,000,000 parts by mass or less, more preferably 100,000,000 parts by mass or less, and even more preferably 10,000,000 parts by mass or less.

[0151] In step 1-1, either solution A or solution B can be used as the first solution. From the viewpoint that it can further remove or reduce polymer decomposition products and suppress the leaching of specific fluorinated polymers, solution A is preferred.

[0152] In particular, when heated solution A is used in step 1-1, the removal of polymer decomposition products is improved compared to unheated solution A, and the leaching of specific fluoropolymers is suppressed compared to solution B described later. Therefore, the recovery rate of specific fluoropolymers in steps 1-3 described later can be further improved.

[0153] From the viewpoint of further maximizing the above-mentioned effects, the temperature of solution A when using heated solution A is preferably 40°C or higher, more preferably 80°C or higher.

[0154] In step 1-1, a drying process can also be performed to dry the membrane electrode assembly after the first solution has been brought into contact with it. By using the membrane electrode assembly that has undergone the drying process in step 1-2, which will be described later, the membrane electrode assembly is easier to input in step 1-2 (i.e., the processability of the membrane electrode assembly is improved), and the concentration of the mixed solution obtained in step 1-2 is easier to adjust.

[0155] Methods of drying include natural drying, heat drying, air drying, and combinations thereof.

[0156] The drying temperature is preferably 10°C or higher, more preferably 20°C or higher, and preferably 160°C or lower, more preferably 120°C or lower.

[0157] As described above, the polymer decomposition products removed or reduced from the membrane electrode assembly in step 1-1 are components generated by the decomposition of specific fluoropolymers, such as low molecular weight compounds and oligomers.

[0158] The molecular weight of the low molecular weight compound is preferably 1000 or less, more preferably 800 or less, and preferably 10 or more, more preferably 100 or more.

[0159] The molecular weight of the oligomer is preferably 10,000 or less, more preferably 5,000 or less, and even more preferably more than 1,000, more preferably 2,000 or more.

[0160] <Process 1-2>

[0161] Step 1-2 is performed after step 1-1 and involves mixing the membrane electrode assembly that has been in contact with the first solution with the second solution to obtain a mixed solution containing a specific fluoropolymer, the second solution, and an insoluble substance containing the catalyst.

[0162] In this process, the catalyst layer of the anode, the catalyst layer of the cathode, and a specific fluoropolymer in the electrolyte membrane contained in the membrane electrode assembly dissolve in the second solution and are included in the mixed solution. Additionally, components such as the catalyst that are insoluble in the second solution are included in the mixed solution as insoluble substances.

[0163] The specific fluoropolymers contained in each material of the membrane electrode assembly (especially the specific fluoropolymers having the unit shown in formula (1) above) have high solubility in a mixed solvent of alcohol and water. In addition, the alcohol content of the second solution is high. Therefore, by carrying out steps 1-2, the specific fluoropolymers contained in each material of the membrane electrode assembly dissolve in the second solution.

[0164] As a specific example of the method for mixing the second solution with the membrane electrode assembly, a method can be given by immersing the membrane electrode assembly in the second solution and stirring it.

[0165] The second solution may or may not be heated, but from the viewpoint of promoting the dissolution of specific fluoropolymers, it is preferred to be heated.

[0166] The temperature of the second solution is preferably 15°C or higher, and more preferably 40°C or higher, and even more preferably 80°C or higher, from the viewpoint of further enhancing the above-mentioned effects.

[0167] The mixing time between the second solution and the membrane electrode assembly is not particularly limited, but is preferably 15 minutes or more, more preferably 60 minutes or more, and preferably 72 hours or less, more preferably 36 hours or less.

[0168] From the viewpoint of achieving better results with the present invention, the amount of the second solution used relative to 100 parts by mass of the membrane electrode assembly is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, and even more preferably 200 parts by mass or more. In addition, from the viewpoint of being able to suppress the concentration of the fluoropolymer in the liquid obtained in the following steps 1-3 from becoming too low and the fluoropolymer-containing liquid obtained in steps 1-3 being easy to reuse, it is preferably 2000 parts by mass or less, more preferably 1500 parts by mass or less, and even more preferably 1000 parts by mass or less.

[0169] In addition to the catalyst, the insoluble material may also include, for example, materials constituting the aforementioned reinforcing material, materials constituting the gas diffusion layer, materials constituting the carbon layer, materials constituting the porous transport layer, etc.

[0170] It should be noted that the components contained in the insoluble matter can be recycled and reused.

[0171] <Process 1-3>

[0172] Step 1-3 is performed after step 1-2. It is a step to remove insoluble substances from the mixed solution and to recover specific fluoropolymers contained in the mixed solution after the insoluble substances have been removed.

[0173] As a method for removing insoluble matter, known methods can be used, such as centrifugation, filtration using a filter, and natural sedimentation. From the viewpoint of superior removal efficiency, it is preferable to combine two or more of these methods (especially centrifugation and filtration using a filter) to implement the process.

[0174] There are no particular limitations on the method for recovering a specific fluoropolymer contained in a mixed solution from which insoluble matter has been removed; known methods may be used.

[0175] The weight-average molecular weight (hereinafter also referred to as "Mw") of the specific fluoropolymer being recycled is preferably 10,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, and preferably 3 million or less, more preferably 2 million or less, and even more preferably 1 million or less.

[0176] The Mw of a specific fluoropolymer is the weight-average molecular weight of polyethylene oxide, calculated using size exclusion gas chromatography (SEC) under the following conditions, after the above mixed solution in steps 1-3 has had insolubles removed.

[0177] Device: Made by Tosoh Corporation, 8320GPC

[0178] Column: Tosoh Corporation, aM and a-3000

[0179] Mobile phase: Methanol (for HPLC) with 10 mM di-n-butylammonium acetate (DBAA) added.

[0180] Flow rate: 1.0 mL / min

[0181] Oven temperature: 37℃

[0182] System temperature: 37℃

[0183] Injection volume: 50μL

[0184] Detector: Evaporative Light Scattering Detector (ELSD)

[0185] The recovered fluoropolymers are suitable for the manufacture of electrolyte membranes, catalyst layers in anodes, catalyst layers in cathodes, etc., but are not limited thereto and can also be used for other purposes.

[0186] [Second Implementation]

[0187] The recovery method of a specific fluoropolymer according to the second embodiment of the present invention (hereinafter also referred to as the "recovery method of the second embodiment") is a method for recovering a specific fluoropolymer contained in an electrolyte membrane from the above-described membrane electrode assembly.

[0188] In addition, the recovery method of the second embodiment includes a step of separating the electrolyte membrane from the above-mentioned membrane electrode assembly (hereinafter also referred to as step "2-0").

[0189] In addition, the recovery method of the second embodiment includes a step (hereinafter also referred to as "step 2-1") after step 2-0, in which the first solution is brought into contact with the separated electrolyte membrane.

[0190] In addition, the recovery method of the second embodiment includes a step after step 2-1, in which the electrolyte membrane that has been in contact with the first solution and the second solution are mixed to obtain a mixed solution containing the specific fluoropolymer, the second solution and the insoluble matter (hereinafter also referred to as "step 2-2").

[0191] In addition, the recovery method of the second embodiment includes a step after step 2-2, removing the insoluble matter contained in the above mixed solution and recovering the specific fluoropolymer contained in the above mixed solution after the removal of the insoluble matter (hereinafter also referred to as "step 2-3").

[0192] The recycling method of the second embodiment is based on the same reason as the recycling method of the first embodiment, that the specific fluoropolymers recycled are not prone to swelling.

[0193] That is, based on the recycling method of the first embodiment, it is speculated that by performing step 2-1 before step 2-2, the low molecular weight compounds contained in the electrolyte membrane dissolve into the first solution, and the polymer decomposition products are removed or reduced from the electrolyte membrane, resulting in the aforementioned excellent effect.

[0194] The recovery method of the second embodiment uses an electrolyte membrane separated from the membrane electrode assembly instead of the membrane electrode assembly; otherwise, it is the same as the recovery method of the first embodiment. Therefore, in the following description of each step in the recovery method of the second embodiment, descriptions of contents identical to those in the recovery method of the first embodiment are sometimes omitted.

[0195] <Process 2-0>

[0196] Step 2-0 is the process of separating the electrolyte membrane from the membrane electrode assembly. The electrolyte membrane obtained through this step (i.e., the separated electrolyte membrane) is used in step 2-1 described later.

[0197] There are no particular limitations on the method for separating the electrolyte membrane from the membrane electrode assembly. Examples include: a method of peeling off the electrode and the adhesive tape together after attaching adhesive tape to the surface of the electrode (anode and cathode); and a method of separating the electrolyte membrane and the electrode after weakening the adhesion between the electrolyte membrane and the electrode by laser irradiation. These methods can also be combined.

[0198] Alternatively, as a method for separating the electrolyte membrane from the membrane electrode assembly, a method can be used to remove the electrode by contacting only the membrane electrode assembly or the electrode with a solution (e.g., the second solution described above) that dissolves the specific fluoropolymer in the electrode. However, using such a solution can sometimes dissolve the specific fluoropolymer in the electrolyte membrane. Therefore, from the viewpoint of suppressing the dissolution of the specific fluoropolymer in the electrolyte membrane, it is preferable to contact the electrode with a small amount of solution (e.g., 100 to 300 parts by mass relative to 100 parts by mass of the membrane electrode assembly or the electrode) for a short time (e.g., 1 to 30 minutes).

[0199] <Process 2-1>

[0200] Step 2-1, performed after step 2-0, involves contacting the first solution with the electrolyte membrane separated from the membrane electrode assembly. Through this step, low-molecular-weight compounds contained in the electrolyte membrane dissolve into the first solution, thus obtaining an electrolyte membrane with removed or reduced polymer decomposition products.

[0201] Specific examples of the method for contacting the first solution with the electrolyte membrane, including preferred methods, are the same as step 1-1 in the first embodiment.

[0202] The first solution may or may not be heated, but from the viewpoint of promoting the dissolution of low molecular weight compounds and being able to further remove or reduce polymer decomposition products from the electrolyte membrane, it is preferred to be heated.

[0203] The temperature of the first solution, including in a preferred manner, is the same as the temperature of the first solution shown in step 1-1 of the first embodiment.

[0204] When the first solution is heated, from the viewpoint of achieving better polymer recovery, the temperature of the first solution is preferably lower than the temperature of the second solution used in step 2-2 described later.

[0205] When the temperature of the first solution is lower than the temperature of the second solution, the temperature difference ((temperature of the second solution) - (temperature of the first solution)) is the same as the temperature difference between the solutions shown in step 1-1 of the first embodiment, including in a preferred manner.

[0206] The contact time between the first solution and the electrolyte membrane, including in the preferred manner, is the same as that shown in step 1-1 of the first embodiment.

[0207] From the viewpoint of achieving better results with the present invention, the amount of the first solution used relative to 100 parts by mass of the electrolyte membrane is preferably 200 parts by mass or more, more preferably 500 parts by mass or more. Furthermore, from the viewpoint of suppressing the amount of waste liquid, it is preferably 1,000,000,000 parts by mass or less, more preferably 100,000,000 parts by mass or less, and even more preferably 10,000,000 parts by mass or less.

[0208] In step 2-1, either solution A or solution B can be used as the first solution. From the viewpoint that it can further remove or reduce polymer decomposition products and inhibit the leaching of specific fluorinated polymers, solution A is preferred.

[0209] In particular, when heated solution A is used in step 2-1, the leaching of specific fluoropolymers can be suppressed, thus further improving the recovery rate of specific fluoropolymers in step 2-3 described later.

[0210] In step 2-1, a drying process to dry the electrolyte membrane can also be performed after the first solution comes into contact with the electrolyte membrane.

[0211] The details of the drying process, including the preferred method, are the same as those shown in step 1-1 of the first embodiment.

[0212] As described above, the polymer decomposition products removed or reduced from the electrolyte membrane in step 2-1 are components generated by the decomposition of specific fluoropolymers, such as low molecular weight compounds and oligomers.

[0213] The molecular weight of the low molecular weight compound is preferably 1000 or less, more preferably 800 or less, and preferably 10 or more, more preferably 100 or more.

[0214] The molecular weight of the oligomer is preferably 10,000 or less, more preferably 5,000 or less, and even more preferably more than 1,000, more preferably 2,000 or more.

[0215] <Process 2-2>

[0216] Step 2-2 is performed after step 2-1. It involves mixing the electrolyte membrane that has been in contact with the first solution with the second solution to obtain a mixed solution containing a specific fluoropolymer, the second solution, and insoluble substances.

[0217] In this process, specific fluoropolymers in the electrolyte membrane dissolve in the second solution and are included in the mixed solution. Additionally, components insoluble in the second solution are included in the mixed solution as insoluble substances.

[0218] As a specific example of the mixing method between the second solution and the electrolyte membrane, it is the same as the mixing method shown in steps 1-2 of the first embodiment, so its description is omitted.

[0219] The second solution may or may not be heated, but from the viewpoint of promoting the dissolution of specific fluoropolymers, it is preferred to be heated.

[0220] The temperature of the second solution, including in a preferred manner, is the same as the temperature of the second solution shown in steps 1-2 of the first embodiment.

[0221] The mixing time of the second solution with the electrolyte membrane, including in the preferred manner, is the same as that shown in steps 1-2 of the first embodiment.

[0222] From the viewpoint of achieving better results with the present invention, the amount of the second solution used relative to 100 parts by mass of the electrolyte membrane is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, and even more preferably 200 parts by mass or more. In addition, from the viewpoint of being able to prevent the concentration of the fluoropolymer in the liquid obtained in the following steps 1-3 from becoming too low and the fluoropolymer-containing liquid obtained in steps 1-3 from being easily reusable, it is preferably 2000 parts by mass or less, more preferably 1500 parts by mass or less, and even more preferably 1000 parts by mass or less.

[0223] Specific examples of insoluble substances include the materials that constitute the aforementioned reinforcing materials.

[0224] It should be noted that the components contained in the insoluble matter can be recycled and reused.

[0225] <Process 2-3>

[0226] Step 2-3 is performed after step 2-2. It is a step to remove insoluble substances from the mixed solution and recover specific fluoropolymers contained in the mixed solution after the insoluble substances have been removed.

[0227] The method for removing insoluble matter is the same as the removal method shown in steps 1-3 of the first embodiment.

[0228] There are no particular limitations on the method for recovering a specific fluoropolymer contained in a mixed solution from which insoluble matter has been removed; known methods may be used.

[0229] The Mw of the specific fluoropolymer being recycled is preferably 10,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, and preferably 3 million or less, more preferably 2 million or less, and even more preferably 1 million or less.

[0230] The Mw of a specific fluoropolymer is determined using the same method as that used for the specific fluoropolymer in the first embodiment.

[0231] The recovered fluoropolymers are suitable for the manufacture of electrolyte membranes, catalyst layers in anodes, catalyst layers in cathodes, etc., but are not limited thereto and can also be used for other purposes.

[0232] [Third Implementation Method]

[0233] The method for recovering a specific fluoropolymer according to the third embodiment of the present invention (hereinafter also referred to as the "recovery method of the third embodiment") is a method for recovering at least one of a specific fluoropolymer contained in the catalyst layer of the anode and a specific fluoropolymer contained in the catalyst layer of the cathode from the above-described membrane electrode assembly.

[0234] In addition, the recycling method of the third embodiment includes a step of separating at least one of the anode and the cathode from the membrane electrode assembly (hereinafter also referred to as step "3-0").

[0235] In addition, the recovery method of the third embodiment includes a step (hereinafter also referred to as step "3-1") after step 3-0, in which the first solution is contacted with at least one of the separated anode and cathode.

[0236] In addition, the recycling method of the third embodiment includes a step (hereinafter also referred to as step "3-2") after step 3-1, in which at least one of the anode and the cathode that has been in contact with the first solution is mixed with the second solution to obtain a mixed solution containing the specific fluoropolymer, the second solution and an insoluble substance containing the catalyst.

[0237] In addition, the recovery method of the third embodiment includes a step after step 3-2, removing the insoluble matter contained in the above mixed solution and recovering the specific fluoropolymer contained in the above mixed solution after the removal of the insoluble matter (hereinafter also referred to as step "3-3").

[0238] The recycling method of the third embodiment is based on the same reason as the recycling method of the first embodiment, that the specific fluoropolymers recycled are not prone to swelling.

[0239] That is, based on the recycling method of the first embodiment, it is speculated that by performing step 3-1 before step 3-2, the low molecular weight compounds contained in the electrode dissolve into the first solution, and the polymer decomposition products are removed or reduced from the electrode, resulting in the aforementioned excellent effect.

[0240] In this specification, unless otherwise specified, "electrode" means at least one of the anode and the cathode.

[0241] <Process 3-0>

[0242] Step 3-0 is the process of separating the electrode from the membrane electrode assembly. The electrode obtained through this step (i.e., the separated electrode) is used in step 3-1 described later. In step 3-0, only the anode may be separated, only the cathode may be separated, or both the anode and cathode may be separated.

[0243] There are no particular limitations on the method for separating the electrode from the membrane electrode assembly. Examples include: attaching an adhesive tape to the surface of the electrode and then peeling the electrode and the adhesive tape together; or separating the electrolyte membrane and the electrode by weakening the adhesion between the electrolyte membrane and the electrode through laser irradiation. These methods can also be combined.

[0244] Alternatively, as a method for separating the electrode from the membrane electrode assembly, a method can be used, for example, to separate the electrode by contacting the membrane electrode assembly with a solution of a specific fluoropolymer dissolved in the electrolyte membrane (e.g., the second solution described above). However, using such a solution can sometimes cause the specific fluoropolymer in the electrode to dissolve. Therefore, from the viewpoint of suppressing the dissolution of the specific fluoropolymer in the electrode, it is preferable to contact the electrode with a small amount of solution (e.g., 100 to 300 parts by mass relative to 100 parts by mass of the membrane electrode assembly or the electrode) for a short time (e.g., 1 to 30 minutes).

[0245] <Process 3-1>

[0246] Step 3-1, performed after step 3-0, involves contacting the first solution with the electrodes separated from the membrane electrode assembly. In step 3-1, only the anode separated from the membrane electrode assembly may be used, only the cathode separated from the membrane electrode assembly may be used, or both the anode and cathode separated from the membrane electrode assembly may be used. It should be noted that when both the anode and cathode are separated from the membrane electrode assembly, in step 3-1, the anode and cathode may be contacted together with the first solution, or the anode and cathode may be contacted with the first solution separately.

[0247] Through this process, the low-molecular-weight compounds contained in the electrode dissolve into the first solution, thus obtaining an electrode with removed or reduced polymer decomposition products.

[0248] Specific examples of the method for contacting the first solution with the electrode, including preferred methods, are the same as step 1-1 in the first embodiment.

[0249] The first solution may or may not be heated, but from the viewpoint of promoting the dissolution of low molecular weight compounds and being able to further remove or reduce polymer decomposition products from the electrode, it is preferred to be heated.

[0250] The temperature of the first solution, including in a preferred manner, is the same as the temperature of the first solution shown in step 1-1 of the first embodiment.

[0251] When the first solution is heated, from the viewpoint of achieving better polymer recovery, the temperature of the first solution is preferably lower than the temperature of the second solution used in step 3-2 described later.

[0252] When the temperature of the first solution is lower than the temperature of the second solution, the temperature difference ((temperature of the second solution) - (temperature of the first solution)) is the same as the temperature difference of each solution shown in step 1-1 of the first embodiment, including in a preferred manner.

[0253] The time for the first solution to contact the electrode, including in the preferred manner, is the same as the time shown in step 1-1 of the first embodiment.

[0254] From the viewpoint of achieving better results with the present invention, the amount of the first solution used relative to 100 parts by mass of the electrode is preferably 200 parts by mass or more, more preferably 500 parts by mass or more. Furthermore, from the viewpoint of suppressing the amount of waste liquid, it is preferably 1,000,000,000 parts by mass or less, more preferably 100,000,000 parts by mass or less, and even more preferably 10,000,000 parts by mass or less.

[0255] It should be noted that the amount of the first solution used in step 3-1 when only the anode is used as the electrode refers to the amount used relative to 100 parts by mass relative to the anode; when only the cathode is used as the electrode in step 3-1, it refers to the amount used relative to 100 parts by mass relative to the cathode; and when both the anode and cathode are used as electrodes in step 3-1, it refers to the amount used relative to a total of 100 parts by mass relative to both the anode and the cathode.

[0256] In step 3-1, either solution A or solution B can be used as the first solution. From the viewpoint that it can further remove or reduce polymer decomposition products and suppress the leaching of specific fluorinated polymers, solution A is preferred.

[0257] In particular, when heated solution A is used in step 3-1, the leaching of specific fluoropolymers can be suppressed, thus further improving the recovery rate of specific fluoropolymers in the subsequent steps 1-3.

[0258] In step 3-1, a drying process to dry the electrode can also be performed after the first solution comes into contact with the electrode.

[0259] The details of the drying process, including the preferred method, are the same as those shown in step 1-1 of the first embodiment.

[0260] As described above, the polymer decomposition products removed or reduced from the electrode in step 3-1 are components generated by the decomposition of specific fluoropolymers, such as low molecular weight compounds and oligomers.

[0261] The molecular weight of the low molecular weight compound is preferably 1000 or less, more preferably 800 or less, and preferably 10 or more, more preferably 100 or more.

[0262] The molecular weight of the oligomer is preferably 10,000 or less, more preferably 5,000 or less, and even more preferably more than 1,000, more preferably 2,000 or more.

[0263] <Process 3-2>

[0264] Step 3-2 is performed after step 3-1. It involves mixing the electrode that has been in contact with the first solution with the second solution to obtain a mixed solution containing a specific fluoropolymer, the second solution, and an insoluble substance containing the catalyst.

[0265] In this process, specific fluoropolymers in the electrodes dissolve in the second solution and are included in the mixed solution. Additionally, components insoluble in the second solution are included in the mixed solution as insoluble substances.

[0266] As a specific example of the mixing method between the second solution and the electrode, it is the same as the mixing method shown in steps 1-2 of the first embodiment, so its description is omitted.

[0267] The second solution may or may not be heated, but from the viewpoint of promoting the dissolution of specific fluoropolymers, it is preferred to be heated.

[0268] The temperature of the second solution, including in a preferred manner, is the same as the temperature of the second solution shown in steps 1-2 of the first embodiment.

[0269] The contact time between the electrode and the second solution, including in the preferred manner, is the same as that shown in steps 1-2 of the first embodiment.

[0270] From the viewpoint of achieving better results with the present invention, the amount of the second solution used relative to 100 parts by mass of the electrode is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, and even more preferably 200 parts by mass or more. In addition, from the viewpoint of being able to suppress the concentration of the fluoropolymer in the liquid obtained in the following steps 1-3 from becoming too low and the fluoropolymer-containing liquid obtained in steps 1-3 being easy to reuse, it is preferably 2000 parts by mass or less, more preferably 1500 parts by mass or less, and even more preferably 1000 parts by mass or less.

[0271] It should be noted that the amount of the second solution used in step 3-2 when only the anode is used as the electrode refers to the amount used relative to 100 parts by mass relative to the anode; when only the cathode is used as the electrode in step 3-2, it refers to the amount used relative to 100 parts by mass relative to the cathode; and when both the anode and cathode are used as electrodes in step 3-2, it refers to the amount used relative to a total of 100 parts by mass relative to both the anode and the cathode.

[0272] In addition to the catalyst, the insoluble matter may also contain materials that constitute the gas diffusion layer.

[0273] It should be noted that the components contained in the insoluble matter can be recycled and reused.

[0274] <Process 3-3>

[0275] Step 3-3 is performed after step 3-2. It is a step to remove insoluble substances from the mixed solution and to recover specific fluoropolymers contained in the mixed solution after the insoluble substances have been removed.

[0276] The method for removing insoluble matter is the same as the removal method shown in steps 1-3 of the first embodiment.

[0277] There are no particular limitations on the method for recovering a specific fluoropolymer contained in a mixed solution from which insoluble matter has been removed; known methods may be used.

[0278] The Mw of the specific fluoropolymer being recycled is preferably 10,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, and preferably 3 million or less, more preferably 2 million or less, and even more preferably 1 million or less.

[0279] The Mw of a specific fluoropolymer is determined using the same method as that used for the specific fluoropolymer in the first embodiment.

[0280] The recovered fluoropolymers are suitable for the manufacture of electrolyte membranes, catalyst layers in anodes, catalyst layers in cathodes, etc., but are not limited thereto and can also be used for other purposes.

[0281] Example

[0282] The present invention will now be described in detail with examples. Examples 1-1 to 1-4, 2-1 to 2-4, and 3-1 to 3-4 are embodiments, and Examples 1-5 to 1-8, 2-5 to 2-8, and 3-5 to 3-8 are comparative examples. However, the present invention is not limited to these examples.

[0283] [TQ value]

[0284] Using a flow testing machine CFT-500A (manufactured by Shimadzu Corporation) with a nozzle of 1 mm length and 1 mm inner diameter, the extrusion rate of fluoropolymers A to C was measured by varying the temperature under an extrusion pressure of 2.94 MPa. The extrusion rate of 100 mm³ was then determined. 3 Temperature per second (TQ value). The results are shown in Table 1.

[0285] [Proportions of each structural unit]

[0286] The proportions of each structural unit in fluoropolymers A to C are determined by 19 The results of the F-NMR measurements were obtained. The results are shown in Table 1.

[0287] [Ion exchange capacity]

[0288] The ion exchange capacity was determined by the proportions of the structural units in fluoropolymers A through C. The results are shown in Table 1.

[0289] [Swelling degree]

[0290] The solutions containing fluoropolymers recovered in Examples 1-1 to 1-5, 2-1 to 2-5, and 3-1 to 3-5 described below are heated at 185°C for 30 minutes to produce cast films.

[0291] After immersing the obtained cast film in 80℃ warm water for 24 hours, the cast film was removed from the warm water, the water adhering to the surface was wiped off, and the quality of the cast film was measured.

[0292] Then, the cast film was dried at 120°C for 60 minutes, and the mass of the dried cast film was measured. The ratio of the mass of water contained in the cast film before drying (the cast film after absorbing water) to the mass of the cast film after drying (mass of water contained in the cast film before drying / mass of the cast film after drying) is defined as the swelling degree.

[0293] [abbreviation]

[0294] TFE: CF2=CF2

[0295] Monomer (m1): CF2 = CFOCF2CF(CF3)OCF2CF2SO2F

[0296] Monomer (m2): The monomer shown in the following formula (m2)

[0297] Monomer (m3): The monomer shown in the following formula (m3)

[0298]

[0299] [Preparation of Fluoropolymer Solution A]

[0300] According to the method described in paragraphs

[0024] to

[0025] of Japanese Patent Application Publication No. 2004-196994, a fluoropolymer containing monomer (m1) units and TFE units is manufactured, and the -SO2F group of the fluoropolymer is converted into the -SO3H group to obtain the -SO3H type fluoropolymer A.

[0301] Then, 27g of the above-mentioned fluoropolymer A, 46g of ethanol and 31g of water were added to a 200ml stainless steel autoclave. Using a spiral blade, the mixture was dissolved and dispersed at 105°C and 300rpm for 6 hours to obtain a dispersion with a solid content of 26% by mass. Hereinafter, this dispersion will be referred to as fluoropolymer solution A.

[0302] [Preparation of Fluoropolymer Solution B]

[0303] A fluoropolymer comprising monomer (m2) units and TFE units was manufactured according to the method described in paragraphs

[0098] to

[0100] of International Publication No. 2017 / 221840. Next, the obtained fluoropolymer was hydrolyzed by heating and mixing in an aqueous KOH solution containing methanol, thereby converting the -SO2F groups of the fluoropolymer to -SO3K groups. Then, the fluoropolymer having -SO3K groups was washed with water and mixed in an aqueous sulfuric acid solution, thereby converting the -SO3K groups of the fluoropolymer to -SO3H groups, yielding a -SO3H type fluoropolymer B.

[0304] Then, 20g of the above-mentioned fluoropolymer B, 34g of ethanol and 79g of water were added to a 200ml stainless steel autoclave. Using a spiral blade, the mixture was dissolved and dispersed at 110°C and 300rpm for 6 hours to obtain a dispersion with a solid content of 15% by mass. Hereinafter, this dispersion will be referred to as fluoropolymer solution B.

[0305] [Preparation of Fluoropolymer Solution C]

[0306] A fluoropolymer comprising monomer (m2) units, monomer (m3) units, and TFE units was manufactured according to the method described in paragraphs

[0114] to

[0115] of International Publication No. 2017 / 006841. Next, the obtained fluoropolymer was hydrolyzed by heating and mixing in an aqueous solution of KOH containing dimethyl sulfoxide, thereby converting the -SO2F groups to -SO3K groups. Then, the fluoropolymer having the -SO3K groups was washed with water and mixed in an aqueous sulfuric acid solution, thereby converting the -SO3K groups of the fluoropolymer to -SO3H groups, yielding a -SO3H type fluoropolymer C.

[0307] Then, 19g of the above-mentioned fluoropolymer C, 64g of 1-propanol, and 64g of water were added to a 200ml stainless steel autoclave. Dissolution / dispersion was carried out at 115°C and 300rpm for 6 hours using a spiral blade to obtain a dispersion with a solid content of 13%. Hereinafter, this dispersion will be referred to as fluoropolymer solution C.

[0308] The composition and properties of the fluoropolymers A to C obtained as described above are shown in Table 1. It should be noted that in the table, meq / g represents milliequinoxes per gram of dry resin.

[0309] [Table 1]

[0310]

[0311] [Manufacturing of solid polymer electrolyte membranes]

[0312] <Electrolyte Membrane A>

[0313] Fluoropolymer solution A was coated onto the surface of a sheet (manufactured by AGC Corporation, AFLEX 100N, 100 μm thick) formed of ethylene-TFE copolymer (hereinafter referred to as ETFE sheet) using a die-coating machine. The sheet was dried at 80°C for 30 minutes and then further heat-treated at 185°C for 30 minutes to obtain a solid polymer electrolyte membrane with a thickness of 20 μm. Hereinafter, this solid polymer electrolyte membrane is referred to as electrolyte membrane A.

[0314] <Electrolyte membrane B>

[0315] The fluoropolymer solution A used to form the solid polymer electrolyte membrane is changed to a fluoropolymer solution B, and the electrolyte membrane B is obtained in the same manner as the electrolyte membrane A.

[0316] [Membrane electrode assembly]

[0317] The liquid composition used in the preparation of the catalyst layer forming liquid uses fluoropolymer solution A or fluoropolymer solution C. Otherwise, the method described in paragraphs

[0136] to

[0138] of International Publication No. 2016 / 104380 is used to prepare membrane electrode junctions MEA1, MEA2 and MEA3, in which an anode is formed on one side of a solid polymer electrolyte membrane and a cathode is formed on the other side.

[0318] The structures of the obtained membrane electrode junctions are shown in Table 2.

[0319] [Table 2]

[0320]

[0321] [Power Generation Test]

[0322] Using the membrane electrode assembly obtained as described above, a power generation test was conducted in the same manner as described in paragraph

[0103] of Japanese Patent No. 5168903.

[0323] [Example 1-1]

[0324] <Process 1-1>

[0325] 10g of MEA1 (i.e., used MEA1) was recovered from a solid polymer fuel cell containing MEA1 after the aforementioned power generation test and impregnated in 100g of water (first solution) at 90°C for 6 hours. Then, the impregnated MEA1 was dried at 80°C for 3 hours. This yielded MEA1 impregnated in the first solution.

[0326] <Process 1-2>

[0327] MEA1, after being impregnated in the first solution, was impregnated in a second solution containing 20g of water and 20g of 1-propanol. The solution was heated to an internal temperature of 105°C and stirred at 105°C for 4 hours. The solution was then cooled to obtain a mixed solution.

[0328] <Process 1-3>

[0329] Centrifuge for 30 minutes (condition: 3000G) to precipitate insoluble components such as catalysts in the mixed solution, and recover the supernatant. Then, filter the supernatant through a 10μm filter to remove fine insoluble components and recover the solution containing fluoropolymers.

[0330] [Example 1-2 and Example 1-3]

[0331] The MEA2 or MEA3 from the power generation test is used instead of the MEA1 from the power generation test. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 1-1.

[0332] [Example 1-4]

[0333] In step 1-1, a first solution containing 95g of water and 5g of ethanol (liquid temperature 25°C) is used instead of 100g of water at 90°C. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 1-1.

[0334] [Example 1-5]

[0335] Step 1-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 1-1.

[0336] [Example 1-6]

[0337] Step 1-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 1-2.

[0338] [Example 1-7]

[0339] Step 1-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Examples 1-3.

[0340] [Example 1-8]

[0341] Step 1-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Examples 1-4.

[0342] [Table 3]

[0343]

[0344] The swelling degree measured using the fluoropolymer recovered in Example 1-1 was lower than that measured using the fluoropolymer recovered in Example 1-5.

[0345] The swelling degree measured using the fluoropolymers recovered in Examples 1-2 was lower than that measured using the fluoropolymers recovered in Examples 1-6.

[0346] The swelling degree measured using the fluoropolymers recovered in Examples 1-3 was lower than that measured using the fluoropolymers recovered in Examples 1-7.

[0347] The swelling degree measured using the fluoropolymers recovered in Examples 1-4 was lower than that measured using the fluoropolymers recovered in Examples 1-8.

[0348] [Example 2-1]

[0349] <Process 2-0>

[0350] 10g of MEA1 (i.e., used MEA1) was recovered from the solid polymer fuel cell with MEA1 after the above power generation test was completed and separated into electrolyte membrane and electrode.

[0351] <Process 2-1>

[0352] 7.7 g of the separated electrolyte membrane was immersed in 100 g of water (first solution) at 90 °C for 6 hours. Then, the immersed electrolyte membrane was dried at 80 °C for 3 hours. Thus, the electrolyte membrane immersed in the first solution was obtained.

[0353] <Process 2-2>

[0354] The electrolyte membrane, after being impregnated with the first solution, was immersed in a second solution containing 20g of water and 20g of 1-propanol. The solution was heated to an internal temperature of 105°C and stirred at 105°C for 4 hours. The solution was then cooled to obtain a mixed solution.

[0355] <Process 2-3>

[0356] Centrifuge for 30 minutes (condition: 3000G) to precipitate the insoluble components in the mixed solution, and recover the supernatant. Then, filter the supernatant through a 10μm filter to remove fine insoluble components and recover the solution containing fluoropolymers.

[0357] [Example 2-2 and Example 2-3]

[0358] The MEA2 or MEA3 obtained after the power generation test was completed was used instead of the MEA1 obtained after the power generation test was completed. Otherwise, the solution containing the fluoropolymer was recovered in the same manner as in Example 2-1.

[0359] [Example 2-4]

[0360] In step 2-1, a first solution containing 95g of water and 5g of ethanol (liquid temperature 25°C) is used instead of 100g of water at 90°C. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 2-1.

[0361] [Example 2-5]

[0362] Step 2-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 2-1.

[0363] [Example 2-6]

[0364] Step 2-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 2-2.

[0365] [Example 2-7]

[0366] Step 2-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 2-3.

[0367] [Example 2-8]

[0368] Step 2-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 2-4.

[0369] [Table 4]

[0370]

[0371] The swelling degree measured using the fluoropolymer recovered in Example 2-1 was lower than that measured using the fluoropolymer recovered in Example 2-5.

[0372] The swelling degree measured using the fluoropolymer recovered in Example 2-2 was lower than that measured using the fluoropolymer recovered in Example 2-6.

[0373] The swelling degree measured using the fluoropolymer recovered in Examples 2-3 was lower than that measured using the fluoropolymer recovered in Examples 2-7.

[0374] The swelling degree measured using the fluoropolymers recovered in Examples 2-4 was lower than that measured using the fluoropolymers recovered in Examples 2-8.

[0375] [Example 3-1]

[0376] 10g of MEA1 (i.e., used MEA1) was recovered from the solid polymer fuel cell with MEA1 after the above power generation test was completed.

[0377] <Process 3-0>

[0378] 10g of used MEA1 was recovered from a solid polymer fuel cell containing the above-mentioned MEA1 and separated into an electrolyte membrane and electrodes (both anode and cathode, hereinafter the same).

[0379] <Process 3-1>

[0380] 2.3g of the separated electrodes (1.15g anode and 1.15g cathode) were immersed in 100g of water (first solution) at 90°C for 6 hours. Then, the immersed electrodes were dried at 80°C for 3 hours. This yielded the electrodes immersed in the first solution.

[0381] <Process 3-2>

[0382] The electrode, after being impregnated with the first solution, was immersed in a second solution containing 20g of water and 20g of 1-propanol. The solution was heated to an internal temperature of 105°C and stirred at 105°C for 4 hours. The solution was then cooled to obtain a mixed solution.

[0383] <Process 3-3>

[0384] Centrifugation is used to precipitate insoluble components such as the catalyst, and the supernatant is recovered. Then, the supernatant is filtered through a 10μm filter to remove fine insoluble components, and the solution containing fluoropolymers is recovered.

[0385] [Example 3-2 and Example 3-3]

[0386] The MEA2 or MEA3 from the power generation test is used instead of the MEA1 from the power generation test. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 3-1.

[0387] [Example 3-4]

[0388] In step 3-1, a first solution containing 95g of water and 5g of ethanol (liquid temperature 25°C) is used instead of 100g of water at 90°C. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 3-1.

[0389] [Example 3-5]

[0390] Step 3-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 3-1.

[0391] [Example 3-6]

[0392] Step 3-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 3-2.

[0393] [Example 3-7]

[0394] Step 3-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 3-3.

[0395] [Example 3-8]

[0396] Step 3-1 is not performed. Otherwise, the solution containing the fluoropolymer is recovered in the same manner as in Example 3-4.

[0397] [Table 5]

[0398]

[0399] The swelling degree measured using the fluoropolymer recovered in Example 3-1 was lower than that measured using the fluoropolymer recovered in Example 3-5.

[0400] The swelling degree measured using the fluoropolymer recovered in Example 3-2 was lower than that measured using the fluoropolymer recovered in Example 3-6.

[0401] The swelling degree measured using the fluoropolymer recovered in Example 3-3 was lower than that measured using the fluoropolymer recovered in Example 3-7.

[0402] The swelling degree measured using the fluoropolymers recovered in Examples 3-4 was lower than that measured using the fluoropolymers recovered in Examples 3-8.

[0403] It should be noted that the entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-221438, filed on December 27, 2023, are incorporated herein by reference as a disclosure of the present invention.

[0404] Explanation of reference numerals in the attached figures

[0405] 10. Membrane electrode assembly

[0406] 11A, 11C catalyst layer

[0407] 12A, 12C gas diffusion layer

[0408] 13 Anode

[0409] 14 Cathode

[0410] 15 Solid polymer electrolyte membrane

Claims

1. A method for recycling fluoropolymers, characterized in that, The method involves recovering a fluoropolymer from a membrane electrode assembly comprising an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode. The anode has a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups. The cathode has a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups. The electrolyte membrane comprises a fluoropolymer having sulfonic acid groups. The first solution is brought into contact with the membrane electrode assembly. The first solution is selected from solution A, which consists only of water, and solution B, which contains water and alcohol, wherein the content of alcohol is less than 10 parts by mass relative to 100 parts by mass of water. Then, The membrane electrode assembly that has been in contact with the first solution, and a second solution comprising water and an alcohol, wherein the alcohol content is 30 parts by mass or more relative to 100 parts by mass of water, are mixed to obtain a mixed solution comprising: the fluoropolymer, the second solution, and an insoluble substance containing the catalyst. The insoluble matter contained in the mixed solution is removed, and the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is recovered.

2. The method for recycling fluoropolymers according to claim 1, wherein, The contact between the first solution and the membrane electrode assembly is the contact between solution A and the membrane electrode assembly, and the heated solution A is used.

3. The method for recycling fluoropolymers according to claim 1 or 2, wherein, When contacting the first solution with the membrane electrode assembly, the first solution is heated. The temperature of the first solution is lower than the temperature of the second solution.

4. The method for recycling fluoropolymers according to claim 1 or 2, wherein, The recovered fluoropolymer has a weight-average molecular weight of 10,000 to 1,000,000.

5. The method for recycling fluoropolymers according to claim 3, wherein, The temperature difference between the first solution and the second solution is greater than 5°C and less than 115°C.

6. A method for recycling fluoropolymers, characterized in that, The method involves recovering a fluoropolymer contained in an electrolyte membrane from a membrane electrode assembly comprising: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, wherein the anode has: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, the cathode has: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, and the electrolyte membrane comprises a fluoropolymer having sulfonic acid groups. Separate the electrolyte membrane from the membrane electrode assembly. The first solution is brought into contact with the separated electrolyte membrane. The first solution is selected from solution A, which consists only of water, and solution B, which contains water and alcohol, wherein the content of alcohol is less than 10 parts by mass relative to 100 parts by mass of water. Then, The electrolyte membrane, which has been in contact with the first solution, and a second solution comprising water and alcohol, wherein the alcohol content is 30 parts by mass or more relative to 100 parts by mass of water, are mixed to obtain a mixed solution comprising the fluoropolymer, the second solution, and insoluble matter. The insoluble matter contained in the mixed solution is removed, and the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is recovered.

7. The method for recycling fluoropolymers according to claim 6, wherein, The contact between the first solution and the electrolyte membrane is the contact between solution A and the electrolyte membrane, and the heated solution A is used.

8. The method for recycling fluoropolymers according to claim 6 or 7, wherein, When contacting the first solution with the electrolyte membrane, the first solution is heated. The temperature of the first solution is lower than the temperature of the second solution.

9. The method for recycling fluoropolymers according to claim 6 or 7, wherein, The recovered fluoropolymer has a weight-average molecular weight of 10,000 to 1,000,000.

10. The method for recycling fluoropolymers according to claim 8, wherein, The temperature difference between the first solution and the second solution is greater than 5°C and less than 115°C.

11. A method for recycling fluoropolymers, characterized in that, At least one of the following fluoropolymers contained in the catalyst layer of the anode and the catalyst layer of the cathode is recovered from a membrane electrode assembly, the membrane electrode assembly comprising: an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, the anode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, the cathode having: a catalyst layer comprising a catalyst and a fluoropolymer having sulfonic acid groups, and the electrolyte membrane comprising a fluoropolymer having sulfonic acid groups, wherein the method, Separate at least one of the anode and the cathode from the membrane electrode assembly. The first solution is brought into contact with at least one of the separated anode and cathode. The first solution is selected from solution A, which consists only of water, and solution B, which contains water and alcohol, wherein the alcohol content is less than 10 parts by mass relative to 100 parts by mass of water. At least one of the anode and the cathode, which has been in contact with the first solution, and a second solution comprising water and an alcohol, wherein the alcohol content is 30 parts by mass or more relative to 100 parts by mass of water, are mixed to obtain a mixed solution comprising the fluoropolymer, the second solution, and an insoluble substance. The insoluble matter contained in the mixed solution is removed, and the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is recovered.

12. The method for recycling fluoropolymers according to claim 11, wherein, The contact between the first solution and at least one of the anode and the cathode is the contact between solution A and the anode and the cathode, and the heated solution A is used.

13. The method for recycling fluoropolymers according to claim 11 or 12, wherein, When contacting the first solution with at least one of the anode and the cathode, the first solution is heated. The temperature of the first solution is lower than the temperature of the second solution.

14. The method for recycling fluoropolymers according to claim 11 or 12, wherein, The recovered fluoropolymer has a weight-average molecular weight of 10,000 to 1,000,000.

15. The method for recovering fluoropolymers according to claim 13, wherein, The temperature difference between the first solution and the second solution is greater than 5°C and less than 115°C.

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