Method for recovering fluorine-containing polymer

Abstract

Provided is a method for recovering a fluorine-containing polymer wherein the recovered fluorine-containing polymer is resistant to swelling.　The method according to the present invention for recovering a fluorine-containing polymer is a method that recovers a fluorine-containing polymer from a membrane-electrode assembly comprising: a cathode and anode having a catalyst layer that contains a catalyst and a fluorine-containing polymer having a sulfonic acid group; and, disposed between the cathode and anode, an electrolyte membrane containing a fluorine-containing polymer having a sulfonic acid group. After the membrane-electrode assembly has been brought into contact with a first solution selected from a solution A comprising only water and a solution B containing water and an alcohol, the membrane-electrode assembly is mixed with a second solution containing water and an alcohol to obtain a mixed solution containing the fluorine-containing polymer, the second solution, and insoluble matter. The insoluble matter contained in the mixed solution is removed and the fluorine-containing polymer contained in the mixed solution from which the insoluble matter has been removed is recovered.

Description

Method for recovering fluoropolymers

[0001] The present invention relates to a method for recovering a fluoropolymer.

[0002] A membrane electrode assembly used in a water electrolysis device or a fuel cell includes an anode having a catalyst layer, a cathode having a catalyst layer, and an electrolyte membrane disposed between the anode and the cathode. In recent years, from the viewpoint of reducing the environmental load, etc., reuse of materials constituting the membrane electrode assembly has been considered. For example, Patent Document 1 discloses a method for recovering a fluoropolymer from a membrane electrode assembly removed from a fuel cell through a process of dissolving the fluoropolymer in the electrolyte membrane into a solvent, etc.

[0003] Japanese Patent Application Laid-Open No. 2004-171921

[0004] When a fluoropolymer having sulfonic acid groups is recovered from a membrane electrode assembly and then the recovered fluoropolymer is reused as a polymer for producing an electrolyte membrane or a catalyst layer, the recovered fluoropolymer is required to have the property of being resistant to swelling with water, etc. The present inventors attempted to recover the fluoropolymer by dissolving a fluoropolymer having sulfonic acid groups in an electrolyte membrane in a solution containing alcohol, referring to the method for recovering a fluoropolymer described in Patent Document 1, but found that swelling of the recovered fluoropolymer was not sufficiently suppressed and there was room for improvement.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for recovering a fluoropolymer in which the recovered fluoropolymer is less likely to swell.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that the desired effect can be obtained when a first solution selected from a solution A consisting only of water and a solution B containing water and alcohol with a low alcohol content is brought into contact with a membrane electrode assembly, an electrolyte membrane, or an electrode (at least one of an anode and a cathode), and then a second solution containing water and alcohol 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, thereby completing the present invention.

[0007] That is, the inventors have found that the above-mentioned problems can be solved by the following configuration: [1] A method for recovering a fluoropolymer from a membrane / electrode assembly comprising an anode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, a cathode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, and an electrolyte membrane disposed between the anode and the cathode and containing a fluoropolymer having sulfonic acid groups, the method comprising contacting the membrane / electrode assembly with a first solution selected from solution A consisting of only water and solution B containing water and alcohol in a content of the alcohol of 10 parts by mass or less per 100 parts by mass of the water, and then mixing the membrane / electrode assembly that has been contacted with the first solution with a second solution containing water and alcohol in a content of 30 parts by mass or more per 100 parts by mass of the water to obtain a mixed solution containing the fluoropolymer, the second solution, and insoluble matter including the catalyst, A method for recovering a fluoropolymer, comprising removing the insoluble matter contained in the mixed solution and recovering the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed. [2] The method for recovering a fluoropolymer according to [1], wherein the contact of the first solution with the membrane / electrode assembly is contact of Solution A with the membrane / electrode assembly, and heated Solution A is used. [3] The method for recovering a fluoropolymer according to [1] or [2], wherein a heated first solution is used when contacting the first solution with the membrane / electrode assembly, and the temperature of the first solution is lower than the temperature of the second solution. [4] The method for recovering a fluoropolymer according to any of [1] to [3], wherein the recovered fluoropolymer has a weight-average molecular weight of 10,000 to 1,000,000. [5] The method for recovering a fluoropolymer according to [3], wherein the temperature difference between the temperature of the first solution and the temperature of the second solution is 5°C or more and 115°C or less.[6] A method for recovering a fluoropolymer contained in an electrolyte membrane from a membrane electrode assembly comprising an anode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, a cathode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, and an electrolyte membrane disposed between the anode and the cathode and containing a fluoropolymer having sulfonic acid groups, comprising the steps of: separating the electrolyte membrane from the membrane electrode assembly; contacting the separated electrolyte membrane with a first solution selected from solution A consisting only of water and solution B containing water and alcohol, wherein the alcohol content is 10 parts by mass or less per 100 parts by mass of the water; and then mixing the electrolyte membrane contacted with the first solution with a second solution containing water and alcohol, wherein the alcohol content is 30 parts by mass or more per 100 parts by mass of the water, to obtain a mixed solution containing the fluoropolymer, the second solution, and insoluble matter; A method for recovering a fluoropolymer, comprising removing the insoluble matter contained in the mixed solution and recovering the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed. [7] The method for recovering a fluoropolymer according to [6], wherein the contact of the first solution with the electrolyte membrane is contact of solution A with the electrolyte membrane, and heated solution A is used. [8] The method for recovering a fluoropolymer according to [6] or [7], wherein a heated first solution is used when contacting the first solution with the electrolyte membrane, and the temperature of the first solution is lower than the temperature of the second solution. [9] The method for recovering a fluoropolymer according to any of [6] to [8], wherein the recovered fluoropolymer has a weight-average molecular weight of 10,000 to 1,000,000.

[10] The method for recovering a fluoropolymer according to [8], wherein the temperature difference between the temperature of the first solution and the temperature of the second solution is 5°C or more and 115°C or less.

[11] A method for recovering a fluoropolymer, comprising recovering at least one of a fluoropolymer contained in the catalyst layer of the anode and a fluoropolymer contained in the catalyst layer of the cathode from a membrane / electrode assembly comprising an anode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, a cathode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, and an electrolyte membrane disposed between the anode and the cathode and containing a fluoropolymer having sulfonic acid groups, the method comprising separating at least one of the anode and the cathode from the membrane / electrode assembly, contacting the separated at least one of the anode and the cathode with a first solution selected from a solution A consisting only of water and a solution B containing water and an alcohol in which the content of the alcohol per 100 parts by mass of the water is 10 parts by mass or less, and then a method for recovering a fluoropolymer, comprising mixing at least one of the anode and the cathode, which has been brought into contact with the first solution, with a second solution containing water and an alcohol, the alcohol content being 30 parts by mass or more per 100 parts by mass of the water, to obtain a mixed solution containing the fluoropolymer, the second solution, and insoluble matter, removing the insoluble matter contained in the mixed solution, and recovering the fluoropolymer contained in the mixed solution from which the insoluble matter has been removed.

[12] The method for recovering a fluoropolymer according to

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

[13] The method for recovering a fluoropolymer according to

[11] or

[12] , wherein heated first solution is used when bringing the first solution into contact with at least one of the anode and the cathode, and the temperature of the first solution is lower than the temperature of the second solution.

[14] The method for recovering a fluoropolymer according to any one of

[11] to

[13] , wherein the recovered fluoropolymer has a weight-average molecular weight of 10,000 to 1,000,000.

[15] The method for recovering a fluoropolymer according to

[13] , wherein the temperature difference between the temperature of the first solution and the temperature of the second solution is 5°C or more and 115°C or less.

[0008] According to the present invention, there can be provided a method for recovering a fluoropolymer in which the recovered fluoropolymer is less likely to swell.

[0009] FIG. 2 is a cross-sectional view showing an example of a membrane electrode assembly.

[0010] The following definitions of terms apply throughout the present specification and claims unless otherwise specified. A "unit" in a polymer refers to an atomic group derived from one molecule of a monomer formed by polymerization of the monomer. A unit may be an atomic group formed directly by the polymerization reaction, or an atomic group in which a portion of the atomic group is converted into a different structure by processing the polymer obtained by the polymerization reaction. Constituent units derived from individual monomers may be referred to by the name of the monomer followed by "unit." A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit stated in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit stated in a certain numerical range may be replaced with a value shown in the examples.

[0011] Hereinafter, the materials used in the method for recovering a fluoropolymer of the present invention will be explained, and then the method for recovering a fluoropolymer of the present invention will be explained for each embodiment.

[0012] [Membrane Electrode Assembly] The membrane electrode assembly used in the method for recovering a fluoropolymer of the present invention comprises an anode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, a cathode having a catalyst layer containing a catalyst and a fluoropolymer having sulfonic acid groups, and an electrolyte membrane disposed between the anode and the cathode and containing a fluoropolymer having sulfonic acid groups. In the following description, unless otherwise specified, the "fluoropolymer having sulfonic acid groups" will be referred to as the "specific fluoropolymer." An example of a membrane electrode assembly will be specifically described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a membrane electrode assembly used in each embodiment described below. The membrane electrode assembly 10 comprises 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. The membrane electrode assembly 10 is preferably a membrane electrode assembly recovered from a fuel cell (polymer electrolyte fuel cell) or a water electrolysis device. The method for recovering the membrane electrode assembly 10 from these devices is not particularly limited, and any known method can be used.

[0013] <Electrolyte Membrane> The solid polymer electrolyte membrane 15 contains a specific fluorine-containing polymer, and a known solid polymer electrolyte membrane can be used. The specific fluorine-containing polymer contained in the solid polymer electrolyte membrane 15 is not particularly limited, but preferably contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid group and a fluorine atom.

[0014] Examples of fluorine-containing olefins include fluoroolefins having one or more fluorine atoms in the molecule and having 2 to 3 carbon atoms. Specific examples of fluoroolefins include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene, with TFE being preferred.

[0015] The unit having a sulfonic acid group and a fluorine atom is preferably a unit represented by formula (1): Formula (1) -[CF ２-CF(-L-(SO ３ H) ｎ )]-

[0016] L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at the terminal of the perfluorohydrocarbon group or between carbon atoms. The (n+1)-valent perfluorohydrocarbon group preferably has 1 or more carbon atoms, more preferably 2 or more carbon atoms, and preferably 20 or less carbon atoms, and particularly preferably 10 or less carbon atoms. L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, and particularly preferably a divalent perfluoroalkylene group which may contain an etheric oxygen atom (n=1), or a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom (n=2). The divalent perfluoroalkylene group may be either linear or branched. n is 1 or 2.

[0017] The unit represented by formula (1) is preferably a unit represented by formula (1-1), a unit represented by formula (1-2), a unit represented by formula (1-3), or a unit represented by formula (1-4). ２ -CF(-O-R ｆ１ -SO ３ H)] - Formula (1-2) - [CF ２ -CF(-R ｆ１ -SO ３ H)]-

[0018]

[0019]

[0020] R ｆ１ R is a perfluoroalkylene group which may contain an etheric oxygen atom. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less. ｆ２R is a perfluoroalkylene group which may contain a single bond or an etheric oxygen atom. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less. ｆ３ is a perfluoroalkylene group which may contain a single bond or an etheric oxygen atom. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less. The etheric oxygen atom may be located at a terminal in the perfluoroalkylene group or between carbon atoms. r is 0 or 1. m is 0 or 1.

[0021] The solid polymer electrolyte membrane 15 may be reinforced with a reinforcing material. Examples of the reinforcing material include a porous body, fiber, woven fabric, and nonwoven fabric. Examples of the reinforcing material include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, polyphenylene sulfide, polyether sulfone, and polyether ether ketone.

[0022] The solid polymer electrolyte membrane 15 may contain one or more atoms selected from the group consisting of cerium and manganese to further improve durability. Cerium and manganese decompose hydrogen peroxide, a substance that causes deterioration of the solid polymer electrolyte membrane 15. Cerium and manganese are preferably present in the solid polymer electrolyte membrane 15 as ions, and may exist in any state in the solid polymer electrolyte membrane 15 as long as they exist as ions. The solid polymer electrolyte membrane 15 may contain silica or heteropolyacid (such as zirconium phosphate, phosphomolybdic acid, or phosphotungstic acid) as a water-retaining agent to prevent drying. The solid polymer electrolyte membrane 15 may contain platinum atoms to consume hydrogen that permeates the membrane within the membrane.

[0023] <Cathode> The catalyst layer 11C of the cathode 14 contains a catalyst and a specific fluorine-containing polymer, and a known catalyst layer for a cathode can be used. The specific fluorine-containing polymer contained in the catalyst layer 11C is not particularly limited, but preferably contains a unit having a sulfonic acid group and a fluorine atom, and at least one unit selected from a unit based on a fluorine-containing olefin and a unit containing a cyclic ether structure.

[0024] Specific examples of the unit having a sulfonic acid group and a fluorine atom, and the unit based on a fluorine-containing olefin are the same as the units that can be contained in the specific fluorine-containing polymer in the above-mentioned solid polymer electrolyte membrane 15. Specific examples of the unit containing a cyclic ether structure include the units containing a cyclic ether structure described in WO 2020 / 145287.

[0025] The catalyst contained in the catalyst layer 11C is not particularly limited, but examples include supported catalysts in which platinum, platinum alloys, or platinum-containing catalysts having a core-shell structure are supported on a carbon support or a metal oxide support; iridium oxide catalysts; alloys containing iridium oxide; and catalysts containing iridium oxide having a core-shell structure. Examples of carbon supports include carbon black powder. Examples of metal oxide supports include oxides of simple metals or complexes of metals such as aluminum, tin, zinc, nickel, cobalt, iron, titanium, cerium, zirconium, palladium, lanthanum, niobium, tantalum, and antimony. Non-metal catalysts with electrocatalytic activity, such as carbon alloy catalysts, may also be used.

[0026] The gas diffusion layer 12C has the functions of uniformly diffusing gas or water in the catalyst layer 11C, discharging gas generated from the catalyst layer 11C, and acting as a current collector. Examples of the gas diffusion layer 12C include carbon paper, carbon cloth, carbon felt, and porous titanium. When the gas diffusion layer 12C is made of carbon, it is preferably treated with polytetrafluoroethylene or the like to be water-repellent. When it is made of porous titanium, it is preferable that the surface be coated with platinum. While the membrane electrode assembly 10 in FIG. 1 includes the gas diffusion layer 12C, the gas diffusion layer is an optional component and need not be included in the membrane electrode assembly.

[0027] <Anode> The catalyst layer 11A of the anode 13 contains a catalyst and a specific fluorine-containing polymer, and a known catalyst layer for an anode can be used. The specific fluorine-containing polymer contained in the catalyst layer 11A is not particularly limited, but preferably contains a unit having a sulfonic acid group and a fluorine atom, and a unit based on a fluorine-containing olefin. Specific examples of the unit having a sulfonic acid group and a fluorine atom, and the unit based on a fluorine-containing olefin are the same as the units that can be contained in the specific fluorine-containing polymer in the solid polymer electrolyte membrane 15 described above.

[0028] The catalyst contained in the catalyst layer 11A is not particularly limited, but may be, for example, a catalyst containing a porous support and a metal supported on the porous support. Specific examples of the porous support and metal are the same as those in the catalyst layer 11C described above.

[0029] Specific examples of the gas diffusion layer 12A of the anode 13 are the same as the specific examples of the gas diffusion layer 12C described above, and the gas diffusion layer 12A is an arbitrary member, similar to the gas diffusion layer 12C.

[0030] <Other Components> The membrane electrode assembly 10 may have a carbon layer (not shown) between the catalyst layer and the gas diffusion layer. The carbon layer contains, for example, carbon and a nonionic fluorine-containing polymer. A specific example of carbon is preferably carbon nanofiber having a fiber diameter of 1 to 1000 nm and a fiber length of 1000 μm or less. A specific example of the nonionic fluorine-containing polymer is polytetrafluoroethylene.

[0031] [First Solution] The first solution is a solution selected from solution A and solution B, and is used in each embodiment described below.

[0032] <Solution A> Solution A consists of water only.

[0033] <Solution B> Solution B contains water and an alcohol. Specific examples of the alcohol 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-tridecafluoro-1-octanol. Of these, ethanol and 1-propanol are preferred in terms of achieving better effects of the present invention. The alcohols may be used alone or in combination of two or more. The content of the alcohol in solution B is 10 parts by mass or less relative to 100 parts by mass of water in solution B, and from the viewpoint of achieving better effects of the present invention, it is preferably 9 parts by mass or less, and more preferably 8 parts by mass or less. The content of the alcohol in solution B is more than 0 parts by mass relative to 100 parts by mass of water in solution B, and is preferably 1 part by mass or more, and more preferably 2 parts by mass or more.

[0034] [Second Solution] The second solution is a solution used in each embodiment described below, and contains water and an alcohol. Specific examples of the alcohol are the same as the specific examples of the alcohol contained in solution B described above. The alcohol may be used alone or in combination of two or more. The content of the alcohol in the second solution is 30 parts by mass or more relative to 100 parts by mass of water in the second solution, and from the viewpoint of better solubility of the specific fluorine-containing polymer, it is preferably 35 parts by mass or more, and more preferably 40 parts by mass or more. The content of the alcohol 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.

[0035] [First Embodiment] A method for recovering a specific fluoropolymer according to a first embodiment of the present invention (hereinafter also referred to as "the recovery method of the first embodiment") is a method for recovering the specific fluoropolymer from the membrane / electrode assembly. The recovery method of the first embodiment also includes a step of bringing the first solution into contact with the membrane / electrode assembly (hereinafter also referred to as "step 1-1"). The recovery method of the first embodiment also includes a step of, after step 1-1, mixing the membrane / electrode assembly that has been contacted with the first solution with the second solution to obtain a mixed solution containing the specific fluoropolymer, the second solution, and insoluble matter containing the catalyst (hereinafter also referred to as "step 1-2"). The recovery method of the first embodiment also includes a step of, after step 1-2, removing the insoluble matter contained in the mixed solution and recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matter has been removed (hereinafter also referred to as "step 1-3").

[0036] According to the recovery method of the first embodiment, the recovered specific fluoropolymer is less likely to swell. The details of the reason for this are not clear, but it is presumed to be due to the following reasons. When a membrane electrode assembly deteriorates or reaches the end of its specified service life after operation of a water electrolysis device or fuel cell including the membrane electrode assembly, the used membrane electrode assembly is recovered and replaced with a new membrane electrode assembly. The catalyst layer and electrolyte membrane contained in the electrodes (at least one of the anode and cathode) of the recovered membrane electrode assembly may contain, together with the specific fluoropolymer, at least one of low-molecular-weight compounds and oligomers that are decomposition products of the specific fluoropolymer. It is believed that such low-molecular-weight compounds and oligomers are generated by decomposition of the specific fluoropolymer during operation of the device. In this specification, such low-molecular-weight compounds and oligomers may also be simply referred to as "polymer decomposition products." When the specific fluoropolymer contained in the membrane electrode assembly is recovered by dissolving it in a solution with a high alcohol content, the polymer decomposition products are also recovered together with the specific fluoropolymer. If polymer decomposition products are mixed in with the specific fluoropolymer in the recovered material, this may cause swelling of the specific fluoropolymer, resulting in a decrease in the performance of the device including the membrane electrode assembly formed using the recovered material (for example, the power generation performance and durability of the device). To address this problem, according to the recovery method of the first embodiment, by carrying out step 1-1 before step 1-2, the polymer decomposition products contained in the membrane electrode assembly are eluted into the first solution, and the polymer decomposition products are removed or reduced from the membrane electrode assembly, and it is presumed that this has resulted in the above-mentioned excellent effect.

[0037] <Step 1-1> Step 1-1 is a step of bringing a first solution into contact with a membrane electrode assembly. This step causes polymer decomposition products contained in the anode catalyst layer, the cathode catalyst layer, and the electrolyte membrane contained in the membrane electrode assembly to elute into the first solution, thereby obtaining a membrane electrode assembly from which the polymer decomposition products have been removed or reduced. In step 1-1, solution A containing no alcohol at all or solution B containing a small amount of alcohol is used as the first solution, so that elution of the specific fluorine-containing polymer into the first solution is suppressed.

[0038] Specific examples of the method for contacting the first solution with the membrane electrode assembly include a method of immersing the membrane electrode assembly in the first solution and a method of spraying the first solution onto the surface of the membrane electrode assembly using a spraying device such as a sprayer. Among these, the immersion method is preferred because it makes it easier for the polymer decomposition products to dissolve into the first solution. Furthermore, stirring the solution during immersion is preferred because it makes it easier for the polymer decomposition products to dissolve into the first solution.

[0039] The first solution may be heated or not, but is preferably heated from the viewpoint of accelerating the elution of polymer decomposition products and further enabling the removal or reduction of polymer decomposition products from the membrane electrode assembly. The temperature of the first solution is preferably 5°C or higher, and from the viewpoint of further demonstrating the above-mentioned effects, more preferably 35°C or higher, and even more preferably 75°C or higher. The temperature of the first solution is preferably 160°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower, from the viewpoint of being able to suppress the elution of the specific fluoropolymer into the first solution and further improving the recovery rate of the specific fluoropolymer in step 1-3.

[0040] When the first solution is heated, the temperature of the first solution is preferably lower than the temperature of the second solution used in Step 1-2 described below, in order to obtain a better polymer recovery rate. 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 preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, in order to obtain a better effect of the present invention, and is preferably 120°C or lower, more preferably 115°C or lower, and even more preferably 100°C or lower.

[0041] The time for which the first solution is brought into contact with the membrane electrode assembly is not particularly limited, but is preferably 1 minute or more, more preferably 5 minutes or more, and is preferably 24 hours or less, more preferably 16 hours or less.

[0042] The amount of the first solution used is preferably 200 parts by mass or more, and more preferably 500 parts by mass or more, relative to 100 parts by mass of the membrane / electrode assembly, from the viewpoint of achieving better effects of the present invention; and is preferably 1000,000,000 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, from the viewpoint of reducing the amount of waste liquid.

[0043] In step 1-1, either solution A or solution B may be used as the first solution, but it is preferable to use solution A from the viewpoints that polymer decomposition products can be further removed or reduced and that elution of the specific fluoropolymer can be suppressed. In particular, when heated solution A is used in step 1-1, the removability of polymer decomposition products is improved compared to non-heated solution A, and elution of the specific fluoropolymer can be suppressed compared to solution B described below. Therefore, the recovery rate of the specific fluoropolymer in step 1-3 described below can be further improved. Here, when heated solution A is used, the temperature of solution A is preferably 40°C or higher, more preferably 80°C or higher, from the viewpoint that the above-mentioned effect can be more fully exerted.

[0044] In step 1-1, after contacting the first solution with the membrane electrode assembly, a drying treatment may be performed to dry the membrane electrode assembly. By using the membrane electrode assembly that has been subjected to the drying treatment in step 1-2 described below, the membrane electrode assembly can be easily charged in step 1-2 (i.e., the handleability of the membrane electrode assembly is improved), and the concentration of the mixed solution obtained in step 1-2 can be easily adjusted. Examples of the drying treatment method include natural drying, heat drying, air drying, and a combination of these. The drying temperature is preferably 10°C or higher, more preferably 20°C or higher, and is preferably 160°C or lower, more preferably 120°C or lower.

[0045] As described above, the polymer decomposition products removed or reduced from the membrane electrode assembly in step 1-1 are components generated by decomposition of the specific fluorine-containing polymer, and examples thereof include low-molecular-weight compounds and oligomers. The molecular weight of the low-molecular-weight compounds is preferably 1,000 or less, more preferably 800 or less, and also preferably 10 or more, more preferably 100 or more. The molecular weight of the oligomers is preferably 10,000 or less, more preferably 5,000 or less, and also preferably more than 1,000, more preferably 2,000 or more.

[0046] <Step 1-2> Step 1-2 is carried out after step 1-1, and is a step of mixing the membrane / electrode assembly that has been contacted with the first solution with the second solution to obtain a mixed solution containing the specific fluorine-containing polymer, the second solution, and insoluble matter containing a catalyst. In this step, the specific fluorine-containing polymer in the anode catalyst layer, the cathode catalyst layer, and the electrolyte membrane contained in the membrane / electrode assembly are eluted into the second solution and contained in the mixed solution. In addition, components such as the catalyst that are insoluble in the second solution are contained in the mixed solution as insoluble matter. The specific fluorine-containing polymer contained in each material of the membrane / electrode assembly (particularly the specific fluorine-containing polymer having a unit represented by the above-mentioned formula (1)) has high solubility in a mixed solvent of alcohol and water, and the second solution has a high alcohol content, so by carrying out step 1-2, the specific fluorine-containing polymer contained in each material of the membrane / electrode assembly is eluted into the second solution.

[0047] A specific example of a method for mixing the second solution with the membrane electrode assembly is a method in which the membrane electrode assembly is immersed in the second solution and stirred.

[0048] The second solution may be heated or not, but is preferably heated in order to promote the elution of the specific fluoropolymer. The temperature of the second solution is preferably 15°C or higher, and in order to more effectively exert the above-mentioned effect, it is more preferably 40°C or higher, and even more preferably 80°C or higher.

[0049] The time for mixing the second solution with the membrane electrode assembly is not particularly limited, but is preferably 15 minutes or more, more preferably 60 minutes or more, and is preferably 72 hours or less, more preferably 36 hours or less.

[0050] The amount of the second solution used 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, per 100 parts by mass of the membrane / electrode assembly, from the viewpoint that the effects of the present invention are more excellent; and 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, from the viewpoint that the concentration of the fluoropolymer in the liquid obtained in step 1-3 described below can be prevented from becoming too low and the liquid containing the fluoropolymer obtained in step 1-3 can be easily reused.

[0051] In addition to the catalyst, the insoluble matter may contain, for example, the material constituting the reinforcing material described above, the material constituting the gas diffusion layer, the material constituting the carbon layer, the material constituting the porous transport layer, etc. The components contained in the insoluble matter may be recovered and reused.

[0052] <Step 1-3> Step 1-3 is carried out after step 1-2, and is a step of removing insoluble matters contained in the mixed solution and recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matters have been removed.

[0053] As a method for removing insoluble matter, known methods can be used, such as centrifugation, filtration through a filter, and natural sedimentation. In terms of more excellent removal efficiency, it is preferable to combine two or more of these methods (particularly, centrifugation and filtration through a filter).

[0054] The method for recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is not particularly limited, and any known method can be used.

[0055] The weight average molecular weight (hereinafter also referred to as "Mw") of the recovered specific fluoropolymer is preferably 10,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, and preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,000,000 or less. The Mw of the specific fluoropolymer is the weight average molecular weight in terms of polyethylene oxide measured using the mixed solution from which insoluble matter has been removed in step 1-3 by size exclusion gas chromatography (SEC) under the following conditions: Apparatus: 8320GPC manufactured by Tosoh Corporation Column: a-M and a-3000 manufactured by Tosoh Corporation Mobile phase: 10 mM di-n-butylammonium acetate (DBAA)-added methanol (for HPLC) Flow rate: 1.0 mL / min Oven temperature: 37°C System temperature: 37°C Injection volume: 50 μL Detector: evaporative light scattering detector (ELSD)

[0056] The recovered specific fluorine-containing polymer is suitable for producing an electrolyte membrane, a catalyst layer in an anode, a catalyst layer in a cathode, etc., but is not limited thereto and may be used for other purposes.

[0057] [Second Embodiment] A method for recovering a specific fluorine-containing polymer according to a 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 fluorine-containing polymer contained in an electrolyte membrane from the above-mentioned membrane electrode assembly. The recovery method of the second embodiment also includes a step of separating the electrolyte membrane from the membrane electrode assembly (hereinafter also referred to as step "2-0"). The recovery method of the second embodiment also includes a step of contacting the separated electrolyte membrane with the first solution (hereinafter also referred to as "step 2-1") after step 2-0. The recovery method of the second embodiment also includes a step of mixing the electrolyte membrane that has been contacted with the first solution with the second solution after step 2-1 to obtain a mixed solution containing the specific fluorine-containing polymer, the second solution, and insoluble matter (hereinafter also referred to as "step 2-2"). The recovery method of the second embodiment also includes, after step 2-2, a step of removing the insoluble matter contained in the mixed solution and recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matter has been removed (hereinafter also referred to as "step 2-3").

[0058] In the recovery method of the second embodiment, the recovered specific fluoropolymer is less likely to swell for the same reason as in the recovery method of the first embodiment. That is, according to the recovery method of the first embodiment, by carrying out step 2-1 before step 2-2, the low-molecular-weight compounds contained in the electrolyte membrane are eluted into the first solution, and polymer decomposition products are removed or reduced from the electrolyte membrane, which is presumably why the above-mentioned excellent effect is achieved.

[0059] The recovery method of the second embodiment is similar to the recovery method of the first embodiment, except that an electrolyte membrane separated from a membrane electrode assembly is used instead of the membrane electrode assembly. Therefore, in the following description of each step in the recovery method of the second embodiment, the description of the same content as in the recovery method of the first embodiment may be omitted.

[0060] <Step 2-0> Step 2-0 is a step of separating the electrolyte membrane from the membrane electrode assembly. The electrolyte membrane obtained in this step (i.e., the separated electrolyte membrane) is used in the later-described step 2-1.

[0061] The method for separating the electrolyte membrane from the membrane electrode assembly is not particularly limited, and examples thereof include a method of attaching adhesive tape to the surfaces of the electrodes (anode and cathode) and then peeling the electrodes together with the adhesive tape, and a method of weakening the adhesive force between the electrolyte membrane and the electrodes by laser irradiation and then separating the electrolyte membrane from the electrodes. These methods may be performed in combination. Furthermore, as a method for separating the electrolyte membrane from the membrane electrode assembly, for example, a method of contacting only the membrane electrode assembly or the electrodes with a solution that dissolves the specific fluorine-containing polymer in the electrodes (e.g., the second solution described above) and removing the electrodes can also be used. However, since methods using such solutions may also dissolve the specific fluorine-containing polymer in the electrolyte membrane, contact with a small amount of solution (e.g., 100 to 300 parts by mass per 100 parts by mass of the membrane electrode assembly or electrodes) for a short period of time (e.g., 1 to 30 minutes) is preferred in order to prevent dissolution of the specific fluorine-containing polymer in the electrolyte membrane.

[0062] <Step 2-1> Step 2-1 is performed after step 2-0, and is a step of bringing the first solution into contact with the electrolyte membrane separated from the membrane electrode assembly. This step causes low-molecular-weight compounds contained in the electrolyte membrane to elute into the first solution, thereby obtaining an electrolyte membrane in which polymer decomposition products have been removed or reduced.

[0063] A specific example of the method for contacting the first solution with the electrolyte membrane is the same as step 1-1 in the first embodiment, including the preferred embodiment.

[0064] The first solution may be heated or not, but is preferably heated because this promotes the elution of low molecular weight compounds and allows the polymer decomposition products to be further removed or reduced from the electrolyte membrane. The temperature of the first solution is the same as that of the first solution shown in step 1-1 of the first embodiment, including preferred embodiments.

[0065] When the first solution is heated, the temperature of the first solution is preferably lower than the temperature of the second solution used in step 2-2 described below, in order to obtain a better polymer recovery rate. 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 preferred embodiments.

[0066] The time for which the first solution is brought into contact with the electrolyte membrane is the same as that shown in step 1-1 of the first embodiment, including the preferred embodiment.

[0067] The amount of the first solution used is preferably 200 parts by mass or more, and more preferably 500 parts by mass or more, per 100 parts by mass of the electrolyte membrane, in order to obtain a better effect of the present invention, and is preferably 100,000,000 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, in order to reduce the amount of waste liquid.

[0068] In step 2-1, either solution A or solution B may be used as the first solution, but it is preferable to use solution A from the viewpoints that polymer decomposition products can be further removed or reduced and elution of the specific fluoropolymer can be suppressed. In particular, when heated solution A is used in step 2-1, elution of the specific fluoropolymer can be suppressed, and therefore the recovery rate of the specific fluoropolymer in step 2-3 described below can be further improved.

[0069] In step 2-1, after the first solution is brought into contact with the electrolyte membrane, a drying treatment may be performed to dry the electrolyte membrane. The details of the drying treatment are the same as those of step 1-1 in the first embodiment, including preferred aspects.

[0070] As described above, the polymer decomposition products removed or reduced from the electrolyte membrane in step 2-1 are components generated by decomposition of the specific fluorine-containing polymer, and examples thereof include low-molecular-weight compounds and oligomers. The molecular weight of the low-molecular-weight compounds is preferably 1,000 or less, more preferably 800 or less, and also preferably 10 or more, more preferably 100 or more. The molecular weight of the oligomers is preferably 10,000 or less, more preferably 5,000 or less, and also preferably more than 1,000, more preferably 2,000 or more.

[0071] <Step 2-2> Step 2-2 is carried out after step 2-1, and is a step of mixing the electrolyte membrane that has been contacted with the first solution with the second solution to obtain a mixed solution containing the specific fluorine-containing polymer, the second solution, and insoluble matter. In this step, the specific fluorine-containing polymer in the electrolyte membrane is eluted into the second solution and is contained in the mixed solution. In addition, components that are insoluble in the second solution are contained in the mixed solution as insoluble matter.

[0072] A specific example of the method for mixing the second solution and the electrolyte membrane is the same as the mixing method shown in step 1-2 in the first embodiment, and therefore the description thereof will be omitted.

[0073] The second solution may be heated or not, but is preferably heated in order to promote the elution of the specific fluoropolymer. The temperature of the second solution is the same as that of the second solution shown in step 1-2 in the first embodiment, including preferred embodiments.

[0074] The time for mixing the second solution with the electrolyte membrane is the same as that shown in step 1-2 in the first embodiment, including the preferred embodiment.

[0075] The amount of the second solution used 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, per 100 parts by mass of the electrolyte membrane, from the viewpoint that the effects of the present invention are more excellent; and 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, from the viewpoint that the concentration of the fluoropolymer in the liquid obtained in step 1-3 described below can be prevented from becoming too low and the liquid containing the fluoropolymer obtained in step 1-3 can be easily reused.

[0076] Specific examples of the insoluble matter include the materials constituting the reinforcing material described above. Note that the components contained in the insoluble matter may be recovered and reused.

[0077] <Step 2-3> Step 2-3 is carried out after step 2-2, and is a step of removing insoluble matters contained in the mixed solution and recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matters have been removed.

[0078] The method for removing the insoluble matter is the same as the removal method shown in step 1-3 in the first embodiment.

[0079] The method for recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is not particularly limited, and any known method can be used.

[0080] The Mw of the recovered specific fluoropolymer is preferably at least 10,000, more preferably at least 30,000, and even more preferably at least 50,000, and is preferably at most 3,000,000, more preferably at most 2,000,000, and even more preferably at most 1,000,000. The Mw of the specific fluoropolymer is measured in the same manner as for the specific fluoropolymer in the first embodiment.

[0081] The recovered specific fluorine-containing polymer is suitable for producing an electrolyte membrane, a catalyst layer in an anode, a catalyst layer in a cathode, etc., but is not limited thereto and may be used for other purposes.

[0082] [Third Embodiment] A method for recovering a specific fluoropolymer according to a third embodiment of the present invention (hereinafter also referred to as "the recovery method of the third embodiment") is a method for recovering a specific fluoropolymer, which recovers at least one of the specific fluoropolymer contained in the catalyst layer of the anode and the specific fluoropolymer contained in the catalyst layer of the cathode, from the above-mentioned membrane / electrode assembly. The recovery method of the third embodiment also includes a step (hereinafter also referred to as "step 3-0") of separating at least one of the anode and the cathode from the above-mentioned membrane / electrode assembly. The recovery method of the third embodiment also includes a step (hereinafter also referred to as "step 3-1") of contacting the above-mentioned first solution with the separated at least one of the anode and the cathode after step 3-0. The recovery method of the third embodiment also includes, after step 3-1, a step of mixing at least one of the anode and the cathode that have been brought into contact with the first solution with the second solution to obtain a mixed solution containing the specific fluorine-containing polymer, the second solution, and insoluble matter containing the catalyst (hereinafter also referred to as step "3-2"). The recovery method of the third embodiment also includes, after step 3-2, a step of removing the insoluble matter contained in the mixed solution and recovering the specific fluorine-containing polymer contained in the mixed solution from which the insoluble matter has been removed (hereinafter also referred to as step "3-3").

[0083] In the recovery method of the third embodiment, the recovered specific fluorine-containing polymer is less likely to swell for the same reason as in the recovery method of the first embodiment. That is, according to the recovery method of the first embodiment, it is presumed that by carrying out step 3-1 before step 3-2, the low-molecular-weight compound contained in the electrode is eluted into the first solution, and polymer decomposition products are removed or reduced from the electrode, resulting in the above-mentioned excellent effect. Here, in this specification, "electrode" means at least one of an anode and a cathode, unless otherwise specified.

[0084] <Step 3-0> Step 3-0 is a step of separating the electrodes from the membrane electrode assembly. The electrodes obtained in this step (i.e., the separated electrodes) are used in Step 3-1 described below. In Step 3-0, only the anode may be separated, only the cathode may be separated, or both the anode and the cathode may be separated. The method for separating the electrodes from the membrane electrode assembly is not particularly limited, and examples include a method of attaching an adhesive tape to the surface of the electrode and then peeling the electrode together with the adhesive tape, and a method of weakening the adhesive force between the electrolyte membrane and the electrode by laser irradiation and then separating the electrolyte membrane and the electrode. These methods may be performed in combination. Furthermore, as a method for separating the electrodes from the membrane electrode assembly, for example, a method of bringing the membrane electrode assembly into contact with a solution that dissolves the specific fluorine-containing polymer in the electrolyte membrane (e.g., the second solution described above) and separating the electrodes can also be used. However, since the method using such a solution may dissolve the specific fluoropolymer in the electrode, it is preferable to bring the electrode into contact with a small amount of the solution (for example, 100 to 300 parts by mass per 100 parts by mass of the membrane / electrode assembly or electrode) for a short period of time (for example, 1 to 30 minutes) in order to prevent dissolution of the specific fluoropolymer in the electrode.

[0085] <Step 3-1> Step 3-1 is performed after step 3-0 and involves contacting the first solution with an electrode 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. Note that when both the anode and the cathode are separated from the membrane electrode assembly, in step 3-1, the anode and the cathode may be contacted together with the first solution, or the anode and the cathode may be contacted separately with the first solution. This step dissolves the low-molecular-weight compound contained in the electrode into the first solution, thereby obtaining an electrode from which polymer decomposition products have been removed or reduced.

[0086] Specific examples of the method for contacting the first solution with the electrode are the same as those in step 1-1 of the first embodiment, including preferred embodiments.

[0087] The first solution may be heated or not, but is preferably heated because this promotes the elution of the low molecular weight compound and allows the polymer decomposition products to be further removed or reduced from the electrode. The temperature of the first solution is the same as that of the first solution shown in step 1-1 of the first embodiment, including preferred embodiments.

[0088] When the first solution is heated, the temperature of the first solution is preferably lower than the temperature of the second solution used in step 3-2 described below, in order to obtain a better polymer recovery rate. 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 preferred embodiments.

[0089] The time for which the first solution is in contact with the electrode is the same as that shown in step 1-1 of the first embodiment, including the preferred embodiment.

[0090] The amount of the first solution used is preferably 200 parts by mass or more, more preferably 500 parts by mass or more, per 100 parts by mass of the electrode, from the viewpoint of achieving better effects of the present invention, and is preferably 100,000,000 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, from the viewpoint of suppressing the amount of waste liquid. Note that the amount of the first solution used refers to the amount used per 100 parts by mass of the anode when only an anode is used as the electrode in step 3-1, the amount used per 100 parts by mass of the cathode when only a cathode is used as the electrode in step 3-1, and the amount used per 100 parts by mass of the anode and cathode combined when both an anode and a cathode are used as electrodes in step 3-1.

[0091] In step 3-1, either solution A or solution B may be used as the first solution, but it is preferable to use solution A from the viewpoints that polymer decomposition products can be further removed or reduced and elution of the specific fluoropolymer can be suppressed. In particular, when heated solution A is used in step 3-1, elution of the specific fluoropolymer can be suppressed, and therefore the recovery rate of the specific fluoropolymer in step 1-3 described below can be further improved.

[0092] In step 3-1, after the first solution is brought into contact with the electrode, a drying treatment may be performed to dry the electrode. The details of the drying treatment are the same as those of step 1-1 in the first embodiment, including preferred aspects.

[0093] As described above, the polymer decomposition products removed or reduced from the electrode in step 3-1 are components generated by decomposition of the specific fluorine-containing polymer, and examples thereof include low-molecular-weight compounds and oligomers. The molecular weight of the low-molecular-weight compounds is preferably 1,000 or less, more preferably 800 or less, and also preferably 10 or more, more preferably 100 or more. The molecular weight of the oligomers is preferably 10,000 or less, more preferably 5,000 or less, and also preferably more than 1,000, more preferably 2,000 or more.

[0094] <Step 3-2> Step 3-2 is carried out after step 3-1, and is a step of mixing the electrode that has been in contact with the first solution with the second solution to obtain a mixed solution containing the specific fluorine-containing polymer, the second solution, and insoluble matter containing a catalyst. In this step, the specific fluorine-containing polymer in the electrode is eluted into the second solution and is contained in the mixed solution. In addition, components that are insoluble in the second solution are contained in the mixed solution as insoluble matter.

[0095] A specific example of the method for mixing the second solution with the electrode is the same as the mixing method shown in step 1-2 in the first embodiment, and therefore a description thereof will be omitted.

[0096] The second solution may be heated or not, but is preferably heated in order to promote the elution of the specific fluoropolymer. The temperature of the second solution is the same as that of the second solution shown in step 1-2 in the first embodiment, including preferred embodiments.

[0097] The time for which the electrode is in contact with the second solution is the same as that shown in step 1-2 in the first embodiment, including the preferred embodiment.

[0098] The amount of the second solution used 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, relative to 100 parts by mass of the electrode, from the viewpoint of better effects of the present invention, and 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, from the viewpoint of preventing the concentration of the fluoropolymer in the liquid obtained in step 1-3 described below from becoming too low and facilitating reuse of the liquid containing the fluoropolymer obtained in step 1-3. The amount of the second solution used means the amount used relative to 100 parts by mass of the anode when only an anode is used as the electrode in step 3-2, means the amount used relative to 100 parts by mass of the cathode when only a cathode is used as the electrode in step 3-2, and means the amount used relative to 100 parts by mass of the anode and cathode combined when both an anode and a cathode are used as electrodes in step 3-2.

[0099] In addition to the catalyst, the insoluble matter may contain, for example, the material constituting the gas diffusion layer described above, etc. The components contained in the insoluble matter may be recovered and reused.

[0100] <Step 3-3> Step 3-3 is carried out after step 3-2, and is a step of removing insoluble matters contained in the mixed solution and recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matters have been removed.

[0101] The method for removing the insoluble matter is the same as the removal method shown in step 1-3 in the first embodiment.

[0102] The method for recovering the specific fluoropolymer contained in the mixed solution from which the insoluble matter has been removed is not particularly limited, and any known method can be used.

[0103] The Mw of the recovered specific fluoropolymer is preferably at least 10,000, more preferably at least 30,000, and even more preferably at least 50,000, and is preferably at most 3,000,000, more preferably at most 2,000,000, and even more preferably at most 1,000,000. The Mw of the specific fluoropolymer is measured in the same manner as for the specific fluoropolymer in the first embodiment.

[0104] The recovered specific fluorine-containing polymer is suitable for producing an electrolyte membrane, a catalyst layer in an anode, a catalyst layer in a cathode, etc., but is not limited thereto and may be used for other purposes.

[0105] The present invention will be described in detail below with reference to examples. Examples 1-1 to 1-4, 2-1 to 2-4, and 3-1 to 3-4 are working examples, 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.

[0106] [TQ value] Using a flow tester CFT-500A (manufactured by Shimadzu Corporation) equipped with a nozzle having a length of 1 mm and an inner diameter of 1 mm, the extrusion amounts of the fluoropolymers A to C were measured at various temperatures under the condition of an extrusion pressure of 2.94 MPa. ３ The results are shown in Table 1.

[0107] [Proportion of Each Structural Unit] The proportion of each structural unit in the fluoropolymers A to C is as follows: １９ The values ​​were determined from the results of F-NMR measurements, and the results are shown in Table 1.

[0108] [Ion Exchange Capacity] The ion exchange capacity was determined from the proportion of each constituent unit in the fluoropolymers A to C. The results are shown in Table 1.

[0109] [Swelling degree] The solutions containing the 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 prepare cast films. The resulting cast films are immersed in 80°C warm water for 24 hours, then removed from the warm water, and the water adhering to the surface is wiped off, and the mass of the cast film is measured. Thereafter, the cast film is dried at 120°C for 60 minutes, and the mass of the cast film after drying is measured. The ratio of the mass of water contained in the cast film before drying (water-absorbed cast film) 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.

[0110] [Abbreviation] TFE:CF ２ =CF ２Monomer (m1): CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ F Monomer (m2): Monomer represented by the following formula (m2) Monomer (m3): Monomer represented by the following formula (m3)

[0111]

[0112] [Preparation of Fluoropolymer Solution A] A fluoropolymer containing monomer (m1) units and TFE units was produced according to the method described in paragraphs

[0024] to

[0025] of JP-A No. 2004-196994, and the -SO ２ F group to -SO ３ Converted to H group, -SO ３ An H-type fluoropolymer A was obtained. Then, 27 g of the above fluoropolymer A, 46 g of ethanol, and 31 g of water were placed in a 200 ml stainless steel autoclave, and dissolution and dispersion were carried out for 6 hours at 105°C and 300 rpm using a helical ribbon impeller, to obtain a dispersion with a solids concentration of 26 mass%. Hereinafter, this dispersion will be referred to as fluoropolymer solution A.

[0113] [Preparation of Fluoropolymer Solution B] A fluoropolymer containing monomer (m2) units and TFE units was produced according to the method described in paragraphs

[0098] to

[0100] of WO 2017 / 221840. Next, the obtained fluoropolymer was mixed in a KOH aqueous solution containing methanol under heating to hydrolyze the -SO ２ F group to -SO ３ It was then converted to a K group. ３ The fluoropolymer having K groups is washed with water and mixed in an aqueous sulfuric acid solution to remove -SO ３ K group to -SO ３ Converted to H group, -SO ３An H-type fluoropolymer B was obtained. Then, 20 g of the above fluoropolymer B, 34 g of ethanol, and 79 g of water were placed in a 200 ml stainless steel autoclave, and dissolution and dispersion were carried out for 6 hours at 110°C and 300 rpm using a helical ribbon impeller, to obtain a dispersion having a solids concentration of 15 mass%. Hereinafter, this dispersion will be referred to as fluoropolymer solution B.

[0114] [Preparation of Fluoropolymer Solution C] A fluoropolymer containing monomer (m2) units, monomer (m3) units and TFE units was produced according to the method described in paragraphs

[0114] to

[0115] of WO 2017 / 006841. Next, the obtained fluoropolymer was mixed in a KOH aqueous solution containing dimethyl sulfoxide under heating to hydrolyze the resulting fluoropolymer to give —SO ２ F group to -SO ３ It was then converted to a K group. ３ The fluoropolymer having K groups is washed with water and mixed in an aqueous sulfuric acid solution to remove -SO ３ K group to -SO ３ Converted to H group, -SO ３ An H-type fluoropolymer C was obtained. Then, 19 g of the above fluoropolymer C, 64 g of 1-propanol, and 64 g of water were placed in a 200 ml stainless steel autoclave, and dissolution and dispersion were carried out for 6 hours at 115°C and 300 rpm using a helical ribbon impeller, yielding a dispersion with a solids concentration of 13%. Hereinafter, this dispersion will be referred to as fluoropolymer solution C.

[0115] The compositions and physical properties of the fluoropolymers A to C obtained as above are shown in Table 1. In the table, meq / g means milliequivalents per gram of dry resin.

[0116]

[0117] [Production of Solid Polymer Electrolyte Membrane] <Electrolyte Membrane A> Fluorine-containing polymer solution A was applied to the surface of a sheet made of an ethylene-TFE copolymer (manufactured by AGC Inc., Aflex (registered trademark) 100N, thickness 100 μm) (hereinafter referred to as ETFE sheet) using a die coater, dried at 80° C. for 30 minutes, and further subjected to heat treatment at 185° C. for 30 minutes to obtain a solid polymer electrolyte membrane having a thickness of 20 μm. Hereinafter, this solid polymer electrolyte membrane will be referred to as electrolyte membrane A.

[0118] <Electrolyte Membrane B> An electrolyte membrane B was obtained in the same manner as in the production of electrolyte membrane A, except that the fluoropolymer solution A used in forming the solid polymer electrolyte membrane was changed to fluoropolymer solution B.

[0119] [Membrane electrode assembly] Membrane electrode assemblies MEA1, MEA2 and MEA3 in which an anode was formed on one surface of a solid polymer electrolyte membrane and a cathode was formed on the other surface were produced in the same manner as described in paragraphs

[0136] to

[0138] of WO 2016 / 104380, except that fluoropolymer solution A or fluoropolymer solution C was used as the liquid composition used in preparing a liquid for forming a catalyst layer. The configuration of each of the obtained membrane electrode assemblies is shown in Table 2.

[0120]

[0121] [Power Generation Test] A power generation test was carried out in the same manner as described in paragraph

[0103] of Japanese Patent No. 5168903, except that the membrane electrode assembly obtained as described above was used.

[0122] [Example 1-1] <Step 1-1> 10 g of MEA 1 (i.e., used MEA 1) was recovered from a polymer electrolyte fuel cell having MEA 1 after the above-mentioned power generation test and immersed in 100 g of water (first solution) at 90°C for 6 hours. The immersed MEA 1 was then dried at 80°C for 3 hours. In this manner, an MEA 1 immersed in the first solution was obtained. <Step 1-2> The MEA 1 immersed in the first solution was immersed in a second solution consisting of 20 g of water and 20 g of 1-propanol, and the temperature was raised to an internal temperature of 105°C. After stirring at 105°C for 4 hours, the solution was cooled to obtain a mixed solution. <Step 1-3> Centrifugation (conditions: 3000 G) was performed for 30 minutes to precipitate insoluble components such as the catalyst contained in the mixed solution, and the supernatant solution was recovered. The supernatant solution was then filtered through a 10 μm filter to remove fine insoluble components, and a solution containing a fluoropolymer was recovered.

[0123] [Examples 1-2 and 1-3] A solution containing a fluoropolymer was recovered in the same manner as in Example 1-1, except that the MEA2 after the power generation test or the MEA3 after the power generation test was used instead of the MEA1 after the power generation test.

[0124] Example 1-4 A solution containing a fluoropolymer was recovered in the same manner as in Example 1-1, except that in step 1-1, a first solution consisting of 95 g of water and 5 g of ethanol (liquid temperature 25°C) was used instead of 100 g of water at 90°C.

[0125] Example 1-5 A solution containing a fluoropolymer was recovered in the same manner as in Example 1-1, except that step 1-1 was not carried out.

[0126] Example 1-6 A solution containing a fluoropolymer was recovered in the same manner as in Example 1-2, except that step 1-1 was not carried out.

[0127] Example 1-7 A solution containing a fluoropolymer was recovered in the same manner as in Example 1-3, except that step 1-1 was not carried out.

[0128] Example 1-8 A solution containing a fluoropolymer was recovered in the same manner as in Example 1-4, except that step 1-1 was not carried out.

[0129]

[0130] The swelling degree measured using the recovered fluoropolymer in Example 1-1 was lower than the swelling degree measured using the recovered fluoropolymer in Example 1-5. The swelling degree measured using the recovered fluoropolymer in Example 1-2 was lower than the swelling degree measured using the recovered fluoropolymer in Example 1-6. The swelling degree measured using the recovered fluoropolymer in Example 1-3 was lower than the swelling degree measured using the recovered fluoropolymer in Example 1-7. The swelling degree measured using the recovered fluoropolymer in Example 1-4 was lower than the swelling degree measured using the recovered fluoropolymer in Example 1-8.

[0131] [Example 2-1] <Step 2-0> 10 g of MEA1 (i.e., used MEA1) was recovered from a polymer electrolyte fuel cell having MEA1 after the power generation test, and separated into an electrolyte membrane and electrodes. <Step 2-1> 7.7 g of the separated electrolyte membrane was immersed in 100 g of water (first solution) at 90°C for 6 hours. The immersed electrolyte membrane was then dried at 80°C for 3 hours. In this manner, an electrolyte membrane immersed in the first solution was obtained. <Step 2-2> The electrolyte membrane immersed in the first solution was immersed in a second solution consisting of 20 g of water and 20 g of 1-propanol, and the temperature was raised to an internal temperature of 105°C. The solution was stirred at 105°C for 4 hours and then cooled to obtain a mixed solution. <Step 2-3> The solution was centrifuged for 30 minutes (conditions: 3000 G) to precipitate insoluble components contained in the mixed solution, and the supernatant solution was recovered. Thereafter, the supernatant solution was filtered through a 10 μm filter to remove fine insoluble components, and a solution containing the fluoropolymer was recovered.

[0132] [Examples 2-2 and 2-3] A solution containing a fluoropolymer was recovered in the same manner as in Example 2-1, except that the MEA2 after the completion of the power generation test or the MEA3 after the completion of the power generation test was used instead of the MEA1 after the completion of the power generation test.

[0133] Example 2-4 A solution containing a fluoropolymer was recovered in the same manner as in Example 2-1, except that in step 2-1, a first solution consisting of 95 g of water and 5 g of ethanol (liquid temperature 25°C) was used instead of 100 g of water at 90°C.

[0134] Example 2-5 A solution containing a fluoropolymer was recovered in the same manner as in Example 2-1, except that step 2-1 was not carried out.

[0135] Example 2-6 A solution containing a fluoropolymer was recovered in the same manner as in Example 2-2, except that step 2-1 was not carried out.

[0136] Example 2-7 A solution containing a fluoropolymer was recovered in the same manner as in Example 2-3, except that step 2-1 was not carried out.

[0137] Example 2-8 A solution containing a fluoropolymer was recovered in the same manner as in Example 2-4, except that step 2-1 was not carried out.

[0138]

[0139] The swelling degree measured using the recovered fluoropolymer in Example 2-1 was lower than the swelling degree measured using the recovered fluoropolymer in Example 2-5. The swelling degree measured using the recovered fluoropolymer in Example 2-2 was lower than the swelling degree measured using the recovered fluoropolymer in Example 2-6. The swelling degree measured using the recovered fluoropolymer in Example 2-3 was lower than the swelling degree measured using the recovered fluoropolymer in Example 2-7. The swelling degree measured using the recovered fluoropolymer in Example 2-4 was lower than the swelling degree measured using the recovered fluoropolymer in Example 2-8.

[0140] [Example 3-1] 10 g of MEA1 (i.e., used MEA1) was recovered from a polymer electrolyte fuel cell having MEA1 after the power generation test. <Step 3-0> 10 g of used MEA1 was recovered from a polymer electrolyte fuel cell having MEA1 and separated into an electrolyte membrane and electrodes (both anode and cathode; the same applies below). <Step 3-1> 2.3 g of the separated electrodes (1.15 g anode, 1.15 g cathode) were immersed in 100 g of water (first solution) at 90°C for 6 hours. The immersed electrodes were then dried at 80°C for 3 hours. In this way, electrodes immersed in the first solution were obtained. <Step 3-2> The electrodes immersed in the first solution were immersed in a second solution consisting of 20 g water and 20 g 1-propanol, and the temperature was raised to an internal temperature of 105°C. The solution was stirred at 105°C for 4 hours and then cooled to obtain a mixed solution. <Step 3-3> Insoluble components such as the catalyst were precipitated by centrifugation, and the supernatant solution was recovered. Thereafter, the supernatant solution was filtered through a 10 μm filter to remove fine insoluble components, and a solution containing the fluoropolymer was recovered.

[0141] [Examples 3-2 and 3-3] A solution containing a fluoropolymer was recovered in the same manner as in Example 3-1, except that the MEA 2 for which the power generation test had been completed or the MEA 3 for which the power generation test had been completed was used instead of the MEA 1 for which the power generation test had been completed. [Example 3-4] A solution containing a fluoropolymer was recovered in the same manner as in Example 3-1, except that a first solution (liquid temperature 25°C) consisting of 95 g of water and 5 g of ethanol was used instead of 100 g of water at 90°C in step 3-1.

[0142] Example 3-5 A solution containing a fluoropolymer was recovered in the same manner as in Example 3-1, except that step 3-1 was not carried out.

[0143] Example 3-6 A solution containing a fluoropolymer was recovered in the same manner as in Example 3-2, except that step 3-1 was not carried out.

[0144] Example 3-7 A solution containing a fluoropolymer was recovered in the same manner as in Example 3-3, except that step 3-1 was not carried out.

[0145] Example 3-8 A solution containing a fluoropolymer was recovered in the same manner as in Example 3-4, except that step 3-1 was not carried out.

[0146]

[0147] The swelling degree measured using the recovered fluoropolymer in Example 3-1 was lower than the swelling degree measured using the recovered fluoropolymer in Example 3-5. The swelling degree measured using the recovered fluoropolymer in Example 3-2 was lower than the swelling degree measured using the recovered fluoropolymer in Example 3-6. The swelling degree measured using the recovered fluoropolymer in Example 3-3 was lower than the swelling degree measured using the recovered fluoropolymer in Example 3-7. The swelling degree measured using the recovered fluoropolymer in Example 3-4 was lower than the swelling degree measured using the recovered fluoropolymer in Example 3-8.

[0148] 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 part of the disclosure of the present invention.

[0149] 10 membrane electrode assembly 11A, 11C catalyst layer 12A, 12C gas diffusion layer 13 anode 14 cathode 15 solid polymer electrolyte membrane

Claims

1. A method for recovering a fluorine-containing polymer from a membrane electrode assembly including an anode having a catalyst layer containing a catalyst and a fluorine-containing polymer having a sulfonic acid group, a cathode having a catalyst layer containing a catalyst and a fluorine-containing polymer having a sulfonic acid group, and an electrolyte membrane disposed between the anode and the cathode and containing a fluorine-containing polymer having a sulfonic acid group, the method comprising: contacting a first solution selected from a solution A consisting only of water and a solution B containing water and alcohol and having an alcohol content of 10 parts by mass or less with respect to 100 parts by mass of water with the membrane electrode assembly; mixing the membrane electrode assembly contacted with the first solution with a second solution containing water and alcohol and having an alcohol content of 30 parts by mass or more with respect to 100 parts by mass of water to obtain a mixed solution containing the fluorine-containing polymer, the second solution, and insoluble matter containing the catalyst; removing the insoluble matter contained in the mixed solution; and recovering the fluorine-containing polymer contained in the mixed solution from which the insoluble matter has been removed.

2. The method for recovering a fluorine-containing polymer according to claim 1, wherein the contact between the first solution and the membrane electrode assembly is the contact between the solution A and the membrane electrode assembly, and the heated solution A is used.

3. The method for recovering a fluorine-containing polymer according to claim 1 or 2, wherein when the first solution and the membrane electrode assembly are contacted, the heated first solution is used, and the temperature of the first solution is lower than the temperature of the second solution.

4. The method for recovering a fluorine-containing polymer according to claim 1 or 2, wherein the weight average molecular weight of the recovered fluorine-containing polymer is 10,000 to 1,000,000.

5. The method for recovering a fluorine-containing polymer according to claim 3, wherein the temperature difference between the temperature of the first solution and the temperature of the second solution is 5°C or more and 115°C or less.

6. A method for recovering a fluorine-containing polymer from a membrane electrode assembly including an anode having a catalyst layer containing a catalyst and a fluorine-containing polymer having a sulfonic acid group, a cathode having a catalyst layer containing a catalyst and a fluorine-containing polymer having a sulfonic acid group, and an electrolyte membrane disposed between the anode and the cathode and containing a fluorine-containing polymer having a sulfonic acid group, the method comprising: separating the electrolyte membrane from the membrane electrode assembly; contacting the separated electrolyte membrane with a first solution selected from a solution A consisting only of water and a solution B containing water and alcohol and having an alcohol content of 10 parts by mass or less with respect to 100 parts by mass of water; mixing the electrolyte membrane contacted with the first solution with a second solution containing water and alcohol and having an alcohol content of 30 parts by mass or more with respect to 100 parts by mass of water to obtain a mixed solution containing the fluorine-containing polymer, the second solution, and insoluble matter; removing the insoluble matter contained in the mixed solution; and recovering the fluorine-containing polymer contained in the mixed solution from which the insoluble matter has been removed.

7. The method for recovering a fluorine-containing polymer according to claim 6, wherein the contact between the first solution and the electrolyte membrane is contact between the solution A and the electrolyte membrane, and the heated solution A is used.

8. The method for recovering a fluorine-containing polymer according to claim 6 or 7, wherein when the first solution and the electrolyte membrane are contacted, the heated first solution is used, and the temperature of the first solution is lower than the temperature of the second solution.

9. The method for recovering a fluorine-containing polymer according to claim 6 or 7, wherein the weight average molecular weight of the recovered fluorine-containing polymer is 10,000 to 1,000,000.

10. The method for recovering a fluorine-containing polymer according to claim 8, wherein the temperature difference between the temperature of the first solution and the temperature of the second solution is 5°C or more and 115°C or less.

11. A method for recovering a fluorine-containing polymer, which comprises recovering at least one of the fluorine-containing polymers contained in the catalyst layer of the anode and the fluorine-containing polymers contained in the catalyst layer of the cathode from a membrane electrode assembly including: an anode having a catalyst layer containing a catalyst and a fluorine-containing polymer having a sulfonic acid group; a cathode having a catalyst layer containing a catalyst and a fluorine-containing polymer having a sulfonic acid group; and an electrolyte membrane disposed between the anode and the cathode and containing a fluorine-containing polymer having a sulfonic acid group. The method includes separating at least one of the anode and the cathode from the membrane electrode assembly, contacting at least one of the separated anode and cathode with a first solution selected from a solution A consisting only of water and a solution B containing water and alcohol and having an alcohol content of 10 parts by mass or less with respect to 100 parts by mass of water, and then mixing at least one of the anode and cathode contacted with the first solution with a second solution containing water and alcohol and having an alcohol content of 30 parts by mass or more with respect to 100 parts by mass of water to obtain a mixed solution containing the fluorine-containing polymer, the second solution, and insoluble matter, and removing the insoluble matter contained in the mixed solution to recover the fluorine-containing polymer contained in the mixed solution from which the insoluble matter has been removed.

12. The method for recovering a fluorine-containing polymer 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 the solution A and the anode and the cathode, and the heated solution A is used.

13. When contacting at least one of the anode and the cathode with the first solution, the heated first solution is used, and the temperature of the first solution is lower than the temperature of the second solution. The method for recovering a fluorine-containing polymer according to claim 11 or 12.

14. The method for recovering a fluorine-containing polymer according to claim 11 or 12, wherein the weight average molecular weight of the recovered fluorine-containing polymer is from 10,000 to 1,000,000.

15. The method for recovering a fluorine-containing polymer according to claim 13, wherein the temperature difference between the temperature of the first solution and the temperature of the second solution is from 5°C to 115°C.

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