Recycling of catalyst coated membrane components

Abstract

A method of recovering a fluorinated polymer from a membrane comprising the fluorinated polymer, the fluorinated polymer comprising a fluorinated polymer backbone and a plurality of groups represented by the formula-SO3Z wherein Z is hydrogen, the method comprising: contacting the membrane with an agent providing a source of cations to form a fluorinated polymer salt wherein Z is a cation, wherein the agent is maintained at a temperature sufficiently low such that the membrane remains in a solid, undispersed form; removing excess unreacted reagent from the solid fluorinated polymer salt; and after removing the excess reagent, dispersing the solid fluorinated polymer salt in a solvent.

Description

Technical Field

[0001] The present description relates to methods for recycling components for catalyst coated membranes, such as those used in fuel cells and hydrogen producing water electrolyzers. Background Art

[0002] With the investment in the global hydrogen economy, the production of fuel cells and hydrogen-producing water electrolyzers will grow rapidly. Catalyst coated membranes (CCMs) are the main functional components of both fuel cells and electrolyzers. Such CCMs generally include a conductive polymer membrane coated with a catalyst layer on either side. CCMs are configured to drive oxidation and reduction reactions and support proton and electron transport, which are required for fuel cell and electrolyzer technologies to function.

[0003] While variations in CCM component materials and configurations exist depending on functional performance requirements in end-use applications, they generally contain several valuable components including one or more platinum group metal (PGM) catalysts and one or more proton conducting polymers.

[0004] Typically, the membrane is formed of one or more ionomers such as perfluorosulfonic acid (PFSA) ionomers. The ionomers may also be disposed in one or both of the catalyst layers. The ionomers in the catalyst layers may be the same or different from the ionomers in the main membrane component and / or other catalyst layers.

[0005] The CCM may contain two different catalysts, one for driving the oxidation reaction on one side of the CCM and one for driving the reduction reaction on the other side of the CCM. The CCM may also contain a recombination catalyst provided to catalyze the recombination of hydrogen and oxygen to form water, thereby reducing the amount of hydrogen that passes through the membrane and mixes with oxygen to form a potentially explosive mixture. The CCM may also contain a metal oxide (e.g., CeO2) as a peroxide scavenger to slow down the degradation of the CCM and increase the life of the CCM.

[0006] The CCM catalyst may be based on a platinum group metal, such as platinum, ruthenium, iridium, palladium, or mixtures thereof. The platinum group metal may be provided in elemental (metal) form, in compound form (e.g., oxide, such as iridium oxide catalyst), or as a PGM-based metal alloy (e.g., PtCo). In addition, the PGM catalyst material may be supported on a substrate material (e.g., carbon, such as a carbon-supported platinum catalyst comprising carbon particles with platinum disposed thereon, or carbon-supported PtCo).

[0007] Catalyst coated membranes (CCMs) can also be provided in combination with additional functional layers to form multilayer membrane electrode assemblies (MEAs). Such MEAs can have, for example, 3, 5 or 7 layers.

[0008] With the increase in the manufacture of CCMs for fuel cells and electrolyzers, there has been an associated increase in CCM waste, including large amounts of waste formed during CCM manufacture (e.g., due to quality control failures) and an increase in end-of-life (EoL) CCMs. Since CCMs contain several rare and / or valuable components, including platinum group metals (particularly Pt, Pd, Ir, and Ru) and ionomers (in both the membrane and catalyst layers), there is a growing need for methods to recycle such components from spent / wasted CCM materials.

[0009] A current method for recovering PGMs from production waste and end-of-life CCM materials involves incineration. The incineration process produces an ash rich in PGMs (typically Pt and Ir) that is processed via conventional PGM refining routes. However, the incineration process releases harmful and toxic gases, such as CO2 and HF, from the polymer that is part of the membrane. Both of these gases have a negative impact because they pollute the atmospheric environment, increase the greenhouse effect and / or have a harmful effect on the human body. Therefore, a cleaner process that reduces or eliminates the emission of these gases is needed.

[0010] In addition to the above, the incineration method destroys the ionomer component, which is also of great value. Therefore, it is also desirable to provide a process capable of recovering both PGM and ionomer components and to provide a cleaner, safer and more environmentally friendly process. The process for recovering perfluorosulfonic acid ionomers is known. See, for example, WO2016 / 156815 and US7255798. In addition, the process for recovering each PGM catalyst component is known. For example, see US7709135. However, in order to enable fuel cells and electrolyzers to become more sustainable technologies, commercially viable and environmentally friendly routes are needed to recover, separate and recycle both PGM and ionomer components from waste CCM materials (including production waste and end-of-life materials).

[0011] The present description relates to a method for recovering ionomer materials (perfluorosulfonic acid (PFSA) polymers) from ionomer membranes of fuel cells or electrolyzers.

[0012] WO2021250576 discloses a process for recovering ionomer materials from ionomer membranes of fuel cells or electrolyzers. It is described that when the fluorinated polymer is heat treated, the solubility of the fluorinated polymer used in such a membrane is reduced, which may occur during the manufacture of the membrane containing the fluorinated polymer. That is, although the fluorinated polymers having a fluorinated backbone and a plurality of groups represented by the formula -SO3H or their salts are easily soluble in water and alcohol mixtures when they are newly prepared, these polymers are generally insoluble in water and water / alcohol mixtures under standard conditions after having been heated to a temperature of at least 100°C. WO2021250576 discloses that such heat-treated fluorinated polymers are soluble when heated in the presence of water and a base. Therefore, WO2021250576 discloses a method involving: dissolving a fluorinated polymer membrane in water and a base to form a fluorinated polymer salt solution, and then converting the fluorinated polymer salt solution back into a fluorinated polymer solution by hydrogen cation exchange. It is noted that the base is typically an alkali metal hydroxide (e.g., lithium hydroxide, sodium hydroxide, or potassium hydroxide) or ammonium hydroxide. It is also noted that the moles of base used may be equal to the moles of fluorinated polymer, or an excess of base may be used (e.g., up to 100, 200, or 300 mole percent excess of base relative to the fluorinated polymer).

[0013] It is an object of the present specification to provide an improved process for recovering ionomers. Summary of the invention

[0014] This specification relates to the recovery of perfluorosulfonic acid (PFSA) polymers from discarded or used membranes, such as those used in fuel cells or electrolyzers. It has been recognized that the use of an equal or excess amount of a base, as described in WO2021250576, can be advantageous in ensuring that all or substantially all of the fluorinated polymer is converted to salt form. Salt formation protects the sulfonic acid groups during the recovery process, so it is advantageous to ensure that all or substantially all of the sulfonic acid groups are converted to salt form during the process. However, it has also been recognized that the use of a base, such as a hydroxide as described in WO2021250576, may cause several problems in the further processing of the ionomer material, particularly if the material being processed also includes one or more platinum group metal catalysts, such as in a catalyst-coated membrane.

[0015] Excessive alkali may cause etching / corrosion problems in the equipment. In addition, excessive alkali may cause material formation and extraction problems of other components (such as platinum group metal catalysts present in the catalyst-coated membrane of a fuel cell or electrolyzer). Further, during the ion exchange process, any excess alkali needs to be recovered to convert the fluorinated polymer salt back to the protonated acid form, which may adversely affect the overall material balance. For example, in the case where hydroxide is used as an alkali to convert the fluorinated polymer into a salt form, excessive hydroxide alkali is corrosive to metal and glass lined containers, which can be used for subsequent dispersion processes at elevated temperatures and pressures. In addition, excessive hydroxide alkali may cause material formation and extraction problems of other components (such as platinum group metal catalysts present in the catalyst-coated membrane of a fuel cell or electrolyzer). Further, during the ion exchange process, any excess hydroxide alkali needs to be recovered to convert the fluorinated polymer salt back to the protonated acid form, which may adversely affect the overall material balance.

[0016] Therefore, it has been recognized that if an excess of alkali is added to the fluorinated polymer to ensure that the fluorinated polymer is substantially completely converted into a salt form, the excess alkali should be substantially removed immediately during or after the fluorinated polymer is converted into a salt form. The removal of excess alkali reduces etching / corrosion problems in the equipment, reduces material formation and extraction problems of other components (such as platinum group metal components), and ensures that during the subsequent ion exchange process, it is not necessary to recycle excess alkali to convert the fluorinated polymer salt back to an acid form, thereby improving the overall material balance. If the film is heated in an alkaline solution to form a dispersion of a fluorinated polymer salt in an alkaline solution as described in WO2021250576, it is difficult to separate the fluorinated polymer salt from the excess alkali. However, it has been found that an alkaline solution can be used to process the membrane material to form a salt without heating the membrane to a temperature at which it is dispersed in an alkaline solution. This allows the membrane to be retained in a solid salt form, which is easily separated from the alkaline solution before further treatment.

[0017] In addition to the above, although WO2021250576 proposes the use of a base in the form of an alkali metal hydroxide (e.g., lithium hydroxide, sodium hydroxide or potassium hydroxide) or ammonium hydroxide, it has been found that other reagents can be used to convert the fluorinated polymer into a salt form. For example, it has been found that carbonates can be used, thereby reducing or avoiding the above-mentioned problems associated with the use of hydroxide bases. Therefore, in addition to removing excess salt-forming agents when converting the fluorinated polymer to a salt form, carbonates can also be advantageously used as salt-forming agents, wherein the carbon dioxide decomposition products produced when forming sulfonates can be removed as gaseous products, thereby avoiding the production of highly corrosive alkaline solutions and avoiding the need for a large number of washing steps.

[0018] It has also been discovered that, as an alternative to using hydroxides and carbonates as salt-forming agents for converting fluorinated polymers to salts, other agents can be used as cation sources to produce polymer salts. Such agents include inorganic salts, such as halide salts (e.g., chlorides, such as metal chlorides such as sodium chloride or lithium chloride). Alternatively, organic salts can be used as cation sources to produce polymer salts (e.g., formates (e.g., lithium formate), acetates, oxalates, citrates, or gluconates). Further, the cation can be an inorganic cation (i.e., a metal ion) or an organic cation (such as NH4 + Other options for reagents include bicarbonates, carbamates, nitrates, phosphates and sulfates, which may be in the form of metal salts or ammonium salts, for example.

[0019] According to the present specification, such reagents are added to the fluorinated polymer to convert the fluorinated polymer to salt form without heating to a temperature sufficient to disperse the film, so that the film remains in a solid, undispersed form. Excess unreacted reagents are then removed from the solid polymer salt before dispersing it in a solvent. The removal of excess unreacted reagents reduces etching / corrosion problems in the device, reduces material formation and extraction problems of other components (such as platinum group metal components), and ensures that excess reagents do not need to be recovered during the subsequent ion exchange process to convert the fluorinated polymer salt back to the acid form, thereby improving the overall material balance.

[0020] Therefore, the present specification provides a method for recovering a fluorinated polymer from a membrane comprising the fluorinated polymer, the fluorinated polymer comprising a fluorinated polymer backbone and a plurality of groups represented by the formula -SO3Z, wherein Z is hydrogen, the method comprising:

[0021] contacting the membrane with a reagent providing a source of cations to form a fluorinated polymer salt wherein Z is a cation, wherein the reagent is maintained at a sufficiently low temperature that the membrane remains in a solid, undispersed form;

[0022] removing excess unreacted reagents from the solid fluorinated polymer salt; and

[0023] After removal of the excess reagent, the solid fluorinated polymer salt is dispersed in a solvent.

[0024] For example, when the reagent is a base, the method comprises:

[0025] contacting the membrane with an alkaline aqueous solution comprising water and a base to form a fluorinated polymer salt wherein Z is a cation, wherein the base is optionally provided in molar excess relative to the -SO3Z groups, and wherein the alkaline aqueous solution is maintained at a sufficiently low temperature that the membrane remains in a solid, undispersed form;

[0026] removing excess / unreacted base by separating the solid fluorinated polymer salt from the basic aqueous solution (e.g., by solid-liquid separation techniques); and

[0027] After removal of the excess base, the solid fluorinated polymer salt is dispersed in a solvent.

[0028] In another example, the reagent is a carbonate, and the method includes:

[0029] contacting the membrane with an aqueous carbonate solution comprising water and carbonate to form a fluorinated polymer salt wherein Z is a cation, wherein optionally a molar excess of carbonate relative to -SO3Z groups is provided to form the fluorinated polymer salt, and wherein the aqueous carbonate solution is maintained at a sufficiently low temperature that the membrane remains in a solid, undispersed form;

[0030] removing excess / unreacted carbonate from the solid fluorinated polymer salt; and

[0031] After removing the excess carbonate, the fluorinated polymer salt is dispersed in a solvent.

[0032] Optionally, after dispersing the solid fluorinated polymer salt in the solvent, the fluorinated polymer salt is converted back to a fluorinated polymer in which Z is hydrogen by cation exchange. This can be done immediately after the dispersion step. Alternatively, the dispersed polymer salt is dried and stored, and then redispersed and converted to the protonated form when needed for use. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to better understand the invention and to show how it may be carried into effect, certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0034] Figure 1 A flow chart showing the method steps for recycling fluorinated polymer membrane material;

[0035] Figure 2 FTIR data for a fluorinated polymer film material, a fluorinated polymer salt material formed after treatment in water and base, and a fluorinated polymer salt material formed after treatment in water and base followed by water washing are shown;

[0036] Figure 3 An example of a process step (pre-autoclaving) is shown, including refluxing the fluorinated polymer membrane in an alkaline LiOH solution to form the fluorinated polymer salt without dispersing the membrane, followed by a water wash;

[0037] Figure 4 are photographs showing the membrane before (left-hand side) and after (right-hand side) the process steps of refluxing the membrane in an alkaline LiOH solution and washing with water;

[0038] Figure 5 It shows that Figure 3 The treatment process shown is followed by an additional step of autoclaving the membrane to disperse the membrane in water;

[0039] Figure 6 Another step of ion exchange (post-autoclaving) is shown to convert the dispersed polymer salt back to the protonated acid form;

[0040] Figure 7 A flow chart showing the steps of a method for recovering a fluorinated polymer membrane material according to another example using a carbonate reagent instead of a hydroxide reagent;

[0041] Figure 8 An example of a process step (before dispersing the film) is shown, including refluxing the fluorinated polymer film in a Li2CO3 solution to form a fluorinated polymer salt without dispersing the film, followed by a water wash; and

[0042] Fig. 9 The results show that the PFSA ionomer membrane has a significant impact on the SO3 content of the membrane. - FTIR ATR spectra were subjected to 1 molar equivalent and 2 molar equivalent of Na based on Na2CO3. DETAILED DESCRIPTION

[0043] like Figure 1 As illustrated, the present specification provides a method for recovering a fluorinated polymer from a film comprising a fluorinated polymer. The fluorinated polymer comprises a fluorinated polymer backbone and a plurality of groups represented by the formula -SO3Z. Z can be hydrogen or a cation such as a metal cation, an alkali metal cation or a quaternary ammonium cation (ammonium or alkylammonium cation). According to an example of the present method, in at least some of the -SO3Z groups, Z is hydrogen.

[0044] The method includes:

[0045] contacting the membrane with an agent providing a source of cations to form a fluorinated polymer salt wherein Z is a cation, wherein the agent is maintained at a sufficiently low temperature (e.g., less than 150°C, 100°C, 80°C, 60°C, or 40°C, optionally greater than 5°C, 10°C, or 15°C) such that the membrane remains in a solid, undispersed form;

[0046] removing excess unreacted reagents from the solid fluorinated polymer salt (e.g., using solid-liquid separation techniques, optionally decantation and filtration); and

[0047] After removing the excess reagent, the solid fluorinated polymer salt is dispersed in a solvent (e.g., water). The ionomer can then be dried and stored as a salt, which can be subsequently redispersed for use. Alternatively, after dispersing the solid fluorinated polymer salt in the solvent, the fluorinated polymer salt can be converted back to a fluorinated polymer in which Z is hydrogen by cation exchange.

[0048] Optionally, the reagent is provided in an equivalent amount or in excess so that the reagent provides a molar equivalent or molar excess of cations relative to the -SO3Z group. After the solid fluorinated polymer salt is separated from the reagent and before the solid fluorinated polymer salt is dispersed in the solvent, the solid fluorinated polymer salt can be washed in a solvent, optionally in water. This ensures that all or substantially all excess unreacted reagents are removed from the film before being dispersed in the solvent. The solid fluorinated polymer salt can then be dispersed in the solvent by, for example, heating the solid fluorinated polymer salt in the solvent to a temperature of at least 180°C, 200°C, 220°C, 240°C or 250°C (optionally not more than 500°C, 400°C or 300°C) using an autoclave.

[0049] The reagent providing the cation source to form the fluorinated polymer salt may be selected from one or more of the following: base; hydroxide; metal hydroxide; ammonium hydroxide; carbonate; metal carbonate; alkali metal carbonate; alkaline earth metal carbonate; ammonium carbonate; halide; metal halide; organic salt; formates; acetates; oxalates; citrates; gluconates; inorganic cation sources; metal cation sources; organic cation sources; NH4 + source; bicarbonate; carbamate; nitrate; phosphate; and sulfate.

[0050] Examples where the reagent is a base (e.g., hydroxide)

[0051] According to certain examples, the reagent is a base, and the method includes: contacting the membrane with an alkaline aqueous solution comprising water and a base (e.g., a hydroxide, such as an alkali metal hydroxide or ammonium hydroxide) to form a fluorinated polymer salt. The solid fluorinated polymer salt can then be dispersed in a solvent, and optionally the fluorinated polymer salt can be converted back to a fluorinated polymer in which Z is hydrogen by cation exchange. A molar excess of base relative to -SO3Z groups can be provided in the step of contacting the membrane with the alkaline aqueous solution to form the fluorinated polymer salt, and the excess base is removed before dispersing the membrane and optionally converting the fluorinated polymer salt into the fluorinated polymer by cation exchange. As described in the Summary of the Invention section, according to this specification, an excess of base is added to the fluorinated polymer to ensure that the fluorinated polymer is substantially completely converted to salt form, but the excess base is substantially removed immediately during or after the fluorinated polymer is converted to salt form. Removal of excess / unreacted base reduces etching / corrosion problems in the equipment, reduces species formation and extraction problems of other components (such as platinum group metal components), and ensures that excess base does not need to be recovered to convert the fluorinated polymer salt back to the acid form during subsequent ion exchange processes, thereby improving the overall material balance.

[0052] The alkaline aqueous solution is maintained at a sufficiently low temperature so that during the step of contacting the film with the alkaline aqueous solution to form the fluorinated polymer salt in a solid, undispersed form, the film remains in a solid, undispersed form. This is in contrast to the prior art method in which the film is heated in an alkaline aqueous solution to disperse the film. It has been found that the film can be converted into a salt form without dispersing the fluorinated polymer film. This is advantageous because the excess alkali is then easily removed by separating the solid fluorinated polymer salt from the alkaline aqueous solution (e.g., by solid-liquid separation techniques, optionally by decantation or filtration). The solid fluorinated polymer salt can then be dispersed in a (non-alkaline) solvent, optionally water, before being converted into the fluorinated polymer by cation exchange. As previously indicated, removing excess alkali in this way reduces etching / corrosion problems in the device, reduces material formation and extraction problems of other components (such as platinum group metal components), and ensures that excess alkali does not need to be recovered during the subsequent ion exchange process to convert the fluorinated polymer salt back into the acid form, thereby improving the overall material balance.

[0053] During the step of contacting the membrane with the alkaline aqueous solution to form the fluorinated polymer salt, the alkaline aqueous solution may be maintained at a temperature (e.g., room temperature) below 150° C., 100° C., 80° C., 60° C., or 40° C., optionally greater than 5° C., 10° C., or 15° C., optionally within the range defined by any one of the aforementioned upper and lower limits. The temperature may be sufficiently low to achieve conversion of the fluorinated polymer to a salt form without dispersing the fluorinated polymer membrane, which remains in a solid, undispersed form.

[0054] After separation of the solid fluorinated polymer salt from the alkaline aqueous solution and before dispersing the solid fluorinated polymer salt in the solvent, the solid fluorinated polymer salt may be washed in a solvent, optionally water.

[0055] After forming the fluorinated polymer salt and optionally washing, the solid fluorinated polymer salt can be dispersed in a solvent (e.g., water) by heating the solid fluorinated polymer salt in the solvent to a temperature of at least 180°C, 200°C, 220°C, 240°C, or 250°C (optionally not exceeding 500°C, 400°C, or 300°C) before converting the fluorinated polymer salt to the fluorinated polymer by cation exchange.

[0056] In the above process, the fluorinated polymer film is converted to the salt form without dispersing the film. Then, in another process step, dispersion is achieved without the use of a base.

[0057] The base used to form the fluorinated polymer salt can be a hydroxide. Optionally, the base is a metal hydroxide, optionally an alkali metal hydroxide (e.g., LiOH or NaOH) or ammonium hydroxide. The solid salt can be stored as an intermediate product until it is needed for the production of a new fluorinated polymer or is immediately converted into a fluorinated polymer. In this regard, then, the fluorinated polymer salt can be dispersed (e.g., by autoclaving in water) before the step of converting the fluorinated polymer salt into the fluorinated polymer by cation exchange. After the fluorinated polymer salt is converted into the fluorinated polymer by cation exchange, the fluorinated polymer can be reused to make a new membrane.

[0058] The membrane can be a catalyst-coated membrane for a fuel cell or an electrolyzer. In this case, it is desirable to circulate the polymer material of the catalyst component and the membrane. Therefore, the membrane can be heated in the presence of water and a base to form at least one catalyst material and the membrane before the fluorinated polymer salt is separated, and / or the membrane can be heated in the presence of water and a base to form at least one catalyst material and the fluorinated polymer or the fluorinated polymer salt after the fluorinated polymer salt is separated.

[0059] experiment

[0060] Cut the perfluorosulfonic acid ionomer membrane into pieces small enough to fit in the container. Weigh 6.0 g of anhydrous LiOH and 250 g of water, and dissolve the LiOH in the water. Immerse the membrane in the LiOH solution and heat to reflux for 1 hour. Wash the resulting mixture with 4×100 mL of water. Decant the remaining water to leave the (wet) membrane. Weigh 250 g of water, add it to the (wet) membrane, and heat to reflux for 1 hour. Then decant the water and dry the solid product under vacuum.

[0061] Figure 2 FTIR data indicating salt formation is shown. FTIR data was collected for untreated fluorinated polymer membrane material 301, fluorinated polymer salt material 303 formed after treatment in aqueous LiOH solution, and fluorinated polymer salt material 304 formed after treatment in aqueous LiOH solution followed by water washing.

[0062] Figure 3 The example of process step (pre-autoclaving) is shown. The film on the roller is cut, and then further cut or folded into a certain size. As indicated in the figure, the film is brown. Then, the film is refluxed in lithium hydroxide solution, wherein the film becomes colorless and is converted into salt form, which is confirmed by spectral analysis. In the case of not dispersing the film, conversion is achieved, and the film keeps solid, undispersed form.

[0063] It may be noted that the color change of the film does not necessarily indicate a chemical change, and the film may have a different color. However, in the illustrative example, the chemical change of the polymer from the protonated form to the salt form is accompanied by an associated color change, as shown.

[0064] exist Figure 3 In the final step of the pre-autoclaving process shown, the solid polymer salt membrane material is washed in water to remove any residual LiOH solution. Figure 4 is a photograph showing the membrane before (left hand side) and after (right hand side) the process steps of refluxing the membrane in an alkaline LiOH solution and washing with water, indicating the fact that the color of the membrane changes from brown to colorless and that the membrane remains in a solid, undispersed form. Spectroscopic analysis confirms that the colorless membrane is in the form of a salt.

[0065] Figure 5 Shown in Figure 3 The treatment process shown is followed by another step of autoclaving the film to disperse the film in water. The colorless, solid, undispersed polymer salt film is autoclaved in water under nitrogen at 250°C and 40 bar (4000 kPa) pressure. This produces a (non-alkaline) aqueous dispersion of the polymer salt.

[0066] Figure 6An additional step of ion exchange (post-autoclaving) is shown to convert the dispersed polymer salt back to the protonated acid form. TM An ion exchange column of 15(H) resin is used for this process step. The dispersion of the (protonated) fluorinated polymer can be reused to make new membranes or dried and stored for future use.

[0067] Example where the reagent is a carbonate

[0068] As an alternative to using a base, such as a hydroxide as described above, according to other examples of the present method, a carbonate is used as an agent for converting the fluorinated polymer membrane into a salt form prior to dispersing the membrane.

[0069] like Figure 7 As illustrated, the method also provides a method for recovering the fluorinated polymer from a film comprising the fluorinated polymer. The fluorinated polymer also comprises a fluorinated polymer backbone and a plurality of groups represented by the formula -SO3Z, wherein Z is hydrogen. The method comprises: contacting the film with an aqueous solution comprising water and a carbonate (e.g., a metal carbonate, an alkali metal carbonate, an alkaline earth metal carbonate, or ammonium carbonate) to form a fluorinated polymer salt. The fluorinated polymer salt can then be dispersed in a solvent and optionally converted back to a fluorinated polymer in which Z is hydrogen by cation exchange.

[0070] As described in the Summary of the Invention, the use of carbonates rather than hydroxides, where the carbon dioxide decomposition products produced when forming the sulfonates can be removed as gaseous products, avoids the production of highly corrosive alkaline solutions and avoids the need for extensive washing steps.

[0071] The carbonate solution can be degassed to remove the carbon dioxide formed during the reaction of the carbonate and the -SO3Z group from the carbonate solution. Degassing can be achieved by heating the carbonate solution and / or reducing the pressure above the carbonate solution. In addition, the step of contacting the film with the carbonate solution to form the fluorinated polymer salt can be carried out in a container with atmosphere control, and the atmosphere control includes a pressure release regulator to ensure that the released carbon dioxide does not overpressure the container. Further, after the step of contacting the film with the carbonate solution to form the fluorinated polymer salt, the atmosphere in the container can be replaced by an inert gas, optionally nitrogen. As an alternative to using a sealed container, the film can be contacted with the carbonate in an open container.

[0072] Thus, according to one example of the present specification, a PFSA membrane (e.g., a waste membrane material generated during the manufacture of a membrane for a fuel cell or electrolyzer or a used / wasted membrane from such a device) is treated with a carbonate solution of sufficient concentration and volume to completely convert the sulfonic acid into the corresponding salt. The material is thoroughly mixed for a sufficient time (optionally with heating) for ion exchange conversion of the sulfonic acid into the salt. The mixture can then be heated to displace carbon dioxide from the solution, and the pressure can be optionally reduced to facilitate degassing of the solution. The carbonate and ionomer can be added directly to an autoclave or pressure reactor equipped with atmosphere control and pressure release regulation to ensure that the released carbon dioxide does not overpressurize the vessel during sulfonate formation, and the atmosphere can be changed from carbon dioxide to nitrogen after sulfonate formation is complete.

[0073] A molar excess of carbonate relative to -SO3Z groups may be provided in the step of contacting the membrane with the carbonate solution to form the fluorinated polymer salt, and the excess carbonate is removed prior to dispersing the membrane and optionally converting the fluorinated polymer salt back to a protonated polymer by cation exchange. Excess carbonate is added to the fluorinated polymer to ensure that the fluorinated polymer is substantially completely converted to salt form, and the excess carbonate may be substantially removed during or immediately after the fluorinated polymer is converted to salt form. Removal of excess carbonate reduces material formation and extraction problems of other components (such as platinum group metal components), and ensures that excess carbonate does not need to be recovered during subsequent ion exchange processes to convert the fluorinated polymer salt back to acid form, thereby improving the overall material balance.

[0074] Advantageously, the carbonate aqueous solution is maintained at a sufficiently low temperature so that during the step of contacting the film with the carbonate aqueous solution to form the fluorinated polymer salt in a solid, undispersed form, the film remains in a solid, undispersed form. This is in contrast to the prior art method in which the film is heated in an alkaline aqueous solution to disperse the film. It has been found that the film can be converted into a salt form using a carbonate reagent without dispersing the fluorinated polymer film. This is advantageous because the excess carbonate can be easily removed by subsequently separating the solid fluorinated polymer salt from the carbonate aqueous solution (by solid-liquid separation techniques, optionally decantation or filtration). Alternatively, excess carbonate (e.g., ammonium carbonate) can be removed using thermal treatment (note that thermal treatment can be used to remove ammonium carbonate, other organic carbonates and / or other ammonium salts as an alternative to solid-liquid separation techniques (such as filtration)). Then, before the fluorinated polymer salt is converted into the fluorinated polymer by cation exchange, the solid fluorinated polymer salt can be dispersed in a (non-alkaline) solvent, optionally water. As previously indicated, removal of excess carbonate reduces material formation and extraction problems for other components, such as platinum group metal components, and ensures that excess carbonate does not need to be recovered during subsequent ion exchange processes to convert the fluorinated polymer salt back to the acid form, thus improving the overall material balance.

[0075] During the step of contacting the membrane with the carbonate aqueous solution to form the fluorinated polymer salt, the carbonate aqueous solution may be maintained at a temperature (e.g., room temperature) below 150° C., 100° C., 80° C., 60° C., or 40° C., optionally greater than 5° C., 10° C., or 15° C., optionally within the range defined by any one of the aforementioned upper and lower limits. The temperature may be sufficiently low to achieve conversion of the fluorinated polymer to the salt form without dispersing the fluorinated polymer membrane, which remains in a solid, undispersed form.

[0076] After separation of the solid fluorinated polymer salt from the aqueous carbonate solution and before dispersing the solid fluorinated polymer salt in a dispersing solvent, the solid fluorinated polymer salt may be washed in a washing solvent, optionally water.

[0077] After forming the fluorinated polymer salt and optionally washing, the solid fluorinated polymer salt can be dispersed in a solvent (e.g., water) by heating the solid fluorinated polymer salt in the solvent to a temperature of at least 180°C, 200°C, 220°C, 240°C or 250°C before converting the fluorinated polymer salt to the fluorinated polymer by cation exchange.

[0078] In the preferred process described above, the fluorinated polymer film is converted to the salt form without dispersing the film. Then, in another process step, dispersion is achieved without the use of alkali / carbonate.

[0079] The solid salt can be stored as an intermediate product until it is needed for the production of new fluorinated polymers or immediately converted to protonated fluorinated polymers. In this regard, the fluorinated polymer salt can then be dispersed (e.g., by autoclaving in water) prior to the step of converting the fluorinated polymer salt to the fluorinated polymer by cation exchange. After converting the fluorinated polymer salt to the fluorinated polymer by cation exchange, the fluorinated polymer can be reused to make new membranes.

[0080] The membrane can be a catalyst-coated membrane for a fuel cell or an electrolyzer. In this case, it is desirable to circulate the polymer material of the catalyst component and the membrane. Therefore, at least one catalyst material can be separated from the membrane before the membrane is contacted with a carbonate solution to form the fluorinated polymer salt, and / or at least one catalyst material can be separated from the fluorinated polymer or the fluorinated polymer salt after the membrane is contacted with a carbonate solution to form the fluorinated polymer salt.

[0081] experiment

[0082] Figure 8 The example of process step (pre-autoclaving) is shown. The film on the roller is cut, and then further cut or folded into a certain size. As indicated in the figure, the film is brown. Then, the film is refluxed in lithium carbonate solution, wherein the film becomes colorless and is converted into salt form, which is confirmed by spectral analysis. In the case of not dispersing the film, conversion is achieved, and the film keeps solid, undispersed form.

[0083] It may be noted that the color change of the film does not necessarily indicate a chemical change, and the film may have a different color. However, in the illustrative example, the chemical change of the polymer from the protonated form to the salt form is accompanied by an associated color change, as shown.

[0084] exist Figure 8 In the final step of the pre-autoclaving process shown, the solid polymer salt film material was washed in water to remove any residual lithium carbonate solution. Spectroscopic analysis confirmed that the colorless film was in salt form.

[0085] According to one example, sodium carbonate (0.73 g, 6.88 mmol) was dissolved in deionized water (200 mL). A portion of the perfluorosulfonic acid ionomer membrane (6.25 mmol SO3 - ) was immersed in a portion of sodium carbonate solution (100 mL) for 1 hour and boiled for another hour. The resulting membrane was washed with deionized water and dried under vacuum. FTIR of the membrane before and after ion exchange (the membrane was subjected to 1 equivalent of Na in terms of Na2CO3, see Fig. 9 ) shows that at about 1050cm-1 Up to 1060cm -1 Sulfinate group (SO3 - ) indicates a change in the environment, which is interpreted as a successful ion exchange. By titration with HCl, the alkalinity of the solution after ion exchange and boiling was increased from 0.04 M [OH - ] is reduced to 0.00M[OH - ].

[0086] The second example follows the same procedure but uses twice the amount of sodium carbonate (1.46 g, 13.75 mmol). FTIR of the membrane before and after ion exchange (the membrane was subjected to 2 equivalents of Na as Na2CO3, see Fig. 9 ) shows that the sulfinate group (SO3 - ) by titration with HCl, the alkalinity of the solution after ion exchange and boiling was increased from 0.06 M [OH - ] is reduced to 0.02M[OH - ], and the pH decreased from 11.1 to 8.4.

[0087] As previously referenced Figure 5 As described in the hydroxide reagent example, Figure 8 Another step of autoclaving the film after the treatment process can be used to disperse the film in water. The colorless, solid, undispersed polymer salt film can be autoclaved in water under nitrogen at 250° C. and 40 bar (4000 kPa). This produces a (non-alkaline) aqueous dispersion of the polymer salt.

[0088] In addition, as previously referenced Figure 6 As described in the case of the hydroxide reagent, an additional step of ion exchange (post-autoclaving) can be used to convert the dispersed polymer salt back to the protonated acid form. TM An ion exchange column of 15(H) resin is used for this process step. The dispersion of the (protonated) fluorinated polymer can then be reused to make new membranes or dried and stored for future use.

[0089] Alternative salt-forming reagents

[0090] It has also been demonstrated that other reagents can be used to provide the cation source required to form the fluorinated polymer salt wherein Z is a cation while the film remains in a solid, undispersed form. For example, metal chloride solutions have been used for this purpose.

[0091] While the invention has been particularly shown and described with reference to certain examples, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined in the following claims.

Claims

1. A method for recovering a fluorinated polymer from a membrane comprising the fluorinated polymer, the fluorinated polymer comprising a fluorinated polymer backbone and a plurality of groups represented by the formula -SO3Z, wherein Z is hydrogen, the method comprising: contacting the membrane with a reagent providing a source of cations to form a fluorinated polymer salt wherein Z is a cation, wherein the reagent is maintained at a sufficiently low temperature that the membrane remains in a solid, undispersed form; removing excess unreacted reagent from the solid fluorinated polymer salt; as well as After removing the excess reagent, the solid fluorinated polymer salt is dispersed in a solvent.

2. The method according to claim 1, The method further comprises: After dispersing the solid fluorinated polymer salt in the solvent, the fluorinated polymer salt is converted back to a fluorinated polymer wherein Z is hydrogen by cation exchange.

3. The method according to claim 1 or 2, wherein the excess unreacted reagents are removed from the solid fluorinated polymer salt using solid-liquid separation techniques, optionally decantation and filtration.

4. A method according to any preceding claim, Wherein the solvent used to disperse the solid fluorinated polymer salt after removal of excess base is water.

5. A method according to any preceding claim, wherein during the step of contacting the membrane with the reagent to form the fluorinated polymer salt, the reagent is maintained at a temperature below 150°C, 100°C, 80°C, 60°C or 40°C.

6. A method according to any preceding claim, wherein the solid fluorinated polymer salt is washed in a solvent, optionally water, after separating the solid fluorinated polymer salt from the reagent and before dispersing the solid fluorinated polymer salt in the solvent.

7. A method according to any preceding claim, wherein the solid fluorinated polymer salt is dispersed in the solvent by heating the solid fluorinated polymer salt in the solvent to a temperature of at least 180°C, 200°C, 220°C, 240°C or 250°C.

8. A method according to any preceding claim, wherein the reagent providing the cation source to form the fluorinated polymer salt is selected from one or more of the following: a base; a hydroxide; a metal hydroxide; an ammonium hydroxide; a carbonate; a metal carbonate; an alkali metal carbonate; an alkaline earth metal carbonate; an ammonium carbonate; a halide; a metal halide; an organic salt; a formates; an acetate; an oxalate; a citrate; a gluconate; an inorganic cation source; a metal cation source; an organic cation source; NH4 + source; bicarbonate; carbamate; nitrate; phosphate; and sulfate.

9. A method according to any preceding claim, wherein the reagent provides a molar equivalent or molar excess of the cation relative to the -SO3Z group.

10. A method according to any preceding claim, The reagent is an aqueous solution.

11. A method according to any preceding claim, wherein the reagent is a base, optionally a hydroxide.

12. The method according to any one of claims 1 to 10, wherein the reagent is an aqueous carbonate solution, optionally a metal carbonate, an alkali metal carbonate, an alkaline earth metal carbonate or ammonium carbonate.

13. The method according to claim 12, The carbonate aqueous solution is degassed to remove carbon dioxide formed during the reaction of the carbonate with the -SO3Z groups, and the degassing is achieved by heating the carbonate aqueous solution and / or reducing the pressure above the carbonate aqueous solution.

14. The method according to any one of claims 12 or 13, The step of contacting the membrane with the aqueous carbonate solution to form the fluorinated polymer salt is performed in a vessel having an atmosphere control including a pressure release regulator to ensure that the released carbon dioxide does not over-pressurize the vessel.

15. The method according to any one of claims 12 to 14, wherein after the step of contacting the membrane with the carbonate aqueous solution to form the fluorinated polymer salt, the atmosphere in the container is replaced with an inert gas, optionally nitrogen.

16. A method according to any preceding claim, wherein after converting the fluorinated polymer salt into the fluorinated polymer by cation exchange, the fluorinated polymer is reused to manufacture a new membrane.

17. A method according to any preceding claim, The membrane is a catalyst-coated membrane for a fuel cell or an electrolyser.

18. The method according to claim 17, wherein at least one catalyst material is separated from the membrane prior to contacting the membrane with the reagent.

19. The method according to claim 17 or 18, wherein after contacting the membrane with the reagent, at least one catalyst material is separated from the fluorinated polymer or the fluorinated polymer salt.

Images