Recycling of catalyst coated membrane components

Abstract

A method for recycling a fluoropolymer from a membrane comprising the fluoropolymer, the fluoropolymer comprising a fluoropolymer backbone and a plurality of groups represented by the formula -SOZ, where Z is hydrogen, the method comprising: contacting the membrane with a reagent that provides a source of cations for forming a fluoropolymer salt, where Z is a cation, the reagent being maintained at a temperature low enough that the membrane remains in a solid, undispersed form; removing excess unreacted reagent from the solid fluoropolymer salt; and dispersing the solid fluoropolymer salt in a solvent after removing the excess reagent.

Description

[Technical Field]

[0001] This specification relates to a method for recycling components of catalyst coated membranes such as those used in fuel cells and hydrogen producing water electrolyzers. [Background technology]

[0002] As investments are made in the global hydrogen economy, the production of fuel cells and hydrogen-producing water electrolyzers is set to grow rapidly. Catalyst-coated membranes (CCMs) are the key functional components of both fuel cells and electrolyzers. Such CCMs generally comprise a conductive polymer membrane coated on both sides with catalyst-containing layers. CCMs are configured to drive oxidation and reduction reactions and support proton and electron transport; these processes are required for fuel cell and electrolyzer technologies to function.

[0003] While there are variations in the materials and composition of CCM components according to the functional performance requirements of the end application, they generally contain several useful components, including one or more platinum group metal (PGM) catalysts and one or more proton conducting polymers.

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

[0005] The CCM can contain two different catalysts, one to drive the oxidation reaction on one side of the CCM and one to drive 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, 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., CeO) as a peroxide scavenger to slow the decomposition of the CCM and extend its lifespan.

[0006] CCM catalysts can be based on platinum group metals such as platinum, ruthenium, iridium, palladium, or mixtures thereof. The platinum group metals may be provided in elemental (metal) form, compound form (e.g., oxides such as iridium oxide catalysts), or PGM-based metal alloys (e.g., PtCo). Additionally, PGM catalyst materials may be supported on a substrate material (e.g., carbon, such as platinum-on-carbon catalysts or PtCo-on-carbon, which include particles of carbon on which platinum is disposed).

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

[0008] With the increase in CCM production for fuel cells and electrolyzers, there is also an associated increase in CCM waste material, including large amounts of scrap material generated during CCM production (e.g., due to failures in quality control), and an increase in end-of-life (EoL) CCM. Because CCMs contain several rare and / or valuable components, including platinum group metals (especially Pt, Pd, Ir, and Ru) and ionomers (in both membranes and catalyst layers), there is an increasing demand for methods to recycle such components from scrap / waste CCM material.

[0009] One current method for recovering PGMs from production scrap and end-of-life CCM materials involves incineration. The incineration process produces a PGM-rich (typically Pt and Ir) ash that is processed through conventional PGM purification routes. However, the incineration process releases harmful and toxic gases, such as CO and HF, from the polymers that are part of the membrane. Both of these gases have adverse effects because they pollute the atmosphere, increase the greenhouse effect, and / or have harmful effects on the human body. Therefore, a cleaner process is needed that reduces or eliminates the release of these gases.

[0010] In addition to the above, incineration methods destroy ionomer components, which also have significant value. Therefore, it is desirable to provide a process that can recover both PGM and ionomer components, as well as to provide a cleaner, safer, and more environmentally friendly process. Processes for recovering perfluorosulfonic acid ionomers are known. See, for example, WO 2016 / 156815 and U.S. Pat. No. 7,255,798. Additionally, processes for recovering individual PGM catalyst components are known. See, for example, U.S. Pat. No. 7,709,135. However, to enable fuel cells and electrolyzers to become more sustainable technologies, a commercially viable and environmentally friendly route is needed to recover, separate, and recycle both PGM and ionomer components from waste CCM materials, including production scrap and end-of-life materials.

[0011] The present specification relates to a method for recycling ionomer material (perfluorosulfonic acid (PFSA) polymer) from ionomer membranes of fuel cells or electrolyzers.

[0012] WO 2021250576 discloses a process for recycling ionomer materials from ionomer membranes in fuel cells or electrolyzers. It describes that the solubility of fluorinated polymers used in such membranes decreases when the fluorinated polymer is heat-treated, as can occur during the manufacture of membranes containing the fluorinated polymer. That is, fluorinated polymers having a fluorinated backbone and multiple groups of the formula -SO3H or salts thereof are readily soluble in water and alcohol mixtures when freshly prepared after being heated to a temperature of at least 100°C. These polymers are typically insoluble in water and water / alcohol mixtures under standard conditions. WO 2021250576 discloses that such heat-treated fluorinated polymers become soluble when heated in the presence of water and a base. Therefore, WO 2021250576 discloses a method comprising dissolving the 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 further noted that the moles of base used may be equivalent to the moles of fluorinated polymer, or an excess of base (e.g., up to 100, 200, or 300 mole percent excess of base relative to fluorinated polymer) may be used.

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

[0014] This specification relates to the recovery of perfluorosulfonic acid (PFSA) polymers from scrap or used membranes, such as those used in fuel cells or electrolyzers. It is recognized that, as described in WO2021250576, the use of an equivalent or excess amount of base can be advantageous to ensure that all or substantially all of the fluorinated polymer is converted to the salt form. Salt formation is advantageous because it protects the sulfonic acid groups during the recovery process and therefore ensures that all or substantially all of the sulfonic acid groups are converted to the salt form during the process. However, it is also recognized that the use of bases such as hydroxides, as described in WO2021250576, can cause some problems in the further processing of the ionomer material, especially when the material being treated also contains one or more platinum group metal catalysts, such as in catalyst-coated membranes.

[0015] Excess base can lead to etching / corrosion problems in the equipment. Furthermore, excess base can cause problems in the speciation and extraction of other components, such as platinum group metal catalysts present in catalyst-coated membranes of fuel cells or electrolyzers. Furthermore, any excess base must be recovered during the ion-exchange process to convert the fluorinated polymer salt back to the protonated acid form, which can adversely affect the overall balance of materials. For example, if hydroxide is used as the base to convert the fluorinated polymer to its salt form, excess hydroxide base is corrosive to metal- and glass-lined vessels that may be used in the subsequent dispersion process at high temperature and pressure. Furthermore, excess hydroxide base can cause problems in the speciation and extraction of other components, such as platinum group metal catalysts present in catalyst-coated membranes of fuel cells or electrolyzers. Furthermore, excess hydroxide base must be recovered during the ion-exchange process to convert the fluorinated polymer salt back to the protonated acid form, which can adversely affect the overall balance of materials.

[0016] Therefore, it has been recognized that when excess base is added to a fluoropolymer to ensure substantially complete conversion of the fluoropolymer to its salt form, the excess base should be substantially removed during or immediately after conversion of the fluoropolymer to its salt form. Removal of excess base reduces etching / corrosion problems in the equipment, reduces problems with speciation and extraction of other components, such as platinum group metal components, and ensures that excess base does not need to be recovered during a subsequent ion exchange process to convert the fluoropolymer salt back to its acid form, thus improving overall material balance. As described in WO2021250576, when a membrane is heated in a basic solution to form a dispersion of the fluoropolymer salt in the basic solution, it is difficult to separate the fluoropolymer salt from the excess base. However, it has been discovered that a membrane material can be treated with a basic solution to form a salt without heating the membrane to a temperature at which it disperses in the basic solution. This allows the membrane to remain in the form of a solid salt that is easily separated from the basic solution before further processing.

[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 to a salt form. For example, it has been found that carbonate salts can be used, thus reducing or avoiding the aforementioned problems associated with the use of hydroxide bases. Therefore, in addition to removing excess salt-forming reagent when converting the fluorinated polymer to a salt form, it can also be advantageous to use carbonate salts as salt-forming reagents in that the carbon dioxide decomposition product produced upon the formation of sulfonate salts can be removed as a gaseous product, thus avoiding the production of highly corrosive alkaline solutions and the need for significant washing steps.

[0018] As a further alternative to using hydroxides and carbonates as salt-forming reagents for converting fluorinated polymers into salts, it has been discovered that other reagents can be used as cation sources to produce polymer salts. Such reagents include inorganic salts such as halide salts (e.g., chlorides, e.g., 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). Furthermore, the cations can be inorganic cations (i.e., metal cations) or NH4 + Other choices of reagents include bicarbonates, carbamates, nitrates, phosphates, and sulfates, which may be in the form of, for example, metal or ammonium salts.

[0019] According to the present disclosure, such a reagent is added to a fluorinated polymer to convert the fluorinated polymer to a salt form without heating to a temperature sufficient to disperse the membrane, so that the membrane remains in a solid, undispersed form. Excess unreacted reagent is then removed from the solid polymer salt before the solid polymer salt is dispersed in a solvent. Removal of excess unreacted reagent reduces etching / corrosion problems in the device, reduces problems in the speciation and extraction of other components, such as platinum group metal components, and ensures that excess reagent does not need to be recovered during a subsequent ion exchange process to convert the fluorinated polymer salt back to its acid form, thus improving the overall material balance.

[0020] Accordingly, provided herein is a method for recycling 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 -SOZ, where Z is hydrogen, the method comprising: contacting the membrane with a reagent that provides a source of cations for forming a fluorinated polymer salt where Z is a cation, the reagent being maintained at a temperature that is sufficiently low so that the membrane remains in a solid, undispersed form; removing excess unreacted reagents from the solid fluorinated polymer salt; removing excess reagents and then dispersing the solid fluorinated polymer salt in a solvent.

[0021] For example, if the reagent is a base, the method comprises: contacting the membrane with a basic aqueous solution comprising water and a base to form a fluorinated polymer salt where Z is a cation, optionally providing a molar excess of base relative to the -SOZ groups, and maintaining the basic aqueous solution at a temperature low enough so that the membrane remains in a solid, undispersed form; removing excess / unreacted base by separating the solid fluorinated polymer salt from the basic aqueous solution (e.g., by solid-liquid separation techniques); removing the excess base and then dispersing the solid fluorinated polymer salt in a solvent.

[0022] In another embodiment, the reagent is a carbonate salt and the method comprises: contacting the membrane with an aqueous carbonate solution comprising water and a carbonate salt to form a fluorinated polymer salt wherein Z is a cation, optionally providing a molar excess of carbonate relative to the -SOZ groups to form the fluorinated polymer salt, and maintaining the aqueous carbonate solution at a temperature sufficiently low so that the membrane remains in a solid, undispersed form; removing excess / unreacted carbonate from the solid fluorinated polymer salt; and removing excess carbonate salt, followed by dispersing the fluorinated polymer salt in a solvent.

[0023] Optionally, after dispersing the solid fluorinated polymer salt in the solvent, the fluorinated polymer salt is converted back to the fluorinated polymer where Z is hydrogen by cation exchange. This can be done immediately after the dispersion step. Alternatively, the dispersed polymer salt can be dried and stored, and then later redispersed and converted to the protonated form when needed for use. [Brief explanation of the drawings]

[0024] For a better understanding of the invention and to show how the same may be carried into effect, specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a flow diagram of method steps for recycling fluorinated polymer membrane materials. [Figure 2] FIG. 1 shows FTIR data for a fluoropolymer membrane material, a fluoropolymer salt material formed after treatment in water and base, and a fluoropolymer salt material formed after treatment in water and base followed by a water wash. [Figure 3] FIG. 1 shows an example of a process step (pre-autoclave) involving refluxing a fluorinated polymer membrane in a basic LiOH solution to form a fluorinated polymer salt without dispersing the membrane, followed by washing with water. [Figure 4] Photographs showing the membrane before (left) and after (right) the process steps of refluxing the membrane in a basic LiOH solution and rinsing with water. [Figure 5] FIG. 4 shows the treatment process shown in FIG. 3 followed by the additional step of autoclaving the membrane to disperse it in water. [Figure 6] FIG. 10 shows a further step of ion exchange (post-autoclave) to convert the dispersed polymer salt back to the protonated acid form. [Figure 7] FIG. 1 is a flow diagram of method steps for recycling fluorinated polymer membrane material according to another embodiment using a carbonate reagent rather than a hydroxide reagent. [Figure 8] FIG. 1 shows an example of a process step (before dispersing the membrane) involving refluxing a fluorinated polymer membrane in a Li2CO3 solution to form a fluorinated polymer salt without dispersing the membrane, followed by washing with water. [Figure 9] FIG. 1 shows FTIR ATR spectra of PFSA ionomer membranes receiving 1 and 2 molar equivalents of Na as Na2CO3 relative to SO3 − in the membrane. DETAILED DESCRIPTION OF THE INVENTION

[0025] As shown in Figure 1, the present specification provides a method for recycling a fluorinated polymer from a membrane containing the 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 method, in at least some of the -SO3Z groups, Z is hydrogen.

[0026] The method comprises: contacting the membrane with a reagent that provides a source of cations for forming a fluorinated polymer salt where Z is a cation, the reagent being maintained at a temperature that is sufficiently low (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) so that the membrane remains in a solid, undispersed form; removing excess unreacted reagents from the solid fluorinated polymer salt (e.g., using solid-liquid separation techniques, optionally decantation and filtration); and dispersing the solid fluorinated polymer salt in a solvent (e.g., water) after removing excess reagents. The ionomer can then be dried and stored as a salt that can be redispersed for later use. Alternatively, after dispersing the solid fluorinated polymer salt in a solvent, the fluorinated polymer salt may be converted back to a fluorinated polymer where Z is hydrogen by cation exchange.

[0027] Optionally, the reagent is provided in an equivalent or excess amount, such that the reagent provides a molar equivalent or molar excess of cations relative to the -SOZ groups. The solid fluorinated polymer salt can be washed in a solvent, optionally in water, after separating the solid fluorinated polymer salt from the reagent and before dispersing the solid fluorinated polymer salt in the solvent. This ensures that all or substantially all of the excess unreacted reagent is removed from the membrane before dispersion in the solvent. The solid fluorinated polymer salt can then be 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 (optionally up to 500°C, 400°C, or 300°C), for example, using an autoclave.

[0028] Reagents that provide a cation source for forming the fluorinated polymer salt include bases, hydroxides, metal hydroxides, ammonium hydroxide, carbonates, metal carbonates, alkali metal carbonates, alkaline earth metal carbonates, ammonium carbonate, halides, metal halides, organic salts, formates, acetates, oxalates, citrates, gluconates, inorganic cation sources, metal cation sources, organic cation sources, NH4 + The source of the phosphate may be selected from one or more of bicarbonate, carbamate, nitrate, phosphate, and sulfate.

[0029] Examples where the reagent is a base (e.g., hydroxide) According to a particular embodiment, the reagent is a base, and the method includes contacting the membrane with a basic aqueous solution containing 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 where Z is hydrogen by cation exchange. In the step of contacting the membrane with the basic aqueous solution to form the fluorinated polymer salt, a molar excess of base over the -SOZ groups can be provided, and the excess base is removed before dispersing the membrane and, optionally, converting the fluorinated polymer salt to a fluorinated polymer by cation exchange. As described in the Overview section, according to the present specification, an excess of base is added to the fluorinated polymer to ensure substantially complete conversion of the fluorinated polymer to the salt form, but the excess base is substantially removed during or immediately after conversion of the fluorinated polymer to the salt form. Removal of excess / unreacted base reduces etching / corrosion problems in the equipment, reduces problems in speciation and extraction of other components such as platinum group metal components, and ensures that excess base does not have to be recovered during the subsequent ion exchange process to convert the fluorinated polymer salt back to the acid form, thus improving the overall material balance.

[0030] The aqueous basic solution is maintained at a temperature low enough that the membrane remains in a solid, non-dispersed form during the step of contacting the membrane with the aqueous basic solution to form the fluorinated polymer salt in a solid, non-dispersed form. This contrasts with prior art methods in which the membrane is heated in an aqueous basic solution to disperse the membrane. It has been discovered that the fluorinated polymer membrane can be converted to the salt form without dispersing the membrane. This is advantageous because excess base is easily removed by separating the solid fluorinated polymer salt from the aqueous basic solution using, for example, solid-liquid separation techniques, optionally by decantation or filtration. The solid fluorinated polymer salt can then be dispersed in a (non-basic) solvent, optionally water, before converting the fluorinated polymer salt to a fluorinated polymer by cation exchange. As previously indicated, removing excess base in this manner reduces etching / corrosion problems in the equipment, reduces problems in the speciation and extraction of other components, such as platinum group metal components, and ensures that excess base does not have to be recovered during the subsequent ion exchange process to convert the fluorinated polymer salt back to its acid form, thus improving the overall material balance.

[0031] During the step of contacting the membrane with the basic aqueous solution to form the fluoropolymer salt, the basic aqueous solution can be maintained at a temperature below 150° C., 100° C., 80° C., 60° C., or 40° C., optionally above 5° C., 10° C., or 15° C., optionally within a range defined by any of the aforementioned upper and lower limits (e.g., room temperature). The temperature can be sufficiently low so that conversion of the fluoropolymer to the salt form is achieved without dispersing the fluoropolymer membrane, which remains in a solid, undispersed form.

[0032] After separating the solid fluoropolymer salt from the basic aqueous solution and before dispersing the solid fluoropolymer salt in the solvent, the solid fluoropolymer salt can be washed with a solvent, optionally with water.

[0033] 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 up to 500°C, 400°C, or 300°C) before converting the fluorinated polymer salt to a fluorinated polymer by cation exchange.

[0034] In the above process, the fluorinated polymer membrane is converted to the salt form without dispersing the membrane, which is then achieved in a further process step without the use of a base.

[0035] 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 may be stored as an intermediate product until needed for use in the production of new fluorinated polymers or immediately converted to a fluorinated polymer. 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 a fluorinated polymer by cation exchange. After converting the fluorinated polymer salt to a fluorinated polymer by cation exchange, the fluorinated polymer can be reused to produce new membranes.

[0036] The membrane may be a catalyst-coated membrane for a fuel cell or electrolyzer. In this case, it may be desirable to recycle the catalyst components and polymeric materials of the membrane. To this end, the at least one catalyst material may be separated from the membrane before heating the membrane in the presence of water and a base to form a fluorinated polymer salt, and / or the at least one catalyst material may be separated from the fluorinated polymer or fluorinated polymer salt after heating the membrane in the presence of water and a base to form a fluorinated polymer salt.

[0037] experiment Perfluorosulfonic acid ionomer membrane pieces were cut into pieces small enough to fit into a container. 6.0 g of anhydrous LiOH and 250 g of water were weighed, and the LiOH was dissolved in the water. The membrane pieces were submerged in the LiOH solution and heated to reflux for 1 hour. The resulting mixture was washed with 4 x 100 mL of water. The remaining water was decanted, leaving the (wet) membrane pieces. 250 g of water was weighed and added to the (wet) membrane pieces and heated to reflux for 1 hour. The water was then decanted, and the solid product was dried under vacuum.

[0038] Figure 2 shows FTIR data indicating salt formation. FTIR data was collected on an untreated fluorinated polymer membrane material 301, a fluorinated polymer salt material formed after treatment in aqueous LiOH 303, and a fluorinated polymer salt material formed after treatment in aqueous LiOH followed by a water wash 304.

[0039] Figure 3 shows an example of the process steps (pre-autoclaving). The membrane on the roll was cut and then further cut or folded to size. The membrane was brown in color as shown in the figure. The membrane was then refluxed in a lithium hydroxide solution, whereupon it turned colorless and was converted to the salt form as confirmed by spectroscopic analysis. The conversion was achieved without dispersing the membrane, which remained in a solid, undispersed form.

[0040] It should be noted that a color change in the membrane does not necessarily indicate a chemical change; membranes may have different colors. However, in the illustrative examples, the chemical change of the polymer from the protonated form to the salt form was accompanied by an associated color change, as shown in the figure.

[0041] In the final step before autoclaving, shown in Figure 3, the solid polymer-salt membrane material was washed in water to remove any residual LiOH solution. Figure 4 shows photographs of the membrane before (left) and after (right) the process steps of refluxing the membrane in basic LiOH solution and washing with water, demonstrating the change in membrane color from brown to colorless and the fact that the membrane remained in a solid, undispersed form. Spectroscopic analysis confirmed that the colorless membrane was in the salt form.

[0042] Figure 5 shows the treatment process shown in Figure 3 followed by the additional step of autoclaving the membrane to disperse it in water. The colorless, solid, non-dispersed polymer salt membrane was autoclaved in water under nitrogen at 250°C and 40 bar (4000 kPa) pressure. This resulted in a (non-basic) aqueous dispersion of the polymer salt.

[0043] Figure 6 shows the further step of ion exchange (post-autoclaving) to convert the dispersed polymer salt back to the protonated acid form. An ion exchange column containing Amberlyst™ 15(H) resin was utilized for this process step. The (protonated) fluorinated polymer dispersion may be reused to fabricate new membranes or may be dried and stored for future use.

[0044] Example where the reagent is a carbonate Instead of using a base such as a hydroxide as described above, according to another embodiment of the method, a carbonate is used as a reagent to convert the fluorinated polymer membrane to the salt form prior to membrane dispersion.

[0045] As shown in Figure 7, this method also provides a method for recycling fluorinated polymer from a membrane containing the fluorinated polymer. The fluorinated polymer again comprises a fluorinated polymer backbone and a plurality of groups of the formula -SOZ, where Z is hydrogen. The method includes contacting the membrane with an aqueous solution containing water and a carbonate salt (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 where Z is hydrogen by cation exchange.

[0046] As described in the Overview section, the use of carbonates (rather than hydroxides) allows the carbon dioxide decomposition product produced during sulfonate formation to be removed as a gaseous product, avoiding the production of highly corrosive alkaline solutions and the need for significant cleaning steps.

[0047] The aqueous carbonate solution can be degassed to remove carbon dioxide from the carbonate solution formed during the reaction of the carbonate with the —SOZ group. Degassing can be achieved by heating the aqueous carbonate solution and / or reducing the pressure above the aqueous carbonate solution. Furthermore, the step of contacting the membrane with the carbonate solution to form the fluorinated polymer salt can be carried out in a vessel with atmospheric control, including a pressure relief regulator to ensure that the released carbon dioxide does not overpressurize the vessel. Furthermore, after the step of contacting the membrane with the carbonate solution to form the fluorinated polymer salt, the atmosphere in the vessel can be replaced with an inert gas, optionally nitrogen. Instead of using a sealed vessel, the membrane can be contacted with the carbonate in an open vessel.

[0048] Thus, according to one embodiment herein, a PFSA membrane (e.g., scrap membrane material produced during the manufacture of membranes for fuel cells or electrolyzers, or used / discarded membranes from such devices) is treated with a solution of carbonate salt at a concentration and volume sufficient to completely convert the sulfonic acid to the corresponding salt. These materials are thoroughly mixed (optionally with heating) for a time sufficient to convert the sulfonic acid to the salt by ion exchange. 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 salt and ionomer can be added directly to an autoclave or pressure reactor equipped with atmosphere control and pressure release adjustment to ensure that the released carbon dioxide does not overpressurize the vessel during sulfonate formation and to allow for a change of atmosphere from carbon dioxide to nitrogen after sulfonate formation is complete.

[0049] In the step of contacting the membrane with a carbonate solution to form the fluorinated polymer salt, a molar excess of carbonate over the -SOZ groups can be provided, and the excess carbonate can be removed before dispersing the membrane and converting the fluorinated polymer salt back to a protonated fluorinated polymer by cation exchange. The excess carbonate can be added to the fluorinated polymer to ensure substantially complete conversion of the fluorinated polymer to the salt form, and the excess carbonate can be substantially removed during or immediately after the conversion of the fluorinated polymer to the salt form. Removal of the excess carbonate reduces problems with speciation and extraction of other components, such as platinum group metal components, and ensures that excess carbonate does not need to be recovered during the subsequent ion exchange process to convert the fluorinated polymer salt back to the acid form, thus improving the overall material balance.

[0050] Advantageously, the aqueous carbonate solution is maintained at a temperature low enough that the membrane remains in a solid, non-dispersed form during the step of contacting the membrane with the aqueous carbonate solution to form the fluorinated polymer salt in a solid, non-dispersed form. This contrasts with prior art methods in which the membrane is heated in an aqueous basic solution to disperse the membrane. It has been found that the fluorinated polymer membrane can be converted to the salt form using a carbonate reagent without dispersing the membrane. This is advantageous because excess carbonate is easily removed by separating the solid fluorinated polymer salt from the aqueous carbonate solution by solid-liquid separation techniques, optionally by decantation or filtration. Alternatively, the carbonate (e.g., ammonium carbonate) can be removed using heat treatment (note that ammonium carbonate, other organic carbonates, and / or other ammonium salts can be removed using heat treatment as an alternative to solid-liquid separation techniques such as filtration). The solid fluorinated polymer salt can then be dispersed in a (non-basic) solvent, optionally water, before converting the fluorinated polymer salt to a fluorinated polymer by cation exchange. As indicated above, removal of excess carbonate reduces problems in the speciation and extraction of other components, such as platinum group metal components, and ensures that excess carbonate does not have to be recovered during the subsequent ion exchange process to convert the fluorinated polymer salt back to the acid form, thus improving the overall material balance.

[0051] During the step of contacting the membrane with the aqueous carbonate solution to form the fluorinated polymer salt, the aqueous carbonate solution can be maintained at a temperature below 150° C., 100° C., 80° C., 60° C., or 40° C., optionally above 5° C., 10° C., or 15° C., optionally within a range defined by any of the aforementioned upper and lower limits (e.g., room temperature). The temperature can be sufficiently low so that conversion of the fluorinated polymer to the salt form is achieved without dispersing the fluorinated polymer membrane, which remains in a solid, undispersed form.

[0052] After separating the solid fluoropolymer salt from the aqueous carbonate solution and before dispersing the solid fluoropolymer salt in the dispersing solvent, the solid fluoropolymer salt may be washed with a wash solvent, optionally water.

[0053] 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 a fluorinated polymer by cation exchange.

[0054] In the preferred process described above, the fluorinated polymer membrane is converted to the salt form without dispersing the membrane. Dispersion is then achieved in a further process step without the use of a base / carbonate.

[0055] The solid salt may be stored as an intermediate product until needed for use in the production of new fluoropolymers or immediately converted to protonated fluoropolymers. In this regard, the fluoropolymer salt may then be dispersed (e.g., by autoclaving in water) prior to the step of converting the fluoropolymer salt to a fluoropolymer by cation exchange. After converting the fluoropolymer salt to a fluoropolymer by cation exchange, the fluoropolymer may be reused to produce new membranes.

[0056] The membrane may be a catalyst-coated membrane for a fuel cell or electrolyzer. In this case, it may be desirable to recycle the catalyst components and the polymeric material of the membrane. Thus, the at least one catalyst material may be separated from the membrane before contacting the membrane with a carbonate solution to form a fluorinated polymer salt, and / or the at least one catalyst material may be separated from the fluorinated polymer or fluorinated polymer salt after contacting the membrane with a carbonate solution to form a fluorinated polymer salt.

[0057] experiment Figure 8 shows an example of the process steps (pre-autoclaving). The membrane on the roll was cut and then further cut or folded to size. The membrane was brown in color as shown in the figure. The membrane was then refluxed in a solution of lithium carbonate, whereupon the membrane turned colorless and was converted to the salt form as confirmed by spectroscopic analysis. The conversion was achieved without dispersing the membrane, which remained in a solid, undispersed form.

[0058] It should be noted that a color change in the membrane does not necessarily indicate a chemical change; membranes may have different colors. However, in the illustrative examples, the chemical change of the polymer from the protonated form to the salt form was accompanied by an associated color change, as shown in the figure.

[0059] In a final step before autoclaving, shown in Figure 8, the solid polymer salt membrane material was washed in water to remove any residual lithium carbonate solution. Spectroscopic analysis confirmed the colorless membrane to be in the salt form.

[0060] 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 - The membrane was immersed in a portion (100 mL) of sodium carbonate solution for 1 hour and then 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 (membrane receiving 1 equivalent of Na as NaCO, see Figure 9) showed a peak at approximately 1050-1060 cm-1 The sulfinate group (SO3 - ) symmetric stretching shift, indicating a change in the environment and interpreted as a successful ion exchange. The basicity of the solution after ion exchange and boiling was determined to be 0.04 M [OH] by titration with HCl. - ] to 0.00M[OH - ] has decreased to.

[0061] The second example followed the same methodology but used twice the amount of sodium carbonate (1.46 g, 13.75 mmol). FTIR of the membrane before and after ion exchange (membrane receiving 2 equivalents of Na as NaCO, see Figure 9) showed the presence of sulfinate groups (SO - ) shows a similar shift in the symmetric stretch. The basicity of the solution after ion exchange and boiling was determined by titration with HCl to 0.06 M [OH - ] to 0.02M[OH - ] and the pH dropped from 11.1 to 8.4.

[0062] As described above in the hydroxide reagent example with reference to Figure 5, the membrane can be dispersed in water using the treatment process of Figure 8 followed by the additional step of autoclaving the membrane. The colorless, solid, non-dispersed polymer salt membrane can be autoclaved in water under nitrogen at 250°C and 40 bar (4000 kPa) pressure. This results in a (non-basic) aqueous dispersion of the polymer salt.

[0063] Additionally, an additional step of ion exchange (post-autoclaving) can be used to convert the dispersed polymer salt back to the protonated acid form, as described above in the hydroxide reagent example with reference to Figure 6. An ion exchange column containing Amberlyst™ 15(H) resin can be utilized for this process step. The (protonated) fluorinated polymer dispersion can then be reused to fabricate new membranes or dried and stored for future use.

[0064] Alternative Salt-Forming Reagents Other reagents can be used to provide the cation source necessary to form the fluorinated polymer salt where Z is a cation, while ensuring that the membrane remains in a solid, non-dispersed form. For example, metal chloride solutions have been used for this purpose.

[0065] While the present invention has been particularly shown and described with reference to specific embodiments, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. 1. A method for recycling a fluorinated polymer from a membrane comprising a fluorinated polymer, the fluorinated polymer comprising a fluorinated polymer backbone and a fluorinated polymer having a structure of the formula -SO ３ and a plurality of groups represented by Z, wherein Z is hydrogen, said method comprising: contacting the membrane with a reagent that provides a source of cations for forming a fluorinated polymer salt where Z is a cation, the reagent being maintained at a temperature that is sufficiently low so that the membrane remains in a solid, undispersed form; removing excess unreacted reagents from said solid fluorinated polymer salt; and after removing the excess reagent, dispersing the solid fluorinated polymer salt in a solvent.

2. 10. The method of claim 1, further comprising, after dispersing the solid fluoropolymer salt in the solvent, converting the fluoropolymer salt back to a fluoropolymer where Z is hydrogen by cation exchange.

3. 3. The method of 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. The method according to any one of claims 1 to 3, wherein the solvent used to disperse the solid fluoropolymer salt after removing the excess base is water.

5. 5. The method of any one of claims 1 to 4, wherein the reagent is maintained at a temperature of less than 150°C, 100°C, 80°C, 60°C, or 40°C during the step of contacting the membrane with the reagent to form the fluorinated polymer salt.

6. 6. The method of any one of claims 1 to 5, 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. 7. The method of any one of claims 1 to 6, 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. The reagent providing the cation source for forming the fluorinated polymer salt may be selected from the group consisting of a base, hydroxide, metal hydroxide, ammonium hydroxide, carbonate, metal carbonate, alkali metal carbonate, alkaline earth metal carbonate, ammonium carbonate, halide, metal halide, organic salt, formate, acetate, oxalate, citrate, gluconate, inorganic cation source, metal cation source, organic cation source, NH ４ ＋ 8. The method of any one of claims 1 to 7, wherein the source of hydroxybenzoates is selected from one or more of bicarbonates, carbamates, nitrates, phosphates, and sulfates.

9. The reagent is -SO ３ 9. The method of any one of claims 1 to 8, wherein a molar equivalent or molar excess of said cation is provided relative to the Z group.

10. The method according to any one of claims 1 to 9, wherein the reagent is an aqueous solution.

11. The method of any one of claims 1 to 10, wherein the reagent is a base, optionally a hydroxide.

12. 11. The method of 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 carbonate aqueous solution is degassed to separate the carbonate and the -SO ３ 13. The method of claim 12, wherein carbon dioxide formed during reaction with the Z group is removed, and degassing is achieved by heating the aqueous carbonate solution and / or reducing the pressure above the aqueous carbonate solution.

14. 14. The method of claim 12 or 13, wherein the step of contacting the membrane with the aqueous carbonate solution to form the fluorinated polymer salt is carried out in a vessel having atmospheric control including a pressure relief regulator to ensure that released carbon dioxide does not overpressurize the vessel.

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

16. 16. The method according to any one of claims 1 to 15, wherein after the fluorinated polymer salt is converted into a fluorinated polymer by cation exchange, the fluorinated polymer is reused to manufacture new membranes.

17. The method of any one of claims 1 to 16, wherein the membrane is a catalyst coated membrane for a fuel cell or electrolyzer.

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

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

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