Recycling of spent catalyst coated membrane components

Abstract

A method for recycling waste ionomer materials, the method comprising: heating the waste ionomer material in a solvent to disperse the waste ionomer material to form a dispersion of the ionomer in the solvent, the dispersion further containing fluoride anions in the solution; contacting the dispersion with a precipitant or adsorbent to form a solid material containing fluoride anions; and separating the ionomer dispersion from the solid material containing fluoride anions.

Description

Technical Field

[0001] This specification relates to methods for recycling components of membranes used for coating spent catalysts (such as those used in fuel cells and hydrogen-producing water electrolyzers). Background Technology

[0002] With investment in the global hydrogen economy, the production of fuel cells and hydrogen-producing water electrolyzers will grow rapidly. Catalyst-coated membranes (CCMs) are key functional components of both fuel cells and electrolyzers. These CCMs typically consist of 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, processes necessary for fuel cell and electrolyzer technologies to function.

[0003] Although variations of CCM component materials and constructions exist depending on the functional performance requirements of the end-use application, they typically 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 from one or more ionomers, such as perfluorosulfonic acid (PFSA) ionomers. Ionomers may also be disposed in one or both catalyst layers. The ionomers in the catalyst layers may be the same as or different from those in the main membrane component and / or other catalyst layers.

[0005] The CCM may contain two different catalysts, one for driving an oxidation reaction on one side of the CCM and the other for driving a reduction reaction on the other side. The CCM may also contain a recombination catalyst, which is provided to catalyze the recombination of hydrogen and oxygen to form water, thereby reducing the amount of hydrogen passing through the membrane and mixing it with oxygen to form a potentially explosive mixture. The CCM may also contain a metal oxide (e.g., CeO2) as a peroxide scavenger.

[0006] CCM catalysts can be based on platinum group metals, such as platinum, ruthenium, iridium, palladium, or mixtures thereof. Platinum group metals can be provided in elemental (metallic) form, in compound form (e.g., oxides, such as iridium oxide catalysts), or as PGM-based metal alloys (e.g., PtCo). Furthermore, PGM catalyst materials can be supported on a substrate material (e.g., carbon, such as carbon-supported platinum catalysts containing carbon particles with platinum disposed thereon, or carbon-supported PtCo).

[0007] Catalyst-coated membranes (CCMs) can also be combined with additional functional layers to form multilayer membrane electrode assemblies (MEAs). Such MEAs may have, for example, three, five, or seven layers.

[0008] With the increase in CCM manufacturing for fuel cells and electrolyzers, there is a corresponding increase in CCM waste, including large amounts of waste generated during CCM manufacturing (e.g., due to quality control failures) and an increase in end-of-life (EoL) CCMs. Because 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 these components from waste CCM materials.

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

[0010] In addition to the above, incineration destroys the ionomer component, which also has significant value. Therefore, it is desirable to provide a process capable of recovering both PGM and the ionomer component, as well as a cleaner, safer, and more environmentally friendly process. Processes for recovering perfluorosulfonic acid ionomers are known. See, for example, WO2016 / 156815 and US7255798. Furthermore, processes for recovering individual PGM catalyst components are known. See, for example, US7709135. However, for 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 purpose of this manual is to solve this problem. Summary of the Invention

[0012] This specification relates to a method for recycling waste ionomer materials, such as waste ionomer membranes, catalyst-coated ionomer membranes, or catalyst layer materials containing ionomers. As described in the Background section, such materials are key components of fuel cells and hydrogen-producing water electrolyzers, and typically contain platinum group metal catalyst materials.

[0013] To recover ionomers from such materials, the waste ionomer material can be heated in a solvent to disperse it, thereby forming an ionomer dispersion that can be separated and recovered.

[0014] However, the inventors have discovered that the process of heating waste ionomer materials in a solvent to form a dispersion may generate unwanted fluoride anions due to the decomposition of the ionomer. Fluorides are an undesirable product because they pose significant health and safety risks and degrade the performance of processing equipment. The presence of fluorides in recycled ionomer streams is considered an obstacle to ionomer reuse. If fluorides are not removed, the ionomers may become unusable because they could cause additional problems in the final application.

[0015] It has been found that the formation of fluoride anions during ionomer dispersion poses a particularly significant problem when platinum group metal (PGM) catalysts are present during the dispersion process. These PMM catalysts have been found to promote the decomposition of ionomers and the formation of fluorides during ionomer dispersion. One possibility for reducing this decomposition mechanism and fluoride formation is to remove the PMMs before the ionomer dispersion process. For example, PMMs can be leached from waste ionomers using oxidizing and / or reducing acid leaching methods before the ionomer dispersion process. However, after such leaching processes, some PMMs may remain as contaminants, which may promote the decomposition of ionomers and the formation of fluorides during the subsequent ionomer dispersion process. Even if substantially all PMMs are removed, small amounts of fluorides may still be present when a noble metal catalyst is substantially absent. In other words, the inventors have discovered that by implementing an efficient PMM leaching method to remove the PMM catalysts before ionomer dispersion, the fluoride problem can be substantially eliminated.

[0016] While the formation of fluorides can be avoided by leaching the platinum group metal material before ionomer dispersion, as described above, it may be useful in certain situations to disperse, separate, and recover the ionomer before processing and recycling the platinum group metal material. In such methods, the formation of fluorides during ionomer dispersion in the presence of platinum group metals has been found to be a significant problem.

[0017] In view of the above, this specification provides a method for recycling waste ionomer materials, the method comprising: heating the waste ionomer material in a solvent to disperse the waste ionomer material to form a dispersion of the ionomer in the solvent, the dispersion further containing fluoride anions in the solution; contacting the dispersion with a precipitant or adsorbent to form a solid material containing the fluoride anions; and separating the ionomer dispersion from the solid material containing the fluoride anions.

[0018] The precipitant is a metal compound that reacts with the fluoride anion in solution to form a solid metal fluoride salt precipitated from the solution. For example, such a metal compound may be selected from one or more of the following: alkaline earth metal compounds; calcium compounds; magnesium compounds; strontium compounds; transition metal compounds; titanium compounds; post-transition metal compounds; aluminum compounds; and hydroxides. Examples include calcium hydroxide and magnesium hydroxide. The precipitated metal fluoride can then be separated from the dispersion by filtration or centrifugation.

[0019] As an alternative to precipitation, fluoride anions can be removed from a dispersion by using an adsorbent capable of adsorbing anions (e.g., via physisorption, ionic bonding, or covalent bonding of fluorides). Such adsorbents are known in water treatment applications, as described in "A comprehensive review of adsorbents for fluoride removal from water: performance, water quality assessment and mechanism", Environmental Science: Water Research & Technology (RSC Publishing) DOI:10.1039 / D1EW00232E. The adsorbent can be a solid, insoluble metal compound that adsorbs fluoride anions. This solid metal compound can be selected from one or more of the following: metal oxides; magnesium oxide; calcium oxide; aluminum oxide; titanium oxide; and mixed metal oxides. This adsorbent can be introduced into a reaction vessel, where the waste ionomer material is dispersed (e.g., in the form of solid particles, solid rods or bars, or in the form of adsorbent material bags), or alternatively, after the ionomer dispersion step, the ionomer dispersion containing fluoride anions can be passed through an adsorbent bed (e.g., an adsorbent bed in an HF-resistant container such as a PTFE-lined container).

[0020] Therefore, this specification recognizes that: (i) fluoride anions are generated during the dispersion of waste ionomer materials, particularly in the presence of platinum group metals; (ii) such fluoride anions in the waste ionomer recycling feed pose problems in terms of health and safety, deterioration of processing equipment, and suitability for reuse of ionomer materials; and (iii) fluorides generated in the waste ionomer recycling feed can be effectively removed by treatment with precipitants or adsorbents to form a solid material containing fluorides, which can then be easily separated from the ionomer dispersion, for example, by filtration.

[0021] This recycling method is particularly useful for waste ionomer materials containing at least one platinum group metal catalyst material. Such materials may include ionomer membranes (in which a recombinant catalyst may be disposed), catalyst-coated ionomer membranes, and / or catalyst layer materials containing ionomers (which may be obtained, for example, by removing the catalyst layer material from the catalyst-coated ionomer membrane). Furthermore, waste ionomer materials may be waste from fuel cell or electrolyzer applications (e.g., manufacturing waste) or used (e.g., end-of-life) ionomer materials.

[0022] Regarding the above, it should be noted that purification processes such as ultrafiltration are utilized during ionomer manufacturing (see, for example, WO2022224105). Furthermore, the removal of fluoride from water by precipitation using calcium hydroxide, for example, has been established in water purification and other industries. Examples of this include CN105384316B (electronics) and US9469549B2 (solar cell manufacturing). However, to the inventors' knowledge, the problem of fluoride generation during the recycling of waste ionomers, particularly in the presence of platinum group metals, has not been identified, and there are no recommendations suggesting that applying this method to the recycling of waste ionomer materials would solve this problem. Attached Figure Description

[0023] To better understand the invention and show how it can be implemented, certain embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, wherein:

[0024] Figure 1 The waste ionomer recycling process according to this specification is shown;

[0025] Figure 2 A more detailed example of a waste ionomer recycling process according to this specification is shown;

[0026] Figure 3 Another example of a waste ionomer recycling process is shown, in which platinum group metals are leached from the waste ionomer material before the ionomer is dispersed, and the ionomer dispersion is subsequently treated to remove any fluorides generated during the dispersion process.

[0027] Figure 4 Another example of a waste ionomer recycling process is shown, in which the ionomer is dispersed and separated from the platinum group metal material, the remaining platinum group metal material is leached to recover the platinum group metal, and the ionomer dispersion is treated to remove fluorides generated during the dispersion process. Fluoride removal is particularly useful in this example because the platinum group metal present during the ionomer dispersion step promotes the formation of fluorides.

[0028] Figure 5FTIR data are shown for fluoropolymer membrane materials, fluoropolymer salt materials formed after treatment in water and alkali, and fluoropolymer salt materials formed after treatment in water and alkali followed by water washing.

[0029] Figure 6 An example of a process step (pre-autoclaving) is shown, which includes refluxing the fluorinated polymer membrane in an alkaline LiOH solution to form a fluorinated polymer salt without dispersing the membrane, followed by washing with water;

[0030] Figure 7 These are photographs of the membrane before (left-hand side) and after (right-hand side) the process steps of reflux in alkaline LiOH solution and washing with water;

[0031] Figure 8 It shows that in such Figure 6 Following the treatment process shown, the membrane undergoes autoclaving to disperse it in the water; and

[0032] Figure 9 Another step in the ion exchange process (post-autoclaving) is shown to convert the dispersed polymer salt back into a protonated acid form. Detailed Implementation

[0033] As described in the summary section of the invention and Figure 1 As illustrated, this specification provides a method for recycling waste ionomer materials. The method includes: heating the waste ionomer material in a solvent to disperse it, forming a dispersion of the ionomer in the solvent, the dispersion further containing fluoride anions; contacting the dispersion with a precipitant or adsorbent to form a solid material containing the fluoride anions; and separating the ionomer dispersion from the solid material containing the fluoride anions. After separating the solid fluorinated material from the ionomer dispersion, any residual metals (from the precipitant or adsorbent) in the dispersion can be removed, for example, via ion exchange.

[0034] As also described in the Summary of the Invention, the precipitant can be a metal compound that reacts with the fluoride anion in solution to form a solid metal fluoride salt precipitated from the solution. For example, such a metal compound may be selected from one or more of the following: alkaline earth metal compounds; calcium compounds; magnesium compounds; strontium compounds; transition metal compounds; titanium compounds; post-transition metal compounds; aluminum compounds; and hydroxides. Examples include calcium hydroxide and magnesium hydroxide. The precipitated metal fluoride can then be separated from the dispersion by filtration or centrifugation.

[0035] As an alternative to precipitation, fluoride anions can be removed from the dispersion using adsorbents capable of adsorbing anions (e.g., via physisorption, ionic bonding, or covalent bonding of fluorides). Such adsorbents are known in water treatment applications, as described in "A comprehensive review of adsorbents for fluoride removal from water: performance, water quality assessment and mechanism", Environmental Science: Water Research & Technology (RSC Publishing) DOI:10.1039 / D1EW00232E. The adsorbent can be a solid, insoluble metal compound that adsorbs fluoride anions. This solid metal compound can be selected from one or more of the following: metal oxides; magnesium oxide; calcium oxide; aluminum oxide; titanium oxide; and mixed metal oxides. This adsorbent can be introduced into a reaction vessel, where the waste ionomer material is dispersed (e.g., in the form of solid particles, solid rods or bars, or in the form of adsorbent material bags), or alternatively, after the ionomer dispersion step, the ionomer dispersion containing fluoride anions can be passed through an adsorbent bed (e.g., an adsorbent bed in an HF-resistant container such as a PTFE-lined container).

[0036] The solvent used to disperse the ionomer can be selected from water, alkaline aqueous solutions, organic solvents, alcohols, or mixtures thereof, such as a mixture of alcohol and water. The solvent used to disperse the ionomer can be heated at the following temperatures: at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; not exceeding 400°C, 300°C, 275°C, or 250°C; or within any combination of the lower and upper limits described above. Furthermore, the waste ionomer material can be heated at least for 15 minutes, 30 minutes, 1 hour, 2 hours, or 3 hours; not exceeding 72 hours, 48 ​​hours, 24 hours, 10 hours, 6 hours, or 4 hours; or within any combination of the lower and upper limits described above. While these process conditions are suitable for dispersing waste ionomer materials, they also lead to the formation of certain fluorides, especially in the presence of platinum group metal catalysts during the process, thus requiring a treatment step to remove the fluorides after the ionomer dispersion.

[0037] Waste ionomer materials may also contain one or both of a carbon catalyst support material and a membrane reinforcement material. In this case, the carbon catalyst support material and / or membrane reinforcement material can be separated from the dispersion along with the precipitated or adsorbed fluoride.

[0038] In a preferred method, the waste ionomer material is converted to a salt form before or during heating to disperse the waste ionomer material. Preferably, the waste ionomer material is converted to a salt form without dispersing it. For example, the waste ionomer material can be converted to a salt form by treatment with an alkaline aqueous solution. Excess alkali can then be removed. Subsequently, the ionomer can be dispersed by heating in a solvent, and after dispersion, the ionomer dispersion can be treated to precipitate / adsorb and remove fluorides. The ionomer can then undergo an ion exchange process to reprotonate the ionomer in the dispersion. The ion exchange process used to reprotonate the ionomer can also be used to remove any residual metals in the dispersion, or a separate ion exchange process can be used to reprotonate the ionomer and remove any residual metals.

[0039] Regarding the above, it has been found that converting the ionomer to a salt form before dispersion is beneficial for achieving good dispersion of the ionomer material while reducing damage to the ionomer material. As previously mentioned, damage to the ionomer can be further reduced by removing PGM material, or at least most of it, before the ionomer dispersion process. Any extent to which ionomer degradation generates fluoride anions can be addressed by precipitating / adsorbing and removing fluorides from the ionomer dispersion as described herein.

[0040] Therefore, as Figure 2 One illustrated process flow is as follows: (i) treating waste ionomer material with alkali to form a solid ionomer salt material; (ii) heating the solid ionomer salt material in a solvent to form a dispersion of the ionomer salt material; (iii) contacting the dispersion with a precipitant or adsorbent to form a solid material containing the fluoride anion; (iv) separating the ionomer dispersion from the solid material containing the fluoride anion; (v) removing any residual metal ions from the dispersion (e.g., via ion exchange); and (vi) subjecting the ionomer dispersion to an ion exchange process to reprotonate the ionomer material (this step can be performed alone or in combination with step (v)).

[0041] This recycling method is particularly useful for waste ionomer materials containing at least one platinum group metal catalyst material, as it has been found that platinum group metal catalyst materials promote the degradation of ionomers and the generation of fluorides during the ionomer dispersion process. Such materials may include ionomer membranes (in which a recombinant catalyst may be disposed), catalyst-coated ionomer membranes (i.e., ionomer membranes coated with PGM catalyst material), and / or catalyst layer materials containing ionomers (which can be obtained, for example, by removing the catalyst layer material from the catalyst-coated ionomer membrane prior to further processing to recover the catalyst and ionomer materials). Furthermore, waste ionomer materials can be waste from fuel cell or electrolyzer applications (e.g., manufacturing waste) or used (e.g., end-of-life) ionomer materials.

[0042] Figure 3 A process flow is illustrated in which platinum group metals are removed from waste ionomer material prior to ionomer dispersion, followed by treatment of the ionomer dispersion to precipitate and separate fluoride material. In this case, removing the platinum group metal material prior to ionomer dispersion reduces the amount of fluoride generated during dispersion, and therefore only fluoride precipitation / adsorption is required to extract any trace amounts of fluoride that may be present in the waste ionomer stream. In the illustrated example, oxidative acid leaching is used to extract platinum (and / or palladium and / or ruthenium) from the waste ionomer material, and reducing acid leaching is used to extract iridium if it is present in the material.

[0043] In comparison, Figure 4 A process flow is shown in which platinum group metals (PGMs) are not removed from the waste ionomer material prior to ionomer dispersion. In this case, it has been found that significant amounts of fluorides are generated during dispersion facilitated by the PMMs. Therefore, using a precipitant / adsorbent to extract significant amounts of fluorides from the waste ionomer stream after employing this method may be crucial to avoiding downstream treatment problems. After separating the PMMs from the ionomer dispersion, the PMMs can be processed as follows... Figure 3 The leaching process discussed is for the extraction of platinum and iridium.

[0044] The acid used in one or both of the iridium leaching and platinum leaching is preferably hydrochloric acid and optionally does not contain nitric acid. Furthermore, one or both of the solutions used for platinum leaching and iridium leaching are preferably heated to the following temperatures: at least 50°C, 60°C, or 70°C; not exceeding 160°C, 120°C, 100°C, or 90°C; or within any combination of the lower and upper limits above, wherein if the solution is heated above 100°C, this is carried out in a pressurized vessel. Example temperatures are about 70°C for platinum leaching and about 105°C for iridium leaching. The solution is heated to increase the leaching rate of the PGM.

[0045] For oxidative acid leaching of platinum (and / or palladium and / or ruthenium), the oxidant may include, for example, chlorates such as sodium chlorate solution, hydrogen peroxide, or chlorine gas. According to a preferred option, the acid used in the leaching of platinum, palladium, and / or ruthenium is hydrochloric acid, and the oxidant is chlorine gas generated from the in-situ electrolysis of hydrochloric acid. The oxidant may be added to the hydrochloric acid solution or generated in situ after heating to a temperature up to the aforementioned levels. Alternatively, the oxidant may be added in multiple aliquots during heating. For example, the oxidant may be added in a series of aliquots during heating. The solution used for leaching platinum, palladium, and / or ruthenium may have the following oxidant concentrations: at least 0.001 mol / L, 0.005 mol / L, or 0.01 mol / L; not exceeding 1 mol / L, 0.5 mol / L, or 0.10 mol / L; or within any combination of the aforementioned lower and upper limits (e.g., a total oxidant concentration in the range of 0.01 mol / L to 0.10 mol / L). One or both of the solutions used for leaching platinum, palladium and / or ruthenium and the solutions used for leaching iridium have the following acid concentrations: not less than 4M, 5M, 5.5M or 6M; not more than 15M, 12M, 10M or 7M; or within the range defined by any combination of the lower and upper limits above.

[0046] Separation of the solution containing leached platinum, palladium, and / or ruthenium can be achieved by filtration or centrifugation. The separated solution can be concentrated to a suitable PGM concentration for further processing by boiling the solution. Alternatively, the leachate can be recycled to leach more platinum, palladium, and / or ruthenium from additional spent catalyst-coated membrane materials, and this recycling can be repeated as needed until a suitable or target concentration of platinum, palladium, and / or ruthenium is achieved. For example, after separating the solution containing leached platinum, palladium, and / or ruthenium from the remaining solids of the spent catalyst-coated membrane material, the solution can be concentrated to produce chloroplatinic acid containing at least 30% by weight Pt.

[0047] One advantage of the above process is its ability to achieve high recovery rates for platinum, palladium, and / or ruthenium. For example, at least 97% by weight of platinum can be recovered from membranes coated with spent catalysts.

[0048] Another advantage of the above process is that using these conditions, virtually no fluorine is leached from the fluoropolymer membrane into the leachate. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled individually. Second, fluorine leaching into the acidic leachate can lead to the formation of HF, which can result in serious environmental health and safety risks as well as damage to downstream processing equipment. Therefore, avoiding HF formation provides a safer and more environmentally friendly process.

[0049] Another advantage of the above process is that, for CCMs containing both platinum and iridium oxide catalysts—a useful combination of cathode and anode catalysts used respectively in hydrogen-producing water electrolyzers—the oxidative leaching conditions are selective for platinum and do not leach iridium to any significant extent. Therefore, this process represents an efficient way to separate platinum from other components of such waste CCMs while preserving the remaining CCM components intact for separate treatment.

[0050] Iridium (which can be in the form of iridium oxide, mixed iridium oxide, or supported iridium oxide) can be extracted separately using an acid leaching process. This differs from that used for platinum leaching. In particular, a reducing agent (e.g., hydrazine) is used instead of an oxidizing agent for iridium leaching. Optionally, the reducing agent is first added to the membrane material coated with the spent catalyst, and then the acid is added.

[0051] One advantage of the above process is its ability to achieve a high recovery rate for iridium. For example, at least 95% by weight of iridium can be recovered from membranes coated with spent catalysts.

[0052] Another advantage of the above process is that using these conditions, virtually no fluorine is leached from the fluoropolymer membrane into the leachate. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled individually. Second, fluorine leaching into the acidic leachate can lead to the formation of HF, which can result in serious environmental health and safety risks as well as damage to downstream processing equipment. Therefore, avoiding HF formation provides a safer and more environmentally friendly process.

[0053] The iridium leaching conditions do indeed leach significant amounts of platinum (e.g., 20%-40% Pt) if any remains in the membrane material coated with the spent catalyst. Therefore, according to the method of the invention, it is advantageous to first remove Pt (and / or palladium and / or ruthenium) by oxidative leaching before applying reducing leaching to recover iridium.

[0054] Example

[0055] PGM recycling

[0056] For the water electrolyzer material, Ir has been recovered via reductive leaching, but these processes have also shown varying levels of Pt recovery. To minimize this mixing of Pt and Ir chlorides, oxidative leaching of Pt was tested first, followed by reductive leaching of Ir. For reliability, the experiment was repeated twice.

[0057] Pt oxidative leaching

[0058] The CCM from five water electrolysis cells was chopped into pieces measuring 1cm x 2cm. The total mass of the CCM was 21.23g.

[0059] A flanged container equipped with a top-mounted stirrer, a condenser with cooling water, a temperature probe, and plugs in all empty ports was placed on a hot plate. CCM was loaded, and 395 mL of 12M HCl was added; the solution immediately turned yellow. It was then set to stir at 200 rpm and the heat was set to 70°C.

[0060] At this temperature, 1.25 mL of 30% peroxide was added to the container at 1 rpm over the first minute using a Watson Marlow peristaltic pump, followed by the remaining addition at 7 rpm. The reaction was then heated for another 50 minutes. Once complete, the heating was turned off and the reactants were allowed to cool. The mixture was then filtered under vacuum using nitrocellulose filter paper.

[0061] Ir reducing leaching

[0062] The leached CCM was suspended in 90 mL of softened water in a beaker, and 1.8 mL of 35% hydrazine was added dropwise while stirring. The area where the CCM came into direct contact with the hydrazine turned gray. The suspension was then sonicated in an ultrasonic bath at room temperature for 5 minutes.

[0063] The flange container was set up with Pt leaching as described previously. The CCM suspension was added to the flange container. 250 mL of 12M HCl was added slowly in increments while stirring at 200 rpm. The CCM flakes began to crack at this point. Samples were collected. The container was heated to 105°C. Once the temperature was reached, a timer was started, and samples were collected every 1.5 hours for a total of 4.5 hours. Afterward, the reaction vessel was cooled, and the suspension was filtered under vacuum. All samples were filtered under vacuum and then filtered using a syringe.

[0064] Pt oxidative leaching (repeated)

[0065] The experiment was repeated using the same method for oxidative leaching, but the sonication step used for reductive leaching was omitted. 21.27 g of CCM was used, heated to 75°C with 400 mL of 12M acid and 1.5 mL of hydrogen peroxide. Heating was carried out for 50 minutes as previously described.

[0066] Ir reducing leaching (repeated)

[0067] The flange container was set up as described previously. CCM was added to the container along with 90 mL of softened water. The container was set to stir at 130 rpm while 1.8 mL of hydrazine was added dropwise. The mixture was stirred for 5 minutes. 250 mL of 12 M HCl was slowly added while stirring at 300 rpm. The container was heated to 105 °C as described previously. Once the temperature was reached, a timer was started, and samples were collected every 1.5 hours for a total of 4.5 hours. Afterward, the reaction vessel was cooled, and the suspension was filtered through a vacuum filter. All samples were filtered under vacuum and then filtered using a syringe.

[0068] Results and Conclusions

[0069] When selective oxidative leaching of Pt was performed, CCM showed successful Pt recovery (approximately 100% within experimental error). Subsequently, reductive leaching showed good Ir recovery, with even stronger recovery (>95%) in repeated experiments. In summary, >97% of PGM was recovered from CCM material.

[0070] Ionomer recycling

[0071] 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 under reflux for 1 hour. Wash the resulting mixture with 4 × 100 mL of water. Decant the remaining water to leave a (wet) membrane. Weigh 250 g of water, add it to the (wet) membrane, and heat under reflux for 1 hour. Then decant the water and dry the solid product under vacuum.

[0072] Figure 5 FTIR data illustrating salt formation are shown. FTIR data were collected for untreated fluorinated polymer membrane material 301, fluorinated polymer salt material 303 formed after treatment in LiOH aqueous solution, and fluorinated polymer salt material 304 formed after treatment in LiOH aqueous solution followed by water washing.

[0073] Figure 6 An example of the process step (pre-autoclaving) is shown. As indicated in the figure, the membrane is brown. After reflux in a lithium hydroxide solution, the membrane becomes colorless and transforms into a salt form, as confirmed by spectroscopic analysis. The transformation is achieved without dispersing the membrane, which remains in a solid, undispersed form. Figure 6 In the final step of the pre-autoclaving process shown, the solid polymer salt film material is washed in water to remove any residual LiOH solution.

[0074] Figure 7These are photographs of the membrane before (left-hand side) and after (right-hand side) the process steps of reflux in alkaline LiOH solution and washing with water, indicating that the membrane's color changed from brown to colorless and that the membrane remained in a solid, undispersed form. Spectroscopic analysis confirmed that the colorless membrane was in salt form.

[0075] Figure 8 It shows that in such Figure 6 The process shown is followed by another step of autoclaving the membrane to disperse it in water. The colorless, solid, undispersed polymer salt membrane was autoclaved in water under nitrogen at 250°C and 40 bar (4000 kPa). This produced a (non-alkaline) aqueous dispersion of the polymer salt.

[0076] The aqueous dispersion of the polymer (ionomer) salt is then treated with a precipitant or adsorbent (e.g., a precipitant such as calcium hydroxide) to precipitate / adsorb any fluoride (e.g., calcium fluoride) from the dispersion, which is then removed, for example, by filtration.

[0077] In one example, calcium hydroxide (75 mg, 1.0 mmol) was added to an ionomer dispersion (6 mL) recycled via high-temperature water treatment as described above. The fluoride content of the dispersion was reduced from approximately 190 µg / mL to approximately 40 µg / mL. Using more calcium hydroxide further reduced the fluoride content. The solid calcium product was then removed by solid-liquid separation, such as filtration. Any unwanted calcium in the dispersion was removed by ion exchange.

[0078] The aqueous dispersion of the polymer (ionomer) salt can then be filtered to separate the ionomer dispersion from the solid carbon catalyst support and the solid polytetrafluoroethylene membrane reinforcement material. These materials can be separated in the same step used to remove the precipitated calcium fluoride, or they can be separated before precipitation and removal of fluoride from the ionomer dispersion.

[0079] Figure 9 Further subsequent steps for ion exchange to convert the dispersed polymer salt back to its protonated acid form are shown. Containing Amberlyst... ™ 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 manufacture new membranes or dried and stored for future use. Ion exchange can also be used to remove any residual calcium from the ionomer dispersion.

[0080] Summarize

[0081] This specification provides a method for recycling waste ionomer materials. This method can separate and recover platinum group metals and ionomer components in purified forms with high yields, while also ensuring that other component materials within the waste ionomer material, such as carbon catalyst support materials and membrane reinforcement materials, are separated and recovered during processing. This specification specifically addresses the problems caused by fluoride generation during recycling, ensuring a safer process, protected equipment, and that the resulting ionomer product material is not contaminated with fluorides, thus making it more suitable for reuse.

[0082] While the invention has been specifically shown and described with reference to certain examples, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for recycling waste ionomer materials, the method comprising: The waste ionomer material is heated in a solvent to disperse it, forming a dispersion of the ionomer in the solvent, the dispersion also containing fluoride anions in the solution; The dispersion is contacted with a precipitant or adsorbent to form a solid material containing the fluoride anion; and The ionomer dispersion is separated from the solid material containing the fluoride anion.

2. The method according to claim 1, The precipitant is a metal compound that reacts with the fluoride anion in the solution to form a solid metal fluoride salt that precipitates from the solution.

3. The method according to claim 2, The metal compound is selected from one or more of the following: alkaline earth metal compounds; calcium compounds; magnesium compounds; strontium compounds; transition metal compounds; titanium compounds; post-transition metal compounds; aluminum compounds; and hydroxides.

4. The method according to claim 2 or 3, The precipitated metal fluorides are separated from the dispersion by filtration or centrifugation.

5. The method according to claim 1, The adsorbent is a solid, insoluble metal compound that adsorbs fluoride anions.

6. The method according to claim 5, The solid metal compound is selected from one or more of the following: metal oxides; magnesium oxide; calcium oxide; aluminum oxide; titanium oxide; and mixed metal oxides.

7. The method according to claim 5 or 6, The adsorbent is introduced into a reaction vessel, and the waste ionomer material is dispersed in the reaction vessel or the ionomer dispersion containing fluoride anions is passed through an adsorbent bed.

8. The method according to any of the preceding claims, During the heating of the waste ionomer material, the waste ionomer material includes at least one platinum group metal catalyst material.

9. The method according to any of the preceding claims, The waste ionomer material mentioned above is an ionomer membrane, a catalyst-coated ionomer membrane, or a catalyst layer material containing ionomers.

10. The method according to any of the preceding claims, The waste ionomer material mentioned above is waste or used ionomer material from fuel cell or electrolyzer applications.

11. The method according to any of the preceding claims, The solvent is water, an alkaline aqueous solution, an organic solvent, an alcohol, or a mixture thereof.

12. The method according to any of the preceding claims, After the solid material containing the fluoride anion is separated from the dispersion, any residual metallic substances from the precipitant or the adsorbent in the dispersion are optionally removed by ion exchange.

13. The method according to any of the preceding claims, The waste ionomer material is heated to the following temperatures: at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; not exceeding 400°C, 300°C, 275°C, or 250°C; or within any combination of the lower and upper limits described above.

14. The method according to any of the preceding claims, The waste ionomer material is heated for at least 15 minutes, 30 minutes, 1 hour, 2 hours or 3 hours; not exceeding 72 hours, 48 ​​hours, 24 hours, 10 hours, 6 hours or 4 hours; or within any combination of the lower and upper limits described above.

15. The method according to any of the preceding claims, The waste ionomer material is converted into a salt form before or during heating to disperse the waste ionomer material.

16. The method according to claim 15, The waste ionomer material is converted into a salt form by treatment with an alkaline aqueous solution.

17. The method according to claim 15 or 16, After dispersing the waste ionomer material, the salt form of the ionomer is converted back to the protonated acid form through ion exchange.

18. The method according to any of the preceding claims, The waste ionomer material comprises one or both of a carbon catalyst support material and a membrane reinforcement material, and the carbon catalyst support material and / or the membrane reinforcement material are separated from the dispersion having the precipitated or adsorbed fluoride.

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