Recycling of catalyst coated membrane components

Abstract

A method of recycling waste ionomer material comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising: (a) mixing the waste ionomer material to homogenize the waste ionomer material; (b) taking a sample of homogenized waste ionomer material; (c) determining a sample of homogenized waste ionomer material to characterize an ionomer content and a platinum group metal content of the waste ionomer material; and (d) recycling the spent ionomer material based on the ionomer content and the platinum group metal content determined by the determination to separate and recover both the ionomer and the platinum group metal material.

Description

Technical Field

[0001] This specification relates to methods for recycling components of membranes used for catalyst coating (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 microparticles 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] As described in the background section, existing methods involve incinerating membrane materials coated with spent catalysts to produce PGM-rich ash, which is then fed to a PGM refining mill for PGM recovery. The PGM-rich ash produced through the incineration process has the beneficial effect of homogenizing with the PGM concentrated in the ash sample residue. Prior to processing the material through the PGM refining process, the material can be easily sampled and measured using the PGM refining mill to determine the representative PGM content.

[0013] The applicant has developed a recycling method for membrane materials coated with spent catalysts that separates and recovers both PGM materials and ionomer materials, and is capable of separating and recovering additional components such as base metals, carbon, and polymer reinforcement materials. From an economic perspective, this is more beneficial than the aforementioned incineration process because additional valuable components are recovered. Furthermore, it is also beneficial from an environmental perspective, as incineration generates significant amounts of CO2 and HF and incurs substantial energy losses. Another problem with the incineration route is that if the spent catalyst-coated membrane materials are incinerated by a third-party company, the PGM refiner may be unable to account for any potential metal losses incurred between the initial receipt of materials for refining and the return of ash from the third-party company. This could represent a significant metal accounting risk and metal loss pathway for the PGM refiner.

[0014] While a PGM recycling process capable of recovering ionomers has been provided to address the aforementioned problems with incineration, the inventors have identified issues with the practical implementation of such a process. Since the PGM-containing input material used in the PGM refining process is PGM-containing waste ionomer material, the PGM content is not homogenized and concentrated as it would be in PGM-rich ash. Therefore, to avoid significant metal accounting risks, the waste ionomer material should be treated to homogenize it before sampling and determining the PGM content. Furthermore, the inventors have recognized that ionomer materials exist in various types and forms, and their molecular weights, equivalent weights, and / or sulfonated side chains can all differ. Moreover, the waste ionomer material may comprise two or more different ionomers, and these different ionomers may be unevenly distributed throughout the waste ionomer material. Therefore, in order to avoid significant ionomer accounting risks, in addition to PGM content, the ionomer content of waste ionomer materials should also be appropriately determined, but only after appropriate treatment to homogenize the waste ionomer materials so that representative samples of both PGM content and ionomer content can be collected.

[0015] In view of the above, according to one aspect of this specification, a method for recycling waste ionomer materials comprising at least one ionomer and at least one platinum group metal catalyst is provided, the method comprising:

[0016] (a) Mixing waste ionomer materials to homogenize the waste ionomer materials, optionally including reducing the particle size of the waste ionomer materials;

[0017] (b) Take a sample (or more than one sample) of homogenized waste ionomer material, optionally including processing the sample to further reduce the particle size;

[0018] (c) To determine the ionomer content and platinum group metal content of homogenized waste ionomer materials; and

[0019] (d) Based on the determined ionomer content and platinum group metal content, the waste ionomer material is recycled to separate and recover both the ionomer and the platinum group metal material.

[0020] For example, the waste ionomer material can be in the form of a membrane material, which is pulverized and mixed in step (a) to reduce particle size and homogenize. Furthermore, after sampling, the size of the material sample can be further reduced by grinding techniques before determining the PGM and ionomer content of the material sample. This process aims to ensure that the measured results represent both the PGM and ionomer content of the bulk waste ionomer material.

[0021] The determination in step (c) may also include characterizing one or more other materials in the sample, wherein, in addition to the ionomer content and platinum group metal content, the one or more other materials include one or more of the base metal content, carbon content, and polymer reinforcement content.

[0022] When implementing a recycling process to recover both PGM and ionomer material (and optionally other material components) from waste ionomer material, it is advantageous to homogenize, sample, and determine the PGM and ionomer content (and optionally other material components) in this manner for several reasons.

[0023] This avoids the risks associated with metal accounting and ionomer accounting. The process allows for the negotiation of a suitable price for recycling waste ionomer materials, based at least on the ionomer content and the platinum group metal content determined by measurement, as well as the optional content of other materials.

[0024] Alternatively, the process enables the determination of appropriate amounts of ionomer and platinum group metal materials to be produced by the recycling process based on the determined ionomer and platinum group metal content, and optionally, the determination of the amount of other materials to be produced based on the determination results of said other materials.

[0025] This method of material accounting also ensures that individual batches of waste ionomer material do not need to be processed separately. Once the content of each batch has been properly assessed and agreed upon, the waste ionomer material can be mixed with one or more other waste ionomer materials from other sources before recycling. This allows for the flexible simultaneous recycling of a range of waste ionomer materials from different sources, thereby improving process efficiency.

[0026] In addition to the above, the results can be used to tailor recycling processes to produce ionomer products that meet target specifications and functional end-use requirements. In this regard, it has been noted that different types of ionomers are currently used to manufacture membranes for fuel cells and electrolyzers. For example, ionomer membranes can differ in their molecular weight, ionomer equivalent weight, and / or contain ionomers with different sulfonated side chains. Blending different types of ionomers has also been proposed to produce membranes with tunable properties. One problem with recycling waste ionomer materials (such as manufacturing waste and used ionomer materials) is that these materials may not have the composition or properties desired for reuse in new applications (such as new fuel cells and electrolyzers). Another problem is that manufacturing waste and used ionomer materials can have a variety of different types and compositions, which need to be recycled into new materials that meet target specifications for reuse in new applications. Yet another issue is ensuring that any recycling process for waste ionomer materials is flexible, energy-efficient, and cost-effective. The inventors have recognized that the aforementioned problems can be solved by integrating the ionomer blending process into the recycling process of waste ionomer materials, so as to adjust the composition and properties of the waste ionomer materials during recycling to meet target specifications for reuse in new applications. Therefore, the determination results of the ionomers can be compared with the target composition of the recycled ionomer products, and during recycling, additional ionomer materials can be blended with the waste ionomer materials, the type and amount of which being selected to achieve the target composition of the ionomer products. It has been found that the process for dispersing and recycling waste ionomer materials is suitable for ensuring proper blending and co-entanglement of different ionomers at the molecular level, and this enables the manufacture of materials with predictable functional performance properties. However, this can only be accurately achieved through appropriate analysis of the starting waste ionomer materials.

[0027] Therefore, the above method is advantageous for several reasons:

[0028] This method enables ionomer membrane materials to be recycled into new membrane components with modified and / or optimized compositions and properties through predictive blending;

[0029] This method offers greater flexibility, enabling the recycling of different types and compositions of ionomer membrane materials to produce new membrane compositions that meet target specifications;

[0030] This method provides the flexibility to blend ionomers from different membrane materials during recycling and / or to blend ionomers from waste or used membrane materials with virgin / fresh ionomer materials;

[0031] This method ensures that different ionomers are properly blended at the molecular level as part of the recycling process; and

[0032] By integrating the ionomer blending step into the membrane material dispersion step as part of the membrane recycling process, this method enables ionomer blending in an energy-efficient manner, thereby reducing costs, minimizing additional equipment requirements, and improving environmental impact. Attached Figure Description

[0033] 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:

[0034] Figure 1 The waste CCM recycling process according to this specification is shown;

[0035] Figure 2 It shows Figure 1 Further details of step (d) in the example illustrate the waste CCM recycling process, which includes platinum leaching, followed by iridium leaching, and then ionomer dispersion.

[0036] Figure 3 It shows Figure 1 Another more detailed example of step (d) illustrates a waste CCM recycling process comprising the following steps performed in the order described: (i) oxidizing acid leaching to recover platinum; (ii) reducing acid leaching to recover iridium; (iii) treating the remaining solid ionomer material with an alkali to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; (v) separating the ionomer dispersion from other components such as carbon and / or membrane reinforcement materials; and (vi) subjecting the ionomer dispersion to an ion exchange process to reprotonate the ionomer material.

[0037] Figure 4 FTIR 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.

[0038] Figure 5 An example of a process step (pre-isopolymer dispersion) 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;

[0039] Figure 6 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;

[0040] Figure 7 It shows that in such Figure 5 The illustrated process is followed by another step of dispersing the ionomer in a solvent at an elevated temperature (e.g., by autoclaving the membrane); and

[0041] Figure 8 Another step in ion exchange (post-dispersion) is shown to convert the dispersed polymer salt back into a protonated acid form. Detailed Implementation

[0042] As described in the summary section of the invention and Figure 1 As shown, this specification provides a method for recycling waste ionomer materials comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising:

[0043] (a) Mixing waste ionomer materials to homogenize the waste ionomer materials, optionally including reducing the particle size of the waste ionomer materials;

[0044] (b) Take a sample (or more than one sample) of homogenized waste ionomer material, optionally including processing the sample to further reduce the particle size;

[0045] (c) To determine the ionomer content and platinum group metal content of homogenized waste ionomer materials; and

[0046] (d) Based on the determined ionomer content and platinum group metal content, the waste ionomer material is recycled to separate and recover both the ionomer and the platinum group metal material.

[0047] For example, the waste ionomer material can be in the form of a membrane material, which is pulverized and mixed in step (a) to reduce particle size and homogenize. Furthermore, after sampling, the size of the material sample can be further reduced by grinding techniques before determining the PGM and ionomer content of the material sample. This process aims to ensure that the measured results represent both the PGM and ionomer content of the bulk waste ionomer material.

[0048] Waste ionomer material can be received as a 7-layer, 5-layer, or 3-layer MEA (catalyst-coated membrane, CCM), partial CCM, catalyst layer, or as an ionomer membrane (which may or may not contain PGM). Initial disassembly prior to obtaining a 7-layer MEA involves mechanically disassembling the fuel cell / water electrolyzer module into a stack by removing peripheral components (e.g., pumps, compressors, etc.). Removal of end plates and insulation allows the stack to be separated into individual cells, which can then be further disassembled into a 7-layer MEA by removing bipolar plates. The PEMWE (proton exchange membrane electrolyzer) may contain a Pt-coated porous transport layer (PTL), which can be further refined to recover the Pt coating.

[0049] A 7-layer MEA can be decomposed into a 5-layer MEA by removing the gas diffusion layer (GDL) manually or through other mechanical or chemical delamination processes. For example, treatment with water and / or another solvent can cause the membrane to swell, thereby causing GDL delamination. The 5-layer MEA can then be further decomposed into a 3-layer MEA / catalyst-coated membrane (CCM) component by removing the associated edge seal / gasket material. This can be achieved through manual or mechanical cutting processes such as scissors, guillotine, punching / pressing, or possible chemical dissolution. Any residues or waste generated by this process can be further recycled to recover trace amounts of PGM.

[0050] When receiving the material as a CCM, partial CCM, catalyst layer (CL), or PGM-containing membrane (MEM), the material in any backing or support material can be removed before size reduction, homogenization, sampling, and measurement.

[0051] Then, the homogenization, sampling, and measurement processes can begin using membrane materials containing CCM / partial-CCM / CL or PGM. These can be reduced in size through a coarse grinding process using a rotary cutter mill, but alternative grinding techniques (e.g., rotary drums, guillotines, etc.) can also be used. Particle size can be reduced to, for example, about 2 square millimeters. During coarse grinding, the material can be wetted or treated in an oxygen-limited (e.g., under N2) and / or humidity-controlled atmosphere.

[0052] Then, a certain proportion of the pulverized material can be sampled. This can be achieved by using a splitter at the pulverizer outlet, by manual sampling (e.g., a spear sampler), or other recognized sampling techniques. The particle size of the sample can then be further reduced to <1 mm using a fine-cutting grinder, rotary grinder, cryogenic grinder, etc., and further segmented using, for example, a rotary crusher, to obtain a sample representative of the bulk relative to the PGM content and ionomer content.

[0053] The determination in step (c) characterizes both the ionomer content and the PGM content. This determination may also include characterizing one or more other materials in the sample, wherein, in addition to the ionomer content and platinum group metal content, the one or more other materials include one or more of the following: base metal content, carbon content, and polymer reinforcement content. For example, the determination in step (c) may follow a characterization workflow to determine one, more, or all of the following:

[0054] The type and amount of platinum group metals, optionally followed by ICP spectroscopy (e.g., ICP optical emission spectroscopy and / or ICP mass spectrometry) and / or XRF (e.g., for granulated solid samples that may be located in a supporting matrix such as wax) after the metal digestion or bulk incineration process.

[0055] The equivalent weight of the ionomer is optionally determined using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and / or titration and / or other spectroscopic techniques, such as XRF and / or EDX;

[0056] The type of ionomer may be determined by NMR, FT-IR, ion chromatography, gel permeation chromatography (GPC) and / or elemental analysis of carbon, fluorine, sulfur and oxygen content and / or IC combustion technology, dynamic scanning calorimetry, XRF, EDX, fire assay, laser ICP, mass spectrometry, UV-Vis and / or AAS.

[0057] The molecular weight of the ionomer can be determined by GPC, mass spectrometry, and / or melt flow index.

[0058] The type and amount of base metals may be determined by ICP spectroscopy and / or XRF, optionally following the metal digestion or bulk incineration process.

[0059] Carbon content, optionally determined by thermogravimetric analysis and / or by thermal conductivity testing, elemental analysis and / or IC combustion technology after combustion;

[0060] The type and amount of polymer reinforcement material, for example, through elemental analysis and / or thermogravimetric analysis (e.g., DSC) techniques.

[0061] As previously described in the Summary of the Invention, when implementing a recycling process to recover both PGM and ionomer material (and optionally other material components) from waste ionomer material, it is advantageous to homogenize, sample, and determine both PGM content and ionomer content (and optionally other material components) in this manner for several reasons, including:

[0062] • This process avoids the risks associated with metal and ionomer accounting and allows for the negotiation of a suitable price for recycling waste ionomer materials, based at least on the ionomer content and the content of platinum group metals determined by measurement, as well as the content of other materials optionally.

[0063] • This process enables the determination of appropriate amounts of ionomer and platinum group metal materials to be produced by the recycling process based on the determined ionomer and platinum group metal content, and optionally, the determination of the amount of other materials to be produced based on the determination results of said other materials.

[0064] • Better material accounting ensures that individual batches of waste ionomer material do not need to be processed separately, allowing the waste ionomer material to be mixed with one or more other waste ionomer materials from other sources before recycling, once the content of each batch has been properly assessed and agreed upon.

[0065] • The measurement results can be used to customize the recycling process to produce ionomer products that meet the functional end-use requirements of the target specifications, including, for example, comparing the measurement results of the ionomer with the target composition of the ionomer and blending additional ionomer with waste ionomer material during recycling, the type and amount of which are selected to achieve the target composition of the ionomer.

[0066] To check if the characterization is correct, the recycled ionomer can be used to manufacture a membrane and tested to confirm that it meets the target specifications.

[0067] Figure 1 The recycling in step (d) may include: treating the waste ionomer material with one or more acid leaching solutions to extract platinum group metals; and an ionomer dispersion step to extract the ionomer material. The leaching and dispersion steps may be performed in any order. However, Figure 2 A preferred method is illustrated, illustrating a waste CCM recycling process comprising platinum leaching, followed by iridium leaching, and then ionomer dispersion. In this example, a method is provided for coating a recycled waste catalyst with a membrane material comprising an ionomer membrane, at least one catalyst comprising platinum (e.g., a carbon-supported platinum catalyst), palladium and / or ruthenium, and at least one catalyst comprising iridium (e.g., an iridium oxide catalyst). The method includes:

[0068] (a) Treating a spent catalyst-coated membrane material with a heated solution containing an acid and an oxidant, wherein platinum, palladium and / or ruthenium are leached from the spent catalyst-coated membrane material into the solution, which is separated from the remaining solid components of the spent catalyst-coated membrane material;

[0069] (b) Following step (a), iridium is leached from the membrane material coated with the spent catalyst using a heated solution containing an acid and a reducing agent, and the solution containing the leached iridium is separated from the remaining solid components of the membrane material coated with the spent catalyst; and

[0070] (c) After steps (a) and (b), the spent catalyst-coated membrane material is treated with a heated solvent to disperse the ionomer membrane and recover the ionomer dispersion.

[0071] It has been found that performing the above steps in the stated order allows for the recovery of platinum, palladium and / or ruthenium, iridium and ionomer materials, respectively, without significant degradation of the ionomers, and ensures that substantially all (e.g., at least 97%) of the PGM is recovered, wherein platinum and iridium are pre-separated in the process.

[0072] 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.

[0073] Oxidizing agents 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 oxidizing agent is chlorine gas generated from the in-situ electrolysis of hydrochloric acid. The oxidizing agent may be added to the hydrochloric acid solution or generated in situ after heating to a temperature up to the aforementioned levels. Alternatively, the oxidizing agent may be added in multiple equal portions during heating. For example, the oxidizing agent may be added in a series of equal portions during heating. The solution used for leaching platinum may have the following oxidizing agent 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 the range defined by any combination of the lower and upper limits above (e.g., a total oxidizing agent concentration in the range of 0.01 mol / L to 0.10 mol / L). One or both of the solutions used for leaching platinum and 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 any combination of the lower and upper limits described above.

[0074] Separation of the solution containing leached platinum can be achieved by filtration or centrifugation. The separated solution can be concentrated to a suitable platinum concentration for further processing by boiling the solution. Alternatively, the leachate can be recycled to leach platinum from other spent catalyst-coated membrane materials, and this recycling can be repeated as needed until a suitable or target concentration of platinum is achieved. For example, after separating the solution containing leached platinum from the residual solids of the spent catalyst-coated membrane material, the solution can be concentrated to produce chloroplatinic acid containing at least 30% by weight Pt.

[0075] 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.

[0076] 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.

[0077] 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 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] As previously indicated, 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, Pt (and / or palladium and / or ruthenium) is first removed by oxidative leaching before applying reducing leaching to recover iridium.

[0082] After recovering platinum and iridium from the membrane coated with spent catalyst, it can be treated with a heated solvent to disperse the ionomer membrane and recover the dispersion of the ionomer. The solvent used to disperse the ionomer can be selected from water, alkaline aqueous solutions, organic solvents, alcohols, or mixtures of alcohols 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.

[0083] In a preferred method, the ionomer is treated with an alkali to convert it into a salt form before dispersing it in a solvent. Subsequently, after dispersion, the ionomer dispersion can be subjected to an ion exchange process to reprotonate the ionomers in the dispersion. It has been found that this method is advantageous for achieving good dispersion of the ionomer material without damaging the ionomer material, provided that the PGM material is removed before the ionomer dispersion process. Therefore, as... Figure 3 The exemplified preferred process flow is as follows: (i) oxidative acid leaching to recover platinum (and / or palladium and / or ruthenium); (ii) reducing acid leaching to recover iridium; (iii) treating the remaining solid ionomer material with alkali to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; (v) separating the ionomer dispersion from other components such as carbon and / or membrane reinforcement materials (e.g., by filtration); and (vi) subjecting the ionomer dispersion to an ion exchange process to reprotonate the ionomer material.

[0084] PGM recycling

[0085] 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.

[0086] Pt oxidative leaching

[0087] The CCM from five water electrolysis cells was chopped into pieces measuring 1cm x 2cm. The total mass of the CCM was 21.23g.

[0088] 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.

[0089] 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.

[0090] Ir reducing leaching

[0091] 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.

[0092] 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.

[0093] Pt oxidative leaching (repeated)

[0094] 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.

[0095] Ir reducing leaching (repeated)

[0096] 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.

[0097] Results and Conclusions

[0098] 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.

[0099] Ionomer recycling

[0100] Anhydrous LiOH (6.0 g) was added to water (250 g) to dissolve the LiOH. The membrane was immersed in the LiOH solution and heated to reflux (1 hour). The resulting mixture was washed with water (4 × 100 mL). The remaining water was decanted to leave a (wet) membrane. Water (250 g) was added to the (wet) membrane and heated to reflux (1 hour). The water was then decanted, and the solid product was dried under vacuum.

[0101] Figure 4 FTIR data indicating 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.

[0102] Figure 5 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 4 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.

[0103] Figure 6 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, 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.

[0104] Figure 7 It shows in Figure 5 The process shown is followed by another step: 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 an autogenous pressure of 40 bar (4000 kPa). This produced a (non-alkaline) aqueous dispersion of the polymer salt.

[0105] Figure 8This illustrates another step in the ion exchange process (post-autoclaving) to convert the dispersed polymer salt back into its protonated acid form. 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.

[0106] Summarize

[0107] This specification provides a method for recycling ionomer waste to recover PGM and ionomer materials, while providing better material accounting and enabling the recycling process to produce ionomer products of target specifications that meet functional end-use requirements.

[0108] 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 comprising at least one ionomer and at least one platinum group metal catalyst, the method comprising: (a) Mixing the waste ionomer material to homogenize the waste ionomer material; (b) Take a sample of the homogenized waste ionomer material; (c) Determining the sample of the homogenized waste ionomer material to characterize the ionomer content and platinum group metal content of the waste ionomer material; and (d) Based on the ionomer content and platinum group metal content determined by the determination, the waste ionomer material is recycled to separate and recover both the ionomer and the platinum group metal material.

2. The method according to claim 1, in, Step (a) includes reducing the particle size of the waste ionomer material.

3. The method according to claim 2, in, The waste ionomer material is in the form of a membrane material, and the waste ionomer material is crushed and mixed in step (a) to reduce particle size and homogenize.

4. The method according to any of the preceding claims, in, Step (b) includes processing the sample to further reduce the particle size.

5. The method according to any of the preceding claims, in, In step (b), one or more samples of the homogenized waste ionomer material are taken for subsequent determination in step (c).

6. The method according to any of the preceding claims, in, The determination in step (c) includes characterizing one or more other materials in the sample, wherein, in addition to the ionomer content and the platinum group metal content, the one or more other materials also include one or more of base metal content, carbon content, and polymer reinforcement content.

7. The method according to any of the preceding claims, in, The determination in step (c) follows a characterization workflow to determine one, more, or all of the following: Types and quantities of platinum group metals; The amount of ionomer; Equivalent weight of the polymer; Types of ionomers; The molecular weight of the ionomer; The types and quantities of base metals; Carbon content; The type and amount of polymer-reinforced materials.

8. The method according to any of the preceding claims, in, After step (c), a price for recycling the waste ionomer material is agreed upon, based at least on the ionomer content and the platinum group metal content determined by the determination, as well as the content of other materials optionally specified in claim 6.

9. The method according to any of the preceding claims, in, Following step (c), based on the ionomer content and the platinum group metal content determined by the determination, the amounts of the ionomer and the platinum group metal materials to be generated by the recycling in step (d) are agreed upon, and optionally based on the determination results of the other materials, the amounts of the other materials specified in claim 6 to be generated by the recycling in step (d) are also agreed upon.

10. The method according to any of the preceding claims, in, After step (c), the determination results of the ionomer are compared with the target composition of the ionomer after recycling in step (d), and in step (d), during recycling, additional ionomer material is blended with the waste ionomer material, the type and amount of which achieve the target composition of the ionomer.

11. The method according to any of the preceding claims, in, After step (c), the waste ionomer material is mixed with one or more other waste ionomer materials, and then the recycling in step (d) is performed.

12. The method according to any of the preceding claims, in, The recycling in step (d) includes: treating the waste ionomer material with one or more acid leaching solutions to extract the platinum group metal material; and an ionomer dispersion step to extract the ionomer material, wherein the leaching and dispersion steps are performed in any order.

13. The method according to claim 12, in, Step (d) includes treating the waste ionomer material with a heated solution containing an acid and an oxidant, wherein platinum, palladium and / or ruthenium are leached from the membrane material coated with the waste catalyst into the solution, and the solution is separated from the remaining solid components of the waste ionomer material.

14. The method according to claim 12 or 13, in, Step (d) includes leaching iridium from the waste ionomer material using a heated solution containing an acid and a reducing agent, and separating the solution containing the leached iridium from the remaining solid components of the waste ionomer material.

15. The method according to any one of claims 12 to 14, in, Step (d) includes treating the waste ionomer material with a heated solvent to disperse the ionomer and recover the dispersion of the ionomer.

16. The method according to claims 13 to 15, in, The oxidative acid leaching of claim 13 is performed prior to the reducing acid leaching of claim 14, and the reducing acid leaching is performed prior to the ionomer dispersion of claim 15.

17. The method according to claim 15 or 16, Before dispersing the ionomer in the solvent, the ionomer is treated with an alkali to convert it into a salt form.

18. The method according to any one of claims 15 to 17, in, The ionomer dispersion is filtered to remove carbon and / or polymer reinforcement.

19. The method according to claim 18, in, The filtered carbon and reinforcing materials are dispersed in a solvent to form a slurry and then separated according to particle size.

20. The method according to any one of claims 15 to 19, in, The ionomer dispersion is subjected to an ion exchange process to reprotonate the ionomers in the dispersion.

21. The method according to any of the preceding claims, in, The recycled ionomers are used to manufacture membranes, and the membranes are tested to confirm that they meet the target specifications.

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