Method for recovering waste ionomer membranes

Abstract

A method of recycling a spent ionomer membrane comprising platinum, palladium and / or ruthenium disposed within an interior region of the spent ionomer membrane, the method comprising: (a) treating the spent ionomer membrane with a solution comprising an acid and an oxidizing agent, where platinum, palladium and / or ruthenium are leached from the interior region of the spent ionomer membrane into the solution; and (b) separating the solution comprising the leached platinum, palladium and / or ruthenium from the waste ionomer membrane that remains in solid form during the leaching.

Description

Technical Field

[0001] This specification relates to recycling methods for waste ionomer membranes, 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 ionomer membrane (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 disposed within the ionomer membrane, 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 within the ionomer membrane.

[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, compound form (e.g., oxides, such as iridium oxide catalysts), or as PGM-based metal alloys (e.g., PtCo or PtNi). 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 or carbon-supported PtNi).

[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. Incineration processes produce ash rich in PGM (typically Pt and Ir), which is then processed via conventional PGM refining routes. However, incineration releases harmful and toxic gases, such as CO2 and HF, from the polymer, which is part of the membrane. Both gases have negative impacts because they pollute the atmosphere, contribute to 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 the ionomer component 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 specifically relates to the recovery of metals from a catalyst coating disposed within the internal region of an ionomer membrane, rather than on its outer surface. As described in the Background section, the ionomer membrane may contain a recombination catalyst disposed within the membrane, 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 with oxygen to form a potentially explosive mixture. Furthermore, the ionomer membrane may contain a base metal-containing component within its interior, including, for example, peroxide scavengers (e.g., metal oxides such as CeO2). Additionally, it has been found that metal components from the catalyst coating on the ionomer membrane can migrate into the interior of the ionomer membrane during use. Therefore, even after the catalyst coating on the ionomer membrane is removed for recycling, a portion of the valuable metal components from the catalyst coating may remain within the interior of the ionomer membrane.

[0013] There are at least two reasons for the desire to recover such metal components from the interior of spent ionomer membranes. First, the metal components are valuable and scarce, thus providing economic and environmental drivers for recycling and reusing these materials. Second, by recovering these metals from the interior of spent ionomer membranes, the ionomers can be subsequently recycled and reused without becoming contaminated with these metals.

[0014] Therefore, this specification provides a method for recycling a waste ionomer membrane containing platinum, palladium, and / or ruthenium disposed in an internal region of the waste ionomer membrane, the method comprising: (a) treating the waste ionomer membrane with a solution containing an acid and an oxidant, wherein platinum, palladium, and / or ruthenium are leached from the internal region of the waste ionomer membrane into the solution; and (b) separating the solution containing the leached platinum, palladium, and / or ruthenium from the waste ionomer membrane, which remains in solid form during the leaching process.

[0015] It has been found that such leaching processes using acids and oxidants can successfully remove the metal components inside waste ionomer membranes, thereby enabling the recovery of these metal materials. At the same time, the internal metal components of the waste ionomer membranes are cleaned, so that the ionomer materials can then be dispersed and recovered for reuse without significant metal contamination.

[0016] Further details of this methodology are provided in the following detailed description. Attached Figure Description

[0017] To better understand the invention and demonstrate 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:

[0018] Figure 1 The waste ionomer membrane recycling process according to this specification is shown. Detailed Implementation

[0019] As described in the summary section of the invention and Figure 1 As shown, according to one aspect of this specification, a method for recycling a waste ionomer membrane is provided, the waste ionomer membrane comprising platinum, palladium and / or ruthenium (and optionally one or more non-PGM metals) disposed in an internal region of the waste ionomer membrane, the method comprising: (a) treating the waste ionomer membrane with a solution comprising an acid and an oxidant, wherein platinum, palladium and / or ruthenium (and optionally one or more non-PGM metals) are leached from the internal region of the waste ionomer membrane into the solution; and (b) separating the solution comprising the leached platinum, palladium and / or ruthenium from the waste ionomer membrane, which remains in solid form during the leaching process.

[0020] The waste ionomer membrane may also contain one or more base metals, other than platinum, palladium, and / or ruthenium, in the internal region of the waste ionomer membrane. One or more base metals are also leached into a solution along with platinum, palladium, and / or ruthenium, and after separation from the waste ionomer membrane, the solution is subsequently treated to separate the one or more base metals from the platinum, palladium, and / or ruthenium. The one or more base metals may include one or more of cerium, nickel, and cobalt, with the cerium optionally in the form of CeO2. As previously discussed, CeO2 can be used as a peroxide scavenger in the ionomer membrane to increase membrane lifetime, while nickel and / or cobalt may migrate from the catalyst coating on the membrane into the ionomer membrane during use. At least a portion of the platinum, palladium, ruthenium, and / or base metals disposed in the internal region of the waste ionomer membrane may also migrate from the catalyst coating into the internal region of the waste ionomer membrane during use. For example, the catalyst coating may comprise a platinum-nickel catalyst, and at least a portion of one or both of platinum and nickel may migrate into the internal region of the waste ionomer membrane during use.

[0021] At least a portion of the platinum, palladium, and / or ruthenium may be in the form of a recombinant catalyst disposed within the internal region of the waste ionomer membrane. The recombinant catalyst may be in the form of a layer disposed within the internal region of the waste ionomer membrane or dispersed across the thickness of the internal region of the waste ionomer membrane. The recombinant catalyst may be a platinum black recombinant catalyst.

[0022] Waste ionomer membranes can be membranes without a catalyst coating on any one or two of their main surfaces. This could be because the waste ionomer membrane is production waste that has never been coated with a catalyst coating, or because the catalyst coating has been removed to remove platinum, palladium, and / or ruthenium from its internal regions before the waste ionomer membrane is leached.

[0023] Hydrochloric acid is advantageously used as the acid in the leaching of platinum, palladium, and / or ruthenium. The solution used for leaching platinum, palladium, and / or ruthenium can be heated, optionally to the following temperatures: at least 50°C, 60°C, or 70°C; not exceeding 160°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. The oxidant in the leaching solution may comprise hydrogen peroxide, chlorate, or chlorine. In a particular example, the acid used in the leaching of platinum, palladium, and / or ruthenium is hydrochloric acid, and the oxidant is chlorine generated from the in-situ electrolysis of hydrochloric acid. The oxidant may be added to the acid solution or generated in situ such that the total concentration of the oxidant is: 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 lower and upper limits above (e.g., in the range of 0.01 mol / L to 0.10 mol / L). Solutions used for leaching platinum, palladium, and / or ruthenium may have the following acid concentrations: not less than 4 M, 5 M, or 5.5 M; not exceeding 12 M, 10 M, 7 M, 6.5 M, or 6 M; or within any combination of the lower and upper limits above.

[0024] After separating the solution containing leached platinum, palladium, and / or ruthenium from the residual solids of the spent catalyst-coated membrane material, the solution can be concentrated by boiling. Alternatively or otherwise, after separating the solution containing leached platinum, palladium, and / or ruthenium from the residual solids of the spent ionomer membrane, the solution is reused to leach platinum, palladium, and / or ruthenium from other spent ionomer membranes. The solution can then be further processed using known PGM and base metal refining techniques to separate and purify the various metal components.

[0025] After subjecting the waste ionomer membrane to one or more leaching steps in the leaching process to remove platinum, palladium and / or ruthenium, the waste ionomer membrane may be heated in a solvent to disperse and recycle the ionomer. Example

[0026] The overall goal is to recover valuable components from fuel cells and water electrolyzers, particularly PGM (Produced Metal Molecules). One aspect of this process is understanding how to obtain and recover PGM and other metals within the ionomer membrane. These include metals leached into the ionomer membrane during operation and metals intentionally placed within the ionomer membrane in the CCM, such as reforming catalysts and / or peroxide scavengers. In some processes, it is desirable to extract metal components before dispersing and processing the ionomer membrane components. The aim of these experiments is to determine whether oxidative leaching of the ionomer membrane can remove metals present within the membrane's interior, allowing subsequent processing of the ionomer membrane to recover the ionomer material. Ionomer membranes leached using HCl and peroxide as oxidants

[0027] In this example, an excess of peroxide is used as the oxidant, and HCl is used as the acid dissolution and chloride ion source. Two different types of ionomer membranes containing metal components are treated: (i) an ionomer membrane containing a platinum black (PtB) recombinant catalyst; and (ii) an ionomer membrane from a catalyst-coated membrane containing a platinum-nickel (PtNi) catalyst coating, wherein nickel has been leached into the ionomer membrane. Leaching membranes containing Pt black

[0028] Cut the membrane into 1×1cm pieces. 2 Small pieces. A 500ml flanged container with a top-mounted PTFE stirrer and stirrer guide is installed on top of the hot plate. A temperature probe connected to the hot plate and a condenser with cooling water are also installed.

[0029] Add 400 mL of 12 M HCl along with 0.5 mL of H₂O₂ to the container. Then add 10 g to 15 g of the membrane containing the Pt black reformed catalyst to the container, and stir the reaction mixture at 250 rpm. Heat the system to 70 °C and maintain that temperature for 50 minutes.

[0030] The solution was cooled to room temperature and filtered using a Buchner funnel and 0.45 μm nitrocellulose filter paper. The remaining leached membrane was washed with water, and the liquid and washings were collected separately.

[0031] Before sending it for analysis, the remaining membrane was air-dried overnight on a petri dish. PtNi CCM leaching membrane

[0032] Install a 500mL round-bottom flask with a stirrer bead rim, a temperature probe connected to a hot plate, a stopper, and a condenser with cooling water.

[0033] Add 200 mL of 12M HCl along with 0.5 mL of H₂O₂ to the container and stir at 1000 rpm. The mixture will be cut into 0.5 × 0.5 cm pieces. 2 A small piece of PtNi CCM is added to the container, and the CCM is washed into the container using a minimal volume of distilled water. The system is heated, and once it reaches a temperature of 70°C, it is reheated for 50 minutes.

[0034] The solution was cooled to room temperature and filtered using a Buchner funnel and 0.45 μm nitrocellulose filter paper. The remaining leached CCM was washed with water. The liquid and washings were collected separately.

[0035] Before sending it for analysis, the remaining CCM sheet was air-dried overnight on a petri dish. result

[0036] Analysis showed that HCl leaching with peroxide as an oxidant recovered all Pt, Ni, and Ce within the ionomer membrane sample. The table below shows examples of XRF data representing the recovery of all Pt and Ce within the ionomer membrane. ICP analysis also showed 100% Ni recovery from the PtNi CCM membrane, where nickel had migrated into the interior of the ionomer membrane.

[0037]

[0038] These results are significant because metals migrate into the ionomer membrane during operation of the fuel cell / water electrolyzer. Furthermore, the metal-containing components are engineered into ionomer membranes to improve membrane functionality and lifespan. This work demonstrates that these metals can be obtained through an oxidative acid leaching process, and that the metals remaining in the ionomer membrane can be extracted before dispersing and recycling the ionomer. Ionomer membranes leached using HCl and NaClO3 as oxidants

[0039] In this example, excess NaClO3 was used as the oxidant, with HCl serving as the acid dissolution and chloride ion source. Two different types of ionomer membranes containing metal components were treated: (i) an ionomer membrane containing a platinum black (PtB) recombinant catalyst; and (ii) an ionomer membrane derived from a catalyst-coated membrane containing a platinum-nickel (PtNi) catalyst coating, wherein nickel had been leached into the ionomer membrane. Leaching membranes containing Pt black

[0040] Cut the membrane into 1×1cm pieces. 2 Small pieces. A 500ml flanged container with a top-mounted PTFE stirrer and stirrer guide is installed on top of the hot plate. A temperature probe connected to the hot plate and a condenser with cooling water are also installed.

[0041] Add 400 mL of 6M HCl along with 0.5 mL of 450 g / L NaClO3 to the container. Then add 10 g to 15 g of the membrane containing the Pt black reformed catalyst to the container, and stir the reaction mixture at 250 rpm. The system is then heated to 70 °C, and once this temperature is reached, it is maintained for another 50 minutes.

[0042] The solution was cooled to room temperature and filtered using a Buchner funnel and 0.45 μm nitrocellulose filter paper. The remaining leached membrane was washed with water. The liquid and washings were collected separately.

[0043] Before sending it for analysis, the remaining membrane was air-dried overnight on a petri dish. PtNi CCM leaching membrane

[0044] Install a 500mL round-bottom flask with a stirrer bead rim, a temperature probe connected to a hot plate, a stopper, and a condenser with cooling water.

[0045] Add 200 mL of 6M HCl along with 0.5 mL of 450 g / L NaClO3 to the container and stir at 1000 rpm. The mixture will be cut into 0.5 × 0.5 cm pieces. 2 A small piece of PtNi CCM is added to the container, and the CCM is washed into the container using a minimal volume of distilled water. The system is heated to 70°C, and once the system reaches this temperature, it is allowed to reheat for 50 minutes.

[0046] The solution was cooled to room temperature and filtered using a Buchner funnel and 0.45 μm nitrocellulose filter paper. The remaining leached CCM was washed with water. The liquid and washings were collected separately.

[0047] Wash the remaining CCM tablets with distilled water and place them on a petri dish to air dry overnight. result

[0048] Analysis showed that HCl leaching with NaCIO3 as an oxidant recovered virtually all Pt, Ni, and Ce within the ionomer membrane sample. The table below shows examples of XRF data representing the recovery of virtually all Pt and Ce within the ionomer membrane. ICP analysis also indicated that most of the Ni was recovered from the PtNi CCM membrane, where nickel had migrated into the interior of the ionomer membrane.

[0049]

[0050] It should be noted that when using H₂O₂ as the oxidant, the metal recovery rate is slightly higher compared to NaCIO₃. However, the recovery rate observed here is still very good. Overview

[0051] This specification provides a leaching process for recovering PGM from within the membrane layer of CCM products used in fuel cells and hydrogen electrolyzer applications. Previous experiments focused on recovering metals from the coating of catalyst-coated membranes. This specification focuses on recovering Pt and other metals from within the membrane, not just from the outer coating. This has been tested on membranes containing Pt black reformed catalysts and PtNi CCMs, where metal migration into the membrane layer has been observed. Nearly 100% metal recovery rates have been achieved. This methodology can be applied to ionomer membrane materials containing reformed catalysts, as well as to end-of-life ionomer membrane materials that experience metal migration into the membrane layer during use.

[0052] The example described herein employs oxidative leaching in HCl, where the oxidant is either sodium chlorate or hydrogen peroxide, both of which achieve the desired effect. However, at scale-up, chlorine can be optionally used as the oxidant. As a result of the leaching process, PGM, base metals, and cerium dioxide are recovered, and they can then be separated and purified using known PGM and base metal refining processes.

[0053] 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 membranes, the waste ionomer membranes comprising platinum, palladium, and / or ruthenium disposed within an internal region of the waste ionomer membranes, the method comprising: (a) Treating the waste ionomer membrane with a solution containing an acid and an oxidizing agent, wherein platinum, palladium, and / or ruthenium are leached from the internal regions of the waste ionomer membrane into the solution; and (b) Separating the solution containing leached platinum, palladium and / or ruthenium from the waste ionomer membrane that remained in solid form during the leaching process.

2. The method according to claim 1, in, The waste ionomer membrane contains one or more base metals, other than platinum, palladium, and / or ruthenium, in the internal region of the waste ionomer membrane. The one or more base metals are leached into the solution containing the platinum, palladium, and / or ruthenium, and After separation from the waste ionomer membrane, the solution is subsequently processed to separate the one or more base metals from the platinum, palladium, and / or ruthenium.

3. The method according to claim 2, in, The one or more base metals include one or more of cerium, nickel, and cobalt, wherein the cerium is optionally in the form of CeO2.

4. The method according to any of the preceding claims, in, At least a portion of the platinum, palladium, and / or ruthenium is in the form of a recombinant catalyst disposed within the internal region of the waste ionomer membrane.

5. The method according to claim 4, in, The recombining catalyst is in the form of a layer disposed within the internal region of the waste ionomer membrane or dispersed across the thickness of the internal region of the waste ionomer membrane.

6. The method according to any one of claims 4 or 5, in, The recombined catalyst is a platinum black recombined catalyst.

7. The method according to any of the preceding claims, in, At least a portion of the platinum, palladium, ruthenium, and / or base metals disposed in the inner region of the waste ionomer membrane have migrated from the catalyst coating into the inner region of the waste ionomer membrane during use.

8. The method according to claim 7, in, The catalyst coating comprises a platinum-nickel catalyst, and at least a portion of one or both of the platinum and nickel has migrated into the interior region of the waste ionomer membrane during use.

9. The method according to any of the preceding claims, in, The waste ionomer membrane undergoing the leaching process does not contain a catalyst coating on the surface of the waste ionomer membrane because the waste ionomer membrane is production waste that has never been coated with a catalyst coating, or because the catalyst coating has been removed to remove platinum, palladium and / or ruthenium from its internal regions before the waste ionomer membrane is leached.

10. The method according to any of the preceding claims, in, The acid used in the leaching of platinum, palladium and / or ruthenium is hydrochloric acid.

11. The method according to any of the preceding claims, in, The solution used for the leaching of platinum, palladium, and / or ruthenium is heated.

12. The method according to claim 11, in, The solution used for the leaching of platinum, palladium, and / or ruthenium is heated to a temperature of at least 50°C, 60°C, or 70°C; not exceeding 160°C, 100°C, or 90°C; or within any combination of the lower and upper limits described above, wherein if the solution is heated to above 100°C, this is done in a pressurized vessel.

13. The method according to any of the preceding claims, in, The oxidant includes hydrogen peroxide, chlorate, or chlorine.

14. The method according to any of the preceding claims, 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 the hydrochloric acid.

15. The method according to any of the preceding claims, in, The oxidant is added to the acid solution or generated such that the total concentration of the oxidant is: 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 lower and upper limits described above.

16. The method according to any of the preceding claims, The solution used for leaching platinum, palladium, and / or ruthenium has the following acid concentrations: not less than 4M, 5M, or 5.5M; not more than 12M, 10M, 7M, 6.5M, or 6M; or within any combination of the lower and upper limits described above.

17. The method according to any of the preceding claims, The solution is concentrated by boiling after separating the solution containing the leached platinum, palladium and / or ruthenium from the remaining solid components of the membrane material coated with the spent catalyst.

18. The method according to any of the preceding claims, in, After separating the solution containing the leached platinum, palladium, and / or ruthenium from the remaining solid waste ionomer membrane, the solution is reused to leach platinum, palladium, and / or ruthenium from other waste ionomer membranes.

19. The method according to any of the preceding claims, in, After subjecting the waste ionomer membrane to one or more leaching steps in the leaching process to remove the platinum, palladium, and / or ruthenium, the waste ionomer membrane is heated in a solvent to disperse and recycle the ionomer.

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