Methods for recycling waste ionomer films

Abstract

A method for recycling a waste ionomer film, wherein the waste ionomer film comprises platinum, palladium, and / or ruthenium disposed within an internal region of the waste ionomer film, the method comprising: (a) treating the waste ionomer film with a solution comprising an acid and an oxidizing agent, wherein the platinum, palladium, and / or ruthenium are leached from the internal region of the waste ionomer film into the solution; and (b) separating the solution containing the leached platinum, palladium, and / or ruthenium from the waste ionomer film, which remains in a solid form during the leaching process.

Description

Technical Field

[0001] This specification relates to a method for recycling waste ionomer membranes such as those used in fuel cells and hydrogen-producing water electrolyzers.

Background Art

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

[0003] The materials and configurations of CCM components vary according to the functional performance requirements in the end use, but they generally contain several useful components including one or more platinum group metal (PGM) catalysts and one or more proton-conductive polymers.

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

[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 of the CCM. The CCM may also contain a recombination catalyst placed inside the ionomer membrane, which is provided to catalyze the recombination of hydrogen and oxygen to form water, reducing the amount of hydrogen passing through the membrane and mixing with oxygen to form a potentially explosive mixture. The CCM may also contain a metal oxide (e.g., CeO2) as a peroxide scavenger inside 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 may be provided in elemental (metallic) form, compound form (e.g., oxides such as iridium oxide catalysts), or PGM-based metal alloys (e.g., PtCo or PtNi). Furthermore, the PGM catalyst material may be supported on a substrate material (e.g., platinum-supported carbon catalysts containing carbon particles on which platinum is arranged, or carbon such as PtCo-supported carbon or PtNi-supported carbon).

[0007] A catalyst coating (CCM) can also be provided in combination with additional functional layers to form a multi-layer membrane electrode assembly (MEA). Such an MEA may have, for example, 3, 5, or 7 layers.

[0008] With the increase in CCM production for fuel cells and electrolytic cells, there is also a corresponding increase in CCM waste materials, including large amounts of scrap material generated during CCM production (e.g., due to quality control failures), and an increase in end-of-life (EoL) CCM. Since CCM contains several rare and / or valuable components, including platinum group metals (particularly Pt, Pd, Ir, and Ru) and ionomers (in both membrane and catalyst layers), there is a growing demand for methods to recycle such components from waste CCM materials.

[0009] One current method for recovering PGMs from production scrap and end-of-life CCM materials involves incineration. The incineration process produces PGM-rich (typically Pt and Ir) ash that is processed through conventional PGM refining routes. However, the incineration process releases harmful and toxic gases such as CO2 and HF from the polymers that are part of the membrane. Both of these gases have adverse effects as they pollute the atmosphere, increase the greenhouse effect, and / or have harmful effects on human health. Therefore, cleaner processes that reduce or eliminate the release of these gases are needed.

[0010] In addition to the above, incineration methods destroy ionomer components, which are of equally important value. Therefore, it is desirable to provide a process that can recover both PGMs and ionomer components, as well as a process that is cleaner, safer, and more environmentally friendly. Processes for recovering perfluorosulfonic acid ionomers are known; see, for example, International Publication No. 2016 / 156815 and U.S. Patent No. 7255798. Furthermore, processes for recovering individual PGM catalyst components are known; see, for example, U.S. Patent No. 7709135. However, in order to enable fuel cells and electrolytic cells to become more sustainable technologies, there is a need for commercially viable and environmentally friendly routes for recovering, separating, and recycling both PGMs and ionomer components from waste CCM materials, including production scrap and end-of-life materials.

[0011] The purpose of this specification is to address this problem. [Overview of the Initiative]

[0012] This specification relates, in particular, to the recovery of metals located within the internal region of an ionomer film, rather than in the catalyst coating on the external surface of the ionomer film. As described in the background art section, an ionomer film may comprise a recombination catalyst located inside the ionomer film, which is provided to catalyze the recombination of hydrogen and oxygen to form water, reducing the amount of hydrogen passing through the film and mixing with oxygen to form a potentially explosive mixture. Furthermore, an ionomer film may comprise base metal-containing components inside the ionomer film, for example, a peroxide scavenger (e.g., a metal oxide such as CeO2). Moreover, it has been found that metal components from the catalyst coating on the ionomer film can migrate into the interior of the ionomer film during use. Therefore, even after the catalyst coating has been removed from the ionomer film for recycling, a portion of the valuable metal components from the catalyst coating can remain inside the ionomer film.

[0013] For at least two reasons, it is desirable to recover such metallic components from within waste ionomer films. Firstly, metallic components are valuable and scarce, and therefore there is an economic and environmental incentive to recover and reuse these materials. Secondly, by recovering these metals from within waste ionomer films, the ionomers can be recovered and reused without being contaminated with these metals.

[0014] Accordingly, this specification provides a method for recycling a waste ionomer film, wherein the waste ionomer film comprises platinum, palladium, and / or ruthenium disposed within an internal region of the waste ionomer film, and the method comprises (a) treating the waste ionomer film with a solution comprising an acid and an oxidizing agent, wherein the platinum, palladium, and / or ruthenium are leached from the internal region of the waste ionomer film into the solution, and (b) separating the solution containing the leached platinum, palladium, and / or ruthenium from the waste ionomer film that remains in a solid form during the leaching process.

[0015] Such leaching processes using acids and oxidizing agents have been found to successfully remove metallic components from within waste ionomer films, enabling the recycling of these metallic materials, while also allowing the internal metallic components of waste ionomer films to be cleaned so that the ionomer material can then be dispersed and recovered for reuse without significant metallic contamination.

[0016] Further details of this method are provided in the detailed description below. [Brief explanation of the drawing]

[0017] For a better understanding of the present invention and to illustrate how it can be implemented, certain embodiments of the present invention are described hereby by reference only to the accompanying drawings.

[0018] [Figure 1] This specification illustrates a waste ionomer film recycling process. [Modes for carrying out the invention]

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

[0020] The waste ionomer film may contain one or more base metals within its internal regions, in addition to platinum, palladium, and / or ruthenium. The one or more base metals are leached into the solution along with the platinum, palladium, and / or ruthenium, and after separation from the waste ionomer film, 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, optionally cerium in the form of CeO2, nickel, and cobalt. As previously mentioned, CeO2 is useful in the ionomer film as a peroxide scavenger to extend the film's lifespan, while nickel and / or cobalt may migrate from the catalyst coating on the film to the ionomer film during use. At least a portion of the platinum, palladium, ruthenium, and / or base metals located within the internal regions of the waste ionomer film may also migrate from the catalyst coating to the internal regions of the waste ionomer film during use. For example, a catalyst coating may contain a platinum-nickel catalyst, and at least a portion of one or both of the platinum and nickel may migrate to the interior region of the waste ionomer film during use.

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

[0022] The waste ionomer film may not have a catalyst coating on either or both of its main surfaces. This may be because the waste ionomer film is production scrap that was not coated with a catalyst, or because the catalyst coating was removed before the waste ionomer film leached out in order to remove platinum, palladium, and / or ruthenium from its internal regions.

[0023] The acid used for the leaching of platinum, palladium, and / or ruthenium is preferably hydrochloric acid. The solution used for the leaching of platinum, palladium, and / or ruthenium may optionally be heated to a temperature within a range defined by at least 50 °C, 60 °C, or 70 °C; 160 °C, 100 °C, or 90 °C or less; or any combination of the aforementioned lower and upper limits. When the solution is heated above 100 °C, this is carried out in a pressure vessel. The oxidizing agent in the leaching solution may include hydrogen peroxide, chlorate, or chlorine gas. In certain examples, the acid used for the leaching of platinum, palladium, and / or ruthenium is hydrochloric acid, and the oxidizing agent is chlorine gas generated electrochemically in situ from hydrochloric acid. The oxidizing agent may be added to the acid solution or generated in situ so as to have a total concentration of the oxidizing agent within a range defined by at least 0.001, 0.005, or 0.01 mol / L; 1, 0.5, or 0.10 mol / L or less; or any combination of the aforementioned lower and upper limits (for example, within the range of 0.01 - 0.10 mol / L). The solution for the leaching of platinum, palladium, and / or ruthenium may have an acid concentration within a range defined by 4 M or more, 5 M or more, or 5.5 M or more; 12 M or less, 10 M or less, 7 M or less, 6.5 M or less, or 6 M or less; or any combination of the aforementioned lower and upper limits.

[0024] After separating the solution containing the leached platinum, palladium, and / or ruthenium from the remaining solid components of the waste catalyst coating material, the solution can be concentrated by boiling. Alternatively or additionally, after separating the solution containing the leached platinum, palladium, and / or ruthenium from the remaining solid waste ionomer membrane, the solution can be reused to leach platinum, palladium, and / or ruthenium from further waste ionomer membranes. The solution can then be further processed to separate and purify the individual metal components using known PGM and base metal purification techniques.

[0025] The waste ionomer membrane is subjected to one or more of the leaching steps to remove platinum, palladium, and / or ruthenium, and then the waste ionomer membrane can be heated in a solvent to disperse and recycle the ionomer.

Example

[0026] The most important objective is to recover valuable components of fuel cells and water electrolyzers, particularly to recover PGM. One aspect of this process involves an understanding of how the PGM and other metals inside the ionomer membrane can be accessed and recovered. These include metals that leach into the ionomer membrane of the CCM during operation, as well as metals intentionally placed inside the ionomer membrane of the CCM such as recombination catalysts and / or peroxide scavengers. In certain processes, it is desirable to extract the metal components before the dispersion and treatment of the ionomer membrane components. The objective of these experiments is to determine whether oxidative leaching of the ionomer membrane can remove the metals present inside the membrane so that the ionomer membrane can be subsequently processed to recover the ionomer material.

[0027] Ionomer membrane leached using HCl and peroxide as the oxidizing agent In this example, an excess of peroxide was used as the oxidizing agent and HCl was used as the acid dissolution and chloride source. Two different types of ionomer membranes containing metal components were treated. That is, (i) an ionomer membrane containing platinum black (PtB) recombination catalyst, and (ii) an ionomer membrane from a catalyst-coated membrane containing a platinum-nickel (PtNi) catalyst coating in which nickel had leached into the ionomer membrane.

[0028] Leaching of Pt-black-containing membrane The membrane was cut into 1×1 cm 2 pieces. A 500 mL flanged container was placed on a hot plate together with an overhead PTFE stirrer and stirrer guide. A temperature probe connected to the hot plate and a condenser with cooling water inlet were also attached.

[0029] 400 mL of 12 M HCl was added to the container along with 0.5 mL of H2O2. Then, 10-15 g of Pt Black recombination catalyst-containing film was added to the container, and the reaction mixture was stirred at 250 rpm. The system was heated to 70°C and then maintained at this temperature for 50 minutes.

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

[0031] The residual film fragments were air-dried overnight on a watch glass before being sent for analysis.

[0032] Membrane leaching from PtNi CCM A 500 mL round-bottom flask was fitted with stirrer beads, a temperature probe connected to a hot plate, a stopper, and a condenser containing cooling water.

[0033] 200 mL of 12 M HCl was added to a container along with 0.5 mL of H2O2 and stirred at 1000 rpm. (0.5 × 0.5 cm) 2 One piece of PtNi CCM, cut into pieces, was added to the container, and the CCM was washed into the container using a minimal amount of distilled water. The system was heated to a temperature of 70°C, and then heated for a further 50 minutes.

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

[0035] The residual CCM samples were air-dried overnight on a watch glass before being sent for analysis.

[0036] result Analysis showed that HCl leaching using peroxide as an oxidizing agent could recover all Pt, Ni, and Ce from ionomer film samples. An example of XRF data is shown in the table below, which shows the recovery of all Pt and Ce from the ionomer film. ICP analysis also showed 100% recovery of Ni in the film from PtNi CCM, where nickel migrates into the interior of the ionomer film.

[0037] [Table 1]

[0038] These results are important because metals migrate to the ionomer membrane during the operation of fuel cells / water electrolyzers. Furthermore, metal-containing components are designed into ionomer membranes to improve the functionality and lifespan of the membrane. This study shows that the inventors can access these metals via an oxidative acid leaching process and that it is possible to extract the metals trapped in the ionomer membrane first, before dispersing and recovering the ionomer.

[0039] Ionomer film leached using HCl and NaCIO3 as an oxidizing agent In this example, NaCIO3 was used in excess as the oxidizing agent, and HCl was used as the acid dissolution and chloride source. Two different types of ionomer films containing metal components were treated: (i) an ionomer film containing a platinum black (PtB) recombination catalyst, and (ii) an ionomer film from a catalyst-coated film containing a platinum-nickel (PtNi) catalyst coating in which nickel leaches into the ionomer film.

[0040] Leaching of Pt-black containing film The membrane is 1 x 1 cm 2 It was cut into pieces. A 500 mL flanged container was placed on a hot plate along with an overhead PTFE stirrer and stirrer guide. A temperature probe connected to the hot plate and a condenser containing cooling water were also attached.

[0041] 400 mL of 6 M HCl was added to a container along with 0.5 mL of NaCIO at a concentration of 450 g / L. Then, 10-15 g of Pt Black recombination catalyst-containing film was added to the container, and the reaction mixture was stirred at 250 rpm. The system was then heated to a temperature of 70°C, and the temperature of the system was maintained therefor for a further 50 minutes.

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

[0043] The residual film fragments were air-dried overnight on a watch glass before being sent for analysis.

[0044] Membrane leaching from PtNi CCM A 500 mL round-bottom flask was fitted with stirrer beads, a temperature probe connected to a hot plate, a stopper, and a condenser containing cooling water.

[0045] 200 mL of 6 M HCl was added to a container along with 0.5 mL of 450 g / L concentration NaCIO3, and the mixture was stirred at 1000 rpm. (0.5 × 0.5 cm) 2 One piece of PtNi CCM, cut into pieces, was added to the container, and the CCM piece was washed inside the container using a minimal amount of distilled water. The system was heated to 70°C, and after the system reached this temperature, it was heated for a further 50 minutes.

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

[0047] The remaining CCM fragments were washed with distilled water and air-dried overnight on a watch glass.

[0048] result Analysis showed that HCl leaching using NaCIO3 as the oxidizing agent could recover virtually all Pt, Ni, and Ce from within ionomer film samples. An example of XRF data is shown in the table below, which demonstrates the recovery of virtually all Pt and Ce within the ionomer film. ICP analysis also showed the recovery of most of the Ni in the film from PtNi CCM, where nickel migrates into the interior of the ionomer film.

[0049] [Table 2]

[0050] Furthermore, the metal recovery rate was slightly higher when H2O2 was used as the oxidizing agent compared to NaCIO3. However, the recovery rates observed here are still very good.

[0051] summary This specification provides a leaching process for recovering PGMs from within the membrane layer of CCM products used in fuel cell and hydrogen production electrolytic cell applications. Previous experiments focused on recovering metals from the coating of catalyst coating films. This specification focuses on recovering Pt and other metals from within the membrane as well as from the outer coating. This was attempted with films containing Pt Black recombination catalyst and PtNi CCM, which were found to exhibit metal migration into the membrane layer. Nearly 100% metal recovery rates were achieved. This method can be applied to ionomer membrane materials containing recombination catalysts, and to ionomer membrane materials at the end of their lifespan that undergo metal migration into the membrane layer during use.

[0052] The examples described herein used oxidative leaching in HCl with either sodium chlorate or hydrogen peroxide as the oxidizing agent, and both were successful. However, when scaled up, chlorine can be used instead as the oxidizing agent. As a result of the leaching process, PGM, base metals, and ceria are all recovered, and these can then be separated and purified using known PGM and base metal purification processes.

[0053] Although the present invention has been specifically illustrated and described with reference to certain examples, it will be understood by those skilled in the art that various modifications of form and detail can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for recycling a waste ionomer film, wherein the waste ionomer film contains platinum, palladium, and / or ruthenium disposed within the internal region of the waste ionomer film, and the method is (a) A step of treating the waste ionomer film with a solution containing an acid and an oxidizing agent, wherein platinum, palladium, and / or ruthenium are leached into the solution from the internal region of the waste ionomer film, (b) A method comprising the step of separating a solution containing leached platinum, palladium, and / or ruthenium from a waste ionomer film that remains in a solid form during the leaching process.

2. The waste ionomer film contains, in addition to platinum, palladium, and / or ruthenium, one or more base metals within the internal region of the waste ionomer film. The one or more base metals are leached into the solution together with the platinum, palladium, and / or ruthenium. The method according to claim 1, wherein, after separation from the waste ionomer film, the solution is subsequently treated to separate the one or more base metals from the platinum, palladium, and / or ruthenium.

3. The one or more base metals mentioned above are cerium, optionally CeO ２ The method according to claim 2, comprising one or more of cerium, nickel, and cobalt in the form of...

4. The method according to any one of claims 1 to 3, wherein at least a portion of the platinum, palladium, and / or ruthenium is in the form of a recombination catalyst disposed within the internal region of the waste ionomer film.

5. The method according to claim 4, wherein the recombination catalyst is in the form of a layer disposed within the internal region of the waste ionomer film, or is dispersed over the thickness of the internal region of the waste ionomer film.

6. The method according to claim 4 or 5, wherein the recombination catalyst is a platinum-black recombination catalyst.

7. The method according to any one of claims 1 to 6, wherein at least a portion of the platinum, palladium, ruthenium, and / or base metal disposed within the internal region of the waste ionomer film moves from the catalyst coating to the internal region of the waste ionomer film during use.

8. The method according to claim 7, wherein the catalyst coating comprises a platinum-nickel catalyst, and at least a portion of one or both of the platinum and nickel migrates to the internal region of the waste ionomer film during use.

9. The method according to any one of claims 1 to 8, wherein the waste ionomer film subjected to the leaching process is production scrap in which the waste ionomer film was not coated with a catalyst coating, or the catalyst coating has been removed before leaching of the waste ionomer film in order to remove platinum, palladium, and / or ruthenium from its internal regions, and therefore the surface of the waste ionomer film is free from a catalyst coating.

10. The method according to any one of claims 1 to 9, wherein the acid used for the leaching of platinum, palladium, and / or ruthenium is hydrochloric acid.

11. The method according to any one of claims 1 to 10, wherein the solution used for the leaching of platinum, palladium, and / or ruthenium is heated.

12. The method according to claim 11, wherein the solution used for the leaching of platinum, palladium, and / or ruthenium is heated to a temperature within the range defined by at least 50°C, 60°C, or 70°C; 160°C, 100°C, or 90°C or less; or any combination of the aforementioned lower and upper limits, and if the solution is heated above 100°C, this is done in a pressurized vessel.

13. The method according to any one of claims 1 to 12, wherein the oxidizing agent comprises hydrogen peroxide, a chlorate, or chlorine gas.

14. The method according to any one of claims 1 to 13, wherein the acid used for the leaching of platinum, palladium, and / or ruthenium is hydrochloric acid, and the oxidizing agent is chlorine gas electrolytically generated in situ from the hydrochloric acid.

15. The method according to any one of claims 1 to 14, wherein the oxidizing agent is added to or generated in the acid solution such that the total concentration of the oxidizing agent is within the range defined by at least 0.001, 0.005, or 0.01 mol / L; 1, 0.5, or 0.10 mol / L or less; or any combination of the aforementioned lower and upper limits.

16. The method according to any one of claims 1 to 15, wherein the solution for leaching platinum, palladium, and / or ruthenium has an acid concentration within the range defined by 4 M or more, 5 M or more, or 5.5 M or more; 12 M or less, 10 M or less, 7 M or less, 6.5 M or less, or 6 M or less; or any combination of the aforementioned lower and upper limits.

17. The method according to any one of claims 1 to 16, wherein the solution containing the leached platinum, palladium, and / or ruthenium is separated from the remaining solid components of the waste catalyst coating material, and the solution is concentrated by boiling.

18. The method according to any one of claims 1 to 17, wherein the solution containing the leached platinum, palladium, and / or ruthenium is separated from the remaining solid waste ionomer film, and the solution is reused to leach platinum, palladium, and / or ruthenium from further waste ionomer film.

19. The method according to any one of claims 1 to 18, wherein the waste ionomer film is subjected to one or more of the leaching steps to remove the platinum, palladium, and / or ruthenium, and then the waste ionomer film is heated in a solvent to disperse and recycle the ionomer.

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