Method for pulverizing used catalyst-coated polymer electrolyte membranes

Abstract

A method for pulverizing spent catalyst coated PEM membranes from PEM fuel cells and / or PEM electrolysis cells in a cutting mill.

Description

[Technical field]

[0001] The present invention relates to a method for pulverizing spent catalyst coated polymer electrolyte membranes (hereinafter abbreviated as "PEM membranes" or simply "PEM") from PEM fuel cells and / or PEM electrolysis cells in a cutting mill. Summary of the Invention [Problem to be solved by the invention]

[0002] In PEM fuel cells and PEM electrolysis cells, the half-cells are separated from each other by a PEM membrane, in particular a PEM membrane with an elastic seal. In particular so-called ionomers, such as copolymers of tetrafluoroethylene and sulfonic acid group-containing (per)fluorovinyl ether, e.g. Nafion® from Chemours, are common as practical PEM materials. The PEM membrane serves as a proton transport medium and electrically separates the electrodes of the PEM fuel cell or PEM electrolysis cell from each other. The front and rear sides of the PEM membrane typically contain a precious metal-containing catalyst layer. The PEM membrane may further comprise an electrically conductive porous gas diffusion layer (e.g. in the form of carbon paper or carbon fiber fabric) applied to the catalyst layer. The catalytically active precious metal contained in the catalyst layer may be one or more of the precious metals, e.g. platinum, rhodium, palladium, iridium and / or ruthenium, in particular platinum, iridium and ruthenium, each of which may be present as a catalytically active substance in elemental (metallic) form and / or in chemically bound form. Typically, the catalyst layer comprises the precious metal in supported form, i.e. on a support made, for example, of a carbon or oxide material. Based on the catalyst coated PEM membrane, any elastomeric seals that may be present, and any gas diffusion layers that may be present, the precious metal content or total precious metal content is, for example, in the range of 0.1-10 wt.%.

[0003] The used catalyst coated PEM membrane may be equipped with an elastic seal and may have an area of, for example, 5 to 5000 cm 2The weight percentage of any elastomeric seal that may be present may range from, for example, 10 to 50 weight percent, based on the combined weight percentage of the elastomeric seal and the catalyst coated PEM membrane. Such a wide range is specified herein as an example because the PEM membrane may originate from a laboratory facility to a commercial plant. Considering a particular case, the weight percentage of any elastomeric seal that may be present may range from, for example, 10 to 50 weight percent, based on the combined weight percentage of the elastomeric seal and the catalyst coated PEM membrane.

[0004] As mentioned above, the catalyst coated PEM membranes described herein may in particular be equipped with elastic seals. Such elastic seals are designed as external seal contours or external edge seals that completely seal or enclose at least the edge or periphery of the PEM membrane, in order to effectively seal each chamber of the half-cell from the outside. The material of the seal is elastic, for example, the elastic material in question is made of or based on rubber, natural rubber, silicone or other elastomeric plastics. Needless to say, it is known to those skilled in the art that the elastic material itself is free of precious metals, or at least is substantially free of precious metals.

[0005] When the operational or useful life of said PEM membranes or their precious metal-containing catalytic layer has come to an end, the relevant PEM fuel cell or PEM electrolysis cell or the PEM membranes provided therein must be replaced. Since valuable precious metals are contained in the catalytic layer of the PEM membrane, used PEM membranes are not simply discarded but sent for precious metal recycling. As a result, said PEM membranes or an assortment of various such PEM membranes must be crushed and homogenized, on the one hand in preparation for the actual precious metal recycling and, on the other hand, in order to obtain material that allows the taking of a representative sample and the measurement of the precious metal content on the basis of said representative sample.

[0006] In investigating how to achieve the above object, it has become apparent that the grinding can be effectively performed by a cutting mill. The present invention therefore comprises a method for grinding used catalyst coated PEM membranes from PEM fuel cells and / or PEM electrolysis cells, characterized in that the grinding is performed by a cutting mill. Thus, used catalyst coated PEM membranes, in particular used catalyst coated PEM membranes with elastic seals, are the grinding material that is ground in the cutting mill.

[0007] Catalyst-coated PEM membranes or catalyst-coated PEM membranes with elastic seals have been described above. They may be identical or different catalyst-coated PEM membranes or identical or different catalyst-coated PEM membranes with elastic seals. Different catalyst-coated PEM membranes with or without elastic seals can, for example, come from different sources and can arrive as batches in an unsorted state in a collector for recyclable waste and arrive at the operator of the method according to the invention. In such cases, the different PEM membranes can, for example, differ in terms of their construction, shape, size, type and content in the catalyst layer precious metal, type of membrane material, presence of elastic seals and / or type of elastic seals.

[0008] The process according to the invention can be carried out batchwise (discontinuously) or continuously.

[0009] It is preferred to operate the process according to the invention with dried or dried ground material subjected to grinding.

[0010] Although not preferred, the method according to the invention can be carried out whilst cooling the ground material undergoing grinding, for example by adding dry ice or liquid nitrogen to the product prior to or during product grinding.

[0011] According to the invention, the grinding itself is carried out in conventional cutting mills known to those skilled in the art, such as those manufactured and sold by Retsch GmbH, Haan or Fritsch GmbH, Idar-Oberstein.

[0012] The grinding step may be carried out until a desired grinding result is achieved, for example, until the desired maximum particle size of the grinding material is in the range of 1-10 mm in the direction of maximum longitudinal extension of the particles formed during grinding. As can be seen above, the ground material may be a mixture of ground catalyst coated PEM membranes and ground elastic seals. The maximum particle size of the ground material depends on the cutting mill used (model and tools used in the cutting mill) and can be adjusted by parameters such as (i) the energy input during the grinding step and / or (ii) the duration of the grinding step.

[0013] When the method according to the present invention is carried out batchwise, in particular when the method according to the present invention is carried out on a collection of used catalyst-coated PEM membranes, optionally including elastic seals, it may be preferable to mix the comminuted ground material before further processing or before use for further homogenization.

[0014] One or more samples can be taken from the crushed ground material, optionally additionally mixed, to measure the average precious metal content. The crushed ground material can also be subjected to a conventional precious metal recycling process, which may generally include several sub-steps. In this respect, the method according to the invention can also include one or more corresponding method steps that are carried out after crushing. For example, after crushing is completed, the method according to the invention includes at least one recycling or processing step selected from the steps of incineration (burning off) and hydrometallurgical processing.

[0015] In a preferred embodiment of the method according to the invention, when the grinding material is ground in the form of used catalyst-coated PEM membranes with elastic seals, the use can advantageously consist of different grinding behaviors, or different grinding possibilities, or grinding properties, of two different material fractions of the grinding material, more precisely of the elastic seal fraction and of the catalyst-coated PEM membrane fraction. It can therefore be determined within the scope of the development of the method according to the invention that the fraction formed from the catalyst-coated PEM membrane can be ground more quickly or more easily than the fraction formed from the elastic seal. The grinding is carried out until the desired grinding result is achieved for the portion of the catalyst-coated PEM membrane in the grinding material to be ground, for example in the form of the maximum particle size desired for the fraction of the catalyst-coated PEM membrane in the grinding material to be ground, and the particle size of the elastic seal fraction is coarser and therefore larger than the maximum particle size of the catalyst-coated PEM membrane fraction. The maximum particle size desired for the fraction of the catalyst-coated PEM membrane in the ground material to be ground can be, for example, in the range of several millimeters, for example in the range of 1 to 5 mm, in the direction of maximum longitudinal extension of the particles.

[0016] After completion of the grinding step according to a preferred embodiment of the method of the present invention, the coarse fraction of the ground elastomeric seals can be separated, for example by screening, from the fine fraction of the catalyst coated PEM membranes, which can then be collected as described above and analyzed for type and proportion of precious metals and / or subjected to precious metal recycling.

[0017] The above-mentioned separation or screening carried out after the grinding step can be carried out by a separate screening device, and in a preferred and advantageous embodiment, can actually be carried out during the grinding step by a screening device integrated into the cutting mill. Examples of such screening devices include, for example, a bottom screen with circular through-holes with a diameter in the range of 1-5 mm, or a bottom screen with square through-holes of 1 mm x 1 mm to 5 mm x 5 mm. In other words, the grinding step according to the present invention can be realized in a sort-separating manner, in the sense that the grinding step and the screening step are carried out in parallel in the case of a preferred embodiment.

[0018] A preferred embodiment of the method according to the invention allows said recovery, said precious metal analysis and / or said precious metal recycling to be carried out substantially solely or substantially solely using the precious metal-containing fine part of the crushed ground material. The separately obtained coarse fraction of the crushed elastomeric seals can be used for other purposes, for example as an additive in floors or road surfaces. EXAMPLES

[0019] 93.88 g of used catalyst coated polymer electrolyte membrane from a PEM fuel cell with edge seals made of silicone elastomer were ground in a cutting mill (model SM300 from Retsch GmbH, Retsch-Allee 1-5, 42781 Haan, Germany) equipped with a bottom screen with 3 mm x 3 mm square through holes, for 30 s in a batch operation. This resulted in 76.33 g of fine fraction and 17.55 g of coarse part on the screen. After ashing and wet chemical treatment of the ash residue, the precious metal content of both fractions was detected by ICP-OES. The following table shows the results obtained for both fractions.

[0020] [Table 1]

Claims

1. 1. A method for comminuting spent catalyst coated PEM membranes from PEM fuel cells and / or PEM electrolysis cells, comprising:

4. The method according to claim 1, wherein the grinding is carried out in a cutting mill.

2. The method of claim 1 , wherein the used catalyst coated PEM membrane is provided with a resilient seal.

3. The method of claim 1 or 2, wherein the catalyst coated PEM membranes are the same or different catalyst coated PEM membranes.

4. The process according to any one of claims 1 to 3, wherein the process is carried out batchwise or continuously.

5. The method according to any one of claims 1 to 4, wherein the grinding step is carried out until a desired grinding result is obtained.

6. The method according to any one of claims 2 to 5, wherein said grinding is carried out only for a fraction of the catalyst coated PEM membranes in the ground material until a desired grinding result is obtained.

7. The method according to any one of claims 2 to 6, wherein after the crushing step is completed, the coarse fraction of the crushed elastomeric seals is separated from the fine fraction of the catalyst coated PEM membrane.

8. The method of claim 7 , wherein the separation is performed by screening.

9. 9. The method according to claim 7 or 8, wherein the separated fine fraction is collected and analysed for type and proportion of precious metals and / or subjected to precious metal recycling.

10. The method according to any one of claims 7 to 9, wherein separation or screening is carried out during the grinding step by a screening device incorporated in the cutting mill.

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