Method for crushing 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 "PEMs") 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, each half-cell is separated from the other by a PEM membrane, particularly a PEM membrane with an elastic seal. So-called ionomers, such as copolymers of tetrafluoroethylene and sulfonic acid group-containing (per)fluorovinyl ethers, are commonly used as PEM materials. The PEM membrane functions as a proton transport medium and electrically separates the electrodes of a 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 also contain a 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 following precious metals: platinum, rhodium, palladium, iridium, and / or ruthenium, particularly platinum, iridium, and ruthenium. Each precious metal may exist as a catalytically active substance in elemental (metallic) form and / or in a chemically bonded form. Typically, the catalyst layer comprises the precious metal in supported form, i.e., on a support made, for example, of a carbonaceous or oxidized 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 to 10 wt. %.

[0003] The used catalyst coated PEM membrane may be equipped with an elastic seal, and the area of ​​such a PEM membrane may be, for example, 5 to 5000 cm 2The reason for specifying such a wide range of examples herein is that PEM membranes can originate from laboratory facilities to commercial plants. Considering individual cases, the weight percentage of any elastic seal that may be present can be in the range of, for example, 10 to 50 wt. % based on the combined weight percentage of the elastic seal and the catalyst-coated PEM membrane.

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

[0005] When the operational or useful life of the PEM membranes or their precious metal-containing catalyst layers ends, the relevant PEM fuel cell, PEM electrolysis cell, or PEM membranes installed therein must be replaced. Because 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. Consequently, such PEM membranes or assortments 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, to obtain material that allows representative samples to be taken and the precious metal content to be measured based on such representative samples.

[0006] In investigating methods for achieving the above object, it was found that the pulverization can be effectively performed by a cutting mill. Accordingly, the present invention comprises a method for pulverizing used catalyst-coated PEM membranes from PEM fuel cells and / or PEM electrolysis cells, characterized in that the pulverization is performed by a cutting mill. Thus, used catalyst-coated PEM membranes, particularly used catalyst-coated PEM membranes with elastic seals, are the pulverized material that is pulverized by the cutting mill.

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

[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 present invention can be carried out while 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 process can be carried out until a desired grinding result is achieved, for example, until the desired maximum particle size of the ground material is in the range of 1 to 10 mm in the direction of maximum longitudinal extension of the particles formed during grinding. As can be seen from the above, the ground material can 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 tooling used in the cutting mill) and can be adjusted by parameters such as (i) the energy input during the grinding process and / or (ii) the duration of the grinding process.

[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 pulverized material before further processing or before use for further homogenization.

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

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

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

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

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

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

[0020] [Table 1]

Claims

1. 1. A method for pulverizing spent catalyst coated PEM membranes from PEM fuel cells and / or PEM electrolysis cells, comprising: The grinding is carried out by a cutting mill, the spent catalyst coated PEM membrane is provided with a resilient seal; After the crushing step is completed, the coarse fraction of the crushed elastomeric seal is separated from the fine fraction of the catalyst coated PEM membrane.

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

3. The method of claim 2, wherein the method is carried out in a batch or continuous mode.

4. 4. The method of claim 3, wherein the grinding step is carried out until a desired grinding result is achieved.

5. 5. The method of claim 4, wherein the fraction of catalyst coated PEM membranes in the pulverized material is pulverized only until a desired pulverization result is achieved.

6. The method of claim 1 , wherein the separation is performed by screening.

7. 10. The method of claim 1, wherein the separated fine fraction is collected and analyzed for type and proportion of precious metals and / or subjected to precious metal recycling.

8. 2. The method according to claim 1, wherein separation or screening is carried out during the grinding step by a screening device incorporated in the cutting mill.

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