Process method for recovering and purifying platinum metal in fuel cell membrane electrode

Abstract

The invention relates to a recovery and purification process method for platinum metal in a fuel cell membrane electrode, and belongs to the technical field of membrane electrode recovery. Comprising the following steps: S1, crushing a recycled membrane electrode through a wall breaking machine; s2, adding the crushed membrane electrode into a small molecule swelling agent, performing ultrasonic blending, then adding quartz sand, and performing stirring and shearing to obtain a blended solution; s3, cooling the blended liquid to room temperature, and performing primary filtration through a screen mesh of 150 meshes or above to obtain a recyclable proton exchange membrane; s4, performing secondary filtration on the filtrate obtained by filtration in S3 through a filter membrane to obtain a filter cake and a recycled micromolecular swelling agent which can be reused, and collecting the filter cake for later use; and S5, the filter cake is refined through a filler roasting or wet refining method, and high-purity platinum metal is obtained. The recovered product is high in purity, and the process tail gas emission is less.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane electrode recovery, and relates to a recovery and purification process method of platinum metal in a fuel cell membrane electrode. BACKGROUND

[0002] The fuel cell membrane electrode usually contains precious metals such as platinum and iridium, and the solid content is much higher than that in ores, so there is high economic value in recovering precious metals in waste and discarded membrane electrodes. However, the membrane electrode itself has a complex structure, and the technical process paths of various membrane electrode manufacturers differ greatly, so the composition is also relatively complex.

[0003] Patent document CN106803596A discloses a method for recovering platinum from waste fuel cells. The method separates the bipolar plate and the membrane electrode of the waste fuel cell, crushes them, performs ultrasonic cleaning with an organic solvent, pyrolyzes them, and soaks them in an organic solvent to obtain recovered platinum. The organic solvent selected in this method is one of acetone, ethanol, ethylene glycol and N, N dimethylacetamide. The cleaning effect of the catalytic layer is not good, and the subsequent only strong means of ultrasonic crushing can be used for stripping. The catalytic layer stripping efficiency is not high and the process batch processing capacity is limited, and the energy consumption is high. Secondly, this process directly uses the method of pyrolyzing the proton membrane, which will release a large amount of fluorine-containing compounds, causing serious environmental pollution.

[0004] Patent document CN112593084A discloses a recovery method for platinum catalyst of waste proton exchange membrane fuel cell. The method uses an oxidation-reduction method to dissolve and recover platinum in the membrane electrode. This method has the problems of insufficient batch processing capacity and poor applicability, that is, it can only process regular whole membrane electrodes, and cannot be applied to irregular membrane electrodes.

[0005] If batch and large-scale recovery work is to be carried out, a recovery process with strong applicability, wide coverage and little pollution must be developed. SUMMARY

[0006] The purpose of the present application is to provide a recovery and purification process method of platinum metal in a fuel cell membrane electrode. The recovered product of the present application has high purity and little tail gas emission.

[0007] The purpose of the present application can be achieved by the following technical solutions: A recovery and purification process method of platinum metal in a fuel cell membrane electrode, characterized in that it comprises the following steps: S1, crushing the recovered membrane electrode by a wall breaking machine to obtain membrane electrode particles with a particle size of 100-2000 μm; S2, add the broken membrane electrode to the small molecule swelling agent, ultrasonic blend for 10-15 min, then add 1-10 % of the total mass of the mixed solution of quartz sand, keep the ambient temperature at 40-80 ℃, and carry out stirring and shearing treatment for 30-60 min to obtain a blended liquid, wherein the stirring and shearing speed is 400-800 r / min; S3, after the blended liquid is cooled to room temperature, the stripped electrolyte layer and the filtrate are filtered once through a 150-mesh sieve to obtain a recoverable proton exchange membrane; S4, the filtrate obtained by filtering in S3 is filtered twice through a filter membrane to obtain a filter cake and the small molecule swelling agent which can be used again after recovery, and the filter cake is collected for use; S5, the filter cake is refined by dry roasting or wet smelting to obtain high-purity platinum metal.

[0008] As a preferred technical solution of the present application, the small molecule swelling agent is one or several of ethylene glycol, acetone and ethanol.

[0009] As a preferred technical solution of the present application, the particle size of the quartz sand is 0.1 mm.

[0010] As a preferred technical solution of the present application, the filter membrane is a polypropylene or polyethylene high molecular filter membrane, and the pore size of the filter membrane is 0.1-10 μm.

[0011] As a preferred technical solution of the present application, in step S5, the specific steps of the filter cake treated by the dry roasting method are as follows: The filter cake and sodium hydroxide are mixed at a mass ratio of 1:3, uniformly stirred, and then put into a muffle furnace for aerobic roasting for 1 h at a roasting temperature of 400 ℃, and after roasting, the slag is taken out, washed and filtered to obtain platinum metal.

[0012] As a preferred technical solution of the present application, in step S5, the specific steps of the filter cake treated by the wet smelting method are as follows: S61, prepare an aqua regia solution with a volume ratio of water: concentrated nitric acid: concentrated hydrochloric acid = 1:1:4, put it into the filter cake to fully dissolve, and add 20-30 % hydrogen peroxide, and stir at 25-60 ℃ for 1 h to obtain a solution containing chloroplatinic acid and a carbon carrier, and then remove the carbon carrier by normal pressure filtration to obtain a chloroplatinic acid solution; S62, heat the obtained chloroplatinic acid solution to 80 ℃, evaporate the nitrate; constantly add pure water during the evaporation process to prevent the solution from evaporating dry; after the nitrate is completely evaporated, add sodium chloride, and completely evaporate and dry the solution to obtain a solid mixture; S63, cool the solid mixture obtained by completely evaporating the solution to room temperature, then add deionized water to fully dissolve, and then filter and purify to obtain a relatively pure sodium chloroplatinate solution; S64, adding excess oxalic acid solution to the obtained sodium chloroplatinate solution to pH 1, and then adding excess ammonia water to adjust the solution to pH>7, and an orange yellow precipitate appears in the solution; S65, filtering the solution to obtain an orange yellow precipitate, heating in a muffle furnace to 360 ℃, and then heating to 720 ℃ after 2 hours to obtain sponge-like pure platinum, and sintering and pressing the pure platinum to obtain high-purity platinum blocks.

[0013] The beneficial effects of the present application are: (1) By using the swelling-shearing method, the fuel cell membrane electrode catalyst layer and electrolyte layer are batch separated, the process is simple, the separation efficiency is high, and it is easy to implement, and in the shearing step, quartz sand is added, which can accelerate the peeling of the catalyst layer and the electrolyte layer, improve the peeling efficiency to achieve higher recovery effect.

[0014] The small molecule swelling agent used in the present application is ethylene glycol, ethanol and acetone, and because the swelling processes of the membrane electrode catalyst layer, electrolyte layer (proton membrane layer) and small molecule solvent are different, the swelling effect is improved by mixing different solvents, the polarity of the swelling agent is changed by adjusting the composition ratio of the swelling agent, the interaction between substances is reduced, the membrane electrode is more easily dissolved in the solvent, which is beneficial to improve the swelling effect and make the proton exchange membrane in the membrane electrode fully peel off; At the same time, the solubility of the solute in the solvent can be increased, so that a solution with higher concentration can be realized.

[0015] By designing the ratio of the mixed small molecule solvent, the optimal design of the membrane electrode swelling is realized to produce a strong swelling effect, so that the catalyst layer and the electrolyte layer are fully dissociated during soaking and shearing. In the present application, when the composition of the swelling agent is 2:1:1 of ethylene glycol, acetone and ethanol, the polarity of the solution is larger and the solubility of the membrane electrode components is also better, the solvent molecules diffuse into the high molecular polymer film composed of the recovered membrane electrode polymer film, so that its volume expands, and the swelling effect is best.

[0016] (2) Since the catalyst particles in the catalyst layer are usually less than 0.1 μm, the proton membrane and the catalyst particles can be separated by means of filtration screening. The filtration screening obtains two components, one is a filter cake layer formed by the proton membrane fragments, which is recycled for later use, and the other is a suspension containing catalyst. The suspension containing catalyst is filtered again to obtain a swelling liquid and a catalyst filter cake. The swelling liquid can be reused in the swelling step, and the filter cake enters the refining step. The refining of the process can take two paths, dry roasting and wet smelting. In the dry roasting process, a filler roasting scheme is adopted, and sodium hydroxide is added by in-situ absorption to perform roasting. The residual fluorine in the recovered catalyst is absorbed in-situ by the alkaline absorbent during roasting to form fluoride, which can reduce the emission of hazardous waste gas, especially fluorine-containing waste gas, and can obtain platinum with a purity of more than 95 %; the platinum obtained by wet refining has a purity of 99.99 % or more. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to facilitate the understanding of those skilled in the art, the present application will be further described below in conjunction with the drawings.

[0018] Figure 1 The process route for recovering platinum metal in the membrane electrode. DETAILED DESCRIPTION

[0019] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined application purposes, the specific embodiments, structures, features and effects according to the present application are described in detail below in conjunction with the drawings and preferred embodiments.

[0020] Example 1 S1, the recovered membrane electrode is crushed by a wall breaking machine to obtain membrane electrode particles with a particle size of 100 ~ 2000 μm; S2, mix ethylene glycol, acetone and ethanol in a ratio of 2:1:1 to obtain a small molecule swelling agent, add the crushed membrane electrode, ultrasonic blend for 15 min, then add 5 % of quartz sand based on the total mass of the mixed solution, keep the environmental temperature at 60 ℃, and perform stirring and shearing treatment for 40 min to obtain a blended liquid, wherein the stirring and shearing speed is 500 r / min; S3, after the blended liquid is cooled to room temperature, the stripped electrolyte layer and the filtrate are filtered once through a 150 mesh screen to obtain a recoverable proton exchange membrane; S4, the filtrate obtained by filtering in S3 is filtered again through a polyethylene filter film with a pore size of 5 microns to obtain a filter cake and a small molecule swelling agent that can be reused after recovery, and the filter cake is collected for later use; S5, the filter cake and sodium hydroxide in S4 are mixed according to a mass ratio of 1:3, and after being fully stirred and uniformly mixed, they are put into a muffle furnace for aerobic roasting for 1 h, the roasting temperature is 400 DEG C, after the roasting is completed, the slag is taken out, and after being washed and filtered, platinum metal is obtained.

[0021] Example 2 S1, the recovered membrane electrode is crushed by a wall breaking machine to obtain membrane electrode particles with a particle size of 100-2000 μm; S2, ethylene glycol, acetone and ethanol are mixed in a ratio of 2:1:1 to obtain a small molecule swelling agent, the crushed membrane electrode is added, ultrasonic blending is carried out for 15 min, 5% of quartz sand based on the total mass of the mixed solution is added, the environmental temperature is kept at 60 DEG C, and stirring and shearing treatment is carried out for 40 min to obtain a blended solution, wherein the stirring and shearing speed is 500 r / min; S3, after the blended solution is cooled to room temperature, the stripped electrolyte layer and the filtrate are filtered once through a 150-mesh screen to obtain a proton exchange membrane which can be recycled; S4, the filtrate obtained by filtering in S3 is subjected to secondary filtration through a polyethylene filter film with a pore size of 5 microns to obtain a filter cake and a small molecule swelling agent which can be used again after being recycled, and the filter cake is collected for use; S5, an aqua regia solution with a volume ratio of water: concentrated nitric acid: concentrated hydrochloric acid = 1:1:4 is prepared, the filter cake is added and fully dissolved, 20% hydrogen peroxide by mass fraction is added, and stirring reaction is carried out at 40 DEG C for 1 h to obtain a solution containing chloroplatinic acid and a carbon carrier, and the carbon carrier is removed by normal pressure filtration to obtain a chloroplatinic acid solution; S6, the obtained chloroplatinic acid solution is heated to 80 DEG C, and nitrate is evaporated; pure water is continuously added during evaporation to prevent the solution from being evaporated dry; after the nitrate is completely evaporated, sodium chloride is added, and the solution is completely evaporated and dried to obtain a solid mixture; S7, the solid mixture after complete evaporation of the solution is cooled to room temperature, and then deionized water is added to fully dissolve, and a relatively pure sodium chloroplatinate solution is obtained after filtration and purification; S8, an excess of oxalic acid solution is added to the obtained sodium chloroplatinate solution until the pH value is 1, and then an excess of ammonia water is added to adjust the solution to pH>7, and an orange yellow precipitate appears in the solution; S9, the solution is filtered to obtain an orange yellow precipitate, which is heated to 360 DEG C in a muffle furnace, and then heated to 720 DEG C after 2 hours to obtain sponge-like pure platinum, and high-purity platinum blocks are obtained after sintering and pressing of the pure platinum.

[0022] Example 3 The difference between example 3 and example 1 is that the small molecule swelling agent used is 1:1:1 ethylene glycol, acetone and ethanol, and the rest of the operations are consistent.

[0023] Example 4 Example 4 differs from Example 2 in that the small molecule swelling agent used is 1:1:1 ethylene glycol, acetone, ethanol, and the rest of the operations are consistent.

[0024] Example 5 Example 5 differs from Example 1 in that the small molecule swelling agent used is 2:1 ethylene glycol, acetone, and the rest of the operations are consistent.

[0025] Comparative Example 1 Comparative Example 1 differs from Example 1 in that no quartz sand is added, and the rest of the operations are consistent.

[0026]

[0027] According to the above data, it can be seen that the purity of the metal platinum obtained by the scheme of roasting the filler in Example 1, 3 and 5 is all above 95%; the purity of the metal platinum obtained by the scheme of wet refining in Example 2 and 4 can reach 99.9%. It can be seen from Comparative Example 1 and 3 that when the composition of the swelling agent is ethylene glycol: acetone: ethanol = 2:1:1, the swelling effect is better and the recovery rate is also higher.

[0028] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with the preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any modification, change and modification of the above embodiments according to the technical essence of the present application, which does not depart from the technical solution of the present application, still belongs to the scope of the technical solution of the present application.

Claims

1. A process for recovering and purifying platinum metal in a fuel cell membrane electrode, characterized in that: The following steps are involved: S1, the recovered membrane electrode is crushed by a wall breaking machine to obtain membrane electrode particles with a particle size of 100 ~ 2000 μm; S2. Add the broken membrane electrode to the small molecule swelling agent, ultrasonically blend for 10-15 min, then add quartz sand (1-10% by weight of the total mass of the mixed solution), maintain the ambient temperature at 40-80°C, and stir and shear for 30-60 min to obtain a blended solution, wherein the stirring and shearing speed is 400-800 r / min; S3, after the mixed solution is cooled to room temperature, it is passed through a 150-mesh sieve to filter the stripped electrolyte layer and the filtrate once to obtain a recyclable proton exchange membrane; S4, filtering the filtrate obtained in S3 through a filter membrane for a second time to obtain a filter cake and a small molecule swelling agent that can be recycled and reused, and collecting the filter cake for later use; S5. The filter cake is refined by dry roasting or wet smelting to obtain high-purity platinum metal.

2. The process for recovering and purifying platinum metal in fuel cell membrane electrode according to claim 1, characterized in that: The small molecule swelling agent is one or more of ethylene glycol, acetone, and ethanol.

3. The process for recovering and purifying platinum metal in fuel cell membrane electrode according to claim 1, characterized in that: The particle size of the quartz sand is 0.1 mm.

4. The process for recovering and purifying platinum metal in fuel cell membrane electrode according to claim 1, characterized in that: The filter membrane is a polypropylene or polyethylene polymer filter membrane with a pore size of 0.1 to 10 μm.

5. The process for recovering and purifying platinum metal in fuel cell membrane electrode according to claim 1, characterized in that: In step S5, the filter cake is subjected to dry roasting process. The filter cake and sodium hydroxide were mixed in a mass ratio of 1:3, stirred thoroughly, and then placed in a muffle furnace for aerobic roasting for 1 hour at a roasting temperature of 400 °C. After the roasting was completed, the slag was taken out, washed and filtered to obtain platinum metal.

6. The process for recovering and purifying platinum metal in fuel cell membrane electrode according to claim 1, characterized in that: In step S5, the filter cake is treated by the hydrometallurgical method in the following specific steps: S61. Prepare an aqua regia solution with a volume ratio of water: concentrated nitric acid: concentrated hydrochloric acid = 1:1:4, add the filter cake to fully dissolve it, add 20-30% by mass of hydrogen peroxide, and stir the reaction at 25-60°C for 1 hour to obtain a solution containing chloroplatinic acid and a carbon support. Filter under normal pressure to remove the carbon support to obtain a chloroplatinic acid solution. S62, heating the obtained chloroplatinic acid solution to 80° C. to evaporate and drive off nitrate ions; continuously adding pure water during the evaporation process to prevent the solution from drying up; adding sodium chloride after the nitrate ions are completely evaporated, and completely evaporating the solution to dryness to obtain a solid mixture; S63, cooling the solid mixture after complete evaporation of the solution to room temperature, adding deionized water to fully dissolve it, filtering and purifying to obtain a relatively pure sodium chloroplatinate solution; S64, adding excess oxalic acid solution to the obtained sodium chloroplatinate solution until the pH value is 1, and then adding excess ammonia water to adjust the solution to pH>7, and an orange-yellow precipitate appears in the solution; S65. Filter the solution to obtain an orange-yellow precipitate, heat it to 360°C in a muffle furnace, and then heat it to 720°C after 2 hours to obtain sponge-like pure platinum. Sinter the pure platinum and press it to obtain a high-purity platinum block.

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