Method for recovering perfluorinated sulfonic acid resin from waste ion exchange membrane

Abstract

The invention belongs to the technical field of ion exchange membranes, and particularly relates to a method for recovering perfluorinated sulfonic acid resin from a waste ion exchange membrane. The method for recovering the perfluorinated sulfonic acid resin from the waste ion exchange membrane comprises the following steps: (1) sequentially carrying out pretreatment, acid washing and alkali washing on the waste ion exchange membrane, and then washing the waste ion exchange membrane until the waste ion exchange membrane is neutral; the pretreatment comprises optional alcohol washing and salt washing treatment; and (2) mixing the waste ion exchange membrane obtained in the step (1), alkyl alcohol and water. The method has the beneficial effects that the waste ion exchange membrane is firstly subjected to salt washing, alcohol washing, acid washing and alkali washing treatment, impurity ions and surface coatings carried in the waste ion exchange membrane can be effectively removed, the color of the waste ion exchange membrane can be faded, the parameters of the prepared perfluorosulfonic acid resin solution are more stable, and the performance of the perfluorosulfonic acid resin solution is improved. And the converted resin product also has better performance.

Description

Technical Field

[0001] The invention belongs to the technical field of ion exchange membranes, and in particular relates to a method for recovering perfluorosulfonic acid resin from waste ion exchange membranes. Background Art

[0002] Proton exchange membrane fuel cell is a power generation device that directly converts chemical energy stored in hydrogen and oxygen into electrical energy through electrode chemical reactions. As the core component of polymer electrolyte fuel cells, proton exchange membrane determines the performance and life of fuel cells. An ideal proton exchange membrane should have the characteristics of high proton conductivity, low gas permeability, high mechanical strength, good chemical stability and low price. The selective permeable resin for preparing proton exchange membrane is currently the most successful commercialized perfluorosulfonic acid resin, which has good stability and long life.

[0003] Perfluorosulfonic acid resin is the core material of proton exchange membrane, which is obtained by copolymerization of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PSVE) containing sulfonyl groups. Tetrafluoroethylene provides a stable fluorocarbon skeleton for the polymer, and perfluoroalkyl vinyl ether introduces key sulfonic acid groups to ensure the excellent electrochemical properties of the proton exchange membrane. The transportation and production of tetrafluoroethylene monomer are relatively difficult, and the resin polymerization is difficult, so the production of perfluorosulfonic acid resin requires extremely strict production conditions and high costs, which increases the difficulty of promoting the application of proton exchange membranes and reducing the cost of hydrogen energy use.

[0004] my country's hydrogen energy and energy storage industries have developed to a certain scale. Ion exchange membranes are used in water electrolysis, fuel cells and flow batteries, and ion exchange membranes contain a considerable amount of perfluorosulfonic acid resin. With the development of my country's energy industry, the scale of the industry using ion exchange membranes is expanding, and a large number of waste ion exchange membranes are produced every year. If the perfluorosulfonic acid resin in the waste ion exchange membrane can be recovered, it will broaden the raw material channels of perfluorosulfonic acid resin, improve the utilization rate of perfluorosulfonic acid resin, reduce the cost of product development, and also be beneficial to the advancement of the entire energy industry.

[0005] The prior art proposes to use alcohol and hydrochloric acid to clean and shred the recovered chlor-alkali membrane containing perfluorosulfonic acid resin, and then dissolve it in dimethylformamide to prepare a resin solution. With the development of ion exchange membrane preparation technology, membrane surface coatings and doped catalysts are becoming more and more common, and the difficulty of recovering high-purity perfluorosulfonic acid resin is increasing. The above recovery method has limited effect on removing impurities and surface coatings in discarded membranes, and the resin itself in the membrane after treatment is acidic, which is highly corrosive to the containers of the subsequent dissolution steps. In addition, dimethylformamide is highly toxic, corrosive, and has an unpleasant odor. It is difficult to operate manually, and the subsequent conversion resin product is prone to residual high-boiling point solvents. Therefore, it is a perfluorosulfonic acid resin recovery method that is simple in recovery method and high in recovery efficiency. It has a broad application prospect. Summary of the invention

[0006] The present application provides a method for recovering perfluorosulfonic acid resin from waste ion exchange membranes, aiming to remove the membrane surface coating or the catalyst doped in the membrane, and extract the pure perfluorosulfonic acid resin in the ion exchange membrane into a non-toxic solvent for further processing and use.

[0007] The first aspect of the present application provides a method for recovering perfluorosulfonic acid resin from waste ion exchange membranes, comprising the following steps:

[0008] (1) subjecting the waste ion exchange membrane to pretreatment, acid washing, and alkali washing in sequence, and then washing to neutrality; the pretreatment may include alcohol washing and salt washing;

[0009] (2) Mixing the waste ion exchange membrane obtained in step (1), alkyl alcohol and water.

[0010] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (1), when the waste ion exchange membrane contains a coating, the pretreatment includes alcohol washing and salt washing;

[0011] When there is no coating in the waste ion exchange membrane, the pre-treatment is a salt washing treatment.

[0012] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (1), the cleaning solution used in the salt washing is a sodium chloride aqueous solution and / or a potassium chloride aqueous solution.

[0013] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass concentration of the cleaning solution used in the salt washing is 5%-30%.

[0014] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass of the cleaning solution used in the salt washing is 5-10 times the mass of the waste ion exchange membrane.

[0015] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the temperature of the salt washing is 75° C.-110° C., and the time of the salt washing is 4-6 hours.

[0016] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (1), the cleaning liquid used in the alcohol washing is one or more of methanol, ethanol, n-propanol and isopropanol.

[0017] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass of the cleaning liquid used in the alcohol washing is 5-10 times the mass of the waste ion exchange membrane;

[0018] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the temperature of the alcohol washing is 60° C.-95° C., and the time of the alcohol washing is 8-12 hours.

[0019] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (1), the cleaning solution used in the acid washing is hydrochloric acid and / or sulfuric acid.

[0020] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass fraction of the sulfuric acid is 25%-40%.

[0021] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass of the cleaning solution used in the acid washing is 5-10 times the mass of the waste ion exchange membrane.

[0022] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the acid washing temperature is 90-110° C., and the acid washing time is 4-6 hours.

[0023] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (1), the cleaning solution used in the alkaline washing is an aqueous solution of sodium hydroxide and / or potassium hydroxide.

[0024] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass concentration of the cleaning solution used in the alkaline washing is 10%-35%.

[0025] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass of the cleaning solution used in the alkaline washing is 5-10 times the mass of the waste ion exchange membrane.

[0026] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the temperature of the alkali washing is 90° C.-120° C., and the time of the alkali washing is 4-6 hours.

[0027] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (2), the mass ratio of the waste ion exchange membrane to the alkyl alcohol is 1:(3-10).

[0028] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mass ratio of the waste ion exchange membrane to the water is 1:(3-10).

[0029] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (2), the alkyl alcohol includes one or more of methanol, ethanol, n-propanol and isopropanol.

[0030] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (2), the mixing temperature is 180° C.-250° C., and the mixing time is 8-9 h.

[0031] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, in step (2), the mixing is performed in an inert atmosphere.

[0032] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the mixing is performed under a nitrogen atmosphere.

[0033] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the method further includes: crushing the waste ion exchange membranes, and then sequentially washing with salt, alcohol, acid, and alkali.

[0034] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the method further comprises: filtering and centrifuging the mixed solution obtained in step (2) in sequence to obtain a solution containing perfluorosulfonic acid resin.

[0035] According to some embodiments of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application, the waste ion exchange membrane is a composite membrane or a homogeneous membrane containing perfluorosulfonic acid resin. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0037] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0038] The present invention provides a method for recovering perfluorosulfonic acid resin from waste ion exchange membranes, comprising the following steps:

[0039] (1) subjecting the waste ion exchange membrane to pretreatment, acid washing, and alkali washing in sequence, and then washing to neutrality; the pretreatment may include alcohol washing and salt washing;

[0040] (2) Mixing the waste ion exchange membrane obtained in step (1), alkyl alcohol and water.

[0041] The method described in the present application first treats the waste ion exchange membrane with salt washing, alcohol washing, acid washing and alkali washing, which can effectively remove the impurity ions and surface coating carried by the waste ion exchange membrane, and can dilute the color of the waste ion exchange membrane, so that the parameters of the prepared perfluorosulfonic acid resin solution are more stable, and the converted resin product also has better performance.

[0042] The method described in the present application has simple process and low cost, and the obtained perfluorosulfonic acid resin polymer solution has good stability. When converted into a resin product, there is no solvent residue and little odor.

[0043] In some embodiments of the present application, in step (1), when the waste ion exchange membrane contains a coating, the pretreatment includes alcohol washing and salt washing; when the waste ion exchange membrane does not contain a coating, the pretreatment is a salt washing treatment.

[0044] When the waste ion exchange membrane contains a coating, it is necessary to first perform alcohol washing to deform and swell the waste ion exchange membrane so that the coating falls off, and then perform salt washing to perform ion exchange on the waste ion exchange membrane to remove related additives and ionic impurities.

[0045] When there is no coating in the discarded ion exchange membrane, it can be washed with salt first. Because some discarded ion exchange membranes are acidic, salt washing can replace hydrogen ions, reducing the difficulty of subsequent cleaning.

[0046] In some embodiments of the present application, in step (1), the cleaning solution used in the salt washing is a sodium chloride aqueous solution and / or a potassium chloride aqueous solution. Sodium chloride and potassium chloride are both low-cost chemical products. The resin in the waste membrane can undergo a certain ion exchange in the salt solution, bringing out the corresponding ion additives doped, which can improve the efficiency of the subsequent cleaning process.

[0047] In some embodiments of the present application, the mass concentration of the cleaning solution used in the salt washing is 5%-30%, for example, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, etc.

[0048] In some embodiments of the present application, the mass of the cleaning solution used in the salt washing is 5-10 times the mass of the waste ion exchange membrane, for example, 5 times, 6 times, 8 times, 10 times, etc.

[0049] In some embodiments of the present application, the temperature of the salt washing is 75°C-110°C, for example, 75°C, 80°C, 90°C, 95°C, 100°C, 105°C, 110°C, etc., and the time of the salt washing is 4-6h.

[0050] In some embodiments of the present application, in step (1), the cleaning liquid used in the alcohol washing is one or more of methanol, ethanol, n-propanol and isopropanol. Sufficient alcohol washing can increase the swelling deformation flexibility of the perfluorosulfonic acid resin. During the alcohol washing and stirring process, the dense coating originally attached to the surface is broken, and the adhesion is also weakened, making it easy to remove the coating. For the discarded composite membrane, alcohol washing also makes the resin layer swell, reduces the adhesion between the resin layer and the reinforcing layer, and makes the resin easy to fall from the reinforcing layer, thereby improving the recovery rate. At the same time, the resin that absorbs alcohol becomes more porous, and the ability of internal liquid flow exchange becomes stronger, which provides more favorable conditions for subsequent salt washing material exchange. Methanol, ethanol, n-propanol and isopropanol have different polarities and boiling points. The alcohol washing solvent is selected according to the characteristics of different discarded ion exchange membrane raw materials, which can further improve the effect of alcohol washing.

[0051] In some embodiments of the present application, the mass of the cleaning liquid used in the alcohol washing is 5-10 times the mass of the waste ion exchange membrane, for example, 5 times, 6 times, 8 times, 10 times, etc.

[0052] In some embodiments of the present application, the alcohol washing temperature is 60°C-95°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 95°C, etc., and the alcohol washing time is 8-12 hours. According to the different boiling points of the alcohol solvents used, different reaction temperatures need to be selected. Heating can accelerate the reaction and the speed of material exchange. High temperature is also conducive to the shedding of the coating on the membrane surface.

[0053] In some embodiments of the present application, in step (1), the cleaning solution used in the pickling is hydrochloric acid and / or sulfuric acid. Since the ion exchange membrane will be exposed to metals and some non-metallic byproducts will be deposited in the working environment, the metal ion impurities in the membrane can be eluted into the acid solution by pickling, and the deposited non-metallic impurities will also be dissolved in the acidic environment, which can further purify the perfluorosulfonic acid resin.

[0054] In some embodiments of the present application, the mass fraction of the hydrochloric acid is 30%-32%, for example, 30%, 31%, 32%, etc.

[0055] In some embodiments of the present application, the mass fraction of the sulfuric acid is 25%-40%, for example, 25%, 30%, 32%, 35%, 38%, 40%, etc.

[0056] In some embodiments of the present application, the mass of the cleaning solution used in the acid wash is 5-10 times the mass of the waste ion exchange membrane.

[0057] In some embodiments of the present application, the pickling temperature is 90-110°C, such as 90°C, 100°C, 105°C, 110°C, etc., and the pickling time is 4-6h.

[0058] In some embodiments of the present application, in step (1), the cleaning solution used for the alkaline washing is an aqueous solution of sodium hydroxide and / or potassium hydroxide.

[0059] In some embodiments of the present application, the mass concentration of the cleaning solution used in the alkaline washing is 10%-35%, for example, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 35%, etc.

[0060] In some embodiments of the present application, the mass of the cleaning solution used in the alkaline washing is 5-10 times the mass of the waste ion exchange membrane.

[0061] In some embodiments of the present application, the temperature of the alkali washing is 90°C-120°C, for example, 90°C, 95°C, 98°C, 100°C, 105°C, 110°C, 120°C, etc., and the time of the alkali washing is 4-6h.

[0062] In some embodiments of the present application, in step (2), the mass ratio of the waste ion exchange membrane to the alkyl alcohol is 1:(3-10); under high temperature and high pressure, the water-alcohol mixed solvent can dissolve the perfluorosulfonic acid resin in the waste ion exchange membrane to form an overall uniform solution. The water-alcohol mixed solution has low cost, low toxicity and odor, and low corrosion to equipment; the water-alcohol solvent has a low boiling point, which is conducive to the subsequent process of extracting the perfluorosulfonic acid resin from the resin solution.

[0063] In some embodiments of the present application, the mass ratio of the waste ion exchange membrane to the water is 1:(3-10), for example, 1:4, 1:5, 1:6, 1:8, 1:10.

[0064] In some embodiments of the present application, in step (2), the alkyl alcohol includes one or more of methanol, ethanol, n-propanol and isopropanol. As a solvent, it is low in cost and not too corrosive to the equipment. At the same time, it has a suitable boiling point, which is conducive to evaporation of the solvent. Methanol, ethanol, n-propanol and isopropanol have different solubility coefficients. By mixing with aqueous solutions, the solubility of polymer resins with different molecular weights can be improved.

[0065] In some embodiments of the present application, in step (2), the mixing temperature is 180°C-250°C, such as 180°C, 190°C, 200°C, 210°C, 220°C, 240°C, 250°C, etc., and the mixing time is 8-9h. When the temperature is too low, the perfluorosulfonic acid resin in the discarded ion exchange membrane is difficult to dissolve into the solvent. This is because the original ion exchange membrane will be thermally processed, and the long molecular chains of the perfluorosulfonic acid resin will fold and crystallize during the thermal processing cooling process, becoming a regular folded state with lower energy. If the molecular chain needs to be unfolded and opened to be dispersed in the solvent, a higher temperature is required to make it in a more active state. However, too high a temperature will bring greater risks to the dissolution process and equipment. The above temperatures can both dissolve the perfluorosulfonic acid resin and ensure the safety of the process.

[0066] In some embodiments of the present application, in step (2), the mixing is performed in an inert atmosphere.

[0067] In some embodiments of the present application, the mixing is performed under a nitrogen atmosphere.

[0068] In some embodiments of the present application, the method further comprises: crushing the waste ion exchange membrane, and then sequentially subjecting the waste ion exchange membrane to salt washing, alcohol washing, acid washing, and alkali washing.

[0069] In some embodiments of the present application, the method further comprises: filtering and centrifuging the mixed solution obtained in step (2) to obtain a solution containing perfluorosulfonic acid resin.

[0070] In some embodiments of the present application, the waste ion exchange membrane is a composite membrane or a homogeneous membrane containing perfluorosulfonic acid resin.

[0071] Example 1

[0072] A method for recovering perfluorosulfonic acid resin from waste ion exchange membranes comprises the following steps:

[0073] Step 1, weighing 5 kg of waste ion composite membrane containing perfluorosulfonic acid resin, and breaking the waste ion exchange membrane into pieces of about 1 cm×1 cm by a crushing device;

[0074] Step 2: Place the broken membrane into a mixed solvent of 50 kg ethanol and isopropanol, stir and wash, wherein the volume ratio of ethanol to isopropanol is 1:5, and wash for 12 hours at a stirring temperature of 85°C, and the reaction is completed.

[0075] Step 3: Place the membrane obtained in step 2 into 50 kg of a 25% potassium chloride solution and stir and wash it. When the solution changes color after 6 hours of washing at a stirring temperature of 105°C, the reaction is complete.

[0076] Step 4, put the membrane obtained in step 3 into 50 kg of hydrochloric acid for stirring and cleaning. Stir and clean for 6 hours at a stirring temperature of 95°C;

[0077] Step 5, placing the membrane obtained in step 4 into 50 kg of an alkaline solution with a mass concentration of 25%, stirring and cleaning, wherein the solute of the alkaline solution is a mixture of potassium hydroxide and sodium hydroxide in a mass ratio of 1:1, and stirring at a stirring temperature of 110° C. for 6 hours.

[0078] Step 6: After washing the membrane obtained in step 5 until it is neutral, 5 kg of ethanol, 10 kg of isopropanol, 5 kg of n-propanol and 30 kg of water are placed in a reactor together with the treated membrane. After sealing the reactor, nitrogen is used to replace the air as a protective gas, and then heating and stirring are performed. The stirring temperature is controlled at 250° C. The reaction is completed after stirring for 8 hours until the membrane is completely dissolved.

[0079] Step 7, after the reaction is completed, open the reactor, filter the reaction solution, remove the middle reinforcement layer of the composite membrane, and then centrifuge the solution to obtain a supernatant that is a polymer solution containing perfluorosulfonic acid resin.

[0080] After the prepared polymer solution is dried, the EW value of the obtained resin product is not higher than 1500 g / mol.

[0081] The purity of the perfluorosulfonic acid resin prepared in Example 1 is above 99%. Since the raw material contains a reinforcing layer which is not within the recovery range, the yield of the perfluorosulfonic acid resin is 73%.

[0082] Note: EW value (Equivalent Weight) indicates the mass of a substance required to exchange one mole of hydrogen ions. EW value is an important parameter to measure the proton density of a substance. The smaller the EW value, the greater the proton density and the better the conductivity.

[0083] Example 2

[0084] Step 1: weigh 10 kg of waste proton exchange homogeneous membrane containing perfluorosulfonic acid resin, and pass the waste proton exchange membrane through a crushing device to crush it into fragments of about 1 cm×1 cm.

[0085] Step 2: Place the broken membrane into a mixed solvent of 60 kg ethanol and isopropanol, stir and wash, wherein the volume ratio of ethanol to isopropanol is 1:5, and wash for 12 hours at a stirring temperature of 85°C, and the reaction is completed.

[0086] Step 3: Place the membrane obtained in step 2 into 60 kg of a 30% potassium chloride solution and stir and wash it. When the solution changes color after 6 hours of washing at a stirring temperature of 75°C, the reaction is complete.

[0087] Step 4: Place the membrane obtained in step 3 in 60 kg of sulfuric acid with a mass concentration of 25% and stir and clean it for 6 hours at a stirring temperature of 95°C.

[0088] Step 5, the membrane obtained in step 4 is placed in 60kg of alkaline solution with a mass concentration of 35% for stirring and cleaning. The solute of the alkaline solution is a mixture of potassium hydroxide and sodium hydroxide, the mass ratio of the two is 3:1, the stirring and cleaning temperature is 120°C, and the stirring and cleaning time is 6 hours.

[0089] Step 6: clean the membrane obtained in step 5 until it is neutral, put 20kg ethanol, 5kg isopropanol, 5kg n-propanol and 30kg water into a reactor together with the treated membrane. After sealing the reactor, replace the air with nitrogen as a protective gas, and then heat and stir at a stirring temperature of 250°C for 8 hours until the membrane is completely dissolved and the reaction is completed.

[0090] Step 7, after the reaction is completed, open the reactor, filter the reaction solution, and then centrifuge the solution to obtain a supernatant that is a polymer solution containing perfluorosulfonic acid resin.

[0091] After the prepared polymer solution is dried, the EW value of the obtained resin product is not higher than 1500 g / mol.

[0092] The purity of the perfluorosulfonic acid resin prepared in Example 2 is above 99%, the homogeneous membrane does not contain a reinforcement layer, and the yield of the perfluorosulfonic acid resin is 95%.

[0093] Example 3

[0094] Step 1, weighing 15 kg of waste chlor-alkali membrane, and crushing the waste chlor-alkali membrane into pieces of about 1 cm×1 cm through a crushing device;

[0095] Step 2: Place the broken membrane into a mixed solvent of 90 kg ethanol, isopropanol and n-propanol and stir and clean it. The ratio of ethanol, isopropanol and n-propanol is 1:3:1. When the surface attachment of the membrane falls off after 12 hours of cleaning at a stirring temperature of 95°C, the reaction is completed.

[0096] Step 3, put the membrane obtained in step 2 into 90 kg of 30% potassium chloride solution and stir and clean it. Under the condition of stirring temperature of 105°C, clean it for 6 hours, and the reaction is completed;

[0097] Step 4, put the membrane obtained in step 3 into 90 kg of hydrochloric acid for stirring and cleaning. Stir and clean for 6 hours at a stirring temperature of 105°C;

[0098] Step 5: Place the membrane obtained in step 4 into 90 kg of 35% alkaline solution for stirring and cleaning. The solute of the alkaline solution is a mixture of potassium hydroxide and sodium hydroxide in a mass ratio of 1:2, and stir at a stirring temperature of 110° C. for 6 hours.

[0099] Step 6: After the membrane obtained in step 5 is washed to neutrality, 30 kg of ethanol, 15 kg of isopropanol, 10 kg of n-propanol and 35 kg of water are placed in a reactor together with the treated membrane. After the reactor is sealed, nitrogen is used to replace the air as a protective gas, and then heating and stirring are performed. The stirring temperature is controlled at 250° C. and the stirring is performed for 8 hours until the membrane is completely dissolved, and the reaction is completed.

[0100] Step 7, after the reaction is completed, open the reactor, filter the reaction solution, remove the waste chlor-alkali membrane intermediate reinforcement layer, and then centrifuge the solution to obtain a supernatant that is a polymer solution containing perfluorosulfonic acid resin.

[0101] After the prepared polymer solution is dried, the EW value of the obtained resin product is not higher than 1500 g / mol.

[0102] The purity of the perfluorosulfonic acid resin prepared in Example 3 is above 99%. Since the raw material contains a reinforcing layer which is not within the recovery range, and the reinforcing layer accounts for nearly 30% of the raw material, the yield of the perfluorosulfonic acid resin is 65%.

[0103] Comparative Example 1

[0104] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 1 is different from that in Example 1 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 1 does not use alcohol for cleaning, but directly puts the broken membrane into potassium chloride solution for cleaning.

[0105] Comparative Example 2

[0106] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 2 is different from that in Example 1 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 2 directly acid washes the membrane after alcohol washing, i.e., potassium chloride solution is not used for cleaning.

[0107] Comparative Example 3

[0108] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 3 is different from that in Example 1 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 3 directly performs alkali washing on the membrane after salt washing, i.e., no acid solution is used for washing.

[0109] Comparative Example 4

[0110] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 4 is different from that in Example 1 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 4 directly cleans the membrane after acid washing to neutrality, i.e., no alkaline solution is used for cleaning.

[0111] The above comparative example recycled resin was tested, and the test results are shown in Table 1:

[0112] Table 1

[0113]

[0114] As can be seen from Table 1: In Comparative Example 1, alcohol solvent was not used for cleaning, and there was no swelling process to weaken the interaction between the resin and the reinforcement layer, resulting in a decrease in the dissolution efficiency of the resin in the subsequent reactor, and the recovery rate was only 62%; In Comparative Example 2, salt solution was not used for cleaning, resulting in Ce ions or additives being doped inside the resin. The residual additives easily turned the resin into brown-black in the subsequent cleaning, and the residual large-radius ions would cause the color of the resin to change and deepen when the subsequent polymer solution was dried; In Comparative Example 3, acid solution was not used for cleaning, and a lot of working condition contact ions would remain on the discarded membrane. The residue of metal ions and large radius ions will cause the color of the resin to change and deepen to brownish yellow when the subsequent polymer solution is dried; in Comparative Example 4, no alkaline solution is used for cleaning, resulting in the waste membrane entering the reactor being acidic, which will accelerate the corrosion of the reactor wall under high temperature and high pressure conditions, resulting in the mixing of metal impurities in the polymer solution, and the residue of large radius ions will cause the color of the resin to change and deepen to brownish yellow when the subsequent polymer solution is dried. At the same time, the acidic perfluorosulfonic acid resin is easily cross-linked to form a gel under high temperature and high pressure conditions, resulting in insolubility, resulting in a reduction in the recovery rate of only 68%;

[0115] Comparative Example 5

[0116] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 5 is different from that in Example 3 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 5 uses water washing to replace the alcohol washing in step (2).

[0117] Comparative Example 6

[0118] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 6 is different from that in Example 3 only in that the stirring temperature during alcohol washing and stirring cleaning in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 6 is 25°C.

[0119] Comparative Example 7

[0120] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 7 is different from that in Example 3 only in that the stirring time during alcohol washing and stirring cleaning in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 7 is 5 hours.

[0121] Comparative Example 8

[0122] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 8 is different from that in Example 3 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 8 uses water washing instead of potassium chloride solution washing.

[0123] Comparative Example 9

[0124] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 9 is different from that in Example 3 only in that the stirring temperature during potassium chloride stirring and washing in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 9 is 25°C.

[0125] Comparative Example 10

[0126] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 10 is different from that in Example 3 only in that: the stirring time of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 10 during potassium chloride stirring and washing is 2 hours.

[0127] Comparative Example 11

[0128] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 11 is different from that in Example 3 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 11 uses water washing instead of hydrochloric acid washing.

[0129] Comparative Example 12

[0130] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 12 is different from that in Example 3 only in that the stirring temperature during the hydrochloric acid stirring and washing in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 12 is 25°C.

[0131] Comparative Example 13

[0132] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 13 is different from that in Example 3 only in that the stirring time during the hydrochloric acid stirring and washing in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 13 is 2 hours.

[0133] Comparative Example 14

[0134] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 14 is different from that in Example 3 only in that the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 14 uses water washing instead of alkali washing.

[0135] Comparative Example 15

[0136] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 15 is different from that in Example 3 only in that the stirring temperature of the alkaline washing in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 15 is 25°C.

[0137] Comparative Example 16

[0138] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 16 is different from that in Example 3 only in that the stirring time of alkaline washing in the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Example 16 is 2 hours.

[0139] The recovery effect of the method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in Comparative Examples 5-16 is shown in Table 2:

[0140] Table 2

[0141] project Appearance Contains metal ions Recovery rate Comparative Example 5 white yellow Zr, Na, K 45％ Comparative Example 6 light white Zr, Na, K 59％ Comparative Example 7 light white Zr, Na, K 61％ Comparative Example 8 Brown and black Ce, Na, K 65％ Comparative Example 9 Brown and black Ce, Na, K 65％ Comparative Example 10 Brown Ce, Na, K 65％ Comparative Example 11 Brown Fe, Al, Cu, Cl, Na, K 65％ Comparative Example 12 Brown Fe, Al, Cu, Cl, Na, K 65％ Comparative Example 13 Brown Fe, Al, Cu, Cl, Na, K 65％ Comparative Example 14 Brown Fe, Mn, Al, Cu, Cr, Na, K 58％ Comparative Example 15 Brown Fe, Mn, Al, Cu, Cr, Na, K 60％ Comparative Example 16 Brown Fe, Mn, Al, Cu, Cr, Na, K 62％

[0142] In Comparative Examples 5-7, because there is a coating containing Zr element on the surface of the waste chlor-alkali membrane, the cleaning solvent is water or the cleaning temperature is room temperature, which cannot make the resin swell and deform, and the bonding force between the coating and the resin and the bonding force between the resin and the reinforcement layer are not weakened, so the final recovery rate is greatly reduced. At the same time, the ability to remove the coating in Comparative Example 5 is the weakest, resulting in a large amount of coating powder mixed in the final recovered resin, which is white and yellow;

[0143] In Comparative Examples 8-10, because Ce metal ion additives and some organic additives are present in the waste chlor-alkali membrane, the solvent is water or the cleaning temperature is room temperature or the cleaning time is insufficient, so that the material exchange in the resin does not proceed or the effect is poor, and the residual additives make the resin turn black when it contacts acid and alkali, and the quality of the recovered resin is poor, which has little effect on the recovery rate;

[0144] In Comparative Examples 11-13, the purpose of acid washing is to remove the chlorine element and metal ion impurities in the waste chlor-alkali membrane. The solvent is water or the room temperature or the reaction time is insufficient, which will cause the metal ions to remain and the resin to change color and deteriorate, but has little effect on the recovery rate.

[0145] In Comparative Examples 14-15, the purpose of alkali washing is to make the resin after acid washing alkaline or neutral, reduce its corrosion to the metal inner wall of the reactor, and at the same time, the alkaline or neutral resin will not cross-link under high temperature and high pressure, which can improve the recovery rate. If water washing is used or the washing temperature is room temperature or the washing time is insufficient, the resin will have different degrees of acidity, which will not only cause the resin to contain metal ions in the end, but also reduce the recovery rate.

[0146] The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes described in the present application is used to study the performance of the recovered perfluorosulfonic acid resin.

[0147] The perfluorosulfonic acid resins recovered from the above Examples 1-3 and Comparative Examples 1-16 were respectively prepared into homogeneous membranes, and their conductivity was tested respectively. The results are shown in Table 3 below.

[0148] Conductivity test method: an electrochemical AC workstation and an AC impedance four-electrode method are used to measure the internal resistance of the water electrolysis membrane. The minimum AC frequency is 1 Hz, the maximum is 1 MHz, the perturbation voltage is 10 mV, and the wet thickness of the membrane is obtained after the test. The test temperature / humidity is 25°C-100% RH. The conductivity is calculated by the membrane conductivity using the formula δ=L / (RS), where δ is the membrane conductivity, L is the membrane thickness, R is the membrane test resistance, and S is the effective test area.

[0149] Table 3

[0150]

[0151]

[0152] In Examples 1-3, perfluorosulfonic acid resin recovered by the method described in the present application was used to recover perfluorosulfonic acid resin from discarded ion exchange composite membranes, discarded ion exchange membrane homogeneous membranes and discarded chlor-alkali membranes, respectively. The conductivity of the proton exchange membrane for flow batteries prepared using the recycled resin was 0.15S / cm, which has good conductive properties and can be fully used in current flow battery products.

[0153] Comparative Examples 1-4, the recycled raw material is a waste ion exchange composite membrane. Compared with the recovery method described in Example 1 of the present application, the perfluorosulfonic acid resin obtained by the recovery method without alcohol washing, salt washing, acid washing, and alkali washing respectively has an electrical conductivity of 0.15S / cm, 0.12S / cm, 0.09S / cm, and 0.07S / cm. Failure to use alcohol washing will lead to a decrease in the recovery rate, but the recovered resin does not have excessive metal ion impurities and still has good conductivity. Although the recovery rate of Comparative Examples 2-4 is improved, the resin contains more metal ion impurities, which occupy the ion channel and reduce the conductivity.

[0154] The recycled resins in Comparative Examples 5-7 contain more coating impurities, resulting in a decrease in the numerical content during film formation and poor conductive properties.

[0155] In Comparative Examples 8-10, only trace amounts of additive impurities remain, and the conductive properties are slightly reduced.

[0156] In Comparative Examples 11-16, the recovered resins all contain a large amount of metal ion impurities, which occupy the ion channels in the resins. The resins have poor proton conduction capabilities and thus poor electrical conductivity.

[0157] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A method for recovering perfluorosulfonic acid resin from waste ion exchange membranes, characterized in that: The following steps are involved: (1) subjecting the waste ion exchange membrane to pretreatment, acid washing, and alkali washing in sequence, and then washing to neutrality; the pretreatment may include alcohol washing and salt washing; (2) Mixing the waste ion exchange membrane obtained in step (1), alkyl alcohol and water.

2. The method for recovering perfluorosulfonic acid resin from waste ion exchange membrane according to claim 1, characterized in that: In step (1), when the waste ion exchange membrane contains a coating, the pretreatment includes alcohol washing and salt washing; When there is no coating in the waste ion exchange membrane, the pre-treatment is salt washing; And / or, in step (1), the cleaning solution used in the salt washing is a sodium chloride aqueous solution and / or a potassium chloride aqueous solution; And / or, the mass concentration of the cleaning solution used in the salt washing is 5%-30%; And / or, the mass of the cleaning solution used in the salt washing is 5-10 times the mass of the waste ion exchange membrane; And / or, the salt washing temperature is 75° C.-110° C., and the salt washing time is 4-6 hours.

3. The method for recovering perfluorosulfonic acid resin from waste ion exchange membrane according to claim 1, characterized in that: In step (1), the cleaning liquid used in the alcohol washing is one or more of methanol, ethanol, n-propanol and isopropanol; And / or, the mass of the cleaning liquid used in the alcohol washing is 5-10 times the mass of the waste ion exchange membrane; And / or, the temperature of the alcohol washing is 60°C-95°C, and the time of the alcohol washing is 8-12h.

4. The method for recovering perfluorosulfonic acid resin from waste ion exchange membrane according to claim 1, characterized in that: In step (1), the cleaning solution used for pickling is hydrochloric acid and / or sulfuric acid; Preferably, the mass fraction of the sulfuric acid is 25%-40%; And / or, the mass of the cleaning liquid used in the pickling is 5-10 times the mass of the waste ion exchange membrane; And / or, the pickling temperature is 90-110° C., and the pickling time is 4-6 hours.

5. The method for recovering perfluorosulfonic acid resin from waste ion exchange membrane according to claim 1, characterized in that: In step (1), the cleaning solution used in the alkali cleaning is an aqueous solution of sodium hydroxide and / or potassium hydroxide; Preferably, the mass concentration of the cleaning solution used in the alkali cleaning is 10%-35%; And / or, the mass of the cleaning solution used in the alkaline cleaning is 5-10 times the mass of the waste ion exchange membrane; And / or, the temperature of the alkali washing is 90° C.-120° C., and the time of the alkali washing is 4-6 hours.

6. The method for recovering perfluorosulfonic acid resin from waste ion exchange membrane according to claim 1, characterized in that: In step (2), the mass ratio of the waste ion exchange membrane to the alkyl alcohol is 1:(3-10); And / or, the mass ratio of the waste ion exchange membrane to the water is 1:(3-10).

7. The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes according to claim 1, characterized in that: In step (2), the alkyl alcohol includes one or more of methanol, ethanol, n-propanol and isopropanol.

8. The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes according to claim 1, characterized in that: In step (2), the mixing temperature is 180°C-250°C, and the mixing time is 8-9h.

9. The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes according to claim 1, characterized in that: In step (2), the mixing is carried out in an inert atmosphere; Preferably, the mixing is performed under a nitrogen atmosphere.

10. The method for recovering perfluorosulfonic acid resin from waste ion exchange membranes according to claim 1, characterized in that: The method further comprises: crushing the waste ion exchange membrane, and then sequentially washing with salt, alcohol, acid and alkali; And / or, the method further comprises: filtering and centrifuging the mixed solution obtained in step (2) to obtain a solution containing perfluorosulfonic acid resin; And / or, the waste ion exchange membrane is a composite membrane or a homogeneous membrane containing perfluorosulfonic acid resin.

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