A method for preparing a high-density semi-homogeneous cation exchange membrane

Abstract

This invention discloses a method for preparing a high-density semi-homogeneous cation exchange membrane. The method comprises: a) mixing EPDM rubber, polyethylene, polyvinylidene fluoride, maleic anhydride, and dicumyl peroxide, and then reactively extruding the mixture using a twin-screw extruder to prepare maleic anhydride-grafted polymer particles; b) impregnating the maleic anhydride-grafted polymer particles with a monomer mixture solution, and then suspending the impregnated particles in an aqueous phase for polymerization, followed by washing to obtain white spheres; c) adding the white spheres, concentrated sulfuric acid, and dichloroethane to a reaction vessel for sulfonation reaction, and then post-processing to obtain strongly acidic cation exchange resin particles; d) drying the strongly acidic cation exchange resin, mixing it with an antioxidant and a crosslinking agent, and then mixing, open-milling, stretching, and hot-pressing to obtain a semi-homogeneous cation exchange membrane. The cation exchange membrane prepared by this invention has a polymer interpenetrating network structure, a uniform and dense internal structure, low membrane surface resistivity, a smooth membrane surface, high strength, and good dimensional stability.

Description

Technical Field

[0001] This invention relates to anion exchange membrane, and more particularly to a method for preparing a highly dense semi-homogeneous cation exchange membrane. Background Technology

[0002] Ion exchange membranes have unique ion exchange characteristics, which enable them to play an increasingly important role in clean production, environmental protection, and energy conversion. They are particularly suitable for the needs of modern industry for new energy sources, energy conservation, reuse of low-grade raw materials, and environmental pollution control, and are also widely used in fields such as seawater desalination.

[0003] Ion exchange membranes can be classified into heterogeneous membranes, semi-homogeneous membranes, and homogeneous membranes based on their structure. Homogeneous ion exchange membranes offer superior performance, but their complex manufacturing process and high technical difficulty limit their production and widespread adoption. Heterogeneous ion exchange membranes, while simpler to produce and less performant overall, are more commonly produced and used in my country. However, due to their non-uniform structure, heterogeneous membranes experience "powdering" during electrodialysis, leading to a sharp decline in membrane performance and necessitating frequent replacement by disassembling the electrodialysis unit. In other words, the structural defects of heterogeneous membranes severely limit their lifespan.

[0004] In order to improve the structure, performance and service life of heterogeneous ion exchange membranes, domestic manufacturers have proposed to develop semi-homogeneous ion exchange membranes to improve membrane performance and extend service life.

[0005] Chinese Patent 201510570174.6 discloses a method for preparing a semi-homogeneous cation exchange membrane. This method involves mixing thermoplastic polyethylene-sulfonated polystyrene-based cation exchange composite resin powder, non-thermoplastic cross-linked sulfonated polystyrene cation exchange resin powder, polyethylene powder, and polyisobutylene powder, followed by internal mixing, open milling, four-roll calendering, and hot-pressing to form a web. The cation exchange membrane in this case is essentially a heterogeneous membrane.

[0006] Chinese Patent Application No. 201510347434.6 discloses a method for the continuous production of polyvinyl chloride (PVC) semi-homogeneous anion and cation exchange membranes. This method involves twin-screw extrusion to form the membrane, adhering a mesh fabric to both sides of the membrane, and then producing rolls of PVC semi-homogeneous ion exchange membranes via four-roll calendering. However, this method adds a large amount of plasticizer during membrane fabrication, which gradually migrates into the material during use, contaminating the material.

[0007] Chinese Patent Application No. 201110417296.3 discloses a method for preparing a polystyrene-based ion exchange alloy membrane. This method involves first melting and granulating a polymer to provide structural support, then immersing it in an excess styrene monomer solution for adsorption. After adsorption for a certain time, excess monomer is removed using a centrifuge. The polymer adsorbed particles are then subjected to suspension polymerization to obtain polymer alloy particles. Sulfonation or chloromethylation / amineation is then used to obtain cation or anion exchange alloy resins. Finally, the resins are obtained through intensive mixing, open milling, sheeting, and hot pressing. The membrane obtained by this patent is a semi-homogeneous ion exchange membrane. However, the sulfonation temperature for preparing the cation exchange resin is as high as 85°C, requiring control of the adsorption time and ratio. Significant differences in adsorption capacity between batches affect product stability.

[0008] Chinese patent applications 201110004257.0, 94106397.6, and 201510002532.3 all employ a base membrane impregnation method to prepare ion exchange membranes. This method typically uses an inert polymer base membrane to impregnate monomers, followed by polymerization, film formation, and functionalization. A typical example is using a polyolefin base membrane to impregnate styrene / divinylbenzene monomers and an initiator, followed by hot pressing, polymerization, sulfonation, or chloromethyl / quaternary ammoniation to prepare cation exchange or anion exchange membranes, respectively. However, the sulfonation temperature needs to be controlled within the range of 60–80°C.

[0009] Tokuyama Soda Co., Ltd. of Japan uses a slurry coating method to manufacture ion exchange membranes. This involves mixing styrene, divinylbenzene, polyvinyl chloride powder, initiator, etc. in a certain proportion, stirring to form a slurry, coating the slurry, hot pressing, and polymerization to first obtain a base membrane. Then, after functionalization, cation exchange membranes and anion exchange membranes are obtained (see Tanaka Ryoshu, translated by Ge Daocai and Ren Qingchun, "Basic Principles and Applications of Ion Exchange Membranes", pp. 8-9, Chemical Industry Press, 2010).

[0010] The ion exchange membranes prepared by the above methods typically involve first forming a base membrane, and then performing a functionalization reaction to introduce ion exchange groups. If the most common styrene / divinylbenzene system is used, membrane burning is prone to occur during sulfonation, making control difficult, especially maintaining the uniformity of ion exchange groups on the surface and inside the entire membrane. The chemical reaction process is complex, requiring highly precise control methods and demanding advanced equipment for hot-pressing polymerization and membrane functionalization, resulting in significant technical challenges. The membranes prepared by both methods are essentially semi-homogeneous ion exchange membranes. Summary of the Invention:

[0011] The purpose of this invention is to address the technical deficiencies in the existing technology by providing a method for preparing a high-density semi-homogeneous cation exchange membrane that can be sulfonated at a lower temperature, has a uniform and dense internal structure, low membrane surface resistance, a smooth membrane surface, no "powder shedding" phenomenon, and good compatibility between its components. The overall performance of the membrane is significantly better than that of heterogeneous membranes.

[0012] The technical solution adopted to achieve the purpose of this invention is:

[0013] The present invention discloses a method for preparing a highly dense semi-homogeneous cation exchange membrane, the implementation steps of which are as follows:

[0014] a) Ethylene propylene diene monomer (EPDM), polyethylene (PE), polyvinylidene fluoride (PVDF), maleic anhydride (MAH), and dicumyl peroxide (DCP) were mixed in a mass ratio of EPDM:PE:PVDF:MAH:DCP = (15-25):(60-80):(5-15):(0.5-1.5):(0.2-1) and then reactively extruded through a twin-screw extruder to prepare maleic anhydride grafted polymer particles ((EPDM / PE / PVDF)-g-MAH);

[0015] b) Impregnate (EPDM / PE / PVDF)-g-MAH polymer particles with a monomer mixture solution containing maleic anhydride, styrene, divinylbenzene and benzoyl peroxide, then perform suspension polymerization of the impregnated particles in an aqueous phase, and obtain white spheres after washing; the mass ratio of maleic anhydride, styrene, divinylbenzene and benzoyl peroxide in the monomer mixture solution is (1~1.5):100:(8~10):(0.2~1);

[0016] c) White spheres, concentrated sulfuric acid, and dichloroethane were added to a reaction vessel in a certain proportion for sulfonation reaction. After the reaction was completed, the granules were subjected to acid treatment, washing, transformation, and washing to obtain strongly acidic cation exchange resin particles.

[0017] d) The strong acid cation exchange resin obtained in step c is dried, and the antioxidant and crosslinking agent are added to a mixer. After the mixture is discharged, it is sent to a two-roll mill. After being milled to a certain thickness, it is fed into a four-roll calender for film stretching to obtain a semi-finished cation exchange membrane. Finally, the semi-finished ion exchange membrane is hot-pressed and coated in a hot press. After cooling, the finished semi-homogeneous cation exchange membrane is obtained.

[0018] Preferably, in step a, the extrusion reaction temperature is 150-200℃.

[0019] Preferably, the Mooney viscosity of the EPDM in step a is 15–70 (ML 125℃ 1±4).

[0020] Preferably, the PVDF in step a has a melting point of 120–145°C.

[0021] Preferably, in step b, the mass ratio of (EPDM / PE / PVDF)-g-MAH polymer particles to styrene in a monomer mixture solution containing maleic anhydride, styrene, divinylbenzene and benzoyl peroxide is 100:70-110.

[0022] Preferably, in step b, the impregnation temperature is 50-65°C until the monomer mixture solution is completely impregnated by the polymer particles.

[0023] Preferably, in step b, the suspension polymerization conditions are as follows: raise the temperature to 80-85°C, carry out suspension polymerization for 6-8 hours, and then raise the temperature to 90-95°C for another 6-8 hours.

[0024] The operation of step c in this invention can be based on the conventional production process of cation exchange resins. Preferably, the sulfonation reaction temperature is 40–50°C, and the reaction time is 5–10 hours. More preferably, step c is specifically implemented as follows: white granules, concentrated sulfuric acid, and dichloroethane are added to a reaction vessel in a mass ratio of 100:650–750:40–60, and the sulfonation reaction is carried out at 40–50°C for 5–10 hours. After the reaction, the granules are subjected to acid treatment, washing, transformation, and washing again to obtain strongly acidic cation exchange resin particles.

[0025] Preferably, the crosslinking agent in step d is a phenolic resin crosslinking agent.

[0026] Preferably, in step d, the antioxidant is antioxidant 1010.

[0027] Preferably, in step d, the mass ratio of the strong acid cation exchange resin drying agent, antioxidant, and crosslinking agent is 100:0.5-2:1-3.

[0028] Preferably, in step d, the mixing temperature is controlled between 145 and 155°C, the mixing time is 15 to 25 minutes, the open mill temperature is controlled between 135 and 140°C, and the rolling temperature is controlled between 130 and 132°C.

[0029] Preferably, in step d, the hot-pressing and covering of the mesh specifically involves placing a layer of polyester mesh on each of the upper and lower surfaces of the semi-finished cation exchange membrane, feeding it into a hot press, controlling the hot-pressing temperature at 158–162°C, the hot-pressing time at 30–35 min, and the hot-pressing pressure at 20–22 MPa.

[0030] Compared with the prior art, the key technologies and beneficial effects of the present invention are as follows:

[0031] 1. Key points of this invention: First, maleic anhydride is grafted onto polymer particles (grafting rate between 0.8% and 1%). Since EPDM and PE are non-polar, while PVDF and sulfonated cross-linked polystyrene are polar, grafting maleic anhydride improves the compatibility of the resin system, which helps to reduce phase separation during film formation and thus improves film performance. Second, maleic anhydride monomer is mixed into the monomer mixture solution, allowing maleic anhydride to participate in the polymerization reaction. This transforms the original styrene-divinylbenzene binary cross-linked white spheres into styrene-maleic anhydride-divinylbenzene ternary cross-linked white spheres, changing the white... The sphere's molecular chain structure increases the space within the molecular chains, allowing sulfonation to proceed at lower temperatures and preventing side reactions during the sulfonation process. Third, the lower sulfonation temperature reduces the corrosive effects of concentrated sulfuric acid on EPDM and PE, preserving the material's plasticity while achieving a higher exchange capacity. Fourth, the incorporation of a phenolic resin crosslinking agent during membrane fabrication allows the phenolic resin to vulcanize the cation exchange resin system (the phenolic resin crosslinking agent reacts with EPDM, causing crosslinking), further crosslinking the entire membrane and improving its density and dimensional stability. Sixth, the suspension polymerization process eliminates the need for polyvinyl alcohol, reducing subsequent wastewater treatment costs.

[0032] 2. The ion exchange resin particles prepared using this invention possess thermoplasticity, thus eliminating the need for additional film-forming aids such as softeners and binders during membrane fabrication, reducing the adverse effects of these aids on membrane performance. Due to the thermoplasticity of these ion exchange resin particles, the essential resin pulverization step in traditional heterogeneous and semi-homogeneous membrane fabrication processes is eliminated, simplifying the process, shortening the process flow, and improving production efficiency. Furthermore, the granular white spheres are easier to clean after the functionalization reaction than powdered granules, saving time and energy.

[0033] 3. This invention uses semi-homogeneous cation exchange membrane technology to prepare ion exchange membranes with thin membrane thickness, high polymer interpenetrating network structure, uniform and dense internal structure (the smaller the solute diffusion coefficient, the better the density), low membrane surface resistance, smooth membrane surface, high strength, good dimensional stability, saving raw material costs, and comprehensive performance superior to heterogeneous ion exchange membranes. Detailed implementation method:

[0034] The technical solution of the present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0035] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained through conventional technical means or commercially available.

[0036] Example 1:

[0037] The preparation method of the high-density semi-homogeneous ion exchange membrane in this example includes the following steps:

[0038] a) First, EPDM rubber (3720P, Mooney viscosity 20 (ML125℃1±4)), polyethylene (LLDPE7042), polyvinylidene fluoride (FR9611, melting point 141℃), maleic anhydride (MAH) and dicumyl peroxide (DCP) are mixed in a mass ratio of 15:80:5:1:0.5. Then, reactive extrusion is performed using a twin-screw extruder (extrusion reaction temperature is 150~200℃) to prepare maleic anhydride grafted polymer particles ((EPDM / LLDPE / PVDF)-g-MAH), with the particle size controlled at about 2~2.5mm.

[0039] b) Prepare a monomer mixture solution according to the following mass ratios: maleic anhydride: styrene: divinylbenzene (content is 63%): benzoyl peroxide = 1.5: 100: 15.87: 1. Then, take polymer particles according to the following mass ratios: (EPDM / LLDPE / PVDF)-g-MAH polymer particles: styrene = 100: 90. Impregnate the monomer mixture solution at a temperature of 65°C until the monomer mixture solution is completely impregnated by the polymer particles. Add water with a weight of 4 times that of the polymer particles, raise the temperature to 83°C, and carry out suspension polymerization. After polymerization for 6 hours, raise the temperature to 93°C and polymerize for another 6 hours to end the polymerization reaction. After washing several times, white balls are obtained.

[0040] c) After drying the white spheres, pulverize them to between 10 and 20 mesh. Referring to the production method of cation exchange resin, add the white spheres, concentrated sulfuric acid, and dichloroethane to the reactor at a mass ratio of 100:700:50. The sulfonation temperature is 45℃ and the sulfonation time is 8 hours. After the reaction, the granules are subjected to acid washing (with sulfuric acid concentrations of 80%, 70%, 60%, 45%, 30%, and 10%, decreasing stepwise), washing, and transformation (adding liquid alkali until the washing water is alkaline, stopping the addition of liquid alkali, and stirring for half an hour until it is still alkaline, which is considered the end of the transformation). After washing, strong acidic cation exchange resin particles are obtained.

[0041] d) Dry the cation exchange resin. Add the cation exchange resin, antioxidant 1010, and phenolic resin crosslinking agent (SP1045) in a mass ratio of 100:1:2 to a Banbury mixer. Maintain the mixing temperature between 145 and 155°C for 20 minutes. After mixing, feed the material into a two-roll mill. Maintain the two-roll mill temperature between 135 and 140°C. After achieving a certain thickness, feed the material into a four-roll calender for film stretching. Maintain the calendering temperature at 130°C. The membrane thickness is controlled between 0.22 and 0.24 mm at a temperature between ~132℃ to obtain a semi-finished cation exchange membrane. Finally, a layer of polyester mesh is placed on the upper and lower surfaces of the semi-finished cation exchange membrane, and it is sent into a hot press. The hot pressing temperature is controlled between 158 and 162℃, the hot pressing time is 30 minutes, and the hot pressing pressure is 20 to 22 MPa. After the hot pressing is completed, water is quickly circulated to cool down, and the finished cation exchange membrane with a thickness of 0.24 to 0.26 mm is obtained.

[0042] Example 2:

[0043] The preparation method of the high-density semi-homogeneous ion exchange membrane in this example includes the following steps:

[0044] a) First, EPDM rubber (3745P, Mooney viscosity 45 (ML125℃1±4)), polyethylene (HDPETR144), polyvinylidene fluoride (FR9613, melting point 134℃), maleic anhydride (MAH) and dicumyl peroxide (DCP) are mixed in a mass ratio of 20:70:10:1:0.5. Then, reactive extrusion is performed using a twin-screw extruder (extrusion reaction temperature is 150~200℃) to prepare maleic anhydride grafted polymer particles ((EPDM / HDPE / PVDF)-g-MAH), with the particle size controlled at about 2~2.5mm.

[0045] b) Prepare a monomer mixture solution according to the following mass ratios: maleic anhydride: styrene: divinylbenzene (content is 63%): benzoyl peroxide = 1:100:12.7:1. Then, take polymer particles according to the following mass ratios: (EPDM / HDPE / PVDF)-g-MAH polymer particles: styrene = 100:75. Impregnate the monomer mixture solution at a temperature of 65℃ until the monomer mixture solution is completely impregnated by the polymer particles. Add water with a weight of 4 times that of the polymer particles, raise the temperature to 83℃, and carry out suspension polymerization. After polymerization for 6 hours, raise the temperature to 93℃ and polymerize for another 6 hours to end the polymerization reaction. After washing several times, white balls are obtained.

[0046] c) After drying the white spheres, pulverize them to between 10 and 20 mesh. Referring to the production method of ion exchange resin, add the white spheres, concentrated sulfuric acid, and dichloroethane to the reactor at a mass ratio of 100:700:50. The sulfonation temperature is 40℃ and the sulfonation time is 10h. After the reaction, the granules are subjected to acid washing (with sulfuric acid concentrations of 80%, 70%, 60%, 45%, 30%, and 10%, decreasing stepwise), washing, and transformation (adding liquid alkali until the washing water is alkaline, stopping the addition of liquid alkali, and stirring for half an hour until it is still alkaline, which is considered the end of the transformation). After washing, strong acidic cation exchange resin particles are obtained.

[0047] d) Dry the cation exchange resin. The cation exchange resin, antioxidant 1010, and phenolic resin crosslinking agent (HY-2055) are added to a Banbury mixer in a mass ratio of 100:1:3. After Banbury mixing, the mixture is fed into a two-roll mill. After being milled to a certain thickness, it is fed into a four-roll calender for film stretching to obtain a semi-finished ion exchange membrane. The Banbury mixing temperature is controlled between 145 and 155°C, and the mixing time is 20 minutes. The two-roll calendering temperature is controlled between 135 and 140°C. During the process, the calendering temperature is controlled between 130 and 132°C, and the film thickness is controlled between 0.22 and 0.24 mm. Finally, a layer of polyester mesh is placed on the upper and lower surfaces of the semi-finished ion exchange membrane, and it is sent into a hot press. The hot pressing temperature is controlled between 158 and 162°C, the hot pressing time is 30 minutes, and the hot pressing pressure is 20 to 22 MPa. After the hot pressing is completed, water is quickly circulated to cool down, and the finished cation exchange membrane is obtained with a thickness of 0.24 to 0.26 mm.

[0048] Example 3:

[0049] The preparation method of the high-density semi-homogeneous ion exchange membrane in this example includes the following steps:

[0050] a) First, EPDM rubber (3092PM, Mooney viscosity 61 (ML125℃1±4)), polyethylene (LLDPE7042), polyvinylidene fluoride (FR9613, melting point 134℃), maleic anhydride (MAH) and dicumyl peroxide (DCP) are mixed in a mass ratio of 25:60:15:1:0.5. Then, reactive extrusion is performed using a twin-screw extruder (extrusion reaction temperature is 150~200℃) to prepare maleic anhydride grafted polymer particles ((EPDM / LLDPE / PVDF)-g-MAH), with the particle size controlled at about 2~2.5mm.

[0051] b) Prepare a monomer mixture solution according to the following mass ratios: maleic anhydride: styrene: divinylbenzene (content 63%): benzoyl peroxide = 1.5: 100: 12.7: 1. Then, take polymer particles according to the following mass ratios: (EPDM / LLDPE / PVDF)-g-MAH polymer particles: styrene = 100: 110. Impregnate the monomer mixture solution at a temperature of 65°C until the monomer mixture solution is completely impregnated by the polymer particles. Add water at a ratio of 4 times the weight of the polymer particles, raise the temperature to 83°C, and carry out suspension polymerization for 6 hours. After polymerization, raise the temperature to 93°C and polymerize for another 6 hours to end the polymerization reaction. After multiple washings, white balls are obtained.

[0052] c) After drying the white spheres, pulverize them to between 10 and 20 mesh. Referring to the production method of ion exchange resin, add the white spheres, concentrated sulfuric acid, and dichloroethane to the reactor at a mass ratio of 100:700:50. The sulfonation temperature is 50℃ and the sulfonation time is 6 hours. After the reaction, the granules are subjected to acid washing (with sulfuric acid concentrations of 80%, 70%, 60%, 45%, 30%, and 10%, decreasing stepwise), washing, and transformation (adding liquid alkali until the washing water is alkaline, stopping the addition of liquid alkali, and stirring for half an hour until it is still alkaline, which is considered the end of the transformation). After washing, strong acidic cation exchange resin particles are obtained.

[0053] d) Dry the cation exchange resin. The cation exchange resin, antioxidant 1010, and phenolic resin crosslinking agent (SP1045) are added to a Banbury mixer in a mass ratio of 100:1:1. After the Banbury mixer discharge, the mixture is fed into a two-roll mill. After being milled to a certain thickness, it is fed into a four-roll calender for film stretching to obtain a semi-finished ion exchange membrane. The Banbury mixer temperature is controlled between 145 and 155°C, and the Banbury mixer time is 20 minutes. The two-roll calender temperature is controlled between 135 and 140°C. During the process, the calendering temperature is controlled between 130 and 132°C, and the film thickness is controlled between 0.22 and 0.24 mm. Finally, a layer of polyester mesh is placed on the upper and lower surfaces of the semi-finished ion exchange membrane, and it is sent into a hot press. The hot pressing temperature is controlled between 158 and 162°C, the hot pressing time is 30 minutes, and the hot pressing pressure is 20 to 22 MPa. After the hot pressing is completed, water is quickly circulated to cool down, and the finished cation exchange membrane is obtained with a thickness of 0.24 to 0.26 mm.

[0054] Comparative Example 1:

[0055] Comparing Comparative Example 1 with Example 1 demonstrates that the introduction of maleic anhydride in steps a and b has a significant impact on the performance of the final cation exchange membrane, specifically by increasing ion exchange capacity and reducing sheet resistance.

[0056] The preparation method of the semi-homogeneous ion exchange membrane in this example includes the following steps:

[0057] a) First, mix EPDM rubber (3720P, Mooney viscosity 20 (ML125℃1±4)), polyethylene (LLDPE7042) and polyvinylidene fluoride (FR9611, melting point 141℃) in a mass ratio of 25:50:25, and then perform reactive extrusion (extrusion reaction temperature 150~200℃) through a twin-screw extruder to prepare polymer particles ((PDM / LLDPE / PVDF), with particle size controlled at about 2~2.5mm;

[0058] b) Prepare a monomer mixture solution according to the following mass ratios: styrene: divinylbenzene (content is 63%): benzoyl peroxide = 100: 15.87: 1. Then, take polymer particles according to the following mass ratios (EPDM / LLDPE / PVDF): polymer particles: styrene = 100: 90. Impregnate the monomer mixture solution at a temperature of 65°C until the monomer mixture solution is completely impregnated by the polymer particles. Add water with a weight of 4 times that of the polymer particles, raise the temperature to 83°C, and carry out suspension polymerization. After polymerization for 6 hours, raise the temperature to 93°C and polymerize for another 6 hours to end the polymerization reaction. After washing several times, white balls are obtained.

[0059] c) After drying the white spheres, pulverize them to between 10 and 20 mesh. Referring to the production method of ion exchange resin, add the white spheres, concentrated sulfuric acid, and dichloroethane to the reactor simultaneously. The sulfonation temperature is 45℃ and the sulfonation time is 8 hours. After the reaction, the spheres are subjected to acid washing (sulfuric acid concentrations of 80%, 70%, 60%, 45%, 30%, and 10%, decreasing stepwise), washing, and transformation (adding liquid alkali until the washing water is alkaline, stopping the addition of liquid alkali, and stirring for half an hour until it is still alkaline, which is considered the end of the transformation). After washing, strong acidic cation exchange resin particles are obtained.

[0060] d) Dry the cation exchange resin. Add the cation exchange resin, antioxidant 1010, and phenolic resin crosslinking agent (SP1045) in a mass ratio of 100:1:2 to a Banbury mixer. Maintain the mixing temperature between 145 and 155°C for 20 minutes. After mixing, feed the material into a two-roll mill. Maintain the two-roll mill temperature between 135 and 140°C. After achieving a certain thickness, feed the material into a four-roll calender for film stretching. Maintain the calendering temperature at 130°C. The membrane thickness is controlled between 0.22 and 0.24 mm at a temperature between ~132℃ to obtain a semi-finished cation exchange membrane. Finally, a layer of polyester mesh is placed on the upper and lower surfaces of the semi-finished cation exchange membrane, and it is sent into a hot press. The hot pressing temperature is controlled between 158 and 162℃, the hot pressing time is 30 minutes, and the hot pressing pressure is 20 to 22 MPa. After the hot pressing is completed, water is quickly circulated to cool down, and the finished cation exchange membrane with a thickness of 0.24 to 0.26 mm is obtained.

[0061] Comparative Example 2:

[0062] Comparing Comparative Example 2 with Example 1 demonstrates that the introduction of a phenolic resin crosslinking agent in step d has a significant impact on the performance of the final cation exchange membrane, specifically by reducing the water content and improving the uniformity and density of the internal structure.

[0063] The preparation method of the semi-homogeneous ion exchange membrane in this example includes the following steps:

[0064] a) First, EPDM rubber (3720P, Mooney viscosity 20 (ML125℃1±4)), polyethylene (LLDPE7042), polyvinylidene fluoride (FR9611, melting point 141℃), maleic anhydride (MAH) and dicumyl peroxide (DCP) are mixed in a mass ratio of 25:50:25:1:0.5. Then, reactive extrusion is performed using a twin-screw extruder (extrusion reaction temperature is 150~200℃) to prepare maleic anhydride grafted polymer particles ((EPDM / LLDPE / PVDF)-g-MAH), with the particle size controlled at about 2~2.5mm.

[0065] b) Prepare a monomer mixture solution according to the following mass ratios: maleic anhydride: styrene: divinylbenzene (content is 63%): benzoyl peroxide = 1.5: 100: 15.87: 1. Then, take polymer particles according to the following mass ratios: (EPDM / LLDPE / PVDF)-g-MAH polymer particles: styrene = 100: 90. Impregnate the monomer mixture solution at a temperature of 65°C until the monomer mixture solution is completely impregnated by the polymer particles. Add water with a weight of 4 times that of the polymer particles, raise the temperature to 83°C, and carry out suspension polymerization. After polymerization for 6 hours, raise the temperature to 93°C and polymerize for another 6 hours to end the polymerization reaction. After washing several times, white balls are obtained.

[0066] c) After drying the white spheres, pulverize them to between 10 and 20 mesh. Referring to the production method of ion exchange resin, add the white spheres, concentrated sulfuric acid, and dichloroethane to the reactor simultaneously. The sulfonation temperature is 45℃ and the sulfonation time is 8 hours. After the reaction, the spheres are subjected to acid washing (sulfuric acid concentrations of 80%, 70%, 60%, 45%, 30%, and 10%, decreasing stepwise), washing, and transformation (adding liquid alkali until the washing water is alkaline, stopping the addition of liquid alkali, and stirring for half an hour until it is still alkaline, which is considered the end of the transformation). After washing, strong acidic cation exchange resin particles are obtained.

[0067] d) Dry the cation exchange resin. Add the cation exchange resin and antioxidant 1010 in a 100:1 mass ratio to a mixer. After mixing, send the mixture to a two-roll mill. After two-roll milling to a certain thickness, send it to a four-roll calender for film stretching to obtain a semi-finished ion exchange membrane. The mixing temperature is controlled between 145 and 155°C for 20 minutes. The two-roll mill temperature is controlled between 135 and 140°C. The calendering temperature is controlled between 130 and 132°C. The film thickness is controlled between 0.22 and 0.24 mm. Finally, place a layer of polyester mesh on the upper and lower surfaces of the semi-finished ion exchange membrane and send it to a hot press. The hot pressing temperature is controlled between 158 and 162°C for 30 minutes. The hot pressing pressure is 20 to 22 MPa. After hot pressing, quickly circulate water to cool down, and the finished cation exchange membrane with a thickness of 0.24 to 0.26 mm is obtained.

[0068] The performance of the prepared cation exchange membrane was measured according to the test method described in the national standard (HY / T 166.1-2013), and the results are shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072] The above description is only a specific embodiment of the present invention, but the structural features and core meaning of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered within the protection scope of the present invention.

Claims

1. A method for preparing a semi-homogeneous cation exchange membrane, wherein the preparation method comprises the following steps: a) Ethylene propylene diene monomer (EPDM), polyethylene, polyvinylidene fluoride (PVDF), maleic anhydride, and dicumyl peroxide (DPO) are mixed in a mass ratio of EPDM:PE:PVDF:maleic anhydride:DPO = (15~25):(60~80):(5~15):(0.5~1.5):(0.2~1) and then reactively extruded using a twin-screw extruder to prepare maleic anhydride-grafted polymer particles. b) Maleic anhydride-grafted polymer particles are impregnated with a monomer mixture solution containing maleic anhydride, styrene, divinylbenzene, and benzoyl peroxide. The impregnated particles are then subjected to suspension polymerization in an aqueous phase, and white spheres are obtained after washing. The mass ratio of maleic anhydride, styrene, divinylbenzene, and benzoyl peroxide in the monomer mixture solution is (1~1.5):100:(8~10):(0.2~1). c) White spheres, concentrated sulfuric acid, and dichloroethane were added to a reaction vessel in a certain proportion for sulfonation reaction. After the reaction was completed, the granules were subjected to acid treatment, washing, transformation, and washing to obtain strongly acidic cation exchange resin particles. d) The strong acid cation exchange resin obtained in step c is dried, and the antioxidant and crosslinking agent are added to a mixer. After the mixture is discharged, it is sent to a two-roll mill. After being milled to a certain thickness, it is fed into a four-roll calender for film stretching to obtain a semi-finished cation exchange membrane. Finally, the semi-finished ion exchange membrane is hot-pressed and coated in a hot press. After cooling, the finished cation exchange membrane is obtained.

2. The production method according to claim 1, characterized by: The Mooney viscosity of the EPDM rubber in step a is 15~70 (ML125℃ 1+4).

3. The production method according to claim 1, wherein: The melting point of the polyvinylidene fluoride in step a is 120~145℃.

4. The production method according to any one of claims 1 to 3, characterized by: In step a, the extrusion reaction temperature is 150~200℃.

5. The production method according to claim 1, wherein: In step b, the mass ratio of maleic anhydride grafted polymer particles to styrene in a monomer mixture solution containing maleic anhydride, styrene, divinylbenzene, and benzoyl peroxide is 100:70~110.

6. The production method according to claim 1 or 5, characterized by: In step b, the impregnation temperature is 50~65℃ until the monomer mixture solution is completely impregnated by the polymer particles. The suspension polymerization conditions are as follows: raise the temperature to 80~85℃, carry out suspension polymerization for 6~8 hours, and then raise the temperature to 90~95℃ for another 6~8 hours.

7. The production method according to claim 1, wherein: In step c, the sulfonation reaction temperature is 40~50℃ and the reaction time is 5~10h.

8. The production method according to claim 1, wherein: The crosslinking agent in step d is a phenolic resin crosslinking agent.

9. The production method according to claim 1, wherein: In step d, the mass ratio of the strong acid cation exchange resin, antioxidant, and crosslinking agent is 100:0.5~2:1~3.

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