A homogeneous membrane and its preparation method

Abstract

The present invention belongs to the technical field of ion exchange membranes, and specifically relates to a homogeneous membrane and a preparation method thereof. The preparation method of the homogeneous cation membrane comprises: sulfonation modification of a mesh cloth to obtain a cation membrane mesh cloth; laying the cation membrane mesh cloth flat on a PET film, uniformly coating the cation membrane slurry on the mesh cloth and the PET film, and separating the PET film after drying to obtain a homogeneous cation membrane; wherein the cation membrane slurry is partially sulfonated polystyrene, and the dehydrating agent is completely dissolved in a good solvent. The preparation method of the homogeneous anion membrane comprises: chloromethylation modification of a mesh cloth to obtain anion membrane mesh cloth; laying the anion membrane mesh cloth flat on a PET film, uniformly coating the anion membrane slurry on the mesh cloth and the PET film, and separating the PET film after drying to obtain a homogeneous anion membrane; wherein the anion membrane slurry is partially chloromethylated polystyrene, a toughening polymer, a double-bond monotertiary amine, a double-bond monotertiary amine, and an initiator is completely dissolved in a good solvent. The homogeneous membrane of the present invention has high strength, low permeability, good dimensional stability, and longer service life.

Description

Technical Field

[0001] The invention belongs to the technical field of ion exchange membranes, and in particular relates to a homogeneous membrane and a preparation method thereof. Background Art

[0002] Homogeneous membranes are mainly divided into homogeneous cation exchange membranes and homogeneous anion exchange membranes. Homogeneous cation exchange membranes contain acidic groups and are polymer membranes that are selectively permeable to cations; homogeneous anion exchange membranes contain basic groups and are polymer membranes that are selectively permeable to anions.

[0003] There are two main types of homogeneous membranes on the market. One is the impregnation type, which uses an impregnable film or porous film, which is made into a base membrane through impregnation polymerization, and then produced through sulfonation and amination. This type of membrane generally has poor dimensional stability during use and relatively low strength. Long-term use will lead to a high permeability due to dimensional changes. The other type uses a high-strength mesh as a support, and forms a polymerizable monomer and mesh together to form a polymerized membrane, which has high strength and good dimensional stability, but there will be gaps between the support and the resin, and the permeability is also relatively high.

[0004] Therefore, the art urgently needs to develop a homogeneous ion exchange membrane with high strength, good dimensional stability, low permeability and long service life, which is conducive to the preparation of high-purity products and effectively reduces operating costs. Summary of the invention

[0005] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to at least solve one or more of the above-mentioned problems in the prior art. In other words, one of the objects of the present invention is to provide a homogeneous membrane and a preparation method thereof that meet one or more of the above-mentioned needs.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A method for preparing a homogeneous membrane comprises the following steps: (1) Sulfonation modification of the mesh to obtain a cationic membrane mesh; (2) Laying the cationic membrane mesh on the PET film, evenly coating the cationic membrane slurry on the mesh and the PET film, and separating the PET film after drying to obtain a homogeneous cationic membrane; The cation membrane slurry is partially sulfonated polystyrene, and the dehydrating agent is completely dissolved in a good solvent.

[0007] As a preferred embodiment, the dehydrating agent is selected from at least one of acidic montmorillonite, phosphotungstic acid silicon oxide, and phosphorus pentoxide; The good solvent is selected from at least one of dichloroethane, N,N-dimethylformamide, dimethylacetamide and dimethyl sulfoxide.

[0008] As a preferred embodiment, in step (2), the drying process includes: first drying at 60-90°C for 2-10 hours, and then drying at 90-150°C for 2-10 hours; The preparation process of partially sulfonated polystyrene includes: The sulfonation liquid is added into the polystyrene solution to carry out the sulfonation reaction, the sulfonation reaction temperature is 30-90°C, and the reaction time is 0.5-10 hours; The feed liquid after the sulfonation reaction is completed is added into an ice-water mixture, and the precipitated solid is filtered, washed and dried to obtain partially sulfonated polystyrene.

[0009] As a preferred solution, the step (1) specifically includes the following steps: (11) Prepare an impregnation liquid with styrene, divinylbenzene and initiator, heat it to 30-70°C, completely immerse the mesh in the impregnation liquid, and take out the mesh after soaking for 5-120 minutes. After removing the excess impregnation liquid, lay it flat between two PET films, and seal the edges of the PET films with tape; (12) placing the PET film and the mesh together in a hot water tank for polymerization reaction, taking them out from the hot water tank after the polymerization reaction is completed, and separating the mesh from the PET film; The hot water temperature of the hot water tank is 65-90°C, and the reaction time is 1-15 hours; (13) The separated mesh is placed in the sulfonation liquid of the sulfonation reaction tank for sulfonation reaction. After the sulfonation reaction is completed, the mesh is washed and dried; The temperature of the sulfonation reaction is 30-90°C, and the reaction time is 0.3-10 hours.

[0010] As a preferred solution, the mesh is a woven fabric, a non-woven fabric or a porous film, and is made of low-density polyethylene LDPE, high-density polyethylene HDPE, polyvinyl chloride PVC, polyphenylene sulfide PPS or polyetheretherketone PEEK.

[0011] As a preferred embodiment, in step (11), the impregnation liquid is heated to 40-60° C., and the immersion time is 10-60 minutes; In step (12), the hot water temperature of the hot water tank is 65-80° C., and the reaction time is 3-10 hours; In the step (13), the temperature of the sulfonation reaction is 30-80° C., and the reaction time is 0.3-4 hours.

[0012] The present invention also provides a method for preparing a homogeneous membrane, comprising the following steps: (a) Chloromethylation modification of the mesh to obtain a cationic membrane mesh; (b) laying the anion membrane mesh on the PET film, evenly coating the anion membrane slurry on the mesh and the PET film, drying and separating the PET film to obtain a homogeneous anion membrane; The anion membrane slurry is partially chloromethylated polystyrene, toughening polymer, secondary amine containing double bonds, secondary amine not containing double bonds, and the initiator is completely dissolved in a good solvent.

[0013] As a preferred solution, the step (a) specifically comprises the following steps: (a1) preparing an impregnation liquid with styrene, divinylbenzene and initiator, heating it to 30-70°C, and then completely immersing the mesh in the impregnation liquid. After immersing for 5-120 minutes, the mesh is taken out, and after removing the excess impregnation liquid, it is laid flat between two PET films, and the edges of the PET films are sealed with tape; (a2) placing the PET film and the mesh together in a hot water tank for polymerization reaction, taking them out from the hot water tank after the polymerization reaction is completed, and separating the mesh from the PET film; The hot water temperature of the hot water tank is 65-90°C, and the reaction time is 1-15 hours; (a3) The separated mesh is placed in chloromethyl ether in a chloromethylation reaction tank for chloromethylation reaction at a reaction temperature of 20-60°C for a reaction time of 0.1-20 hours. After the chloromethylation reaction is completed, the mesh is washed and dried, and then immersed in a double-bond monotertiary amine solution at a temperature of 20-60°C for a time of 0.1-10 hours. After the immersion is completed, the mesh is taken out to remove excess double-bond monotertiary amine solution on the surface of the membrane, and then dried at 40-90°C for 2-10 hours.

[0014] As a preferred embodiment, the preparation process of the partially chloromethylated polystyrene comprises: Adding chloromethyl ether to a polystyrene solution for chloromethylation reaction at a reaction temperature of 20-60° C. for a reaction time of 1-20 hours to obtain a chloromethylation-completed feed solution; The chloromethylated feed liquid is added into methanol, and the precipitated solid is filtered, washed and dried to obtain partially chloromethylated polystyrene.

[0015] As a preferred embodiment, in step (b), the double-bond-containing monotertiary amine is selected from at least one of N,N-dimethylallylamine, N,N,2-trimethylallylamine, and 3-(dimethylamino)acrylonitrile; The monotertiary amine without double bonds is selected from at least one of triethanolamine, triethylamine, dodecyldimethyl tertiary amine and dioctylmethyl tertiary amine; The drying temperature is 60-110°C and the drying time is 2-10 hours.

[0016] The present invention also provides a homogeneous membrane, which is a homogeneous cation membrane prepared by the preparation method described in any one of the above schemes or a homogeneous anion membrane prepared by the preparation method described in any one of the above schemes.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The mesh of the homogeneous membrane of the present invention is functionally modified and chemically bonded to the resins of the cation and cationic layers, resulting in tight bonding and low permeability; (2) The present invention adopts a unique cross-linking method of cross-linking after film formation, which makes film formation more controllable and has a higher yield rate; (3) Compared with the existing impregnation-type homogeneous membrane, the homogeneous membrane of the present invention has higher strength, better dimensional stability and longer service life; and the bonding force between the mesh support material and the cation and anode resins is enhanced, effectively reducing the leakage and penetration of solutes directly through the gap between the resin and the mesh, thereby improving product quality and helping to reduce energy consumption. DETAILED DESCRIPTION

[0018] The preparation method of the homogeneous membrane provided by the present invention will be further described below.

[0019] The homogeneous membrane of the present invention is divided into two types: homogeneous cation membrane and homogeneous anion membrane.

[0020] The preparation method of the homogeneous cation membrane of the present invention comprises the following steps: The hydrophilicity of the mesh is improved by impregnation, polymerization, resulfonation or direct sulfonation to prepare a cationic membrane mesh; Using polystyrene as a raw material, partially sulfonating the polystyrene to prepare partially sulfonated polystyrene, dissolving the polystyrene in a solvent after purification, adding a dehydrating agent, and preparing a cationic membrane slurry after dissolution; A cationic membrane mesh is laid on the PET film, and the cationic membrane slurry is evenly coated on the cationic membrane mesh and the PET film. After drying, the PET film is separated to obtain a cationic membrane.

[0021] The preparation method of the homogeneous anion membrane of the present invention comprises the following steps: The mesh is chloromethyl modified by impregnation, polymerization, chloromethylation or direct chloromethylation, and then immersed in a double-bond monotertiary amine solution for a certain period of time, and then taken out and dried to obtain a negative membrane mesh; Using polystyrene as raw material, partially chloromethylating it, dissolving it in a solvent together with a toughening polymer after purification, adding a certain amount of monotertiary amine containing double bonds and monotertiary amine without double bonds and an initiator after dissolution, and mixing them evenly to prepare a negative film slurry; A negative membrane mesh is laid on the PET film, and the negative membrane slurry is evenly coated on the negative membrane mesh and the PET film. After drying, the PET film is separated to obtain a negative membrane.

[0022] The homogeneous cation membrane and the homogeneous anion membrane prepared by the invention have high mechanical strength, stable product size and low permeability.

[0023] Specifically, the preparation method of the homogeneous cation membrane and the homogeneous anion membrane of the present invention comprises the following steps: 1. Preparation of modified mesh; a) Material selection: Select mesh fabrics made of materials impregnated with styrene or capable of direct sulfonation or chloromethylation. The mesh fabrics may be in the form of woven fabrics, non-woven fabrics, or porous films. The materials include but are not limited to low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyvinyl chloride (PVC), polyphenylene sulfide (PPS) or polyetheretherketone (PEEK), bisphenol A polysulfone (PSU), polyethersulfone (PES), etc. b) Impregnation: Prepare an impregnation liquid with styrene, divinylbenzene and initiator, heat it to 30-70℃, and completely immerse the mesh in the impregnation liquid to ensure that the mesh is in full contact with the impregnation liquid. Take out the mesh after soaking for 5-120 minutes, remove the excess impregnation liquid, and lay it flat between two PET films. Seal the edges of the PET with tape; The weight ratio of styrene, divinylbenzene and initiator is 1:0.01-0.4:0.001-0.1; the initiator is mainly a substance capable of forming free radicals, selected from organic peroxides such as lauroyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisobutyrate, benzoyl peroxide BPO, di-tert-butyl peroxide, and at least one of azo organic substances such as azobisisobutyronitrile AIBN, azobisisoheptanenitrile ABVN, and dimethyl azobisisobutyrate AIBME; c) Polymerization: Put the PET film and mesh together into a hot water tank for polymerization reaction. The hot water temperature is 65-90°C and the reaction time is 1-15 hours; d) Stripping: After the polymerization is completed, the mesh is taken out from the hot water tank, and the mesh is separated from the PET film. The mesh is used for subsequent reactions; e) Preparation of sulfonation liquid: The sulfonation liquid is a reagent that can introduce sulfonic acid groups on the benzene ring, such as 90-98wt% sulfuric acid, chlorosulfonic acid, a mixture of chlorosulfonic acid and sulfuric acid in a weight ratio of 1:0.1-9, a mixture of acetic anhydride and sulfuric acid in a weight ratio of 1:0.1-1, etc.; f) Sulfonation: first add the sulfonation liquid into the sulfonation reaction tank, then place the mesh cloth of step d) in the sulfonation reaction tank for sulfonation reaction, the reaction temperature is 30-90°C, the reaction time is 0.3-10 hours, and the mesh cloth after sulfonation is first washed in low concentration acid, then washed with clean water and dried for use; at this point, the preparation of the cationic membrane mesh cloth is completed.

[0024] g) Chloromethylation: Place the mesh cloth of step d) in a chloromethylation reaction tank, and then inject chloromethyl ether to carry out chloromethylation reaction, the reaction temperature is 20-60°C, the reaction time is 0.1-20 hours, after the reaction is completed, wash with clean water, dry, and then soak it in a double bond monotertiary amine solution at a temperature of 20-60°C for 0.2-10 hours, take it out after completion, remove the excess double bond monotertiary amine solution on the membrane surface, and then dry it at 40-90°C for 2-10 hours; at this point, the preparation of the anion membrane mesh cloth is completed.

[0025] 2. Preparation of partially sulfonated polystyrene; h) Preparation of polystyrene solution: In a stirred reactor, a certain amount of a good polystyrene solvent, such as dichloroethane (DCE), N,N-dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), etc., is preferably injected. After stirring, an appropriate amount of polystyrene is added and stirred until the polystyrene is completely dissolved for later use; i) Sulfonation: first, in a stirred reactor, add a portion of the polystyrene solution prepared in step h) into the reactor, start stirring and start heating, and after reaching the set temperature, slowly add a certain amount of the sulfonation solution prepared in step e) into the reactor. The sulfonation reaction temperature is 30-90° C. and the reaction time is 0.5-10 hours; j) Partially sulfonated polystyrene: Add an appropriate amount of ice-water mixture into a stirred reactor, start stirring, and slowly pour the sulfonated liquid from step i) into the reactor. Filter and wash the precipitated solid several times, and then dry it for later use. Thus, partially sulfonated polystyrene is prepared.

[0026] 3. Preparation of partially chloromethylated polystyrene; k) Chloromethylation: In a stirred reactor, first add a portion of the polystyrene solution prepared in step h) into the reactor, start stirring and start heating, and after reaching the set temperature, slowly add a certain amount of chloromethyl ether into the reactor. The chloromethylation reaction temperature is 20-60°C and the reaction time is 1-20 hours; l) Partially chloromethylated polystyrene: In a stirred reactor, add an appropriate amount of methanol, start stirring, and slowly pour the chloromethylated solution in step k) into the reactor, filter and wash the precipitated solids several times, and then dry them for later use; thus, partially chloromethylated polystyrene is prepared; 4. Preparation of homogeneous cation membrane; m) Preparation of cationic membrane slurry: In a stirred reactor, a certain amount of sulfonated polystyrene good solvent, such as DCE, DMF, DMAC, DMSO, etc., is preferentially injected. After stirring, an appropriate amount of part of the sulfonated polystyrene in step j) is first added, and then a dehydrating agent is added. After the polystyrene is completely dissolved, a cationic membrane slurry is prepared; Among them, the dehydrating agent is mainly a kind of auxiliary agent that can catalyze the dehydration reaction, including acidic montmorillonite, phosphotungstic acid silicon oxide, phosphorus pentoxide, etc.; the weight ratio of partially sulfonated polystyrene to dehydrating agent in the cation membrane slurry is 1:0.005-0.3; n) Cationic film coating: Spread the cationic film mesh from step f) on the PET film, then evenly coat the cationic film slurry from step m) on the cationic film mesh and the PET film, and then bake at 60-90°C for 2-10 hours, and then bake at 90-150°C for 2-10 hours. After being completely dried, separate the cationic film from the PET film; at this point, the preparation of the homogeneous cationic film is completed.

[0027] 5. Preparation of homogeneous anion membrane; o) Preparation of chloromethylated polystyrene slurry: In a stirred reactor, a certain amount of chloromethylated polystyrene good solvent, such as DCE, DMF, DMAC, DMSO, etc., is preferentially injected, and after stirring, the partially chloromethylated polystyrene in step 1) is first added, and then an appropriate amount of toughening polymer is added, such polymer can be one or a mixture of more than one of ether bond-containing polymers, amides, lipids, rubbers, etc., and then a certain amount of initiator, double bond-containing monotertiary amine, and non-double bond-containing monotertiary amine are added, and after complete dissolution, a negative membrane slurry is prepared; The above-mentioned double-bond-containing monotertiary amine is selected from at least one of N,N-dimethylallylamine, N,N,2-trimethylallylamine, and 3-(dimethylamino)acrylonitrile; The above-mentioned monotertiary amine without double bonds is selected from at least one of triethanolamine, triethylamine, dodecyldimethyl tertiary amine and dioctylmethyl tertiary amine; p) Negative film coating: Spread the negative film mesh from step g) on ​​the PET film, then evenly coat the negative film slurry from step o) on the negative film mesh and the PET film, and then dry at 60-110°C for 2-10 hours. After complete drying, separate the negative film from the PET film; at this point, the preparation of the homogeneous negative film is completed.

[0028] In one embodiment, in the above step b), the impregnation temperature is 40-60° C. and the time is 10-60 minutes; In one embodiment, in the above step c), the polymerization temperature is 65-80° C. and the time is 3-10 hours; In one embodiment, in the above step f), the sulfonation reaction temperature is 30-80° C., and the reaction time is 0.3-4 hours; In one embodiment, in the above step g), the chloromethylation reaction temperature is 20-50°C, and the reaction time is 0.1-8 hours; the soaking temperature of the dried membrane is 30-50°C, and the soaking time is 0.5-6 hours; the drying temperature after soaking is 40-80°C, and the drying time is 4-8 hours; In one embodiment, in the above step i), the sulfonation reaction temperature is 40-80° C., and the reaction time is 2-8 hours; In one embodiment, in the above step k), the chloromethylation reaction temperature is 30-50°C, and the reaction time is 2-8 hours; In one embodiment, in the above step n), the first stage drying temperature is 70-80°C, the drying time is 4-8 hours, and the second stage drying temperature is 100-140°C, the drying time is 4-8 hours; In one embodiment, in the above step p), the drying temperature is 70-90° C. and the drying time is 4-8 hours; The homogeneous membrane and the preparation method thereof of the present invention are further described below by means of specific examples:

[0029] Embodiment 1: The preparation method of the homogeneous cation membrane of this embodiment comprises the following steps: Step 1: Take 1000g of styrene, 140g of divinylbenzene, and 1g of azobisisobutyronitrile, stir and mix at room temperature to prepare an impregnation solution; take a piece of HDPE woven mesh with a thickness of about 0.1mm, completely immerse it in the impregnation solution, heat it to 55°C, and keep it warm for 15 minutes; after the impregnation is completed, take out the mesh, remove the impregnation solution attached to the surface, and lay it flat between two PET films. The edges of the PET films are sealed with tape, and then put it into a hot water tank at 80°C, keep it warm for 5 hours, take it out, separate the mesh from the PET film, and immerse the obtained mesh in 98% concentrated sulfuric acid, react at 80°C for 3 hours, wash it with clean water, and dry it to obtain a cationic mesh; Step 2: In a 500mL three-necked flask, inject 250mL DCE, start stirring, add 10g polystyrene, heat to 50°C in a constant temperature water area, slowly add 98% concentrated sulfuric acid after it is completely dissolved, and control the addition time to add 8mL concentrated sulfuric acid within about 45 minutes. After keeping warm for 5 hours, pour the reaction liquid into ice water for precipitation, filter and wash it several times, and then dry it for use; Step 3: Take 5 g of the partially sulfonated polystyrene prepared in step 2, dissolve it in 45 mL of DMAC, and after it is completely dissolved, add 0.5 g of phosphorus pentoxide, and after it is completely dissolved, prepare a cationic membrane slurry for standby use; Step 4: Lay a piece of PET film on the glass plate, and then lay the cationic membrane mesh obtained in step 1 on the PET film and fix it, then evenly apply the cationic membrane slurry on the mesh and the PET film, and then put it in an oven to dry. The first drying temperature is set to 70°C and the drying time is 5 hours. The second drying temperature is set to 120°C and the drying time is 7 hours. After drying, separate the membrane from the PET film to obtain a homogeneous cationic membrane.

[0030] Embodiment 2: The method for preparing the homogeneous anion membrane of this embodiment comprises the following steps: Step 1: Take 1000g styrene, 140g divinylbenzene, and 1g azobisisobutyronitrile, stir and mix at room temperature to make an impregnation solution; take a piece of HDPE woven mesh with a thickness of about 0.1mm, completely immerse it in the impregnation solution, heat it to 55℃, and keep it warm for 15 minutes; after the impregnation is completed, take out the mesh, remove the impregnation solution attached to the surface, and lay it flat between two PET films, then seal the edges of the PET films with tape, and then put it in a hot water tank at 80℃ and keep it warm. After 5 hours of warming, take it out, separate the mesh from the PET film, soak the obtained mesh in a chloromethyl ether solution, react at 35°C for 3 hours, wash it with clean water, dry it, and then soak it in an N,N-dimethylallylamine solution at a temperature of 20-60°C for 0.2-10 hours. After completion, take it out, remove the excess N,N-dimethylallylamine solution on the surface of the membrane, and then dry it at 40-90°C for 2-10 hours; at this point, the preparation of the negative membrane mesh is completed; Step 2: In a 500mL three-necked flask, inject 250mL DCE, start stirring, add 10g polystyrene and 0.2g SnCl4, heat to 35°C in a constant temperature water area, slowly add chloromethyl ether after complete dissolution, and control the addition time to add 30mL chloromethyl ether within about 65 minutes. After keeping the temperature for 4 hours, pour the reaction liquid into methanol for precipitation, filter and wash it several times, and then dry it for use; Step 3: Take 5 g of partially chloromethylated polystyrene prepared in step 2 and 1 g of polyethersulfone, dissolve them in 54 mL of DMAC, and after they are completely dissolved, add 1.1 mL of N,N-dimethylallylamine, 1.64 g of triethanolamine, and 0.012 g of BPO and mix and dissolve them to prepare a negative membrane slurry for later use; Step 4: Lay a piece of PET film on the glass plate, and then lay the negative membrane mesh obtained in step 1 on the PET film and fix it. Then evenly apply the negative membrane slurry on the mesh and the PET film. After completion, put them in an oven to dry at a temperature of 70-90°C and a drying time of 4-8 hours. After drying, take them out and separate the membrane from the PET film to obtain a homogeneous negative membrane.

[0031] Embodiment 3: The method for preparing a homogeneous cation membrane in this embodiment is different from that in embodiment 1 in that: step 1 is different; Specifically, step 1 selects a 0.1 mm thick PPS mesh, directly soaks the PPS mesh in 93% sulfuric acid, reacts for 20 minutes at 30° C., takes out the mesh, washes the residual acid with clean water, and then dries it for later use; The other steps are the same as in Example 1.

[0032] Embodiment 4: The method for preparing the homogeneous anion membrane of this embodiment is different from that of embodiment 2 in that: step 1 is different; Specifically, in step 1, a 0.1 mm thick PPS mesh is selected, and the PPS mesh is directly immersed in chloromethyl ether. After reacting for 8 minutes at 20° C., the mesh is taken out, the residue is washed with clean water, and then dried for standby use; The other steps are the same as in Example 2.

[0033] Comparative Example 1: The preparation method of the homogeneous cation membrane of this comparative example is different from that of Example 1 in that: Step 1 is different; Specifically, the mesh is not subjected to hydrophilic modification in step 1, but is directly used for membrane preparation; The other steps are the same as in Example 1.

[0034] Comparative Example 2: The preparation method of the homogeneous cation membrane of this comparative example is different from that of Example 1 in that: Step 1 is different; Specifically, after being impregnated, the mesh is not subjected to sulfuric acid sulfonation and is directly used for film making; The other steps are the same as in Example 1.

[0035] Comparative Example 3: The preparation method of the homogeneous anion membrane of this comparative example is different from that of Example 2 in that: Step 1 is different; Specifically, the mesh is not subjected to hydrophilic modification in step 1, but is directly used for membrane preparation; The other steps are the same as in Example 2.

[0036] The homogeneous membranes of Examples 1-4 and Comparative Examples 1-3 are tested below, and the test results are shown in Table 1.

[0037] Table 1 Test results of homogeneous membrane ; Among them, the permeation test method of the homogeneous membrane is as follows: Device: Two hollow cubes with a side length of 8 cm and a wall thickness of 1.2 cm, one side is not sealed and the other side has a small hole with a diameter of 5 mm; place the unsealed surfaces of the two hollow cubes facing each other, making sure that the surface with the small hole faces upward, then place a sealing gasket on each side of the 8*8 cm diaphragm to be tested, and then place it between the hollow cubes, and finally lock the device with an external screw to ensure that the seal is intact and there is no leakage.

[0038] Test method: Place the above device in water at 25°C, place a small magnetic stirrer at the bottom of the device and in the center of the cube, and place a magnet in each of the two cubic containers, then pour preheated 100mL of 4mol / L sodium chloride solution and 100mL of pure water into the two containers respectively, start stirring, stop stirring after 1 hour, and suck out all the solution on the pure water side, then rinse with pure water 3 times and suck out all of it, all of it is injected into a 250mL volumetric flask to make up the volume, and then take 100mL to test the chloride ion concentration to determine the amount of NaCl in the 250mL solution.

[0039] The permeability of the present invention is characterized by the solute permeability coefficient, which is calculated as follows: ; ; in: s is the solute permeability coefficient, unit: mmol / (m 2 ·h·mol / L); q is the total amount of sodium chloride permeated into pure water, in mmol; A is the effective area of ​​the test membrane, in m 2 , generally 0.00314m 2 ; Δ C is the concentration difference, in mol / L, i.e. the initial concentration of the permeate is taken as the concentration difference, which is 4 mol / L here; t is the test duration, in hours, usually 1 hour; c Ag is the concentration of silver nitrate standard solution, in mol / L; V is the amount of silver nitrate standard solution consumed during titration, in mL.

[0040] The membranes of the above-mentioned embodiments 1-4 and comparative examples 1-3 have been tested to have a tensile rupture strength of ≥40MPa and a bursting strength of ≥1.0MPa, which are greatly improved compared to the tensile rupture strength (≤10MPa) and bursting strength (≤0.5Mpa) of the self-developed membranes without mesh support, and this has also correspondingly improved the adaptability and life of the membranes.

[0041] It can be seen from Table 1 that as long as the present invention is implemented under appropriate conditions, the permeability of the homogeneous membrane can be effectively reduced, which is conducive to the preparation of high-purity products and effectively reduces energy consumption and operating costs.

[0042] In view of the numerous embodiments of the scheme of the present invention, the raw materials and dosage involved can be selected according to actual needs within the limited range, and the experimental data of each embodiment is huge and numerous, which is not suitable for listing and explaining one by one here, but the content required to be verified and the final conclusion obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be explained one by one here.

[0043] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, according to the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a homogeneous membrane, characterized in that: The following steps are involved: (1) Sulfonation modification of the mesh to obtain a cationic membrane mesh; (2) Laying the cationic membrane mesh on the PET film, evenly coating the cationic membrane slurry on the mesh and the PET film, and separating the PET film after drying to obtain a homogeneous cationic membrane; The cation membrane slurry is partially sulfonated polystyrene, and the dehydrating agent is completely dissolved in a good solvent.

2. The preparation method according to claim 1, characterized in that: The dehydrating agent is selected from at least one of acidic montmorillonite, phosphotungstic acid silicon oxide, and phosphorus pentoxide; The good solvent is selected from at least one of dichloroethane, N,N-dimethylformamide, dimethylacetamide and dimethyl sulfoxide.

3. The preparation method according to claim 1, characterized in that: In step (2), the drying process includes: first drying at 60-90°C for 2-10 hours, and then drying at 90-150°C for 2-10 hours; The preparation process of partially sulfonated polystyrene includes: The sulfonation liquid is added into the polystyrene solution to carry out the sulfonation reaction, the sulfonation reaction temperature is 30-90°C, and the reaction time is 0.5-10 hours; The feed liquid after the sulfonation reaction is completed is added into an ice-water mixture, and the precipitated solid is filtered, washed and dried to obtain partially sulfonated polystyrene.

4. The preparation method according to claim 1, characterized in that: The step (1) specifically includes the following steps: (11) Prepare an impregnation liquid with styrene, divinylbenzene and initiator, heat it to 30-70°C, completely immerse the mesh in the impregnation liquid, and take out the mesh after soaking for 5-120 minutes. After removing the excess impregnation liquid, lay it flat between two PET films, and seal the edges of the PET films with tape; (12) placing the PET film and the mesh together in a hot water tank for polymerization reaction, taking them out from the hot water tank after the polymerization reaction is completed, and separating the mesh from the PET film; The hot water temperature of the hot water tank is 65-90°C, and the reaction time is 1-15 hours; (13) The separated mesh is placed in the sulfonation liquid of the sulfonation reaction tank for sulfonation reaction. After the sulfonation reaction is completed, the mesh is washed and dried; The temperature of the sulfonation reaction is 30-90°C, and the reaction time is 0.3-10 hours.

5. The preparation method according to claim 1 or 4, characterized in that: The mesh cloth is a woven cloth, a non-woven cloth or a porous film, and is made of low-density polyethylene LDPE, high-density polyethylene HDPE, polyvinyl chloride PVC, polyphenylene sulfide PPS or polyetheretherketone PEEK.

6. A method for preparing a homogeneous membrane, characterized in that: The following steps are involved: (a) Chloromethylation modification of the mesh to obtain a cationic membrane mesh; (b) laying the anion membrane mesh on the PET film, evenly coating the anion membrane slurry on the mesh and the PET film, drying and separating the PET film to obtain a homogeneous anion membrane; The anion membrane slurry is partially chloromethylated polystyrene, toughening polymer, monotertiary amine containing double bonds, monotertiary amine not containing double bonds, and initiator completely dissolved in a good solvent.

7. The preparation method according to claim 6, characterized in that: The step (a) specifically comprises the following steps: (a1) preparing an impregnation liquid with styrene, divinylbenzene and initiator, heating it to 30-70°C, and then completely immersing the mesh in the impregnation liquid. After immersing for 5-120 minutes, the mesh is taken out, and after removing the excess impregnation liquid, it is laid flat between two PET films, and the edges of the PET films are sealed with tape; (a2) placing the PET film and the mesh together in a hot water tank for polymerization reaction, taking them out from the hot water tank after the polymerization reaction is completed, and separating the mesh from the PET film; The hot water temperature of the hot water tank is 65-90°C, and the reaction time is 1-15 hours; (a3) The separated mesh is placed in chloromethyl ether in a chloromethylation reaction tank for chloromethylation reaction at a reaction temperature of 20-60°C for a reaction time of 0.1-20 hours. After the chloromethylation reaction is completed, the mesh is washed and dried, and then immersed in a double-bond monotertiary amine solution at a temperature of 20-60°C for a time of 0.1-10 hours. After the immersion is completed, the mesh is taken out to remove excess double-bond monotertiary amine solution on the surface of the membrane, and then dried at 40-90°C for 2-10 hours.

8. The preparation method according to claim 6, characterized in that: The preparation process of the partially chloromethylated polystyrene comprises: Adding chloromethyl ether to a polystyrene solution for chloromethylation reaction at a reaction temperature of 20-60° C. for a reaction time of 1-20 hours to obtain a chloromethylation-completed feed solution; The chloromethylated feed liquid is added into methanol, and the precipitated solid is filtered, washed and dried to obtain partially chloromethylated polystyrene.

9. The preparation method according to claim 6, characterized in that: In the step (b), the double-bond-containing monotertiary amine is selected from at least one of N,N-dimethylallylamine, N,N,2-trimethylallylamine, and 3-(dimethylamino)acrylonitrile; The monotertiary amine without double bonds is selected from at least one of triethanolamine, triethylamine, dodecyldimethyl tertiary amine and dioctylmethyl tertiary amine; The drying temperature is 60-110°C and the drying time is 2-10 hours.

10. A homogeneous membrane, characterized in that The homogeneous membrane is a homogeneous cation membrane prepared by the preparation method according to any one of claims 1 to 5 or a homogeneous anion membrane prepared by the preparation method according to any one of claims 6 to 9.