A bipolar membrane and its preparation method

Abstract

The present invention relates to a bipolar membrane and a preparation method thereof, including: hydrophilic modification of a mesh cloth; laying the hydrophilic mesh cloth flat on a PET film, uniformly coating a positive membrane slurry on the mesh cloth and the PET film, and drying to obtain a partially sulfonated positive membrane; spraying a catalyst layer slurry on the positive membrane and drying to obtain a positive membrane with a catalyst layer; the catalyst layer slurry contains partially chloromethylated polystyrene, a toughening polymer, a double-bond-containing mono-secondary amine, a non-double-bond-containing mono-secondary amine, an initiator, and a dehydrating agent; uniformly coating a negative layer slurry on the catalyst layer of the positive membrane and drying, separating the PET film after drying to obtain a bipolar membrane; the negative layer slurry contains partially chloromethylated polystyrene, a toughening polymer, a double-bond-containing mono-tertiary amine, a non-double-bond-containing mono-tertiary amine, and an initiator; transforming the bipolar membrane. The bipolar membrane of the present invention has clear interfaces between layers, a low transmembrane voltage, high mechanical strength, a high product qualification rate, and stable dimensions during use.

Description

Technical Field

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

[0002] A bipolar membrane is a composite membrane formed by laminating a cation exchange membrane and an anion exchange membrane, and has a function called hydrolysis phenomenon: water in the membrane is dissociated into protons and hydroxide ions by applying a voltage to both sides of the bipolar membrane immersed in an aqueous solution; by using this function, the bipolar membrane is combined with a cation exchange membrane and an anion exchange membrane for electrodialysis, and thus, for example, acids and bases can be produced from neutral salts.

[0003] Currently, there are mainly two types of bipolar membranes on the market. One is a single-piece bipolar membrane, and the other is a composite bipolar membrane. The single-piece bipolar membrane is generally made by impregnating a thin film or filling a porous substrate membrane with a monomer, polymerizing it into a bottom membrane containing a benzene ring, then sulfonating one side and aminating the other side, and then performing post-treatment. The composite bipolar membrane is generally made by first polymerizing a support mesh cloth and a monomer to form a cation layer or an anion layer, and then coating the corresponding anion layer or cation layer to form a bipolar membrane. Each of the two bipolar membranes has its own advantages and disadvantages. The single-piece bipolar membrane has good bonding strength between the cation and anion layers due to its one-piece molding, and has strong applicability under various working conditions. However, because there is no high-strength support material, the swelling during use is relatively large, which will affect the service life. The composite bipolar membrane has a high-strength support material and small swelling, but is not suitable for use under specific working conditions.

[0004] In view of the advantages and disadvantages of the above two bipolar membranes, if the advantages of both can be integrated, a bipolar membrane with small swelling, stable dimensions, strong working condition applicability, long service life, lower transmembrane voltage, and beneficial to energy consumption reduction and effective reduction of operating costs can be made. Summary of the Invention

[0005] Based on the above-mentioned drawbacks and deficiencies existing in the prior art, one of the purposes of the present invention is to at least solve one or more of the above-mentioned problems existing in the prior art. In other words, one of the purposes of the present invention is to provide a bipolar membrane and a preparation method thereof that meet one or more of the foregoing requirements.

[0006] In order to achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0007] A preparation method of a bipolar membrane, comprising the following steps:

[0008] (1) Hydrophilic modification of a mesh cloth to obtain a hydrophilic mesh cloth;

[0009] (2) Laying the hydrophilic mesh cloth flat on a PET film, uniformly coating a cation membrane slurry on the mesh cloth and the PET film, and drying to obtain a partially sulfonated cation membrane;

[0010] Among them, the positive membrane slurry is that partially sulfonated polystyrene and a dehydrating agent are completely dissolved in a good solvent;

[0011] (3) Spray the catalytic layer slurry on the partially sulfonated positive membrane and dry it. After drying, a positive membrane with a catalytic layer is obtained;

[0012] Among them, the catalytic layer slurry is that partially chloromethylated polystyrene, a toughening polymer, a double-bond-containing mono-secondary amine, a non-double-bond-containing mono-secondary amine, an initiator, and a dehydrating agent are completely dissolved in a good solvent;

[0013] (4) Uniformly coat the negative layer slurry on the catalytic layer of the positive membrane with a catalytic layer and dry it. After drying, separate the PET film to obtain a bipolar membrane;

[0014] Among them, the negative layer slurry is that partially chloromethylated polystyrene, a toughening polymer, a double-bond-containing mono-tertiary amine, a non-double-bond-containing mono-tertiary amine, and an initiator are completely dissolved in a good solvent;

[0015] (5) Immerse the bipolar membrane in a metal ion solution, take it out after immersion is completed, and transfer it to an alkali solution for transformation.

[0016] As a preferred solution, step (1) specifically includes the following steps:

[0017] (11) Prepare an impregnating solution with styrene, divinylbenzene, and an initiator. After heating to 30 - 70 °C, completely immerse the mesh cloth in the impregnating solution, and take out the mesh cloth after soaking for 5 - 120 minutes. After removing the excess impregnating solution, lay it flat between two PET films, and seal the edges of the PET films with tape;

[0018] (12) Put the PET film and the mesh cloth into a hot water tank for polymerization reaction. After the polymerization reaction is completed, take it out from the hot water tank and separate the mesh cloth from the PET film;

[0019] Among them, the hot water temperature of the hot water tank is 65 - 90 °C, and the reaction time is 1 - 15 hours;

[0020] (13) Place the separated mesh cloth in the sulfonation solution of the sulfonation reaction tank for sulfonation reaction. After the sulfonation reaction is completed, wash and dry the mesh cloth;

[0021] Among them, the temperature of the sulfonation reaction is 30 - 90 °C, and the reaction time is 0.5 - 10 hours.

[0022] As a preferred solution, the mesh cloth is a woven cloth, a non-woven fabric, or a porous film, and the material is low-density polyethylene LDPE, high-density polyethylene HDPE, polyvinyl chloride PVC, polyphenylene sulfide PPS, or polyether ether ketone PEEK.

[0023] As a preferred embodiment, in the step (11), the impregnating solution is heated to 40 - 60 °C, and the soaking time is 10 - 60 minutes;

[0024] In the step (12), the hot water temperature in the hot water tank is 65 - 80 °C, and the reaction time is 3 - 10 hours;

[0025] In the step (13), the temperature of the sulfonation reaction is 40 - 80 °C, and the reaction time is 2 - 4 hours.

[0026] As a preferred embodiment, in the 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;

[0027] The preparation process of the partially sulfonated polystyrene includes:

[0028] Adding the sulfonation solution to the polystyrene solution for sulfonation reaction, the sulfonation reaction temperature is 30 - 90 °C, and the reaction time is 0.5 - 10 hours;

[0029] Adding the material liquid after the sulfonation reaction is completed to the ice - water mixture, and the precipitated solid is filtered, washed, and dried to obtain the partially sulfonated polystyrene.

[0030] As a preferred embodiment, the step (3) specifically includes:

[0031] Spraying the catalytic layer slurry on the partially sulfonated cationic membrane, and drying at 60 - 110 °C for 2 - 10 hours to obtain the cationic membrane with a catalytic layer.

[0032] As a preferred embodiment, the preparation process of the partially chloromethylated polystyrene includes:

[0033] Adding chloromethyl ether to the polystyrene solution for chloromethylation reaction, the reaction temperature is 20 - 60 °C, and the reaction time is 1 - 20 hours to obtain the material liquid after chloromethylation is completed;

[0034] Adding the material liquid after chloromethylation is completed to methanol, and the precipitated solid is filtered, washed, and dried to obtain the partially chloromethylated polystyrene.

[0035] As a preferred embodiment, in the step (4), the drying temperature is 60 - 110 °C, and the time is 2 - 10 hours.

[0036] As a preferred embodiment, the dehydrating agent includes at least one of acidic montmorillonite, phosphotungstic acid silica, and phosphorus pentoxide;

[0037] The initiator includes at least one of lauroyl peroxide, tert-butyl lauroyl peroxide, tert-butyl peroxyisobutyrate, benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate.

[0038] The present invention also provides a bipolar membrane prepared by the preparation method described in any of the above solutions.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) Compared with the existing bipolar membranes, the bipolar membrane of the present invention enhances the bonding force between the mesh support material and the cation layer, as well as between the cation and anion layers, effectively reduces the permeability of anions through the cation layer and the transmembrane voltage, improves the lifespan of the bipolar membrane, and is beneficial to reducing energy consumption and operating costs;

[0041] (2) The mesh of the present invention adopts a unique hydrophilic modification, is chemically bonded to the hydrophilic cation layer, has a tight combination, and has low leakage caused by anions passing through the cation layer;

[0042] (3) There is a chemical bond connection between the cation layer and the intermediate catalytic layer of the present invention, and there is a chemical bond connection between the intermediate catalytic layer and the anion layer. The layers are firmly combined, and unlike traditional composite bipolar membranes, delamination is not likely to occur, and the transmembrane voltage is lower;

[0043] (4) The present invention adopts a unique cross-linking method of cross-linking after film formation, with more controllable film formation and higher product yield;

[0044] (5) Compared with traditional single-piece bipolar membranes and composite bipolar membranes with mesh support, the bipolar membrane of the present invention has higher strength, better dimensional stability, and longer lifespan. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic cross-sectional structure diagram of the bipolar membrane of Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] The following will further illustrate the bipolar membrane and its preparation method provided by the present invention.

[0047] The preparation method of the bipolar membrane of the present invention includes: hydrophilically modifying a mesh cloth by means of impregnation, polymerization, re-sulfonation or direct sulfonation to prepare a hydrophilic mesh cloth; using polystyrene as a raw material, performing partial sulfonation to prepare partially sulfonated polystyrene, dissolving it in a good solvent after purification, adding a dehydrating agent, and formulating a slurry 1 after dissolution; using polystyrene as a raw material, performing partial chloromethylation to prepare partially chloromethylated polystyrene, dissolving it in a good solvent after purification, and adding a toughening polymer and formulating a slurry 2 after dissolution; diluting the slurry 2 with a good solvent to prepare a slurry 3; laying the hydrophilic mesh cloth on a PET film, uniformly coating the slurry 1 on the hydrophilic mesh cloth and the PET film to obtain a cation exchange membrane with a mesh cloth; crosslinking the cation exchange membrane to achieve both crosslinking within the cation exchange resin and chemical bond connection between the cation exchange resin and the mesh cloth; mixing the slurry 3 with a double-bonded mono-secondary amine, a non-double-bonded mono-secondary amine, an initiator, and a dehydrating agent to prepare a catalytic layer slurry, and then spraying it on the surface of the cation exchange membrane to prepare an intermediate catalytic layer; mixing the slurry 2 with a double-bonded mono-tertiary amine, a non-double-bonded mono-tertiary amine, and an initiator to prepare an anion layer slurry, and then coating it on the intermediate catalytic layer, and after curing, obtaining a bipolar membrane; soaking the obtained bipolar membrane in a metal ion solution with hydrolysis catalytic ability, and then performing deposition transformation to obtain a bipolar membrane with a lower hydrolysis voltage. Each layer of the bipolar membrane has clear interfaces, a low transmembrane voltage, high mechanical strength, a high product qualification rate, and stable dimensions during use.

[0048] Specifically, the preparation method of the bipolar membrane of the present invention includes the following steps:

[0049] 1. Preparation of the hydrophilic mesh cloth;

[0050] a) Material selection: Select a mesh cloth prepared from a material capable of impregnating styrene or directly sulfonating. The form of the mesh cloth can be a woven cloth, a non-woven cloth, or a porous film, and the materials include but are not limited to low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), or polyether ether ketone (PEEK), etc.;

[0051] b) Impregnation: Prepare an impregnating solution with styrene, divinylbenzene, and an initiator, heat it to 30 - 70 °C, then completely immerse the mesh cloth in the impregnating solution to ensure full contact between the mesh cloth and the impregnating solution. After soaking for 5 - 120 minutes, take out the mesh cloth, remove the excess impregnating solution, and lay it flat between two PET films. Seal the edges of the PET films with tape;

[0052] Among them, the weight ratio of styrene, divinylbenzene, and initiator is 1: 0.01 - 0.4: 0.001 - 0.1; the initiator is mainly a type of substance that can form free radicals, selected from organic peroxides such as lauroyl peroxide, tert-butyl peroxy laurate, tert-butyl peroxy isobutyrate, benzoyl peroxide BPO, di-tert-butyl peroxide, etc., and at least one of azo organic compounds such as azobisisobutyronitrile AIBN, azobisisoheptonitrile ABVN, dimethyl azobisisobutyrate AIBME, etc.;

[0053] c) Polymerization: Put the PET film and the mesh cloth into a hot water tank together for polymerization reaction. The hot water temperature is 65 - 90 °C, and the reaction time is 1 - 15 hours;

[0054] d) Stripping: Take out the mesh cloth after the polymerization is completed from the hot water tank, separate the mesh cloth from the PET film, and the mesh cloth is used for subsequent reactions;

[0055] e) Preparation of sulfonation solution: The sulfonation solution is a reagent that can introduce sulfonic acid groups onto the benzene ring, such as 90 - 98 wt% sulfuric acid, chlorosulfonic acid, a mixed solution of chlorosulfonic acid and sulfuric acid with a weight ratio of 1: 0.1 - 9, a mixed solution of acetic anhydride and sulfuric acid with a weight ratio of 1: 0.1 - 1, etc.;

[0056] f) Sulfonation: First, add the sulfonation solution into the sulfonation reaction tank, and then place the mesh cloth in step d) in the sulfonation reaction tank for sulfonation reaction. The reaction temperature is 30 - 90 °C, and the reaction time is 0.5 - 10 hours. After the sulfonation is completed, the mesh cloth is first rinsed in a low-concentration acid, then washed with clean water and dried for standby. Thus, the preparation of the hydrophilic mesh cloth is completed.

[0057] 2. Preparation of partially sulfonated polystyrene;

[0058] g) Preparation of polystyrene solution: In a reaction kettle with stirring, first inject a certain amount of good solvent for polystyrene, such as dichloroethane DCE, N,N-dimethylformamide DMF, dimethylacetamide DMAC, dimethyl sulfoxide DMSO, etc. After starting the stirring, add polystyrene, and stir until the polystyrene is completely dissolved for standby;

[0059] h) Sulfonation: In a reaction kettle with stirring, first take a part of the polystyrene solution prepared in step g) and add it to the reaction kettle. After starting the stirring, start heating. After reaching the set temperature, slowly add the sulfonation solution in step e) to the reaction kettle. The sulfonation reaction temperature is 30 - 90 °C, and the reaction time is 0.5 - 10 hours;

[0060] Among them, the molar ratio of polystyrene to the sulfonic acid groups of the sulfonation solution is 1: 0.1 - 2;

[0061] i) Partially sulfonated polystyrene: In a reaction kettle equipped with stirring, add an ice-water mixture. After starting the stirring, slowly pour the liquid material after the sulfonation in step h) into it. The precipitated solid is filtered and washed several times and then dried for standby; thus, partially sulfonated polystyrene is prepared.

[0062] 3. Preparation of partially chloromethylated polystyrene;

[0063] j) Chloromethylation: In a reaction kettle equipped with stirring, first take a part of the polystyrene solution prepared in step g) and add it to the reaction kettle. After starting the stirring, start heating. After reaching the set temperature, slowly add chloromethyl methyl ether to the reaction kettle. The chloromethylation reaction temperature is 20 - 60 °C, and the reaction time is 1 - 20 hours;

[0064] Among them, the molar ratio of polystyrene to chloromethyl methyl ether is 1:0.1 - 20;

[0065] k) Partially chloromethylated polystyrene: In a reaction kettle equipped with stirring, add methanol. After starting the stirring, slowly pour the liquid material after the chloromethylation in step j) into it. The precipitated solid is filtered and washed several times and then dried for standby; thus, partially chloromethylated polystyrene is prepared.

[0066] 4. Preparation of the cation exchange membrane;

[0067] l) Preparation of the cation exchange membrane slurry: In a reaction kettle equipped with stirring, first inject a good solvent for sulfonated polystyrene, such as DCE, DMF, DMAC, DMSO, etc. After starting the stirring, first add the partially sulfonated polystyrene in step i), and then add a dehydrating agent. After complete dissolution, it is reserved for standby and named slurry 1;

[0068] Among them, the dehydrating agent is mainly a kind of auxiliary agent that can catalyze the dehydration reaction, including acidic montmorillonite, phosphotungstic acid silica, phosphorus pentoxide, etc.; the weight ratio of the partially sulfonated polystyrene to the dehydrating agent in the cation exchange membrane slurry is 1:0.005 - 0.3;

[0069] m) Coating of the cation exchange membrane: Lay the hydrophilic mesh cloth in step f) flat on the PET film, then evenly coat the cation exchange membrane slurry in step l) on the mesh cloth 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 complete drying, a partially sulfonated cation exchange membrane is prepared.

[0070] 5. Preparation of the intermediate catalytic layer;

[0071] n) Preparation of partially chloromethylated polystyrene slurry: In a reaction kettle equipped with stirring, first inject a good solvent for chloromethylated polystyrene, such as the above-mentioned DCE, DMF, DMAC, DMSO, etc. After starting the stirring, first add the partially chloromethylated polystyrene from step k), and then add a toughening polymer, which can be one or more mixtures of polymers such as ether bond-containing polymers, amides, lipids, rubber-like polymers, etc. After complete dissolution, it is reserved for use and named slurry 2;

[0072] o) Preparation of catalytic layer slurry: In a reaction kettle equipped with stirring, first inject slurry 2 from step n). After starting the stirring, add a certain amount of the good solvent in step n). After stirring evenly, it is named slurry 3; Continue to add a double-bond-containing mono-secondary amine, a non-double-bond-containing mono-secondary amine, an initiator, and a dehydrating agent to slurry 3. After complete dissolution and stirring evenly, it is reserved for use;

[0073] Among them, the molar ratio of partially chloromethylated polystyrene, double-bond-containing mono-secondary amine, non-double-bond-containing mono-secondary amine, initiator, and dehydrating agent in the catalytic layer slurry is 1:0.01 - 0.5:0.1 - 0.5:0.001 - 0.1:0.005 - 0.2;

[0074] The above-mentioned double-bond-containing mono-secondary amine is selected from at least one of N-methylallylamine and N-ethylmethacrylamide;

[0075] The above-mentioned non-double-bond-containing mono-secondary amine is selected from at least one of diethanolamine, di-n-propylamine, diisopropylamine, and diethylamine;

[0076] The above-mentioned initiator includes at least one of lauroyl peroxide, tert-butyl lauroate, tert-butyl peroxyisobutyrate, benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate;

[0077] p) Preparation of catalytic layer: Spray the catalytic layer slurry from step o) on the partially sulfonated cationic membrane in step m), and then dry it at 60 - 110 °C for 2 - 10 hours. After drying, it is the cationic membrane with a catalytic layer.

[0078] 6. Preparation of bipolar membrane;

[0079] q) Preparation of cathode layer slurry: In a reaction kettle equipped with stirring, first inject slurry 2 from step n). After starting the stirring, add a double-bond-containing mono-tertiary amine, a non-double-bond-containing mono-tertiary amine, and an initiator. After complete dissolution and stirring evenly, it is reserved for use;

[0080] Among them, the molar ratio of partially chloromethylated polystyrene, double-bond-containing mono-tertiary amine, non-double-bond-containing mono-tertiary amine, and initiator in the cathode layer slurry is 1:0.01 - 0.5:0.1 - 0.5:0.001 - 0.1;

[0081] The above-mentioned mono-tertiary amine containing double bonds is selected from at least one of N,N-dimethylallylamine, N,N,2-trimethylallylamine, and 3-(dimethylamino)acrylonitrile;

[0082] The above-mentioned mono-tertiary amine without double bonds is selected from at least one of triethanolamine, triethylamine, dodecyldimethyltertiary amine, and dioctylmethyltertiary amine;

[0083] r) Preparation of bipolar membrane: Place the catalytic layer side of the positive membrane with the catalytic layer facing upwards, and then evenly coat the negative layer material on it. Then, dry it at 60-110 °C for 2-10 hours. After drying, it is the bipolar membrane;

[0084] s) Performance optimization of bipolar membrane: Immerse the bipolar membrane obtained in step r) in a metal ion solution, such as FeCl 2 solution. After soaking for a certain period of time, take out the membrane and soak it in an alkaline solution for transformation to obtain the finally performance-optimized bipolar membrane.

[0085] In the present invention, the monoamine containing double bonds (mono-secondary amine containing double bonds, mono-tertiary amine containing double bonds) is first combined with chloromethyl, and then crosslinked by the polymerization of double bonds. Compared with the direct combination of diamine or polyamine with chloromethyl to form crosslinking, it is mainly considered from the perspective of industrialization. If diamine or polyamine is used as the amination and crosslinking agent, because the reaction rate of amine and chloromethyl is very fast, once the reaction occurs, the crosslinked polymer will quickly precipitate from the solvent, hindering film formation. To form a film smoothly, it is necessary to ensure that no reaction occurs before film formation, which requires very strict environmental requirements for industrial production. However, when using monoamine containing double bonds, this problem does not exist. After the amine is combined with chloromethyl, the polymer still exists in a linear form and will not affect film formation, which is beneficial to industrial production.

[0086] In one or more embodiments, the impregnation temperature in step b) is 40-60 °C and the time is 10-60 minutes;

[0087] In one or more embodiments, the polymerization temperature in step c) is 65-80 °C and the time is 3-10 hours;

[0088] In one or more embodiments, the sulfonation reaction temperature in step f) is 40-80 °C and the reaction time is 2-4 hours;

[0089] In one or more embodiments, the sulfonation reaction temperature in step h) is 40-80 °C and the reaction time is 2-8 hours;

[0090] In one or more embodiments, the chloromethyl reaction temperature in step j) is 30-50 °C and the reaction time is 2-8 hours;

[0091] In one or more embodiments, the drying temperature of the first stage in step m) is 70 - 80 °C, the drying time is 4 - 8 hours, the drying temperature of the second stage is 100 - 140 °C, and the drying time is 4 - 8 hours;

[0092] In one or more embodiments, the drying temperature after spraying the catalytic layer in step p) is 70 - 90 °C, the drying time is 4 - 8 hours; the soaking temperature of the diaphragm after drying is 30 - 50 °C, 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;

[0093] In one or more embodiments, the drying temperature in step r) is 70 - 90 °C, and the drying time is 4 - 8 hours;

[0094] In one or more embodiments, the concentration of the metal ion solution in step s) is 0.5 - 5 wt%, the temperature for transformation is 25 - 60 °C, and the time is 5 - 30 min;

[0095] In one or more embodiments, the metal ion solution in step s) may be one or a combination of more than one of FeCl 2 、FeCl 3 、CrCl 3 、SnCl 2 、SnCl 4 、TiCl 4 ;

[0096] In one or more embodiments, the lye in step s) may be a strong alkaline inorganic solution such as NaOH, KOH, etc., and the concentration is 0.5 - 10 wt%.

[0097] The bipolar membrane of the present invention and its preparation method are further described below through specific examples:

[0098] Example 1:

[0099] The preparation method of the bipolar membrane in this example includes the following steps:

[0100] Step 1: Take 1000 g of styrene, 140 g of divinylbenzene, and 1 g of azobisisobutyronitrile, stir and mix evenly at room temperature to prepare an impregnating solution; take a HDPE woven mesh cloth with a thickness of about 0.1 mm, completely immerse it in the impregnating solution, after heating to 55 °C, keep the temperature for impregnation for 15 minutes; after the impregnation is completed, take out the mesh cloth, remove the impregnating solution attached to the surface, lay it flat between two PET films, seal the edges of the PET films with tape, then put it into a hot water bath at 80 °C, take it out after keeping the temperature for 5 hours, separate the mesh cloth from the PET film, and then place the mesh cloth in 98% concentrated sulfuric acid, react at 80 °C for 3 hours, wash and dry to obtain a hydrophilic mesh cloth;

[0101] Step 2: Inject 250 mL of DCE into a 500 mL three-necked flask. After starting stirring, add 10 g of polystyrene. Heat it to 50 °C in a constant temperature water bath. After complete dissolution, slowly add 98% concentrated sulfuric acid dropwise thereto. Control the dropping time to add 5 mL of concentrated sulfuric acid in about 30 minutes. After holding the reaction for 5 hours, pour the reaction solution into ice water for precipitation. After filtration and washing for many times, dry it for standby;

[0102] Step 3: Inject 250 mL of DCE into a 500 mL three-necked flask. After starting stirring, add 10 g of polystyrene and 0.2 g of SnCl 4 , heat it to 35 °C in a constant temperature water bath. After complete dissolution, slowly add chloromethyl ether dropwise thereto. Control the dropping time to add 20 mL of chloromethyl ether in about 45 minutes. After holding the reaction for 4 hours, pour the reaction solution into methanol for precipitation. After filtration and washing for many times, dry it for standby;

[0103] Step 4: Take 5 g of the partially sulfonated polystyrene prepared in Step 2, dissolve it in 45 mL of DMAC. After complete dissolution, add 0.5 g of acidic montmorillonite. After complete dissolution, prepare Slurry 1 for standby;

[0104] Step 5: Take 5 g of the partially chloromethylated polystyrene and 1 g of polyethersulfone prepared in Step 3, dissolve them in 54 mL of DMAC. After complete dissolution, prepare Slurry 2 for standby; Take 10 mL of Slurry 2, add another 40 mL of DMAC, mix well, and prepare Slurry 3 with a solid content of about 2.0% for standby;

[0105] Step 6: Lay a PET film flat on a glass plate, then lay the mesh cloth obtained in Step 1 flat on the PET film and fix it. Then evenly coat Slurry 1 on the mesh cloth and the PET film, and then put it into an oven for drying. Set the first drying temperature to 70 °C and the drying time to 5 hours. Set the second drying temperature to 120 °C and the drying time to 7 hours; After drying, take out the film together with the glass plate for standby;

[0106] Step 7: Vertically place the film obtained in Step 6 together with the glass plate. Take 40 mL of Slurry 3 and dissolve it with 0.08 g of N-methylallylamine, 0.12 g of diethanolamine, 0.04 g of acidic montmorillonite, and 0.004 g of BPO. After mixing and dissolving, load it into a sprayer and spray it onto the film. After completion, remove the residual slurry at the bottom, then place the glass plate horizontally for drying. Set the drying temperature to 90 °C and the drying time to 7 hours. After completion, take it out for standby;

[0107] Step 8: Place the diaphragm from Step 7 horizontally upward. Take 30 mL of Slurry 2, mix and dissolve it with 0.8 mL of N,N-dimethylallylamine, 1.5 g of triethanolamine, and 0.012 g of BPO, then uniformly coat it on the diaphragm. After completion, place it in an oven for drying. The drying temperature is 80 °C and the drying time is 5 hours. After drying, take it out and peel the diaphragm from the PET to obtain the bipolar membrane;

[0108] Step 9: To further reduce the transmembrane voltage of the bipolar membrane, directly immerse the diaphragm prepared in Step 8 in a 2 wt% FeCl 2 solution. After soaking for 1 hour, take it out, wash it with clear water, then immerse the diaphragm in an 8 wt% sodium hydroxide solution, heat it to 40 °C, and react for 25 minutes for transformation. After the transformation is completed, a bipolar membrane with a lower hydrolysis voltage is obtained.

[0109] As Figure 1 shown, the bipolar membrane of this embodiment has a three-layer structure, including a cation exchange layer II containing sulfonic acid groups, which is supported by a hydrophilic-improved mesh cloth I; it also includes an anion exchange layer IV containing quaternary ammonium groups, and an intermediate layer III with the ability of hydrolysis dissociation catalysis is in the middle of the two layers.

[0110] Example 2:

[0111] The preparation method of the bipolar membrane in this embodiment is different from that in Example 1 in that: Steps 5 and 7 are different;

[0112] Specifically, the Slurry 3 in Step 5 is prepared by taking 5 mL of Slurry 2 and adding 95 mL of DMAC and mixing well, and the solid content of Slurry 3 is about 0.5%;

[0113] Step 7 is to take 40 mL of Slurry 3 and mix and dissolve it with 0.02 g of N-methylallylamine, 0.03 g of diethanolamine, 0.01 g of acidic montmorillonite, and 0.001 g of BPO;

[0114] Other steps are the same as in Example 1.

[0115] Example 3:

[0116] The preparation method of the bipolar membrane in this embodiment is different from that in Example 1 in that: Steps 5 and 7 are different;

[0117] Specifically, the Slurry 3 in Step 5 is prepared by taking 10 mL of Slurry 2 and adding 90 mL of DMAC and mixing well, and the solid content of Slurry 3 is about 1.0%;

[0118] Step 7 is to take 40 mL of Slurry 3 and mix and dissolve it with 0.04 g of N-methylallylamine, 0.06 g of diethanolamine, 0.02 g of acidic montmorillonite, and 0.002 g of BPO;

[0119] The other steps are the same as those in Example 1.

[0120] Example 4:

[0121] The preparation method of the bipolar membrane in this example is different from that in Example 1 in that: steps 5 and 7 are different;

[0122] Specifically, the slurry 3 in step 5 is prepared by taking 30 mL of slurry 2 and adding 70 mL of DMAC and mixing evenly, and the solid content of the slurry 3 is about 3.0%;

[0123] Step 7 is to take 40 mL of slurry 3 and mix and dissolve it with 0.12 g of N-methylallylamine, 0.18 g of diethanolamine, 0.06 g of acidic montmorillonite, and 0.006 g of BPO;

[0124] The other steps are the same as those in Example 1.

[0125] Example 5:

[0126] The preparation method of the bipolar membrane in this example is different from that in Example 1 in that: steps 5 and 7 are different;

[0127] Specifically, the slurry 3 in step 5 is prepared by taking 30 mL of slurry 2 and adding 45 mL of DMAC and mixing evenly, and the solid content of the slurry 3 is about 4.0%;

[0128] Step 7 is to take 40 mL of slurry 3 and mix and dissolve it with 0.16 g of N-methylallylamine, 0.24 g of diethanolamine, 0.08 g of acidic montmorillonite, and 0.008 g of BPO;

[0129] The other steps are the same as those in Example 1.

[0130] Comparative Example 1:

[0131] The preparation method of the bipolar membrane in this comparative example is different from that in Example 1 in that:

[0132] Specifically, the mesh cloth is not hydrophilically modified in step 1, but is directly used for film preparation;

[0133] The other steps are the same as those in Example 1.

[0134] Comparative Example 2:

[0135] The preparation method of the bipolar membrane in this comparative example is different from that in Example 1 in that:

[0136] It is not subjected to the treatment of step 7;

[0137] The other steps are the same as those in Example 1.

[0138] Comparative Example 3:

[0139] The preparation method of the bipolar membrane in this comparative example is different from that in Example 1 in that:

[0140] It is not subjected to the treatment in Step 9;

[0141] Other steps are the same as those in Example 1.

[0142] Comparative Example 4:

[0143] The preparation method of the bipolar membrane in this comparative example is different from that in Example 1 in that:

[0144] It is not subjected to the treatment in Step 7 and Step 9;

[0145] Other steps are the same as those in Example 1.

[0146] The bipolar membranes of the above Examples 1-5 and Comparative Examples 1-4 are respectively tested below, and the test results are shown in Table 1.

[0147] Among them, the bonding strength between the anode and cathode layers of the bipolar membrane sheet is characterized by whether it foams, and the determination method of whether it foams is as follows:

[0148] The membrane sheet is soaked in a 4 mol / L NaOH solution at room temperature for 2 hours, then taken out and immediately put into clear water. If foaming occurs within 10 minutes, it is determined that it will foam; otherwise, it is determined that it will not foam.

[0149] In addition, the test method for the permeation amount of the bipolar membrane sheet is as follows:

[0150] Test device: Two hollow cubes with a side length of 8 cm and a wall thickness of 1.2 cm, one side of which is not closed and there is a small hole with a diameter of 5 mm on one side; the non-closed sides of the two hollow cubes are placed facing each other, ensuring that the side with the small hole faces up. Then, after placing a sealing gasket on each side of the 8*8 cm membrane sheet to be tested, it is placed between the hollow cubes. Finally, the device is locked with an external screw to ensure good sealing and no liquid leakage;

[0151] Test method: The above device is placed in a water bath at 25°C. A small magnetic stirrer is placed at the bottom of the device and at the center of the cube. A magnetic stir bar is placed in each of the two cube containers. Then, 100 mL of preheated 4 mol / L sodium chloride solution and 100 mL of pure water are respectively poured into the two containers. Stirring is started, and after 1 hour, stirring is stopped. All the solution on the pure water side is sucked out, and after rinsing 3 times with pure water, it is also all sucked out and all injected into a 250 mL volumetric flask for volume fixation. Then, 100 mL is taken to test the chloride ion concentration to determine the amount of NaCl in the 250 mL solution;

[0152] Table 1 Test results of bipolar membranes

[0153] ;

[0154] The permeation amount of the present invention is characterized by the solute permeability coefficient, and its calculation formula is as follows:

[0155] ;

[0156] ;

[0157] Wherein: σ is the solute permeability coefficient, with the unit of mmol / (m 2 ·h·mol / L); q is the total amount of sodium chloride permeated into pure water, with the unit of mmol; A is the effective area of the test membrane, with the unit of m 2 , generally 0.00314 m 2 ; Δ C is the concentration difference, with the unit of mol / L, that is, the initial concentration of the permeate is used as the concentration difference, which is 4 mol / L here; t is the test duration, with the unit of h, usually 1 h; c Ag is the concentration of the silver nitrate standard solution, with the unit of mol / L; V is the amount of the silver nitrate standard solution consumed during titration, with the unit of mL.

[0158] For the bipolar membrane sheets of the above Examples 1-5 and Comparative Examples 1-4, after testing, the tensile fracture strength is ≥40 MPa and the bursting strength is ≥1.0 MPa. Compared with the tensile fracture strength (≤10 MPa) and bursting strength (≤0.5 Mpa) of the existing single-piece bipolar membrane without mesh support, there is a significant improvement, which also correspondingly improves the service adaptability and lifespan of the membrane.

[0159] As can be seen from Table 1, as long as the present invention is implemented under suitable conditions, the transmembrane voltage of the bipolar membrane can be effectively reduced and no foaming phenomenon will occur, which is beneficial to reducing energy consumption and saving energy.

[0160] In view of the large number of embodiments of the present invention, the raw materials and dosages involved can be selected according to actual needs within the limited range. The experimental data of each embodiment are numerous and not suitable for listing one by one here. However, the verification contents and the final conclusions obtained in each embodiment are close. Therefore, the verification contents of each embodiment will not be described one by one here.

[0161] The above is only a detailed description of the preferred embodiments and principles of the present invention. For those of ordinary skill in the art, according to the idea provided by the present invention, there will be changes in the specific implementation manners, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a bipolar membrane, characterized in that: The following steps are involved: (1) Hydrophilic modification of the mesh to obtain a hydrophilic mesh; (2) Laying the hydrophilic mesh on the PET film, evenly coating the cationic membrane slurry on the mesh and the PET film, and drying to obtain a partially sulfonated cationic membrane; The cation membrane slurry is partially sulfonated polystyrene, and the dehydrating agent is completely dissolved in a good solvent; (3) spraying a catalytic layer slurry on the partially sulfonated cationic membrane and drying the slurry to obtain a cationic membrane with a catalytic layer; The catalyst layer slurry is partially chloromethylated polystyrene, toughening polymer, mono-secondary amine containing double bonds, mono-secondary amine not containing double bonds, initiator, and dehydrating agent completely dissolved in a good solvent; (4) uniformly coating the cathode layer slurry on the catalyst layer of the cation membrane with the catalyst layer and drying it, and separating the PET film after drying to obtain a bipolar membrane; The cathode layer slurry is partially chloromethylated polystyrene, toughening polymer, double-bond monotertiary amine, non-double-bond monotertiary amine, and initiator completely dissolved in a good solvent; (5) Soaking the bipolar membrane in a metal ion solution, taking it out after soaking and transferring it to an alkaline solution for transformation; 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 0.5-10 hours.

2. The preparation method according to claim 1, 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.

3. The preparation method according to claim 1, characterized in that: In the 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 40-80° C., and the reaction time is 2-4 hours.

4. 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.

5. The preparation method according to claim 1, characterized in that: The step (3) specifically includes: The catalytic layer slurry is sprayed on the partially sulfonated cation membrane, and dried at 60-110° C. for 2-10 hours to obtain a cation membrane with a catalytic layer.

6. The preparation method according to claim 1, 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.

7. The preparation method according to claim 1, characterized in that: In the step (4), the drying temperature is 60-110° C. and the drying time is 2-10 hours.

8. The preparation method according to claim 1, characterized in that: The dehydrating agent includes at least one of acidic montmorillonite, phosphotungstic acid silicon oxide, and phosphorus pentoxide; The initiator includes at least one of lauroyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisobutyrate, benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

9. A bipolar membrane obtained by the preparation method according to any one of claims 1 to 8.

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