Monomolecular bipolar ion exchange membrane containing dissolution promoting layer and preparation method of monomolecular bipolar ion exchange membrane

Abstract

The invention relates to the technical field of separation membrane materials. A monomolecular bipolar ion exchange membrane sequentially comprises a positive membrane layer, a solution promoting layer and a negative membrane layer, and further comprises at least one support body, the positive membrane layer and the negative membrane layer are cross-linked and polymerized monomolecules, and the solution promoting layer is an amine polymer complexed with metal; the positive membrane layer and the negative membrane layer are combined with the decomposition promoting layer through carbon-nitrogen covalent bonds. The preparation method comprises the following steps: preparing the cation membrane containing halogenated alkyl, enabling amino of the decomposition promoting layer to react with the halogenated alkyl in the cation membrane to realize covalent bond combination, then coating the anion membrane containing halogenated alkyl, and enabling chlorinated alkyl in the anion membrane to be combined with the amino of the decomposition promoting layer through covalent bonds. The obtained product film is high in efficiency and stable in structure.

Description

Technical Field The invention relates to the technical field of separation membrane materials and discloses a bipolar ion exchange membrane and a preparation method thereof. Background Art

[0001] Anion exchange membranes (referred to as anion membranes), cation exchange membranes (referred to as cation membranes) and bipolar ion exchange membranes (referred to as bipolar membranes) can be used to manufacture devices such as electrodialysis, electro-desalination, and diffusion dialysis, and are used in water desalination and seawater desalination, purification and concentration of brine or chemical aqueous solutions, separation of ions of different valence states, and water-promoted decomposition to prepare acids and alkalis, and can also be used in electrolytic hydrogen production, electrolytic alkali production, and various battery devices. Among them, bipolar membranes promote water decomposition and separate hydrogen ions and hydroxide ions under the action of an electric field, so they can be used to produce acids and alkalis from salts, and have good application prospects.

[0002] In the known technology, most bipolar membrane preparation methods are to prepare the anionic membrane separately and then composite them together. This composite method includes physical bonding with a binder and chemical cross-linking bonding with a binder. However, there is no chemical bond between the anionic membrane layer and the cationic membrane layer in these composite methods, and long-term use will produce a "bubbling" phenomenon, that is, the separation of the two membrane layers. On the other hand, the chemical bond that is used to combine the two membranes by chemical cross-linking in the known technology is usually an ether bond, a lipid bond or an amide bond that is easily hydrolyzed in a strong acid or alkali environment.

[0003] U.S. Patent No. 4,024,043 uses a high-density polyethylene film as a substrate, and impregnates styrene, divinylbenzene and an initiator into the substrate to initiate cross-linking polymerization to obtain a base membrane, and then sulfonates one side of the base membrane, and chloromethylates and ammonates the other side to obtain a bipolar membrane. This method covalently connects the positive membrane functional group and the negative membrane functional group to a single molecule through cross-linking polymerization and post-functionalization to form a "single molecule bipolar membrane". Similar to the above method, Chinese Patent No. 2010102819974 replaces the substrate material with a binary blend of polyethylene and ethylene and octene copolymer elastomer or a ternary blend of polyethylene, ethylene and octene copolymer elastomer and butene rubber, thereby improving the performance of the membrane product obtained by this method. In these methods, there is inhomogeneity at the microscopic level during the process of styrene and divinylbenzene being impregnated into the substrate. The reason is that there are high crystalline areas and non-crystalline areas in the substrate structure, and the rate at which the coated liquid enters the non-crystalline area is relatively fast, so the impregnation in this area is high, and the relative strength of the product membrane here is relatively low. At the same time, there are defects in the film-forming process of the substrate, and the coating liquid has a higher impregnation ratio at the defect point, and starting from this point, a dendritic high impregnation area is formed. The final result is that this defect is magnified in the finished film, greatly reducing the qualified rate of the finished film. On the other hand, since a non-porous membrane is used, its swelling impregnation temperature is high, the time is long, and the consumption of coating liquid is large; the polyethylene substrate has insufficient chemical stability, and there is carbonization during the sulfonation process, which affects the strength of the product. When reacting on one side of a single film, the reaction conditions are difficult to control, and the yield rate is low.

[0004] Some studies have found that setting a so-called "catalytic layer" between the positive and negative sides of the bipolar membrane can help improve the efficiency of the bipolar membrane. In fact, the so-called "catalytic layer" promotes the dissociation of water, but it is not necessarily a catalytic process in the traditional sense. Therefore, this article calls it a "water dissociation promoting layer" or simply "promoting layer".

[0005] The physical structure of the bipolar membrane containing a dissolution-promoting layer prepared by multi-layer coating and physical bonding is not stable enough and has a short lifespan. The metal dissolution promoter may also be dissolved under the action of acid or alkali. For example, Chinese Patent 201911255856.2 obtains a bipolar membrane containing an iron dissolution-promoting layer by attaching / adsorbing / depositing iron colloid into the cation membrane through the surface reaction of the cation exchange membrane surface with the trivalent iron compound, and then spraying the anion membrane casting liquid. There is no covalent chemical bond between the cation membrane molecules, the dissolution-promoting layer molecules and the anion membrane molecules, and the strength of the mutual bonding is not high. Iron compounds may also be dissolved and lost under the action of strong acid. Summary of the invention

[0006] The purpose of the invention is to disclose a bipolar membrane with good stability and high efficiency and a preparation method thereof.

[0007] In order to achieve the above-mentioned purpose, the monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer of the present invention comprises, in sequence, a cation membrane layer, a dissolution-promoting layer, an anion membrane layer and at least one support body; the cation membrane layer and the anion membrane layer are both cross-linked polymerized monomolecules, and the dissolution-promoting layer is a polyimide polymer complexed with metal ions; the cation membrane layer and the anion membrane layer are both bonded to the dissolution-promoting layer via carbon-nitrogen covalent bonds.

[0008] The preparation method comprises: (1) preparing a cationic membrane casting liquid which is a mixture of halogenated olefins, olefins containing cationic membrane functional groups, crosslinking agents, polymerization initiators and solvents; (2) applying the cationic membrane casting liquid to a support to initiate crosslinking polymerization to obtain a cationic membrane containing halogenated alkyl groups; (3) dissolving a metal compound in water and mixing it with a polyimide polymer to obtain a promoter solution; (4) applying the promoter solution to at least one side of the cationic membrane to initiate a substitution reaction between the chloroalkyl groups in the cationic membrane and the polyimine; (5) washing away the unreacted promoter, drying and obtaining a promoter layer; (6) preparing a cationic membrane casting liquid which is a mixture of halogenated olefins, olefins containing cationic membrane functional groups, crosslinking agents, polymerization initiators, polymer enhancers and solvents; (7) applying the cationic membrane casting liquid to the surface of at least one of the promoter layers; and (8) initiating a crosslinking polymerization reaction of the cationic membrane casting liquid and a substitution reaction between the chloroalkyl groups in the cationic membrane casting liquid and the amine groups in the promoter layer.

[0009] The metal compounds include, but are not limited to, compounds containing iron, manganese, chromium, nickel, aluminum, and mixtures thereof.

[0010] The polyimines include but are not limited to polyethyleneimine, branched polyethyleneimine, polypropyleneimine, branched polypropyleneimine and mixtures thereof.

[0011] The halogenated olefins include, but are not limited to, chloromethylstyrene, 3-chloropropylene, 2-methyl-3-chloropropylene, bromomethylstyrene, 3-bromopropylene, 2-methyl-3-bromopropylene, 3-iodopropylene, 2-methyl-3-iodopropylene and mixtures thereof.

[0012] The weight percentage of the halogenated olefin in the cation casting solution or the anion casting solution is 5-25%.

[0013] The olefins containing cationic functional groups include, but are not limited to, styrene sulfonic acid, styrene sulfonic acid organic ammonium salt, styrene sulfonate lithium, olefin sulfonic acid compounds, olefin sulfonic acid organic ammonium salt compounds, olefin sulfonate lithium compounds, olefin acid compounds, acrylic acid organic ammonium salt compounds, acrylic acid lithium compounds and mixtures of the above compounds.

[0014] The weight percentage of the olefin containing cationic functional groups in the cationic casting solution is 35-55%.

[0015] The olefin containing anionic functional groups is any compound containing an ammonium group and a double bond and a mixture thereof, such as vinylbenzyltrimethylammonium, vinylbenzylpyridinium, benzylvinylimidazole and a mixture thereof.

[0016] The weight percentage of the olefin containing anionic membrane functional groups in the cation membrane casting solution is 30-65%.

[0017] The crosslinking agent is a compound containing two or more carbon-carbon double bonds and a mixture thereof, such as divinylbenzene, vinylbenzylvinylpyrazole ammonium, ethylene glycol dimethacrylate and a mixture thereof.

[0018] The weight percentage of the cross-linking agent in the casting solution is 4-25%.

[0019] The polymerization initiator includes, but is not limited to, azoisobutyronitrile, azoisoheptanenitrile, benzoyl peroxide, tert-butyl peroxyethylhexanoate, and mixtures thereof.

[0020] The solvent includes, but is not limited to, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dioxane, and mixtures thereof.

[0021] The weight percentage of the solvent in the casting solution is 0-22%.

[0022] The support includes but is not limited to microporous membranes made of polymers, woven fabrics and non-woven fabrics, and composites of microporous membranes and non-woven fabrics.

[0023] The coating includes but is not limited to dipping, spraying, scraping and rolling.

[0024] The beneficial effects of the present invention include: (1) both the cathodic membrane and the anionic membrane are cross-linked polymerized single-molecule structures and are bonded to the promoting layer through carbon-nitrogen covalent bonds to form a single-molecule structure, and the structure is stable; (2) the metal promoter is complexed with polyimide and is not easily lost in an acidic or alkaline environment; (3) the metal compound and polyimide of the promoting layer both have a promoting effect; (4) the electrochemical performance and mechanical strength of the bipolar membrane can be optimized by changing the ratio of chlorinated olefins to functional group compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic cross-sectional view of a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer according to the present invention.

[0026] In the figure, 1. positive membrane layer, 2. promoting layer, 3. negative membrane layer. DETAILED DESCRIPTION Example 1

[0027] (1) preparing a cation casting solution by mixing 15 g of p-styrene chloromethyl, 85 g of p-styrene pyridinium sulfonate, 15 g of divinylbenzene, 2 g of azobisisobutyronitrile and 35 g of N-methylpyrrolidone; (2) applying the cation casting solution to a 70 μm thick polypropylene microporous membrane, protecting it with a polyester film, and reacting it at 90° C. for 4 hours under vacuum to obtain a cation film; (3) dissolving 5 g of ferric chloride in 25 ml of water, mixing 20 g of a 50% aqueous solution of branched polyethyleneimine with 25 ml of water, and mixing the two aqueous solutions to obtain a brown-red viscous catalyst solution; (4) brushing the said accelerator solution on one side of the said cation membrane and drying it in an oven at 70°C for 4 hours; (5) washing with water and drying it to obtain a base membrane with a brown-red color on one side; (6) preparing a mixture of 15 g of p-styrene chloromethyl, 85 g of p-vinylbenzyltriethylammonium, 15 g of divinylbenzene, 2 g of azobisisobutyronitrile and 55 g of N-methylpyrrolidone to obtain a negative membrane casting solution; (7) brushing the said negative membrane casting solution on the brown-red side of the said base membrane; (8) protecting it with a polyester film, reacting it at 90°C under vacuum for 4 hours to obtain the said monomolecular bipolar ion membrane containing the accelerator layer.

[0028] According to the detection method disclosed in Chinese Patent ZL022186794, the transmembrane voltage of the bipolar ion membrane was measured to be 2.1V under the condition of a current density of 1000A / m2 in a 0.5mole / L NaCl aqueous solution. Example 2

[0029] (1) preparing a cation casting solution by mixing 15 g of p-styrene chloromethyl, 35 g of p-styrene pyridinium sulfonate, 50 g of methacrylic acid, 15 g of divinylbenzene, 2 g of azobisisobutyronitrile and 25 g of N-methylpyrrolidone; (2) applying the cation casting solution to a polypropylene non-woven fabric of a 82 μm thick single-sided composite polypropylene microporous membrane to completely wet it, protecting it with a polyester film, and reacting it at 90° C. under vacuum for 4 hours to obtain a cation film; (3) dissolving 10 g of ferric chloride in 100 ml of water, mixing 20 g of a 50% aqueous solution of branched polyethyleneimine with 50 ml of water, and mixing the two aqueous solutions to obtain a brown-red viscous accelerator solution; (4) immersing the cation film in the accelerator solution and keeping it at 60° C. for 5 hours; (5) washing with water and drying, A brown-red base film is obtained; (6) 15.3 grams of p-chloromethylstyrene, 9.4 grams of N-vinylpyrazole and 15 grams of N-methylpyrrolidone are reacted at room temperature for 16 hours to obtain a vinylbenzyl vinylpyrazole ammonium crosslinker solution; 38.0 grams of benzyl chloride, 26.5 grams of N-vinylpyrazole and 25 grams of N-methylpyrrolidone are reacted at room temperature for 16 hours to obtain an N-vinylbenzyl ammonium solution, 15 grams of p-chloromethylstyrene, the N-vinylbenzyl ammonium solution, the vinylbenzyl vinylpyrazole ammonium crosslinker solution and 3.2 grams of azobisisobutyronitrile are mixed to obtain a negative membrane casting liquid; (7) The negative membrane casting liquid is sprayed on the non-woven fabric surface of the base membrane; (8) Protected by a polyester film, the reaction is carried out at 90°C under vacuum for 4 hours to obtain the monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer.

[0030] According to the detection method disclosed in Chinese Patent ZL022186794, the transmembrane voltage of the bipolar ion membrane was measured to be 2.36V under the condition of current density of 1000A / m2 in 0.5mole / L NaCl aqueous solution.

Claims

1. A monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer, characterized in that It comprises a cation layer, a dissolution-promoting layer and a negative membrane layer in sequence, and also comprises at least one support body; the cation layer and the negative membrane layer are both cross-linked polymerized single molecules, and the dissolution-promoting layer is a polyimide polymer complexed with metal ions; the cation layer and the negative membrane layer are both bonded to the dissolution-promoting layer via carbon-nitrogen covalent bonds.

2. A method for preparing a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer, characterized in that The method comprises: (1) preparing a cationic membrane casting liquid which is mixed with halogenated olefins, olefins containing cationic membrane functional groups, crosslinking agents, polymerization initiators and solvents; (2) applying the cationic membrane casting liquid to a support to initiate crosslinking polymerization to obtain a cationic membrane; (3) dissolving a metal compound in water and mixing it with a polyimide polymer to obtain a promoter solution; (4) applying the promoter solution to at least one side of the cationic membrane to initiate a substitution reaction between the chloroalkyl group in the cationic membrane and the polyimide; (5) washing away the unreacted promoter, drying and obtaining a promoter layer; (6) preparing a cationic membrane casting liquid which is mixed with halogenated olefins, olefins containing cationic membrane functional groups, crosslinking agents, polymerization initiators, polymer reinforcements and solvents; (7) applying the cationic membrane casting liquid on at least one surface of the promoter layer; and (8) initiating a crosslinking polymerization reaction of the cationic membrane casting liquid and a substitution reaction between the chloroalkyl group in the cationic membrane casting liquid and the amine group in the promoter layer.

3. The monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer and the preparation method according to claims 1 and 2, characterized in that The metal ions include, but are not limited to, iron ions, manganese ions, chromium ions, nickel ions, aluminum ions, and mixtures thereof.

4. The monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer and the preparation method according to claims 1 and 2, characterized in that The polyimines include, but are not limited to, polyethyleneimine, branched polyethyleneimine, polypropyleneimine, branched polypropyleneimine and mixtures thereof.

5. The method for preparing a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer according to claim 2, characterized in that The halogenated olefins include, but are not limited to, chloromethylstyrene, 3-chloropropylene, 2-methyl-3-chloropropylene, bromomethylstyrene, 3-bromopropylene, 2-methyl-3-bromopropylene, 3-iodopropylene, 2-methyl-3-iodopropylene and mixtures thereof.

6. The method for preparing a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer according to claim 2, characterized in that The olefins containing cationic functional groups include, but are not limited to, styrene sulfonic acid, styrene sulfonic acid organic ammonium salt, styrene sulfonate lithium, olefin sulfonic acid mixtures, olefin sulfonic acid organic ammonium salt mixtures, olefin sulfonate lithium mixtures, olefin acid mixtures, acrylic acid organic ammonium salt mixtures, acrylic acid lithium mixtures and mixtures thereof.

7. The method for preparing a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer according to claim 2, characterized in that The olefin containing anionic functional groups is any mixture containing ammonium groups and double bonds and mixtures thereof, such as vinylbenzyltrimethylammonium, vinylbenzylpyridinium, benzylvinylimidazole.

8. The method for preparing a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer according to claim 2, characterized in that The crosslinking agent is a compound containing two or more carbon-carbon double bonds and a mixture thereof, such as divinylbenzene, vinylbenzylvinylpyrazole ammonium, and ethylene glycol dimethacrylate.

9. The method for preparing a monomolecular bipolar ion exchange membrane containing a dissolution-promoting layer according to claim 2, characterized in that The support includes, but is not limited to, microporous membranes, woven fabrics, non-woven fabrics, and composites thereof made of polymers.

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