A method for preparing a cation / anion exchange layer cross-linked bipolar membrane

Abstract

The application discloses a preparation method of a bipolar membrane with cation / anion exchange layers crosslinked, comprising the following steps: synthesizing a sulfonated polymer containing an alkaline structure and a chloro / bromo-methylated polymer; respectively configuring the two polymers into polymer solutions, first casting one of the polymer solutions, drying the polymer solution, then adding a hydrolysis catalyst on the surface of the polymer solution, and then casting the other polymer solution, and drying the polymer solution to form a membrane with a two-layer crosslinked structure; and performing quaternary ammonium treatment on the double-layer membrane to obtain a bipolar membrane with cation / anion exchange layers crosslinked with each other; and the bipolar membrane prepared by the method is crosslinked through covalent bonds between two membrane layers, has good interface stability, and part of the chloro / bromo-methyl groups in the chloro / bromo-methylated polymer is crosslinked with the alkaline structure, so that the structural stability between the membrane layers of the bipolar membrane is ensured.

Description

Technical Field

[0001] This invention belongs to the field of bipolar membrane preparation technology, and specifically relates to a method for preparing a bipolar membrane with cross-linked anion / cation exchange layers. Background Technology

[0002] A bipolar membrane consists of a cation exchange layer, an interfacial intermediate layer, and an anion exchange layer. It is a dual-sided ion exchange composite membrane; under forward bias, the H+ ions on both sides of the membrane... + and OH - Under the influence of an electric field, water molecules migrate to the interfacial intermediate layer and form water molecules; while under reverse bias, the bipolar film can dissociate water molecules into H+. + and OH - And under the action of the electric field, H + Through the cation exchange membrane, OH - Through an anion exchange membrane, a salt solution can be separated into its corresponding acid and base.

[0003] The main methods for preparing bipolar membranes include hot pressing, bonding, casting, electrodeposition, and introducing cation and anion exchange groups on both sides of the membrane. Hot pressing involves stacking cation and anion membranes and heating them under high pressure, but this can easily lead to a high-resistivity region in the interfacial layer, and the adhesion between the two membrane layers may not be tight. Bonding uses an adhesive to combine the anion and cation membranes, but problems such as air bubbles and excessive adhesive thickness may occur, making it difficult to control the membrane performance. Introducing cation and anion exchange groups on both sides of a base membrane, while preventing membrane detachment, can result in significant loss of ion exchange groups and difficulty in controlling the reaction conditions. Casting is a simple process, involving casting an anion membrane solution onto the cation membrane and drying it to obtain the bipolar membrane. However, the casting process can lead to weak bonding between the two membrane layers, making them prone to detachment.

[0004] Patent CN116407955A discloses a bipolar membrane and its preparation method. The crosslinking method used is to form a bipolar membrane by chemical bonding of double bonds existing at the interface of the two membrane layers under the action of ultraviolet light. This crosslinking method may cause other side reactions induced by ultraviolet light, which may affect the membrane performance of the bipolar membrane.

[0005] Patent CN114188584A discloses a method for preparing bipolar membranes based on electrospinning and ultrasonic spraying. This patent employs a method of depositing a cation exchange membrane solution onto a homogeneous cation exchange membrane via electrospinning to form a porous network of electrospun fibers. Then, an anion exchange membrane solution is ultrasonically sprayed onto the electrospun fibers, allowing some of the anion exchange membrane solution to permeate into the porous structure. This enhances the compatibility of the cation and anion exchange membrane interfaces and improves interfacial adhesion. The interfacial adhesion is enhanced by constructing a structure where the intermediate layers of the bipolar membrane are mutually permeable.

[0006] While the casting method for preparing bipolar films is simple, it suffers from the problem of anion and cation film layer detachment during prolonged operation, significantly impacting the film's lifespan. Developing a bipolar film with high interfacial stability using the casting method requires breakthroughs, and overcoming the challenge of maintaining stable interfacial bonding between the two layers is a key focus of current research. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for preparing a bipolar membrane with cross-linked anion / cation exchange layers. The bipolar membrane prepared by this invention has tight bonding between the membrane layers and is not easily detached.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing a bipolar membrane with crosslinked anion / cation exchange layers includes the following steps:

[0010] 1) Synthesis of sulfonated polymers with basic structures

[0011] A bisphenol monomer containing an alkaline structure, other bisphenol monomers, difluorine monomers, sulfonated difluorine monomers, salt-forming agents, solvents, and dehydrating agents are mixed and subjected to a polycondensation reaction at 120–260°C for 1–30 h to obtain a sulfonated polymer containing an alkaline structure.

[0012] Among bisphenol monomers containing a basic structure, the basic structure is a benzimidazole group, a piperidine group, or an imidazole group, etc.; specific examples of bisphenol monomers containing a basic structure include: benzimidazole bisphenol, 4,4'-methylene-2,2'-benzimidazole bisphenol, etc.

[0013] Other bisphenol monomers are bisphenol A, bisphenol S, hexafluorobisphenol A or tetramethylbiphenyl;

[0014] The difluoro monomer is 4,4'-difluorobenzophenone, 4,4'-difluorodiphenyl sulfone or 4,4'-difluorotriphenyl ketone;

[0015] The sulfonated difluoro monomer is a sulfonated form of 4,4'-difluorobenzophenone, 4,4'-difluorodiphenyl sulfone, or 4,4'-difluorotriphenyldione.

[0016] Anhydrous potassium carbonate is preferred as the salt-forming agent;

[0017] The preferred solvent is N,N-dimethylacetamide (DMAc);

[0018] Toluene is preferred as a dehydrating agent;

[0019] In the synthesized sulfonated polymers containing basic structures, the basic groups are not limited to the benzimidazole structure, but also include structures such as piperidine and imidazole;

[0020] The preferred molar ratio of the bisphenol monomer containing the basic structure to other bisphenol monomers is 1:5 to 10;

[0021] The preferred molar ratio of sulfonated difluorinated monomer to difluorinated monomer is 1:0.1 to 5;

[0022] The preferred conditions for the polycondensation reaction are: first react at 150°C for 4 hours, then react at 170°C for 24 hours;

[0023] Specifically, the structures of the bisphenol monomers benzimidazole bisphenol and 4-4'-methylene-2,2'-benzimidazole bisphenol, which contain a basic structure, are shown in formulas (I) and (II):

[0024]

[0025] The structures of the synthesized sulfonated polymers containing basic structures are shown in formulas (IA) and (II-A):

[0026]

[0027] In formula (IA), (II-A),

[0028] A1 and A3 are independent of each other: A2 is:

[0029] 2) Synthesis of halogenated methylated polymers

[0030] The polymer, halomethyl ether, and anhydrous zinc chloride were mixed and reacted at 40–60 °C for 2–12 h to obtain the halomethylated polymer.

[0031] The polymer is selected from polyaryletherketone, polyethersulfone, polyphenylene ether, polystyrene, polyvinylidene fluoride, or polysulfone;

[0032] Halogenated methyl ethers are preferably chloromethyl ether or bromomethyl ether;

[0033] The preferred polymer-to-chloromethyl ether mass-to-volume ratio is 1:3-10, kg / L;

[0034] The preferred mass ratio of polymer to anhydrous zinc chloride is 1:1 to 2;

[0035] The structure of the halomethylated polymer is shown in formula (III):

[0036]

[0037] In formula (III),

[0038] X is: Cl, Br, or F;

[0039] 3) The sulfonated polymer with an alkaline structure obtained in step 1) is mixed with a solvent to prepare polymer solution A, and the first film is prepared by casting.

[0040] In polymer solution A, the content of sulfonated polymer with basic structure is 3-10 wt%;

[0041] The solvent is selected from one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP);

[0042] The specific operation of the casting method is as follows: the polymer solution is poured into a glass mold and dried at 40-200℃ for 8-24 hours to remove the solvent and prepare the first film.

[0043] 4) Add a water dissociation catalyst to the first membrane obtained in step 3) to obtain a first composite membrane with the water dissociation catalyst on its surface;

[0044] The water dissociation catalyst is selected from tin dioxide, iridium dioxide, nickel oxide, iron hydroxide, or graphene oxide;

[0045] 5) Mix the halogenated methylated polymer obtained in step 2) with a solvent to prepare polymer solution B. Cast polymer solution B onto the first composite membrane obtained in step 4) to form a membrane. After drying the solvent, a membrane with a two-layer cross-linked structure is obtained.

[0046] In polymer solution B, the content of the halogenated methylated polymer is 3–10 wt%.

[0047] The solvent is selected from one or more of DMF, DMAc, and NMP;

[0048] After casting the first composite membrane, the solvent is removed by drying at 40–200℃ for 8–24 hours to obtain a membrane with a two-layer cross-linked structure.

[0049] The cross-linking reaction formula is shown below:

[0050]

[0051] The cross-linked structure of the two-layer membrane is shown in formulas (IV) and (V):

[0052]

[0053]

[0054] In equations (IV) and (V), the definitions of A1, A2, and A3 are the same as in equations (IA) and (II-A), and the definition of X is the same as in equation (III);

[0055] 6) Quaternize the two-layer cross-linked membrane obtained in step 5) using amine compounds, and then dry it to obtain a bipolar membrane;

[0056] Amine compounds are secondary or tertiary amines. Examples of secondary amines include dimethylamine, diethylamine, or dipropylamine, while examples of tertiary amines include trimethylamine.

[0057] The structures of bipolar films are shown in formulas (VI) and (VII):

[0058]

[0059] In the above preparation method, the order of polymer solution casting in steps 3) and 5) can be changed. That is, the polymer solution B prepared by mixing the halogenated methylated polymer with the solvent is first cast into the first film, and a water dissociation catalyst is added on it. Then, the polymer solution A prepared by mixing the sulfonated polymer with the basic structure with the solvent is cast to form a two-layer cross-linked film.

[0060] The basic principles of this invention include:

[0061] The basic structure contains groups that can crosslink with chloro / bromomethyl groups, creating a crosslinked structure at the interface between the anion and cation exchange membranes of the bipolar membrane. Specifically, a layer of chloro / bromomethylated polymer is uniformly cast onto the cation exchange membrane containing the basic structure. The crosslinking between the chloro / bromomethyl group and the basic structure enhances the bonding force between the two membrane layers, overcoming problems such as easy detachment from the bipolar membrane interface.

[0062] The beneficial effects of this invention are as follows:

[0063] Currently, bipolar membranes prepared by casting method in this field have problems such as easy detachment between the two membrane layers. This invention innovatively enhances the bonding force between the two membrane layers of the bipolar membrane through cross-linking of anion / cation exchange layers, overcoming the problem of easy detachment of the bipolar membrane interface, and providing a good development direction for the preparation of bipolar membranes with high stability membrane layer interface. Attached Figure Description

[0064] Figure 1 This invention provides a schematic flowchart of a method for preparing a bipolar membrane with cross-linked anion / cation exchange layers.

[0065] Figure 2The present invention provides a current-voltage curve of a bipolar membrane with cross-linked anion / cation exchange layers. Detailed Implementation

[0066] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0067] In the following embodiments,

[0068] The raw material benzimidazole bisphenol was synthesized by referring to the thesis (Liao Junbin. Preparation, characterization and application of zwitterionic exchange membranes in vanadium batteries [D]. Zhejiang University of Technology, 2016.).

[0069] The raw material 4,4'-methylene-2,2'-benzimidazole bisphenol was synthesized with reference to the authorized patent (CN106279693B A side-chain benzimidazole-containing polyarylene ether ketone / sulfone and its preparation method and application).

[0070] Example 1:

[0071] Benzimidazole bisphenol (1.6738 g, 4 mmol), 4,4'-difluorobenzophenone (0.8728 g, 4 mmol), sulfonated 4,4'-difluorobenzophenone (2.5377 g, 6 mmol), bisphenol A (1.3697 g, 6 mmol), anhydrous potassium carbonate (1.5894 g, 11.5 mmol), 70 mL DMAc, and 35 mL toluene were added to a three-necked flask. The mixture was first refluxed at 150 °C for 4 h, and then reacted at 170 °C for 24 h. After the reaction was completed, the reaction solution was placed in anhydrous ethanol to precipitate the precipitate, and the precipitate was washed and dried to obtain a sulfonated polyarylether ketone with a main chain containing 40% benzimidazole.

[0072] 10g of polyarylether ketone, 100mL of chloromethyl ether and 10g of anhydrous zinc chloride were added to a three-necked flask and reacted at 40℃ for 12h. After the reaction was completed, the precipitate was washed and dried to obtain chloromethylated polyarylether ketone.

[0073] 5g of sulfonated polyaryletherketone with a benzimidazole backbone was dissolved in 100mL of DMAc. The cation exchange solution was then poured into a glass mold, and the solvent was dried at 60℃ for 12h to obtain a cation exchange membrane layer. 25mg of tin dioxide was then added to the surface of the cation exchange membrane. 5g of chloromethylated polyaryletherketone was dissolved in 100mL of DMAc and poured onto the cation exchange membrane layer. The solvent was dried at 60℃ for 12h to obtain a membrane with a bilayer structure (7cm in length, 5cm in width, and 181μm in thickness). Finally, the bilayer membrane was immersed in a 1.5wt.% diethylamine solution at 60℃ for 10h for quaternization treatment to obtain a bipolar membrane.

[0074] Example 2:

[0075] 4,4'-methylene-2,2'-benzimidazole bisphenol (0.4325 g, 1 mmol), 4,4'-difluorobenzophenone (0.8728 g, 4 mmol), sulfonated 4,4'-difluorobenzophenone (2.5377 g, 6 mmol), bisphenol A (2.0546 g, 9 mmol), anhydrous potassium carbonate (1.5894 g, 11.5 mmol), 50 mL DMAc, and 20 mL toluene were added to a three-necked flask. The mixture was refluxed at 150 °C for 4 h, and then reacted at 170 °C for 24 h. After the reaction was completed, the reaction solution was placed in anhydrous ethanol to precipitate the precipitate, and the precipitate was washed and dried to obtain sulfonated polyarylether ketone containing 10% benzimidazole side chain.

[0076] The other steps are the same as in Example 1, and a bipolar film is obtained.

[0077] Example 3:

[0078] Compared with Example 1, the content of benzimidazole bisphenol monomer was increased, and the reaction bisphenol monomer was adjusted to benzimidazole bisphenol (2.5107g, 6mmol) and bisphenol A (0.9131g, 4mmol), while the other reaction conditions remained unchanged, to obtain sulfonated polyarylether ketone with a main chain containing 60% benzimidazole.

[0079] The other steps are the same as in Example 1, and a bipolar film is obtained.

[0080] Example 4:

[0081] Compared with Example 2, the content of 4,4'-methylene-2,2'-benzimidazole bisphenol monomer was increased, and the reaction bisphenol monomers were adjusted to 4,4'-methylene-2,2'-benzimidazole bisphenol (0.9649, 2 mmol) and bisphenol A (1.8263 g, 8 mmol), while the other reaction conditions remained unchanged, to obtain sulfonated polyarylether ketone containing 20% ​​side-chain benzimidazole.

[0082] The other steps are the same as in Example 1, and a bipolar film is obtained.

[0083] Table 1 Relevant performance of Examples 1-4

[0084] Example 1 26.7 12.2 26.6 22.5 Example 2 23.1 10.7 26.8 21.8 Example 3 28.5 8.6 23.4 17.4 Example 4 24.6 7.9 22.5 18.6

Claims

1. A method for preparing a bipolar membrane with cross-linked anion / cation exchange layers, characterized in that, Includes the following steps: 1) Synthesis of sulfonated polymers with basic structures A bisphenol monomer containing an alkaline structure, other bisphenol monomers, difluorine monomers, sulfonated difluorine monomers, salt-forming agents, solvents, and dehydrating agents are mixed and subjected to a polycondensation reaction at 120~260℃ for 1~30h to obtain a sulfonated polymer containing an alkaline structure. The bisphenol monomer containing a basic structure is benzimidazole bisphenol or 4,4'-methylene-2,2'-benzimidazole bisphenol, with the structure shown in formula (I) or formula (II): （I） (II) Other bisphenol monomers are bisphenol A, bisphenol S, hexafluorobisphenol A, or tetramethylbiphenylhydrazine; difluoro monomers are 4,4'-difluorobenzophenone, 4,4'-difluorodiphenyl sulfone, or 4,4'-difluorotriphenyldione; sulfonated difluoro monomers are sulfonates of 4,4'-difluorobenzophenone, 4,4'-difluorodiphenyl sulfone, or 4,4'-difluorotriphenyldione; the salting agent is anhydrous potassium carbonate; the solvent is N,N-dimethylacetamide; and the dehydrating agent is toluene. 2) Synthesis of halogenated methylated polymers The polymer, halomethyl ether, and anhydrous zinc chloride were mixed and reacted at 40-60°C for 2-12 hours to obtain the halomethylated polymer. The polymer is selected from polyaryletherketone, polyethersulfone, polyphenylene ether, polystyrene, polyvinylidene fluoride, or polysulfone; 3) The sulfonated polymer with an alkaline structure obtained in step 1) is mixed with a solvent to prepare polymer solution A, and the first film is prepared by casting. 4) Add a water dissociation catalyst to the first membrane obtained in step 3) to obtain a first composite membrane with the water dissociation catalyst on its surface; The water dissociation catalyst is selected from tin dioxide, iridium dioxide, nickel oxide, iron hydroxide, or graphene oxide; 5) Mix the halogenated methylated polymer obtained in step 2) with a solvent to prepare polymer solution B. Cast polymer solution B onto the first composite membrane obtained in step 4) to form a membrane. After drying the solvent, a membrane with a two-layer cross-linked structure is obtained. 6) The membrane with the two-layer cross-linked structure obtained in step 5) is quaternized using amine compounds and dried to obtain a bipolar membrane.

2. The method for preparing the bipolar membrane with cross-linked anion / cation exchange layers as described in claim 1, characterized in that, In step 2), the halomethyl ether is chloromethyl ether or bromomethyl ether.

3. The method for preparing the bipolar membrane with cross-linked anion / cation exchange layers as described in claim 1, characterized in that, In step 3) or step 5), the solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

4. The method for preparing the bipolar membrane with cross-linked anion / cation exchange layers as described in claim 1, characterized in that, In step 6), the amine compound is a secondary amine or a tertiary amine. The secondary amine is selected from dimethylamine, diethylamine or dipropylamine, and the tertiary amine is selected from trimethylamine.

5. The method for preparing the bipolar membrane with crosslinked anion / cation exchange layers as described in any one of claims 1 to 4, characterized in that, The casting order of polymer solutions in steps 3) and 5) is changed. Specifically, the polymer solution B prepared by mixing the halogenated methylated polymer with a solvent is first cast into the first film. After adding a water dissociation catalyst on it, the polymer solution A prepared by mixing the sulfonated polymer with an alkaline structure with a solvent is then cast to form a two-layer cross-linked film.

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