Homopolymerized bipolar ionic membrane and preparation method thereof

Abstract

The invention relates to the technical field of separation membrane materials. The homopolymerized bipolar ionic membrane comprises at least one bottom lining and a functional membrane layer, the functional membrane layer comprises a cation exchange membrane layer, an anion exchange membrane layer and a performance improving component, and the cation exchange membrane layer, the anion exchange membrane layer and the performance improving component are crosslinked and polymerized into a whole through a carbon-carbon covalent bond. The preparation method of the homopolymerized bipolar ionic membrane comprises the following steps: preparing a coating solution A from styrene, divinylbenzene, an initiator, a performance improving component and a solvent; preparing a coating solution B from chloromethyl styrene, divinylbenzene, an initiator, a performance improving component and a solvent; coating a microporous membrane A with the coating liquid A, coating a microporous membrane B with the coating liquid B, compounding the membrane A and the membrane B, and carrying out pressurized cross-linking polymerization to form a base membrane; aminating the base membrane to obtain a B-side functionalized membrane; and protecting the surface B, and sulfonating to obtain the bipolar membrane. And the obtained product has good stability and high selectivity.

Description

Technical Field

[0001] The invention relates to the technical field of separation membrane materials and discloses a homopolymeric bipolar ion membrane and a preparation method thereof. Background Art

[0002] Ion exchange membranes can be used to manufacture devices such as electrodialysis, electro-desalting, 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 preparation of acids and alkalis by water dissociation. They can also be used in electrolytic hydrogen production, electrolytic alkali production, and various battery devices. The bipolar membrane dissociates water and separates hydrogen ions and hydroxide ions under the action of an electric field, so it can be used to produce acids and alkalis from salt, and has good application prospects.

[0003] 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.

[0004] U.S. Patent No. 4,024,043 uses a high-density polyethylene film as a substrate, impregnates styrene, divinylbenzene and an initiator into the substrate, initiates 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. Chinese Patent No. 2010102819974 uses the same method, but replaces the substrate material with a binary blend of polyethylene and ethylene-octene copolymer elastomer or a ternary blend of polyethylene, ethylene-octene copolymer elastomer and butene rubber, thereby improving the performance of the membrane product obtained by this method. In these methods, there is unevenness 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 coating liquid enters the non-crystalline area at a faster rate, so the impregnation in this area is higher, and the relative strength of the product film here is lower. At the same time, the substrate has defects in the film forming process, and the impregnation ratio of the coating liquid at the defective point is higher, and starting from this point, a dendritic high impregnation area is formed. The final result is that this defect is magnified in the finished membrane, greatly reducing the qualified rate of the finished membrane. On the other hand, since a non-porous membrane is used, its swelling and impregnation temperature is high, the time is long, and the consumption of coating liquid is large; the chemical stability of the polyethylene backing is insufficient, and carbonization occurs during the sulfonation process, which affects the strength of the product. Summary of the invention

[0005] The purpose of the invention is to disclose a bipolar ion membrane with good stability and higher energy saving and a preparation method thereof.

[0006] The homopolymeric bipolar ion membrane of the present invention comprises at least one substrate and a functional membrane layer, wherein the functional membrane layer comprises a cation exchange membrane layer, an anion exchange membrane layer and a performance improvement component, and the cation exchange membrane layer, anion exchange membrane layer and the performance improvement component are cross-linked and polymerized into one through carbon-carbon covalent bonds.

[0007] The preparation method of the homopolymeric bipolar ion membrane of the present invention comprises: (1) preparing a coating liquid A and a coating liquid B, cutting two substrates to the same size, marking them as substrate A and substrate B respectively, cutting a polyester film, the polyester film being slightly larger than the size of the substrate; (2) laying a layer of polyester film; (3) laying a layer of substrate A on the polyester film; (4) uniformly coating the coating liquid A on the substrate A, and removing air bubbles; (5) laying a substrate B on the substrate A coated with the coating liquid A; (6) coating the coating liquid B on the substrate B, and removing air bubbles; (7) laying a polyester film on the substrate B coated with the coating liquid B; (8) repeating (3) to (7) for multiple times. The method comprises the steps of: (1) performing vacuum degassing on the coated stack AB; (10) polymerizing the coated stack AB at 65-120° C. for 12-24 hours at a pressure of 0.2-10 MPa; (11) removing the polyester film to obtain a base film; (12) immersing the base film in an amine solution, heating and aminating for 6-12 hours to generate an anion exchange membrane layer, removing the base film and washing it to obtain a B-side functionalized membrane; (13) dehydrating the B-side functionalized membrane to protect the B-side; (14) functionalizing the A-side of the B-side functionalized membrane to generate a cation exchange membrane layer; and (15) washing the base film thoroughly to obtain the homopolymeric bipolar ion membrane of the present invention.

[0008] The base liner is a microporous membrane made of polyolefin, polyvinylidene fluoride or polytetrafluoroethylene through a stretching or phase transfer process.

[0009] The backing is a mesh made of various organic polymer fibers or inorganic fibers, including but not limited to chlorofluorocarbon fibers, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, glass fiber woven fabric or non-woven fabric.

[0010] The substrate is a composite material of a microporous membrane made by stretching or phase transfer process and a mesh made of organic polymer fibers or inorganic fibers, such as a composite membrane in which a polytetrafluoroethylene microporous membrane is composited on at least one side of a polypropylene non-woven fabric.

[0011] The performance-improving component is a high molecular polymer containing carbon-carbon double bonds and a mixture thereof. The high molecular polymer containing carbon-carbon double bonds includes but is not limited to butyl rubber, nitrile rubber, styrene-butadiene rubber, chloroprene rubber and natural rubber.

[0012] The cation exchange membrane layer is a sulfonated product of a cross-linked copolymer A, which includes but is not limited to a cross-linked copolymer of styrene, diphenylethylene and the performance-improving component, a cross-linked copolymer of methacrylic acid, diphenylethylene and the performance-improving component, and a cross-linked copolymer of methacrylic anhydride, diphenylethylene and the performance-improving component.

[0013] The cation exchange functionalization includes benzene ring sulfonation, carboxylic acid base neutralization and carboxylic anhydride base hydrolysis.

[0014] The anion exchange membrane layer is a product of amination reaction of a cross-linked copolymer B and an amine, wherein the cross-linked copolymer B includes but is not limited to a cross-linked copolymer of chloromethylstyrene, diphenylethylene and a performance-improving component.

[0015] The amines are any tertiary amine, secondary amine or primary amine and mixtures thereof, including but not limited to trimethylamine, triethylamine, dimethylamine, diethylamine, methylamine, ethylamine, pyrrole, pyridine, and furan.

[0016] The coating liquid A comprises but is not limited to divinylbenzene, a performance-improving component, a polymerization initiator, and also comprises but is not limited to chloromethylstyrene, olefin carboxylic acid, and olefin carboxylic anhydride.

[0017] The coating liquid B includes but is not limited to a mixture of chloromethylstyrene, diphenylethylene, a performance-improving component, and a polymerization initiator.

[0018] The initiator is any initiating compound and a mixture thereof that can initiate crosslinking polymerization between styrene, divinylbenzene and the performance improving component at 650-120° C., and the initiating compound includes but is not limited to azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide tert-butyl peroxyethylhexanoate.

[0019] The beneficial effects of the network interpenetrating homogeneous bipolar ion membrane of the present invention are:

[0020] (1) The anion membrane layer, the cationic membrane layer and the performance-improving component in the network interpenetrating homogeneous bipolar ion membrane of the present invention are integrated into one by carbon-carbon covalent bonds and form a submicron-scale network interpenetrating structure with the base membrane, and the structure is stable.

[0021] (2) The selectivity, resistivity, water permeability, swelling rate and flexibility of the product membrane can be adjusted by adjusting the ratio of the performance-improving components in the anion and cation exchange membrane layer and the degree of cross-linking of the polymer.

[0022] (3) In the prior art, the polyolefin substrate needs to be swollen at high temperature before styrene, divinylbenzene and polymerization initiator can be impregnated into the substrate. However, the high temperature and long time of swelling and impregnation make the coating liquid unstable, and the impregnation amount and impregnation uniformity are difficult to accurately control. The present invention avoids the swelling process of the base film by using a microporous membrane, making the impregnation process simple and controllable. It avoids the waste of excess coating liquid.

[0023] (4) The substrate is preferably a biaxially stretched polytetrafluoroethylene microporous membrane, because its chemical stability is significantly better than that of polyolefin materials, so the sulfonation process will not significantly reduce the strength of the membrane.

[0024] (5) The porosity of the polymer microporous membrane is as high as over 80%, so an extremely high impregnation amount can be obtained, thereby reducing the mass ratio of the substrate and obtaining a high-performance bipolar ion membrane.

[0025] (6) By utilizing the characteristics of polymer microporous membranes, the thickness of the membrane can be greatly reduced, thereby reducing the resistance of the finished membrane and achieving energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The network interpenetrating homogeneous bipolar ion membrane of the present invention is a simplified chemical structure diagram of the functional membrane layer that is cross-linked and polymerized into one by carbon-carbon covalent bonds in Example 1. Wherein a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w are integers including 0; wherein A represents an anion exchange membrane layer, and B represents a cation exchange membrane layer. DETAILED DESCRIPTION Example 1

[0027] (1) 81.5 g of styrene (50%), 12 g of divinylbenzene (12%), 1.5 g of benzoyl peroxide (1.5%), and 5 g of nitrile rubber (5%) were mixed to form coating solution A; 1 g of chloromethylstyrene (30%), 8 g of divinylbenzene (8%), 1 g of benzoyl peroxide (1%), and 5 g of nitrile rubber (5%) were mixed to form coating solution B; a polytetrafluoroethylene microporous membrane (pore size) with a thickness of 0.05 mm was coated with a PTFE film. A polytetrafluoroethylene microporous membrane (porosity 80%, average pore size 0.4 μm) with a thickness of 0.05 mm (porosity 80%, average pore size 0.4 μm) was loaded into a size of 260*500 mm and marked as backing A. A polyester film was cut into a size of 310*550 mm; (2) a layer of polyester film was laid flat; (3) a layer of backing A was laid flat on the polyester film; (4) the backing A was evenly coated with the above-mentioned (5) Lay a substrate B on the substrate A coated with coating liquid A, (6) Apply coating liquid B on the substrate B, and remove bubbles; (7) Lay a polyester film on the substrate B coated with coating liquid B, (8) Repeat (3)-(7) 20 times to obtain a coating pile AB; (9) Vacuum degas the coating pile AB, (10) Polymerize the coating pile AB at 80°C for 8 hours under a pressure of 2MPa; (11) Remove the polyester film to obtain a base membrane; (12) Place the base membrane in a trimethylamine solution and perform amination at 35°C for 6-12 hours to generate an anion exchange membrane layer Y, which is then taken out and washed to obtain a B-side functionalized membrane; (13) Dehydrate the B-side functionalized membrane to protect the B side, (14) Functionalize the B-side functionalized membrane for cation exchange to generate a cation exchange membrane layer Z; (15) Thoroughly wash to obtain the homopolymeric bipolar ion membrane of the present invention.

[0028] According to the detection method disclosed in Chinese Patent ZL022186794, the transmembrane voltage of the bipolar ion membrane was measured to be 2.12V under the condition of current density of 1000A / m2 in 0.5mole / L NaCl aqueous solution.

Claims

1. Homopolymeric bipolar ion membrane, characterized in that The invention comprises at least one substrate and one functional membrane layer, wherein the functional membrane layer comprises a cation exchange membrane layer, an anion exchange membrane layer and a performance improvement component, and the cation exchange membrane layer, anion exchange membrane layer and the performance improvement component are cross-linked and polymerized into one through carbon-carbon covalent bonds.

2. A method for preparing a homopolymeric bipolar ion membrane, characterized in that The method comprises: (1) preparing coating liquid A and coating liquid B, cutting two substrates to the same size, marking them as substrate A and substrate B respectively, cutting a polyester film, the polyester film being slightly larger than the substrate size; (2) laying a layer of polyester film; (3) laying a layer of substrate A on the polyester film; (4) evenly coating the coating liquid A on the substrate A and removing air bubbles; (5) laying a substrate B on the substrate A coated with the coating liquid A; (6) coating the coating liquid B on the substrate B and removing air bubbles; (7) A polyester film is laid flat on a substrate B coated with a coating liquid B, (8) (3) to (7) are repeated multiple times to obtain a coating stack AB; (9) the coating stack AB is vacuum degassed, (10) the coating stack AB is polymerized at 65-120° C. for 12-24 hours under a pressure of 0.2-10 MPa; (11) the polyester film is removed to obtain a base film; (12) the base film is immersed in an amine solution, heated for amination for 6-12 hours to generate an anion exchange membrane layer, and the base film is removed and cleaned to obtain a functionalized membrane on the B surface; (13) dehydrating the B-side functionalized membrane to protect the B-side, (14) functionalizing the A-side of the B-side functionalized membrane for cation exchange to generate a cation exchange membrane layer; (15) The homopolymeric bipolar ion membrane of the present invention is obtained by thorough cleaning.

3. According to claims 1 and 2, the homopolymeric bipolar ion membrane and the preparation method are characterized in that The substrate is a microporous membrane made of polymer by stretching or phase transfer process, or a mesh made of various organic polymer fibers or inorganic fibers, or a composite material of the microporous membrane and a mesh made of organic polymer fibers or inorganic fibers.

4. The homopolymeric bipolar ion membrane and preparation method according to claims 1 and 2, characterized in that The performance-improving component is a high molecular polymer containing carbon-carbon double bonds and a mixture thereof. The high molecular polymer containing carbon-carbon double bonds includes but is not limited to butyl rubber, nitrile rubber, styrene-butadiene rubber, chloroprene rubber and natural rubber.

5. The homopolymeric bipolar ion membrane and preparation method according to claims 1 and 2, characterized in that The cation exchange membrane layer is a sulfonated product of a cross-linked copolymer A, which includes but is not limited to a cross-linked copolymer of styrene, diphenylethylene and the performance-improving component, a cross-linked copolymer of methacrylic acid, diphenylethylene and the performance-improving component, and a cross-linked copolymer of methacrylic anhydride, diphenylethylene and the performance-improving component.

6. The homopolymeric bipolar ion membrane and preparation method according to claims 1 and 2, characterized in that The anion exchange membrane layer is a product of amination reaction of a cross-linked copolymer B and an amine, wherein the cross-linked copolymer B includes but is not limited to a cross-linked copolymer of chloromethylstyrene, diphenylethylene and a performance-improving component.

7. The method for preparing a homopolymeric bipolar ion membrane according to claim 2, characterized in that The cation exchange functionalization includes benzene ring sulfonation, carboxylic acid base neutralization and carboxylic anhydride base hydrolysis.

8. The method for preparing a homogeneous bipolar ion membrane according to claim 2, characterized in that The amines are any tertiary amine, secondary amine or primary amine and mixtures thereof, including but not limited to trimethylamine, triethylamine, dimethylamine, diethylamine, methylamine, ethylamine, pyrrole, pyridine, and furan.

9. The method for preparing a homogeneous bipolar ion membrane according to claim 2, characterized in that The coating liquid A comprises but is not limited to divinylbenzene, a performance-improving component, a polymerization initiator, and also comprises but is not limited to chloromethylstyrene, olefin carboxylic acid, and olefin carboxylic anhydride.

10. The method for preparing a homopolymeric bipolar ion membrane according to claim 2, characterized in that The coating liquid B includes but is not limited to a mixture of chloromethylstyrene, diphenylethylene, a performance-improving component, and a polymerization initiator.

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