Preparation method of homogeneous cation exchange membrane

Abstract

The invention provides a preparation method of a homogeneous cation exchange membrane, and belongs to the technical field of ion exchange membrane preparation, the preparation method comprises the following steps: adding a certain mass of a pre-sulfonated membrane preparation raw material into a certain volume of an organic solvent, adding a certain amount of a cross-linking agent, and continuously stirring to dissolve the raw material to prepare a membrane casting solution with a certain concentration; and directly spraying a certain amount of the membrane casting solution on the surface layer of the supporting layer, carrying out heat treatment in a drying oven, and washing with deionized water after the treatment is completed to separate the membrane, thereby obtaining the homogeneous cation exchange membrane. The ionic membrane disclosed by the invention is more stable in structure and relatively strong in mechanical property, and the cross-linking agent is added, so that the compatibility between the coating and the supporting layer is improved, and the binding property between the coating and the supporting layer is improved, and therefore, the coating and the supporting layer are not easy to separate in a long-term use process. A cross-linking agent is added in the membrane preparation process, so that a tighter structure can be formed between molecular chains of the polymer, the influence and damage of the external environment effect on the molecular chains of the polymer are reduced, and the acid and alkali resistance of the material is improved.

Description

Technical Field

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

[0002] Electrodialysis technology is a widely used water treatment and water resource extraction technology. As the core component of electrodialysis technology, the performance of ion exchange membrane is particularly important. According to different structures, ion exchange membranes can be divided into heterogeneous membranes, semi-homogeneous membranes and homogeneous membranes. Among them, homogeneous ion exchange membranes have the best performance, but their production process is complicated and has high technical difficulty. Therefore, their production and promotion are limited.

[0003] The method for preparing homogeneous cation exchange membrane that has been commercially applied at present mainly immerses the basement membrane in a solution containing styrene and divinylbenzene, or coats the solution containing styrene and divinylbenzene on the basement membrane, and then polymerizes the basement membrane under the conditions of pressurization and heating to obtain the basement membrane, and finally modifies the surface of the basement membrane to introduce sulfonic acid groups to form a homogeneous ion exchange membrane (such as the Chinese invention patent application with publication numbers CN107321199A and CN102134327A). Although this preparation method has been widely used, it still has some disadvantages. First, the method requires a violent sulfonation reaction of a single film or a rolled film, and the remaining sulfonating agent needs to be removed after the reaction is completed. These processes are cumbersome and difficult to control, and can also cause the destruction of the basement membrane. Since the acid and alkali resistance of styrene-divinylbenzene is not significant, it cannot be used in the application scenario of strong acid and alkali. In addition, styrene-divinylbenzene has poor thermal stability, and loses elasticity and toughness during long-term use, resulting in a decrease in mechanical strength. During long-term use of the membrane, the ion membrane will undergo repeated swelling. Since the bonding force between the membrane coating synthesized by the preparation method and the base membrane is insufficient, separation is likely to occur during the swelling process of the membrane. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a homogeneous cation exchange membrane to solve at least one technical problem existing in the above-mentioned background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for preparing a homogeneous cation exchange membrane, comprising:

[0007] A certain mass of pre-sulfonated film-making raw materials is added into a certain volume of organic solvent, and a certain amount of cross-linking agent is added, and the mixture is stirred continuously to dissolve the raw materials, so as to obtain a film casting solution of a certain concentration;

[0008] A certain amount of casting liquid is poured into the mold and scraped flat or the casting liquid is directly sprayed on the surface of the support layer, and heat-treated in an oven. After the treatment, the membrane is soaked in deionized water to separate from the mold to obtain a homogeneous cation exchange membrane.

[0009] The preparation of new sulfonated polymers adopts pre-sulfonation, that is, in the process of polymer synthesis, sulfonic acid groups are introduced into the monomers in advance and then the sulfonated monomers are polymerized to form new sulfonated polymers. This method has the following advantages: a. More uniform distribution of sulfonic acid groups: The pre-sulfonation method introduces sulfonic acid groups evenly into the molecular chain, avoiding the instability of sulfonation positions that may occur in the post-sulfonation process, which is prone to chain breaking, branching, cross-linking or side reactions. b. Improve the ion selectivity of the membrane: Due to the uniform distribution of sulfonic acid groups, the electric field distribution inside the membrane is more consistent, thereby enhancing the selective transmission capacity of ions and reducing the interference of impurity ions on membrane performance. c. Improve the dimensional stability of the membrane: The uniform sulfonation distribution reduces the uneven swelling of the membrane, allowing it to maintain a stable dimensional shape under working conditions and improve the long-term service life of the membrane. In the present invention, a new type of sulfonated product is directly used to prepare a cation exchange membrane. Compared with the traditional method of first preparing a base membrane and then subjecting the base membrane to a sulfonation reaction, the reaction is more controllable, the main chain structure of the molecular chain is not destroyed, and the chain breaking or brittleness problems that may be caused during the membrane preparation process are avoided, so that the membrane material maintains high mechanical strength and can work stably for a long time in a dynamic environment.

[0010] Optionally, the pre-sulfonated membrane-forming raw material is a mixture of one or more of sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polyetherketoneketone, sulfonated polyetheretherketoneketone, sulfonated polyetherketoneetherketoneketone, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyphenylsulfone or sulfonated polyarylsulfone.

[0011] Optionally, the sulfonation degree of the pre-sulfonated membrane raw material is 10%-60%; the sulfonation degree is the core source of the conductivity of the cationic membrane, and its proportion directly determines the ion exchange capacity and conductivity of the membrane. Too high a sulfonation degree will lead to excessive hydrophilicity of the membrane, increased water solubility, and decreased mechanical strength; too low a sulfonation degree will reduce the conductivity of the cationic membrane, increase membrane resistance, and affect the actual performance of the equipment. The present invention controls the sulfonation degree of the sulfonated polymer between 10% and 60%, ensuring that the membrane has good mechanical strength and dimensional stability while having efficient ion conduction.

[0012] Optionally, the concentration of the pre-sulfonated membrane-making raw material is 3%-60%;

[0013] Optionally, the cross-linking agent is a mixture of one or more of polyvinyl alcohol, polyvinyl pyrrolidone, divinyl benzene, formaldehyde, maleic acid or glutaraldehyde cross-linking agents.

[0014] Optionally, the concentration of the crosslinking agent is 1%-10%. Ratio of crosslinking agent: The crosslinking agent enhances the mechanical properties of the membrane by forming an intermolecular crosslinking network. A high ratio may reduce the sulfonation sites of the membrane and affect the conductivity; a low ratio may loosen the structure of the membrane, and reduce durability and stability. The crosslinking agent concentration of the present invention is optimized at 1-10%, so that the membrane has better conductivity, mechanical strength and flexibility, further reduces the swelling phenomenon of the membrane, and prolongs the service life of the membrane.

[0015] Optionally, the organic solvent is a mixture of one or more solvents selected from dimethyl sulfoxide, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dichloromethane or chloroform.

[0016] Optionally, the support layer is in the form of mesh, non-woven fabric or porous membrane.

[0017] Optionally, the support layer is made of one of polypropylene, polyethylene, polyvinyl chloride, polytetrafluoroethylene, polyethylene terephthalate or glass fiber, and has a thickness of 10 μm-200 μm.

[0018] Too high a temperature will lead to polymer degradation or excessive cross-linking, weaken the activity of the sulfonic acid group, reduce the ion exchange performance, and also cause the lining mesh to deform, reducing the product qualification rate; too low a temperature will lead to insufficient cross-linking and insufficient mechanical properties of the membrane. Optionally, the drying temperature described in the present invention is 40℃-200℃, and too long a heat treatment time will lead to excessive curing of the membrane and reduced flexibility; too short a time will result in insufficient cross-linking and unstable membrane structure. The drying time described in the present invention is 10-120min, which balances the cross-linking effect and the flexibility of the membrane, ensuring mechanical strength and conductivity. The present invention adopts a gradient heating and cooling method, and a total of five stages of temperature are used for drying, namely low temperature drying-medium temperature drying-high temperature drying-medium temperature drying-low temperature drying. Among them, the drying temperature is 40℃-80℃ for low temperature drying, 80℃-120℃ for medium temperature drying, and 120℃-200℃ for high temperature drying. The drying time for each stage is 1-60min, which ensures uniform cross-linking, reduces the deformation of the lining mesh, and ensures the stability and mechanical properties of the membrane.

[0019] The beneficial effects of the present invention are as follows: a pre-sulfonated raw material for making a film is mixed with a cross-linking agent as a film precursor, and an organic solvent is used to dissolve the raw material for making a film, and the film can be formed after heat treatment. The operation process is simple and easy to control automatically. The pre-sulfonated raw material for making a film is dissolved and then formed into a film. The raw material for making a film with excellent mechanical properties, high strength and good impact resistance can be selected. In addition, the addition of the cross-linking agent promotes the formation of covalent bonds or ionic bonds between polymer molecules, making the structure of the ion membrane more stable, thereby enhancing its mechanical properties. And it can be coated on a reinforced mesh, further increasing the strength and having no significant effect on the conductivity of the membrane. Due to the addition of the cross-linking agent, the compatibility of the coating and the support layer is improved, thereby improving the bonding between them, so that the coating and the support layer are not easy to separate during long-term use. Adding a cross-linking agent in the film-making process can form a tighter structure between the molecular chains of the polymer, thereby reducing the influence and damage on the polymer molecular chains due to the external environment, and improving the acid and alkali resistance of the material.

[0020] Additional advantages of the present invention will be more clearly given in the following description or learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0022] Figure 1 This is a flow chart of the method for preparing a homogeneous cation exchange membrane according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below by the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0024] It should be understood by those skilled in the art that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0025] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with that in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0026] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements and / or groups thereof.

[0027] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0028] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings, and the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0029] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0030] Ion exchange membrane is the core component of electrodialysis technology. According to the different membrane structures, ion exchange membranes can be divided into heterogeneous membranes, semi-homogeneous membranes and homogeneous membranes. Among them, the performance of homogeneous ion exchange membranes is excellent, but the manufacturing method is complicated and the technical difficulty is high. Therefore, production and promotion are restricted. The homogeneous cation exchange membrane manufacturing method of the present invention is easy to operate and the manufacturing conditions are easy to control, which solves the problem that the existing homogeneous cation exchange membrane manufacturing method is complicated and difficult to control. The homogeneous cation exchange membrane manufactured by the traditional method has poor mechanical properties and is not conducive to long-term use. The homogeneous cation exchange membrane produced by the manufacturing method of the present invention has sufficient mechanical strength and can be used under harsh operating conditions, solving the problem of poor mechanical strength of the existing homogeneous cation exchange membrane. The cation exchange membrane prepared by the traditional method, due to the insufficient bonding between the coating and the support layer, causes repeated swelling of the membrane during the long-term use of the membrane, making the support layer and the coating easy to separate, seriously affecting the service life of the ion exchange membrane, and solving the problem that the coating and the support layer of the existing homogeneous cation exchange membrane are easy to separate. The cation exchange membrane prepared by the traditional method has poor acid and alkali resistance and is limited in the use scenario. The homogeneous cation exchange membrane prepared by the present invention has high tolerance to acid and alkali solutions, and can be applied to application scenarios requiring high acid and alkali resistance, thereby solving the problem of poor acid and alkali resistance of existing homogeneous cation exchange membranes.

[0031] In addition to comparing the basic performance of the ion exchange membrane with two commercial ion exchange membranes, the membrane was concentrated using a laboratory-made micro ED device (10 membrane pairs), with the initial NaCl concentration of both the dilution and the concentrate being 1 mol / L, and compared with a commercial ion exchange membrane. When the operation time was the same and the concentration multiple was the same, the energy consumption of the prepared membrane and the commercial membrane was also compared. The results are listed in Table 1.

[0032] Example 1

[0033] In this embodiment 1, a method for preparing a homogeneous cation exchange membrane is provided, comprising: mixing 400 g of sulfonated polyether ketone with a sulfonation degree of 25%, 20 g of polyvinyl alcohol and 2000 g of N,N-dimethylacetamide, stirring at 40°C for 20 hours, obtaining a casting solution after complete dissolution, taking 60 mL of the casting solution and pouring it into a stainless steel mold with a length and width of 10 cm*20 cm, putting it into an oven, evaporating the solvent at temperatures of 50°C, 90°C, 125°C, 90°C and 50°C for 15 min, 7 min, 5 min, 7 min and 15 min, respectively, then taking it out of the oven and cooling it, pouring deionized water into the mold, and the ion membrane automatically falls off from the stainless steel mold, which is the homogeneous cation exchange membrane described in the present invention.

[0034] Example 2

[0035] In this embodiment 2, a method for preparing a homogeneous cation exchange membrane is provided, comprising: mixing 500g of sulfonated polyethersulfone with a sulfonation degree of 40%, 20g of polyvinyl alcohol and 2000g of N,N-dimethylformamide, stirring at 40°C for 20 hours, and obtaining a casting solution after complete dissolution, taking 40mL of the casting solution and spraying it evenly on a PET non-woven fabric with a length and width of 10*20cm and a thickness of 55μm, putting it in an oven, and evaporating the solvent at 40°C, 85°C, 150°C, 85°C, and 40°C for 12min, 6min, 3min, 6min, and 12min, respectively, to obtain the homogeneous cation exchange membrane described in the present invention. The obtained ion membrane is soaked in 0.1M hydrochloric acid solution and 0.1M sodium hydroxide solution for 24h, and repeated for 10 cycles, and no separation occurs between the surface coating of the ion membrane and the supporting layer.

[0036] Example 3

[0037] In this embodiment 3, a method for preparing a homogeneous cation exchange membrane is provided, comprising: mixing 500g of sulfonated polyetheretherketone with a sulfonation degree of 40%, 20g of polyvinyl pyrrolidone and 2000g of dimethyl sulfoxide, stirring at 40°C for 20 hours, and obtaining a casting solution after complete dissolution, taking 40mL of the casting solution and spraying it evenly on a PET non-woven fabric with a length and width of 10*20cm and a thickness of 55μm, putting it in an oven, and evaporating the solvent at 60°C, 100°C, 180°C, 100°C, and 60°C for 15min, 10min, 5min, 10min, and 15min, respectively, to obtain the homogeneous cation exchange membrane described in this embodiment. The obtained ion membrane is soaked in 0.1M hydrochloric acid solution and 0.1M sodium hydroxide solution for 24h, and repeated for 10 cycles, and no separation occurs between the surface coating of the ion membrane and the supporting layer.

[0038] Table 1 Performance comparison of membranes made from three embodiments and two commercial membranes

[0039]

[0040] In summary, the preparation method of the commercial homogeneous cation exchange membrane is to coat styrene, divinylbenzene and other components on a polyvinyl chloride or polypropylene reinforced net, and then heat to obtain a base film, and then introduce sulfonic acid groups through a chemical reaction. This requires a violent sulfonation reaction of the membrane, and after the reaction is completed, the unreacted sulfonating agent needs to be removed. These reaction processes are relatively complex and difficult to control. The method for preparing a homogeneous cation exchange membrane used in the present invention uses a pre-sulfonated film-making raw material mixed with a cross-linking agent as a film-making precursor, and an organic solvent is used to dissolve the film, and the film can be formed after heat treatment. The operation process is simple and easy to automatically control. The homogeneous cation exchange membrane currently used in commercial applications has poor mechanical strength and a short service life. The method adopted by the present invention dissolves the film-making raw material sulfonated in advance to form a film, and can select a film-making raw material with excellent mechanical properties, high strength, and good impact resistance. In addition, the addition of a cross-linking agent promotes the formation of covalent bonds or ionic bonds between polymer molecules, so that the structure of the ion membrane is more stable, thereby enhancing its mechanical properties. And it can be coated on a reinforcing mesh to further increase the strength and have no significant effect on the conductivity of the membrane. The cation exchange membrane prepared by the traditional method is prone to swelling during long-term use. During the repeated swelling of the membrane, the supporting mesh and the coating are easily separated. Due to the addition of a cross-linking agent, the method for preparing a cation exchange membrane of the present invention improves the compatibility of the coating and the supporting layer, thereby improving the bonding between them, so that the coating and the supporting layer are not easy to separate during long-term use. The cation exchange membrane prepared by the traditional method has poor acid and alkali resistance and is limited in its use scenarios. In the present invention, the addition of a cross-linking agent during the membrane preparation process can form a tighter structure between the molecular chains of the polymer, thereby reducing the impact and damage to the polymer molecular chains due to the external environment, thereby improving the acid and alkali resistance of the ion membrane. Therefore, the homogeneous cation exchange membrane prepared by the present invention can be applied to application scenarios that require high acid and alkali resistance.

[0041] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative work on the basis of the technical solution disclosed in the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a homogeneous cation exchange membrane, characterized in that: include: A certain mass of pre-sulfonated film-making raw materials is added into a certain volume of organic solvent, and a certain amount of cross-linking agent is added, and the mixture is stirred continuously to dissolve the raw materials, so as to obtain a film casting solution of a certain concentration; A certain amount of casting liquid is directly sprayed on the surface of the support layer, and heat-treated in an oven. After the treatment, the membrane is soaked in deionized water to separate it from the mold to obtain a homogeneous cation exchange membrane.

2. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The pre-sulfonated membrane-forming raw material is a mixture of one or more of sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polyetherketoneketone, sulfonated polyetheretherketoneketone, sulfonated polyetherketoneetherketoneketone, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyphenylsulfone or sulfonated polyarylsulfone.

3. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The sulfonation degree of the pre-sulfonated membrane-making raw material is 10%-60%.

4. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The concentration of the pre-sulfonated membrane-making raw material is 3%-60%.

5. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The cross-linking agent is a mixture of one or more of polyvinyl alcohol, polyvinyl pyrrolidone, divinyl benzene, formaldehyde, maleic acid or glutaraldehyde cross-linking agents.

6. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The concentration of the cross-linking agent is 1%-10%.

7. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The organic solvent is a mixture of one or more solvents selected from dimethyl sulfoxide, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dichloromethane or chloroform.

8. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The support layer is in the form of mesh, non-woven fabric or porous membrane.

9. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The support layer is made of one of polypropylene, polyethylene, polyvinyl chloride, polytetrafluoroethylene, polyethylene terephthalate or glass fiber, and has a thickness of 10 μm-200 μm.

10. The method for preparing a homogeneous cation exchange membrane according to claim 1, characterized in that: The drying temperature is 40° C.-200° C., and the drying time is 10-120 min.

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