Semi-homogeneous cation selective exchange membrane, preparation method and application

Abstract

The invention relates to the technical field of composite membrane materials, in particular to a semi-homogeneous cation selective exchange membrane, a preparation method and application, and the method comprises the following steps: uniformly mixing linear low-density polyethylene, cation exchange resin containing sulfonic acid groups, base membrane resin containing carboxyl groups, a filler and an antioxidant; and mixing and molding the mixture to obtain the semi-homogeneous cation selective exchange membrane. On the basis of using cation exchange resin containing sulfonic acid groups, a base membrane resin material containing carboxyl groups is used at the same time, and the cation exchange semi-homogeneous membrane with the sulfonic acid groups and the carboxyl functional groups is prepared. A part of fixed groups of the membrane are combined with a polymer matrix in a physical form, and the other part of fixed groups are combined with the polymer matrix through chemical bonds, so that the membrane has the characteristics of a heterogeneous membrane and a homogeneous membrane.

Description

Technical Field

[0001] The invention relates to the technical field of composite membrane materials, and in particular to a semi-homogeneous cation selective exchange membrane, a preparation method and application thereof. Background Art

[0002] Ion exchange membrane is an important ion separation tool in the purification or treatment of water, food, beverage, chemicals and wastewater, as well as in equipment for fractionation, migration consumption and electrical regeneration. Ion exchange membranes can be divided into heterogeneous membranes, semi-homogeneous membranes and homogeneous membranes. Considering the manufacturing difficulty, manufacturing cost and performance, semi-homogeneous membranes are the current mainstream choice.

[0003] However, the ion migration number of the semi-homogeneous cation selective exchange membrane currently prepared is not high enough, the surface resistance is high, and the properties such as temperature resistance, oxidation resistance, and dimensional stability are not ideal. Summary of the invention

[0004] The present invention aims to provide a semi-homogeneous cation selective exchange membrane, a preparation method and an application thereof, so as to solve the above-mentioned problems.

[0005] To achieve the above object, the present invention provides a method for preparing a semi-homogeneous cation selective exchange membrane, comprising:

[0006] The linear low-density polyethylene, the cation exchange resin containing the sulfonic acid group, the base film resin containing the carboxyl group, the filler and the antioxidant are uniformly mixed;

[0007] The mixture is kneaded and molded to obtain a semi-homogeneous cation selective exchange membrane.

[0008] The invention also provides a semi-homogeneous cation selective exchange membrane.

[0009] The present invention also provides an application of a semi-homogeneous cation selective exchange membrane, wherein the semi-homogeneous cation selective exchange membrane is used in electrochemical equipment;

[0010] Among them, electrochemical equipment includes: alkaline chlorine electrolysis equipment, electrophoretic paint purification equipment, and electro-organic synthesis equipment.

[0011] Technical effects and advantages of the present invention:

[0012] 1. The present invention uses a cation exchange resin containing a sulfonic acid group and a base membrane resin material containing a carboxyl group to prepare a cation exchange semi-homogeneous membrane having sulfonic acid and carboxyl functional groups. A part of the fixed groups of the membrane is physically bonded to the polymer matrix, and another part of the fixed groups is chemically bonded to the polymer matrix, which has the characteristics of both heterogeneous membrane and homogeneous membrane.

[0013] 2. In addition to providing weakly electronegative carboxyl groups, the base film resin containing carboxyl groups in the present invention can also be used as a base film material to provide abundant ion exchange active points in the base film material, so that the cation exchange resin containing sulfonic acid groups has stronger cation adsorption and exchange capacity, especially higher exchange capacity for weakly electrolytic ions. At the same time, the base film resin containing carboxyl groups can also improve the lubrication processing performance in the mixed manufacturing process of linear low-density polyethylene and cation exchange resin containing sulfonic acid groups, so that the cation exchange resin containing sulfonic acid groups can be evenly dispersed in the linear low-density polyethylene / base film resin containing carboxyl groups using simple extrusion processing equipment.

[0014] 3. The addition of the base film resin containing carboxyl groups can make the cation exchange resin with sulfonic acid groups wet the surface during the activation process and have a larger specific surface area, so that more cation exchange resin materials with sulfonic acid groups are exposed to the processing fluid in the membrane equipment, thereby making the semi-homogeneous cation selective exchange membrane obtain excellent ion exchange performance within the thickness range of (0.20mm-1.00mm). At the same time, the addition of the base film resin containing carboxyl groups makes the membrane surface resistance of the semi-homogeneous cation selective exchange membrane lower and the migration number higher.

[0015] 4. The present invention directly adopts the open refining and screw extrusion method in the process of preparing the semi-homogeneous cation selective exchange membrane, which is easy to manufacture and has low processing cost. At the same time, the assembly and preparation technology process of this membrane is simple and low in cost. Except for the cost of raw materials, the formulation, extrusion or heat treatment steps used in the manufacture of the semi-homogeneous cation selective exchange membrane all use standard low-cost manufacturing equipment, so it can be realized without special equipment design and upgrading.

[0016] 5. No harmful substances are used or generated during the production and preparation of the semi-homogeneous cation selective exchange membrane. The selected base membrane resin containing carboxyl groups has a suitable acid value, glass transition temperature and softening point temperature. During the melting and mixing process of linear low-density polyethylene and sulfonic acid group cation exchange resin, the addition of the base membrane resin containing carboxyl groups can reduce the extrusion molding temperature required for the membrane material, thereby reducing the thermal damage to the sulfonic acid group cation exchange resin during the thermoforming process.

[0017] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work. Figure 1 The present invention is a flow chart of a method for preparing a semi-homogeneous cation selective exchange membrane. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0021] To solve the deficiencies of the prior art, the present invention discloses a method for preparing a semi-homogeneous cation selective exchange membrane, such as Figure 1 As shown, specifically including:

[0022] 1. Evenly mix linear low-density polyethylene, cation exchange resin containing sulfonic acid groups, base film resin containing carboxyl groups, fillers and antioxidants.

[0023] The raw material ratio is as follows: 1-1.1 parts by weight of linear low-density polyethylene, 0.9-1.0 parts by weight of cationic exchange resin containing sulfonic acid groups, 0.1-0.2 parts by weight of base film resin containing carboxyl groups, 0.1-0.5 parts by weight of filler, and 0.2-0.5 parts by weight of antioxidant.

[0024] The base film resin containing a carboxyl group includes at least one of the following: a polyester resin containing a carboxyl group and an acrylic resin containing a carboxyl group.

[0025] Wherein, the filler includes at least one of the following: calcium stearate, zinc stearate, and magnesium stearate.

[0026] The antioxidant comprises at least one of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine.

[0027] Among them, linear low-density polyethylene is produced by copolymerization of propylene, butene, 4-methyl-1-pentene, hexene or octene, and the molecular weight of linear low-density polyethylene is 50,000-100,000 and the density is 0.915-0.935 g / cm 3 , the melting point is 115-120°C. This type of linear low-density polyethylene has smoothness and hydrophobicity, which simplifies the filling of ion exchange resins in the preparation of ion exchange membrane materials and eliminates the content of extractables in the adhesive.

[0028] Among them, the water content of the cation exchange resin containing sulfonic acid groups is less than 20%. And the cation exchange resin containing sulfonic acid groups includes at least one of the following: beaded polystyrene sulfonate cation powder resin containing 8% DVB, macroporous polystyrene divinylbenzene sulfonate cation powder resin containing 6% DVB. For example, BC121 domestic cation resin is a beaded polystyrene sulfonate cation powder resin containing 8-10% DVB. The main polymerizable monomers are styrene and divinylbenzene. It has the appearance of transparent spherical particles. Its functional group is R—(SO 3 )-M + , moisture content 10-20%, particle size range MESH ≥ 250.

[0029] The base film resin containing carboxyl groups includes at least one of the following: polyester resin containing carboxyl groups, acrylic resin containing carboxyl groups. The selected acrylic resin and polyester resin containing carboxyl groups are insoluble in water and have a melting point temperature and melt processing molding temperature close to those of polyethylene.

[0030] The synthesis process of the polyester resin containing a carboxyl group is as follows: 200 parts of methoxydiphenyl ether, 127 parts of neopentyl glycol, 77 parts of maleic anhydride, 55 parts of isophthalic acid, 28 parts of trihydroxyethyl isocyanurate, 0.25 parts of hydroquinone, 0.35 parts of p-tert-butylcatechol, and 8 parts of diisopropylbenzene peroxide are polymerized at 200-220° C. for 12-16 hours. After the polymerization is completed, the material is discharged under pressure at 200-220° C. and crushed and packaged.

[0031] The main technical indicators of polyester resins containing carboxyl groups are as follows: acid value controlled at 30-35 mgKOH / g (after the polyester resin ratio is determined, the reaction end point is generally controlled by the acid value), glass transition temperature 60-65°C, softening point 110-115°C, melting point 120-140°C. While providing chemically bonded ion exchange groups, polyester resins with carboxyl groups can also be used as base film materials and act as lubricants during the preparation and molding of base film materials.

[0032] Among them, the synthesis process of the acrylic resin containing a carboxyl group is as follows: 20 parts of methyl methacrylate, 20 parts of methyl acrylate, 40 parts of ethyl acrylate, 10 parts of styrene, 10 parts of maleic anhydride, 5 parts of divinylbenzene, 0.25 parts of hydroquinone, 0.35 parts of p-tert-butylcatechol, and 5 parts of dibenzoyl peroxide are added dropwise to a toluene solvent for free radical polymerization according to the above proportions. Before the dropwise addition, the toluene is refluxed at a boiling point for 2-3 hours to ensure the removal of trace moisture in the solvent. The polymerization is performed at 114-120°C for 2-4 hours. After the polymerization is completed, the solvent toluene is extracted by vacuum, the material is pressurized at 130-140°C, and it is crushed and packaged.

[0033] The main technical indicators of the acrylic resin containing carboxyl groups are as follows: the acid value is controlled at 30-35 mgKOH / g, the glass transition temperature is 60-65°C, the softening point is 80-95°C, and the melting point is 110-140°C. Like the aforementioned polyester resin containing carboxyl groups, the acrylic resin containing carboxyl groups can provide chemically bonded ion exchange groups while also being used as a base film material and acting as a lubricant during the preparation and molding of the base film material.

[0034] 2. The mixture is kneaded and molded to obtain a semi-homogeneous cation selective exchange membrane.

[0035] Specifically, it includes: using an open mill for mixing, crushing and then entering a screw extruder, installing a mold of required thickness at the end of the extruder, and using double rollers to gloss the film surface.

[0036] The film forming speed is controlled at 0.5-0.8 m / min, the temperature of the mixing and extruding film is 150-180° C., and the thickness of the extruded film is 0.20-1.00 mm.

[0037] In addition, after the gloss treatment, the membrane was immersed in a 5% by mass sodium chloride solution at 25° C. for 48 hours to condition and activate the membrane material.

[0038] Among them, the surface resistance of the semi-homogeneous cation selective exchange membrane is less than 10Ω.cm 2 , migration number>96%, with properties of heat resistance, oxidation resistance, high strength, etc.

[0039] The present invention also provides a semi-homogeneous cation selective exchange membrane, which not only combines the advantages of homogeneous membrane and heterogeneous membrane, but also has a higher migration number> 96% and a surface resistance< 10Ω.cm 2 , temperature resistance, oxidation resistance, high strength and other properties, it is a more excellent membrane material for engineering applications.

[0040] The present invention also provides an application of a semi-homogeneous cation selective exchange membrane, which is used in electrochemical equipment; wherein the electrochemical equipment includes: alkaline chlorine electrolysis equipment, electrophoretic paint purification equipment, electro-organic synthesis equipment, especially electrodialysis and electrodeionization equipment (EDI).

[0041] In order to better understand the present scheme, examples and comparative examples are provided below.

[0042] The raw material composition in this embodiment mainly contains: linear low-density polyethylene (LLDPE, density 0.915 ~ 0.935g / cm 3 ), a cation exchange resin containing a sulfonic acid group, a polyester resin containing a carboxyl group having a melt extrusion processing temperature similar to that of linear low-density polyethylene, and an acrylic resin containing a carboxyl group. The specific formula materials for preparing the semi-homogeneous cation selective exchange membrane are shown in Table 1:

[0043] Table 1 Semi-homogeneous cation selective exchange membrane raw material formula table / number of parts

[0044]

[0045]

[0046] The semi-homogeneous cation selective exchange membranes in the embodiments and comparative examples were evaluated by indicators such as membrane thickness, ion exchange capacity, surface resistance, and migration number. These indicators can be used to test the main ion exchange capacity and effect evaluation. The indicator data results are shown in Table 2.

[0047] Table 2 Index data of semi-homogeneous cation selective exchange membrane

[0048] Serial number Thickness d(mm) Sheet resistance R(Ω) Ion exchange capacity mmol / g Migration number % Example 1 0.73 9 4.5 0.967 Example 2 0.74 10 4.6 0.964 Example 3 0.75 8 4.6 0.967 Comparative Example 4 0.75 17 4.4 0.960 Comparative Example 5 0.75 8 4.6 0.960

[0049] It can be seen from the table that the semi-homogeneous cation selective exchange membranes of the embodiment and the comparative example have similar permeability selectivity and permeability, and when the membrane thickness and the proportion of the cation exchange resin with sulfonic acid groups are basically the same, the semi-homogeneous cation selective exchange membrane prepared by the present invention has lower surface resistance and comparable ion migration number.

[0050] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a semi-homogeneous cation selective exchange membrane, characterized in that: include: The linear low-density polyethylene, the cation exchange resin containing the sulfonic acid group, the base film resin containing the carboxyl group, the filler and the antioxidant are uniformly mixed; The mixture is kneaded and molded to obtain a semi-homogeneous cation selective exchange membrane.

2. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 1, characterized in that: In parts by weight, the mixture contains 1-1.1 parts of linear low-density polyethylene, 0.9-1.0 parts of cationic exchange resin containing sulfonic acid groups, 0.1-0.2 parts of base film resin containing carboxyl groups, 0.1-0.5 parts of filler, and 0.2-0.5 parts of antioxidant.

3. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 1, characterized in that: The base film resin containing carboxyl groups includes at least one of the following: polyester resin containing carboxyl groups, acrylic resin containing carboxyl groups; the filler includes at least one of the following: calcium stearate, zinc stearate, magnesium stearate; the antioxidant includes at least one of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine.

4. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 1, characterized in that: Linear low-density polyethylene is obtained by copolymerization of propylene, butene, 4-methyl-1-pentene, hexene or octene; Among them, the molecular weight of linear low-density polyethylene is 50,000-100,000 and the density is 0.915-0.935 g / cm 3 , the melting point temperature is 115-120℃.

5. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 1, characterized in that: The water content of the cation exchange resin containing sulfonic acid groups is less than 20%, and the cation exchange resin containing sulfonic acid groups includes at least one of the following: beaded polystyrene sulfonate cation powder resin containing 8% DVB, macroporous polystyrene divinylbenzene sulfonate cation powder resin containing 6% DVB.

6. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 3, characterized in that: A polyester resin containing carboxyl groups is obtained, comprising: The methoxy diphenyl ether, neopentyl glycol, maleic anhydride, isophthalic acid, tris (2-hydroxyethyl) isocyanurate, hydroquinone, p-tert-butyl catechol and DCP are polymerized at 200-220° C. for 12-16 hours; After the polymerization is completed, the material is discharged under pressure at 200-220°C and crushed; The polyester resin containing a carboxyl group has an acid value of 30-35 mgKOH / g, a glass transition temperature of 60-65°C, a softening point of 110-115°C, and a melting point of 120-140°C.

7. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 3, characterized in that: Acrylic resins containing carboxyl groups are obtained, including: Mixing methyl methacrylate, methyl acrylate, ethyl acrylate, styrene, maleic anhydride, divinylbenzene, hydroquinone, p-tert-butylcatechol and BPO; The mixed solution was added dropwise to toluene solvent at 114-120°C for polymerization for 2-4 hours; After the polymerization is completed, the solvent toluene is separated and the material is discharged under pressure at 130-140°C and crushed to obtain an acrylic resin containing a carboxyl group; The acrylic resin containing a carboxyl group has an acid value of 30-35 mgKOH / g, a glass transition temperature of 60-65°C, a softening point of 80-95°C, and a melting point of 110-140°C.

8. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 1, characterized in that: The mixture is kneaded and molded to obtain a semi-homogeneous cation selective exchange membrane, comprising: Mixing and crushing the mixture; The crushed mixture is sequentially fed into an extruder and a die to obtain an initial film; The surface of the initial membrane is subjected to gloss treatment to obtain a semi-homogeneous cation selective exchange membrane.

9. The method for preparing a semi-homogeneous cation selective exchange membrane according to claim 8, characterized in that: The temperature of mixing and extrusion is 150-180°C, and the extrusion speed is 0.5-0.8 m / min.

10. A semi-homogeneous cation selective exchange membrane obtained by the method according to any one of claims 1 to 9.

11. The semi-homogeneous cation selective exchange membrane according to claim 10, characterized in that: The semi-homogeneous cation selective exchange membrane has a thickness of 0.20-1.00 mm, a migration number of >96%, and a surface resistance of <10Ω.cm 2 .

12. Use of the semi-homogeneous cation selective exchange membrane according to claim 10, characterized in that: Semi-homogeneous cation-selective exchange membranes for electrochemical devices; Among them, electrochemical equipment includes: alkaline chlorine electrolysis equipment, electrophoretic paint purification equipment, and electro-organic synthesis equipment.

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