Monomolecular valence selection cation exchange membrane and preparation method thereof

Abstract

The invention relates to the technical field of separation membrane materials. The monomolecular valence selection cation exchange membrane comprises a cation membrane layer, a space barrier layer and a support body, the positive membrane layer is a monomolecule containing load electric functional group cross-linked polymerization, and the spatial barrier layer is carbon-nitrogen covalent bond cross-linked polyene imine; and the positive film layer and the space barrier layer are combined through a carbon-nitrogen covalent bond. The preparation method comprises the following steps: preparing a cation membrane containing chlorinated alkyl, coating polyethyleneimine and enabling the polyethyleneimine to be covalently bonded with the chlorinated alkyl, and initiating a cross-linking reaction of the polyethyleneimine by using polychlorinated alkane or polyhalogenated acyl chloride to obtain the single molecule valence selection cation exchange membrane.

Description

Technical Field

[0001] The invention relates to the technical field of separation membrane materials, and discloses a monomolecular valence selective cation exchange membrane and a preparation method thereof. Background Art

[0002] Anion exchange membranes (referred to as anion membranes), cation exchange membranes (referred to as cation membranes) and bipolar ion exchange membranes (referred to as bipolar membranes) can be used to manufacture devices such as electrodialysis, electro-desalination, and diffusion dialysis, and are used in water desalination and seawater desalination, purification and concentration of brine or chemical aqueous solutions, separation of ions of different valence states, and preparation of acids and alkalis by water dissociation. They can also be used in electrolytic hydrogen production, electrolytic alkali production, and various battery devices. Among them, bipolar membranes dissociate water and separate hydrogen ions and hydroxide ions under the action of an electric field, so they can be used to produce acids and alkalis from salts, and have good application prospects.

[0003] Valence selective membranes can separate monovalent cations from multivalent cations. Due to the extensive application of lithium batteries in recent years, the acquisition of lithium has become very important. The method of extracting lithium from salt lake water with a high magnesium-to-lithium ratio using a monovalent selective cation exchange membrane has attracted much attention. In this technical field, although there have been many studies, commercially available monovalent selective cation exchange membranes with excellent performance are quite lacking.

[0004] It is generally believed that the working principle of cation valence selective membranes is to introduce an amine membrane layer to make the repulsion force to high-valence cations higher than that to low-valence cations. On the other hand, since the volume of water and high-valence cations is usually larger than that of water and low-valence cations, the introduction of a spatial barrier layer can also improve the valence separation effect.

[0005] Chinese patent applications 2012800627860 and 2019800624472 disclose a polymer microporous membrane substrate, a cross-linked ion transfer polymer layer on the surface of the substrate, and a charged functionalized layer covalently bonded to the ion transfer layer. The core preparation method of this membrane is to chlorosulfonate the cross-linked copolymer of styrene and divinylbenzene, and then provide partial amination to form a sulfate amide ion transfer polymer layer on both sides of the membrane, and then alkaline hydrolyze the remaining sulfonic acid groups to obtain a charged functionalized layer with sodium sulfonate as the functional group. This monovalent selective ion exchange membrane has good Na / Ca selectivity. However, the chlorosulfonating agent is highly dangerous and is not conducive to large-scale production; among them, sulfonic acid amide is easily hydrolyzed to produce sulfonate under the action of hydroxide, which reduces the stability of the membrane. The membrane has the ion transfer polymer layer on both sides of the charged functionalized layer, and one ion transfer polymer layer forms an obstacle to the ions passing through the charged functionalized layer, increasing the resistance of the membrane. The membrane has a single selection mechanism for monovalent cations, so its selectivity needs to be improved. Summary of the invention

[0006] The monomolecular valence selective cation exchange membrane comprises a cation layer, a space barrier layer and a support; the cation layer is a monomolecule containing cross-linked polymerized loaded electrical functional groups, and the space barrier layer is a polyimide cross-linked by carbon-nitrogen covalent bonds; the cation layer and the space barrier layer are bonded by carbon-nitrogen covalent bonds.

[0007] The method for preparing a monomolecular valence selective cation exchange membrane comprises: (1) preparing a cation casting liquid composed of a halogenated olefin, an olefin containing a cation functional group, a crosslinking agent, a polymerization initiator, and a solvent; (2) applying the cation casting liquid to a support to initiate crosslinking polymerization to obtain a reactive cation membrane; (3) immersing the reactive cation membrane in an aqueous solution of a polyolefin imine polymer to initiate a substitution reaction between the halogenated alkyl in the reactive cation membrane and the polyolefin imine, connecting the polyolefin imine to the reactive cation membrane via a carbon-nitrogen covalent bond, so that the polyolefin imine and the reactive cation membrane become a single molecule; and (4) washing away the unreacted polyolefin imine to obtain the first monomolecular valence selective cation exchange membrane.

[0008] The method for preparing a monomolecular valence selective cation exchange membrane comprises: (1) preparing a cation casting liquid composed of a halogenated olefin, an olefin containing a cation functional group, a crosslinking agent, a polymerization initiator, and a solvent; (2) applying the cation casting liquid to a support to initiate crosslinking polymerization to obtain a reactive cation membrane; (3) immersing the reactive cation membrane in an aqueous solution of a polyolefin imine polymer to initiate a substitution reaction between the halogenated alkyl in the reactive cation membrane and the polyolefin imine, connecting the polyolefin imine to the reactive cation membrane via a carbon-nitrogen covalent bond, so that the polyolefin imine and the reactive cation membrane become a single molecule; (4) washing away the unreacted polyolefin imine to obtain a first monomolecular valence selective cation exchange membrane; and (5) applying a polychlorinated alkane, polyacyl chloride or polyanhydride solution to the polyolefin imine surface of the dried first monomolecular valence selective cation exchange membrane to initiate an amination or amidation crosslinking reaction to obtain a second monomolecular valence selective cation exchange membrane.

[0009] Since the halogenated olefin, the olefin containing the cationic functional group and the cross-linking agent are cross-linked and polymerized into a single molecule, and then the halogenated group reacts with the polyolefin imine to form a NC covalent bond, the overall membrane is a single molecule structure. The polychlorinated alkane, polyacyl chloride or polyanhydride compound is further cross-linked with the already covalently cross-linked polyolefin imine, and the overall membrane is still a single molecule structure.

[0010] The support 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.

[0011] Since the functional film forms a single molecule and forms a molecular-level interpenetrating structure with the support, the integrity of the product film is better.

[0012] The polyalkylene imine includes but is not limited to polyethylene imine, branched polyethylene imine, polypropylene imine, and branched polypropylene imine.

[0013] The chlorinated olefins include, but are not limited to, chloromethylstyrene, 3-chloropropylene, 2-methyl-3-chloropropylene, bromomethylstyrene, 3-bromopropylene, 2-methyl-3-bromopropylene, 3-iodopropylene, 2-methyl-3-iodopropylene and mixtures thereof.

[0014] The polychlorinated alkanes, polyacyl chlorides or polyanhydrides include, but are not limited to, phthaloyl chloride, trimellitic chloride, maleoyl chloride, isophthalic anhydride, maleic anhydride and mixtures thereof.

[0015] The beneficial effects of the present invention include: (1) Since polyimide and cross-linked polyimide have both charge and space blocking effects on high-valent cations, the single-molecule valence selective cation exchange membrane has higher valence selectivity. (2) Since the functional groups in the single-molecule valence selective cation exchange membrane are cross-linked and polymerized into a single molecule through covalent bonds, the membrane has good stability and long life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the cross section of the first and second monomolecular valence selective cation exchange membranes of the present invention.

[0017] In the figure, 1. positive film layer, 2. space barrier layer. DETAILED DESCRIPTION Example 1

[0018] (1) Prepare a mixture of 5 g of p-styrene chloromethyl, 35 g of methacrylic acid, 5 g of divinylbenzene, 0.9 g of azobisisobutyronitrile and 15 g of N-methylpyrrolidone to obtain a cation casting solution; (2) Scrape the cation casting solution onto a 100 μm thick polypropylene microporous membrane, protect it with a polyester film, and react it at 90°C for 8 hours under vacuum to obtain a reactive cation membrane; (3) Dissolve 10 g of a 50% aqueous solution of branched polyethyleneimine in 35 ml of water to appropriately buffer the pH to obtain an amination solution, and then immerse the reactive cation membrane in the amination solution at 60°C for 2 hours; (4) Wash with water to obtain the monomolecular valence selective cation exchange membrane of Example 1. Example 2

[0019] 10% p-dichlorobenzyl N-methylpyrrolidone solution was sprayed on both sides of the dried monomolecular valence selective cation exchange membrane of Example 1, reacted at 60 degrees under vacuum for 4 hours, and washed with water to obtain the monomolecular valence selective cation exchange membrane of Example 2. Example 3

[0020] A 10% benzyltricarbonyl chloride octane solution was sprayed on the dried polyethyleneimine surface of the monomolecular valence selective cation exchange membrane of Example 1, reacted at room temperature for 2 hours, and washed with water to obtain the monomolecular valence selective cation exchange membrane of Example 3.

[0021] The performance indicators of the obtained membrane were tested according to the Chinese industry standard HY / T 166.1-2013, and the selectivity was tested according to the method disclosed in Chinese patent application 2019800627860. The test results are shown in the table. parameter thickness Switching capacity Moisture content Sheet resistance Selectivity Lithium / Mg selectivity unit mm mmole / g ％ <![CDATA[Ω / cm 2 ]]> ％ Example 1 0.095 1.82 32.5 4.90 93.6 8.2 Example 2 0.095 1.83 30.6 8.21 94.5 12.7 Example 3 0.095 1.79 28.1 9.62 95.2 15.6

Claims

1. Single molecule valence selective cation exchange membrane, characterized by It includes a cationic film layer, a space barrier layer and a support; the cationic film layer is a single molecule containing cross-linked polymerized electric functional groups, and the space barrier layer is a polyimide cross-linked by carbon-nitrogen covalent bonds; the cationic film layer and the space barrier layer are combined by carbon-nitrogen covalent bonds.

2. A method for preparing a monomolecular valence selective cation exchange membrane, characterized in that The method comprises: (1) preparing a cationic membrane casting liquid which is mixed with a halogenated olefin, an olefin containing a cationic functional group, a crosslinking agent, a polymerization initiator, and a solvent; (2) applying the cationic membrane casting liquid to a support to initiate crosslinking polymerization to obtain a reactive cationic membrane; (3) immersing the reactive cationic membrane in an aqueous solution of a polyolefin imine polymer to initiate a substitution reaction between the halogenated alkyl in the reactive cationic membrane and the polyolefin imine, connecting the polyolefin imine to the reactive cationic membrane through a carbon-nitrogen covalent bond, so that the polyolefin imine and the reactive cationic membrane become a single molecule; and (4) washing away the unreacted polyolefin imine to obtain a first monomolecular valence selective cation exchange membrane.

3. A method for preparing a monomolecular valence selective cation exchange membrane, characterized in that The method comprises: (1) preparing a cationic membrane casting liquid which is mixed with a halogenated olefin, an olefin containing a cationic functional group, a crosslinking agent, a polymerization initiator, and a solvent; (2) applying the cationic membrane casting liquid to a support to initiate crosslinking polymerization to obtain a reactive cationic membrane; (3) immersing the reactive cationic membrane in an aqueous solution of a polyolefin imine polymer to initiate a substitution reaction between the halogenated alkyl in the reactive cationic membrane and the polyolefin imine, and connecting the polyolefin imine to the reactive cationic membrane through a carbon-nitrogen covalent bond, so that the polyolefin imine and the reactive cationic membrane become a single molecule; (4) washing away the unreacted polyolefin imine to obtain a first monomolecular valence selective cation exchange membrane; and (5) applying a polychlorinated alkane, polyacyl chloride or polyanhydride solution to the polyolefin imine surface of the dried first monomolecular valence selective cation exchange membrane to initiate an amination or amidation crosslinking reaction to obtain a second monomolecular valence selective cation exchange membrane.

4. The monomolecular valence selective cation exchange membrane and preparation method according to claims 1, 2 and 3, characterized in that The support 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.

5. The monomolecular valence selective cation exchange membrane and preparation method according to claims 1, 2 and 3, characterized in that The polyalkylene imine includes but is not limited to polyethylene imine, branched polyethylene imine, polypropylene imine, and branched polypropylene imine.

6. The monomolecular valence selective cation exchange membrane and preparation method according to claims 2 and 3, characterized in that The chlorinated olefins include, but are not limited to, chloromethylstyrene, 3-chloropropylene, 2-methyl-3-chloropropylene, bromomethylstyrene, 3-bromopropylene, 2-methyl-3-bromopropylene, 3-iodopropylene, 2-methyl-3-iodopropylene and mixtures thereof.

7. The monomolecular valence selective cation exchange membrane and preparation method according to claim 3, characterized in that The polychlorinated alkanes, polyacyl chlorides or polyanhydrides include, but are not limited to, phthaloyl chloride, trimellitic chloride, maleoyl chloride, isophthalic anhydride, maleic anhydride and mixtures thereof.

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