Positively charged composite membranes, methods of making and using the same

Abstract

The application relates to the field of membranes, and discloses a positively charged composite membrane and a preparation method and application thereof. The composite membrane comprises a bottom layer, a porous support layer and a polyamide separation layer arranged in sequence; the polyamide separation layer contains a quaternary ammonium salt structure shown in formula I and / or formula II; X is halogen; Ar1 and Ar2 are independently residues after monomer reaction containing a sulfonyl chloride group. The polyamide separation layer of the positively charged composite membrane contains a specific quaternary ammonium salt structure, so that the positively charged composite membrane has a high magnesium-lithium separation coefficient while maintaining a high water flux, and is particularly suitable for the water treatment and separation field.

Description

Technical Field

[0001] This invention relates to the field of membranes, and more specifically, to a positively charged composite membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration membranes are pressure-driven membranes with pore sizes between ultrafiltration and reverse osmosis, typically less than 1 nm. Due to their advantages such as high rejection rates for divalent salts and small organic molecules, good permeability, and low operating pressure, they are widely used in groundwater hardening removal, surface water organic matter removal, color analysis, oil-water separation, and organic solvent recovery.

[0003] Currently, commercially available nanofiltration membranes use polyamide as their separation layer, which is formed by the interfacial polymerization of polyamines and polyacrylamide chlorides. Because the residual acrylamide chloride groups on the membrane surface hydrolyze into carboxyl groups, the polyamide membrane surface carries a negative charge. Due to the Donnan effect, polyamide nanofiltration membranes exhibit excellent retention performance for divalent anions, such as sulfate; however, they are less effective against polyvalent metal cations, such as Mg²⁺. 2+ or Ca 2+ The retention effect is low. Groundwater contains a large amount of Mg. 2+ With Ca 2+ However, achieving efficient removal of these ions using ordinary polyamide nanofiltration membranes is difficult. To improve the retention of polyvalent metal ions by nanofiltration membranes, researchers often introduce positively charged groups, such as amino groups, quaternary ammonium salts, quaternary phosphine salts, and guanidine groups, into the functional layer of the nanofiltration membrane. This is done through the Donnan effect to enhance the retention of polyvalent metal ions by the nanofiltration membrane.

[0004] Positively charged nanofiltration membranes are not only used for groundwater hardening, but also have important applications in electroplating wastewater treatment and lithium extraction from salt lakes. Therefore, developing positively charged nanofiltration membrane materials and preparation processes with industrialization prospects is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of low magnesium-lithium separation efficiency of existing nanofiltration membranes, and to provide a positively charged composite membrane, its preparation method and application. The polyamide separation layer of the positively charged composite membrane contains a specific quaternary ammonium salt structure, which enables the positively charged composite membrane to maintain a high water flux while having a high magnesium-lithium separation coefficient, making it particularly suitable for the field of water treatment separation.

[0006] To achieve the above objectives, the first aspect of the present invention provides a positively charged composite membrane, wherein the composite membrane comprises a bottom layer, a porous support layer and a polyamide separation layer disposed sequentially.

[0007] The polyamide separation layer contains a quaternary ammonium salt structure represented by Formula I and / or Formula II;

[0008]

[0009] Where X is a halogen; Ar1 ​​and Ar2 are each an independent residue of a monomer containing a sulfonyl chloride group after reaction.

[0010] A second aspect of the present invention provides a method for preparing a positively charged composite film, characterized in that the preparation method includes the following steps:

[0011] S1. Prepare a porous support layer on the bottom layer;

[0012] S2. The membrane obtained in step S1 is first contacted with an aqueous phase containing a polyamine containing tertiary amine groups, and then second contacted with an organic phase containing polyacrylamide chlorides. After heat treatment, a composite membrane containing a polyamide separation layer is obtained.

[0013] S3. The composite membrane is contacted with an organic solution containing a monomer containing sulfonyl chloride groups, and then dried to obtain the positively charged composite membrane.

[0014] A third aspect of the present invention provides a positively charged composite film prepared by the above-described preparation method.

[0015] A fourth aspect of the present invention provides an application of the above-mentioned positively charged composite membrane in the field of water treatment separation.

[0016] Through the above technical solutions, the positively charged composite film, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0017] The polyamide separation layer of the positively charged composite membrane provided by this invention contains a specific quaternary ammonium salt structure, which significantly increases the positive charge density of the composite membrane. The repulsion effect between positive charges improves the retention effect of magnesium ions in the composite membrane, thereby improving the magnesium-lithium separation efficiency of the composite membrane while maintaining the high water flux of the composite membrane.

[0018] In the preparation method of the positively charged composite membrane provided by the present invention, the monomer containing sulfonyl chloride group reacts with the tertiary amine in the polyamide separation layer, and the tertiary amine is converted into a positively charged quaternary ammonium salt group. The repulsion effect between positive charges improves the retention effect of the composite membrane on magnesium ions, thereby improving the magnesium-lithium separation efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the reaction between benzenesulfonyl chloride and the tertiary amine on the surface of the polyamide separation layer in Example 1 of the present invention;

[0020] Figure 2a This is the XPS spectrum of nitrogen atoms on the surface of the composite film in Example 1;

[0021] Figure 2b This is the XPS spectrum of nitrogen atoms on the surface of the composite film in Comparative Example 1;

[0022] Figure 3 This is the XPS spectrum of sulfur atoms on the surface of the composite membrane in Example 1. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of the present invention provides a positively charged composite membrane, wherein the composite membrane comprises a bottom layer, a porous support layer and a polyamide separation layer disposed sequentially;

[0025] The polyamide separation layer contains a quaternary ammonium salt structure represented by Formula I and / or Formula II;

[0026]

[0027] Where X is a halogen; Ar1 ​​and Ar2 are each an independent residue of a monomer containing a sulfonyl chloride group after reaction.

[0028] In this invention, the polyamide separation layer of the positively charged composite membrane contains a specific quaternary ammonium salt structure, which significantly increases the positive charge density of the composite membrane. The repulsion effect between positive charges improves the retention effect of the composite membrane on magnesium ions, thereby improving the magnesium-lithium separation efficiency of the composite membrane while maintaining the high water flux of the composite membrane.

[0029] In this invention, * refers to the bonding position where the quaternary ammonium salt structure connects to the polyamide separation layer.

[0030] According to the present invention, X is Cl, Br or I.

[0031] According to the present invention, the monomer containing the sulfonyl chloride group is selected from benzenesulfonyl chloride, o-toluenesulfonyl chloride, m-toluenesulfonyl chloride, p-toluenesulfonyl chloride, 2-ethylbenzenesulfonyl chloride, 3-ethylbenzenesulfonyl chloride, 4-ethylbenzenesulfonyl chloride, 2-chlorobenzenesulfonyl chloride, 3-chlorobenzenesulfonyl chloride, 4-chlorobenzenesulfonyl chloride, 2-fluorobenzenesulfonyl chloride, 3-fluorobenzenesulfonyl chloride, 4-fluorobenzenesulfonyl chloride, 2-nitrobenzenesulfonyl chloride, 3-nitrobenzenesulfonyl chloride, 4-nitrobenzenesulfonyl chloride, 2-bromobenzenesulfonyl chloride, 3-bromobenzenesulfonyl chloride, 4- Bromobenzenesulfonyl chloride, 2-iodobenzenesulfonyl chloride, 3-iodobenzenesulfonyl chloride, 4-iodobenzenesulfonyl chloride, 4-chloro-3-nitrobenzenesulfonyl chloride, 2-chloro-4-fluorobenzenesulfonyl chloride, p-dodecylbenzenesulfonyl chloride, p-butylbenzenesulfonyl chloride, 5-chloro-2-methylbenzenesulfonyl chloride, 3,5-dichlorobenzenesulfonyl chloride, 4-isopropoxybenzenesulfonyl chloride, 4-(trifluoromethoxy)benzenesulfonyl chloride, p-acetaminobenzenesulfonyl chloride, 2-cyanobenzenesulfonyl chloride, 3-cyanobenzenesulfonyl chloride, 4-cyanobenzenesulfonyl chloride, 2,4,6-trimethylbenzenesulfonyl chloride Benzenesulfonyl chloride, 2,4,6-triisopropylbenzenesulfonyl chloride, 2,4,5-trichlorobenzenesulfonyl chloride, 2,5-dimethoxybenzenesulfonyl chloride, p-tert-butylbenzenesulfonyl chloride, 4-bromo-2-fluorobenzenesulfonyl chloride, 1-naphthalenesulfonyl chloride, 2-naphthalenesulfonyl chloride, 6-chloro-2-naphthalenesulfonyl chloride, 7-chloro-2-naphthalenesulfonyl chloride, 5-chloro-2-naphthalenesulfonyl chloride, 8-chloro-2-naphthalenesulfonyl chloride, 2-thiophenesulfonyl chloride, 2-chloropyridinesulfonyl chloride, 4,4'-oxobisbenzenesulfonyl chloride, 1,4-benzenedisulfonyl chloride, 1,3 At least one of the following: benzene disulfonyl chloride, 4-amino-6-chloro-1,3-benzene disulfonyl chloride, 1,2-benzene disulfonyl chloride, 4,5-dichloro-1,3-benzene disulfonyl chloride, 4,4'-biphenyl disulfonyl chloride, methyl sulfonyl chloride, trichloromethyl sulfonyl chloride, ethyl sulfonyl chloride, 2-chloroethane sulfonyl chloride, propyl sulfonyl chloride, butyl sulfonyl chloride, 1,4-butane disulfonyl chloride, 1,3-propane disulfonyl chloride, 1,5-pentane disulfonyl chloride, naphthalene-1,5-disulfonyl chloride, and naphthalene-2,6-disulfonyl chloride.

[0032] Further, the monomer containing the sulfonyl chloride group is selected from at least one of benzenesulfonyl chloride, 1,4-benzene disulfonyl chloride, 1,3-benzene disulfonyl chloride, ethylsulfonyl chloride, 1,4-butane disulfonyl chloride, 1,3-propane disulfonyl chloride, 1,5-pentane disulfonyl chloride and naphthalene-2,6-disulfonyl chloride.

[0033] According to the present invention, the nitrogen atom content in the quaternary ammonium salt structure of the positively charged composite film is 0.1-2 at.%; or, the sulfur atom content in the positively charged composite film is 0.1-2 at.%.

[0034] In this invention, when the content of at least one of nitrogen atoms or sulfur atoms in the quaternary ammonium salt structure of the positively charged composite membrane meets the above-mentioned range, it indicates that the surface of the composite membrane has a high positive potential, which significantly improves the rejection rate of the composite membrane for polyvalent metal cations.

[0035] Furthermore, the nitrogen atom content in the quaternary ammonium salt structure of the positively charged composite film is 0.5-1.5 at.%, or the sulfur atom content in the positively charged composite film is 0.5-1.5 at.%.

[0036] According to the present invention, the surface zeta potential of the composite film is -10mV to 5mV.

[0037] In this invention, when the surface zeta potential of the composite membrane meets the above-mentioned range, it indicates that the composite membrane has a high surface electrode potential. When used for lithium-magnesium separation, it can better repel divalent magnesium ions, making it difficult for magnesium ions in the liquid to pass through the composite membrane, while allowing monovalent lithium ions to pass through as much as possible, thereby obtaining a high magnesium-lithium separation efficiency.

[0038] Furthermore, the surface zeta potential of the composite film is -5mV to 5mV.

[0039] According to the present invention, the average pore size of the composite membrane is 0.1-0.4 nm.

[0040] In this invention, when the average pore size of the composite membrane meets the above-mentioned range, it indicates that the positively charged composite membrane has high density. When used for lithium-magnesium separation, it can better repel divalent magnesium ions, making it difficult for magnesium ions in the liquid to pass through the composite membrane, while allowing monovalent lithium ions to pass through as much as possible, thereby obtaining a high magnesium-lithium separation efficiency.

[0041] Furthermore, the average pore size of the composite membrane is 0.15-0.3 nm.

[0042] According to the present invention, the contact angle of the positively charged composite film is 40-70°.

[0043] In this invention, when the contact angle of the positively charged composite membrane meets the above-mentioned range, the positively charged composite membrane exhibits excellent hydrophilicity, which can further improve the water flux of the composite membrane when used for magnesium-lithium separation.

[0044] Furthermore, the contact angle of the positively charged composite film is 40-60°.

[0045] In this invention, the bottom layer and the porous support layer are not specifically limited and can be made of various existing materials with certain strength that can be used for nanofiltration and reverse osmosis membranes.

[0046] In this invention, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0047] In this invention, the porous support layer material can be at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0048] According to the present invention, the thickness of the bottom layer, the porous support layer, and the polyamide separation layer is not particularly limited and can be a conventional choice in the art. However, in order to enable these three layers to play a better synergistic role and enable the resulting composite nanofiltration membrane to better combine excellent magnesium-lithium separation coefficient and high water flux, preferably, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; and the thickness of the polyamide separation layer is 10-500 nm, preferably 50-300 nm.

[0049] A second aspect of the present invention provides a method for preparing a positively charged composite film, characterized in that the preparation method includes the following steps:

[0050] S1. Prepare a porous support layer on the bottom layer;

[0051] S2. The membrane obtained in step S1 is first contacted with an aqueous phase containing a polyamine containing tertiary amine groups, and then second contacted with an organic phase containing polyacrylamide chlorides. After heat treatment, a composite membrane containing a polyamide separation layer is obtained.

[0052] S3. The composite membrane is contacted with an organic solution containing a monomer containing sulfonyl chloride groups, and then dried to obtain the positively charged composite membrane.

[0053] In this invention, during the preparation of the composite membrane, a monomer containing a sulfonyl chloride group undergoes a chemical reaction with a tertiary amine in the polyamide separation layer. The tertiary amine is converted into a positively charged quaternary ammonium salt group. The repulsion effect between the positive charges improves the retention effect of the composite membrane on magnesium ions, thereby improving the magnesium-lithium separation efficiency.

[0054] In this invention, there is no particular limitation on the method for preparing the porous support layer on the bottom layer. Conventional methods in the art can be used for preparation, with phase inversion method preferred. Specifically, a polymer solution of porous support layer material is coated on one surface of the bottom layer, and the porous support layer is obtained through phase inversion.

[0055] In this invention, the phase inversion method is preferably as follows: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20% by weight, degassing at 20-40°C for 10-180 min; then coating the polymer solution onto the bottom layer to obtain an initial film, and then immersing it in water at a temperature of 10-30°C for 10-60 min, thus forming the support layer polymer porous membrane through the phase inversion layer.

[0056] The solvent may be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0057] According to the present invention, in step S2, the polyamine containing a tertiary amine group is selected from at least one of polyethyleneimine, polyethylene polyamine, 1-aminopiperazine, 1,4-diaminopiperazine, 1,4-piperazine diethylamine, and 1,4-diaminopropylpiperazine. Preferably, the polyamine containing a tertiary amine group is selected from polyethyleneimine and / or polyethylene polyamine.

[0058] According to the present invention, the concentration of the polyamine containing tertiary amine groups in the aqueous phase is 0.1 wt%-10 wt%, preferably 0.5 wt%-2.5 wt%.

[0059] According to the present invention, the polyacryl chloride is selected from at least one of 1,3,5-benzenetricarboxyl chloride, 1,2-benzenedicarboxyl chloride, 1,3-benzenedicarboxyl chloride, 1,4-benzenedicarboxyl chloride and adipyl chloride; preferably, the polyacryl chloride containing a tertiary amine group is selected from 1,3,5-benzenetricarboxyl chloride and / or 1,4-benzenedicarboxyl chloride.

[0060] According to the present invention, the concentration of polyacryl chloride in the organic phase containing polyacryl chloride is 0.01wt%-1wt%, preferably 0.1wt%-0.5wt%.

[0061] According to the present invention, the amounts of the aqueous phase containing the tertiary amine group and the organic phase containing the polyacrylamide chloride are such that the mass ratio of the polyacrylamide containing the tertiary amine group to the polyacrylamide chloride is 0.1-10:1.

[0062] In this invention, when the mass ratio of polyamine containing tertiary amine groups to polyacrylamide chloride is controlled to meet the above-mentioned range, it can ensure that the interfacial polymerization reaction between polyamine containing tertiary amine groups and polyacrylamide chloride is sufficient, thereby increasing the positive charge density on the surface of the obtained polyamide separation layer and increasing the rejection rate of divalent or higher metal salts.

[0063] Furthermore, the amounts of the aqueous phase containing the tertiary amine group and the organic phase containing the polyacrylamide chloride are such that the mass ratio of the polyacrylamide containing the tertiary amine group to the polyacrylamide chloride is 0.5-5:1.

[0064] In this invention, there is no particular limitation on the type of solvent in the organic phase containing polyacryl chloride, as long as it can dissolve the polyacryl chloride. Preferably, the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, and alkane solvent oils (Isopar E, Isopar G, Isopar H, Isopar L and Isopar M).

[0065] According to the present invention, there are no particular limitations on the interfacial polymerization conditions of polyamines containing tertiary amine groups and polyacrylamide chlorides, and they can be carried out according to conventional conditions in the art. However, in order to enable the three layers to play a better synergistic role and enable the resulting composite nanofiltration membrane to better combine excellent magnesium-lithium separation coefficient and high water flux, preferably, the first contact time is 5-100s, preferably 10-60s; the second contact time is 10-200s, preferably 20-120s; the heat treatment conditions include: heat treatment temperature of 40-150℃, preferably 50-120℃; and heat treatment time of 0.5-10min, preferably 1-5min.

[0066] In this invention, in step S2, the ratio of the volume of the aqueous phase containing the tertiary amine group to the membrane area of ​​the membrane layer obtained in step S1 is 0.05-1 mL / cm². 2 Preferably, it is 0.1-0.5 mL / cm 2 .

[0067] In this invention, in step S2, the ratio of the volume of the organic phase containing polyacrylamide chloride to the membrane area of ​​the membrane obtained in step S1 is 0.01-0.5 mL / cm². 2 Preferably, the concentration is 0.05-0.25 mL / cm³. 2 .

[0068] According to the present invention, in step S3, the monomer containing the sulfonyl chloride group is selected from benzenesulfonyl chloride, o-toluenesulfonyl chloride, m-toluenesulfonyl chloride, p-toluenesulfonyl chloride, 2-ethylbenzenesulfonyl chloride, 3-ethylbenzenesulfonyl chloride, 4-ethylbenzenesulfonyl chloride, 2-chlorobenzenesulfonyl chloride, 3-chlorobenzenesulfonyl chloride, 4-chlorobenzenesulfonyl chloride, 2-fluorobenzenesulfonyl chloride, 3-fluorobenzenesulfonyl chloride, 4-fluorobenzenesulfonyl chloride, 2-nitrobenzenesulfonyl chloride, 3-nitrobenzenesulfonyl chloride, 4-nitrobenzenesulfonyl chloride, 2-bromobenzenesulfonyl chloride, 3-bromobenzenesulfonyl chloride. Chlorine, 4-bromobenzenesulfonyl chloride, 2-iodobenzenesulfonyl chloride, 3-iodobenzenesulfonyl chloride, 4-iodobenzenesulfonyl chloride, 4-chloro-3-nitrobenzenesulfonyl chloride, 2-chloro-4-fluorobenzenesulfonyl chloride, p-dodecylbenzenesulfonyl chloride, p-butylbenzenesulfonyl chloride, 5-chloro-2-methylbenzenesulfonyl chloride, 3,5-dichlorobenzenesulfonyl chloride, 4-isopropoxybenzenesulfonyl chloride, 4-(trifluoromethoxy)benzenesulfonyl chloride, p-acetaminobenzenesulfonyl chloride, 2-cyanobenzenesulfonyl chloride, 3-cyanobenzenesulfonyl chloride, 4-cyanobenzenesulfonyl chloride, 2,4,6- Trimethylbenzenesulfonyl chloride, 2,4,6-triisopropylbenzenesulfonyl chloride, 2,4,5-trichlorobenzenesulfonyl chloride, 2,5-dimethoxybenzenesulfonyl chloride, p-tert-butylbenzenesulfonyl chloride, 4-bromo-2-fluorobenzenesulfonyl chloride, 1-naphthalenesulfonyl chloride, 2-naphthalenesulfonyl chloride, 6-chloro-2-naphthalenesulfonyl chloride, 7-chloro-2-naphthalenesulfonyl chloride, 5-chloro-2-naphthalenesulfonyl chloride, 8-chloro-2-naphthalenesulfonyl chloride, 2-thiophenesulfonyl chloride, 2-chloropyridinesulfonyl chloride, 4,4'-oxobisbenzenesulfonyl chloride, 1,4-benzenedisulfonyl chloride, 1 At least one of 3-benzene disulfonyl chloride, 4-amino-6-chloro-1,3-benzene disulfonyl chloride, 1,2-benzene disulfonyl chloride, 4,5-dichloro-1,3-benzene disulfonyl chloride, 4,4'-biphenyl disulfonyl chloride, methyl sulfonyl chloride, trichloromethyl sulfonyl chloride, ethyl sulfonyl chloride, 2-chloroethane sulfonyl chloride, propyl sulfonyl chloride, butyl sulfonyl chloride, 1,4-butane disulfonyl chloride, 1,3-propane disulfonyl chloride, 1,5-pentane disulfonyl chloride, naphthalene-1,5-disulfonyl chloride, and naphthalene-2,6-disulfonyl chloride.

[0069] Further, the monomer containing the sulfonyl chloride group is selected from at least one of benzenesulfonyl chloride, 1,4-benzene disulfonyl chloride, 1,3-benzene disulfonyl chloride, ethylsulfonyl chloride, 1,4-butane disulfonyl chloride, 1,3-propane disulfonyl chloride, 1,5-pentane disulfonyl chloride and naphthalene-2,6-disulfonyl chloride.

[0070] According to the present invention, in step S3, the concentration of the monomer containing the sulfonyl chloride group in the organic solution is 0.01wt%-5wt%.

[0071] In this invention, when the concentration of the monomer containing sulfonyl chloride groups in the organic solvent in step S3 meets the above-mentioned range, it can be ensured that the monomer containing sulfonyl chloride groups can fully react with the tertiary amine groups in the polyamide separation layer, thereby further increasing the positive charge density on the surface of the obtained positively charged composite film and further reducing the average pore size of the positively charged composite film.

[0072] Further, in step S3, the concentration of the monomer containing the sulfonyl chloride group in the organic solution is 0.1wt%-2.5wt%.

[0073] In this invention, there is no particular limitation on the type of solvent in the organic solution in step S3; for example, it can be n-hexane.

[0074] According to the present invention, the volume ratio of the organic solvent to the membrane area of ​​the composite membrane is 0.05-1 mL / cm². 2 .

[0075] In this invention, by controlling the volume of the organic solvent and the membrane area of ​​the composite membrane to meet the above-mentioned range, it is possible to ensure sufficient contact between the surface of the composite membrane and the monomer containing sulfonyl chloride groups, and to ensure that the monomer containing sulfonyl chloride groups can have a high reaction efficiency with the tertiary amine on the surface of the polyamide separation layer of the composite membrane, ultimately resulting in a positively charged composite membrane surface containing more quaternary ammonium salt groups.

[0076] Furthermore, the ratio of the volume of the organic solvent to the membrane area of ​​the composite membrane is 0.1-0.25 mL / cm². 2 .

[0077] According to the present invention, the contact conditions include a contact time of 10s-10min, preferably 1min-5min.

[0078] In this invention, there is no particular limitation on the temperature of the contact, for example, it can be room temperature (20-30°C).

[0079] According to the present invention, the drying conditions include: a drying temperature of 30-80°C, preferably 40-60°C; and a drying time of 0.5-5 min, preferably 1-3 min.

[0080] A third aspect of the present invention provides a positively charged composite film prepared by the above-described preparation method.

[0081] A fourth aspect of the present invention provides an application of the above-mentioned positively charged composite membrane in the field of water treatment separation.

[0082] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0083] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0084] In the following embodiments and comparative examples:

[0085] (1) The water flux of the composite membrane was obtained by testing it using the following method: The composite membrane was placed in a membrane tank, and the water permeation rate of the composite membrane was measured over a certain period of time at 0.5 MPa and a temperature of 25°C. The water flux was then calculated using the following formula:

[0086] J = Q / (A·t), where J is the water flux, Q is the water permeation rate (L), and A is the effective membrane area of ​​the composite membrane (m²). 2 ), where t is time (h).

[0087] (2) The desalination rate of the composite membrane was tested using the following method: The composite membrane was loaded into a membrane tank, and the original aqueous solution was 2000 ppm magnesium chloride or 2000 ppm lithium chloride. After pre-pressurization at 0.2 MPa for 0.5 h, the permeate was obtained at a pressure of 0.5 MPa. The concentrations of magnesium chloride and lithium chloride in the permeate were measured by ion chromatography, and the desalination rate was calculated using the following formula:

[0088] R = (C f -C p ) / C f ×100%, where R is the desalination rate, and C is the desalination rate. f C represents the concentration of magnesium chloride or lithium chloride in the original solution (measured by a conductivity meter). p The concentration of magnesium chloride or lithium chloride in the permeate (measured by a conductivity meter).

[0089] (3) The magnesium-lithium separation coefficient of the composite membrane was obtained by the following method: The composite membrane was loaded into the membrane tank. The original aqueous solution was a mixture of 2000 ppm magnesium chloride and 100 ppm lithium chloride. After pre-pressurization at 0.2 MPa for 0.5 h, the permeate was obtained at a pressure of 0.5 MPa.

[0090] The magnesium-lithium separation coefficient is calculated using the following formula:

[0091] Where S is the magnesium-lithium separation coefficient, C Li，p and C Li，f The concentrations of lithium ions in the permeate and feed solution, respectively (measured by ion chromatography); C Mg，p and C Mg，f The concentrations of magnesium ions in the permeate and feed solution are respectively (measured by ion chromatography).

[0092] (4) The nitrogen atom content in the quaternary ammonium salt structure of the positively charged composite film was determined by the following method:

[0093] Before measurement, the composite membrane was dried to constant weight in an oven, and the elemental composition of the composite membrane surface was determined using a SigmaProbe X-ray photoelectron spectrometer manufactured by Thermo VG, UK. The nitrogen atom content in the quaternary ammonium salt groups of the composite membrane was calculated using the following formula:

[0094]

[0095] Among them, A N + The peak area of ​​the nitrogen atom in the quaternary ammonium salt group in the XPS spectrum ( Figure 2a (peak area at the intermediate bond energy of 400-403 eV); A N The peak area of ​​nitrogen atoms in the separated layer in the XPS spectrum represents ( Figure 2a (The sum of peak areas at 396-403 eV); S N This represents the atomic content (at.%) of nitrogen atoms in the composite membrane separation layer.

[0096] (5) The sulfur atom content in the positively charged recombination was directly measured by a Sigma Probe X-ray photoelectron spectrometer manufactured by Thermo VG in the UK.

[0097] (6) Average pore size test of positively charged composite membrane: The average pore size was measured using the PEG solute transfer method, and the detailed steps are as follows:

[0098] (i) Test the retention rate of composite membranes for PEG of different molecular sizes;

[0099] (ii) Linearly fit the PEG size and the rejection rate in a log-probability coordinate system. The PEG size corresponding to a 50% rejection rate is the average pore size of the separation membrane.

[0100] (7) Surface Zeta potential test of positively charged composite film: The test was performed using a Surpass electric analyzer (Anton Paar), with the circulating solution being a dilute aqueous solution of KCl and the pH of the test solution being 7.

[0101] (8) Contact angle of positively charged composite film: The surface contact angle of composite film samples was tested by static drop method using DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany. Before the test, the sample was dried in a vacuum oven at 60℃ for 30 minutes to remove surface and internal moisture. Then, the dried film was attached to a flat glass slide with double-sided tape. The volume of water droplets was 2μL each time during the test. The water droplets were dropped onto the film surface for 3 seconds and the test was performed immediately. The final contact angle was determined by taking the average value after multiple measurements.

[0102] (9) The thickness of each layer in the positively charged composite film was measured using a scanning electron microscope (SEM) of Hitachi S-4800.

[0103] Additionally, in the following embodiments and comparative examples:

[0104] Branched polyethyleneimine (weight average molecular weight 25000 g / mol), polyethylene polyamine, 1-aminopiperazine, 1,4-diaminopiperazine, 1,3,5-benzenetricarboxyl chloride, benzenesulfonyl chloride, 1,4-benzenedisulfonyl chloride, 1,3-benzenedisulfonyl chloride, ethylsulfonyl chloride, 1,4-butanedisulfonyl chloride, 1,3-propanedisulfonyl chloride, 1,5-pentanedisulfonyl chloride, and naphthalene-2,6-disulfonyl chloride were all purchased from Bailingwei Technology Co., Ltd., and other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0105] The support layer is prepared using a phase transformation method, and the specific steps are as follows:

[0106] A certain amount of polysulfone (number average molecular weight of 80,000 g / mol) was dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18% by weight. The solution was degassed at 25°C for 120 min. Then, the polysulfone solution was coated onto a polyester nonwoven fabric (75 μm thick) using a doctor blade to obtain an initial film. The film was then immersed in water at 25°C for 60 min, which allowed the polysulfone layer on the surface of the polyester nonwoven fabric to undergo phase transformation into a porous film. Finally, after three water washes, a bottom layer-porous support layer with a total thickness of 115 μm was obtained.

[0107] Comparative Example 1

[0108] The above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethyleneimine at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.1 wt% 1,3,5-benzotriacyl chloride at 25°C for 60 s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain composite membrane D1. The mass ratio of polyethyleneimine to 1,3,5-benzotriacyl chloride was 10:1.

[0109] Example 1

[0110] (1) The above area is 400cm² 2The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethyleneimine at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.1 wt% 1,3,5-benzenetricarboxylic acid chloride at 25°C for 60 s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain the composite membrane. The mass ratio of polyethyleneimine to 1,3,5-benzenetricarboxylic acid chloride was 10:1.

[0111] (2) The obtained composite membrane was immersed in 200 mL of n-hexane solution containing 0.5% by weight benzenesulfonyl chloride. After 1 min, it was taken out and dried at 50 °C for 1 min to obtain positively charged composite membrane N1.

[0112] Figure 1 A schematic diagram of the reaction between benzenesulfonyl chloride and the tertiary amine on the surface of the polyamide separation layer is given: benzenesulfonyl chloride reacts with the tertiary amine groups in the polyamide separation layer to generate positively charged quaternary ammonium salt groups.

[0113] Figure 2a and Figure 2b XPS spectra of nitrogen atoms on the surface of the composite film of Example 1 and Comparative Example 1, respectively. Figure 2a and Figure 2b It can be seen that after the composite membrane was modified with benzenesulfonyl chloride, a new signal peak appeared at 401-402 eV, which corresponds to the signal peak of the nitrogen atom in the quaternary ammonium salt group.

[0114] Figure 3 The XPS spectrum of sulfur atoms on the surface of the composite film in Example 1 is shown below. Figure 3 It can be seen that a signal peak corresponding to sulfur atoms appeared at 166-170 eV, confirming that benzenesulfonyl chloride was successfully modified onto the film surface.

[0115] Example 2

[0116] (1) The above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethylenepolyamine at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.1 wt% 1,3,5-benzenetricarboxylic acid chloride at 25°C for 60 s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain the composite membrane. The mass ratio of polyethylenepolyamine to 1,3,5-benzenetricarboxylic acid chloride was 10:1.

[0117] (2) The obtained composite membrane was immersed in 200 mL of n-hexane solution containing 0.1% by weight of benzenesulfonyl chloride. After 1 min, it was taken out and dried at 50 °C for 1 min to obtain positively charged composite membrane N2.

[0118] Example 3

[0119] (1) The above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 0.5 wt% 1,4-diaminopiperazine at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.1 wt% 1,3,5-benzenetricarboxylic acid chloride at 25°C for 60 s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain the composite membrane. The mass ratio of 1,4-diaminopiperazine to 1,3,5-benzenetricarboxylic acid chloride was 10:1.

[0120] (2) The obtained composite membrane was immersed in 200 mL of n-hexane solution containing 2.5% by weight benzenesulfonyl chloride. After 1 min, it was taken out and dried at 50 °C for 1 min to obtain positively charged composite membrane N3.

[0121] Example 4

[0122] The preparation method is the same as in Example 1, except that in step (2), 1,4-benzene disulfonyl chloride is used to replace benzenesulfonyl chloride to obtain a positively charged composite film N4.

[0123] Example 5

[0124] The preparation method is the same as in Example 1, except that in step (2), 1,3-benzene disulfonyl chloride is used to replace benzenesulfonyl chloride to obtain a positively charged composite film N5.

[0125] Example 6

[0126] The preparation method is the same as in Example 1, except that in step (2), ethyl sulfonyl chloride is used to replace benzene sulfonyl chloride to prepare the positively charged composite film N6.

[0127] Example 7

[0128] The preparation method is the same as in Example 1, except that in step (2), 1,4-butanedisulfonyl chloride is used to replace benzenesulfonyl chloride to prepare a positively charged composite film N7.

[0129] Example 8

[0130] The preparation method is the same as in Example 1, except that in step (2), 1,5-pentanedisulfonyl chloride is used to replace benzenesulfonyl chloride to prepare the positively charged composite film N8.

[0131] Example 9

[0132] The preparation method is the same as in Example 1, except that in step (2), naphthalene-2,6-disulfonyl chloride is used to replace benzenesulfonyl chloride to prepare the positively charged composite film N9.

[0133] Example 10

[0134] The preparation method is the same as in Example 1, except that in step (2), benzenesulfonyl chloride and 1,4-benzenedisulfonyl chloride are used to replace benzenesulfonyl chloride, wherein the concentrations of benzenesulfonyl chloride and 1,4-benzenedisulfonyl chloride are 0.25% by weight, respectively, to obtain the positively charged composite membrane N10.

[0135] Example 11

[0136] The preparation method is the same as in Example 1, except that in step (2), the concentration of benzenesulfonyl chloride is 0.01% by weight, and a positively charged composite membrane N11 is obtained.

[0137] Example 12

[0138] The preparation method is the same as in Example 1, except that in step (2), the concentration of benzenesulfonyl chloride is 5% by weight, and a positively charged composite membrane N11 is obtained.

[0139] Example 13

[0140] The method of Example 1 is different except that in step (2), the concentration of benzenesulfonyl chloride is 7.5% by weight to prepare the positively charged composite membrane N13.

[0141] Example 14

[0142] The method of Example 1 is different except that in step (2), the concentration of benzenesulfonyl chloride is 0.001% by weight, and a positively charged composite membrane N14 is prepared.

[0143] Comparative Example 2

[0144] The method of Example 1 was followed, except that in step (1), 1,4-cyclohexanediamine was used instead of polyethyleneimine. Composite membrane D2 was obtained.

[0145] The thickness, surface Zeta potential, average pore size, nitrogen atom content in the quaternary ammonium salt structure of the positively charged composite membrane, sulfur atom content in the positively charged composite membrane, and contact angle of each layer in the examples and comparative examples are shown in Table 1.

[0146] Table 1

[0147]

[0148] a This refers to the nitrogen atom content in the quaternary ammonium salt structure of a positively charged composite film.

[0149] bThis refers to the content of sulfur atoms in the positively charged composite film.

[0150] As shown in Table 1, when the composite membrane is contacted with a monomer containing sulfonyl chloride groups, the tertiary amine in the polyamide separation layer reacts chemically with the sulfonyl chloride groups, converting the tertiary amine into positively charged quaternary ammonium salt groups. This results in an increase in the positive charge density and hydrophilicity of the positively charged composite membrane surface. Furthermore, after the sulfonyl chloride groups are modified into the polyamide separation layer, the average pore size of the nanofiltration membrane separation layer decreases, indicating that the modification of the polyamide separation layer with sulfonyl chloride monomers reduces the free volume between molecules.

[0151] As can be seen from Comparative Example 2, only when the polyamide separation layer contains tertiary amine groups can quaternary ammonium salt groups be generated on the polyamide surface through chemical reaction with sulfonyl chloride groups.

[0152] The water flux, MgCl2 desalination rate, LiCl desalination rate, and magnesium-lithium separation factor of the composite membranes in the examples and comparative examples were tested, and the results are shown in Table 2.

[0153] Table 2

[0154]

[0155] As shown in Table 2, the sulfonyl chloride groups in the monomer containing sulfonyl chloride groups react with the tertiary amine groups in the polyamide separation layer, converting the tertiary amine into positively charged quaternary ammonium salt groups. The repulsion effect between positive charges improves the retention effect of the separation membrane for magnesium ions, thereby improving the magnesium-lithium separation efficiency.

[0156] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positively charged composite film, characterized in that, The composite membrane comprises a bottom layer, a porous support layer, and a polyamide separation layer arranged sequentially. The polyamide separation layer contains a quaternary ammonium salt structure as shown in Formula I and / or Formula II; Formula I; Formula II; Where X is a halogen; Ar1 ​​and Ar2 are each independently residues of monomers containing sulfonyl chloride groups after reaction; The polyamide separation layer is obtained by polymerizing a polyamine containing tertiary amine groups with a polyacrylamide chloride.

2. The positively charged composite film according to claim 1, wherein, X is Cl, Br, or I; And / or, the monomer containing the sulfonyl chloride group is selected from benzenesulfonyl chloride, o-toluenesulfonyl chloride, m-toluenesulfonyl chloride, p-toluenesulfonyl chloride, 2-ethylbenzenesulfonyl chloride, 3-ethylbenzenesulfonyl chloride, 4-ethylbenzenesulfonyl chloride, 2-chlorobenzenesulfonyl chloride, 3-chlorobenzenesulfonyl chloride, 4-chlorobenzenesulfonyl chloride, 2-fluorobenzenesulfonyl chloride, 3-fluorobenzenesulfonyl chloride, 4-fluorobenzenesulfonyl chloride, 2-nitrobenzenesulfonyl chloride, 3-nitrobenzenesulfonyl chloride, 4-nitrobenzenesulfonyl chloride, 2-bromobenzenesulfonyl chloride, 3-bromobenzenesulfonyl chloride, 4-bromobenzenesulfonyl chloride. Sulfonyl chloride, 2-iodobenzenesulfonyl chloride, 3-iodobenzenesulfonyl chloride, 4-iodobenzenesulfonyl chloride, 4-chloro-3-nitrobenzenesulfonyl chloride, 2-chloro-4-fluorobenzenesulfonyl chloride, p-dodecylbenzenesulfonyl chloride, p-butylbenzenesulfonyl chloride, 5-chloro-2-methylbenzenesulfonyl chloride, 3,5-dichlorobenzenesulfonyl chloride, 4-isopropoxybenzenesulfonyl chloride, 4-(trifluoromethoxy)benzenesulfonyl chloride, p-acetaminobenzenesulfonyl chloride, 2-cyanobenzenesulfonyl chloride, 3-cyanobenzenesulfonyl chloride, 4-cyanobenzenesulfonyl chloride, 2,4,6-trimethylbenzene Sulfonyl chloride, 2,4,6-triisopropylbenzenesulfonyl chloride, 2,4,5-trichlorobenzenesulfonyl chloride, 2,5-dimethoxybenzenesulfonyl chloride, p-tert-butylbenzenesulfonyl chloride, 4-bromo-2-fluorobenzenesulfonyl chloride, 1-naphthalenesulfonyl chloride, 2-naphthalenesulfonyl chloride, 6-chloro-2-naphthalenesulfonyl chloride, 7-chloro-2-naphthalenesulfonyl chloride, 5-chloro-2-naphthalenesulfonyl chloride, 8-chloro-2-naphthalenesulfonyl chloride, 2-thiophenesulfonyl chloride, 2-chloropyridinesulfonyl chloride, 4,4'-oxobisbenzenesulfonyl chloride, 1,4-benzenedisulfonyl chloride, 1,3 At least one of the following: benzene disulfonyl chloride, 4-amino-6-chloro-1,3-benzene disulfonyl chloride, 1,2-benzene disulfonyl chloride, 4,5-dichloro-1,3-benzene disulfonyl chloride, 4,4'-biphenyl disulfonyl chloride, methyl sulfonyl chloride, trichloromethyl sulfonyl chloride, ethyl sulfonyl chloride, 2-chloroethane sulfonyl chloride, propyl sulfonyl chloride, butyl sulfonyl chloride, 1,4-butane disulfonyl chloride, 1,3-propane disulfonyl chloride, 1,5-pentane disulfonyl chloride, naphthalene-1,5-disulfonyl chloride, and naphthalene-2,6-disulfonyl chloride.

3. The positively charged composite film according to claim 1 or 2, wherein, The nitrogen atom content in the quaternary ammonium salt structure of the positively charged composite film is 0.1-2 at.%; And / or, the sulfur atom content in the positively charged composite film is 0.1-2 at.%.

4. The positively charged composite film according to claim 3, wherein, The nitrogen atom content in the quaternary ammonium salt structure of the positively charged composite film is 0.5-1.5 at.%; And / or, the sulfur atom content in the positively charged composite film is 0.5-1.5 at.%.

5. The positively charged composite film according to claim 1 or 2, wherein, The surface zeta potential of the positively charged composite film is -10mV to 5mV.

6. The positively charged composite film according to claim 5, wherein, The surface zeta potential of the positively charged composite film is -5mV to 5mV.

7. The positively charged composite film according to claim 1 or 2, wherein, The average pore size of the positively charged composite film is 0.1-0.4 nm.

8. The positively charged composite film according to claim 7, wherein, The average pore size of the positively charged composite film is 0.15-0.3 nm.

9. The positively charged composite film according to claim 1 or 2, wherein, The contact angle of the positively charged composite film is 40-70°.

10. The positively charged composite film according to claim 9, wherein, The contact angle of the positively charged composite film is 40-60°.

11. The positively charged composite film according to claim 1 or 2, wherein, The thickness of the bottom layer is 30-150 μm; And / or, the thickness of the porous support layer is 10-100 μm; And / or, the thickness of the polyamide separation layer is 10-500 nm.

12. The positively charged composite film according to claim 11, wherein, The thickness of the bottom layer is 50-120 μm; And / or, the thickness of the porous support layer is 30-60 μm; And / or, the thickness of the polyamide separation layer is 50-300 nm.

13. A method for preparing a positively charged composite film according to any one of claims 1-12, characterized in that, The preparation method includes the following steps: S1. Prepare a porous support layer on the bottom layer; S2. The membrane obtained in step S1 is first contacted with an aqueous phase containing a polyamine containing tertiary amine groups, and then second contacted with an organic phase containing polyacrylamide chlorides. After heat treatment, a composite membrane containing a polyamide separation layer is obtained. S3. The composite membrane is contacted with an organic solution containing a monomer containing sulfonyl chloride groups, and then dried to obtain the positively charged composite membrane.

14. The preparation method according to claim 13, wherein, In step S2, the polyamine containing a tertiary amine group is selected from at least one of polyethyleneimine, 1-aminopiperazine, 1,4-piperazine diethylamine, and 1,4-diaminopropylpiperazine. And / or, the concentration of the polyamine containing tertiary amine groups in the aqueous phase is 0.1 wt%-10 wt%; And / or, the polyacryl chloride is selected from at least one of 1,3,5-benzotricarboxyl chloride, 1,2-benzoyl chloride, 1,3-benzoyl chloride, 1,4-benzoyl chloride and adipyl chloride; And / or, the concentration of the polyacryl chloride in the organic phase containing the polyacryl chloride is 0.01 wt% - 1 wt%; And / or, the amount of the aqueous phase containing the polyamine containing the tertiary amine group and the organic phase containing the polyacrylamide chloride is such that the mass ratio of the polyamine containing the tertiary amine group to the polyacrylamide chloride is 0.1-10:1; And / or, the duration of the first contact is 5-100 seconds; And / or, the duration of the second contact is 10-200 s; And / or, the conditions for the heat treatment include: a heat treatment temperature of 40-150℃ and a heat treatment time of 0.5-10min.

15. The preparation method according to claim 14, wherein, The concentration of the polyamine containing tertiary amine groups in the aqueous phase is 0.5 wt%-2.5 wt%. And / or, the concentration of the polyacryl chloride in the organic phase containing the polyacryl chloride is 0.1wt%-0.5wt%; And / or, the amount of the aqueous phase containing the tertiary amine group and the organic phase containing the polyacryl chloride is such that the mass ratio of the polyamine containing the tertiary amine group to the polyacryl chloride is 0.5-5:1; And / or, the duration of the first contact is 10-60 seconds; And / or, the duration of the second contact is 20-120 seconds; And / or, the conditions for the heat treatment include: a heat treatment temperature of 50-120°C and a heat treatment time of 1-5 min.

16. The preparation method according to claim 13 or 14, wherein, In step S3, the monomer containing the sulfonyl chloride group is selected from benzenesulfonyl chloride, o-toluenesulfonyl chloride, m-toluenesulfonyl chloride, p-toluenesulfonyl chloride, 2-ethylbenzenesulfonyl chloride, 3-ethylbenzenesulfonyl chloride, 4-ethylbenzenesulfonyl chloride, 2-chlorobenzenesulfonyl chloride, 3-chlorobenzenesulfonyl chloride, 4-chlorobenzenesulfonyl chloride, 2-fluorobenzenesulfonyl chloride, 3-fluorobenzenesulfonyl chloride, 4-fluorobenzenesulfonyl chloride, 2-nitrobenzenesulfonyl chloride, 3-nitrobenzenesulfonyl chloride, 4-nitrobenzenesulfonyl chloride, 2-bromobenzenesulfonyl chloride, 3-bromobenzenesulfonyl chloride, 4- Bromobenzenesulfonyl chloride, 2-iodobenzenesulfonyl chloride, 3-iodobenzenesulfonyl chloride, 4-iodobenzenesulfonyl chloride, 4-chloro-3-nitrobenzenesulfonyl chloride, 2-chloro-4-fluorobenzenesulfonyl chloride, p-dodecylbenzenesulfonyl chloride, p-butylbenzenesulfonyl chloride, 5-chloro-2-methylbenzenesulfonyl chloride, 3,5-dichlorobenzenesulfonyl chloride, 4-isopropoxybenzenesulfonyl chloride, 4-(trifluoromethoxy)benzenesulfonyl chloride, p-acetaminobenzenesulfonyl chloride, 2-cyanobenzenesulfonyl chloride, 3-cyanobenzenesulfonyl chloride, 4-cyanobenzenesulfonyl chloride, 2,4,6-trimethylbenzenesulfonyl chloride Benzenesulfonyl chloride, 2,4,6-triisopropylbenzenesulfonyl chloride, 2,4,5-trichlorobenzenesulfonyl chloride, 2,5-dimethoxybenzenesulfonyl chloride, p-tert-butylbenzenesulfonyl chloride, 4-bromo-2-fluorobenzenesulfonyl chloride, 1-naphthalenesulfonyl chloride, 2-naphthalenesulfonyl chloride, 6-chloro-2-naphthalenesulfonyl chloride, 7-chloro-2-naphthalenesulfonyl chloride, 5-chloro-2-naphthalenesulfonyl chloride, 8-chloro-2-naphthalenesulfonyl chloride, 2-thiophenesulfonyl chloride, 2-chloropyridinesulfonyl chloride, 4,4'-oxobisbenzenesulfonyl chloride, 1,4-benzenedisulfonyl chloride, 1,3 At least one of the following: benzene disulfonyl chloride, 4-amino-6-chloro-1,3-benzene disulfonyl chloride, 1,2-benzene disulfonyl chloride, 4,5-dichloro-1,3-benzene disulfonyl chloride, 4,4'-biphenyl disulfonyl chloride, methyl sulfonyl chloride, trichloromethyl sulfonyl chloride, ethyl sulfonyl chloride, 2-chloroethane sulfonyl chloride, propyl sulfonyl chloride, butyl sulfonyl chloride, 1,4-butane disulfonyl chloride, 1,3-propane disulfonyl chloride, 1,5-pentane disulfonyl chloride, naphthalene-1,5-disulfonyl chloride, and naphthalene-2,6-disulfonyl chloride.

17. The preparation method according to claim 13, wherein, In step S3, the concentration of the monomer containing the sulfonyl chloride group in the organic solution is 0.01 wt%-5 wt%. And / or, the ratio of the volume of the organic solution to the membrane area of ​​the composite membrane is 0.05-1 mL / cm². 2 ; And / or, the contact conditions include: a contact time of 10s-10min; And / or, the drying conditions include: a drying temperature of 30-80℃ and a drying time of 0.5-5 min.

18. The preparation method according to claim 17, wherein, In step S3, the concentration of the monomer containing the sulfonyl chloride group in the organic solution is 0.1 wt%-2.5 wt%. And / or, the contact conditions include: a contact time of 1 min to 5 min; And / or, the drying conditions include: a drying temperature of 40-60°C and a drying time of 1-3 minutes.

19. A positively charged composite film prepared by the preparation method according to any one of claims 13-18.

20. The application of the positively charged composite membrane according to any one of claims 1-12 and 19 in the field of water treatment separation.

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