Nanofiltration membrane and preparation method thereof

Abstract

The nanofiltration membrane comprises a base membrane and a functional layer, the functional layer comprises a polymer, polymerization unit monomers of the polymer comprise amine monomers and cyanuric chloride, the amine monomers comprise aliphatic amine and aromatic amine derivatives, the aliphatic amine comprises at least two primary amine or secondary amine groups, and the aromatic amine derivatives comprise at least two aromatic amine derivatives. The aromatic amine derivative comprises at least two reaction functional groups and at least one hydrophilic group, the reaction functional groups comprise at least one of amino groups and hydroxyl groups, and the hydrophilic group comprises at least one of sulfonic acid groups, amino groups, hydroxyl groups, carboxyl groups and phosphate groups. Therefore, the nanofiltration membrane provided by the invention has relatively high desalination rate and stable alkali resistance.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membranes, and in particular to a high-performance nanofiltration membrane and a preparation method thereof. Background Art

[0002] Nanofiltration membranes are increasingly used in wastewater treatment and material recovery. Some complex industries such as papermaking, textiles, dairy beverages, and pharmaceuticals produce strong alkaline waste liquids during production. Using membrane separation methods to treat these waste liquids not only alleviates the pollution caused by waste liquid discharge to the environment, but also brings certain economic benefits to the company by reusing the treated alkaline liquid. Traditional nanofiltration membrane materials are polyamides, but because the amide bonds are easily broken under strong alkali, resulting in defects in its functional layer, the membrane performance is reduced, and it cannot meet the application requirements of alkaline waste liquids.

[0003] At present, poly(oxazine)amine nanofiltration membrane is the main nanofiltration membrane that can withstand more than 20% strong alkali solution. Poly(oxazine)amine nanofiltration membranes are generally prepared by interfacial polymerization reaction on a porous base membrane with polyamine monomers as the water phase and halogen-substituted diazine, triazine or tetrazine compounds as the oil phase. However, the poly(oxazine)amine nanofiltration membrane in the prior art has low membrane polymerization degree and many unreacted residual groups, which leads to the fact that the performance of the nanofiltration membrane, such as alkali resistance and salt rejection rate, still cannot meet the requirements in some application fields. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art to a certain extent. To this end, the present invention provides a nanofiltration membrane and a preparation method thereof. The nanofiltration membrane of the present invention has a high salt rejection rate and alkali resistance.

[0005] Therefore, in the first aspect of the present invention, the present invention proposes a nanofiltration membrane, comprising: a base membrane, a functional layer, the functional layer comprising a polymer, the polymerization unit monomer of the polymer comprising an amine monomer and cyanuric chloride, the amine monomer comprising aliphatic amine and aromatic amine derivatives, the aliphatic amine comprising at least two primary amine or secondary amine groups, the aromatic amine derivative comprising at least two reactive functional groups and at least one hydrophilic group, the reactive functional group comprising at least one of an amino group and a hydroxyl group, and the hydrophilic group comprising at least one of a sulfonic acid group, an amino group, a hydroxyl group, a carboxyl group, and a phosphoric acid group. Thus, the nanofiltration membrane of the present invention has a high salt rejection rate and stable alkali resistance.

[0006] In some embodiments, the fatty amine includes at least one of polyethyleneimine, tetraethylenepentamine, and triethylenetetramine, and the molecular weight range of polyethyleneimine is 300Da to 10000Da; the aromatic amine derivative includes at least one of diaminobenzenesulfonic acid, diaminophenol, aminobenzenediol, 2,4-diaminobenzenesulfonic acid, 4-aminobenzene-1,3-diol, 3-amino-4-hydroxybenzoic acid, 5-amino-2-hydroxybenzoic acid, 2-amino-3-hydroxybenzoic acid, 4-amino-2-hydroxyphenylphosphoric acid, 2-amino-4-hydroxyphenylphosphoric acid, and 3-amino-4-hydroxyphenylphosphoric acid.

[0007] In some embodiments, the mass ratio of the aliphatic amine to the aromatic amine derivative is 3:1 to 15:1.

[0008] In the second aspect of the present invention, the present invention provides a method for preparing a nanofiltration membrane according to the first aspect, comprising: preparing a base membrane on a support layer by a phase inversion method; and forming a functional layer on the surface of the base membrane. Thus, the method for preparing a nanofiltration membrane provided by the embodiment of the present invention can obtain a nanofiltration membrane with excellent performance.

[0009] In some embodiments, the step of forming a functional layer on the surface of the base film includes: contacting the base film with an aqueous solution, the aqueous solution including amine monomers; contacting the base film with an oil solution to form a functional layer, the oil solution including cyanuric chloride.

[0010] In some embodiments, the step of forming a functional layer on the surface of the base film includes: contacting the base film with an aqueous solution A and then with solution B, wherein the aqueous solution A includes an aromatic amine derivative and the aqueous solution B includes a fatty amine; contacting the base film with an oil phase solution to form a functional layer, wherein the oil phase solution includes cyanuric chloride.

[0011] In some embodiments, the aqueous solution further comprises an aqueous solvent, a catalyst, a proton absorber, a surfactant and a solubilizing agent; the aqueous solution satisfies at least one of the following: (1) the aqueous solvent comprises water; (2) the catalyst comprises at least one of polyaminopyridine, 4-(NN-dimethylamino)pyridine and 4-(NN-diallylamine)pyridine, and the content of the catalyst is 0.1% to 0.8% of the mass of the aqueous solution; (3) the proton absorber comprises at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, pyridine, imidazole and indole, and the content of the proton absorber is 0.5% to 2.0% of the mass of the aqueous solution; (4) the surfactant comprises a carboxylate, phosphate and sulfonate fluorocarbon surfactant, and the content of the surfactant is 0.1% to 3% of the mass of the aqueous solution; (5) the solubilizing agent comprises a fatty amine solvent, and the content of the solubilizing agent is 0.1% to 2% of the mass of the aqueous solution; (6) the total content of the amine monomers is 2% to 6% of the mass of the aqueous solution.

[0012] In some embodiments, the oil phase solution further includes adding a co-solvent and an organic solvent, and the oil phase solution satisfies at least one of the following: (A) the co-solvent includes ethers, benzene rings, esters, and ketones, and the content of the co-solvent is 1% to 5% of the mass of the oil phase solution; (B) the organic solvent includes saturated alkanes; (C) the content of cyanuric chloride is 0.1% to 0.5% of the mass of the oil phase solution.

[0013] In some embodiments, in the step of contacting the base film with the aqueous solution, the contact time is 5s to 180s; the contact method includes any one of dipping, rolling, slit, and spraying; and / or, in the step of contacting the base film with the oil phase solution, the contact time is 5s to 180s, and the temperature of the oil phase solution is 50°C to 70°C; the contact method includes any one of dipping, rolling, slit, and spraying.

[0014] In some embodiments, after the step of contacting the basement membrane with the oil phase solution, the step further includes: heat treating, cleaning, acid treating, and soaking the basement membrane to obtain a nanofiltration membrane; the heat treatment temperature is 60°C to 90°C, and the time is 1 min to 5 min.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects:

[0016] 1. The present invention adds small molecule aromatic amine derivative monomers to the aqueous solution. The aromatic amine derivatives usually have a small molecular weight and a high reaction activity. When used in combination with long-chain fatty amines, the problem of low functional group utilization in the polymerization process of long-chain fatty amines is improved, the polymerization efficiency is accelerated, the degree of polymerization of the membrane layer is increased, the amount of residual groups after the reaction is reduced, the desalination rate of the nanofiltration membrane is improved, and the alkali resistance is stabilized.

[0017] 2. The monomer structure of aromatic amine derivatives has an adjusting effect on the pore size of the membrane, which is beneficial to improving the flux of the nanofiltration membrane. At the same time, the monomer of aromatic amine derivatives has a rigid structure, which improves the mechanical stability of the nanofiltration membrane to a certain extent.

[0018] 3. Introducing hydrophilic groups into aromatic amine derivative monomers further increases the water wettability of the membrane surface and improves the water flux of the nanofiltration membrane.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0020] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0021] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0022] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0023] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0024] In the first aspect of the embodiments of the present invention, the present invention proposes a nanofiltration membrane, comprising: a base membrane; a functional layer, the functional layer comprising a polymer, the polymerization unit monomers of the polymer comprising amine monomers and cyanuric chloride, the amine monomers comprising aliphatic amines and aromatic amine derivatives, the aliphatic amines comprising at least two primary amine or secondary amine groups, the aromatic amine derivatives comprising at least two reactive functional groups and at least one hydrophilic group, the reactive functional groups comprising at least one of amino and hydroxyl groups, the hydrophilic groups comprising at least one of sulfonic acid groups, amino groups, hydroxyl groups, carboxyl groups and phosphoric acid groups.

[0025] The amine monomers provided in the embodiments of the present invention and cyanuric chloride mainly undergo polymerization reaction to form a three-dimensional network macromolecular polymer film. The aliphatic amine and aromatic amine derivatives in the amine monomers contain amino groups (-NH 2 , -NH-), and the reactive functional groups of aromatic amine derivatives also include hydroxyl groups (-OH). Therefore, the amino groups (-NH 2, -NH-) and hydroxyl (-OH) react with chlorine (-Cl-) in cyanuric chloride by nucleophilic substitution reaction, with amino group and hydroxyl group acting as nucleophilic reagents to attack chlorine atom in cyanuric chloride, generate CN bond and CO bond, form corresponding substitution product, connect amine monomer and cyanuric chloride by chemical bond, so that small molecule monomer becomes a network macromolecular structure, and form nanofiltration membrane. In addition, due to the molecular morphology characteristics, aliphatic amine monomer has low reaction activity, and there are many residual groups after reaction, so it is not easy to prepare a functional layer with high polymerization degree. Aromatic amine derivatives usually have small molecular weight and high reaction activity. Therefore, the combination of aliphatic amine and aromatic amine derivatives can improve the polymerization degree of the functional layer and reduce the residual groups. Due to the increase of polymerization degree and the reduction of residual groups, the structure of the functional layer is more compact and the interaction force between molecular chains is stronger, so it can effectively block the passage of salt ions while allowing water molecules to pass through, thereby improving the desalination rate and stabilizing the alkali resistance. In addition, the hydrophilic groups in the aromatic amine derivatives can increase the moisture content of the membrane surface, thereby improving the flux of the nanofiltration membrane to a certain extent. At the same time, the aromatic amine derivative molecules have a rigid structure, thereby improving the mechanical stability of the nanofiltration membrane to a certain extent. Therefore, the nanofiltration membrane of the present invention has a high salt rejection rate and stable alkali resistance.

[0026] In some embodiments of the present invention, the fatty amine includes at least one of polyethyleneimine, tetraethylenepentamine, and triethylenetetramine, and the molecular weight range of polyethyleneimine is 300Da to 10000Da; the aromatic amine derivative includes at least one of diaminobenzenesulfonic acid, diaminophenol, aminobenzenediol, 2,4-diaminobenzenesulfonic acid, 4-aminobenzene-1,3-diol, 3-amino-4-hydroxybenzoic acid, 5-amino-2-hydroxybenzoic acid, 2-amino-3-hydroxybenzoic acid, 4-amino-2-hydroxyphenylphosphoric acid, 2-amino-4-hydroxyphenylphosphoric acid, and 3-amino-4-hydroxyphenylphosphoric acid.

[0027] In the present invention, polyethyleneimine (PEI), tetraethylenepentamine (TEPA) and triethylenetetramine (TETA), these polyamine monomers have multiple amino groups, and these functional groups can undergo interfacial polymerization reaction with cyanuric chloride to form a highly cross-linked macromolecular network structure. Therefore, the nanofiltration membrane of the present invention has a higher salt rejection rate and stable alkali resistance.

[0028] As an example, the molecular weight of polyethyleneimine is 300 Da, 600 Da, 1000 Da, 2000 Da, 3000 Da, 4000 Da, 5000 Da, 6000 Da, 7000 Da, 8000 Da, 9000 Da, 10000 Da, etc.

[0029] In some embodiments of the present invention, the mass ratio of the aliphatic amine to the aromatic amine derivative is 3:1 to 15:1, preferably 5:1 to 8:1.

[0030] When the mass ratio of the aliphatic amine and the aromatic amine derivative provided by the embodiment of the present invention meets the above conditions, it is conducive to the carrying out of the polymerization reaction, improves the polymerization degree of the functional layer, reduces the residual groups, and simultaneously improves the hydrophilicity of the membrane surface, thereby improving the flux of the nanofiltration membrane to a certain extent. The aromatic amine derivative has a rigid structure of a benzene ring and contains a hydrophilic group, which plays a role in regulating the pore size, increasing the hydrophilicity and mechanical stability, and mainly improves the flux of the membrane. Therefore, its dosage is less, which is conducive to the retention rate and flux balance of the membrane. If the dosage of the aromatic amine derivative is too high, the functional layer of the nanofiltration membrane will be loosened, and the retention rate will decrease. Thus, the nanofiltration membrane of the present invention has a higher salt rejection rate and stable alkali resistance.

[0031] As an example, the mass ratio is 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, etc.

[0032] In some embodiments of the present invention, the molecular weight cutoff range of the base membrane is 3K to 50k, preferably 5K to 10K.

[0033] When the molecular weight cut-off range of the base membrane of the present invention meets the above conditions, it is conducive to forming a thinner and more stable functional layer. Therefore, the nanofiltration membrane of the present invention has a stable rejection rate and stable alkali resistance.

[0034] In a second aspect of the embodiment of the present invention, the present invention provides a method for preparing a nanofiltration membrane according to the first aspect, comprising: preparing a base membrane on a support layer by a phase inversion method; and forming a functional layer on the surface of the base membrane. Thus, the method for preparing a nanofiltration membrane according to the embodiment of the present invention can obtain a nanofiltration membrane with excellent performance.

[0035] In some embodiments of the present invention, the step of forming a functional layer on the surface of the base film includes: contacting the base film with an aqueous solution, or contacting the base film with an aqueous solution A and then with an aqueous solution B, the aqueous solution includes an amine monomer, the aqueous solution A includes an aromatic amine derivative, and the aqueous solution B includes a fatty amine; contacting the base film with an oil solution to form a functional layer, the oil solution includes cyanuric chloride.

[0036] In the method for preparing the nanofiltration membrane provided by the embodiment of the present invention, a basement membrane is first prepared. The basement membrane is a porous matrix. During the process of contacting the aqueous solution, the amine monomers in the aqueous solution are evenly spread in the shallow layer and surface layer of the basement membrane nanopores in the form of a solution. Then, when the basement membrane contacts the oil phase solution, the amine monomers and cyanuric chloride rapidly undergo a polymerization reaction to form a functional layer. Since the chlorine (-Cl) of cyanuric chloride in the oil phase solution is a strong electron-withdrawing group, the C connected to it is electron-deficient, and the amino group (-NH 2The N or O of the chlorine (-Cl) or hydroxyl (-OH) is rich in electrons, so it acts as a nucleophilic agent to replace chlorine (-Cl), and a nucleophilic substitution reaction occurs, thereby polymerizing to form a macromolecular polymer containing a CN bond or a CO bond, thereby preparing a nanofiltration membrane with a complete structure. Therefore, the nanofiltration membrane of the present invention has excellent performance.

[0037] In some embodiments of the present invention, the step of forming a functional layer on the surface of the base film includes: contacting the base film with an aqueous solution A and then with an aqueous solution B, wherein the aqueous solution A includes an aromatic amine derivative and the aqueous solution B includes a fatty amine; contacting the base film with an oil solution to form a functional layer, wherein the oil solution includes cyanuric chloride.

[0038] In the method for preparing the nanofiltration membrane provided by the embodiment of the present invention, the base membrane is contacted with the aqueous solution A and then with the aqueous solution B. This method can to a certain extent avoid the problem that due to the flexibility of the long-chain structure of the fatty amine, some of the segments on the porous base membrane are easy to penetrate into the deeper parts of the pores, resulting in low amine group reaction activity and low degree of polymerization of the membrane layer. Therefore, the nanofiltration membrane of the present invention will have excellent performance.

[0039] In some embodiments of the present invention, the aqueous solution further comprises an aqueous solvent, a catalyst, a proton absorber, a surfactant and a solubilizing agent; the aqueous solution satisfies at least one of the following conditions: (1) the aqueous solvent comprises water; (2) the catalyst comprises at least one of polyaminopyridine, 4-(NN-dimethylamino)pyridine and 4-(NN-diallylamine)pyridine, and the content of the catalyst is 0.1% to 0.8% by mass of the aqueous solution; (3) the proton absorber comprises at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, pyridine, imidazole and indole, and the content of the proton absorber is 0.5% to 2.0% by mass of the aqueous solution; (4) the surfactant comprises a carboxylate, phosphate or sulfonate fluorocarbon surfactant, and the content of the surfactant is 0.1% to 3% by mass of the aqueous solution; (5) the solubilizing agent comprises a fatty amine good solvent, and the content of the solubilizing agent is 0.1% to 2% by mass of the aqueous solution; (6) the total content of the amine monomers is 2% to 6% by mass of the aqueous solution.

[0040] In the present invention, the catalyst mainly plays a catalytic role to accelerate the polymerization reaction. During the polymerization reaction, the reactive group generates protons, and the proton absorber mainly plays a role in combining and neutralizing the protons to promote the reaction. The surfactant mainly improves the hydrophilicity and anti-pollution performance of the membrane surface. The role of the solubilizer is to increase the stretchability of the polymer chain and improve the solubility of the amine monomer. As a result, the nanofiltration membrane of the present invention has excellent salt rejection and stable alkali resistance.

[0041] As an example, the catalyst content is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., of the mass of the aqueous solution;

[0042] As an example, the content of the proton absorber is 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, etc., based on the mass of the aqueous solution.

[0043] As an example, the content of the surfactant is 0.1%, 0.15%, 0.2%, 0.25%, 3%, etc., based on the mass of the aqueous phase solution.

[0044] As an example, the content of the amine monomer is 2%, 3%, 4%, 5%, 6%, etc., of the mass of the aqueous phase solution.

[0045] As an example, the surfactant includes at least one of DuPont FS, FSA, FSP, FSJ, and FSE.

[0046] As an example, the solubilizing agent includes at least one of THF (tetrahydrofuran), DMAC (N,N-dimethylacetamide), and DMF (N,N-dimethylformamide).

[0047] In some embodiments of the present invention, the oil phase solution further includes a co-solvent and an organic solvent, and the oil phase solution satisfies at least one of the following: (A) the co-solvent includes ethers, benzene rings, esters, and ketones, and the content of the co-solvent is 1% to 5% of the mass of the oil phase solution; (B) the organic solvent includes saturated alkanes; (C) the content of cyanuric chloride is 0.1% to 0.5% of the mass of the oil phase solution.

[0048] When the method for preparing the nanofiltration membrane provided by the embodiment of the present invention meets the above conditions, a nanofiltration membrane with excellent performance can be obtained, thereby further improving the salt rejection rate and alkali resistance of the nanofiltration membrane.

[0049] As an example, the content of the co-solvent is 1%, 2%, 3%, 4%, 5%, etc., of the mass of the oil phase solution.

[0050] As an example, the content of cyanuric chloride is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc., of the mass of the oil phase solution.

[0051] As an example, the ethers include at least one of dioxane, tetrahydrofuran, diethylene glycol dimethyl ether, and ethylene glycol dimethyl ether.

[0052] As an example, the benzene rings include at least one of toluene and xylene.

[0053] As an example, the ester includes at least one of tributyl phosphate and triethyl phosphate.

[0054] As an example, the ketone includes at least one of acetone and butanone.

[0055] As an example, the saturated alkanes include at least one of ethylcyclohexane, n-hexane, and isoalkanes.

[0056] In some embodiments of the present invention, the support layer comprises a polyolefin nonwoven fabric.

[0057] In some embodiments of the present invention, the step of preparing a base membrane on a support layer by a phase inversion method includes: mixing polyethersulfone (PES) and / or polysulfone (PS) with a solvent to obtain a casting liquid; contacting the support layer with the casting liquid, and treating it by a phase inversion method to obtain a base membrane.

[0058] In some embodiments of the present invention, the base membrane includes a polyethersulfone (PES) base membrane, a polysulfone (PS) base membrane, and a base membrane mixed with polyethersulfone (PES) and polysulfone (PS); the mass ratio of polysulfone to polyethersulfone is 10:3 to 3:1; the mass concentration range of the mixture of polysulfone and polyethersulfone is 8 to 20%; the solvent includes any one of DMF (N,N-dimethylformamide), DMAC (N,N-dimethylacetamide) and NMP (N-methylpyrrolidone). In the present invention, when polysulfone and polyethersulfone are mixed and applied, a better balance can be obtained in terms of the basic performance of the base membrane and the application adaptability (such as hydrophilicity and mechanical stability).

[0059] In some embodiments of the present invention, in the step of contacting the base film with the aqueous solution, the contact time is 5s to 180s; and / or the contact method includes any one of dipping, rolling, slit coating, and spraying.

[0060] When the method for preparing the nanofiltration membrane provided by the embodiment of the present invention meets the above conditions, the contact time of 5s to 180s ensures that the aqueous solution completely wets the surface of the porous base membrane, which is conducive to preparing a nanofiltration membrane with excellent performance.

[0061] As an example, the contact time is 5s, 10s, 20s, 40s, 60s, 80s, 120s, 140s, 160s, 180s, etc.

[0062] In some embodiments of the present invention, after the base film is in contact with the aqueous solution, the method further comprises: removing excess solution from the surface of the base film by squeezing with a rubber roller or blowing with an air knife.

[0063] In some embodiments of the present invention, in the step of contacting the base film with the oil phase solution, the contact time is 5s to 180s, the temperature of the oil phase solution is 50°C to 70°C; and / or the contact method includes any one of dipping, rolling, slit coating, and spraying.

[0064] In the present invention, the base film is in contact with the aqueous phase solution and then with the oil phase solution, and the contact time of 5s to 180s ensures that the polymerization reaction is fully carried out. In addition, the three-substitution reaction of cyanuric chloride is a step-by-step decreasing process, and the second and third substitution reactions can only occur at above 50°C. Therefore, when the temperature of the oil phase solution is 50°C to 70°C, it is conducive to the polymerization reaction, while avoiding the volatilization of the co-solvent in the oil phase solution, ensuring the stability of the oil phase solution. Thus, the prepared nanofiltration membrane will have excellent salt rejection and stable alkali resistance.

[0065] As an example, the contact time is 5s, 10s, 20s, 40s, 60s, 80s, 120s, 140s, 160s, 180s, etc.

[0066] In some embodiments of the present invention, after the step of contacting the basement membrane with the oil phase solution, the step further includes: heat treating, cleaning, acid treating, and soaking the basement membrane to obtain a nanofiltration membrane; the heat treatment temperature is 60°C to 90°C, and the time is 1 min to 5 min.

[0067] In the present invention, after the basement membrane is in contact with the oil phase solution, the basement membrane is subjected to heat treatment to remove the organic solvent, promote further cross-linking reaction of the membrane surface layer, and stabilize the pore size and pore structure of the functional layer. If the heat treatment temperature is too high for a long time, the cross-linking degree of the functional layer will be too high, and the membrane thickness will increase, resulting in a decrease in water flux. After the heat treatment, the membrane is fully cleaned and then treated with acid (such as citric acid) to wash away unreacted monomers, solvents and small molecule polymer fragments, reduce these residues, and stabilize the membrane performance. Then soak in water for a certain period of time to further remove unreacted monomers and other small molecule substances in the formula and stabilize the membrane performance. Thus, the prepared nanofiltration membrane will have excellent salt rejection and stable alkali resistance.

[0068] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0069] Embodiment 1:

[0070] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0071] (2) Preparation of aqueous solution: Add 1.5% polyethyleneimine (molecular weight 1800Da), 0.5% 2,4-diaminobenzenesulfonic acid, 0.4% 4-(NN-diallylamine)pyridine, 0.8% sodium hydroxide and 2% DMAC in deionized water, stir well to dissolve and mix evenly.

[0072] (3) Preparation of oil phase solution: Add 0.3% cyanuric chloride and 3% diethylene glycol dimethyl ether in a mass concentration into ethyl cyclohexane solvent, stir thoroughly to dissolve, and mix evenly.

[0073] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 30 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 10 seconds, then taken out to drain the solvent and placed in a 90°C oven for 2 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0074] Embodiment 2:

[0075] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0076] (2) Preparation of aqueous solution: Add 5% ethylenediamine-terminated polyethyleneimine, 1% 2,4-diaminobenzenesulfonic acid, 0.8% 4-(NN-diallylamine)pyridine, 2% sodium hydroxide and 1% FS-63 in deionized water, stir well to dissolve and mix evenly.

[0077] (3) Preparation of oil phase solution: Add 0.5% cyanuric chloride and 5% diethylene glycol dimethyl ether in a mass concentration into ethyl cyclohexane solvent, stir thoroughly to dissolve, and mix evenly.

[0078] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 60 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 30 seconds, then taken out to drain the solvent and placed in an 80°C oven for 3 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0079] Embodiment 3:

[0080] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0081] (2) Prepare an aqueous solution: add 2.8% ethylenediamine-terminated polyethyleneimine, 0.2% 2,4-diaminobenzenesulfonic acid, 0.3% 4-(NN-dimethylamine)pyridine, 0.8% sodium hydroxide and 0.6% FSA in a mass concentration into deionized water, stir well to dissolve, and mix well.

[0082] (3) Preparation of oil phase solution: Add 0.2% cyanuric chloride and 2% diethylene glycol dimethyl ether to the solvent ethyl cyclohexane, stir thoroughly to dissolve, and mix evenly.

[0083] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 20 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 20 seconds, then taken out to drain the solvent and placed in an 80°C oven for 3 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0084] Embodiment 4:

[0085] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0086] (2) Preparation of aqueous solution: Add 3.5% polyethyleneimine (molecular weight 300Da), 0.5% 2-aminoresorcinol, 0.4% 4-(NN-dimethylamine)pyridine, 0.8% sodium carbonate, 3% sodium dodecyl sulfate and 0.2% DMAC in deionized water, stir well to dissolve and mix evenly.

[0087] (3) Preparation of oil phase solution: Add 0.5% cyanuric chloride and 3% tetrahydrofuran in a mass concentration into ethylcyclohexane solvent, stir thoroughly to dissolve, and mix evenly.

[0088] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 30 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 10 seconds, then taken out to drain the solvent and placed in a 70°C oven for 3 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0089] Embodiment 5:

[0090] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0091] (2) preparing an aqueous solution: adding 0.2% 4-aminobenzene-1,3-diol and 0.1% FSA to deionized water, stirring and dissolving them, mixing them evenly, to prepare an aqueous solution A; adding 1.8% ethylenediamine-terminated polyethyleneimine, 0.1% 4-(NN-diallylamine)pyridine, 0.5% sodium hydroxide, and 0.1% FS-35 to deionized water, stirring and dissolving them, mixing them evenly, to prepare an aqueous solution B.

[0092] (3) Preparation of oil phase solution: Add 0.1% cyanuric chloride and 1% tetrahydrofuran to the solvent ethylcyclohexane, stir thoroughly to dissolve, and mix evenly.

[0093] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and aqueous solution A was dip-coated on the surface of the base membrane for 10 seconds. The excess solution was squeezed out with a roller, and then the base membrane was in contact with aqueous solution B for 10 seconds. The excess solution on the surface of the base membrane was then blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 20 seconds, then taken out to drain the solvent, and placed in an 80°C oven for 3 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0094] Embodiment 6:

[0095] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0096] (2) Preparation of aqueous solution: Add 0.2% 4-aminobenzene-1,3-diol, 0.1% FSA, 1.8% ethylenediamine-terminated polyethyleneimine, 0.1% 4-(NN-diallylamine)pyridine, and 0.5% sodium hydroxide to deionized water, stir and dissolve thoroughly, mix well, and prepare an aqueous solution.

[0097] (3) Preparation of oil phase solution: Add 0.1% cyanuric chloride and 1% tetrahydrofuran to the solvent ethylcyclohexane, stir thoroughly to dissolve, and mix evenly.

[0098] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 20 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 20 seconds, then taken out to drain the solvent and placed in an 80°C oven for 3 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0099] Embodiment 7:

[0100] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0101] (2) Preparation of aqueous solution: Add 0.5% polyethyleneimine (molecular weight 1800Da), 1.5% 2,4-diaminobenzenesulfonic acid, 0.4% 4-(NN-diallylamine)pyridine, 0.8% sodium hydroxide and 2% DMAC in deionized water, stir well to dissolve and mix evenly.

[0102] (3) Preparation of oil phase solution: Add 0.3% cyanuric chloride and 3% diethylene glycol dimethyl ether in a mass concentration into ethyl cyclohexane solvent, stir thoroughly to dissolve, and mix evenly.

[0103] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 30 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 10 seconds, then taken out to drain the solvent and placed in a 90°C oven for 2 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0104] Comparative Example 1:

[0105] (1) Preparation of base membrane: 13% by weight of polyethersulfone was added to the solvent DMF to prepare a casting solution, and a polyethersulfone base membrane was prepared on a polypropylene non-woven fabric by a phase inversion method.

[0106] (2) Preparation of aqueous solution: Add 2% polyethyleneimine (molecular weight 1800Da), 0.4% 4-(NN-diallylamine)pyridine, 1% sodium hydroxide and 1.5% FS-63 in deionized water, stir thoroughly to dissolve and mix evenly.

[0107] (3) Preparation of oil phase solution: Add 0.3% cyanuric chloride and 3% diethylene glycol dimethyl ether in a mass concentration into ethyl cyclohexane solvent, stir thoroughly to dissolve, and mix evenly.

[0108] (4) Preparation of functional layer: The polyethersulfone base membrane was washed with deionized water to remove surface impurities, and the aqueous solution was dip-coated on the surface of the base membrane for 30 seconds. Then, the excess solution on the surface of the base membrane was blown off with an air knife, and the base membrane was immersed in a 60°C oil phase solution for 10 seconds, then taken out to drain the solvent and placed in an 80°C oven for 3 minutes. The base membrane was washed with deionized water to remove the substances and solvent that did not participate in the reaction, and then treated with a 15% citric acid solution, and then immersed in deionized water for more than 24 hours for testing.

[0109] 1. Performance test:

[0110] 1. Test of water flux and desalination rate performance of nanofiltration membrane: The test liquid is 2000ppm magnesium sulfate aqueous solution, pH value is 6.5-7.5, operating temperature is 25℃, and the membrane is operated at 1MPa operating pressure for 30min to test the water flux and desalination rate of the membrane.

[0111] 2. Nanofiltration membrane alkali resistance test: Use 20% sodium hydroxide solution to soak the base membrane for 1 month at a temperature of 25°C. After the treated base membrane is fully rinsed with deionized water, the desalination rate of the nanofiltration membrane before and after soaking is tested, and the change rate and attenuation rate before and after are calculated to indicate the alkali resistance.

[0112] 2. Test Results

[0113] The test results of the above embodiments and comparative examples are shown in Table 1.

[0114] Table 1 Desalination rate, water flux and alkali resistance test results of each embodiment and comparative example

[0115] Serial number Desalination rate % Alkali resistance% Water flux(LMH) Example 1 96.8 1.7 32.6 Example 2 97.6 1.5 28.7 Example 3 97.3 0.9 29.4 Example 4 96.9 1.4 31.3 Example 5 97.0 1.3 34.3 Example 6 96.7 1.9 33.7 Example 7 95.3 2.7 42.1 Comparative Example 1 96.0 3.6 18.7

[0116] As shown in Table 1, the rejection rate, alkali resistance and water flux of the nanofiltration membranes in Examples 1 to 6 are significantly better than those in the comparative examples. The retention rate of the nanofiltration membrane in Example 7 is lower than that in Comparative Example 1 because the amount of aromatic amine derivatives added is too high, which increases the pore size of the polymer and significantly improves the water flux. The pore size will also affect the alkali resistance of the membrane to a certain extent. Generally, the polymer of the functional layer has alkali swelling phenomenon, and the free volume change of the functional layer with a larger pore size under the action of alkali solution will be more obvious, resulting in poor alkali resistance. Due to the lack of aromatic amine derivatives in the aqueous phase solution of Comparative Example 1, the polyethyleneimine in Comparative Example 1 has a slow movement speed of chain macromolecules in the solution, and its random coil morphology causes obvious steric hindrance effect, and the reaction activity is low, which leads to a low degree of polymerization of the prepared nanofiltration membrane, a thicker membrane layer, and many unreacted residual groups, thereby affecting its performance. Therefore, the preparation method of the present invention can further improve the rejection rate, alkali resistance and water flux of the nanofiltration membrane.

[0117] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be in any embodiment or example.

[0118] One or more embodiments or examples may be combined in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without mutual contradiction.

[0119] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A nanofiltration membrane, characterized in that: include: Basement membrane, The functional layer comprises a polymer, wherein the polymerization unit monomers of the polymer comprise amine monomers and cyanuric chloride, the amine monomers comprise aliphatic amines and aromatic amine derivatives, the aliphatic amines comprise at least two primary amine or secondary amine groups, the aromatic amine derivatives comprise at least two reactive functional groups and at least one hydrophilic group, the reactive functional groups comprise at least one of amino and hydroxyl groups, and the hydrophilic groups comprise at least one of sulfonic acid group, amino group, hydroxyl group, carboxyl group and phosphoric acid group.

2. The nanofiltration membrane according to claim 1, characterized in that The fatty amine includes at least one of polyethyleneimine, tetraethylenepentamine and triethylenetetramine, and the molecular weight of the polyethyleneimine ranges from 300Da to 10000Da; And / or, the aromatic amine derivative includes at least one of diaminobenzenesulfonic acid, diaminophenol, aminophenyl glycol, 2,4-diaminobenzenesulfonic acid, 4-aminobenzene-1,3-diol, 3-amino-4-hydroxybenzoic acid, 5-amino-2-hydroxybenzoic acid, 2-amino-3-hydroxybenzoic acid, 4-amino-2-hydroxyphenyl phosphoric acid, 2-amino-4-hydroxyphenyl phosphoric acid, and 3-amino-4-hydroxyphenyl phosphoric acid.

3. The nanofiltration membrane according to claim 1 or 2, characterized in that: The mass ratio of the aliphatic amine to the aromatic amine derivative is 3:1 to 15:

1.

4. The method for preparing the nanofiltration membrane according to any one of claims 1 to 3, characterized in that: include: A base film is prepared on the support layer by a phase inversion method; A functional layer is formed on the surface of the base film.

5. The preparation method according to claim 4, characterized in that: The step of forming a functional layer on the surface of the base film includes: contacting the base film with an aqueous solution, wherein the aqueous solution includes the amine monomer; The base film is contacted with an oil phase solution to form a functional layer, wherein the oil phase solution includes the cyanuric chloride.

6. The preparation method according to claim 4, characterized in that: The step of forming a functional layer on the surface of the base film includes: The base film is contacted with an aqueous solution A and then with an aqueous solution B, wherein the aqueous solution A includes the aromatic amine derivative and the aqueous solution B includes the fatty amine; The base film is contacted with an oil phase solution to form a functional layer, wherein the oil phase solution includes the cyanuric chloride.

7. The preparation method according to claim 5 or 6, characterized in that: The aqueous phase solution further includes an aqueous phase solvent, a catalyst, a proton absorber, a surfactant and a solubilizer; the aqueous phase solution satisfies at least one of the following: (1) The aqueous phase solvent includes water; (2) The catalyst comprises at least one of polyaminopyridine, 4-(NN-dimethylamino)pyridine, and 4-(NN-diallylamine)pyridine, and the content of the catalyst is 0.1% to 0.8% by mass of the aqueous solution; (3) The proton absorber includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, pyridine, imidazole, and indole, and the content of the proton absorber is 0.5% to 2.0% by mass of the aqueous solution; (4) The surfactant includes a carboxylate, phosphate, or sulfonate fluorocarbon surfactant, and the content of the surfactant is 0.1% to 3% of the mass of the aqueous solution; (5) The solubilizer includes a fatty amine good solvent, and the content of the solubilizer is 0.1% to 2% of the mass of the aqueous phase solution; (6) The total content of the amine monomers is 2% to 6% of the mass of the aqueous phase solution.

8. The preparation method according to claim 5 or 6, characterized in that: The oil phase solution further includes a co-solvent and an organic solvent, and the oil phase solution satisfies at least one of the following: (A) the cosolvent includes ethers, benzene rings, esters, and ketones, and the content of the cosolvent is 1% to 5% of the mass of the oil phase solution; (B) the organic solvent comprises saturated alkanes; (C) The content of cyanuric chloride is 0.1% to 0.5% of the mass of the oil phase solution.

9. The preparation method according to any one of claims 5 to 7, characterized in that: In the step of contacting the base film with the aqueous solution, the contact time is 5s to 180s; the contact method includes any one of dipping, rolling, slit coating, and spraying; And / or, in the step of contacting the base film with the oil phase solution, the contact time is 5s to 180s, the temperature of the oil phase solution is 50°C to 70°C; the contact method includes any one of dipping, rolling, slit coating, and spraying.

10. The preparation method according to any one of claims 5 to 9, characterized in that: After the step of contacting the base film with the oil phase solution, the method further comprises: The base film is subjected to heat treatment, cleaning, acid treatment and soaking to obtain a nanofiltration membrane; the heat treatment temperature is 60° C. to 90° C. and the time is 1 min to 5 min.