Composite nanofiltration membrane, method for preparing the same, and use thereof

Abstract

The application relates to the field of separation membranes, and discloses a composite nanofiltration membrane and a preparation method and application thereof. The nanofiltration membrane comprises a bottom layer, a porous support layer, a polyamide separation layer and a pollution-resistant layer which are sequentially stacked on the bottom layer, the pollution-resistant layer comprises a polyphenol compound and a polyhydroxy polymer, and the mutually-adhered surfaces of the pollution-resistant layer and the polyamide separation layer are crosslinked with each other. The nanofiltration membrane has excellent pollution-resistant performance, good salt rejection and high water flux.

Description

Technical Field

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

[0002] Nanofiltration is a pressure-driven membrane separation process that falls between reverse osmosis and ultrafiltration. Nanofiltration membranes have pore sizes ranging from a few nanometers. They are less effective at removing monovalent ions and organic compounds with molecular weights less than 200, but have higher removal rates for divalent or polyvalent ions and organic compounds with molecular weights between 200 and 500. Nanofiltration membranes can be widely used in water softening, drinking water purification, water quality improvement, oil-water separation, wastewater treatment and reuse, seawater softening, and the classification, purification, and concentration of chemical products such as dyes, antibiotics, peptides, and polysaccharides.

[0003] Most existing commercial nanofiltration membranes are composite membranes with polyamide as the separation layer. These nanofiltration membranes not only have high salt rejection rates but also good permeability, a wide pH range (2–12), and low operating pressure. However, membrane fouling remains a significant factor affecting membrane performance and reducing its lifespan. Membrane fouling refers to the irreversible phenomenon where particulates, colloidal particles, or large solute molecules in the feed solution that come into contact with the membrane are adsorbed and deposited on the membrane surface or within the pores due to physical and chemical interactions with the membrane, concentration polarization causing certain solutes to exceed their solubility, and mechanical effects. This leads to reduced pore size or blockage, resulting in a significant decrease in membrane flux and separation characteristics. The flux decline and reduced membrane separation capacity caused by the adsorption of pollutants on the membrane surface and within the pores, especially protein adsorption, are the main causes of membrane flux decline. Therefore, the research and development of fouling-resistant nanofiltration membrane materials can not only extend membrane lifespan and reduce water treatment costs but also reduce raw material usage, which is of great significance for carbon emission reduction goals. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing nanofiltration membranes in terms of poor fouling resistance, and to provide a nanofiltration membrane with excellent fouling resistance, as well as the application of this nanofiltration membrane and the nanofiltration membrane prepared by this method in the field of water treatment.

[0005] Through in-depth research, the inventors of this invention discovered that by adding a trace amount of polyphenols to the stock solution of the nanofiltration membrane testing system, the polyphenols can undergo a cross-linking reaction with the amino groups remaining on the surface of the polyamide nanofiltration membrane, thereby increasing the cross-linking density of the separation layer and thus improving the salt rejection performance of the nanofiltration membrane. On the other hand, the polyphenols bonded to the surface of the polyamide undergo hydrogen bond self-assembly with the polyhydroxy polymer to form a hydrophilic antifouling layer, which improves the antifouling resistance of the nanofiltration membrane.

[0006] To achieve the above objectives, the present invention provides a composite nanofiltration membrane, which includes a bottom layer and a porous support layer, a polyamide separation layer and a fouling-resistant layer sequentially stacked on the bottom layer. The fouling-resistant layer includes a polyphenolic compound and a polyhydroxy polymer, and the surfaces of the fouling-resistant layer and the polyamide separation layer that are in contact with each other are cross-linked.

[0007] Preferably, the porous support layer is made of one or more of the following materials: polyethersulfone, polysulfone, polyaromatic ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryletherketone.

[0008] Preferably, the polyamide separation layer is generated by interfacial polymerization of polyamines and polyacrylamide chlorides.

[0009] Preferably, the polyamine is one or more of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine, and p-phenylenediamine; more preferably, it is polyethyleneimine and / or piperazine.

[0010] Preferably, the polyacryl chloride is one or more of pyromellitic chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride, and more preferably pyromellitic chloride and / or terephthaloyl chloride; preferably, the mass concentration ratio of the polyamine to the polyacryl chloride is 0.5-100:1, and more preferably 1-50:1.

[0011] Preferably, the polyphenolic compounds and polyhydroxy polymers in the stain-resistant layer are cross-linked with each other through hydrogen bonds.

[0012] Preferably, the anti-fouling layer is formed by the self-assembly of polyphenolic compounds and polyhydroxy polymers on the surface of the polyamide separation layer.

[0013] Preferably, the polyphenolic compound is one or more of tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein, with tannic acid and / or lignin being more preferred.

[0014] Preferably, the multi-hydroxy polymer is one or more selected from polyvinyl alcohol, hydroxy-terminated polyethylene glycol, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and chitosan.

[0015] Preferably, the bottom layer is a nonwoven fabric layer, and more preferably a polyester nonwoven fabric layer, a polyethylene nonwoven fabric layer, or a polyester-polyethylene composite nonwoven fabric layer.

[0016] Preferably, the thickness of the bottom layer is 30-150 μm, and more preferably 50-120 μm.

[0017] Preferably, the thickness of the porous support layer is 10-100 μm, and more preferably 30-60 μm.

[0018] Preferably, the thickness of the polyamide separation layer is 10-500 nm, and more preferably 50-300 nm.

[0019] Preferably, the thickness of the anti-fouling layer is 1-200 nm, and more preferably 5-50 nm.

[0020] A second aspect of the present invention provides a method for preparing a composite nanofiltration membrane, the method comprising the following steps:

[0021] (1) A porous support layer is formed on one surface of the bottom layer;

[0022] (2) The porous support layer obtained in step (1) is sequentially contacted with an aqueous phase containing polyamine and an organic phase containing polyacryl chloride. After heat treatment, a polyamide separation layer is obtained by polymerization at the surface interface of the porous support layer.

[0023] (3) Under pressure, the product of step (2) is brought into contact with a solution of polyphenolic compounds and a solution of polyhydroxy polymers in sequence, thereby forming a contamination-resistant layer on the surface of the polyamide separation layer.

[0024] Preferably, in step (3), the polyphenolic compound is one or more of tannic acid, tea polyphenol, lignin, sodium lignin sulfonate, apple polyphenol, grape polyphenol, senna glycoside, naringin, epicatechin, ospermicin, apigenin, calciferol, myricetin and genistein, preferably tannic acid and / or lignin.

[0025] Preferably, the multi-hydroxy polymer is one or more selected from polyvinyl alcohol, hydroxy-terminated polyethylene glycol, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and chitosan.

[0026] Preferably, the concentration of the polyphenolic compound is 0.00001-1% by weight, more preferably 0.0001-0.1% by weight.

[0027] Preferably, the concentration of the polyhydroxy polymer is 0.00001-1% by weight, more preferably 0.0001-0.1% by weight.

[0028] Preferably, the contact time between the product of step (2) and the solution of polyphenolic compounds is 1-120 min, more preferably 10-60 min.

[0029] Preferably, the contact time between the product of step (2) and the solution of the polyhydroxy polymer is 1-120 min, more preferably 10-60 min.

[0030] Preferably, the pressure of the pressurization condition is 0.1-4 MPa, and more preferably 0.5-2 MPa.

[0031] Preferably, in step (3), the product of step (2) is contacted sequentially with a solution of polyphenolic compound and a solution of polyhydroxy polymer by passing the solution of polyphenolic compound and the solution of polyhydroxy polymer through the product of step (2) under pressure.

[0032] Preferably, in step (2), the polyamine is one or more of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine and p-phenylenediamine; preferably polyethyleneimine and / or piperazine.

[0033] Preferably, the polyacrylamide chloride is one or more of pyromellitic chloride, terephthaloyl chloride, isophthaloyl chloride and orthophthaloyl chloride, and more preferably pyromellitic chloride and / or terephthaloyl chloride.

[0034] Preferably, in the aqueous phase containing polyamine, the concentration of polyamine is 0.1-10% by weight, preferably 0.5-2.5% by weight; in the organic phase containing polyacrylamide chloride, the concentration of polyacrylamide chloride is 0.01-1% by weight, preferably 0.1-0.5% by weight.

[0035] Preferably, the mass concentration ratio of the polyamine to the polyacryl chloride is 0.1-10:1, more preferably 0.5-5:1.

[0036] Preferably, in step (2), the contact time between the porous support layer and the aqueous phase containing polyamine is 5-100s, preferably 10-60s; and / or, the contact time between the porous support layer and the organic phase containing polyacrylamide chloride is 10-200s, preferably 20-120s; and / or, the temperature of the heat treatment is 40-150℃, preferably 50-120℃; and the heat treatment time is 0.5-10min, preferably 1-5min.

[0037] Preferably, in step (1), the porous support layer is made of one or more of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0038] Preferably, the bottom layer is a nonwoven fabric layer, and more preferably a polyester nonwoven fabric layer, a polyethylene nonwoven fabric layer, or a polyester-polyethylene composite nonwoven fabric layer.

[0039] Preferably, the thickness of the bottom layer is 30-150 μm, and more preferably 50-120 μm.

[0040] Preferably, the thickness of the porous support layer is 10-100 μm, and more preferably 30-60 μm.

[0041] Preferably, the thickness of the polyamide separation layer is 10-500 nm, and more preferably 50-300 nm.

[0042] Preferably, the thickness of the anti-fouling layer is 1-200 nm, and more preferably 5-50 nm.

[0043] The third aspect of the present invention provides a composite nanofiltration membrane obtained by the preparation method of the second aspect of the present invention described above.

[0044] The fourth aspect of the present invention provides the application of the composite nanofiltration membrane described in the first or third aspect of the present invention in the field of water treatment.

[0045] Through the above technical solution, this invention provides a composite nanofiltration membrane with excellent salt rejection rate, high water flux, and good fouling resistance, as well as its preparation method and application. The composite nanofiltration membrane of this invention comprises a bottom layer, a middle porous support layer, a polyurea separation layer, and a fouling-resistant layer. The fouling-resistant layer is formed by the self-assembly of polyphenolic compounds and polyhydroxy polymers through hydrogen bonding, and is bonded to the polyamide layer through crosslinking between the polyphenols and the residual amino groups in the polyamide layer. This provides a composite nanofiltration membrane with excellent fouling resistance, good salt rejection rate, and high water flux. The preparation method of this invention is simple and has broad industrialization prospects.

[0046] Furthermore, the composite nanofiltration membrane of the present invention, by adding trace amounts of polyphenols to the stock solution of the nanofiltration membrane testing system, after testing cycles, the polyphenolic compounds and polyhydroxy polymers undergo a self-assembly reaction on the surface of the polyamide separation layer to form the fouling-resistant layer of the present invention, thereby significantly improving the salt rejection rate and fouling resistance. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the process of modifying nanofiltration membranes with tannic acid and polyvinyl alcohol.

[0048] Figure 2 These are the infrared spectra of the nanofiltration membrane after self-assembly modification with tannic acid and polyvinyl alcohol, as well as the surface of the original polyamide nanofiltration membrane. Detailed Implementation

[0049] 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.

[0050] The composite nanofiltration membrane provided by the present invention includes a bottom layer and a porous support layer, a polyamide separation layer and a fouling-resistant layer sequentially stacked on the bottom layer. The fouling-resistant layer includes a polyphenolic compound and a polyhydroxy polymer, and the surfaces of the fouling-resistant layer and the polyamide separation layer that are in contact with each other are cross-linked.

[0051] According to the present 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. This will be known to those skilled in the art, and will not be elaborated further here. Preferably, the bottom layer can be, for example, a nonwoven fabric layer; specifically, the nonwoven fabric layer can be a polyester nonwoven fabric layer, a polyethylene nonwoven fabric layer, or a polyester-polyethylene composite nonwoven fabric layer.

[0052] In a preferred embodiment, the porous support layer may be made of one or more of the following materials: polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0053] According to the present invention, the polyamide separation layer is a polyamide film having a cross-linked polyamide structure and formed on the surface of the porous support layer and bonded to the porous support layer.

[0054] As the polyamide separation layer of the present invention described above, it is preferably generated by interfacial polymerization of a polyamine and a polyacryl chloride. Here, the term "interfacial polymerization," also known as "interfacial condensation polymerization," refers to an irreversible polymerization reaction in which two highly reactive monomers are dissolved in two immiscible solvents and the polymerization occurs at the interface between the two liquid phases. The polymer obtained from the interfacial polymerization reaction is insoluble in the solvent and precipitates at the interface.

[0055] In this invention, the polyamine may preferably be one or more of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine, and p-phenylenediamine; preferably polyethyleneimine and / or piperazine.

[0056] In interfacial polymerization, the polyamine is preferably used in solution form, and more preferably in an aqueous phase containing the polyamine. The concentration of the polyamine, for example in the aqueous phase containing the polyamine, is 0.1-10% by weight, preferably 0.5-2.5% by weight, specifically 0.5%, 0.8%, 1%, 1.5%, 2%, or 2.5% by weight.

[0057] In this invention, the polyacrylamide chloride is one or more of pyromellitic chloride, terephthaloyl chloride, isophthaloyl chloride and orthophthaloyl chloride, preferably pyromellitic chloride and / or terephthaloyl chloride.

[0058] When performing interfacial polymerization, the polyacryl chloride is preferably used in solution form, and more preferably in an organic phase containing the polyacryl chloride. The concentration of the polyacryl chloride, for example in the organic phase containing the polyacryl chloride, is 0.01-1 wt%, preferably 0.1-0.5 wt%, specifically 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0059] The amounts of the polyamine and the polyacryl chloride can vary within a wide range. Preferably, the mass concentration ratio of the polyamine to the polyacryl chloride is 0.5-100:1, more preferably 1-50:1, further preferably 1-20:1, and even more preferably 1-10:1. Specific examples of the mass concentration ratio of the polyamine to the polyacryl chloride include 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0060] As a method for interfacially polymerizing the polyamine with the polyacrylamide chloride to obtain the polyamide separation layer of the present invention, various conventional contact methods used in the art for interfacial polymerization of polyamines with polyacrylamide chlorides can be used. In the present invention, it is preferable to sequentially contact the support layer with a solution containing a polyamine and a solution containing a polyacrylamide chloride, followed by heat treatment. Specifically, this can be carried out according to the relevant conditions in the preparation method of the second aspect of the present invention.

[0061] According to the present invention, the antifouling layer is used to modify the polyamide separation layer, thereby simultaneously improving the salt rejection rate, water flux, and antifouling performance of the composite nanofiltration membrane. The polyphenolic compounds and polyhydroxy polymers in the antifouling layer are cross-linked through hydrogen bonds. Preferably, the antifouling layer is formed by the self-assembly of polyphenolic compounds and polyhydroxy polymers on the surface of the polyamide separation layer. The formed antifouling layer and the polyamide layer are bonded through cross-linking between the polyphenols and the residual amino groups in the polyamide layer.

[0062] According to the present invention, the polyphenolic compound may be one or more of tannic acid, tea polyphenol, lignin, sodium lignin sulfonate, apple polyphenol, grape polyphenol, senna glycoside, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein, preferably tannic acid and / or lignin.

[0063] According to the present invention, the multi-hydroxy polymer can be one or more of polyvinyl alcohol, hydroxy-terminated polyethylene glycol, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and chitosan.

[0064] According to some preferred embodiments of the present invention, the polyphenolic compound is tannic acid and the polyhydroxy polymer is polyvinyl alcohol; or the polyphenolic compound is tannic acid and the polyhydroxy polymer is polyethylene glycol, preferably hydroxyl-terminated polyethylene glycol; or the polyphenolic compound is tannic acid and the polyhydroxy polymer is hydroxymethyl cellulose.

[0065] According to the present invention, the thickness of the bottom layer, the porous support layer, the polyamide separation layer, and the fouling-resistant self-assembly layer is not particularly limited, and can be a conventional choice in the art. However, in order to enable these four layers to play a better synergistic role and to enable the resulting composite nanofiltration membrane to better combine excellent salt rejection rate, high water flux, and excellent fouling resistance, 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; the thickness of the polyamide separation layer is 10-500 nm, preferably 50-300 nm; and the thickness of the fouling-resistant self-assembly layer is 1-200 nm, preferably 5-50 nm.

[0066] A second aspect of the present invention provides a method for preparing a composite nanofiltration membrane, the method comprising the following steps:

[0067] (1) A porous support layer is formed on one surface of the bottom layer;

[0068] (2) The porous support layer obtained in step (1) is sequentially contacted with an aqueous phase containing polyamine and an organic phase containing polyacryl chloride. After heat treatment, a polyamide separation layer is obtained by polymerization at the surface interface of the porous support layer.

[0069] (3) Under pressure, the product of step (2) is brought into contact with a solution of polyphenolic compounds and a solution of polyhydroxy polymers in sequence, thereby forming a contamination-resistant layer on the surface of the polyamide separation layer.

[0070] The preparation method of the second aspect of the present invention can be used to prepare the composite nanofiltration membrane of the first aspect.

[0071] In this invention, there are no specific limitations on the preparation methods of the bottom layer and the porous support layer, as long as a material with a certain strength can be obtained and it can be used for nanofiltration and reverse osmosis membranes. This is something that those skilled in the art will understand, and will not be elaborated further here.

[0072] According to the present invention, in step (1), the bottom layer is a nonwoven fabric layer, preferably a polyester nonwoven fabric layer, a polyethylene nonwoven fabric layer, or a polyester-polyethylene composite nonwoven fabric layer. Preferably, the thickness of the bottom layer can be 30-150 μm, more preferably 50-120 μm.

[0073] According to some specific embodiments of the present invention, the preparation method of the porous support layer can preferably adopt the phase transformation method. Specifically, a polymer solution of the porous support layer material can be coated on one surface of the bottom layer, and the porous support layer is obtained through phase transformation.

[0074] The phase inversion method preferably involves: dissolving the polymer material used to form the porous support layer in a solvent to obtain a polymer solution with a concentration of 10-20% by weight; degassing the solution at 20-40°C for 10-180 min; then coating the polymer solution onto the substrate to obtain an initial film, which is subsequently immersed in water at 10-30°C for 10-60 min, resulting in a phase inversion layer to obtain the support layer polymer porous membrane. The solvent used can be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0075] According to the present invention, in step (2), the polyamide separation layer of the present invention described above is preferably generated by interfacial polymerization of polyamine and polyacrylamide chloride.

[0076] In this invention, the polyamine may be one or more of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine, and p-phenylenediamine; preferably polyethyleneimine and / or piperazine.

[0077] In interfacial polymerization, the polyamine is preferably used in solution form, and more preferably in an aqueous phase containing the polyamine. The concentration of the polyamine, for example in the aqueous phase containing the polyamine, is 0.1-10% by weight, preferably 0.5-2.5% by weight, specifically 0.5%, 0.8%, 1%, 1.5%, 2%, or 2.5% by weight.

[0078] In this invention, the polyacryl chloride can be a polyacryl chloride commonly used to prepare polyamides. For example, the polyacryl chloride can be one or more of pyromellitic chloride, terephthalic chloride, isophthalic chloride and phthaloyl chloride, preferably pyromellitic chloride and / or terephthalic chloride.

[0079] In interfacial polymerization, the polyacryl chloride is preferably used in solution form, and more preferably in an organic phase containing the polyacryl chloride. Preferably, the concentration of the polyacryl chloride in the organic phase is 0.01-1 wt%, more preferably 0.1-0.5 wt%; specifically, it can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0080] The type of solvent used for the organic phase is not particularly limited, as long as it can dissolve the polyacrylamide chloride. Preferably, the solvent for the organic phase is one or more of hexane, dodecane, heptane, and alkane solvent oils (Isopar E, Isopar G, Isopar H, Isopar L and Isopar M).

[0081] The amounts of the polyamine and the polyacryl chloride can vary within a wide range. Preferably, the mass concentration ratio of the polyamine to the polyacryl chloride is 0.5-100:1, more preferably 1-50:1, further preferably 1-20:1, and even more preferably 1-10:1. Specific examples of the mass concentration ratio of the polyamine to the polyacryl chloride include 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0082] According to the invention, preferably, the thickness of the polyamide separation layer is 10-500 nm, more preferably 50-300 nm.

[0083] As a method for interfacially polymerizing the polyamine and the polyacrylamide chloride to obtain the polyamide separation layer of the present invention, various conventional contact methods used in the art for interfacial polymerization of polyamine and polyacrylamide chloride can be used. The present invention does not particularly limit the conditions of interfacial polymerization, and conventional choices in the art can be used. However, in order to enable these four layers to play a better synergistic role and to enable the resulting composite nanofiltration membrane to better combine excellent fouling resistance, good salt rejection rate, and high water flux, preferably, the contact time between the porous support layer and the aqueous phase containing the polyamine is 5-100 s, preferably 10-60 s; the contact time between the porous support layer and the organic phase containing the polyacrylamide chloride is 10-200 s, preferably 20-120 s; the heat treatment temperature is 40-150°C, preferably 50-120°C; and the heat treatment time is 0.5-10 min, preferably 1-5 min.

[0084] According to the present invention, in step (3), the anti-fouling layer of the present invention is formed by reacting polyphenolic compounds and polyhydroxy polymers with the polyamide separation layer.

[0085] According to the present invention, preferably, the polyphenolic compound can be one or more of tannic acid, tea polyphenol, lignin, sodium lignin sulfonate, apple polyphenol, grape polyphenol, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin and genistein, preferably tannic acid and / or lignin.

[0086] According to the present invention, preferably, the multi-hydroxy polymer is one or more selected from polyvinyl alcohol, hydroxy-terminated polyethylene glycol, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and chitosan.

[0087] According to some preferred embodiments of the present invention, the polyphenolic compound is tannic acid and the polyhydroxy polymer is polyvinyl alcohol; or the polyphenolic compound is tannic acid and the polyhydroxy polymer is polyethylene glycol, preferably hydroxyl-terminated polyethylene glycol; or the polyphenolic compound is tannic acid and the polyhydroxy polymer is hydroxymethyl cellulose.

[0088] According to the present invention, the contact in step (3) is carried out in solution. To enable the four layers to work together more effectively, the resulting composite nanofiltration membrane can better combine excellent fouling resistance with good salt rejection and high water flux. Preferably, the concentration of the polyphenolic compound is 0.00001-1 wt%, more preferably 0.0001-0.1 wt%, and even more preferably 0.0005-0.05 wt%. Specific concentrations can be 0.0005 wt%, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, etc. Furthermore, preferably, the concentration of the polyhydroxy polymer is 0.00001-1 wt%, more preferably 0.0001-0.1 wt%, and even more preferably 0.0005-0.05 wt%. Specific concentrations can be 0.0005 wt%, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, etc.

[0089] In addition, in order to better combine the polyphenolic compound and the polyhydroxy polymer, the mass concentration ratio of the polyphenolic compound solution to the polyhydroxy polymer solution is 1:0.1-10, preferably 1:0.5-5, more preferably 1:0.6-3, 1:0.8-2 or 1:0.9-1.2.

[0090] According to the present invention, preferably, the pH of the solution of the polyphenolic compound is 6-12, more preferably 8-10. By selecting the above pH, the polyphenolic compound can be fully dissolved, thereby better forming a stain-resistant layer.

[0091] According to the present invention, preferably, the contact time between the product of step (2) and the polyphenolic compound, and the contact time between the product and the solution of the polyhydroxy polymer, are each independently 1-120 min, preferably 10-90 min; specifically, the time can be 1 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min, etc. Preferably, the pressure of the pressurization condition is 0.1-4 MPa, preferably 0.5-2 MPa; specifically, the pressure can be 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, etc.

[0092] In the above process, the polyphenolic compound and the polyhydroxy polymer self-assemble through hydrogen bonding to form a stain-resistant layer. The stain-resistant layer and the polyamide separation layer are bonded together through cross-linking between the polyphenolic compound and the residual amino groups in the polyamide layer. Preferably, the thickness of the stain-resistant layer is 1-200 nm, more preferably 5-50 nm.

[0093] According to some preferred embodiments of the present invention, in step (3), the contact between the product of step (2) and the polyphenolic compound or polyhydroxy polymer is carried out by passing a solution of the polyphenolic compound or a solution of the polyhydroxy polymer through the product of step (2) under pressure. That is, by continuously circulating the polyphenolic compound or polyhydroxy polymer in the composite membrane obtained in step (2), the antifouling layer of the present invention is formed. The process of forming the antifouling layer described above can, for example, be completed in a membrane sheet or membrane module testing system, such as... Figure 1 As shown, the system includes a membrane housing, a pump, and a raw water storage tank. The product from step (2) is placed in the membrane housing, and a solution of polyphenolic compounds from the raw water storage tank is pumped through the membrane housing, returning both the product water and the return water to the raw water storage tank. This process is continuously repeated to form the fouling-resistant layer of this invention.

[0094] The third aspect of the present invention provides a composite nanofiltration membrane obtained by the preparation method described in the second aspect of the present invention.

[0095] The fourth aspect of the present invention provides the application of the composite nanofiltration membrane described in the first or third aspect of the present invention in the field of water treatment.

[0096] The present invention will be described in detail below through embodiments.

[0097] In the following embodiments and comparative examples:

[0098] (1) The water flux of the composite nanofiltration membrane was obtained by testing it using the following method: The composite nanofiltration membrane was placed in a membrane tank, and the water permeation rate of the nanofiltration membrane was measured over a certain period of time at 0.6 MPa and a temperature of 25°C. The water flux was then calculated using the following formula:

[0099] J = Q1 / (A·t), where J is the water flux, Q1 is the water permeation rate (L), and A is the effective membrane area of ​​the composite nanofiltration membrane (m²). 2 ), where t is time (h).

[0100] (2) The desalination rate of the composite nanofiltration membrane was obtained by the following method: The composite nanofiltration membrane was loaded into the membrane tank. The original aqueous solution was 2000 ppm magnesium sulfate. After pre-pressurization at 0.2 MPa for 0.5 h, the permeate was obtained at a pressure of 0.6 MPa. The concentration of magnesium sulfate in the permeate was measured by a conductivity meter, and the desalination rate was calculated by the following formula:

[0101] R = (C p -C f ) / C p ×100%, where R is the desalination rate, and C is the desalination rate. p C represents the concentration of magnesium sulfate in the original solution. f This represents the concentration of magnesium sulfate in the permeate.

[0102] (3) Fouling resistance test of composite nanofiltration membrane: The composite nanofiltration membrane was placed in a membrane tank, and the circulating test solution was 2000 ppm magnesium sulfate and 1000 ppm bovine serum albumin (BSA). After running for 6 hours at a pressure of 0.6 MPa and a temperature of 25℃, the water flux Q2 of the composite membrane was measured. Then, the nanofiltration membrane was rinsed with clean water for 0.5 hours, and its water flux Q3 was tested under the same pressure conditions with a circulating solution of 2000 ppm magnesium sulfate. The water flux reduction rate of the composite membrane was obtained by the following formula: D=(Q1-Q2) / Q1×100%; the water flux of the composite membrane after water washing was obtained by the following formula:

[0103] H = Q3 / Q1 × 100%

[0104] In addition, in the following examples and comparative examples, branched polyethyleneimine (weight average molecular weight of 25,000), piperazine, pyromellitic terephthaloyl chloride, chitosan, hydroxymethyl cellulose, tannic acid and lignin were purchased from Bailingwei Technology Co., Ltd., polyvinyl alcohol (PVA-124) was purchased from Xilong Chemical Co., Ltd., and other chemical reagents and solvents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0105] Preparation Example

[0106] In the following embodiments and comparative examples, the support layer was prepared using a phase transformation method, and the specific steps are as follows:

[0107] Polysulfone (number average molecular weight of 80,000) was dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18% by weight. The solution was allowed to stand at 25°C for 120 min to degas. 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 support layer with a total thickness of 115 μm was obtained.

[0108] Example 1

[0109] The upper surface of the polysulfone support layer was contacted with an aqueous solution containing 0.3 wt% polyethyleneimine and 0.2 wt% piperazine at 25°C for 60 s, and then drained. Then, the upper surface of the support layer was contacted again with an Isopar E solution containing 0.02 wt% trimesoyl chloride and 0.08 wt% terephthaloyl chloride at 25°C for 60 s, and then drained. Finally, the membrane was placed in an oven and heated at 70°C for 3 min to obtain the composite membrane.

[0110] like Figure 1 As shown, the composite membrane was loaded into the cross-flow membrane tank. The feed solution was a 0.001% by weight tannic acid aqueous solution (the pH of the solution was adjusted to 8.0). After the test system was run at 0.6 MPa for 30 minutes, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual tannic acid in the system and on the membrane surface. Then, a 0.001% by weight polyvinyl alcohol aqueous solution was added to the feed tank. After the test system was run at 0.6 MPa for 30 minutes, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual polyvinyl alcohol in the system, thus obtaining the fouling-resistant composite nanofiltration membrane N1.

[0111] The obtained composite nanofiltration membrane N1 was soaked in water for 24 h, and its water flux and magnesium sulfate rejection rate were measured under conditions of 0.6 MPa and 25 °C. The results are shown in Table 1. Its fouling resistance was also tested under the same temperature and pressure conditions. The water flux of the membrane after running for 6 h in an aqueous solution containing 1000 ppm bovine serum albumin and after water washing are shown in Table 1.

[0112] Example 2

[0113] The upper surface of the polysulfone support layer was contacted with an aqueous solution containing 0.5 wt% piperazine at 25°C for 60 s, and then drained. Then, the upper surface of the support layer was contacted again with an Isopar E solution containing 0.1 wt% trimesoyl chloride at 25°C for 60 s, and then drained. Finally, the membrane was placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane.

[0114] The composite nanofiltration membrane was loaded into a cross-flow membrane tank. The feed solution was a 0.01 wt% aqueous solution of tannic acid. After the test system was run at 0.6 MPa for 30 minutes, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual tannic acid. Then, a 0.01 wt% aqueous solution of hydroxyl-terminated polyethylene glycol was added to the feed tank. After the test system was run at 0.6 MPa for 30 minutes, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual hydroxyl-terminated polyethylene glycol, thus obtaining the fouling-resistant composite nanofiltration membrane N2.

[0115] The performance of the composite membrane N2 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0116] Example 3

[0117] The upper surface of the polysulfone support layer was contacted with an aqueous solution containing 0.3 wt% polyethyleneimine and 0.2 wt% piperazine, and the solution was drained after 60 s at 25 °C. Then, the upper surface of the support layer was contacted again with an Isopar E solution containing 0.02 wt% trimesoyl chloride and 0.08 wt% terephthaloyl chloride, and the solution was drained after 60 s at 25 °C. The membrane was then placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane.

[0118] The composite nanofiltration membrane was loaded into a cross-flow membrane tank. The feed solution was a 0.001% by weight aqueous solution of tannic acid. After the test system was run at 0.6 MPa for 30 minutes, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual tannic acid. Then, a 0.001% by weight aqueous solution of hydroxymethyl cellulose was added to the feed tank. After the test system was run at 0.6 MPa for 30 minutes, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual hydroxymethyl cellulose, thus obtaining the fouling-resistant composite nanofiltration membrane N3.

[0119] The performance of the composite membrane N3 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0120] Example 4

[0121] The preparation method is the same as in Example 1, except that lignin is used instead of tannic acid during the self-assembly process.

[0122] The performance of the composite membrane N4 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0123] Example 5

[0124] The preparation method is the same as in Example 1, except that tea polyphenols are used instead of tannic acid in the self-assembly modification process.

[0125] The performance of the composite membrane N5 obtained according to the method of Example 1 was measured, and the results are shown in Table 1.

[0126] Example 6

[0127] The preparation method is the same as in Example 1, except that chitosan is used instead of polyvinyl alcohol in the self-assembly modification process.

[0128] The performance of the composite membrane N6 obtained according to the method of Example 1 was measured, and the results are shown in Table 1.

[0129] Example 7

[0130] The composite nanofiltration membrane was prepared according to the preparation method of Example 1, the only difference being that no composite nanofiltration membrane was used. Figure 1 Instead of using a conventional testing system, the composite membrane was immersed in a 0.001% by weight tannic acid aqueous solution at 0.6 MPa for 30 min, and then repeatedly rinsed with deionized water to remove residual tannic acid from the membrane surface; the composite membrane was then immersed in a 0.001% by weight polyvinyl alcohol aqueous solution at 0.6 MPa for 30 min to obtain the fouling-resistant composite nanofiltration membrane N7.

[0131] The performance of the composite membrane N6 obtained according to the method of Example 1 was measured, and the results are shown in Table 1.

[0132] Example 8

[0133] The composite nanofiltration membrane was prepared according to the preparation method of Example 1, except that the concentrations of the tannic acid aqueous solution and the polyvinyl alcohol aqueous solution used were both 0.01 wt%.

[0134] The performance of the composite membrane N8 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0135] Example 9

[0136] The composite nanofiltration membrane was prepared according to the preparation method of Example 1, except that the concentrations of the tannic acid aqueous solution and the polyvinyl alcohol aqueous solution used were both 0.1% by weight.

[0137] The performance of the composite membrane N9 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0138] Comparative Example 1

[0139] The upper surface of the polysulfone support layer was contacted with an aqueous solution containing 0.3 wt% polyethyleneimine and 0.2 wt% piperazine, and the solution was drained after 60 s at 25 °C. Then, the upper surface of the support layer was contacted again with an Isopar E solution containing 0.02 wt% trimesoyl chloride and 0.08 wt% terephthaloyl chloride, and the solution was drained after 60 s at 25 °C. The membrane was then placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane D1.

[0140] The performance of the composite membrane D1 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0141] Comparative Example 2

[0142] The upper surface of the polysulfone support layer was contacted with an aqueous solution containing 0.5 wt% piperazine at 25°C for 60 s, and then drained. Then, the upper surface of the support layer was contacted again with an Isopar E solution containing 0.1 wt% trimesoyl chloride at 25°C for 60 s, and then drained. Finally, the membrane was placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane.

[0143] The performance of the composite membrane D2 obtained was determined according to the method of Example 1, and the results are shown in Table 1.

[0144] Comparative Example 3

[0145] The upper surface of the polysulfone support layer was contacted with an aqueous solution containing 0.3 wt% polyethyleneimine and 0.2 wt% piperazine at 25°C for 60 s, and then drained. Then, the upper surface of the support layer was contacted again with an Isopar E solution containing 0.02 wt% trimesoyl chloride and 0.08 wt% terephthaloyl 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 a composite nanofiltration membrane.

[0146] The composite nanofiltration membrane was loaded into a cross-flow membrane tank. The feed solution was a 0.001% by weight aqueous solution of tannic acid. After the test system was run at 0.6 MPa for 30 minutes, the solution was drained and the test system was repeatedly rinsed with deionized water to clean the residual tannic acid in the system and on the membrane surface, thus obtaining the composite nanofiltration membrane D3.

[0147] The performance of the composite membrane D3 obtained was determined according to the method in Example 1, and the results are shown in Table 1.

[0148] The infrared spectra of the composite membrane D1 and the composite nanofiltration membrane N1 were tested (ThermoFisher, Nicolet 6700 model), and the results are shown below. Figure 2 .Depend on Figure 2 It can be seen that the hydroxyl absorption signal and CN signal on the surface of the modified composite nanofiltration membrane are significantly enhanced, confirming that tannic acid and polyvinyl alcohol undergo a self-assembly reaction on the surface of the polyamide separation layer.

[0149] Table 1

[0150]

[0151] As can be seen from the results in Table 1, adding a trace amount of tannic acid to the original aqueous solution in the test system will cause the tannic acid to undergo a reverse crosslinking reaction with the amino groups remaining in the polyamide separation layer, thereby increasing the salt rejection rate of the nanofiltration membrane. On the other hand, the tannic acid bonded to the polyamide surface will undergo self-assembly with the polyhydroxy polymer under pressure, thereby bonding the polyhydroxy polymer to the membrane surface and improving the fouling resistance of the nanofiltration membrane.

[0152] 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 method for preparing a composite nanofiltration membrane, characterized in that, The method includes the following steps: (1) A porous support layer is formed on one surface of the bottom layer; (2) The porous support layer obtained in step (1) is sequentially contacted with an aqueous phase containing polyamine and an organic phase containing polyacryl chloride. After heat treatment, a polyamide separation layer is obtained by polymerization at the surface interface of the porous support layer. (3) Under pressure, the product of step (2) is brought into contact with a solution of polyphenolic compounds and a solution of polyhydroxy polymers in sequence, thereby forming a contamination-resistant layer on the surface of the polyamide separation layer; The pressure under the pressurization conditions is 0.1-4 MPa; The pH of the solution of the polyphenolic compound is 8-10; In step (3), the contact is carried out by passing a solution of polyphenolic compounds and a solution of polyhydroxy polymers through the product of step (2) under pressure, and the contact is carried out in a cross-flow membrane pool.

2. The preparation method according to claim 1, wherein, In step (3), the polyphenolic compound is one or more of the following: tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, senna glycoside, naringin, epicatechin, ospermicin, apigenin, calciferol, myricetin, and genistein.

3. The preparation method according to claim 1, wherein, In step (3), the polyphenolic compound is tannic acid and / or lignin.

4. The preparation method according to claim 1, wherein, In step (3), the multi-hydroxy polymer is one or more of polyvinyl alcohol, hydroxy-terminated polyethylene glycol, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and chitosan.

5. The preparation method according to claim 1, wherein, In step (3), the concentration of the polyphenolic compound is 0.00001-1 by weight.

6. The preparation method according to claim 1, wherein, In step (3), the concentration of the polyphenolic compound is 0.0001-0.1 by weight.

7. The preparation method according to claim 1, wherein, In step (3), the concentration of the polyhydroxy polymer is 0.00001-1 by weight.

8. The preparation method according to claim 1, wherein, In step (3), the concentration of the polyhydroxy polymer is 0.0001-0.1% by weight.

9. The preparation method according to claim 1, wherein, In step (3), the product from step (2) is in contact with the solution of polyphenolic compounds for 1-120 min.

10. The preparation method according to claim 1, wherein, In step (3), the product from step (2) is in contact with the solution of polyphenolic compounds for 10-60 minutes.

11. The preparation method according to claim 1, wherein, In step (3), the product from step (2) is in contact with the solution of the polyhydroxy polymer for 1-120 min.

12. The preparation method according to claim 1, wherein, In step (3), the product from step (2) is in contact with the solution of the polyhydroxy polymer for 10-60 min.

13. The preparation method according to claim 1, wherein, In step (3), the pressure of the pressurization condition is 0.5-2 MPa.

14. The preparation method according to claim 1, wherein, In step (2), the polyamine is one or more of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine and p-phenylenediamine.

15. The preparation method according to claim 1, wherein, In step (2), the polyamine is polyethyleneimine and / or piperazine.

16. The preparation method according to claim 1, wherein, In step (2), the polyacryl chloride is one or more of pyromellitic chloroformyl chloride, terephthalic chloroformyl chloride, isophthalic chloroformyl chloride and orthophthalic chloroformyl chloride.

17. The preparation method according to claim 1, wherein, In step (2), the polyacryl chloride is pyromellitic methyl chloride and / or terephthaloyl chloride.

18. The preparation method according to claim 1, wherein, In step (2), the concentration of the polyamine in the aqueous phase containing the polyamine is 0.1-10% by weight; and the concentration of the polyacrylamide in the organic phase containing the polyacrylamide is 0.01-1% by weight.

19. The preparation method according to claim 1, wherein, In step (2), the concentration of polyamine in the aqueous phase containing polyamine is 0.5-2.5% by weight; and the concentration of polyacrylamide in the organic phase containing polyacrylamide is 0.1-0.5% by weight.

20. The preparation method according to claim 1, wherein, In step (2), the mass concentration ratio of the polyamine to the polyacrylamide is 0.1-10:

1.

21. The preparation method according to claim 1, wherein, In step (2), the mass concentration ratio of the polyamine to the polyacrylamide is 0.5-5:

1.

22. The preparation method according to claim 1, wherein, In step (2), the porous support layer is in contact with the aqueous phase containing polyamines for 5-100 seconds; and / or, The porous support layer is in contact with the organic phase containing polyacryl chloride for 10-200 s; and / or, The heat treatment temperature is 40-150℃; the heat treatment time is 0.5-10min.

23. The preparation method according to claim 1, wherein, In step (2), the porous support layer is in contact with the aqueous phase containing polyamines for 10-60 seconds; and / or, The porous support layer is in contact with the organic phase containing polyacryl chloride for 20-120 s; and / or, The heat treatment temperature is 50-120℃; the heat treatment time is 1-5 minutes.

24. The preparation method according to claim 1, wherein, In step (1), the porous support layer is made of one or more of the following materials: polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

25. The preparation method according to claim 1, wherein, In step (1), the bottom layer is a non-woven fabric layer.

26. The preparation method according to claim 1, wherein, In step (1), the bottom layer is a polyester nonwoven fabric layer, a polyethylene nonwoven fabric layer, or a polyester-polyethylene composite nonwoven fabric layer.

27. The preparation method according to any one of claims 1-26, wherein, The thickness of the bottom layer is 30-150 μm.

28. The preparation method according to any one of claims 1-26, wherein, The thickness of the bottom layer is 50-120 μm.

29. The preparation method according to any one of claims 1-26, wherein, The thickness of the porous support layer is 10-100 μm.

30. The preparation method according to any one of claims 1-26, wherein, The thickness of the porous support layer is 30-60 μm.

31. The preparation method according to any one of claims 1-26, wherein, The thickness of the polyamide separation layer is 10-500 nm.

32. The preparation method according to any one of claims 1-26, wherein, The thickness of the polyamide separation layer is 50-300 nm.

33. The preparation method according to any one of claims 1-26, wherein, The thickness of the anti-fouling layer is 1-200 nm.

34. The preparation method according to any one of claims 1-26, wherein, The thickness of the anti-fouling layer is 5-50 nm.

35. The composite nanofiltration membrane obtained by the preparation method according to any one of claims 1-34.

36. The composite nanofiltration membrane according to claim 35, wherein, The composite nanofiltration membrane includes a bottom layer and a porous support layer, a polyamide separation layer and a fouling-resistant layer sequentially stacked on the bottom layer. The fouling-resistant layer includes a polyphenolic compound and a polyhydroxy polymer. The surfaces of the fouling-resistant layer and the polyamide separation layer that are in contact with each other are cross-linked.

37. The composite nanofiltration membrane according to claim 36, wherein, The porous support layer is made of one or more of the following materials: polyethersulfone, polysulfone, polyaromatic ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryletherketone.

38. The composite nanofiltration membrane according to claim 36, wherein, The polyamide separation layer is generated by interfacial polymerization of polyamines and polyacrylamide chlorides.

39. The composite nanofiltration membrane according to claim 38, wherein, The polyamine is one or more of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine, and p-phenylenediamine.

40. The composite nanofiltration membrane according to claim 38, wherein, The polyamine is polyethyleneimine and / or piperazine.

41. The composite nanofiltration membrane according to claim 38, wherein, The polyacrylic chloride is one or more of pyromellitic chloride, terephthalic chloride, isophthalic chloride and phthaloyl chloride.

42. The composite nanofiltration membrane according to claim 38, wherein, The polyacryl chloride is pyromellitic trimethylolpropionate chloride and / or terephthaloyl chloride.

43. The composite nanofiltration membrane according to any one of claims 38-42, wherein, The mass concentration ratio of the polyamine to the polyacrylamide is 0.5-100:

1.

44. The composite nanofiltration membrane according to any one of claims 38-42, wherein, The mass concentration ratio of the polyamine to the polyacrylamide is 1-50:

1.

45. The composite nanofiltration membrane according to claim 36, wherein, The polyphenolic compounds and polyhydroxy polymers in the stain-resistant layer are cross-linked with each other through hydrogen bonds.

46. ​​The composite nanofiltration membrane according to claim 36, wherein, The anti-fouling layer is formed by the self-assembly of polyphenolic compounds and polyhydroxy polymers on the surface of the polyamide separation layer.

47. The composite nanofiltration membrane according to claim 45 or 46, wherein, The polyphenolic compounds are one or more of the following: tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein.

48. The composite nanofiltration membrane according to claim 45 or 46, wherein, The polyphenolic compounds are tannic acid and / or lignin.

49. The composite nanofiltration membrane according to claim 45 or 46, wherein, The polyhydroxy polymer is one or more of polyvinyl alcohol, hydroxy-terminated polyethylene glycol, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and chitosan.

50. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The bottom layer is a non-woven fabric layer.

51. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The bottom layer is a polyester nonwoven fabric layer, a polyethylene nonwoven fabric layer, or a polyester-polyethylene composite nonwoven fabric layer.

52. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the bottom layer is 30-150 μm.

53. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the bottom layer is 50-120 μm.

54. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the porous support layer is 10-100 μm.

55. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the porous support layer is 30-60 μm.

56. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the polyamide separation layer is 10-500 nm.

57. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the polyamide separation layer is 50-300 nm.

58. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the anti-fouling layer is 1-200 nm.

59. The composite nanofiltration membrane according to any one of claims 36-42, wherein, The thickness of the anti-fouling layer is 5-50 nm.

60. The application of the composite nanofiltration membrane according to any one of claims 35-59 in the field of water treatment.

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