Preparation method of composite nanofiltration membrane and composite nanofiltration membrane prepared thereby

Abstract

The present invention relates to a method for preparing a composite nanofiltration membrane and a composite nanofiltration membrane prepared thereby. The method for preparing the composite nanofiltration membrane comprises the following steps: preparing a polymer solution as a casting liquid, solidifying the casting liquid on a reinforcing material to form a base membrane; then sequentially contacting with an aqueous solution containing an amine compound, a silane coupling agent and a biomass acid, and an oil phase solution containing a polyacid chloride to form a functional layer; and obtaining a composite nanofiltration membrane after post-treatment and drying. In the preparation method of the present invention, base membranes with different surface average pore sizes are obtained by adjusting the concentration of the polymer in the casting liquid; by adding a silane coupling agent and a biomass acid to the aqueous solution to eliminate other reaction variable factors, the interfacial polymerization reaction is only affected by the average pore size of the base membrane, and accordingly, composite nanofiltration membranes with functional layers with different surface average pore sizes are obtained, thereby having different maximum retention molecular weights.

Description

Technical Field

[0001] The present invention relates to the technical field of composite nanofiltration membranes, in particular to a method for preparing a composite nanofiltration membrane and the composite nanofiltration membrane prepared thereby. Background Art

[0002] Composite nanofiltration membrane separation technology is a membrane separation technology with a molecular weight cutoff between reverse osmosis and ultrafiltration membranes, separating substances with molecular weights between 200 and 1000 Da. The market has developed demand for composite nanofiltration membrane technology that can separate substances with different molecular weights at a more detailed level. For example, the composite nanofiltration membranes used in the separation of the main components of some pharmaceuticals need to separate substances with molecular weights between 200 and 400 Da. This requires the development of composite nanofiltration membranes that can filter substances with molecular weights below 200 Da and retain substances with molecular weights above 400 Da.

[0003] This demand for more refined component separation necessitates that composite nanofiltration membranes possess a narrow pore size distribution range. Therefore, preparing composite nanofiltration membranes with highly selective functional layers with adjustable structures is essential. Only by achieving structurally adjustable functional layers can composite nanofiltration membranes with a narrow pore size distribution range be achieved. Prior art methods for adjusting the pore size structure of composite nanofiltration membranes typically employ conditions during interfacial polymerization to achieve structural changes in the functional layer of the resulting composite nanofiltration membrane.

[0004] However, during the preparation of composite nanofiltration membranes, the structure and surface morphology of the basement membrane significantly influence the interfacial polymerization reaction. Therefore, adjusting the structure of the functional layer by changing the structure and surface morphology of the basement membrane can be a direct, simple, and effective method. However, conventional coating methods vary greatly in terms of the interfacial polymerization reaction conditions caused by changes in the structure and surface morphology of the basement membrane. Consequently, it is difficult to understand how these changes affect the pore size and distribution of the functional layer of the composite nanofiltration membrane.

[0005] This requires consideration of the following two situations: First, the functional layer is prepared by interfacial polymerization, that is, based on the classic Schotten-Bauman reaction in organic chemistry, a step-growth mechanism is used to prepare a high-molecular-weight polymer desalination layer with a separation effect. In this process, two monomers or prepolymers with different active groups are dissolved in two immiscible solvents, and then react at the interface when the two solutions come into contact with each other. Because the interfacial polymerization reaction is extremely fast and the functional layer generated is very thin, and the polymerization reaction involves multiple processes such as simultaneous monomer mass transfer and reaction, polymer chain growth, and polymer phase separation, it is difficult to monitor the interfacial polymerization process and thus achieve accurate kinetic analysis of the reaction process. Secondly, the polysulfone layer that provides this interface and serves as a supporting material will directly affect the formation process of the polyamide functional layer, thereby affecting the performance of the composite nanofiltration membrane.

[0006] The polysulfone layer that provides the interface for the interfacial polymerization reaction and serves as the supporting material is typically referred to as the base membrane. Generally, the cross-sectional structure of the base membrane primarily determines the mechanical properties of the composite membrane. The surface structure (surface pore size, pore distribution) and hydrophilicity of the base membrane, among other factors, influence the mass transfer rate and distribution of aqueous monomers from the membrane pores on the base membrane surface to the organic phase for interfacial polymerization, thereby affecting the structure of the functional layer and the performance of the composite membrane. Furthermore, interactions such as covalent bonds, hydrogen bonds, and electrostatic attraction exist at the interface between the base membrane and the nascent functional layer formed by interfacial polymerization. These interactions influence the assembly of polymer chains, thereby affecting the structure of the functional layer.

[0007] Therefore, regarding the formation of surface roughness in interfacial polymerization membranes, specifically within the context of the "influence of the basement membrane on the structure and performance of the functional layer," several different theoretical and mathematical models have been proposed. When considering influencing the structure of the functional layer of a composite nanofiltration membrane through changes in the basement membrane's structure and surface morphology, it is necessary to minimize the impact of certain minor factors and focus solely on the primary factors affecting interfacial polymerization.

[0008] The surface pore size of the basement membrane affects the mass transfer rate of aqueous monomers during interfacial polymerization. Under the same coating formulation, the solvent environment in the miscible zone of the interfacial polymerization reaction on different basement membranes can vary. In addition to changes in the mass transfer rate of aqueous monomers, other factors, such as the distribution of aqueous monomers, must also be considered in determining how interfacial polymerization is affected. This multi-factor influence makes it difficult to define a simple rule governing the influence of the basement membrane on the preparation of composite nanofiltration membranes. Summary of the Invention

[0009] Problems to be solved by the invention

[0010] In order to solve the above-mentioned problems existing in the prior art, the present invention aims to weaken the influencing factors of different mass transfer rates of aqueous phase monomers in interfacial polymerization reactions caused by the size of the surface pore size of the base membrane, and obtain a functional layer with adjustable structure under the influence of fewer factors, thereby obtaining a composite nanofiltration membrane with different maximum retention molecular weights.

[0011] Solutions for solving problems

[0012] Through in-depth research, the inventors of the present invention found that in the preparation process of the base membrane, by adjusting the concentration of the polymer in the casting solution, a base membrane with different surface average pore sizes can be obtained; further, by adding silane coupling agent and biomass acid to the aqueous solution to respectively eliminate the influence of the mass transfer rate of the aqueous phase monomer and other reaction variable factors such as the change in the interfacial polymerization reaction rate caused by different monomer mass transfer distribution ranges, the interfacial polymerization reaction can be only affected by the different average pore sizes of the base membrane. When considering the structural changes of the functional layer of the composite nanofiltration membrane caused by the corresponding base membrane, it is only necessary to consider the influence of the mass transfer distribution of the aqueous phase monomer caused by the surface average pore size of the base membrane.

[0013] Under the same coating formula and interfacial polymerization reaction conditions, when the surface average pore size of the base membrane changes from large to small, a composite nanofiltration membrane with a surface average pore size of the functional layer changing from large to small can be obtained accordingly, thereby obtaining a composite nanofiltration membrane with different maximum retention molecular weights, i.e., a selective separation function.

[0014] In summary, after the mass transfer rate and reaction rate are reduced by the influence of the average surface pore size of the base membrane, when the interfacial polymerization reaction is coated on base membranes with different average surface pore sizes under the same formulation conditions, the functional layer structures of the corresponding nanofiltration membranes obtained only differ significantly in average pore size. In other words, the functional layer of the composite nanofiltration membrane obtained by coating on the surface of the base membrane with a larger average pore size has a larger average surface pore size, while the functional layer of the composite nanofiltration membrane obtained by coating on the surface of the base membrane with a smaller average pore size has a smaller average surface pore size.

[0015] The present invention provides a method for preparing a composite nanofiltration membrane, the method comprising the following steps:

[0016] preparing a polymer solution as a casting solution, and curing the casting solution on a reinforcing material to form a base film, wherein the polymer is at least one selected from bisphenol A polysulfone, polyarylsulfone, and polyethersulfone, and the concentration of the polymer is 10-20 wt % based on the weight of the polymer solution;

[0017] The base film obtained in the above steps is sequentially contacted with an aqueous solution containing an amine compound, a silane coupling agent and a biomass acid, and an oily solution containing a polyacid chloride to form a functional layer;

[0018] After post-treatment and drying, a composite nanofiltration membrane is obtained.

[0019] According to the preparation method of the present invention, the bisphenol A type polysulfone, polyarylsulfone, and polyethersulfone respectively have structural units represented by the following general formulas (1) to (3):

[0020]

[0021] Where n is the number of structural units in a single molecular chain, and its value is between 5 and 50.

[0022] According to the preparation method of the present invention, the amine compound is one or more selected from m-phenylenediamine, p-phenylenediamine, ethylenediamine, and piperazine. Preferably, the concentration of the amine compound is 3-5 wt % based on the weight of the aqueous solution.

[0023] According to the preparation method of the present invention, the concentration of the silane coupling agent is 0.01-1 wt % based on the weight of the aqueous solution.

[0024] According to the preparation method of the present invention, the silane coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, and 3-aminopropyltriethoxysilane.

[0025] According to the preparation method of the present invention, the concentration of the biomass acid is 0.1-10 wt % based on the weight of the aqueous solution.

[0026] According to the preparation method of the present invention, the biomass acid is at least one selected from tannic acid, tartaric acid, citric acid, and gluconic acid.

[0027] According to the preparation method of the present invention, the polybasic acid chloride is at least one selected from trimesoyl chloride, terephthaloyl chloride, and oxalyl chloride.

[0028] According to the preparation method of the present invention, the concentration of the polyacyl chloride is 0.10-0.50 wt % based on the weight of the oil phase solution.

[0029] The present invention also provides a composite nanofiltration membrane prepared according to the preparation method of the present invention.

[0030] Effects of the Invention

[0031] The preparation method of the present invention can obtain a base membrane with different surface average pore sizes as a support layer, and then coat the base membrane through an interfacial polymerization reaction to obtain a functional layer with different surface average pore sizes. The obtained composite nanofiltration membrane has different maximum retention molecular weights and can be used to highly selectively filter and separate substances with molecular weights between 200Da and 800Da. DETAILED DESCRIPTION

[0032] The present invention relates to a method for preparing a composite nanofiltration membrane, which comprises the following steps:

[0033] preparing a polymer solution as a casting solution, and curing the casting solution on a reinforcing material to form a base film, wherein the polymer is at least one selected from bisphenol A polysulfone, polyarylsulfone, and polyethersulfone, and the concentration of the polymer is 10-20 wt % based on the weight of the polymer solution;

[0034] The base film obtained in the above steps is sequentially contacted with an aqueous solution containing an amine compound, a silane coupling agent and a biomass acid, and an oily solution containing a polyacid chloride to form a functional layer;

[0035] After post-treatment and drying, a composite nanofiltration membrane is obtained.

[0036] The technical concept of the preparation method of the present invention is to obtain a base membrane with different surface average pore sizes by adjusting the concentration of the polymer in the polymer solution, and then use the base membrane as a support layer. By adding a silane coupling agent and a biomass acid to the aqueous phase solution, the influence of the mass transfer rate of the aqueous phase monomer and other reaction variable factors such as the change in the interfacial polymerization reaction rate caused by different monomer mass transfer distribution ranges are eliminated respectively, so that the interfacial polymerization reaction is only affected by the different surface average pore sizes of the base membrane. Functional layers with different surface average pore sizes are correspondingly obtained through the interfacial polymerization reaction, and the surface average pore size of the functional layer can be adjusted in a simple way.

[0037] Under the same coating formula and interfacial polymerization reaction conditions, when the surface average pore size of the base membrane changes from large to small, a composite nanofiltration membrane with a surface average pore size of the functional layer changing from large to small can be obtained accordingly, thereby obtaining a composite nanofiltration membrane with different maximum retention molecular weights, i.e., a selective separation function.

[0038] In the preparation method of the present invention, the polymer solution is coated on the reinforcing material as a casting solution. Preferably, the reinforcing material is a non-woven fabric, such as PP non-woven fabric, PET non-woven fabric, or PA non-woven fabric.

[0039] There are no particular limitations on the coating method, and any of the coating methods commonly used in the field of nanofiltration membrane preparation may be used, such as casting, dip coating, blade coating, and spin coating, with blade coating being more preferred. After coating on the nonwoven fabric, the nonwoven fabric is then immersed in a coagulation bath to coagulate into a membrane.

[0040] In the preparation method of the present invention, preferably, the coagulation bath is pure water, and the coagulation bath temperature is 10-15°C.

[0041] In the preparation method of the present invention, the base film is preferably immersed in an aqueous solution of an alkali metal hydroxide at a concentration of 1-10 wt%, rinsed with pure water, and dried before use in subsequent steps. The purpose of the immersion is to remove any residual solvent from the casting solution. The alkali metal hydroxide may be, for example, sodium hydroxide or potassium hydroxide.

[0042] In the preparation method of the present invention, preferably, the bisphenol A type polysulfone, polyarylsulfone, and polyethersulfone each have a structural unit represented by the following general formulas (1) to (3):

[0043]

[0044] Wherein, n is the number of structural units in a single molecular chain, and its value is between 5-50. Preferably, the value of n is between 10-15.

[0045] In the preparation method of the present invention, preferably, the concentration of the polymer is 10-20 wt % based on the weight of the polymer solution.

[0046] In the preparation method of the present invention, preferably, by performing scanning electron microscopy (SEM) analysis on the surface of the base film, the average surface pore size of the base film (also known as the support layer) is in the range of 5-20 nm.

[0047] In the preparation method of the present invention, the addition of a silane coupling agent allows the amine compound, which serves as the aqueous phase monomer, to spread more evenly within the pores on the surface of the base membrane. This significantly accelerates the mass transfer rate of the amine compound during the interfacial polymerization reaction, mitigates variations in the mass transfer rate of the amine compound caused by differences in the average pore size of the base membrane surface, and reduces differences in mass transfer rate due to differences in the average pore size of the base membrane surface. This results in a substantially consistent mass transfer rate of the amine compound when coated on base membranes with different average pore sizes. Therefore, the functional layer structure of the resulting composite nanofiltration membrane is affected only by the mass transfer distribution range of the amine compound, and not by its mass transfer rate.

[0048] In the preparation method of the present invention, preferably, the concentration of the silane coupling agent is 0.01-1 wt % based on the weight of the aqueous solution.

[0049] In the preparation method of the present invention, the silane coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, and 3-aminopropyltriethoxysilane.

[0050] The addition of biomass acid modifies the pH of the miscible region of the interfacial polymerization reaction. According to Le Chatelier's principle, this alters the rate of HCl release during the interfacial polymerization reaction to form polyamide, thereby reducing the interfacial polymerization rate. This effect consistently slows the interfacial polymerization rate when coating films on substrates with varying average surface pore sizes, eliminating variations in the interfacial polymerization rate caused by varying monomer mass transfer distributions.

[0051] In the preparation method of the present invention, preferably, the concentration of the biomass acid is 0.1-10 wt % based on the weight of the aqueous solution.

[0052] In the preparation method of the present invention, preferably, the biomass acid is at least one selected from tannic acid, tartaric acid, citric acid, and gluconic acid.

[0053] In the preparation method of the present invention, there is no particular limitation on the amine compound used as the aqueous phase monomer, and amine compounds commonly used in interfacial polymerization reactions can be used. Preferably, the amine compound is one or more selected from m-phenylenediamine, p-phenylenediamine, ethylenediamine, and piperazine; more preferably, the concentration of the amine compound is 3-5wt% based on the weight of the aqueous phase solution.

[0054] In the preparation method of the present invention, preferably, triethylamine and camphorsulfonic acid may be further included in the aqueous phase solution to form an aqueous phase buffer system triethylamine camphorsulfonic acid salt (TEA-CSA), thereby adjusting the pH value of the aqueous phase solution to be within the range of 8 to 10, so as to be more conducive to the diffusion of the amine compound and promote the miscibility of the aqueous phase and the oil phase to promote the interfacial polymerization reaction.

[0055] In the preparation method of the present invention, there is no particular limitation on the polyacyl chloride used as the oil phase monomer, and polyacyl chlorides commonly used in interfacial polymerization reactions can be used. Preferably, the polyacyl chloride is at least one selected from trimesoyl chloride, terephthaloyl chloride, and oxalyl chloride; more preferably, the concentration of the polyacyl chloride is 0.10-0.50 wt % based on the weight of the oil phase solution.

[0056] In the preparation method of the present invention, preferably, the solvent in the oil phase solution is at least one selected from dichloromethane, chloroform, dichloroethane, n-hexane, ethylcyclohexane, and propylene oxide.

[0057] As a non-limiting example, the method for preparing the composite nanofiltration membrane of the present invention comprises the following steps:

[0058] A polymer solution with a concentration of 10-20 wt% is prepared as a casting solution, and the casting solution is solidified on a non-woven fabric to form a base film, wherein the polymer is at least one selected from bisphenol A type polysulfone, polyarylsulfone, and polyethersulfone;

[0059] Preferably, the base film is soaked in an alkali metal hydroxide aqueous solution with a concentration of 1-5 wt%, then washed with pure water and dried for later use;

[0060] The base film obtained in the above steps is sequentially contacted with an aqueous solution containing an amine compound with a concentration of 3-5 wt%, a silane coupling agent with a concentration of 0.01-1 wt% and a biomass acid with a concentration of 0.1-10 wt%, and an oily solution containing a polyacid chloride with a concentration of 0.10-0.50 wt% to form a functional layer;

[0061] After post-treatment and drying, a composite nanofiltration membrane is obtained.

[0062] There is no particular limitation on the contact time with the aqueous phase solution and the oil phase solution, and it can be, for example, 5 to 300 seconds. Preferably, the solution is removed after contact to remove excess solution on the surface.

[0063] In the preparation method of the present invention, the post-treatment is preferably to remove excess surface solution, followed by washing, for example, with deionized water. There is no particular restriction on the drying temperature, typically 50-70°C; and there is no particular restriction on the drying time, typically 1-30 minutes.

[0064] The present invention also relates to a composite nanofiltration membrane prepared by the preparation method according to the present invention. Preferably, the composite nanofiltration membrane comprises, from bottom to top, a non-woven fabric layer, a polymer-based membrane support layer, and a functional layer.

[0065] Example

[0066] The present invention is further described in detail below with reference to specific examples, but the technical solutions of the present invention are by no means limited to the following examples. It should be noted that the reagents, raw materials and equipment used in the examples are all commercially available conventional products unless otherwise specified.

[0067] Example 1

[0068] A casting solution with a polysulfone concentration of 20 wt% was prepared, and the film was scraped onto a non-woven fabric. The film was solidified in a water bath at 12°C to prepare a polysulfone-based membrane support layer I with an average surface pore size of 5 nm. The membrane was then immersed in a 1 wt% sodium hydroxide aqueous solution for 30 minutes, washed with ultrapure water, and air-dried. The membrane was then contacted with an aqueous solution containing 3.0 wt% m-phenylenediamine, 0.1 wt% 3-aminopropyltriethoxysilane, 1 wt% tannic acid, 4 wt% camphorsulfonic acid, and 2 wt% triethylamine for 20 seconds, removed, and excess water droplets on the surface were removed. The membrane was then contacted with an ethylcyclohexane solution containing 0.15 wt% trimesoyl chloride for 20 seconds, removed, and the membrane sheet prepared above was heat-treated at 70°C for 10 minutes. The resulting nanofiltration membrane I can filter molecules with a molecular weight below 400 Da and retain molecules with a molecular weight above 400 Da.

[0069] Example 2

[0070] The same method as in Example 1 was followed, except that a casting solution with a polysulfone concentration of 15 wt% was prepared and a polysulfone-based membrane support layer II with an average surface pore size of 10 nm was prepared by scraping the membrane onto a non-woven fabric. The resulting nanofiltration membrane II was capable of filtering molecules with a molecular weight below 600 Da and retaining molecules with a molecular weight above 600 Da.

[0071] Example 3

[0072] The same method as in Example 1 was followed, except that a casting solution with a polysulfone concentration of 10 wt% was prepared and a polysulfone-based membrane support layer III with an average surface pore size of 20 nm was prepared by scraping the membrane onto a non-woven fabric. The resulting nanofiltration membrane III can filter molecules with a molecular weight below 800 Da and retain molecules with a molecular weight above 800 Da.

[0073] Example 4

[0074] A casting solution with a polysulfone concentration of 20 wt% was prepared and scraped onto a non-woven fabric to prepare a polysulfone-based membrane support layer I with an average surface pore size of 5 nm. The membrane was then immersed in a 1 wt% sodium hydroxide aqueous solution for 30 minutes, washed with ultrapure water, and air-dried. The membrane was then contacted with an aqueous solution containing 3.0 wt% m-phenylenediamine, 0.2 wt% 3-aminopropyltriethoxysilane, 2 wt% gluconic acid, 4 wt% camphorsulfonic acid, and 2 wt% triethylamine for 20 seconds, after which excess surface water droplets were removed. The membrane was then contacted with an ethylcyclohexane solution containing 0.15 wt% trimesoyl chloride for 20 seconds, removed, and heat-treated at 70°C for 10 minutes. The resulting nanofiltration membrane IV can filter molecules with a molecular weight below 400 Da and retain molecules with a molecular weight above 400 Da.

[0075] Example 5

[0076] The same method as in Example 4 was followed, except that a casting solution with a polysulfone concentration of 15 wt% was prepared and a polysulfone-based membrane support layer II with an average surface area of ​​10 nm was prepared by scraping the film on a non-woven fabric. The resulting nanofiltration membrane V was capable of filtering molecules with a molecular weight below 600 Da and retaining molecules with a molecular weight above 600 Da.

[0077] Example 6

[0078] The same method as in Example 4 was followed, except that a casting solution with a polysulfone concentration of 10 wt% was prepared and a polysulfone-based membrane support layer III with an average surface pore size of 20 nm was prepared by scraping the membrane onto a non-woven fabric. The resulting nanofiltration membrane VI was capable of filtering molecules with a molecular weight below 800 Da and retaining molecules with a molecular weight above 800 Da.

[0079] Diaphragm performance test:

[0080] Four target substances with different molecular weights were selected as follows: PEG200 (Da=200), crystal violet (Da=407), bromothymol blue (Da=624), and fast green (Da=809), which were respectively dissolved in water to obtain solutions with a concentration of 1 wt% as concentrated water. The composite nanofiltration membranes in the above Examples 1-6 were then used to filter under a pressure of 100 psi to obtain product water. The water flux was recorded and the retention rate of the membrane was calculated using the TOC detection method. The retention rates and water fluxes of the composite nanofiltration membranes obtained in Examples 1-6 are listed in Table 1 below.

[0081] Table 1

[0082]

[0083] It can be seen from the above results that the preparation method of the present invention can obtain a base membrane with different surface average pore sizes as a support layer, and then add a silane coupling agent and a biomass acid to the aqueous phase solution to respectively eliminate the influence of the mass transfer rate of the aqueous phase monomer and other reaction variable factors such as the change in the interfacial polymerization reaction rate caused by different monomer mass transfer distribution ranges, so that the interfacial polymerization reaction is only affected by the different surface average pore sizes of the base membrane. The functional layer with different surface average pore sizes is obtained by coating the base membrane through the interfacial polymerization reaction. The obtained composite nanofiltration membrane not only maintains a higher water flux but also has different maximum retention molecular weights, and can be used to highly selectively filter and separate substances with molecular weights between 200Da and 400Da, between 400Da and 600Da, and between 600Da and 800Da.

[0084] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles and spirit of the present invention should be included in the scope of protection of the present invention.

[0085] Industrial applicability

[0086] The preparation method of the present invention obtains base membranes with different surface average pore sizes by adjusting the concentration of the polymer solution, and then adds a silane coupling agent and a biomass acid to the aqueous phase solution to respectively eliminate the influence of the mass transfer rate of the aqueous phase monomer and other reaction variable factors such as the change in the interfacial polymerization reaction rate caused by different monomer mass transfer distribution ranges. The interfacial polymerization reaction can be affected only by the different surface average pore sizes of the base membrane, thereby correspondingly obtaining functional layers with different surface average pore sizes. The surface average pore size of the functional layer can be adjusted in a simple method, and finally a composite nanofiltration membrane with different maximum retention molecular weights is obtained, which can be used to highly selectively filter and separate substances with molecular weights between 200Da and 400Da, between 400Da and 600Da, and between 600Da and 800Da.

Claims

1. A method for preparing a composite nanofiltration membrane, characterized in that: The following steps are involved: preparing a polymer solution as a casting solution, and curing the casting solution on a reinforcing material to form a base film, wherein the polymer is at least one selected from bisphenol A polysulfone, polyarylsulfone, and polyethersulfone, and the concentration of the polymer is 10-20 wt % based on the weight of the polymer solution; The base film obtained in the above steps is contacted with an aqueous solution containing an amine compound, a silane coupling agent and a biomass acid, and an oil phase solution containing a polyacid chloride in sequence to form a functional layer, wherein the silane coupling agent and the biomass acid are added to the aqueous solution to respectively eliminate the influence of the mass transfer rate of the aqueous phase monomer and the change in the interfacial polymerization reaction rate caused by the different mass transfer distribution ranges of the monomers, so that the interfacial polymerization reaction is only affected by the different surface average pore sizes of the base film, wherein the silane coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, and 3-aminopropyltriethoxysilane, and the concentration of the silane coupling agent is 0.1-1wt% based on the weight of the aqueous solution; and the biomass acid is at least one selected from tannic acid, tartaric acid, citric acid, and gluconic acid, and the concentration of the biomass acid is 1-10wt% based on the weight of the aqueous solution; After post-treatment and drying, a composite nanofiltration membrane is obtained.

2. The preparation method according to claim 1, wherein the bisphenol A type polysulfone, polyarylsulfone, and polyethersulfone each have a structural unit represented by the following general formulas (1) to (3): in, n is the number of structural units in a single molecular chain, and its value is between 5 and 50.

3. The preparation method according to claim 1 or 2, wherein the amine compound is one or more selected from m-phenylenediamine, p-phenylenediamine, ethylenediamine, and piperazine.

4. The preparation method according to claim 1 or 2, wherein the concentration of the amine compound is 3-5 wt% based on the weight of the aqueous solution.

5. The preparation method according to claim 1 or 2, wherein the polyacyl chloride is at least one selected from trimesoyl chloride, terephthaloyl chloride, and oxalyl chloride.

6. The preparation method according to claim 1 or 2, wherein the concentration of the polyacid chloride is 0.10-0.50 wt% based on the weight of the oil phase solution.

7. A composite nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 6.

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