A nanofiltration membrane and a method for its preparation

Abstract

The application relates to the technical field of water treatment membranes, in particular to a nanofiltration membrane and a preparation method thereof. The application provides a nanofiltration membrane which comprises a non-woven fabric layer, a support layer and a polyester separation layer which are sequentially compounded; the polyester separation layer is formed by carrying out an interfacial polymerization reaction of an aqueous phase solution and an oil phase solution on the support layer; the aqueous phase solution comprises saturated hydrocarbon-substituted resorcinol; the oil phase solution comprises a polybasic acid halide monomer; the saturated hydrocarbon-substituted resorcinol has a structure shown in formula I; in formula I, R is a saturated hydrocarbon group. The nanofiltration membrane provided by the application can have better chlorine oxidation resistance and acid resistance.

Description

A nanofiltration membrane and its preparation method Technical Field

[0001] This invention relates to the field of water treatment membrane technology, and in particular to a nanofiltration membrane and its preparation method. Background Technology

[0002] Nanofiltration membranes, due to their selective separation properties, can effectively retain large molecules (substances with a weight average molecular weight of 200-1000) and divalent or higher ions, while allowing most small molecules and monovalent ions to pass through. This property also allows them to operate at lower pressures compared to reverse osmosis membranes.

[0003] Existing nanofiltration membranes are mostly synthesized by reacting piperazine with polyacrylamide chlorides. Due to the weak resistance of the amide structure to active chlorine oxidation, membrane elements are susceptible to microbial contamination during practical applications. Pretreatment requires the addition of oxidizing agents to remove microorganisms, but small amounts of unreduced oxidizing agents can enter the membrane system, causing oxidative degradation of the functional layer. The weak oxidation resistance of the amide bond structure makes pretreatment of membrane elements complex. Because the system strictly controls oxidizing agents, bacteria can easily grow during membrane element use, leading to severe microbial contamination and requiring regular cleaning, increasing maintenance costs.

[0004] The amide structure exhibits weak resistance to chlorine oxidation, primarily because the nitrogen atom in the amide bond has a relatively loose electron cloud, making it susceptible to attack by positively charged reactive chlorine, forming an N-Cl structure. This structure is unstable and undergoes Orton rearrangement, forming a cyclic chloride structure, which in turn leads to the breaking of the amide bond. Previous studies have used polyphenols to react with polyacrylamide chlorides to form polyester structures. Because polyester lacks the reactive sites of Cl (amide nitrogen), oxidation can only occur through cyclic chlorination, but this step has very low reactivity and is difficult to perform, resulting in the polyester structure exhibiting stronger oxidation resistance. However, the acid hydrolysis resistance of the polyester structure is significantly lower than that of polyamide. In engineering applications, acid and alkali chemical cleaning is unavoidable for nanofiltration membrane elements. After cleaning, the polyester structure is damaged, the separation performance irreversibly decreases, the service life of the nanofiltration membrane is significantly reduced, and the cost increases.

[0005] Therefore, existing technologies still have the following drawbacks: While polyester materials improve the chlorine resistance of nanofiltration membranes, they significantly reduce their acid resistance. Under acidic conditions, ester bonds are more prone to hydrolysis than amide bonds, causing membrane material degradation and loss of separation ability. Furthermore, polyester materials have low reactivity, resulting in membrane materials with low polymerization degrees and limited separation effects. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a nanofiltration membrane and a method for preparing the same, wherein the nanofiltration membrane provided by the present invention has superior resistance to chlorine oxidation and acid resistance.

[0007] The present invention provides a nanofiltration membrane comprising a nonwoven fabric layer, a support layer and a polyester separation layer sequentially laminated together;

[0008] The polyester separation layer is formed by interfacial polymerization of an aqueous solution and an oil solution on a support layer; the aqueous solution includes saturated hydrocarbon-substituted resorcinol; the oil solution includes polyacrylamide halide monomers.

[0009] The saturated hydrocarbon-substituted resorcinol has the structure shown in Formula I;

[0010] Formula I;

[0011] In Formula I, R is a saturated hydrocarbon group.

[0012] Preferably, R is an alkyl group.

[0013] Preferably, R is an alkyl group having 1 to 10 carbon atoms.

[0014] Preferably, R is methyl, ethyl, or n-propyl.

[0015] Preferably, the aqueous solution is composed of saturated hydrocarbon-substituted resorcinol, surfactant, acid absorbent, catalyst, and water;

[0016] In the aqueous solution, the mass content of saturated hydrocarbon-substituted resorcinol is 0.5%~1%, the mass content of surfactant is 0.5%~1%, the mass content of acid absorbent is 2%~4%, and the mass content of catalyst is 0.1%~0.5%.

[0017] Preferably, the surfactant is sodium dodecyl sulfonate; the acid absorbent is triethylamine; and the catalyst is 4-dimethylaminopyridine.

[0018] Preferably, the oil phase solution is composed of a polyacrylamide halide monomer and an oil phase solvent;

[0019] The polyacryl halide monomer is pyromellitic tricarboxylate chloride;

[0020] The oil phase solvent is ethylcyclohexane and monochloroethane, with a mass ratio of 70~75:25~30;

[0021] The mass content of acyl halide in the oil phase solution is 0.1% to 0.5%.

[0022] The present invention also provides a method for preparing the nanofiltration membrane described above, comprising the following steps:

[0023] S1. The casting solution is coated onto one side of the nonwoven fabric layer and cured into a film by phase inversion to obtain a base film; the base film includes a nonwoven fabric layer and a support layer formed on the nonwoven fabric layer.

[0024] S2. The base membrane is immersed in an aqueous solution, and after being removed and dried, an oil-phase solution is coated on one side of the support layer of the base membrane to carry out an interfacial polymerization reaction. After curing, a polyester separation layer is formed to obtain a nanofiltration membrane.

[0025] Preferably, the phase transformation curing temperature is 13~17℃ and the time is 30~50 s.

[0026] Preferably, the immersion time in the aqueous solution is 10-20 seconds;

[0027] The temperature of the oil phase solution is 50~70℃;

[0028] The interfacial polymerization reaction is carried out at a temperature of 50~70℃ for a time of 25~35 s;

[0029] The curing method is drying, with a temperature of 50~70℃.

[0030] This invention uses resorcinol-based materials to replace the conventional piperazine structure to prepare a polyester-structured nanofiltration membrane. By adjusting the monomer structure, the resulting polyester material exhibits certain acid resistance, thereby improving its service life. Considering the low reactivity of phenols with acyl chlorides, an aqueous phase additive is added, and a blending solvent is added to the oil phase solution to enhance the reactivity. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] The present invention provides a nanofiltration membrane comprising a nonwoven fabric layer, a support layer and a polyester separation layer sequentially laminated together;

[0033] The polyester separation layer is formed by interfacial polymerization of an aqueous solution and an oil solution on a support layer; the aqueous solution includes saturated hydrocarbon-substituted resorcinol; the oil solution includes polyacrylamide halide monomers.

[0034] The saturated hydrocarbon-substituted resorcinol has the structure shown in Formula I;

[0035] Formula I;

[0036] In Formula I, R is a saturated hydrocarbon group.

[0037] In some embodiments of the present invention, the thickness of the nonwoven fabric layer is 90~110 μm, for example, 100 μm. The air permeability of the nonwoven fabric layer is 2.3~2.7 cc / cm². 2 / s, for example, 2.5 cc / cm 2 / s.

[0038] In some embodiments of the present invention, the support layer is formed by curing a casting solution onto the surface of a nonwoven fabric layer; the casting solution comprises polysulfone, polyvinylpyrrolidone, and an organic solvent; the mass ratio is 13~17:0.8~1.2:82~86; for example, 15:1:84. The polysulfone is supplied by BASF, Germany. The number average molecular weight of the polyvinylpyrrolidone is 24,000~130,000; for example, 50,000. The organic solvent includes, but is not limited to, N,N-dimethylformamide. The casting solution is obtained by mixing polysulfone, polyvinylpyrrolidone, and an organic solvent. The mixing can be by stirring. The mixing temperature is 60~80°C, for example, 70°C; the time is 3~5 h, for example, 4 h; and the stirring speed is 1000~2000 rpm, for example, 1500 rpm.

[0039] In some embodiments of the present invention, the thickness of the support layer is 30~50 μm, for example 40 μm.

[0040] In this invention, the polyester separation layer is formed by the interfacial polymerization reaction of an aqueous solution and an oil solution on a support layer.

[0041] In some embodiments of the present invention, the aqueous solution comprises saturated hydrocarbon-substituted resorcinol, a surfactant, an acid absorbent, a catalyst, and water. In the aqueous solution, the mass content of the saturated hydrocarbon-substituted resorcinol is 0.5% to 1%, for example, 1%; the mass content of the surfactant is 0.5% to 1%, for example, 0.5%; the mass content of the acid absorbent is 2% to 4%, for example, 2%; and the mass content of the catalyst is 0.1% to 0.5%, for example, 0.1%.

[0042] In this invention, the saturated hydrocarbon-substituted resorcinol has the structure shown in Formula I. In some embodiments of this invention, R is an alkyl group; it can be an alkyl group with 1 to 30 carbon atoms; it can be an alkyl group with 1 to 10 carbon atoms, such as methyl, ethyl, or n-propyl. Specifically, the saturated hydrocarbon-substituted resorcinol is 2-methylresorcinol (i.e., R is methyl), 2-ethylresorcinol (i.e., R is ethyl), or 2-n-propylresorcinol (i.e., R is n-propyl).

[0043] In some embodiments of the present invention, the surfactant is sodium dodecyl sulfonate. The acid absorbent is triethylamine. The catalyst is 4-dimethylaminopyridine. The water is RO water.

[0044] The present invention does not impose any special limitations on the preparation method of the aqueous solution. In some embodiments of the present invention, the preparation method of the aqueous solution includes the following steps: stirring and mixing saturated hydrocarbon-substituted resorcinol, surfactant, acid absorbent, catalyst and water to obtain an aqueous solution.

[0045] In some embodiments of the present invention, the oil phase solution is composed of a polyacrylamide halide monomer and an oil phase solvent. The polyacrylamide halide monomer is trimesoyl chloride. The oil phase solvent is ethylcyclohexane and monochloroethane; the mass ratio is 70-75:25-30, for example, 74.8:25. In the oil phase solution, the mass content of the acryl halide is 0.1%-0.5%, for example, 0.2%.

[0046] The present invention does not impose any special limitations on the preparation method of the oil phase solution. In some embodiments of the present invention, the preparation method of the oil phase solution includes the following steps: stirring and mixing the polyacrylamide monomer and the oil phase solvent to obtain the oil phase solution.

[0047] In some embodiments of the present invention, the thickness of the polyester separation layer is 100~300 nm, for example 100 nm.

[0048] The present invention also provides a method for preparing the nanofiltration membrane described above, comprising the following steps:

[0049] S1. The casting solution is coated onto one side of the nonwoven fabric layer and cured into a film by phase inversion to obtain a base film; the base film includes a nonwoven fabric layer and a support layer formed on the nonwoven fabric layer.

[0050] S2. The base membrane is immersed in an aqueous solution, and after being removed and dried, an oil-phase solution is coated on one side of the support layer of the base membrane to carry out an interfacial polymerization reaction. After curing, a polyester separation layer is formed to obtain a nanofiltration membrane.

[0051] Regarding step S1:

[0052] A casting solution is coated onto one side of a nonwoven fabric layer and cured into a film by phase inversion to obtain a base film; the base film includes a nonwoven fabric layer and a support layer formed on the nonwoven fabric layer.

[0053] In some embodiments of the present invention, the phase transformation curing temperature is 13~17°C, for example 15°C; and the time is 30~50 s, for example 50 s. The phase transformation curing is carried out in RO water.

[0054] Regarding step S2:

[0055] The base membrane is immersed in an aqueous solution, and after being removed and dried, an oil-phase solution is coated on one side of the support layer of the base membrane to carry out an interfacial polymerization reaction. After curing, a polyester separation layer is formed, and a nanofiltration membrane is obtained.

[0056] In some embodiments of the present invention, the immersion time in the aqueous solution is 10-20 seconds, for example, 15 seconds.

[0057] In some embodiments of the present invention, the surface drying method is as follows:

[0058] Excess aqueous solution on the surface is removed by rolling with a rubber roller, and then residual aqueous solution on the front and back of the membrane is removed by hot air and vacuum suction, so that there is no visible aqueous solution on the base membrane.

[0059] The present invention does not impose any special restrictions on the amount of coating of the oil phase solution; generally, it allows for excessive coating.

[0060] In some embodiments of the present invention, the temperature of the oil phase solution is 50~70°C, for example 60°C, 50°C, or 70°C.

[0061] In some embodiments of the present invention, the temperature of the interfacial polymerization reaction is 50~70°C, such as 60°C, 50°C, or 70°C, and the time is 25~35 seconds, such as 30 seconds.

[0062] In some embodiments of the present invention, after the interfacial polymerization reaction, the method further includes: removing excess oil phase solution using a rubber roller and an air knife.

[0063] In some embodiments of the present invention, the curing method is drying, with a temperature of 50~70℃, such as 60℃ or 50℃, and a time of 3~8 min, such as 5 min.

[0064] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0065] To further illustrate the present invention, the following detailed description of a nanofiltration membrane and its preparation method provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0066] Example 1

[0067] 1) Base film preparation: 84 parts by weight of N,N-dimethylformamide, 15 parts by weight of polysulfone (BASF, Germany), and 1 part by weight of polyvinylpyrrolidone (number average molecular weight 50,000) were mixed at 70°C for 4 hours at a stirring speed of 1500 rpm to obtain a uniform and transparent casting solution. The casting solution was then coated onto a nonwoven fabric (100 μm thickness, air permeability 2.5 cc / cm²). 2A single-sided surface of a polysulfone-based membrane was immersed in RO water at 15°C for 50 seconds to form a support layer (40 μm thick).

[0068] 2) Preparation of aqueous solution: Mix 1 part by weight of 2-methylresorcinol, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine, 0.1 parts by weight of 4-dimethylaminopyridine, and 96.4 parts by weight of RO water to obtain an aqueous solution.

[0069] 3) Preparation of oil phase solution: Mix 0.2 parts by weight of trimesoyl chloride, 74.8 parts by weight of ethylcyclohexane, and 25 parts by weight of monochloroethane to obtain an oil phase solution.

[0070] 4) Nanofiltration membrane preparation: The base membrane is immersed in an aqueous solution for 15 seconds, and excess solution on the surface is removed by rolling with a rubber roller. Then, residual aqueous solution on the front and back of the membrane is removed by hot air and vacuum dewatering, so that there is no visible aqueous solution on the base membrane. Then, an oil phase solution at 60℃ is coated on one side of the support layer of the base membrane. After reacting at 60℃ for 30 seconds, excess oil phase solution is removed by rubber roller and air knife. Then, the membrane is placed in a 60℃ oven and dried for 5 minutes to form a polyester separation layer (100nm thick), thus obtaining the nanofiltration membrane.

[0071] Example 2

[0072] The difference from Example 1 is as follows:

[0073] 2) Preparation of aqueous solution: Mix 1 part by weight of 2-ethylresorcinol, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine, 0.1 parts by weight of 4-dimethylaminopyridine, and 96.4 parts by weight of RO water to obtain an aqueous solution.

[0074] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0075] Example 3

[0076] The difference from Example 1 is as follows:

[0077] 2) Preparation of aqueous solution: Mix 1 part by weight of 2-n-propylresorcinol, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine, 0.1 parts by weight of 4-dimethylaminopyridine, and 96.4 parts by weight of RO water to obtain an aqueous solution.

[0078] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0079] Example 4

[0080] The difference from Example 2 is as follows:

[0081] 4) Nanofiltration membrane preparation: The base membrane is immersed in an aqueous solution for 15 seconds, and excess solution on the surface is removed by rolling with a rubber roller. Then, the residual aqueous solution on the front and back of the membrane is removed by hot air and vacuum dewatering, so that there is no visible aqueous solution on the base membrane. Then, an oil phase solution at 50°C is coated on one side of the support layer of the base membrane. After reacting at 50°C for 30 seconds, excess oil phase solution is removed by rubber roller and air knife. Then, the membrane is placed in a 50°C oven and dried for 5 minutes to obtain the nanofiltration membrane.

[0082] Example 5

[0083] The difference from Example 2 is as follows:

[0084] 4) Nanofiltration membrane preparation: The base membrane is immersed in an aqueous solution for 15 seconds, and excess solution on the surface is removed by rolling with a rubber roller. Then, residual aqueous solution on the front and back of the membrane is removed by hot air and vacuum dewatering, so that there is no visible aqueous solution on the base membrane. Then, an oil phase solution at 60℃ is coated on one side of the support layer of the base membrane. After reacting at 60℃ for 30 seconds, excess oil phase solution is removed by rubber roller and air knife. Then, the membrane is placed in a 50℃ oven and dried for 5 minutes to obtain the nanofiltration membrane.

[0085] Example 6

[0086] The difference from Example 2 is as follows:

[0087] 4) Nanofiltration membrane preparation: The base membrane is immersed in an aqueous solution for 15 seconds, and excess solution on the surface is removed by rolling with a rubber roller. Then, residual aqueous solution on the front and back of the membrane is removed by hot air and vacuum dewatering, so that there is no visible aqueous solution on the base membrane. Then, an oil phase solution at 70℃ is coated on one side of the support layer of the base membrane. After reacting at 70℃ for 30 seconds, excess oil phase solution is removed by rubber roller and air knife. Then, the membrane is placed in a 70℃ oven and dried for 5 minutes to obtain the nanofiltration membrane.

[0088] Comparative Example 1

[0089] The difference from Example 1 is as follows:

[0090] 2) Preparation of aqueous solution: Mix 0.5 parts by weight of piperazine, 0.5 parts by weight of 2-ethylresorcinol, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine, 0.1 parts by weight of 4-dimethylaminopyridine, and 96.4 parts by weight of RO water to obtain an aqueous solution.

[0091] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0092] Comparative Example 2

[0093] The difference from Example 1 is as follows:

[0094] 2) Preparation of aqueous solution: Mix 1 part by weight of piperazine, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine and 96.5 parts by weight of RO water to obtain an aqueous solution.

[0095] 3) Preparation of oil phase solution: Mix 0.2 parts by weight of trimesoyl chloride and 99.8 parts by weight of ethylcyclohexane to obtain an oil phase solution.

[0096] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0097] Comparative Example 3

[0098] The difference from Example 1 is as follows:

[0099] 2) Preparation of aqueous solution: Mix 1 part by weight of resorcinol, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine, 0.1 parts by weight of 4-dimethylaminopyridine, and 96.4 parts by weight of RO water to obtain an aqueous solution.

[0100] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0101] Comparative Example 4

[0102] The difference from Example 1 is that the aqueous solution does not contain a catalyst;

[0103] That is: 2) Preparation of aqueous solution: Mix 1 part by weight of 2-methylresorcinol, 0.5 parts by weight of sodium dodecyl sulfonate, 2 parts by weight of triethylamine and 96.5 parts by weight of RO water to obtain an aqueous solution.

[0104] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0105] Comparative Example 5

[0106] The difference from Example 1 is that the oil phase solution does not contain ethane chloride;

[0107] That is: 3) Preparation of oil phase solution: Mix 0.2 parts by weight of pyromellitic methyl chloride and 99.8 parts by weight of ethylcyclohexane to obtain oil phase solution.

[0108] The remaining steps are the same as in Example 1, and a nanofiltration membrane is obtained.

[0109] The nanofiltration membranes obtained in the above comparative examples and embodiments were subjected to performance tests on a standard membrane test bench. The membrane performance was tested using a 2000 mg / L magnesium sulfate aqueous solution at a pressure of 110 psi and a temperature of 25 ± 1 °C.

[0110] The formula for calculating flux F is shown in equation (1):

[0111] Equation (1);

[0112] In equation (1), V is the volume of permeate in gallons; S is the effective membrane area in square feet; and t is the time in days.

[0113] The formula for calculating the desalination rate R is shown in equation (2):

[0114] Equation (2);

[0115] In equation (2), C f The concentration of magnesium sulfate in the original solution is ppm; C p The concentration of magnesium sulfate in the permeate is expressed in ppm.

[0116] The test results are shown in Table 1.

[0117] Table 1 Performance test results of nanofiltration membranes obtained from comparative examples and embodiments

[0118]

[0119] Comparing Examples 1-3, it can be seen that as the number of carbon atoms in the substituent at position 2 decreases, the steric hindrance effect decreases, the reactivity increases, and both membrane flux and desalination rate increase. Increasing the oil phase temperature and oven temperature can improve the reactivity and membrane performance. When the mixed monomers of piperazine and 2-ethylresorcinol react with acyl chloride (i.e., Comparative Example 1), because the reactivity of the amino group is much greater than that of the hydroxyl group, the membrane performance is close to that of Comparative Example 2 (reaction of pure piperazine monomer).

[0120] To verify that the membrane prepared in this invention has antioxidant properties, the prepared membrane was soaked in a 1000 ppm sodium hypochlorite aqueous solution for 24 h and then subjected to the MgSO4 standard test. The results are shown in Table 2.

[0121] Table 2. Antioxidant performance test results of nanofiltration membranes obtained from comparative examples and embodiments.

[0122]

[0123] Table 2 shows that the membrane material obtained by reacting phenol with acyl chloride exhibits significantly better chlorine resistance than the amide membrane material obtained by reacting piperazine. Comparative Example 1, due to the addition of some 2-ethylresorcinol, shows a certain improvement in chlorine resistance compared to Comparative Example 2.

[0124] To verify that the nanofiltration membrane prepared in this invention can improve chlorine resistance while overcoming the poor acid hydrolysis resistance of polyester, it was immersed in an acid solution, and the changes in membrane performance before and after immersion were evaluated. A 0.1% hydrochloric acid solution was prepared, heated and maintained at 40±1 ℃, and the membrane was immersed for 24 h before a magnesium sulfate standard test was performed. The test results are shown in Table 3.

[0125] Table 3. Test results of acid hydrolysis resistance of nanofiltration membranes obtained from comparative examples and embodiments.

[0126]

[0127] In terms of performance after acid treatment, the polyester material in Comparative Example 3 has worse acid resistance than the polyamide in Comparative Example 2. However, after introducing substituents on the benzene ring, all examples showed a certain degree of resistance to acid hydrolysis.

[0128] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nanofiltration membrane, characterized in that, The material comprises a nonwoven fabric layer, a support layer, and a polyester separation layer, which are sequentially laminated. The polyester separation layer is formed by interfacial polymerization of an aqueous solution and an oil solution on the support layer. The aqueous solution comprises saturated hydrocarbon-substituted resorcinol. The oil solution comprises a polyacrylamide halide monomer. The saturated hydrocarbon-substituted resorcinol has the structure shown in Formula I. Formula I; in Formula I, R is an alkyl group having 1 to 10 carbon atoms.

2. The nanofiltration membrane according to claim 1, characterized in that, R is methyl, ethyl, or n-propyl.

3. The nanofiltration membrane according to claim 1, characterized in that, The aqueous solution is composed of saturated hydrocarbon-substituted resorcinol, surfactant, acid absorbent, catalyst and water; in the aqueous solution, the mass content of saturated hydrocarbon-substituted resorcinol is 0.5%~1%, the mass content of surfactant is 0.5%~1%, the mass content of acid absorbent is 2%~4%, and the mass content of catalyst is 0.1%~0.5%.

4. The nanofiltration membrane according to claim 3, characterized in that, The surfactant is sodium dodecyl sulfonate; the acid absorbent is triethylamine; and the catalyst is 4-dimethylaminopyridine.

5. The nanofiltration membrane according to claim 1, characterized in that, The oil phase solution is composed of a polyacrylamide halide monomer and an oil phase solvent; the polyacrylamide halide monomer is pyromellitic tricarboxylate chloride; the oil phase solvent is ethylcyclohexane and monochloroethane in a mass ratio of 70~75:25~30; the mass content of the acryl halide in the oil phase solution is 0.1%~0.5%.

6. A method for preparing the nanofiltration membrane according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The casting solution is coated onto one side of the nonwoven fabric layer and cured into a film by phase inversion to obtain a base film; the base film includes a nonwoven fabric layer and a support layer formed on the nonwoven fabric layer. S2. The base membrane is immersed in an aqueous solution, and after being removed and dried, an oil-phase solution is coated on one side of the support layer of the base membrane to carry out an interfacial polymerization reaction. After curing, a polyester separation layer is formed to obtain a nanofiltration membrane.

7. The preparation method according to claim 6, characterized in that, The phase transformation and solidification temperature is 13~17℃, and the time is 30~50 s.

8. The preparation method according to claim 6, characterized in that, The immersion time in the aqueous solution is 10-20 s; the temperature of the oil solution is 50-70℃; the temperature of the interfacial polymerization reaction is 50-70℃ and the time is 25-35 s; the curing method is drying at a temperature of 50-70℃.

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