Acid and alkali resistant anti-pollution nanofiltration membrane, preparation method thereof and filter

Abstract

This application relates to the field of membrane filtration, and in particular to an acid and alkali resistant and fouling-resistant nanofiltration membrane, its preparation method and filter. By first introducing isocyanate into the base membrane, and then forming a polyamide layer through the co-reaction of aromatic sulfonamide and PIP, the overall cross-linking degree of the system is improved by using isocyanate, and the cross-linking system with a certain rigidity is formed by using aromatic sulfonamide in the system. This ensures the water flux under high inlet water pressure, and also improves the acid and alkali resistance of the membrane.

Description

Technical Field

[0001] This application relates to the field of membrane filtration, and in particular to an acid and alkali resistant and fouling-resistant nanofiltration membrane, its preparation method, and a filter. Background Technology

[0002] Nanofiltration membranes, as a pressure-driven separation membrane between reverse osmosis and ultrafiltration, have been widely used in drinking water purification, industrial wastewater treatment, material concentration and separation, and resource recovery due to their high efficiency in retaining divalent and multivalent ions and small organic molecules at relatively low operating pressures. Currently, most commercially available nanofiltration membranes employ a composite membrane structure, using polysulfone (PSF) or polyethersulfone (PES) porous membranes as the support layer, and forming a polyamide (PA) functional separation layer on its surface through interfacial polymerization. A common interfacial polymerization system uses piperazine (PIP) as the aqueous phase monomer and trimesoyl chloride (TMC) as the oil phase monomer. The resulting polyamide layer can achieve a retention rate of over 96% for divalent salts such as magnesium sulfate under suitable conditions, making it the mainstream technology in the industry.

[0003] However, traditional polyamide nanofiltration membranes still have the following problems. First, their acid and alkali resistance is poor. The amide bonds in the polyamide molecule have poor chemical stability under extreme pH conditions. Under strong acid conditions (pH < 3), the amide bonds are prone to acid-catalyzed hydrolysis, leading to polymer chain breakage, damage to the functional layer structure, and a sharp decrease in desalination rate. Under strong alkaline conditions (pH > 11), there is also a risk of alkaline hydrolysis, and their antifouling ability is also poor. Currently, some foreign companies (such as DuPont, Toray, Veolia, etc.) have launched some commercially available acid and alkali resistant filter membranes, but their water flux is generally low, usually below 10 L·m -2 ·h -1 ·bar -1 Especially under strong acid and alkaline conditions, the node structure formed by PIP and TMC on the nanofiltration membrane is prone to polarization and the formation of a hydration layer on the surface, which actually increases the resistance of water molecules to passing through the membrane pores. Although increasing the inlet water pressure can increase the water flux to a certain extent, the huge pressure drop it generates can easily cause the nanofiltration membrane to be compressed due to the pressure difference between the inlet and outlet liquid surfaces. Therefore, after the pressure reaches a certain level, it will also lead to a decrease in the water flux of the nanofiltration membrane. Summary of the Invention

[0004] Based on the above problems, the purpose of this application is to provide a polyamide nanofiltration membrane that maintains good retention efficiency while providing high water flux under acidic and alkaline conditions.

[0005] First, this application provides a method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane, comprising the following steps: S1. Isocyanate groups are introduced onto the surface of the base film by chemical grafting; S2. Prepare a solution of PIP and amino-substituted aromatic sulfonamide to cover the active surface of the base film and let it stand. The molar ratio of PIP to amino-substituted aromatic sulfonamide is 10 to 100:1. S3. Remove excess solvent phase and quickly pour in TMC solution to completely cover the active surface of the base film and allow for full reaction; S4. Remove excess solvent phase, then heat-treat the membrane to complete the preparation; The base membrane is any one of polysulfone membrane, polyethersulfone membrane, and polyvinylidene fluoride membrane, and the PMI pore size of the base membrane is 10-50 nm. The solvent in the TMC solution is an isoparaffin or n-hexane containing at least 90% by mass.

[0006] The above scheme provides a method for preparing a nanofiltration membrane, the core of which lies in the following two points: 1. The surface of the base membrane is modified with isocyanate; 2. Polymerization is carried out by PIP and aromatic sulfonamide. Firstly, in the above scheme, isocyanate can react with the amino groups in PIP and amino-substituted aromatic sulfonamides to form urea bonds, which have better acid and alkali resistance than amide bonds, and also improve the strength between the polyamide layer and the base membrane. Simultaneously, a certain amount of aromatic sulfonamide is incorporated into the PIP system. On the one hand, the sulfonamide groups provide a strong negative charge donor in the system. This significantly enhances the Donnan repulsion effect of the membrane, improving the selective retention capacity for polyvalent anions, especially sulfate ions. Furthermore, the aromatic ring structure of the aromatic sulfonamide increases the rigidity of the polyamide molecular chain segments, reducing membrane deformation under high pressure conditions. It can also act as an ion buffer system, reducing the attack of strong acids / bases on the amide bonds in the system. Meanwhile, the introduction of amino groups endows the molecule with zwitterionic properties, allowing it to undergo grafting reactions with isocyanates and polyamide systems. This also provides improved acid and alkali resistance, resistance to components such as proteins, and enhanced antifouling capabilities. Overall, the system maintains the dense cross-linked network resulting from the high reactivity of PIP while reducing cross-linking density and increasing free volume through copolymerization of a small amount of sulfonamide monomers, thus preventing excessive flux degradation.

[0007] Preferably, step S2 specifically includes the following sub-steps: S2-1: Prepare the first PIP solution, cover the active surface of the base film with it, and let it stand; in the first PIP solution, the solvent is a miscible system of water and DMF, and the mass ratio of water to DMF is 99 to 24:1; S2-2: Remove excess solvent phase, prepare a second PIP solution, cover the active surface of the base film with it, and let it stand; in the second PIP solution, the solvent is water, and the concentration of PIP in the second PIP solution is 1.5 to 3 times the concentration of PIP in the first PIP solution.

[0008] In the above scheme, the distribution process of the dual PIP solution is further defined. First, a solution with a low concentration of PIP is used, and DMF (i.e., N,N-dimethylformamide) is added as a co-solvent. On the one hand, DMF can reduce the surface tension of the aqueous phase and improve its spreading on the hydrophobic membrane surface. At the same time, DMF can penetrate into the pores of the base membrane to achieve uniform adsorption and a certain degree of penetration of PIP on the base membrane surface, so as to form a uniform monomolecular or oligomolecular layer. This avoids regional agglomeration defects caused by local supersaturation when high concentration of PIP directly impacts the base membrane surface. In the second PIP solution, a higher concentration of PIP is used on the basis of the first reaction. It further reacts on the basis of the preliminary reaction layer to build a denser polyamide surface layer. Overall, the liquid mass transfer resistance is reduced by the bottom transport layer, while a dense barrier layer is formed on the surface, which is not easily embedded by contaminants into the membrane surface and causes damage. The dense layer on the surface also helps to improve its acid and alkali resistance.

[0009] Preferably, the amino-substituted aromatic sulfonamide is added in step S2-1.

[0010] In the above scheme, amino-substituted aromatic sulfonamides are added only to the first PIP solution. This can effectively prevent the inner polyamide structure from collapsing under stronger pressure by utilizing the overall rigidity. It can maintain good water flux even under high pressure drop conditions. At the same time, it prevents the amino-substituted aromatic sulfonamides from forming hydrophobic structures on the membrane surface, thereby preventing the reduction in water flux caused by the hydrophobic properties of the benzene ring. Overall, this scheme can achieve high retention performance. Its strong electron capacity can achieve overall stability even on the inner side. At the same time, it prevents the benzene ring from playing a water-blocking role on the surface, which has little impact on water flux. It also avoids the adsorption and contamination of pollutants such as proteins caused by excessive hydrophobicity on the surface. On the contrary, the better rigidity improves the membrane pore collapse caused by high inlet pressure.

[0011] Preferably, the aromatic sulfonamide is 5-(dimethylamino)-1-naphthalenesulfonamide.

[0012] Overall, 5-(dimethylamino)-1-naphthalenesulfonamide significantly enhances the rigidity of the polyamide molecular chain through its biphenyl ring conjugated structure. This restricts the thermal motion of the chain segments, reduces compaction deformation of the membrane under high pressure, and provides better stability. Simultaneously, the planar structure of the naphthalene ring optimizes the molecular stacking, resulting in a more uniform free volume distribution of the polyamide layer. Furthermore, when this structure is linked to the isocyanate-modified base membrane surface via amino groups, the sulfonamide groups provide maximized charge effect and spatial accessibility on the outward and outer sides. Overall, under normal pressure, it has virtually no impact on membrane flux while improving membrane retention capacity, and under high pressure, it significantly increases membrane flux.

[0013] Preferably, step S1 is as follows: S1-1, Treat the active surface of the base film with alkali; S1-2. Prepare an anhydrous TDI or MDI solution, add a catalyst to cover the active surface of the base film, and rinse to remove unreacted TDI or MDI after the reaction.

[0014] The above method involves first treating with an alkaline solution, followed by treatment with anhydrous TDI or MDI solution. Sodium hydroxide can hydrolyze some of the sulfone groups on the surface of polysulfone, forming reaction sites such as phenolic hydroxyl groups. The operation is simple and consumes less energy. Based on the above, MDI or TDI can be grafted onto the membrane surface better, and it is not easy to cause damage to the membrane strength. Under the action of the catalyst, the grafting reaction can occur quickly and uniformly, and the overall reaction rate is good.

[0015] Preferably, for each 1cm 2 The base film uses 0.1–1 μmol of TDI or MDI.

[0016] In the above schemes, the isocyanates in TDI or MDI are essentially grafted onto the membrane surface as monomers. TDI has a higher grafting rate, providing a higher grafting density and improving acid and alkali resistance and retention rate. However, compared to MDI, it slightly reduces the system flux. Furthermore, its stronger hydrophobicity makes it more prone to adsorbing amphiphilic components such as proteins in highly polluted environments. (0.1–1 μmol / cm) 2 The grafting density is set to ensure the lowest effective grafting density while avoiding excessive grafting, which could lead to self-polymerization or multilayer adsorption on the base film, causing blockage of the base film pores. It also avoids an excessively thick rigid urea bond layer between the polyamide and the base film, which would increase interfacial stress concentration and raise the risk of peeling during long-term operation.

[0017] Preferably, in step S1-1, the pH value of the alkaline solution is 13-14, and / or, The temperature for alkali treatment is 30–50℃, and the treatment time is 0.5–2 hours.

[0018] In the above scheme, the conditions of the alkaline reaction are controlled as a whole, and a higher pH value and a shorter treatment temperature are used. This allows for rapid activation reaction on the membrane surface while avoiding penetration into the inner side of the base membrane and causing structural damage to the base membrane. In addition, in the above scheme, the reaction is more concentrated on the surface and in the shallow pores, which can ensure the bonding strength between the base membrane and the polyamide layer and improve the reactivity of the base membrane.

[0019] Preferably, in step S3, the solvent in the TMC solution is expressed in the following mass percentages: Toluene 2-8% The balance is isoalkanes or n-hexane.

[0020] In the above scheme, 2-8% toluene is introduced into the TMC solvent system. Toluene has good solubility, which can prevent TMC precipitation at higher TMC concentrations and lower temperatures. At the same time, it can appropriately accelerate the diffusion rate of TMC into the aqueous phase, maintain a good reaction kinetic window, improve the overall diffusion performance, and allow for more uniform control of the polyamide layer thickness, resulting in a more uniform film.

[0021] This application also includes the acid- and alkali-resistant, anti-fouling nanofiltration membrane prepared by the above-described preparation method.

[0022] The nanofiltration membrane prepared by the above method can operate stably for a long time in a pH range of 1–3, avoiding the problem of acid sensitivity caused by amide bonds. At the same time, in a strongly alkaline environment, the sulfonamide groups can adsorb electrons, improving alkalinity stability. Overall, it has good water flux, high magnesium sulfate rejection rate, and good antifouling performance.

[0023] This application also relates to membrane filters that include the above-mentioned nanofiltration membranes, including but not limited to tangential flow filters such as plate and frame membrane packs, wound filter cartridges, hollow fiber membranes, and tubular membranes, or dead-end filtration systems such as filter cartridges, filter cylinders, bag filters, and pleated filter cartridges. Overall, these filters can be used in extreme acidic or alkaline environments and can maintain good water flux.

[0024] In summary, this application provides an antifouling filter membrane. By first introducing isocyanate groups onto the base membrane, and then forming a polyamide layer through the co-reaction of aromatic sulfonamide and PIP, the overall cross-linking degree of the system is improved by using isocyanate, and the cross-linking system with a certain rigidity is formed by using aromatic sulfonamide. This ensures the water flux under high inlet water pressure and also improves the acid and alkali resistance of the membrane. Detailed Implementation

[0025] The technical solutions in this application will be further described through the following specific embodiments.

[0026] Example 1: This example provides a method for preparing an acid and alkali resistant and antifouling nanofiltration membrane, which generally includes the following steps: S1. Selection and pretreatment of the base film: The base film is a polysulfone film with a PMI pore size of 30±5nm and a thickness of 150μm. Its active side is a polysulfone (PSF) layer and the other side is a polypropylene (PP) nonwoven fabric substrate. Depending on the actual needs, a composite base film of polyethersulfone (PES) and PP nonwoven fabric, or a pure PSF film or a pure PES film can also be used.

[0027] The base film was first cleaned with anhydrous ethanol in an ultrasonic bath for 15 minutes, then rinsed three times with deionized water, and then air-dried until no water droplets remained on the surface. It was then fixed onto a plastic frame with the active layer facing upwards, ensuring no wrinkles or bubbles. Isocyanate groups were then grafted onto the surface using the following method: S1-1. Prepare a 1.2% sodium hydroxide aqueous solution (pH=13.5) and slowly pour it into the frame to ensure that it completely covers the surface. Keep the environment at 40°C for 1 hour. After treatment, pour off the excess liquid and rinse with deionized water until neutral. S1-2. Prepare an anhydrous toluene solution of TDI (toluene is pre-dried with CaCl2), where the concentration of TDI is 5 mmol / L. For each square centimeter of base membrane, control the amount of TDI to be 0.5 μmol (the volume of the solution used is 2.5 mL for a membrane area of ​​5 cm × 5 cm). Pour it onto the active surface of the membrane on the frame to completely cover it. Then dissolve the catalyst dibutyltin dilaurate (DBTDL) with a small amount of toluene. React at 50 °C for 6 h under nitrogen protection. After the reaction is completed, pour off the excess liquid, wash three times with anhydrous toluene, and then rinse twice with n-hexane.

[0028] S2. This step involves preliminary treatment of the base film surface using PIP, specifically including the following steps: S2-1, prepare a 0.5% PIP solution, adjust the pH to 12.5 with sodium hydroxide, and add DNSA (approximately 0.025% by mass) at a PIP to 5-(dimethylamino)-1-naphthalenesulfonamide (DNSA) molar ratio of 20:1. The solvent used is a miscible system of water and DMF, with a water to DMF mass ratio of 98:2. Slowly pour the solution along the edge of the frame, ensuring complete coverage of the membrane surface. Let it stand for 120 seconds, then tilt the frame to allow excess water to drain. Gently roll the surface in one direction with a soft rubber roller to remove any remaining water droplets.

[0029] S2-2, Prepare a second PIP solution with a mass concentration of 1.0% using deionized water as the solvent. Quickly and slowly pour the second PIP solution along the edge of the frame, ensuring complete coverage of the membrane surface. Let it stand and soak for 120 seconds, then tilt the frame to allow excess water to drain out. Gently roll the surface in one direction with a soft rubber roller to remove any remaining water droplets.

[0030] S3. In this step, crosslinking is achieved by adding TMC, as detailed below: Prepare a TMC / n-hexane / toluene solution in advance (0.6wt%, 0.015mol / L, hexane:toluene mass ratio of 95:5), pour it quickly and ensure it covers the membrane surface, react for 60s, then tilt the frame to drain the organic phase.

[0031] In steps S2 and S3, the amount of solution poured each time is generally sufficient to cover the surface of the base film, typically maintaining a solution depth of 2 mm. For example, for a 5 cm × 5 cm base film, the amount of solution poured each time is 5 mL. The reaction temperature is controlled at room temperature (25 °C). In step S2, the total amount of PIP to the mass ratio of DNSA is 60:1.

[0032] S4. Transfer the membrane along with the frame into an oven and heat-treat at 65°C for 5 minutes. After removal, rinse the membrane surface with deionized water at least 3 times to remove residual reagents. Immerse the membrane in deionized water and store at 4°C for later use.

[0033] Based on Example 1, by adjusting some experimental steps and parameters, the following examples and control examples can be obtained.

[0034] First, the basic scheme of Example 1 was adjusted to obtain the following comparative example.

[0035] Compared with Example 1, the difference is that in step S1, steps S1-1 and S1-2 are not performed. After cleaning and wetting the base film, step S2 is performed directly.

[0036] Compared with Example 1, the difference in Example 2 is that DNSA is not added when preparing the solution in step S2.

[0037] Furthermore, based on Example 1, the selection and dosage of amino-substituted aromatic sulfonamides were adjusted. The orthogonal experiment selected examples and control examples as shown in Table 1.

[0038]

[0039] Furthermore, the PIP solution impregnation step in Example 1 was adjusted to obtain the following example.

[0040] Example 3-1 differs from Example 1 in that, in step S2, there are no separate steps S2-1 and S2-2. Instead, a one-time impregnation is used, that is, step S2-2 is not performed. Based on step S2-1, the mass concentration of PIP in the first PIP solution is adjusted to 1.25%.

[0041] Example 3-2 differs from Example 3-1 in that the solvent is replaced with deionized water and DMF is not added.

[0042] Example 3-3 differs from Example 1 in that DMF is not added in step S2-1.

[0043] Examples 3-4 differ from Example 1 in that, in step S2-1, the mass ratio of water to DMF is 99:1.

[0044] Examples 3-5 differ from Example 1 in that, in step S2-1, the mass ratio of water to DMF is 24:1.

[0045] Examples 3-6 differ from Example 1 in that, in step S2-1, the mass ratio of water to DMF is 19:1.

[0046] Examples 3-7 differ from Example 3-1 in that 5-(dimethylamino)-1-naphthalenesulfonamide is not added in step S2-1, but is added in step S2-2 instead.

[0047] Examples 3-8 differ from Example 3-1 in that, in S2-1, the mass concentration of PIP is 0.4%, and in S2-2, the mass concentration of PIP is 1.2%.

[0048] Examples 3-9 differ from Example 3-1 in that, in S2-1, the mass concentration of PIP is 0.6%, and in S2-2, the mass concentration of PIP is 0.9%.

[0049] The difference between Example 3-10 and Example 3-1 is that in S2-1, the mass concentration of PIP is 0.75, and in S2-2, the mass concentration of PIP is 0.75%.

[0050] Furthermore, in Example 1, the amount and selection of isocyanate during the base film treatment process were experimentally adjusted to obtain the examples shown in Table 2.

[0051]

[0052] The above embodiments and control examples were cut to an effective test area of ​​33.5 cm². 2A circular diaphragm was placed in a cross-flow filtration test cell, and its performance was evaluated under the conditions of 25℃, operating pressure of 0.6MPa, and feed flow rate of 3L / min. The rejection rate was determined by preparing 2000mg / L magnesium sulfate and 2000mg / L sodium chloride solutions, respectively, and the water flux was determined by using a hydrochloric acid solution at pH=2.

[0053] Based on the above, the membrane was immersed in a sodium hydroxide solution with pH=13 for 720 h at 25°C and then removed. The membrane was then immersed in a hydrochloric acid solution with pH=2 for 720 h at 25°C and then removed again to measure the water flux and rejection rate of the system.

[0054] In addition, simulated wastewater containing bovine serum albumin (BSA, 100 ppm) and humic acid (50 ppm) was prepared as feed, and after continuous operation for 24 hours, it was rinsed with deionized water, and the water flux of deionized water was measured again.

[0055] The experimental results of the above embodiments are shown in Table 3.

[0056]

[0057] In the table above, " / " indicates that it was not measured.

[0058] Through the above examples, it can be seen that Example 1 exhibits good overall water flux and retention performance, with a sodium chloride retention rate exceeding 35% and a magnesium sulfate retention rate exceeding 97%, while also demonstrating good water flux. In Comparative Example 1, due to the lack of treatment of the base membrane, its overall performance against acids and alkalis is significantly weakened. In Comparative Example 2, the absence of DNSA not only significantly reduces acid and alkali resistance but also has a slight adverse effect on the system's water flux and severely reduces its antifouling ability.

[0059] In Examples 2 and Comparative Examples 3 and 4, it can be seen that benzoic acid and sulfonic acid systems were used in Comparative Examples 3 and 4, respectively. Although their acid and alkali resistance was improved compared to Comparative Example 2, they still could not reach the level of Example 1. Under high pollution conditions, there was a significant loss in water flux, and the overall water flux was also significantly reduced. The strong polarization effect made it easier for excess positive charges to attach to the benzoic acid and benzenesulfonic acid groups and form a dense water layer, which inhibited water flow and also had a certain adverse effect on antifouling performance. In the experiments of Examples 2-1 to 2-6, it can be seen that the use of DNSA compared to p-aminobenzenesulfonamide (ABSA) showed a slight increase in flux and better antifouling effect. This may be because the naphthalene ring provides better structural rigidity, reduces surface depression, and avoids the embedding of large molecules such as proteins into the membrane, which would cause membrane fouling and a permanent decrease in flux.

[0060] In the series of Examples 3, step S2 was adjusted. Examples 3-1 and 3-2 show that regardless of whether DMF is added, the overall antifouling performance is significantly weakened by using a single-addition PIP method, and the retention rate is also reduced. This may be because DNSA (or possibly ABSA) is more easily enriched on the surface during the preparation process, causing hydrophobic adsorption of proteins. It may also be that DNSA has a negative impact on surface density, leading to pores on the membrane surface that allow proteins to embed. Furthermore, excessive polarization of the system may cause electrostatic adsorption of proteins. DNSA may also interfere with the formation of the polyamide membrane, resulting in more membrane defects and weakened ion barrier performance. Similar phenomena were observed in Examples 3-7. Additionally, Examples 3-3 to 3-6 show that adding DMF as the solvent for the first reaction effectively improves acid and alkali resistance and also improves the system flux and reduces mass transfer resistance to some extent. However, excessive use of DMF can also lead to a decrease in overall retention performance. By comparing Examples 3-7 to 3-10, it can be seen that in 3-10, the same mass concentration of PIP solution was added twice, and its ion rejection performance and anti-fouling performance were reduced to a certain extent. This may be because the surface density was reduced in this treatment method, which led to the instability of the overall pores.

[0061] In Examples 4-1 to 4-8, it can be seen that both TDI and MDI can achieve good overall retention rates and high water flux. The experimental group using TDI showed relatively higher retention efficiency, but also exhibited a slight decrease in water flux compared to the MDI experimental group. Excessive addition of TDI (or MDI) led to pore blockage and a significant decrease in water flux, while insufficient addition resulted in no significant improvement in acid and alkali resistance compared to Control Example 1. In fact, the alkaline treatment of the base membrane weakened the system strength, and during actual manufacturing, a significant decrease in membrane integrity and a certain reduction in yield were observed.

[0062] Furthermore, based on Example 1, the following filter example is provided.

[0063] Example 5: This example describes a filter element using the nanofiltration membrane from Example 1, based on the Haitong TW-NF1-1812 membrane, with an effective membrane area of ​​0.39 m². 2 The maximum operating pressure of the above components is 300 psi. Within a pH range of 7.5–8.0, the removal rate of sodium chloride at a concentration of 250 mg / L is 45%, and within a pH range of 6.5–7.0, the removal rate of magnesium sulfate at a concentration of 250 mg / L is no less than 96%. Overall, the system exhibits high water flux and maintains good retention rates even after prolonged exposure to acidic and alkaline environments.

[0064] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane, characterized in that, Includes the following steps: S1. Isocyanate groups are introduced onto the surface of the base film by chemical grafting; S2. Prepare a solution of PIP and amino-substituted aromatic sulfonamide to cover the active surface of the base film and let it stand. The molar ratio of PIP to amino-substituted aromatic sulfonamide is 10 to 100:

1. S3. Remove excess solvent phase and quickly pour in TMC solution to completely cover the active surface of the base film and allow for full reaction; S4. Remove excess solvent phase, then heat-treat the membrane to complete the preparation; The base membrane is any one of polysulfone membrane, polyethersulfone membrane, and polyvinylidene fluoride membrane, and the PMI pore size of the base membrane is 10-50 nm. In the TMC solution, the solvent is an isoparaffin or n-hexane containing at least 90% by mass. Step S2 specifically includes the following sub-steps: S2-1: Prepare the first PIP solution, cover the active surface of the base film with it, and let it stand; in the first PIP solution, the solvent is a miscible system of water and DMF, and the mass ratio of water to DMF is 99 to 24:1; S2-2: Remove excess solvent phase, prepare a second PIP solution to cover the active surface of the base film, and let it stand; In the second PIP solution, the solvent is water, and the concentration of PIP in the second PIP solution is 1.5 to 3 times that in the first PIP solution.

2. The method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane according to claim 1, characterized in that, The amino-substituted aromatic sulfonamide is added in step S2-1.

3. The method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane according to claim 1, characterized in that, The amino-substituted aromatic sulfonamide is 5-(dimethylamino)-1-naphthalenesulfonamide.

4. The method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane according to claim 1, characterized in that, Step S1 is as follows: S1-1, Treat the active surface of the base film with alkali; S1-2. Prepare an anhydrous TDI or MDI solution, add a catalyst to cover the active surface of the base film, and rinse to remove unreacted TDI or MDI after the reaction.

5. The method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane according to claim 4, characterized in that, For each 1cm 2 The base film uses 0.1–1 μmol of TDI or MDI.

6. The method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane according to claim 4, characterized in that, In step S1-1, the pH value of the alkaline solution is 13-14, and / or, The temperature for alkali treatment is 30–50℃, and the treatment time is 0.5–2 hours.

7. The method for preparing an acid- and alkali-resistant, anti-fouling nanofiltration membrane according to claim 1, characterized in that, In step S3, the solvent in the TMC solution is expressed in the following mass percentages: Toluene 2-8% The balance is isoalkanes or n-hexane.

8. The acid- and alkali-resistant, anti-fouling nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 7.

9. A filter comprising an acid- and alkali-resistant, anti-fouling nanofiltration membrane prepared by any one of claims 1 to 7.

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