High-flux acid-resistant nanofiltration membrane and preparation method thereof

Abstract

The invention belongs to the technical field of membrane materials, and discloses a high-flux acid-resistant nanofiltration membrane and a preparation method thereof. The method comprises the following steps: (1) coating a porous supporting base membrane with a nitrogen heterocyclic quaternary ammonium salt aqueous solution, infiltrating, and removing excess liquid; (2) coating the surface of the membrane prepared in the step (1) with an n-hexane solution dissolved with cyanuric chloride, and infiltrating to enable the nitrogen-containing hybridized quaternary ammonium salt and cyanuric chloride to be subjected to a substitution reaction; after the reaction is finished, drying to obtain a nanofiltration membrane; wherein the structure of the nitrogen-containing heterocyclic quaternary ammonium salt is nitrogen-containing heterocyclic quaternary ammonium salt containing two or more amino groups, a quaternary ammonium group is positioned on a nitrogen heterocyclic ring, the amino groups are positioned on the nitrogen heterocyclic ring or are directly connected with carbon atoms forming the nitrogen heterocyclic ring, and counter ions are Cl <->, Br <-> or I <->. According to the invention, specific nitrogen-containing heterocyclic quaternary ammonium salt is designed as a water-phase monomer, so that cyanuric chloride is subjected to trisubstitution reaction at room temperature to form a compact separation layer.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, and more specifically, relates to a high-flux acid-resistant nanofiltration membrane and its preparation method. Background Technology

[0002] With the acceleration of industrialization, my country faces an increasingly severe problem of industrial waste acid. Statistics show that my country's annual waste acid production has reached hundreds of millions of tons, containing valuable metal ions such as iron, cobalt, nickel, and copper, causing both environmental pollution and a huge waste of resources. Nanofiltration, as a pressure-driven membrane separation technology, is widely used in fields such as lithium extraction from salt lakes, heavy metal removal, hard water softening, and the chlor-alkali industry, showing promising application prospects in the recovery of metal ions from waste acid. However, most commercially available nanofiltration membranes are currently made of polyamide, whose amide bonds are easily degraded in strong acid environments, causing the membrane to lose its separation performance.

[0003] Cyanide, containing three highly reactive chlorine atoms, can undergo nucleophilic substitution reactions with amine monomers to form strong acid-resistant CN bonds, making it an ideal monomer for constructing acid-resistant nanofiltration membranes. However, when two chlorine atoms in cyanide are replaced by amine monomers, the electron cloud density of the triazine ring increases significantly, and the electrophilicity of the remaining carbon atoms decreases, leading to a substantial reduction in the leaving activity of the third chlorine atom. This makes it difficult for cyanide to undergo a sufficient trisubstitution reaction with small-molecule amine monomers at room temperature, thus preventing the formation of the highly cross-linked polymer network structure necessary for the separation layer.

[0004] To overcome this challenge, researchers attempted to use amino-rich polymers (such as polyethyleneimine) as aqueous monomers to perform interfacial polymerization with cyanuric chloride to prepare acid-resistant membranes (Sep. Purif. Technol., 2023, 320, 124108; Sep. Purif. Technol., 2020, 250, 117245; J. Membr. Sci., 2021, 640, 119833). However, the highly entangled polymer chains of polyethyleneimine and other polymers easily form a dense separation layer, leading to a significant increase in mass transfer resistance and generally low membrane permeation flux (<5 L m). -2 h -1 bar -1 Another study synthesized trifunctional triazine ring derivatives and prepared acid-resistant membranes through interfacial polymerization with 1,3,5-benzenetricarboxylic acid chloride (J. Membr. Sci., 2018, 546, 225-233). However, these membranes typically have a negatively charged surface, resulting in low rejection rates for metal ions, and their permeation flux remains unsatisfactory (<10). 5 L m -2 h -1 bar-1 ).

[0005] In summary, the existing technology still lacks a small molecule amine monomer that can both rapidly undergo a trisubstituted reaction with cyanuric chloride at room temperature and form a highly permeable separation layer. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a high-flux acid-resistant nanofiltration membrane and its preparation method. By designing a specific nitrogen-containing heterocyclic quaternary ammonium salt as an aqueous phase monomer, cyanuric chloride undergoes a tri-substitution reaction at room temperature to form a dense separation layer. This solves the problems of cyanuric chloride's difficulty in undergoing a tri-substitution reaction with small molecule amines at room temperature and the low permeation flux of existing acid-resistant nanofiltration membranes.

[0007] To achieve the above objectives, in one aspect of the present invention, a method for preparing a high-flux acid-resistant nanofiltration membrane is provided, comprising the following steps: (1) Coat the porous support substrate with an aqueous solution of nitrogen-containing heterocyclic quaternary ammonium salt, and after wetting, remove excess liquid; (2) Subsequently, the surface of the material obtained in step (1) is coated with a hexane solution containing cyanuric chloride, and the nitrogen-containing hybrid quaternary ammonium salt is immersed to undergo a substitution reaction with cyanuric chloride; after the reaction is completed, it is dried to obtain a nanofiltration membrane; The nitrogen-containing heterocyclic quaternary ammonium salt has the structure of a nitrogen-containing heterocyclic quaternary ammonium salt containing two or more amino groups. The quaternary ammonium group is located on the nitrogen heterocycle, and the amino group is located on the nitrogen heterocycle or directly bonded to a carbon atom constituting the nitrogen heterocycle. The counterion is Cl. - ,Br - Or I - .

[0008] Preferably, the nitrogen heterocycle is a monocyclic, bicyclic, or spirocyclic structure containing at least one quaternary ammonium group.

[0009] The nitrogen-containing heterocyclic quaternary ammonium salt is selected from any of the following structures, with the counterion being Cl. - ,Br - Or I - : Equation (1); Equation (2); Equation (3); Equation (4); Formula (5); , Equation (6); Equation (7).

[0010] Preferably, in step (1), the mass concentration of the nitrogen-containing heterocyclic quaternary ammonium salt in the aqueous solution is 0.5-3 wt%, the pH is 9-12, and the soaking time is 0.5-3 min; the pH is preferably 12.

[0011] Preferably, the concentration of the hexane solution containing cyanuric chloride is 0.1 to 0.5 wt%.

[0012] Preferably, in step (2), the soaking time is 0.5 to 3 min.

[0013] Preferably, in step (2), the drying film formation conditions are: drying temperature of 50-70°C and drying time of 10-20 min.

[0014] Preferably, the preparation of the nitrogen-containing heterocyclic quaternary ammonium salt includes the following steps: dissolving a nitrogen-containing heterocyclic primary amine and a halogenating reagent in ethanol at a molar ratio, stirring and reacting; after the reaction is complete, filtering the reaction solution and drying it under vacuum to obtain the nitrogen-containing heterocyclic quaternary ammonium salt.

[0015] Preferably, the porous support substrate is a polysulfone membrane, a polyethersulfone membrane, or a polyacrylonitrile membrane.

[0016] In another aspect of the present invention, a high-flux acid-resistant nanofiltration membrane prepared according to the method described above is provided.

[0017] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. This invention designs specific nitrogen-containing heterocyclic quaternary ammonium salt small molecules as aqueous phase monomers, and utilizes the strong electron-withdrawing effect of quaternary ammonium groups to effectively promote the tri-substitution reaction of cyanuric chloride at room temperature, thereby constructing a highly cross-linked separation layer and avoiding the problems of dense membrane and low flux caused by the use of polymers.

[0018] 2. The nanofiltration membrane prepared by this invention exhibits excellent separation performance, with a permeation flux greater than 20 L / m³. -2 h -1 bar -1 , for Co 2+ The retention rate is higher than 95%.

[0019] 3. The nanofiltration membrane prepared by this invention exhibits acid resistance. After immersion in 2M sulfuric acid for 1000 h, its resistance to Co... 2+ The retention rate can still be maintained above 92%, which has application potential in fields such as waste acid treatment.

[0020] 4. The preparation method of the present invention is based on mature interfacial polymerization technology, which is highly compatible with the existing commercial nanofiltration membrane production process and is easy to achieve large-scale production and promotion. Attached Figure Description

[0021] Figure 1 The diagram shows the substitution reaction mechanism of cyanuric chloride (a) and the tri-substitution mechanism of cyanuric chloride promoted by nitrogen-containing heterocyclic quaternary ammonium salt (b) in this invention.

[0022] Figure 2 The 1H NMR spectrum of compound 1-methyl-3,5-diaminopyridine iodonium salt of formula (2) is an example of the present invention.

[0023] Figure 3 The 1H NMR spectra of nitrogen-containing heterocyclic quaternary ammonium salts prepared from piperazine and 4,4-bipyridine, which are examples of the present invention; Figure 3 In the diagram, 'a' is the 1H NMR spectrum of the corresponding nitrogen-containing heterocyclic quaternary ammonium salt in Example 1, and 'b' is the 1H NMR spectrum of the corresponding nitrogen-containing heterocyclic quaternary ammonium salt in Example 3.

[0024] Figure 4 The graphs (a) and (b) show the nickel chloride retention rate and permeability data of Example 1 and Comparative Example 3 after immersion in 2M hydrochloric acid for different times. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] To achieve the above objectives, the technical solution of the present invention is as follows: First, this invention provides a method for preparing a high-flux acid-resistant nanofiltration membrane, comprising the following steps: (1) Coat the porous support substrate with an aqueous solution of nitrogen-containing heterocyclic quaternary ammonium salt, soak it for a period of time, remove the excess liquid, and let it air dry until there are no visible droplets.

[0027] (2) Subsequently, the surface of the material obtained in step (1) is coated with a hexane solution containing cyanuric chloride. Wetting occurs, causing the nitrogen-containing hybrid quaternary ammonium salt to undergo a substitution reaction with the cyanuric chloride. Excess liquid is then removed from the surface to obtain a polymer membrane, which is dried in a forced-air drying oven to obtain a high-flux acid-resistant nanofiltration membrane. Figure 1As shown, interfacial polymerization occurs during the wetting process. At this time, cyanuric chloride undergoes a substitution reaction with nitrogen-containing hybrid quaternary ammonium salt. The quaternary ammonium salt has a strong electron-withdrawing effect, which can cause the electron cloud on the triazine ring of cyanuric chloride to shift towards the quaternary ammonium group, reduce the electron cloud density of the triazine ring, thereby increasing the electrophilicity of the third carbon atom, promoting the tri-substitution reaction of cyanuric chloride, and rapidly forming a defect-free separation membrane.

[0028] Preferably, the structure of the nitrogen-containing heterocyclic quaternary ammonium salt is a nitrogen-containing heterocyclic quaternary ammonium salt containing two or more amino groups, wherein the quaternary ammonium group is located on the nitrogen heterocycle, and the amino group is located on the nitrogen heterocycle or directly bonded to the carbon atom constituting the nitrogen heterocycle, without any intervening atoms; its counterion X - For Cl - ,Br - Or I - .

[0029] The general formula for nitrogen-containing heterocyclic quaternary ammonium salts is shown below: ; Preferably, the nitrogen heterocycle is a monocyclic, bicyclic, or spirocyclic structure containing at least one quaternized nitrogen atom.

[0030] Preferably, the nitrogen-containing heterocyclic quaternary ammonium salt in step (1) is selected from any one of the following structures, and its counterion is Cl. - ,Br - Or I - : Equation (1); Equation (2); Equation (3); Equation (4); Formula (5); , Equation (6); Equation (7); Equation (8).

[0031] Preferably, the aqueous solution of the amino-containing quaternary ammonium salt has a mass concentration of 0.5–3 wt%, a soaking time of 3–10 min, and a pH of 9–12; the pH is preferably 12.

[0032] Preferably, the concentration of the hexane solution containing cyanuric chloride is 0.1–0.5 wt%, and the soaking time is 0.5–3 min.

[0033] Preferably, the porous support substrate is a polysulfone membrane, a polyethersulfone membrane, or a polyacrylonitrile membrane.

[0034] Preferably, the drying temperature in the oven is 50–70 °C and the drying time is 10–20 min.

[0035] Preferably, the nitrogen-containing heterocyclic quaternary ammonium salt used in this invention can be prepared by a quaternization reaction, comprising the following steps: dissolving a nitrogen-containing heterocyclic primary amine and a halogenating reagent in ethanol at a molar ratio, stirring the reaction mixture; after the reaction is complete, filtering the reaction solution and drying it under vacuum to obtain the nitrogen-containing heterocyclic quaternary ammonium salt. Its general synthetic route is shown in the following reaction route: .

[0036] Specifically, the substrate (a nitrogen-containing heterocyclic primary amine) and the halogenating reagent were dissolved in ethanol at a molar ratio of 1:1.2, and the reaction was carried out at 70°C for 12 hours with stirring. After the reaction was completed, the quaternary ammonium salt product precipitated from the ethanol due to increased polarity. The reaction solution was filtered, and the resulting solid was dried under vacuum to obtain the target quaternary ammonium salt monomer. Taking the synthesis of compound (1-methyl-3,5-diaminopyridine iodonium salt) of formula (2) as an example: 3,5-diaminopyridine and iodomethane were dissolved in ethanol at a molar ratio of 1:1.2, and the reaction was carried out at 70°C for 12 hours. After the reaction was completed, the solution was filtered and dried under vacuum to obtain the target product. Figure 2 The 1H NMR spectrum indicates that compound (2) has been successfully prepared with a yield of 82%.

[0037] The present invention also provides a high-flux acid-resistant nanofiltration membrane prepared according to any one of the above methods.

[0038] The following specific embodiments further illustrate the preparation method of the high-throughput acid-resistant nanofiltration membrane of this application.

[0039] Example 1 This embodiment provides a method for preparing a high-flux acid-resistant nanofiltration membrane, the specific steps of which are as follows: (1) The aqueous solution of the nitrogen heterocyclic quaternary ammonium salt with the structure of formula (1) was coated on the polysulfone support membrane. The mass fraction of the solution was 2wt%, the pH was 12, and the immersion time was 5min. Then the excess liquid on the membrane surface was removed and the membrane was allowed to air dry naturally.

[0040] (2) Coat the membrane surface with a hexane solution of cyanuric chloride. The solution mass fraction is 0.3 wt%, the wetting time is 1 min, and then the surface liquid is removed.

[0041] (3) Place the membrane obtained in step (2) in a 50°C oven and dry for 10 minutes to obtain a high-flux acid-resistant nanofiltration membrane.

[0042] Examples 2-3 The preparation steps of Examples 2 and 3 are basically the same as those of Example 1, except that nitrogen-containing heterocyclic quaternary ammonium salts with different structures are used as aqueous monomers. Specific monomer structures and other parameters for each example are detailed in Table 1.

[0043] Examples 4-6 The preparation steps of Examples 4-6 are basically the same as those of Example 1, except that the concentration and / or soaking time of the nitrogen-containing heterocyclic quaternary ammonium salt aqueous solution in step (1) are changed. Specific parameters for each example are detailed in Table 1.

[0044] Examples 7-9 The preparation steps of Examples 7-9 are basically the same as those of Example 1, except that the concentration of the hexane solution of cyanuric chloride and / or the soaking time in step (2) are changed. Specific parameters for each example are detailed in Table 1.

[0045] Table 1: Parameter Table of the Embodiment

[0046] The preparation methods of the nitrogen-containing heterocyclic quaternary ammonium salts involved in Examples 2-9 are the same as those for the compound (1-methyl-3,5-diaminopyridine iodonium salt) of formula (2) above, except that the substrates are replaced with piperazine and 4,4-bipyridine, respectively. And according to the following... Figure 3 The 1H NMR spectrum results shown indicate that the nitrogen-containing heterocyclic quaternary ammonium salts involved in Examples 2-9 were successfully prepared.

[0047] Comparative Example 1 (1) A 3,9-diazaspiro[5.5]undecane aqueous solution was coated onto a polysulfone support film with a mass fraction of 2wt%, a pH of 12, and a wetting time of 5 min. Then, excess liquid was removed and the film was allowed to air dry.

[0048] (2) Coat the membrane surface with a hexane solution of cyanuric chloride. The solution mass fraction is 0.3 wt%, the wetting time is 1 min, and then the surface liquid is removed.

[0049] (3) The membrane was dried in a 50°C oven for 10 min to obtain a high-flux acid-resistant nanofiltration membrane.

[0050] Comparative Example 2 (1) An aqueous solution of 3,9-diaminoethyl-3,9-diaza-6-aza-spiro[5.5]undecane was coated onto a polysulfone support film. The solution had a mass fraction of 2 wt%, a pH of 12, and a wetting time of 5 min. Then, excess liquid was removed and the film was allowed to air dry.

[0051] (2) Coat the membrane surface with a hexane solution of 1,3,5-benzenetricarboxylic acid chloride. The solution mass fraction is 0.3 wt%, the wetting time is 1 min, and then the surface liquid is removed.

[0052] (3) The membrane was dried in a 50°C oven for 10 min to obtain a high-flux acid-resistant nanofiltration membrane.

[0053] Comparative Example 3 (1) An aqueous solution of 3,9-diaza-6-aza-spiro[5.5]undecane was coated onto a polysulfone support film. The solution had a mass fraction of 2 wt%, a pH of 12, and a wetting time of 5 min. Then, excess liquid was removed and the film was allowed to air dry.

[0054] (2) Coat the membrane surface with a hexane solution of 1,3,5-benzenetricarboxylic acid chloride. The solution mass fraction is 0.3 wt%, the wetting time is 1 min, and then the surface liquid is removed.

[0055] (3) The membrane was dried in a 50°C oven for 10 min to obtain a high-flux acid-resistant nanofiltration membrane.

[0056] Table 2: Comparative Monomer Structures

[0057] Nanofiltration performance tests were conducted on the nanofiltration membranes prepared in Examples 1-10 and Comparative Examples 1-3. The test mode was cross-flow, and the shear flow rate was 0.5 L / min. Test conditions: 1000 ppm nickel chloride solution, test pressure and temperature of 6 bar and 30°C, respectively. In this invention, permeability ( J ), retention rate ( R The calculation formula is as follows:

[0058] in, S The effective test area of ​​the membrane (m²) 2 ), t The operation time is in seconds. V for t The volume of liquid permeating within a time interval (L) is given, and p is the instrument operating pressure (bar).

[0059]

[0060] in, C f and C p These are the solute concentrations of the feed liquid and the permeate, respectively.

[0061] Membrane acid resistance test: The membrane was immersed in 2M sulfuric acid aqueous solution, and the solution was changed every two days. After a certain period of time, the membrane was taken out and repeatedly washed with deionized water. Then the membrane was immersed in deionized water for 24 hours. After that, it was taken out and nanofiltration test was performed.

[0062] The test results are shown in Table 3 below.

[0063] Table 3: Test Results Table

[0064] Combined with Table 3, Figure 1 and Figure 2 The reaction mechanism and membrane performance of this invention were analyzed: like Figure 1 As shown, the 3,9-diazaspiro[5.5]undecane used in Comparative Example 1 is a traditional secondary amine monomer. When it reacts with cyanuric chloride, the electron cloud density increases after the two chlorine atoms on the triazine ring are substituted, and the electrophilicity of the remaining carbon atoms decreases, resulting in a significant reduction in the reactivity of the third chlorine atom. It cannot undergo a trisubstitution reaction to form a highly cross-linked network structure, and can only generate oligomers or linear polymers. Therefore, the resulting separation layer has poor density and virtually no retention effect on nickel chloride (retention rate is only 1.2%, Table 3).

[0065] Although the monomer used in Comparative Example 2 also contains a quaternary ammonium salt group, its reactive amino group is separated from the nitrogen heterocycle containing the quaternary ammonium salt by an ethyl group (-CH2CH2-). This spacer group weakens the strong electron-withdrawing inductive effect of the quaternary ammonium salt, preventing it from effectively transferring to the reaction site of the triazine ring to lower the energy barrier of the trisubstitution reaction. Therefore, a dense cross-linked network cannot be formed, resulting in extremely poor membrane separation performance (retention rate of only 5.1%, Table 3). This also confirms the key technical feature of the present invention: the amino group is located on the nitrogen heterocycle or directly connected to the carbon atom constituting the nitrogen heterocycle, without any spacer atoms in between.

[0066] Examples 1-3, using the nitrogen-containing heterocyclic quaternary ammonium salt described in this invention as the aqueous monomer, produced membranes with a NiCl2 rejection rate exceeding 92% (Table 3). This is because the quaternary ammonium group is a strong electron-withdrawing group. When the two chlorine atoms of cyanuric chloride are substituted, the electron cloud density on the triazine ring shifts towards the positively charged quaternary ammonium salt group, thereby increasing the electrophilicity of the third carbon atom on the triazine ring. This effectively promotes the tri-substitution reaction of cyanuric chloride at room temperature, forming a highly cross-linked and dense separation layer. Table 3 also shows that when the monomer concentration and reaction time of the aqueous or organic phase vary within the range defined in this invention (Examples 4-9), membranes with both high permeability flux (>14 L m) can still be prepared. -2 h -1 bar -1 The presence of nanofiltration membranes with high rejection rates (>95%) indicates that the technical solution of this invention has good process stability.

[0067] In addition, Comparative Example 3 used 1,3,5-benzenetriformyl chloride as the organic phase monomer and prepared a conventional polyamide nanofiltration membrane via interfacial polymerization with an amine monomer. Figure 4As can be seen, the polyamide membrane prepared in Comparative Example 3 exhibited a sharp decrease in NiCl2 retention rate to 3.2% after immersion in 2M sulfuric acid for 400 hours, demonstrating extremely poor acid resistance. In contrast, the membrane prepared in Example 1 of this invention, due to the separation layer being composed of CN bonds and lacking acid-sensitive amide bonds, maintained a NiCl2 retention rate of over 92% even after immersion in 2M sulfuric acid for 1000 hours, demonstrating excellent acid resistance.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-flux acid-resistant nanofiltration membrane, characterized in that, Includes the following steps: (1) Coat the porous support substrate with an aqueous solution of nitrogen-containing heterocyclic quaternary ammonium salt, and remove excess liquid after wetting; (2) Subsequently, the surface of the material obtained in step (1) is coated with a hexane solution containing cyanuric chloride, and the nitrogen-containing hybrid quaternary ammonium salt is immersed to undergo a substitution reaction with cyanuric chloride; after the reaction is completed, it is dried to obtain a nanofiltration membrane; The nitrogen-containing heterocyclic quaternary ammonium salt has the structure of a nitrogen-containing heterocyclic quaternary ammonium salt containing two or more amino groups, wherein the quaternary ammonium group is located on the nitrogen heterocycle, and the amino group is located on the nitrogen heterocycle or directly bonded to the carbon atom constituting the nitrogen heterocycle. The counterion is Cl. - ,Br - Or I - .

2. The method for preparing a high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, The nitrogen heterocycle is a monocyclic, bicyclic, or spirocyclic structure containing at least one quaternary ammonium group.

3. The method for preparing a high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, The nitrogen-containing heterocyclic quaternary ammonium salt is selected from any of the following structures, with the counterion being Cl. - ,Br - Or I - : Equation (1); Equation (2); Equation (3); Equation (4); Formula (5); Equation (6); Equation (7).

4. The method for preparing the high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, In step (1), the mass concentration of the nitrogen-containing heterocyclic quaternary ammonium salt in the aqueous solution is 0.5-3 wt%, the pH is 9-12, and the soaking time is 0.5-3 min; the pH is preferably 12.

5. The method for preparing the high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, In step (2), the mass concentration of cyanuric chloride in the hexane solution containing cyanuric chloride is 0.1 to 0.5 wt%.

6. The method for preparing the high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, In step (2), the soaking time is 0.5 to 3 minutes.

7. The method for preparing the high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, In step (2), the drying film formation conditions are: drying temperature of 50-70℃ and time of 10-20 min.

8. The method for preparing a high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, The preparation of the nitrogen-containing heterocyclic quaternary ammonium salt includes the following steps: dissolving a nitrogen-containing heterocyclic primary amine and a halogenated reagent in ethanol at a molar ratio, stirring and reacting; after the reaction is complete, filtering the reaction solution and drying it under vacuum to obtain the nitrogen-containing heterocyclic quaternary ammonium salt.

9. The method for preparing a high-flux acid-resistant nanofiltration membrane according to claim 1, characterized in that, The porous support substrate is a polysulfone membrane, a polyethersulfone membrane, or a polyacrylonitrile membrane.

10. A high-flux acid-resistant nanofiltration membrane prepared by the method according to any one of claims 1-9.

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