Preparation method of positively charged nanofiltration membrane and positively charged nanofiltration membrane

Abstract

The invention discloses a preparation method of a positively charged nanofiltration membrane and the positively charged nanofiltration membrane. The preparation method of the positively charged nanofiltration membrane comprises the following steps: coating at least part of the surface of a base membrane with an aqueous solution containing a polyamine monomer to obtain a first coating; and coating one side, far away from the base membrane, of the first coating with an organic solution containing a binary sulfonyl chloride monomer, and reacting to obtain the positively charged nanofiltration membrane. Therefore, the positively charged nanofiltration membrane prepared by the method provided by the invention has high retention rate and high water flux.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer separation membranes, and in particular relates to a preparation method of a positively charged nanofiltration membrane and the positively charged nanofiltration membrane. Background Art

[0002] Nanofiltration is a pressure-driven membrane separation process between ultrafiltration and reverse osmosis. The membrane pore size is nanometer-level, and it has a good removal effect on multivalent ions and organic matter with a molecular weight of 200 to 1000. Nanofiltration membranes have been widely used in water purification, wastewater treatment, material separation and other fields.

[0003] Acid-resistant nanofiltration membrane solves the problem of unstable hydrolysis of polyamide structure in conventional nanofiltration membrane under strong acidic environment, and can be stable in 20% sulfuric acid strong acidic environment. At present, the main materials for preparing acid-resistant nanofiltration membrane mainly include polysulfonamide, triazine ring, and sulfonated polymer. Acid-resistant nanofiltration membrane has good application prospects in the field of separation and recovery of metal ions and acids in acid-containing waste liquid, involving many fields such as steel, coal, offset printing plate, etc.

[0004] The separation mechanism of nanofiltration membrane mainly includes pore size mechanism and charge mechanism. According to the Donan effect, charges of the same name have a repulsive effect, and the larger the charge, the higher the ion valence, the stronger the repulsive effect, and the higher the retention rate. For the separation of metal cations, it is obvious that positively charged nanofiltration membranes have better separation and recovery performance, but most commercial nanofiltration membranes, including acid-resistant nanofiltration membranes, are negatively charged nanofiltration membranes, and the retention rate for metal cations is low. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, one purpose of the present invention is to provide a method for preparing a positively charged nanofiltration membrane and an acid-resistant positively charged nanofiltration membrane. The positively charged nanofiltration membrane can be obtained by the method provided by the present application, and has a high rejection rate and a high water flux for metal cations.

[0006] In the first aspect of the present invention, a method for preparing a positively charged nanofiltration membrane is proposed. According to an embodiment of the present invention, the method comprises: coating an aqueous solution containing a polyamine monomer on at least a portion of the surface of a base membrane to obtain a first coating; coating an organic solution containing a disulfonyl chloride monomer on a side of the first coating away from the base membrane, reacting to obtain a positively charged nanofiltration membrane.

[0007] According to the preparation method of the above embodiment of the present invention, by coating the aqueous solution containing polyamine monomers on at least part of the surface of the base film, a uniform and tight first coating layer can be formed, ensuring good contact between the polyamine monomers and the base film, coating the organic solution containing disulfonyl chloride monomers on the side of the first coating layer away from the base film, so that the polyamine monomers and the disulfonyl chloride monomers can contact each other, and the amino groups in the polyamines and the sulfonyl chloride groups in the disulfonyl chlorides undergo interfacial polymerization at the interface. Compared with aromatic amines, aliphatic amines have less steric hindrance and greater reactivity, which is conducive to the rapid passage of water molecules and can improve the water flux of the positively charged nanofiltration membrane. The polyamine monomers will leave some unreacted amino groups in the reaction, and the residual amino groups will undergo protonation in the presence of water, and combine with hydrogen ions to form positively charged ammonium ions, which can improve the positive charge of the acid-resistant positively charged nanofiltration membrane. When the positively charged nanofiltration membrane contacts cations, the rejection rate of the positively charged nanofiltration membrane for positively charged substances is improved through repulsion. Therefore, the method provided in the present application can be used to obtain a positively charged nanofiltration membrane, which has a higher retention rate and a higher water flux for metal cations.

[0008] In addition, the preparation method according to the above embodiment of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, the base membrane includes at least one of a polysulfone membrane, a polyethersulfone membrane and a polyacrylonitrile membrane, thereby providing necessary physical support for the positively charged nanofiltration membrane to ensure its stability and durability during operation.

[0010] In some embodiments of the present invention, the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is (5-30): 1. Thus, a positively charged nanofiltration membrane with high rejection rate and high water flux can be obtained.

[0011] In some embodiments of the present invention, the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is (10-20): 1. Thus, a positively charged nanofiltration membrane with high rejection rate and high water flux can be obtained.

[0012] In some embodiments of the present invention, the mass proportion of the polyamine monomer is 1% to 10% based on the total mass of the aqueous solution. Thus, a positively charged nanofiltration membrane with high rejection rate and high water flux can be obtained.

[0013] In some embodiments of the present invention, based on the total mass of the aqueous solution, the mass proportion of the polyamine monomer is 2% to 5%. Thus, a positively charged nanofiltration membrane with high rejection rate and high water flux can be obtained.

[0014] In some embodiments of the present invention, based on the total mass of the organic solution, the mass proportion of the disulfonyl chloride monomer is 0.1% to 1%. Thus, a positively charged nanofiltration membrane with high rejection rate and high water flux can be obtained.

[0015] In some embodiments of the present invention, based on the total mass of the organic solution, the mass proportion of the disulfonyl chloride monomer is 0.1% to 0.5%, thereby obtaining a positively charged nanofiltration membrane with high rejection rate and high water flux.

[0016] In some embodiments of the present invention, the polyamine monomer includes aliphatic amine, which helps to form a more uniform and dense separation layer, thereby improving the rejection rate and water flux of the positively charged nanofiltration membrane.

[0017] In some embodiments of the present invention, the fatty amine includes at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, bis(hexamethylene)triamine and s-triazine. Thus, it is helpful to form a more uniform and dense separation layer, thereby improving the rejection rate and water flux of the positively charged nanofiltration membrane.

[0018] In some embodiments of the present invention, the disulfonyl chloride monomer includes at least one of 1,2-benzenedisulfonyl chloride, 1,3-benzenedisulfonyl chloride and 1,4-benzenedisulfonyl chloride. Thus, a positively charged nanofiltration membrane with a higher retention rate and water flux can be obtained.

[0019] In some embodiments of the present invention, the solvent of the organic solution includes at least one of n-hexane, ethylcyclohexane and isomeric alkanes, thereby facilitating the formation of a dry, dense, positively charged nanofiltration membrane.

[0020] In the second aspect of the present invention, the present invention provides a positively charged nanofiltration membrane, which is prepared by the above-mentioned method. Therefore, the positively charged nanofiltration membrane has a higher retention rate and water flux.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0023] Figure 1 The flowchart of the preparation of the positively charged nanofiltration membrane according to the embodiment of the present application is shown. DETAILED DESCRIPTION

[0024] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0025] In a first aspect of the present invention, the present invention provides a method for preparing a positively charged nanofiltration membrane. According to an embodiment of the present invention, the method comprises:

[0026] S1, coating an aqueous solution containing a polyamine monomer on at least a portion of the surface of the base film to obtain a first coating;

[0027] In this step, a uniform first coating layer can be obtained by coating an aqueous solution containing polyamine monomers on at least a portion of the surface of the base film. Specifically, an aqueous solution containing polyamine monomers is first prepared, and then the aqueous solution is coated on at least a portion of the surface of the base film to remove excess surface water, thereby forming a uniform and tight first coating layer, thereby ensuring good contact between the polyamine monomers and the base film.

[0028] It should be noted that the term "at least a portion of the surface" in "coated on at least a portion of the surface of the base film" refers to one or more specific areas on the surface of the base film, indicating that the coating operation can be performed on the entire, most, a portion, or only a small area of ​​the surface of the base film. For example, in some cases, it may be necessary to apply the coating to only one side of the base film, while in other cases, it may be necessary to apply the coating to multiple areas or the entire surface of the base film.

[0029] There is no particular limitation on the coating method, for example, it may be spray coating, dip coating, spin coating, etc. Those skilled in the art may flexibly select the coating method according to their needs.

[0030] Polyamine refers to an amine containing three or more amino groups (-NH2) in the molecule, such as hexamethylenetetramine (CH2)6N4.

[0031] According to some specific embodiments of the present invention, the base membrane includes at least one of a polysulfone membrane, a polyethersulfone membrane and a polyacrylonitrile membrane. The polysulfone membrane, the polyethersulfone membrane and the polyacrylonitrile membrane all have good mechanical strength and stability, and can provide necessary physical support for the positively charged nanofiltration membrane, ensuring its stability and durability during operation.

[0032] According to some specific embodiments of the present invention, based on the total mass of the aqueous solution, the mass proportion of the polyamine monomer is 1% to 10%. For example, it can be 1%, 3%, 5%, 7%, 10%, etc. By limiting the mass proportion of the polyamine monomer to the above range, on the one hand, the reaction rate between the polyamine monomer and the disulfonyl chloride monomer in the oil phase can be controlled. On the other hand, it can fully ensure that a certain number of amino functional groups remain after interfacial polymerization, provide sufficient positive charge, and prepare a positively charged nanofiltration membrane with high retention rate and high water flux. Further, based on the total mass of the aqueous solution, the mass proportion of the polyamine monomer can preferably be 2% to 5%.

[0033] According to some specific embodiments of the present invention, the polyamine monomer includes a fatty amine. The molecular structure of the fatty amine is relatively simple, and the carbon atoms on its molecular chain are usually connected to hydrogen atoms, so that when the fatty amine participates in a chemical reaction, the reaction sites on its molecular chain are more accessible, thereby reducing the influence of steric hindrance, and the reaction sites such as amino groups on the fatty amine molecular chain are relatively exposed and more easily react with reactants, so that the fatty amine can react more quickly with disulfonyl chloride when preparing a positively charged nanofiltration membrane, which helps to form a more uniform and dense separation layer, thereby improving the retention rate and water flux of the positively charged nanofiltration membrane.

[0034] As an example, the aliphatic amine includes, but is not limited to, at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, bis(hexamethylene)triamine and s-triazine.

[0035] S2. Applying an organic solution containing a disulfonyl chloride monomer on the side of the first coating layer away from the base membrane to react and obtain a positively charged nanofiltration membrane.

[0036] In this step, an organic solution containing a disulfonyl chloride monomer is coated on the side of the first coating away from the base membrane, so that the polyamine monomer and the disulfonyl chloride monomer can contact each other, and the amino groups in the polyamine and the sulfonyl chloride groups in the disulfonyl chloride undergo interfacial polymerization reaction at the interface, thereby obtaining a uniform and dense positively charged nanofiltration membrane.

[0037] There is no particular limitation on the reaction temperature and reaction time, and those skilled in the art can flexibly select them as needed. According to some specific embodiments of the present invention, the reaction temperature can be 25° C.-60° C., and the reaction time can be 30 s-10 min.

[0038] As an example, the reaction temperature can be 25°C, 30°C, 40°C, 50°C, 60°C, etc.; the reaction time can be 30s, 1min, 3min, 5min, 8min, 10min, etc.

[0039] According to some specific embodiments of the present invention, based on the total mass of the organic solution, the mass proportion of the disulfonyl chloride monomer is 0.1% to 1%. For example, it can be 0.1%, 0.3%, 0.5%, 0.7%, 1%, etc. By limiting the mass proportion of the disulfonyl chloride monomer to the above range, on the one hand, the reaction rate between the polyamine monomer in the aqueous phase and the disulfonyl chloride monomer in the oil phase can be controlled. On the other hand, the amount of consumed amino groups can be controlled to ensure sufficient positive charge, and a positively charged nanofiltration membrane with high retention rate and high water flux can be prepared. Further, based on the total mass of the organic solution, the mass proportion of the disulfonyl chloride monomer can preferably be 0.1% to 0.5%.

[0040] According to some specific embodiments of the present invention, the binary sulfonyl chloride monomer includes at least one of 1,2-benzenedisulfonyl chloride, 1,3-benzenedisulfonyl chloride and 1,4-benzenedisulfonyl chloride. By selecting at least one of 1,2-benzenedisulfonyl chloride, 1,3-benzenedisulfonyl chloride and 1,4-benzenedisulfonyl chloride as the binary sulfonyl chloride monomer, the binary sulfonyl chloride monomer can form a cross-linked network and improve the interception rate compared with the monosulfonyl chloride during the reaction process. At the same time, compared with the ternary or more ternary sulfonyl chloride monomers, a large amount of acyl chloride groups will not remain after the interfacial polymerization is completed, and then hydrolyze to generate carboxyl groups with negative charge properties, which is conducive to obtaining an acid-resistant positively charged nanofiltration membrane with high positive charge.

[0041] According to some specific embodiments of the present invention, the solvent of the organic solution includes at least one of n-hexane, ethylcyclohexane and isoparaffin. By selecting at least one of n-hexane, ethylcyclohexane and isoparaffin as the solvent of the organic solution, the solvent has high volatility and can evaporate quickly after the reaction is completed, thereby helping to form a dry, dense, positively charged nanofiltration membrane.

[0042] According to some specific embodiments of the present invention, the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is (5-30):1. For example, it can be 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, etc. By limiting the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution within the above range, the polyamine monomer in the aqueous phase and the disulfonyl chloride monomer in the oil phase can fully react, which can give the positively charged nanofiltration membrane good positive charge, so that it can effectively intercept positively charged ions or molecules. If the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is too small, the number of residual amine groups will be insufficient, resulting in insufficient positive charge, which affects the charge and interception performance of the positively charged nanofiltration membrane. On the other hand, a uniform and dense separation layer can be formed, which can effectively intercept the target substance. If the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is too large, it may lead to insufficient reaction, uneven separation layer structure or defects, thereby reducing the retention performance of the positively charged nanofiltration membrane. Further, the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution can be preferably (10-20):1.

[0043] According to the preparation method of the above embodiment of the present invention, by coating an aqueous solution containing a polyamine monomer on at least part of the surface of the base film, a uniform and tight first coating layer can be formed, ensuring good contact between the polyamine monomer and the base film, and coating an organic solution containing a disulfonyl chloride monomer on the side of the first coating layer away from the base film, so that the polyamine monomer and the disulfonyl chloride monomer can be in close contact, and the amino groups in the polyamine and the sulfonyl chloride groups in the disulfonyl chloride undergo interfacial polymerization at the interface, and the polyamine monomer will leave some unreacted amino groups in the reaction, and the residual amino groups will undergo protonation in the presence of water, and combine with hydrogen ions to form positively charged ammonium ions, which can enhance the positive charge of the positively charged nanofiltration membrane and improve the interception rate of the positively charged nanofiltration membrane for positively charged substances. Further, the method provided by the present application has a simple preparation process, the prepared positively charged nanofiltration membrane has good acid resistance, and the process steps are consistent with the traditional positively charged nanofiltration membrane, and no new process steps need to be introduced, which is convenient for industrialized mass production. Therefore, the positively charged nanofiltration membrane prepared by the method provided in the present application has a higher retention rate and water flux.

[0044] In the second aspect of the present invention, the present invention provides a positively charged nanofiltration membrane. According to an embodiment of the present invention, the positively charged nanofiltration membrane is prepared by the above-mentioned method. By using the interfacial polymerization reaction of the polyvalent fatty amine monomer and the disulfonyl chloride monomer, the positive charge of the positively charged nanofiltration membrane is further improved by using the residual amino group of the polyvalent amine, thereby improving the rejection rate of the positively charged nanofiltration membrane for positively charged substances. As a result, the positively charged nanofiltration membrane has a higher rejection rate and water flux.

[0045] The scheme of the present disclosure will be explained below in conjunction with the examples. Those skilled in the art will appreciate that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific techniques or conditions are not indicated in the examples, the techniques or conditions described in the literature in this area or the product instructions are used. Where the manufacturers of reagents or instruments are not indicated, they are all conventional products that can be obtained commercially.

[0046] Example 1

[0047] 1. Dissolve diethylenetriamine in water to prepare an aqueous solution, wherein the mass proportion of diethylenetriamine is 2%, and then dip the cleaned polysulfone ultrafiltration base membrane in the aqueous solution, and use an air knife to blow dry excess water on the surface to obtain a first coating;

[0048] 2. Dissolve 1,3-benzenedisulfonyl chloride in isoparaffin to prepare an organic solution, wherein the mass proportion of 1,3-benzenedisulfonyl chloride is 0.1%. Then immerse the polysulfone ultrafiltration base membrane containing the first coating obtained in step 1 in the organic solution, react at a temperature of 30°C for 5 minutes, take out and place in deionized water, wash away excess oil phase, and obtain a positively charged nanofiltration membrane.

[0049] Example 2

[0050] 1. Dissolve diethylenetriamine in water to prepare an aqueous solution, wherein the mass proportion of diethylenetriamine is 8%, and then dip the cleaned polysulfone ultrafiltration base membrane in the aqueous solution, and use an air knife to blow dry excess water on the surface to obtain a first coating;

[0051] 2. Dissolve 1,3-benzenedisulfonyl chloride in isoparaffin to prepare an organic solution, wherein the mass proportion of 1,3-benzenedisulfonyl chloride is 0.4%. Then immerse the polysulfone ultrafiltration base membrane containing the first coating obtained in step 1 in the organic solution, react at a temperature of 30°C for 5 minutes, take out and place in deionized water, wash away excess oil phase, and obtain a positively charged nanofiltration membrane.

[0052] Example 3

[0053] 1. Dissolve s-triazine in water to prepare an aqueous solution, in which the mass proportion of s-triazine is 5%, then dip the cleaned polysulfone ultrafiltration base membrane in the aqueous solution, and use an air knife to blow dry excess water on the surface to obtain a first coating;

[0054] 2. Dissolve 1,4-benzenedisulfonyl chloride in isoparaffin to prepare an organic solution, wherein the mass proportion of 1,4-benzenedisulfonyl chloride is 0.5%, and then immerse the polysulfone ultrafiltration base membrane containing the first coating obtained in step 1 in the organic solution, react at a temperature of 30°C for 5 minutes, take out and place in deionized water, wash away excess oil phase, and obtain a positively charged nanofiltration membrane.

[0055] Example 4

[0056] 1. Dissolve triethylenetetramine in water to prepare an aqueous solution, wherein the mass proportion of triethylenetetramine is 4%, and then dip the cleaned polysulfone ultrafiltration base membrane in the aqueous solution, and use an air knife to blow dry excess water on the surface to obtain a first coating;

[0057] 2. Dissolve 1,4-benzenedisulfonyl chloride in isoparaffin to prepare an organic solution, wherein the mass proportion of 1,4-benzenedisulfonyl chloride is 0.2%. Then immerse the polysulfone ultrafiltration base membrane containing the first coating obtained in step 1 in the organic solution, react at a temperature of 30°C for 5 minutes, take out and place in deionized water, wash away excess oil phase, and obtain a positively charged nanofiltration membrane.

[0058] The positively charged nanofiltration membranes of Examples 5-9 are the same as those of Example 1 except for some experimental parameters.

[0059] Some experimental parameters of the positively charged nanofiltration membranes of Examples 1-9 are shown in Table 1.

[0060] Table 1

[0061]

[0062] Comparative Example 1

[0063] 1. Dissolve anhydrous piperazine in water to prepare an aqueous solution, wherein the mass proportion of anhydrous piperazine is 2%, and then dip the cleaned polysulfone ultrafiltration base membrane into the aqueous solution, and use an air knife to blow off excess water on the surface to obtain a first coating;

[0064] 2. Dissolve 1,3,6-naphthalenetrisulfonyl chloride in isoparaffin to prepare an organic solution, wherein the mass proportion of 1,3,6-naphthalenetrisulfonyl chloride is 0.1%, and then immerse the polysulfone ultrafiltration base membrane containing the first coating obtained in step 1 in the organic solution, take it out and place it in deionized water, wash away the excess oil phase, and obtain a positively charged nanofiltration membrane.

[0065] Testing and analysis

[0066] Under the same conditions, the positively charged nanofiltration membranes obtained in the above Examples 1-9 and Comparative Example 1 were subjected to Zeta potential test, water flux test and magnesium sulfate retention rate test respectively. The specific test methods are as follows:

[0067] Zeta potential test: The solid surface streaming potential test system (SurPASS) was used to test the Zeta potential of the positively charged nanofiltration membrane surface, and the size of the Zeta potential of the membrane surface was measured at pH = 7.

[0068] Water flux test: Under certain test conditions, the water production per unit membrane area per unit time (L / m 2 ·h). Specifically, at 25°C and 0.7MPa, a commercial triple high-pressure flat membrane device was used for measurement. The specific test steps refer to the national standard GB / T 34242-2017 to obtain the water flux (F) of the positively charged nanofiltration membrane;

[0069] The calculation formula of water flux (F) is: Where F is the water flux, the unit is L / (m 2 ·h); V is the volume of permeate collected in time t, in L; A is the effective membrane area, in m 2 ; t is the time taken to collect the permeation of volume V, in hours. Average water flux of nanofiltration membrane sample It is the arithmetic mean of the water flux of each sample.

[0070] Magnesium sulfate retention rate test: Under certain test conditions, the magnesium sulfate concentration in the influent (C f ) and the magnesium sulfate concentration in the produced water (C p ) divided by the influent magnesium sulfate concentration:

[0071]

[0072] Specifically, at 25° C. and 0.7 MPa, a commercial triple high-pressure flat membrane device was used for measurement. The specific test steps were referred to the national standard GB / T 34242-2017 to obtain the retention rate of the positively charged nanofiltration membrane.

[0073] The test results are shown in Table 2.

[0074] Table 2

[0075] Zeta potential (mV) <![CDATA[Water flux (L / m 2 ·h)]]> Magnesium sulfate retention rate (%) Example 1 17 27.4 96.4 Example 2 21 26.8 97.2 Example 3 15 28.9 96.7 Example 4 24 26.3 97.0 Example 5 13 28.4 96.2 Example 6 27 27.3 95.2 Example 7 18 25.4 97.9 Example 8 19 27.2 96.5 Example 9 21 28.3 95.9 Comparative Example 1 -25 25.2 95.8

[0076] Combining Table 1 and Table 2, it can be seen that compared with Comparative Example 1, the positively charged nanofiltration membranes obtained in Examples 1-9 all have obvious positive charge, and the flux and retention rate are improved to a certain extent, while Comparative Example 1 is a conventional nanofiltration membrane with normal negative charge.

[0077] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", "some implementation schemes" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0078] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a positively charged nanofiltration membrane, characterized in that: include: coating an aqueous solution containing a polyamine monomer on at least a portion of the surface of the base film to obtain a first coating; An organic solution containing a disulfonyl chloride monomer is coated on the side of the first coating layer away from the base membrane to react and obtain a positively charged nanofiltration membrane.

2. The preparation method according to claim 1, characterized in that: The base film includes at least one of a polysulfone film, a polyethersulfone film, and a polyacrylonitrile film.

3. The preparation method according to claim 1, characterized in that: The ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is (5-30):1; Optionally, the ratio of the mass proportion of the polyamine monomer in the aqueous solution to the mass proportion of the disulfonyl chloride monomer in the organic solution is (10-20):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that Based on the total mass of the aqueous solution, the mass proportion of the polyamine monomer is 1% to 10%; Optionally, based on the total mass of the aqueous solution, the mass proportion of the polyamine monomer is 2% to 5%.

5. The preparation method according to any one of claims 1 to 3, characterized in that: Based on the total mass of the organic solution, the mass proportion of the disulfonyl chloride monomer is 0.1% to 1%; Optionally, based on the total mass of the organic solution, the mass proportion of the disulfonyl chloride monomer is 0.1% to 0.5%.

6. The preparation method according to any one of claims 1 to 3, characterized in that: The polyamine monomer includes aliphatic amines.

7. The preparation method according to claim 6, characterized in that: The fatty amine includes at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, bis(hexamethylene)triamine and s-triazine.

8. The preparation method according to any one of claims 1 to 3, characterized in that The disulfonyl chloride monomer includes at least one of 1,2-benzenedisulfonyl chloride, 1,3-benzenedisulfonyl chloride and 1,4-benzenedisulfonyl chloride.

9. The preparation method according to any one of claims 1 to 3, characterized in that: The organic solvent of the organic solution includes at least one of n-hexane, ethylcyclohexane and isoparaffin.

10. A positively charged nanofiltration membrane, characterized in that: The positively charged nanofiltration membrane is prepared by the method described in any one of claims 1-9.

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