Nanofiltration membranes, methods for their preparation and use

Abstract

The application relates to a nanofiltration membrane and a preparation method and application thereof. The preparation method of the nanofiltration membrane comprises the following steps: mixing a polysulfone polymer, guar gum, a soluble calcium salt and a first organic solvent to form a casting solution; mixing an alkali metal carbonate, a hydroxyl-containing polymer and water to form a gel bath; placing the casting solution on the surface of a substrate to form a preformed membrane, then placing the preformed membrane in the gel bath, and obtaining the nanofiltration membrane after reaction. When the nanofiltration membrane formed by the preparation method is applied to dye wastewater treatment, the nanofiltration membrane has high water flux and dye retention rate, and has high permeation performance for inorganic salts.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, in particular to a nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] At present, the finished nanofiltration membrane in the market is basically a polyamide membrane with a negative surface prepared based on an interfacial polymerization method. However, when the polyamide membrane is used to treat dye wastewater, it is difficult to achieve high water flux and inorganic salt permeability while having excellent rejection rate for dyes, and the production cost is high and the production process is complex. Although the phase inversion method can reduce the production cost and simplify the production process, the nanofiltration membrane prepared by the phase inversion method has too large internal pore size and cannot effectively intercept dye molecules. SUMMARY

[0003] Therefore, it is necessary to provide a nanofiltration membrane and a preparation method and application thereof aiming at the above problems. The nanofiltration membrane prepared by the preparation method has excellent rejection rate for dyes while maintaining high water flux and inorganic salt permeability when used to treat dye wastewater.

[0004] The present application provides a preparation method of a nanofiltration membrane, comprising the following steps:

[0005] Mixing a polysulfone-based polymer, guar gum, a soluble calcium salt and a first organic solvent to form a casting solution;

[0006] Mixing an alkali metal carbonate, a hydroxyl-containing polymer and water to form a gel bath;

[0007] Placing the casting solution on the surface of a substrate to form a preformed membrane, and then placing the preformed membrane in the gel bath to obtain a nanofiltration membrane after reaction.

[0008] In an embodiment, the mass fraction of the guar gum in the casting solution is 0.05%-0.15%.

[0009] In an embodiment, the mass ratio of the hydroxyl-containing polymer to the guar gum is 5:1-20:1.

[0010] In an embodiment, the mass fraction of the soluble calcium salt in the casting solution is 0.5%-1.5%.

[0011] In an embodiment, the mass ratio of the alkali metal carbonate to the soluble calcium salt is 3:1-8:1.

[0012] In an embodiment, the soluble calcium salt is selected from calcium chloride;

[0013] and / or, the alkali metal carbonate is selected from sodium carbonate;

[0014] and / or, the hydroxyl-containing polymer is selected from polyvinyl alcohol.

[0015] In one embodiment, the polysulfone-based polymer is a mixture of polysulfone and sulfonated polyether sulfone, and the mass ratio of the polysulfone to the sulfonated polyether sulfone is 3:1-5:1.

[0016] In one embodiment, the gel bath further comprises a second organic solvent.

[0017] A nanofiltration membrane prepared by the method for preparing a nanofiltration membrane as described above.

[0018] Use of the nanofiltration membrane as described above in treatment of dye wastewater.

[0019] In the method for preparing a nanofiltration membrane of the present application, when the preformed membrane is placed in the gel bath, the hydroxyl-containing polymer in the gel bath can cross-link with the guar gum in the preformed membrane, thereby forming a three-dimensional network structure inside the preformed membrane, at the same time, the alkali metal carbonate in the gel bath can react with the soluble calcium salt in the preformed membrane to generate nanoparticle precipitates, which are dispersed and embedded in the three-dimensional network structure as the three-dimensional network structure is formed, thereby forming gaps between the three-dimensional network structure and the nanoparticles, and the generated nanoparticles have high hydrophilicity, thus the water flux of the nanofiltration membrane can be increased. Therefore, when the nanofiltration membrane prepared by the method of the present application is used for treatment of dye wastewater, it has excellent rejection rate for dyes while maintaining high water flux and inorganic salt permeability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A diagram showing the filtration effect of the nanofiltration membrane obtained in Example 1 on dye wastewater. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related examples. However, the present application can be realized in many different forms and is not limited to the examples described herein. On the contrary, the purpose of providing these examples is to make the disclosure of the present application more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0023] It should be noted that the terms "first", "second" involved in the embodiments of the present application are only to distinguish similar objects, and do not represent a specific order of the objects, and the "first", "second" can be interchanged in a specific order or sequence as allowed. It can be understood that the objects distinguished by "first", "second" can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than those described herein.

[0024] The application provides a preparation method of the nanofiltration membrane, comprising the following steps:

[0025] S10, mixing polysulfone polymer, guar gum, soluble calcium salt and first organic solvent to form casting solution;

[0026] S20, mixing alkali metal carbonate, hydroxyl-containing polymer and water to form gel bath;

[0027] S30, placing the casting solution on the surface of the substrate to form a preformed membrane, and then placing the preformed membrane in the gel bath, and obtaining the nanofiltration membrane after the reaction is completed.

[0028] The application does not limit the selection of polysulfone polymer, which can be polysulfone, sulfonated polyether sulfone, polyether sulfone or sulfonated polysulfone, etc. Since polysulfone is a thermoplastic resin containing sulfone group and arylene in the molecular backbone, it is cheap and easy to obtain, the membrane is simple to make, has good mechanical strength, good compression resistance, stable chemical properties, is non-toxic and can resist biological degradation, but its hydrophilicity is not high, and the hydrophilicity of sulfonated polyether sulfone is good. Therefore, in step S10, the polysulfone polymer is preferably a mixture of polysulfone and sulfonated polyether sulfone, so that a nanofiltration membrane with excellent properties such as rigidity, toughness and hydrophilicity can be prepared.

[0029] Further, in order to better form a nanofiltration membrane with excellent properties, in an embodiment, the mass ratio of polysulfone to sulfonated polyether sulfone is 3:1-5:1, and the sulfonation degree of sulfonated polyether sulfone is 30%-40%.

[0030] The application does not limit the selection of soluble calcium salt, which can be calcium chloride, calcium bicarbonate, etc., and is preferably selected from calcium chloride. The selection of the first organic solvent is not limited, and is preferably at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0031] In an embodiment, the mass fraction of the guar gum in the casting solution is 0.05%-0.15%, and the mass fraction of the soluble calcium salt in the casting solution is 0.5%-1.5%.

[0032] In order to make the dissolving process more sufficient, the step S10 of mixing the polysulfone polymer, the guar gum, the soluble calcium salt and the first organic solvent can be carried out under heating, and the heating temperature is 50-90℃.

[0033] In order to reduce the bubbles in the casting solution, so that the preformed membrane has better flatness, in an embodiment, the obtained casting solution is subjected to static defoaming, and the static time is greater than or equal to 24h.

[0034] In the gel bath of the present application, the selection of the alkali metal carbonate and the hydroxyl-containing polymer is not limited, the alkali metal carbonate can be selected from sodium carbonate, potassium carbonate and the like, and the hydroxyl-containing polymer can be selected from polyvinyl alcohol, polypropylene alcohol and the like, in the step S20, the alkali metal carbonate is preferably sodium carbonate, and the hydroxyl-containing polymer is preferably polyvinyl alcohol.

[0035] In order to better make the hydroxyl-containing polymer and the guar gum crosslinking reaction, in an embodiment, the mass ratio of the hydroxyl-containing polymer to the guar gum in the gel bath is 5:1-20:1.

[0036] In order to better generate nanoparticle precipitation, in an embodiment, the mass ratio of the alkali metal carbonate to the soluble calcium salt in the gel bath is 3:1-8:1.

[0037] In an embodiment, the gel bath further comprises a second organic solvent, the second organic solvent does not react in the formation process of the nanofiltration membrane, but can better improve the water flux of the nanofiltration membrane. The present application does not limit the selection of the second organic solvent, and in the step S20, the second organic solvent can be selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and the like.

[0038] It should be noted that the order of the step S10 and the step S20 is not limited, the casting solution can be configured first, and then the gel bath is configured, or the gel bath is configured first, and then the casting solution is configured, or the gel bath and the casting solution are configured together.

[0039] In step S30, since the casting solution contains both guar gum and soluble calcium salt, the preformed membrane formed by placing the casting solution on the surface of the substrate also contains both guar gum and soluble calcium salt, and the gel bath contains alkali metal carbonate and hydroxyl-containing polymer, so when the preformed membrane is placed in the gel bath, the hydroxyl-containing polymer in the gel bath contains a large number of hydroxyl groups, which can crosslink with the hydroxyl groups in the guar gum segment in the preformed membrane, thereby forming a three-dimensional network structure inside the preformed membrane. At the same time, the carbonate ions in the alkali metal carbonate in the gel bath react with the calcium ions in the soluble calcium salt in the preformed membrane to form nanoparticle precipitates, which are dispersed in the three-dimensional network structure as it forms, thereby forming a nanofiltration membrane. The nanoparticle precipitates in the nanofiltration membrane can form gaps between the three-dimensional network structure and the nanoparticles, and the nanoparticles generated at the same time have high hydrophilicity, thereby increasing the water flux of the nanofiltration membrane.

[0040] To better react the gel bath with the guar gum and soluble calcium salt in the preformed membrane, preferably, in the step of placing the preformed membrane in the gel bath, the temperature of the gel bath is preferably 20-30°C.

[0041] In an embodiment, in the step of placing the casting solution on the surface of the substrate, the substrate can be selected to be a glass plate, and after the reaction is completed, the glass plate is peeled off to obtain the nanofiltration membrane. To better increase the strength of the nanofiltration membrane, a non-woven fabric can be first fixed on the glass plate, and then the casting solution is applied to the non-woven fabric, and after the reaction is completed, the glass plate is peeled off to obtain the nanofiltration membrane which also includes a non-woven fabric layer.

[0042] The application also provides a nanofiltration membrane obtained by the method for preparing a nanofiltration membrane as described above, and the application of the nanofiltration membrane in dye wastewater treatment. When the nanofiltration membrane obtained is applied to wastewater treatment, it can maintain high water flux and inorganic salt permeability while having excellent rejection rate for dyes, thereby realizing the separation of dyes and inorganic salts.

[0043] In the following, the nanofiltration membrane, the method for preparing the nanofiltration membrane, and the application of the nanofiltration membrane will be further described through the following specific examples.

[0044] Example 1

[0045] Poly sulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, with the mass ratio of poly sulfone to sulfonated polyether sulfone being 4:1, and then guar gum and calcium chloride were added. N,N-dimethylformamide was used as the solvent to place the mixture in a round flask for stirring and dissolving. The dissolving process was carried out in a 60°C oil bath, and after 7h of dissolving to make the mixture uniformly dissolved, it was poured into a conical flask with a ground stopper for sealing and storage. After 24h of standing, a casting solution was obtained. In the casting solution, the mass fraction of guar gum was 0.1%, and the mass fraction of calcium chloride was 1%.

[0046] The dissolved sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide were added to 30 L of deionized water, stirred uniformly, and the temperature was controlled at 25°C to obtain a gel bath, in which the mass fraction of sodium carbonate was 5%, the mass fraction of polyvinyl alcohol was 1%, and the mass fraction of N,N-dimethylformamide was 3%.

[0047] The non-woven fabric was fixed on a glass plate, and then the casting solution was coated on the non-woven fabric to form a thin film, and then immersed in the gel bath for 4 min. After the reaction was completed, the glass plate was peeled off to obtain the nanofiltration membrane.

[0048] The water flux and the rejection rate of dyes and inorganic salts of the nanofiltration membrane obtained in this example were tested, and the test conditions were as follows: the concentrated water was a mixture of 1 g / L of methyl blue and 10 g / L of sodium sulfate, the test pressure was 0.5 MPa, and the ambient temperature was room temperature. The results are described in Table 1.

[0049] In addition, Figure 1 The filtration effect diagram of this example was tested, and according to Figure 1 It can be seen that the nanofiltration membrane obtained in this example can effectively retain dyes while allowing water and inorganic salts to pass through.

[0050] Comparative Example 1

[0051] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, and the mass ratio of polysulfone to sulfonated polyether sulfone was 4:1. N,N-dimethylformamide was used as a solvent and placed in a round flask for stirring and dissolving. The dissolving process was carried out in a 60°C oil bath, and the solution was poured out after being stirred for 7 h to store in a conical flask with a ground stopper and sealed for preservation. After standing for 24 h, the casting solution was obtained.

[0052] N,N-dimethylformamide was added to 30 L of deionized water, stirred uniformly, and the temperature was controlled at 25°C to obtain a gel bath, in which the mass fraction of N,N-dimethylformamide was 3%.

[0053] The non-woven fabric was fixed on a glass plate, and then the casting solution was coated on the non-woven fabric to form a thin film, and then immersed in the gel bath for 4 min. After the reaction was completed, the glass plate was peeled off to obtain the nanofiltration membrane.

[0054] The test steps of the nanofiltration membrane obtained in this comparative example were carried out according to Example 1, and the results are described in Table 1.

[0055] Comparative Example 2

[0056] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, with the mass ratio of the polysulfone to the sulfonated polyether sulfone being 4:1, and then guar gum was added, and stirring and dissolution were performed in a round flask with N,N-dimethylformamide as a solvent, the dissolution process was performed in a 60°C oil bath, and after 7h of dissolution to make the solution uniform, the solution was poured into a conical flask with a ground stopper for storage, and after 24h of standing, a casting solution was obtained. In the casting solution, the mass fraction of the guar gum was 0.1%.

[0057] The dissolved polyvinyl alcohol and N,N-dimethylformamide were added to 30L deionized water, and stirring was performed until the temperature was controlled to be 25°C, to obtain a gel bath, in which the mass fraction of the polyvinyl alcohol was 1% and the mass fraction of N,N-dimethylformamide was 3%.

[0058] The non-woven fabric was fixed on a glass plate, and then the casting solution was coated on the non-woven fabric to form a thin film, and then the glass plate was immersed in the gel bath for 4min of reaction, and after the reaction was completed, the glass plate was peeled off to obtain a nanofiltration membrane.

[0059] The test steps of the nanofiltration membrane obtained in the example 1 were performed, and the results are described in Table 1.

[0060] Comparative Example 3

[0061] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, with the mass ratio of the polysulfone to the sulfonated polyether sulfone being 4:1, and then calcium chloride was added, and stirring and dissolution were performed in a round flask with N,N-dimethylformamide as a solvent, the dissolution process was performed in a 60°C oil bath, and after 7h of dissolution to make the solution uniform, the solution was poured into a conical flask with a ground stopper for storage, and after 24h of standing, a casting solution was obtained. In the casting solution, the mass fraction of the calcium chloride was 1%.

[0062] The dissolved polyvinyl alcohol and N,N-dimethylformamide were added to 30L deionized water, and stirring was performed until the temperature was controlled to be 25°C, to obtain a gel bath, in which the mass fraction of the polyvinyl alcohol was 1% and the mass fraction of N,N-dimethylformamide was 3%.

[0063] The non-woven fabric was fixed on a glass plate, and then the casting solution was coated on the non-woven fabric to form a thin film, and then the glass plate was immersed in the gel bath for 4min of reaction, and after the reaction was completed, the glass plate was peeled off to obtain a nanofiltration membrane.

[0064] The test steps of the nanofiltration membrane obtained in the example 1 were performed, and the results are described in Table 1.

[0065] Table 1

[0066]

[0067] According to Table 1, the nanofiltration membrane prepared by the preparation method of the application has excellent rejection rate for dyes while maintaining high water flux and inorganic salt permeability, and from the examples and comparative examples, it can be seen that the three-dimensional network structure formed in the membrane during preparation is beneficial to improve the dye rejection rate, but will affect the permeation of inorganic salt, and the nanoparticles formed in the membrane during preparation are beneficial to increase the water flux of the nanofiltration membrane.

[0068] Example 2

[0069] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% are mixed, wherein the mass ratio of the polysulfone to the sulfonated polyether sulfone is 4:1, then guar gum and calcium chloride are added, and N,N-dimethylformamide is used as a solvent to be stirred and dissolved in a round-bottom flask, the dissolving process is carried out in a 60°C oil bath, and after being dissolved uniformly for 7h, the solution is poured into a conical flask with a ground stopper for sealed storage, and is statically placed for 24h to obtain a casting solution. In the casting solution, the mass fraction of the guar gum is 0.05%, and the mass fraction of the calcium chloride is 1%.

[0070] The dissolved sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide are added to 30L deionized water, stirred uniformly, and the temperature is controlled at 25°C to obtain a gel bath, wherein the mass fraction of the sodium carbonate in the gel bath is 5%, the mass fraction of the polyvinyl alcohol is 1%, and the mass fraction of the N,N-dimethylformamide is 3%.

[0071] The non-woven fabric is fixed on a glass plate, the casting solution is coated on the non-woven fabric to form a thin film, then the thin film is immersed in the gel bath for 4min, and after the reaction is completed, the glass plate is peeled off to obtain the nanofiltration membrane.

[0072] The test steps of the nanofiltration membrane obtained in this example are carried out according to Example 1, and the results are described in Table 2.

[0073] Example 3

[0074] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% are mixed, wherein the mass ratio of the polysulfone to the sulfonated polyether sulfone is 4:1, then guar gum and calcium chloride are added, and N,N-dimethylformamide is used as a solvent to be stirred and dissolved in a round-bottom flask, the dissolving process is carried out in a 60°C oil bath, and after being dissolved uniformly for 7h, the solution is poured into a conical flask with a ground stopper for sealed storage, and is statically placed for 24h to obtain a casting solution. In the casting solution, the mass fraction of the guar gum is 0.15%, and the mass fraction of the calcium chloride is 1%.

[0075] The dissolved sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide are added to 30L deionized water, stirred uniformly, and the temperature is controlled at 25°C to obtain a gel bath, wherein the mass fraction of the sodium carbonate in the gel bath is 5%, the mass fraction of the polyvinyl alcohol is 1%, and the mass fraction of the N,N-dimethylformamide is 3%.

[0076] The non-woven fabric was fixed on a glass plate, and the casting solution was coated on the non-woven fabric to form a thin film, and then immersed in the gel bath for 4 min. After the reaction was completed, the glass plate was peeled off to obtain the nanofiltration membrane.

[0077] The test steps of the nanofiltration membrane obtained in this example were carried out according to Example 1, and the results are described in Table 2.

[0078] Example 4

[0079] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, and the mass ratio of the polysulfone to the sulfonated polyether sulfone was 4:1. Then guar gum and calcium chloride were added. N,N-dimethylformamide was used as a solvent to be placed in a round flask for stirring and dissolving. The dissolving process was carried out in a 60°C oil bath. After being dissolved uniformly for 7 h, it was poured into a conical flask with a ground stopper for sealed storage. After standing for 24 h, the casting solution was obtained. In the casting solution, the mass fraction of guar gum was 0.1%, and the mass fraction of calcium chloride was 1%.

[0080] The dissolved sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide were added to 30 L of deionized water, and stirred uniformly. The temperature was controlled at 25°C to obtain the gel bath. In the gel bath, the mass fraction of sodium carbonate was 5%, the mass fraction of polyvinyl alcohol was 0.5%, and the mass fraction of N,N-dimethylformamide was 3%.

[0081] The non-woven fabric was fixed on a glass plate, and the casting solution was coated on the non-woven fabric to form a thin film, and then immersed in the gel bath for 4 min. After the reaction was completed, the glass plate was peeled off to obtain the nanofiltration membrane.

[0082] The test steps of the nanofiltration membrane obtained in this example were carried out according to Example 1, and the results are described in Table 2.

[0083] Example 5

[0084] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, and the mass ratio of the polysulfone to the sulfonated polyether sulfone was 4:1. Then guar gum and calcium chloride were added. N,N-dimethylformamide was used as a solvent to be placed in a round flask for stirring and dissolving. The dissolving process was carried out in a 60°C oil bath. After being dissolved uniformly for 7 h, it was poured into a conical flask with a ground stopper for sealed storage. After standing for 24 h, the casting solution was obtained. In the casting solution, the mass fraction of guar gum was 0.1%, and the mass fraction of calcium chloride was 1%.

[0085] The dissolved sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide were added to 30 L of deionized water, stirred uniformly, and the temperature was controlled at 25°C to obtain a gel bath. In the gel bath, the mass fraction of sodium carbonate was 5%, the mass fraction of polyvinyl alcohol was 1.5%, and the mass fraction of N,N-dimethylformamide was 3%.

[0086] The non-woven fabric was fixed on a glass plate, the casting solution was coated on the non-woven fabric to form a thin film, and then the glass plate was immersed in the gel bath for 4 min. After the reaction was completed, the glass plate was peeled off to obtain a nanofiltration membrane.

[0087] The test steps of the nanofiltration membrane obtained in this example were carried out according to Example 1, and the results are described in Table 2.

[0088] Example 6

[0089] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, and the mass ratio of the polysulfone to the sulfonated polyether sulfone was 4:1. Then guar gum and calcium chloride were added, and N,N-dimethylformamide was used as a solvent to dissolve and stir in a round-bottom flask. The dissolution process was carried out in a 60°C oil bath for 7 h. After uniform dissolution, the solution was poured into a conical flask with a ground stopper and sealed for storage. After standing for 24 h, a casting solution was obtained. In the casting solution, the mass fraction of guar gum was 0.1%, and the mass fraction of calcium chloride was 1.5%.

[0090] The dissolved sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide were added to 30 L of deionized water, stirred uniformly, and the temperature was controlled at 25°C to obtain a gel bath. In the gel bath, the mass fraction of sodium carbonate was 12%, the mass fraction of polyvinyl alcohol was 1%, and the mass fraction of N,N-dimethylformamide was 3%.

[0091] The non-woven fabric was fixed on a glass plate, the casting solution was coated on the non-woven fabric to form a thin film, and then the glass plate was immersed in the gel bath for 4 min. After the reaction was completed, the glass plate was peeled off to obtain a nanofiltration membrane.

[0092] The test steps of the nanofiltration membrane obtained in this example were carried out according to Example 1, and the results are described in Table 2.

[0093] Example 7

[0094] The polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, and the mass ratio of the polysulfone to the sulfonated polyether sulfone was 4:1. Then guar gum and calcium chloride were added, and N,N-dimethylformamide was used as a solvent to dissolve and stir in a round-bottom flask. The dissolution process was carried out in a 60°C oil bath for 7 h. After uniform dissolution, the solution was poured into a conical flask with a ground stopper and sealed for storage. After standing for 24 h, a casting solution was obtained. In the casting solution, the mass fraction of guar gum was 0.1%, and the mass fraction of calcium chloride was 0.8%.

[0095] Dissolve sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide into 30L deionized water, stir evenly, control the temperature at 25℃, get the gel bath, in the gel bath, the mass fraction of sodium carbonate is 5%, the mass fraction of polyvinyl alcohol is 1%, the mass fraction of N,N-dimethylformamide is 3%.

[0096] Fix the non-woven fabric on the glass plate, then coat the casting solution on the non-woven fabric to form a thin film, then immerse it in the gel bath, react for 4min, after the reaction is completed, peel off the glass plate, get the nanofiltration membrane.

[0097] The test steps of the nanofiltration membrane are carried out according to Example 1, and the results are described in Table 2.

[0098] Example 8

[0099] Mix polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35%, wherein the mass ratio of polysulfone to sulfonated polyether sulfone is 4:1, then add guar gum and calcium chloride, and use N,N-dimethylformamide as the solvent to stir and dissolve in a round-bottom flask, the dissolving process is carried out in a 60℃ oil bath, and after dissolving for 7h, pour out and store in a conical flask with a ground stopper for sealed preservation, stand for 24h, get the casting solution. In the casting solution, the mass fraction of guar gum is 0.1%, and the mass fraction of calcium chloride is 0.5%.

[0100] Dissolve sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide into 30L deionized water, stir evenly, control the temperature at 25℃, get the gel bath, in the gel bath, the mass fraction of sodium carbonate is 1.5%, the mass fraction of polyvinyl alcohol is 1%, the mass fraction of N,N-dimethylformamide is 3%.

[0101] Fix the non-woven fabric on the glass plate, then coat the casting solution on the non-woven fabric to form a thin film, then immerse it in the gel bath, react for 4min, after the reaction is completed, peel off the glass plate, get the nanofiltration membrane.

[0102] The test steps of the nanofiltration membrane are carried out according to Example 1, and the results are described in Table 2.

[0103] Example 9

[0104] Mix polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35%, wherein the mass ratio of polysulfone to sulfonated polyether sulfone is 4:1, then add guar gum and calcium chloride, and use N,N-dimethylformamide as the solvent to stir and dissolve in a round-bottom flask, the dissolving process is carried out in a 60℃ oil bath, and after dissolving for 7h, pour out and store in a conical flask with a ground stopper for sealed preservation, stand for 24h, get the casting solution. In the casting solution, the mass fraction of guar gum is 0.02%, and the mass fraction of calcium chloride is 1%.

[0105] Dissolve sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide into 30L deionized water, stir evenly, control the temperature at 25℃, get the gel bath, in the gel bath, the mass fraction of sodium carbonate is 5%, the mass fraction of polyvinyl alcohol is 0.06%, the mass fraction of N,N-dimethylformamide is 3%.

[0106] Fix the non-woven fabric on the glass plate, then coat the casting solution on the non-woven fabric to form a thin film, then immerse it in the gel bath, react for 4min, after the reaction is completed, peel off the glass plate, get the nanofiltration membrane.

[0107] The test steps of the nanofiltration membrane are carried out according to Example 1, and the results are described in Table 2.

[0108] Example 10

[0109] Mix polysulfone and sulfonated polyether sulfone with a sulfonation degree of 35%, wherein the mass ratio of polysulfone to sulfonated polyether sulfone is 4:1, then add guar gum and calcium chloride, and stir and dissolve in a round flask with N,N-dimethylformamide as a solvent, the dissolving process is carried out in a 60℃ oil bath, and after 7h of dissolving to make it uniformly dissolved, pour it out and store it in a conical flask with a ground stopper for sealing and preservation, and stand for 24h, get the casting solution. In the casting solution, the mass fraction of guar gum is 0.1%, and the mass fraction of calcium chloride is 0.2%.

[0110] Dissolve sodium carbonate, polyvinyl alcohol and N,N-dimethylformamide into 30L deionized water, stir evenly, control the temperature at 25℃, get the gel bath, in the gel bath, the mass fraction of sodium carbonate is 0.5%, the mass fraction of polyvinyl alcohol is 1%, the mass fraction of N,N-dimethylformamide is 3%.

[0111] Fix the non-woven fabric on the glass plate, then coat the casting solution on the non-woven fabric to form a thin film, then immerse it in the gel bath, react for 4min, after the reaction is completed, peel off the glass plate, get the nanofiltration membrane.

[0112] The test steps of the nanofiltration membrane are carried out according to Example 1, and the results are described in Table 2.

[0113] Table 2

[0114]

[0115] From Comparative Examples 1-8 and Example 9, it can be seen that when the mass fraction of guar gum in the casting solution is 0.05%-0.15% and the mass ratio of the polymer containing hydroxyl groups to guar gum is 5:1-20:1, it is beneficial to improve the water flux and dye rejection rate of the nanofiltration membrane and reduce the inorganic salt rejection rate.

[0116] From Comparative Examples 1-9 and Example 10, it can be seen that when the mass fraction of the soluble calcium salt in the casting solution is 0.5%-1.5% and the mass ratio of the alkali metal carbonate to the soluble calcium salt is 3:1-8:1, the water flux and the dye rejection rate of the nanofiltration membrane are improved, and the inorganic salt rejection rate is reduced.

[0117] Example 11

[0118] The polysulfone and the sulfonated polyether sulfone with a sulfonation degree of 35% were mixed, with the mass ratio of the polysulfone to the sulfonated polyether sulfone being 4:1, and then the guar gum and the calcium chloride were added, and the mixture was stirred and dissolved in a round flask with N,N-dimethylformamide as the solvent. The dissolving process was carried out in a 60°C oil bath, and the mixture was stirred and dissolved for 7h. After uniform dissolution, the mixture was poured into a conical flask with a ground stopper and stored after sealing. After standing for 24h, the casting solution was obtained. In the casting solution, the mass fraction of the guar gum was 0.1%, and the mass fraction of the calcium chloride was 1%.

[0119] The sodium carbonate and the polyvinyl alcohol were added to 30L of deionized water, and stirred uniformly to obtain a gel bath, with the mass fraction of the sodium carbonate being 5% and the mass fraction of the polyvinyl alcohol being 1% in the gel bath.

[0120] The non-woven fabric was fixed on a glass plate, and the casting solution was coated on the non-woven fabric to form a thin film. Then the glass plate was immersed in the gel bath for 4min, and after the reaction was completed, the glass plate was peeled off to obtain the nanofiltration membrane.

[0121] The test steps of the nanofiltration membrane were carried out according to Example 1, and the results are described in Table 3.

[0122] Table 3

[0123]

[0124] From Comparative Examples 1-10 and Example 11, it can be seen that the organic solvent in the gel bath can better improve the water flux of the nanofiltration membrane.

[0125] In the above examples and comparative examples, the calculation methods of the membrane water flux and the rejection rate are as follows:

[0126] The membrane water flux (F) is calculated by the amount of fluid passing through a unit area of the positively charged nanofiltration membrane per unit time, and the formula is: F=V / (A×T), wherein V is the volume of water passing through the positively charged nanofiltration membrane per unit time, A is the effective membrane area, and T is the time.

[0127] The rejection rate (R) is the ability of the membrane to prevent a certain component in the feed liquid from passing through or to retain a certain component therein. It is calculated by the concentration of the feed liquid and the concentration of the permeate, and the calculation formula is: R=(1-C1 / C0)×100%, wherein C1 is the concentration of the permeate, and C0 is the concentration of the feed liquid.

[0128] Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, as long as there is no conflict, any combination of the technical features should be considered within the scope of the present disclosure.

[0129] The above-described embodiments only express several implementation manners of the present application, which are described in a more specific and detailed manner, but should not be understood as a limitation on the patent scope of the present application. It should be noted that, for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A method for producing a nanofiltration membrane, characterized by, The method comprises the following steps: mixing polysulfone polymer, guar gum, soluble calcium salt and first organic solvent to form casting solution; mixing alkali metal carbonate, hydroxyl-containing polymer and water to form gel bath; placing the casting solution on the surface of a substrate to form a preformed film, and then placing the preformed film in the gel bath, so that the hydroxyl-containing polymer in the gel bath and the guar gum in the preformed film undergo cross-linking reaction and form three-dimensional network structure inside the preformed film, while the alkali metal carbonate reacts with the soluble calcium salt in the preformed film to form nanoparticle precipitate and disperse in the three-dimensional network structure, and after the reaction, a nanofiltration membrane is obtained, wherein the hydroxyl-containing polymer is selected from polyvinyl alcohol.

2. The method for producing a nanofiltration membrane according to claim 1, characterized by, The mass fraction of the guar gum in the casting solution is 0.05%-0.15%.

3. The method for producing a nanofiltration membrane according to claim 2, characterized by, The mass ratio of the hydroxyl-containing polymer to the guar gum is 5:1-20:

1.

4. The method for producing a nanofiltration membrane according to claim 1, characterized by, The mass fraction of the soluble calcium salt in the casting solution is 0.5%-1.5%.

5. The method for producing a nanofiltration membrane according to claim 4, characterized by, The mass ratio of the alkali metal carbonate to the soluble calcium salt is 3:1-8:

1.

6. The method for producing a nanofiltration membrane according to any one of claims 1 to 5, characterized in that, The soluble calcium salt is selected from calcium chloride. The alkali metal carbonate is selected from sodium carbonate.

7. The method of producing a nanofiltration membrane according to any one of claims 1 to 5, characterized in that, The polysulfone polymer is a mixture of polysulfone and sulfonated polyether sulfone, and the mass ratio of the polysulfone to the sulfonated polyether sulfone is 3:1-5:

1.

8. The method for producing a nanofiltration membrane according to any one of claims 1 to 5, characterized in that, The gel bath further comprises second organic solvent.

9. The nanofiltration membrane prepared by the method of any one of claims 1-8.

10. The application of the nanofiltration membrane of claim 9 in dye wastewater treatment.

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