An antifouling nanofiltration membrane, its preparation method and applications

Abstract

This invention relates to an antifouling nanofiltration membrane, its preparation method, and its applications. The preparation method includes: (1) mixing and dissolving a membrane-forming material and an organic solvent to obtain a casting solution; sequentially performing membrane formation and phase inversion on a substrate material using the casting solution to obtain a substrate membrane; (2) performing interfacial polymerization on the substrate membrane obtained in step (1) using a reactive aqueous phase and a reactive oil phase to obtain a nanofiltration membrane; a modifier, including polyethylene oxide, is added to the reactive aqueous phase. The nanofiltration membrane provided by this invention has advantages such as high pure water flux, good surface hydrophilicity, and strong antifouling performance. It can operate stably for a long time, and the preparation method is simple, which is beneficial for industrial applications.

Description

Technical Field

[0001] This invention relates to the field of water treatment membrane materials, specifically to an antifouling nanofiltration membrane, its preparation method, and its applications. Background Technology

[0002] Due to the scarcity of freshwater resources and the continuous increase in industrial water consumption, the proportion of water costs in total industrial production costs is constantly rising, limiting the development of water-intensive industrial manufacturing. Therefore, how to conserve water and recycle water resources is an important research direction at present.

[0003] Membrane water treatment technology is a highly efficient and environmentally friendly water treatment technology that has been widely researched and applied in my country in recent years. This technology utilizes special membrane materials to separate harmful substances from water through physical or chemical methods, achieving water purification. Membrane water treatment technology has advantages such as simple operation, high efficiency, small footprint, and good water quality, and can effectively solve the problems of water scarcity and water pollution in my country.

[0004] Research on membrane-based water treatment technology mainly focuses on the development of membrane materials, optimization of membrane processes, and control of membrane fouling. With the continuous advancement of materials science and membrane technology, new membrane materials and processes are constantly emerging, such as nanofiltration, reverse osmosis, and ultrafiltration. These new membrane materials and processes offer higher filtration efficiency, better anti-fouling performance, and longer service life, providing strong support for the development of membrane-based water treatment technology. Theoretically, membrane-based water treatment technology is based on the principle of molecular sieves, using the selective separation effect of membranes to separate harmful substances from water. In this process, factors such as the properties of the membrane material, the design of the membrane process, and operating conditions all affect the treatment effect. Therefore, for different application scenarios and water treatment needs, it is necessary to select appropriate membrane materials and processes and optimize operating conditions to achieve efficient and stable water treatment results.

[0005] Nanofiltration membranes, as a key technology in membrane-based water treatment, have broad application prospects in seawater desalination pretreatment and zero-discharge of industrial wastewater due to their excellent selective separation capabilities. Traditional nanofiltration membranes, similar to reverse osmosis membranes, are mainly composed of a polyester nonwoven fabric support layer, a polysulfone / polyethersulfone base layer, and a polyamide separation layer. Unlike reverse osmosis membranes, the separation layer structure of nanofiltration membranes is primarily composed of semi-aromatic polyamides, mainly polymerized from piperazine (PIP) and acyl chlorides through interfacial polymerization. Therefore, its separation layer has a relatively low degree of cross-linking, and its separation capability is significantly affected by surface charge, exhibiting remarkable selective separation ability. However, traditional nanofiltration membranes often suffer from drawbacks such as low flux and poor fouling resistance, resulting in high operating costs for membrane systems in industrial applications and severely hindering their wider application.

[0006] Therefore, providing a nanofiltration membrane with good flux and antifouling properties is a technical problem that needs to be solved in this field. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an antifouling nanofiltration membrane, its preparation method and application. Compared with the existing technology, the nanofiltration membrane provided by this invention has the advantages of high pure water flux, good surface hydrophilicity and strong antifouling performance. It can operate stably for a long time, and the preparation method is simple, which is conducive to industrial application.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing an antifouling nanofiltration membrane, the method comprising the following steps:

[0010] (1) Mix the film-forming material and the organic solvent and dissolve them to obtain a casting solution; then apply the casting solution to the substrate material to form a film and undergo phase transformation to obtain a substrate film.

[0011] (2) Interfacial polymerization is carried out on the substrate membrane obtained in step (1) using the aqueous and oil phases to obtain a nanofiltration membrane;

[0012] A modifier, including polyethylene oxide, is added to the aqueous phase of the reaction.

[0013] In the preparation method provided by this invention, a separation layer is prepared on the bottom membrane by interfacial polymerization. Polyethylene oxide (PEO) is introduced into the aqueous reaction phase of the interfacial polymerization, which enables the interfacial polymerization process to enter a thermodynamically unstable state, resulting in the formation of a large number of regular Turing structures on the membrane surface. The presence of this structure can significantly improve the surface roughness of the membrane, thereby increasing the effective area of ​​the membrane and thus improving the flux. Furthermore, polyethylene oxide itself is non-toxic and does not participate in the reaction, so it has little impact on the density of the polyamide layer. Its longer polymer chains are embedded in the membrane surface by the polymerization reaction, thereby enhancing the hydrophilicity of the membrane and improving flux and antifouling properties.

[0014] Preferably, the film-forming material in step (1) includes any one or a combination of at least two of polysulfone, polyethersulfone, or polyvinyl chloride.

[0015] In this invention, the weight-average molecular weight of the polysulfone is generally 60,000-80,000 Da, for example, it can be 60,000 Da, 65,000 Da, 70,000 Da, 75,000 Da or 80,000 Da, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; the weight-average molecular weight of the polyethersulfone is 50,000-200,000 Da, for example, it can be 50,000 Da, 100,000 Da, 150,000 Da or 200,000 Da, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; the molecular weight of the polyvinyl chloride is 50,000-110,000 Da, for example, it can be 50,000 Da, 60,000 Da, 80,000 Da, 100,000 Da or 110,000 Da, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0016] Preferably, the mass percentage of film-forming material in the casting solution is 15-20%, for example, it can be 15%, 16%, 17%, 18%, 19% or 20%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the organic solvent in step (1) includes any one or a combination of at least two of N,N dimethylformamide, N,N dimethylacetamide or dimethyl sulfoxide.

[0018] Preferably, the dissolution temperature in step (1) is 60-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the dissolution time is 6-8 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, stirring is performed during the dissolution process.

[0021] Preferably, after dissolution, the mixture is further kept at a constant temperature and allowed to stand for degassing.

[0022] Preferably, the film-forming process in step (1) includes: using the casting solution to perform a doctor blade coating on the surface of the substrate material to form a film.

[0023] Preferably, the phase transformation process includes: immersing the substrate material after film formation in a coagulation bath to obtain a base film.

[0024] Preferably, the substrate material comprises a nonwoven fabric.

[0025] In this invention, the nonwoven fabric may be, for example, a polyester nonwoven fabric.

[0026] Preferably, the coagulation bath comprises water.

[0027] Preferably, N,N dimethylformamide is also added to the coagulation bath.

[0028] Preferably, the mass percentage of N,N-dimethylformamide in the coagulation bath is ≤5%, for example, it can be 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5% or 1%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the aqueous phase of the reaction in step (2) includes a water-soluble monomer, polyethylene oxide, and water.

[0030] Preferably, the water-soluble monomer includes piperazine.

[0031] Preferably, the mass percentage of water-soluble monomers in the aqueous reaction phase is 0.5-2%, for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the mass percentage of polyethylene oxide in the aqueous reaction phase is 0.1-2%, for example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] In this invention, by optimally controlling the mass percentage of polyethylene oxide in the aqueous reaction phase, the viscosity of the aqueous reaction phase can be effectively controlled, thereby regulating the diffusion rate of PIP during interfacial polymerization.

[0034] Preferably, the reaction oil phase in step (2) includes an oil-soluble monomer and an organic solvent.

[0035] Preferably, the oil-soluble monomer includes pyromellitic acid trimethylolpropionate chloride and / or terephthaloyl chloride.

[0036] Preferably, the organic solvent in step (2) includes any one or a combination of at least two of n-hexane, n-heptane, isoalkanes E or G.

[0037] Preferably, the mass percentage of oil-soluble monomers in the reaction oil phase is 0.01-0.15%, for example, it can be 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14% or 0.15%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the interfacial polymerization process in step (2) includes: contacting the side of the bottom membrane containing the film-forming material with the aqueous reaction phase for 30-120s, for example, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s or 120s, but not limited to the listed values, and other unlisted values ​​within the range are also applicable, and then removing the excess aqueous reaction phase; then contacting the side that has been in contact with the aqueous reaction phase with the oil reaction phase for 30-120s, for example, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s or 120s, but not limited to the listed values, and other unlisted values ​​within the range are also applicable, and then removing the excess oil reaction phase, and finally performing heat treatment to obtain the nanofiltration membrane.

[0039] Preferably, the heat treatment temperature is 40-60℃, for example, it can be 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, 52℃, 54℃, 56℃, 58℃ or 60℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0040] In this invention, the heat treatment time generally needs to be selected according to the type of organic solvent used.

[0041] As a preferred embodiment of the first aspect of the present invention, the preparation method includes the following steps:

[0042] (1) Mix the film-forming material and organic solvent and stir to dissolve at a temperature of 60-80℃ for 6-8 hours. The film-forming material includes any one or a combination of at least two of polysulfone, polyethersulfone, or polyvinyl chloride. The organic solvent includes any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide. Then, keep the mixture at a constant temperature and allow it to stand to remove bubbles to obtain a casting solution. The mass percentage of the film-forming material in the casting solution is 15-20%. Apply the casting solution to the surface of a nonwoven fabric using a doctor blade to form a film. Then, immerse the fabric in a coagulation bath to obtain a base film.

[0043] (2) Interfacial polymerization is carried out on the substrate film obtained in step (1) using an aqueous reaction phase and an oil reaction phase. The aqueous reaction phase includes piperazine, polyethylene oxide, and water. The mass percentage of piperazine in the aqueous reaction phase is 0.5-2%, and the mass percentage of polyethylene oxide is 0.1-2%. The oil reaction phase includes an oil-soluble monomer and an organic solvent. The oil-soluble monomer includes trimesoyl chloride and / or terephthaloyl chloride, and the organic solvent includes n-hexane, n-heptane, isoalkanes E, or isoalkanes. The membrane comprises any one or at least two of hydrocarbons G, wherein the mass percentage of oil-soluble monomers in the reaction oil phase is 0.01-0.15%, and the interfacial polymerization process includes: contacting the side of the bottom membrane containing the film-forming material with the reaction aqueous phase for 30-120 seconds, and then removing the excess reaction aqueous phase; then contacting the side that has been in contact with the reaction aqueous phase with the reaction oil phase for 30-120 seconds, and then removing the excess reaction oil phase; and finally performing heat treatment at a temperature of 40-60℃ to obtain a nanofiltration membrane.

[0044] In a second aspect, the present invention provides an antifouling nanofiltration membrane, which is obtained by the preparation method of the antifouling nanofiltration membrane described in the first aspect of the present invention.

[0045] The antifouling nanofiltration membrane provided by this invention has a large number of regular Turing structures on the surface of the polyamide separation layer, which has high surface roughness and strong hydrophilicity, thus improving its flux and antifouling properties. Furthermore, the surface structure is stable, enabling long-term stable operation.

[0046] Thirdly, the present invention provides an application of the antifouling nanofiltration membrane as described in the second aspect of the present invention, wherein the antifouling nanofiltration membrane is used in the field of water treatment.

[0047] The antifouling nanofiltration membrane provided by this invention can be used in the field of water treatment, and can give full play to its advantages of flux and hydrophilicity. It has good antifouling properties and has broad application prospects.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) In the preparation method provided by the present invention, by introducing polyethylene oxide into the reaction aqueous phase used for interfacial polymerization, on the one hand, the interfacial polymerization process can be thermodynamically unstable, thereby forming a large number of regular Turing structures on the membrane surface, which can significantly improve the surface roughness of the membrane, increase the effective area of ​​the membrane, and thus improve the flux; on the other hand, polyethylene oxide itself is non-toxic and does not participate in the reaction, so it has little effect on the density of the polyamide separation layer, and its long polymer chain segments will be embedded in the membrane surface by the polymerization reaction, thereby enhancing its hydrophilicity and further improving its flux and antifouling properties.

[0050] (2) The polyethylene oxide modifier used in the preparation method provided by the present invention is green and environmentally friendly, and inexpensive, which is conducive to industrial application.

[0051] (3) The antifouling nanofiltration membrane provided by the present invention has the advantages of good hydrophilicity, strong antifouling properties and stable surface structure, and can operate stably for a long time. It has broad application prospects in the field of water treatment.

[0052] (4) Specifically, taking the membrane separation performance test of Na2SO4 as an example, under optimal conditions, the Na2SO4 flux of the nanofiltration membrane provided by this invention can reach 61.9 L / (m²). 2 With a pressure of ·h·MPa or above, the Na2SO4 retention rate reaches over 92.64%. Taking the antifouling performance test of bovine serum albumin as an example, the flux decline rate reaches below 9.30%, and the flux recovery rate reaches over 88.33%. Attached Figure Description

[0053] Figure 1 This is a comparison of the Fourier transform infrared spectra of Embodiment 7 and Comparative Example 1 of the present invention;

[0054] Figure 2 This is a SEM image of the nanofiltration membrane surface provided in Embodiment 7 of the present invention;

[0055] Figure 3 This is a SEM image of the nanofiltration membrane surface provided in Comparative Example 1 of the present invention. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] Example 1

[0058] This embodiment provides a method for preparing an antifouling nanofiltration membrane, the method comprising the following steps:

[0059] (1) Mix polysulfone (molecular weight 60000-70000 Da, manufacturer: Solvay, USA) and N,N'-dimethylformamide and stir to dissolve at 60°C for 7 hours. Then keep it at the temperature and let it stand to remove bubbles to obtain a casting solution. The mass percentage of polysulfone in the casting solution is 18%. The casting solution is coated onto the surface of a polyester nonwoven fabric by a doctor blade to form a film. Then it is immersed in a coagulation bath, which includes water and N,N'-dimethylformamide. The mass percentage of N,N'-dimethylformamide in the coagulation bath is 4% to obtain a base film.

[0060] (2) Piperazine, polyethylene oxide (molecular weight 50000 Da, manufacturer: BASF, Germany) and water are used as the aqueous reaction phase, wherein the mass percentage of piperazine is 2% and the mass percentage of polyethylene oxide is 0.1%. Tristyrene chloride and n-hexane are used as the oil reaction phase, wherein the mass percentage of tristyrene chloride is 0.15%. Interfacial polymerization is carried out on the substrate membrane obtained in step (1) using the aqueous reaction phase and the oil reaction phase. The interfacial polymerization process includes: holding the substrate membrane with a polytetrafluoroethylene frame and metal clamps, pouring the aqueous phase into the frame so that the side of the substrate membrane containing polysulfone is in contact with the aqueous reaction phase for 120s, then pouring off the excess aqueous phase, and using a rubber roller to remove the excess aqueous phase from the surface; then pouring the oil reaction phase into the frame so that the side that has been in contact with the aqueous reaction phase is in contact with the oil reaction phase for 60s, then pouring off the excess oil reaction phase, and finally transferring it into an oven at 50°C for heat treatment for 5min to obtain a nanofiltration membrane.

[0061] Example 2

[0062] This embodiment provides a method for preparing an antifouling nanofiltration membrane, the method comprising the following steps:

[0063] (1) Mix polysulfone (molecular weight 60000-70000 Da, manufacturer: Solvay, USA) and N,N'-dimethylformamide and stir to dissolve at 60°C for 6 hours. Then keep it at the temperature and let it stand to remove bubbles to obtain a casting solution. The mass percentage of polysulfone in the casting solution is 20%. The casting solution is coated onto the surface of a polyester nonwoven fabric by a doctor blade to form a film. Then it is immersed in a coagulation bath, which includes water and N,N'-dimethylformamide. The mass percentage of N,N'-dimethylformamide in the coagulation bath is 3% to obtain a base film.

[0064] (2) Piperazine, polyethylene oxide (molecular weight 50000 Da, manufacturer: BASF, Germany) and water are used as the aqueous reaction phase, wherein the mass percentage of piperazine is 0.5% and the mass percentage of polyethylene oxide is 1%. Tristyrene chloride and n-heptane are used as the oil reaction phase, wherein the mass percentage of tristyrene chloride is 0.07%. Interfacial polymerization is carried out on the substrate membrane obtained in step (1) using the aqueous reaction phase and the oil reaction phase. The interfacial polymerization process includes: holding the substrate membrane with a polytetrafluoroethylene frame and metal clamps, pouring the aqueous phase into the frame so that the side of the substrate membrane containing polyethersulfone is in contact with the aqueous reaction phase for 60s, then pouring off the excess aqueous phase, and using a rubber roller to remove the excess aqueous phase from the surface; then pouring the oil reaction phase into the frame so that the side that has been in contact with the aqueous reaction phase is in contact with the oil reaction phase for 120s, then pouring off the excess oil reaction phase, and finally transferring it into an oven at 60°C for heat treatment for 4min to obtain a nanofiltration membrane.

[0065] Example 3

[0066] This embodiment provides a method for preparing an antifouling nanofiltration membrane, the method comprising the following steps:

[0067] (1) Mix polysulfone (molecular weight 60,000-70,000 Da, manufacturer: Solvay, USA) and N,N'-dimethylacetamide and stir to dissolve at 60°C for 8 hours. Then keep it at the temperature and let it stand to remove bubbles to obtain a casting solution. The mass percentage of polysulfone in the casting solution is 15%. The casting solution is coated onto the surface of a polyester nonwoven fabric by a doctor blade to form a film. Then it is immersed in a coagulation bath, which includes water and N,N'-dimethylacetamide. The mass percentage of N,N'-dimethylacetamide in the coagulation bath is 2% to obtain a base film.

[0068] (2) Piperazine, polyethylene oxide (molecular weight 50000 Da, manufacturer: BASF, Germany) and water were used as the aqueous reaction phase, wherein the mass percentage of piperazine was 1.2% and the mass percentage of polyethylene oxide was 2%. Tristyrene chloride and isoparaffin E were used as the oil reaction phase, wherein the mass percentage of tristyrene chloride was 0.02%. Interfacial polymerization was carried out on the substrate membrane obtained in step (1) using the aqueous reaction phase and the oil reaction phase. The interfacial polymerization process included: holding the substrate membrane with a polytetrafluoroethylene frame and metal clamps, pouring the aqueous phase into the frame so that the side of the substrate membrane containing polysulfone was in contact with the aqueous reaction phase for 30s, then pouring off the excess aqueous phase, and using a rubber roller to remove the excess aqueous phase from the surface; then pouring the oil reaction phase into the frame so that the side that had been in contact with the aqueous reaction phase was in contact with the oil reaction phase for 30s, then pouring off the excess oil reaction phase, and finally transferring it into an oven at 40°C for heat treatment for 6min to obtain a nanofiltration membrane.

[0069] Example 4

[0070] This embodiment provides a method for preparing an antifouling nanofiltration membrane. The only difference between this method and Example 1 is that the mass percentage of polyethylene oxide in the aqueous reaction phase is 0.3%.

[0071] Example 5

[0072] This embodiment provides a method for preparing an antifouling nanofiltration membrane. The only difference between this method and Example 1 is that the mass percentage of polyethylene oxide in the aqueous reaction phase is 0.5%.

[0073] Example 6

[0074] This embodiment provides a method for preparing an antifouling nanofiltration membrane. The only difference between this method and Example 1 is that the mass percentage of polyethylene oxide in the aqueous reaction phase is 0.7%.

[0075] Example 7

[0076] This embodiment provides a method for preparing an antifouling nanofiltration membrane. The only difference between this method and Example 1 is that the mass percentage of polyethylene oxide in the aqueous reaction phase is 1%.

[0077] Example 8

[0078] This embodiment provides a method for preparing an antifouling nanofiltration membrane. The only difference between this method and Example 7 is that the mass percentage of polyethylene oxide in the aqueous reaction phase is 3%.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing an antifouling nanofiltration membrane, the only difference from Example 7 being that polyethylene oxide is not added to the aqueous reaction phase.

[0081] Performance testing:

[0082] (1) Membrane separation performance test: A 2 g / L sodium sulfate solution was prepared as the feed liquid, and the separation performance of the prepared nanofiltration membrane was tested using a laboratory-assembled nanofiltration membrane separation performance test device. The conductivity of the feed liquid and the product water was measured using a conductivity meter, and the salt rejection rate of the membrane was calculated. The data of Examples 1-8 are shown in Table 1, and the data of Comparative Example 1 are shown in Table 2.

[0083] (2) Membrane antifouling performance test: 1 g / L bovine serum albumin solution was prepared as feed liquid. The membrane antifouling performance against bovine serum albumin and the performance recovery after rinsing were tested. The results were expressed as flux reduction rate and flux recovery rate. The data of Examples 1-8 are shown in Table 1, and the data of Comparative Example 1 are shown in Table 2.

[0084] Table 1

[0085]

[0086]

[0087] As can be seen from the data in Table 1:

[0088] (1) Data from Examples 1-7 demonstrate that the nanofiltration membrane provided by this invention exhibits excellent separation and antifouling properties. Taking the membrane separation performance test for Na2SO4 as an example, under optimal conditions, the Na2SO4 flux of the nanofiltration membrane provided by this invention can reach 61.9 L / (m²). 2 With a pressure of ·h·MPa or above, the Na2SO4 retention rate reaches over 92.64%. Taking the antifouling performance test of bovine serum albumin as an example, the flux decline rate reaches below 9.30%, and the flux recovery rate reaches over 88.33%.

[0089] (2) The data from Examples 1 and 4-7 show that the salt flux of the membrane gradually increases and tends to stabilize as the concentration of polyethylene oxide in the aqueous reaction phase increases. When the PEO concentration is 1%, both the flux and the rejection rate are good, and the overall performance is the best.

[0090] (3) By comparing Example 1 and Example 8, it can be seen that when PEO is in excess, the viscosity of the reaction aqueous phase is too high, which makes it difficult to remove the excess aqueous phase on the surface, resulting in uneven distribution of the surface aqueous phase, defects in the polyamide layer formed, reduced salt rejection rate, and because the defective parts are more susceptible to fouling, the anti-fouling performance is not ideal. Therefore, the addition of PEO should not be excessive.

[0091] Table 2

[0092]

[0093]

[0094] Taking the comparison between Example 7 and Comparative Example 1 as an example, it can be seen from the data in Table 2 that by adding polyethylene oxide to the aqueous phase of the reaction in Example 7, the Na2SO4 flux in Example 1 reached more than three times that of Comparative Example 1 under the condition of similar Na2SO4 rejection rate, indicating that the antifouling nanofiltration membrane provided by the present invention has excellent membrane separation performance; at the same time, under the same operating conditions, the antifouling performance in Example 7 is significantly better than that in Comparative Example 1, thus it can be seen that the antifouling nanofiltration membrane provided by the present invention also has excellent antifouling performance.

[0095] Based on the above data results, the Fourier transform infrared spectra of the nanofiltration membranes in Example 7 and Comparative Example 1 are compared as follows: Figure 1 As shown, from Figure 1 It can be seen that the addition of polyethylene oxide did not cause any additional peaks or prominent peak intensity changes in the infrared spectrum of the membrane surface. This proves that polyethylene oxide did not participate in the interfacial polymerization and only played a role in regulating the reaction rate during the entire interfacial polymerization process. The SEM images of the nanofiltration membranes obtained in Example 7 and Comparative Example 1 are shown below. Figure 2 and Figure 3 As shown in the figure, it can be seen that the addition of polyethylene oxide in Example 7 can form a regular Turing structure. The appearance of a regular Turing structure is usually considered to be due to the large difference in diffusion rates between the two monomers participating in the reaction at the interface. The SEM image shows that the addition of polyethylene oxide caused a large change in the diffusion rate of the water-soluble monomer piperazine, which further confirms that the preparation method provided by the present invention can improve the separation performance and antifouling performance of nanofiltration membrane by adding polyethylene oxide to the aqueous reaction phase.

[0096] In summary, the nanofiltration membrane provided by this invention has advantages such as high pure water flux, good surface hydrophilicity, and strong antifouling performance. It can operate stably for a long time, and the preparation method is simple, which is conducive to industrial application.

[0097] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an antifouling nanofiltration membrane, characterized in that, The preparation method includes the following steps: (1) Mix the film-forming material and the organic solvent and dissolve them to obtain a casting solution; then apply the casting solution to the substrate material to form a film and perform phase transformation in sequence to obtain a substrate film; (2) Interfacial polymerization is carried out on the substrate membrane obtained in step (1) using the aqueous and oil phases to obtain a nanofiltration membrane; The aqueous phase of the reaction comprises water-soluble monomers, polyethylene oxide, and water; The mass percentage of polyethylene oxide in the aqueous reaction phase is 0.1-2%; The molecular weight of the polyethylene oxide is 50,000 Da.

2. The preparation method according to claim 1, characterized in that, The film-forming material in step (1) includes any one or a combination of at least two of polysulfone, polyethersulfone, or polyvinyl chloride.

3. The preparation method according to claim 1, characterized in that, The mass percentage of film-forming material in the casting solution is 15-20%.

4. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) includes any one or a combination of at least two of N,N dimethylformamide, N,N dimethylacetamide or dimethyl sulfoxide.

5. The preparation method according to claim 1, characterized in that, The dissolution temperature in step (1) is 60-80℃.

6. The preparation method according to claim 1, characterized in that, The dissolution time is 6-8 hours.

7. The preparation method according to claim 1, characterized in that, Stirring is performed during the dissolution process.

8. The preparation method according to claim 1, characterized in that, After dissolution, the mixture is kept at a constant temperature and allowed to stand for degassing.

9. The preparation method according to claim 1, characterized in that, The film-forming process in step (1) includes: using the casting solution to coat the substrate material with a doctor blade to form a film.

10. The preparation method according to claim 1, characterized in that, The phase transformation process includes immersing the substrate material after film formation in a coagulation bath to obtain a base film.

11. The preparation method according to claim 10, characterized in that, The substrate material includes nonwoven fabric.

12. The preparation method according to claim 10, characterized in that, The coagulation bath comprises water.

13. The preparation method according to claim 12, characterized in that, N,N dimethylformamide was also added to the coagulation bath.

14. The preparation method according to claim 13, characterized in that, The mass percentage of N,N-dimethylformamide in the coagulation bath is ≤5%.

15. The preparation method according to claim 1, characterized in that, The water-soluble monomer in step (2) includes piperazine.

16. The preparation method according to claim 1, characterized in that, The mass percentage of water-soluble monomers in the aqueous reaction phase is 0.5-2%.

17. The preparation method according to claim 1, characterized in that, The reaction oil phase in step (2) includes oil-soluble monomers and organic solvents.

18. The preparation method according to claim 17, characterized in that, The oil-soluble monomers include pyromellitic acid trimethylolpropionate chloride and / or terephthaloyl chloride.

19. The preparation method according to claim 17, characterized in that, The organic solvent in step (2) includes any one or a combination of at least two of the following: n-hexane, n-heptane, isoalkanes E or G.

20. The preparation method according to claim 17, characterized in that, The mass percentage of oil-soluble monomers in the reaction oil phase is 0.01-0.15%.

21. The preparation method according to claim 1, characterized in that, The interfacial polymerization process in step (2) includes: contacting the side of the bottom membrane containing the film-forming material with the aqueous reaction phase for 30-120s, and then removing the excess aqueous reaction phase; then contacting the side that has been in contact with the aqueous reaction phase with the oil reaction phase for 30-120s, and then removing the excess oil reaction phase; finally, performing heat treatment to obtain a nanofiltration membrane.

22. The preparation method according to claim 21, characterized in that, The heat treatment temperature is 40-60℃.

23. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix the film-forming material and organic solvent and stir and dissolve them at a temperature of 60-80℃ for 6-8 hours. The film-forming material includes any one or a combination of at least two of polysulfone, polyethersulfone or polyvinyl chloride. The organic solvent includes any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide. Then keep it at a constant temperature and let it stand to remove bubbles to obtain a casting solution. The mass percentage of the film-forming material in the casting solution is 15-20%. Apply the casting solution to the surface of a nonwoven fabric by a doctor blade to form a film. Then immerse it in a coagulation bath to obtain a base film. (2) Interfacial polymerization is carried out on the substrate film obtained in step (1) using an aqueous reaction phase and an oil reaction phase. The aqueous reaction phase includes piperazine, polyethylene oxide, and water. The mass percentage of piperazine in the aqueous reaction phase is 0.5-2%, and the mass percentage of polyethylene oxide is 0.1-2%. The molecular weight of polyethylene oxide is 50,000 Da. The oil reaction phase includes oil-soluble monomers and organic solvents. The oil-soluble monomers include trimesoyl chloride and / or terephthaloyl chloride, and the organic solvents include n-hexane and n-heptane. The reaction oil phase contains any one or a combination of at least two of isoalkane E or isoalkane G, wherein the mass percentage of oil-soluble monomers in the reaction oil phase is 0.01-0.15%, and the interfacial polymerization process includes: contacting the side of the bottom membrane containing the film-forming material with the reaction aqueous phase for 30-120 seconds, and then removing the excess reaction aqueous phase; then contacting the side that has been in contact with the reaction aqueous phase with the reaction oil phase for 30-120 seconds, and then removing the excess reaction oil phase; and finally performing heat treatment at a temperature of 40-60℃ to obtain a nanofiltration membrane.

24. An antifouling nanofiltration membrane, characterized in that, The antifouling nanofiltration membrane is obtained by the preparation method of the antifouling nanofiltration membrane according to any one of claims 1-23.

25. Use of the antifouling nanofiltration membrane as described in claim 24, characterized in that, The antifouling nanofiltration membrane is used in the field of water treatment.

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