A method for preparing a crystallization-assisted high-flux nanofiltration membrane

Abstract

The application relates to a preparation method of a crystallization-assisted high-flux nanofiltration membrane, which comprises the following steps: nanofiltration base membrane pretreatment; preparing a salt solution by using sodium hypophosphite; preparing a trans-2,5-dimethylpiperazine solution by using trans-2,5-dimethylpiperazine, mixing the salt solution and the trans-2,5-dimethylpiperazine solution to prepare an aqueous phase solution; mixing 1,3,5-benzene trichloride and a hexane solvent to prepare an organic phase solution; placing the pretreated nanofiltration base membrane into the aqueous phase solution, taking out and drying, then placing into the low-temperature controlled organic phase solution to perform a low-temperature interfacial polymerization reaction, taking out and drying again to obtain the crystallization-assisted high-flux nanofiltration membrane. The method introduces the new aqueous phase monomer trans-2,5-dimethylpiperazine and sodium hypophosphite as an aqueous phase additive, controls the temperature of the organic phase and then controls the interfacial polymerization temperature, and the crystallization-assisted high-flux nanofiltration membrane is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of separation membrane preparation, and particularly relates to a preparation method of a crystallization-assisted high-flux nanofiltration membrane. BACKGROUND

[0002] Nanofiltration membrane technology is a new technology for separating organic matter and inorganic salts with a molecular weight of 200 Da-1000 Da through size screening and Donnan effect. In order to improve the filtration performance of the nanofiltration membrane, people have made many attempts to adjust the physical and chemical properties of the surface of the nanofiltration membrane, such as pore size, surface charge, wettability and roughness. However, due to the limitation of the chain stiffness and inter-chain spacing of the polymer matrix, the polymer-based membrane has inherent limitations of selectivity-permeability compromise. SUMMARY

[0003] Therefore, the present application provides a preparation method of a crystallization-assisted high-flux nanofiltration membrane, which solves the problem of inherent limitations of selectivity-permeability compromise of the polymer-based membrane due to the limitation of the chain stiffness and inter-chain spacing of the polymer matrix in the prior art.

[0004] To this end, the present application provides a preparation method of a crystallization-assisted high-flux nanofiltration membrane, comprising the following steps:

[0005] pretreating the nanofiltration base membrane;

[0006] configuring sodium hypophosphite into a salt solution;

[0007] preparing a water phase solution by mixing the salt solution with a trans-2,5-dimethylpiperazine solution prepared by configuring trans-2,5-dimethylpiperazine;

[0008] preparing an organic phase solution by mixing 1,3,5-benzene tricarbonyl chloride and n-hexane solvent;

[0009] putting the pretreated nanofiltration base membrane into the water phase solution, taking out the nanofiltration base membrane, drying, and then putting into a low-temperature organic phase solution for low-temperature interfacial polymerization reaction, taking out, and drying again to obtain the crystallization-assisted high-flux nanofiltration membrane.

[0010] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the present application, the nanofiltration base membrane is made of polyether sulfone.

[0011] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the present application, the membrane molecular weight cut-off of the nanofiltration base membrane is greater than 50 KDa and less than 150 KDa.

[0012] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the present application, the pretreatment of the nanofiltration base membrane comprises:

[0013] The nanofiltration base film is immersed in deionized water at 15-30℃ for 48-98h, and the deionized water is replaced every 6-12h.

[0014] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the application, the concentration of sodium hypophosphite is 0.01wt%-5.00wt%.

[0015] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the application, the concentration of trans-2,5-dimethylpiperazine is 0.05wt%-1.00wt%.

[0016] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the application, the concentration of 1,3,5-benzene trichloride in the organic phase solution is 0.025wt%-0.25wt%.

[0017] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the application, the pretreated nanofiltration base film is placed in the aqueous phase solution, taken out and dried, and then placed in a low-temperature organic phase solution for a low-temperature interfacial polymerization reaction, and the obtained crystallization-assisted high-flux nanofiltration membrane is dried again, wherein the temperature of the organic phase solution is adjusted to-15℃-20℃.

[0018] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the application, in the step of placing the pretreated nanofiltration base film in the aqueous phase solution, the nanofiltration base film stays in the aqueous phase solution for 2-7min, the interfacial polymerization reaction time is 20-120s, and the drying is roller drying.

[0019] According to the preparation method of the crystallization-assisted high-flux nanofiltration membrane provided by the application, in the step of taking out and drying again to obtain the crystallization-assisted high-flux nanofiltration membrane, the drying time is 0.5-2.5min, and the drying temperature is 20-80℃.

[0020] The application provides a preparation method of a crystallization-assisted high-flux nanofiltration membrane. The application provides a preparation method of a crystallization-assisted high-flux nanofiltration membrane. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.

[0022] Figure 1 FIG. 1 shows a flowchart of a method for preparing a crystallization-assisted high-flux nanofiltration membrane according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present disclosure will be clearly and completely described in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present disclosure.

[0024] As shown in FIG. 1, the present disclosure provides a method for preparing a crystallization-assisted high-flux nanofiltration membrane, which comprises the following steps: Figure 1 As shown in FIG. 1, the present disclosure provides a method for preparing a crystallization-assisted high-flux nanofiltration membrane, which comprises the following steps:

[0025] S1, pretreating a nanofiltration base membrane.

[0026] Optionally, the nanofiltration base membrane is made of polyethersulfone.

[0027] Optionally, the molecular weight cut-off of the nanofiltration base membrane is greater than 50 KDa and less than 150 KDa, for example, the molecular weight cut-off of the nanofiltration base membrane is 80 KDa or 100 KDa.

[0028] Optionally, the pretreatment of the nanofiltration base membrane comprises:

[0029] immersing the nanofiltration base membrane in deionized water at 15-30°C for 48-98h, and replacing the deionized water every 6-12h.

[0030] S2, preparing a salt solution by dissolving sodium hypophosphite.

[0031] Optionally, the concentration of sodium hypophosphite is 0.01wt%-5.00wt%. For example, the concentration of sodium hypophosphite is 0.05wt%, 2wt%, 3wt% or 5.00wt%.

[0032] S3, preparing a trans-2,5-dimethylpiperazine solution by dissolving trans-2,5-dimethylpiperazine, and then mixing the salt solution and the trans-2,5-dimethylpiperazine solution to prepare an aqueous phase solution.

[0033] Optionally, the concentration of trans-2,5-dimethylpiperazine is 0.05wt%-1.00wt%, for example, 0.05wt%, 0.07wt%, 0.08wt% or 1.00wt%.

[0034] S4, mixing 1,3,5-benzene tricarbonyl chloride and n-hexane solvent to prepare an organic phase solution.

[0035] Optionally, the concentration of 1,3,5-benzene tricarbonyl chloride in the organic phase solution is 0.025wt%-0.25wt%, for example, 0.025wt%, 0.125wt%, 0.20wt% or 0.025wt%.

[0036] S5, the pretreated nanofiltration base film is placed in the aqueous phase solution, the nanofiltration base film is taken out, dried and then placed in a low-temperature organic phase solution for a low-temperature interfacial polymerization reaction, taken out and dried again to obtain a crystallization-assisted high-flux nanofiltration membrane.

[0037] Optionally, in step S5, the temperature of the organic phase solution is adjusted to-15℃-20℃.

[0038] Optionally, in the step of placing the pretreated nanofiltration base film in the aqueous phase solution in step S5, the nanofiltration base film stays in the aqueous phase solution for 2min-7min, the interfacial polymerization reaction time is 20s-120s, and the drying is roller drying.

[0039] Optionally, in the step of taking out and drying again to obtain a crystallization-assisted high-flux nanofiltration membrane in step S5, the drying time is 0.5min-2.5min, and the drying temperature is 20℃-80℃.

[0040] Sodium hypophosphite is an inorganic compound, mainly used as a preservative and antioxidant in the food industry. When sodium hypophosphite is added to the aqueous phase solution, the aqueous phase solution is filled with hypophosphite and sodium ions, which slow down the diffusion of the organic phase reactant into the aqueous phase through steric hindrance effect. At the same time, after drying, the solution reaches a supersaturated state, and sodium hypophosphite precipitates on the surface of the base film to form protrusions. After interfacial polymerization, the separation layer formed has an increased specific surface area, thereby improving the permeation flux of the nanofiltration membrane. At the same time, the interfacial polymerization reaction is an exothermic reaction, and when the organic phase temperature is low, not only can the diffusion rate of the oil phase be reduced, but also the reaction rate of the interfacial polymerization can be accelerated, thereby forming a crystallization-assisted high-flux nanofiltration membrane with low thickness and high crosslinking degree. Therefore, the addition of low temperature and sodium hypophosphite has excellent application prospects in the preparation of nanofiltration membranes.

[0041] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0042] Example 1

[0043] A crystallization-assisted high-flux nanofiltration membrane was prepared. The following steps without temperature indication were carried out at room temperature.

[0044] (1) A polyethersulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was immersed in deionized water for pretreatment, and the immersion time was 48 h. The deionized water needed to be replaced every 12 h.

[0045] (2) 0.1 g of sodium hypophosphite was mixed with 99.9 g of deionized water to prepare a salt solution with a sodium hypophosphite concentration of 0.1 wt%.

[0046] (3) 0.2 g of trans-2,5-dimethylpiperazine was mixed with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt%. The salt solution and the trans-2,5-dimethylpiperazine solution were mixed in equal proportions to prepare an aqueous solution with a sodium hypophosphite concentration of 0.05 wt% and a trans-2,5-dimethylpiperazine concentration of 0.1 wt%.

[0047] (4) 0.3 g of 1,3,5-benzene tricarbonyl chloride was mixed with 199.7 g of n-hexane solvent to prepare an organic phase solution with a 1,3,5-benzene tricarbonyl chloride concentration of 0.15 wt%.

[0048] (5) The temperature of the organic phase was adjusted to -5°C; the pretreated polyethersulfone membrane was immersed in the prepared aqueous solution, and after 5 min, it was taken out. The residual water on the surface of the membrane was dried with a rubber roller, and then it was placed in the organic phase solution for interfacial polymerization. After 0.5 min, it was taken out and placed in a constant temperature drying box at 20°C. After 2 min, a crystallization-assisted high-flux nanofiltration membrane was obtained.

[0049] The dried crystallization-assisted high-flux nanofiltration membrane was taken out and sealed in a water environment for measurement. Under a pressure of 0.2 MPa, the performance of the prepared crystallization-assisted high-flux nanofiltration membrane was tested using pure water, a 2000 ppm Na2SO4 aqueous solution, and a 2000 ppm Na2SO4 aqueous solution, respectively. The test results showed that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane was 35.26 L·m-2h-1bar-1, and the rejection rate of the Na2SO4 aqueous solution was 97.46%.

[0050] Example 2

[0051] A crystallization-assisted high-flux nanofiltration membrane was prepared. The following steps without temperature indication were carried out at room temperature.

[0052] (1) A polyethersulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was immersed in deionized water for pretreatment, and the immersion time was 48 h. The deionized water needed to be replaced every 12 h.

[0053] (2) Take 0.1 g of sodium hypophosphite and mix it with 99.9 g of deionized water to prepare a salt solution with a concentration of 0.1 wt% sodium hypophosphite.

[0054] (3) Take 0.2 g of trans-2,5-dimethylpiperazine and mix it with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt% trans-2,5-dimethylpiperazine; mix the salt solution and the trans-2,5-dimethylpiperazine solution in equal proportions to prepare an aqueous phase solution with a concentration of 0.05 wt% sodium hypophosphite and a concentration of 0.1 wt% trans-2,5-dimethylpiperazine.

[0055] (4) Mix 0.3 g of 1,3,5-benzene tricarbonyl chloride and 199.7 g of n-hexane solvent to prepare an organic phase solution with a concentration of 0.15 wt% 1,3,5-benzene tricarbonyl chloride.

[0056] (5) Adjust the temperature of the organic phase to -10°C; immerse the pretreated polyether sulfone membrane in the prepared aqueous phase solution, and take it out after 5 minutes. Dry the residual water on the membrane surface with a rubber roller, then place it in the organic phase solution for interfacial polymerization. Take it out after 0.5 minutes and place it in a constant temperature drying box at 20°C. After 2 minutes, the crystallization-assisted high-flux nanofiltration membrane is obtained.

[0057] Take out the dried crystallization-assisted high-flux nanofiltration membrane and seal it in a water environment for measurement. Under a pressure of 0.2 MPa, test the performance of the prepared crystallization-assisted high-flux nanofiltration membrane using pure water, a 2000 ppm Na2SO4 aqueous solution, and a 2000 ppm Na2SO4 aqueous solution, respectively. The test results show that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane is 37.45 L·m-2h-1bar-1, and the Na2SO4 aqueous solution rejection rate is 96.32%.

[0058] Example 3

[0059] Prepare the crystallization-assisted high-flux nanofiltration membrane. The following steps without temperature specifications are performed at room temperature.

[0060] (1) Soak a polyether sulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa in deionized water for pretreatment. The soaking time is 48 hours, and the deionized water needs to be replaced every 12 hours.

[0061] (2) Take 0.1 g of sodium hypophosphite and mix it with 99.9 g of deionized water to prepare a salt solution with a concentration of 0.1 wt% sodium hypophosphite.

[0062] (3) Take 0.2 g of trans-2,5-dimethylpiperazine and mix with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt% trans-2,5-dimethylpiperazine; mix the salt solution and the trans-2,5-dimethylpiperazine solution in equal proportions to prepare an aqueous phase solution with a concentration of 0.05 wt% sodium hypophosphite and a concentration of 0.1 wt% trans-2,5-dimethylpiperazine.

[0063] (4) Mix 0.3 g of 1,3,5-benzene tricarbonyl chloride and 199.7 g of n-hexane solvent to prepare an organic phase solution with a concentration of 0.15 wt% 1,3,5-benzene tricarbonyl chloride.

[0064] (5) Adjust the temperature of the organic phase to -15°C; immerse the pretreated polyether sulfone membrane in the prepared aqueous phase solution, and take it out after 5 min. Dry the residual water on the membrane surface with a rubber roller, and then place it in the organic phase solution for interfacial polymerization. Take it out after 0.5 min and place it in a constant temperature drying box at 20°C. After 2 min, the crystallization-assisted high-flux nanofiltration membrane is obtained.

[0065] Take out the dried crystallization-assisted high-flux nanofiltration membrane and seal it in a water environment for measurement. Under a pressure of 0.2 MPa, the performance of the prepared crystallization-assisted high-flux nanofiltration membrane is tested with pure water, a 2000 ppm Na2SO4 aqueous solution, and a 2000 ppm Na2SO4 aqueous solution, respectively. The test results show that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane is 39.16 L·m-2h-1bar-1, and the Na2SO4 aqueous solution rejection rate is 96.88%.

[0066] Example 4

[0067] Prepare the crystallization-assisted high-flux nanofiltration membrane. The following steps without temperature specifications are carried out at room temperature.

[0068] (1) Soak a polyether sulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa in deionized water for pretreatment, with a soaking time of 48 h and deionized water changed every 12 h.

[0069] (2) Take 10 g of sodium hypophosphite and mix with 90 g of deionized water to prepare a salt solution with a concentration of 10 wt% sodium hypophosphite.

[0070] (3) Take 0.2 g of trans-2,5-dimethylpiperazine and mix with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt% trans-2,5-dimethylpiperazine; mix the salt solution and the trans-2,5-dimethylpiperazine solution in equal proportions to prepare an aqueous phase solution with a concentration of 5 wt% sodium hypophosphite and a concentration of 0.1 wt% trans-2,5-dimethylpiperazine.

[0071] (4) Mix 0.3 g of 1,3,5-benzene tricarbonyl chloride and 199.7 g of n-hexane solvent to prepare an organic phase solution with a concentration of 0.15 wt% 1,3,5-benzene tricarbonyl chloride.

[0072] (5) Adjust the temperature of the organic phase to -15°C; immerse the pretreated polyether sulfone membrane in the prepared aqueous phase solution, and take it out after 5 min. Dry the residual water on the membrane surface with a rubber roller, and then place it in the organic phase solution for interfacial polymerization. Take it out after 0.5 min and place it in a constant temperature drying box at 20°C. After 2 min, the crystallization-assisted high-flux nanofiltration membrane is obtained.

[0073] Take out the dried crystallization-assisted high-flux nanofiltration membrane and seal it in a water environment for measurement. Under a pressure of 0.2 MPa, the performance of the prepared crystallization-assisted high-flux nanofiltration membrane is tested with pure water, a 2000 ppm Na2SO4 aqueous solution, and a 2000 ppm Na2SO4 aqueous solution, respectively. The test results show that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane is 40.20 L·m-2h-1bar-1, and the Na2SO4 aqueous solution rejection rate is 95.99%.

[0074] Example 5

[0075] Prepare the crystallization-assisted high-flux nanofiltration membrane. The following steps without temperature indication are carried out at room temperature.

[0076] (1) Soak a polyether sulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa in deionized water for pretreatment. The soaking time is 48 h, and the deionized water needs to be replaced every 12 h.

[0077] (2) Take 3 g of sodium hypophosphite and mix with 97 g of deionized water to prepare a salt solution with a concentration of 3 wt% sodium hypophosphite.

[0078] (3) Take 0.2 g of trans-2,5-dimethylpiperazine and mix with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt% trans-2,5-dimethylpiperazine; mix the salt solution and the trans-2,5-dimethylpiperazine solution in equal proportions to prepare an aqueous phase solution with a concentration of 1.5 wt% sodium hypophosphite and a concentration of 0.1 wt% trans-2,5-dimethylpiperazine.

[0079] (4) 0.3 g of 1,3,5-benzene tricarbonyl chloride and 199.7 g of n-hexane solvent were mixed to prepare an organic phase solution with a concentration of 0.15 wt% of 1,3,5-benzene tricarbonyl chloride.

[0080] (5) The temperature of the organic phase was adjusted to -15°C; the pretreated polyether sulfone membrane was immersed in the prepared aqueous phase solution, and after 5 min, it was taken out. The residual moisture on the surface of the membrane was dried with a rubber roller, and then it was placed in the organic phase solution for interfacial polymerization. After 0.5 min, it was taken out and placed in a constant temperature drying box at 20°C, and after 2 min, a crystallization-assisted high-flux nanofiltration membrane was obtained.

[0081] The dried crystallization-assisted high-flux nanofiltration membrane was taken out and sealed in a water environment for measurement. Under a pressure of 0.2 MPa, the performance of the prepared crystallization-assisted high-flux nanofiltration membrane was tested with pure water, a 2000 ppm Na2SO4 aqueous solution, and a 2000 ppm Na2SO4 aqueous solution, respectively. The test results showed that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane was 45.31 L·m-2h-1bar-1, and the rejection rate of the Na2SO4 aqueous solution was 96.83%.

[0082] Comparative Example 1

[0083] A nanofiltration membrane was prepared, and the following steps without temperature indicated were carried out at room temperature.

[0084] (1) A polyether sulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was immersed in deionized water for pretreatment, and the immersion time was 48 h, and the deionized water needed to be replaced every 12 h.

[0085] (2) 3 g of sodium sulfate was mixed with 97 g of deionized water to prepare a salt solution with a concentration of 3 wt% of sodium sulfate.

[0086] (3) 0.2 g of trans-2,5-dimethylpiperazine was mixed with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt% of trans-2,5-dimethylpiperazine; the salt solution and the trans-2,5-dimethylpiperazine solution were mixed in equal proportions to prepare an aqueous phase solution with a concentration of 1.5 wt% of sodium sulfate and a concentration of 0.1 wt% of trans-2,5-dimethylpiperazine.

[0087] (4) 0.3 g of 1,3,5-benzene tricarbonyl chloride and 199.7 g of n-hexane solvent were mixed to prepare an organic phase solution with a concentration of 0.15 wt% of 1,3,5-benzene tricarbonyl chloride.

[0088] (5) The temperature of the organic phase was adjusted to -15°C; the pretreated polyether sulfone membrane was immersed in the prepared aqueous solution, and taken out after 5 min. The residual moisture on the membrane surface was dried with a rubber roller, and then placed in the organic phase solution for interfacial polymerization. It was taken out after 0.5 min and placed in a constant temperature drying box at 20°C. The crystallization-assisted high-flux nanofiltration membrane was obtained after 2 min.

[0089] The dried crystallization-assisted high-flux nanofiltration membrane was taken out and sealed in a water environment for measurement. The performance of the prepared crystallization-assisted high-flux nanofiltration membrane was tested with pure water, 2000 ppm Na2SO4 aqueous solution and 2000 ppm Na2SO4 aqueous solution respectively under a pressure of 0.2 MPa. The test results showed that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane was 40.47 L·m-2h-1bar-1, and the rejection rate of Na2SO4 aqueous solution was 95.14%.

[0090] Comparative Example 2

[0091] The nanofiltration membrane was prepared, and the following steps without temperature indicated were carried out at room temperature.

[0092] (1) A polyether sulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was soaked in deionized water for pretreatment, and the soaking time was 48 h, and the deionized water needed to be replaced every 12 h.

[0093] (2) 3 g of sodium bicarbonate was mixed with 97 g of deionized water to prepare a salt solution with a sodium bicarbonate concentration of 3 wt%.

[0094] (3) 0.2 g of trans-2,5-dimethylpiperazine was mixed with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt%; the salt solution and the trans-2,5-dimethylpiperazine solution were mixed in equal proportions to prepare an aqueous solution with a sodium sulfate concentration of 1.5 wt% and a trans-2,5-dimethylpiperazine concentration of 0.1 wt%.

[0095] (4) 0.3 g of 1,3,5-benzene tricarbonyl chloride was mixed with 199.7 g of n-hexane solvent to prepare an organic phase solution with a 1,3,5-benzene tricarbonyl chloride concentration of 0.15 wt%.

[0096] (5) The temperature of the organic phase was adjusted to -15°C; the pretreated polyether sulfone membrane was immersed in the prepared aqueous solution, and taken out after 5 min. The residual moisture on the membrane surface was dried with a rubber roller, and then placed in the organic phase solution for interfacial polymerization. It was taken out after 0.5 min and placed in a constant temperature drying box at 20°C. The crystallization-assisted high-flux nanofiltration membrane was obtained after 2 min.

[0097] The dried crystallization-assisted high-flux nanofiltration membrane was taken out and sealed in a water environment for measurement. The performance of the prepared crystallization-assisted high-flux nanofiltration membrane was tested with pure water, 2000 ppm Na2SO4 aqueous solution and 2000 ppm Na2SO4 aqueous solution respectively under a pressure of 0.2 MPa. The test results showed that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane was 29.23 L·m-2h-1bar-1, and the rejection rate of Na2SO4 aqueous solution was 83.42%.

[0098] Comparative Example 3

[0099] The nanofiltration membrane was prepared, and the following steps without temperature indicated were carried out at room temperature.

[0100] (1) A polyether sulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was immersed in deionized water for pretreatment, and the immersion time was 48 h, and the deionized water needed to be replaced every 12 h.

[0101] (2) 3 g of sodium hypophosphite was mixed with 97 g of deionized water to prepare a salt solution with a concentration of 3 wt% of sodium hypophosphite.

[0102] (3) 0.2 g of piperazine was mixed with 99.8 g of deionized water to prepare a piperazine solution with a concentration of 0.2 wt% of piperazine; the salt solution and the piperazine solution were mixed in equal proportions to prepare an aqueous solution with a concentration of 1.5 wt% of sodium hypophosphite and a concentration of 0.1 wt% of piperazine.

[0103] (4) 0.3 g of 1,3,5-benzene tricarbonyl chloride was mixed with 199.7 g of n-hexane solvent to prepare an organic phase solution with a concentration of 0.15 wt% of 1,3,5-benzene tricarbonyl chloride.

[0104] (5) The temperature of the organic phase was adjusted to -15°C; the pretreated polyether sulfone membrane was immersed in the prepared aqueous solution, and taken out after 5 min. The residual water on the surface of the membrane was dried with a rubber roller, and then placed in the organic phase solution for interfacial polymerization. After 0.5 min, it was taken out and placed in a constant temperature drying box at 20°C, and after 2 min, a crystallization-assisted high-flux nanofiltration membrane was obtained.

[0105] The dried crystallization-assisted high-flux nanofiltration membrane was taken out and sealed in a water environment for measurement. The performance of the prepared crystallization-assisted high-flux nanofiltration membrane was tested with pure water, 2000 ppm Na2SO4 aqueous solution and 2000 ppm Na2SO4 aqueous solution respectively under a pressure of 0.2 MPa. The test results showed that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane was 27.97 L·m-2h-1bar-1, and the rejection rate of Na2SO4 aqueous solution was 95.64%.

[0106] Comparative Example 4

[0107] The nanofiltration membrane was prepared, and the following steps without temperature were carried out at room temperature.

[0108] (1) The polyethersulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was immersed in deionized water for pretreatment, and the immersion time was 48 h, and the deionized water needed to be replaced every 12 h.

[0109] (2) 3 g of sodium hypophosphite was mixed with 97 g of deionized water to prepare a salt solution with a concentration of 3 wt% of sodium hypophosphite.

[0110] (3) 0.2 g of trans-2,5-dimethylpiperazine was mixed with 99.8 g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2 wt% of trans-2,5-dimethylpiperazine; the salt solution and the trans-2,5-dimethylpiperazine solution were mixed in equal proportions to prepare an aqueous solution with a concentration of 1.5 wt% of sodium hypophosphite and a concentration of 0.1 wt% of trans-2,5-dimethylpiperazine.

[0111] (4) 0.3 g of 1,3,5-benzene tricarbonyl chloride was mixed with 199.7 g of n-hexane solvent to prepare an organic phase solution with a concentration of 0.15 wt% of 1,3,5-benzene tricarbonyl chloride.

[0112] (5) The temperature of the organic phase was adjusted to -15°C; the pretreated polyethersulfone membrane was immersed in the prepared aqueous solution, and after 5 min, it was taken out. The residual moisture on the surface of the membrane was dried with a rubber roller, and then it was placed in the organic phase solution for interfacial polymerization. After 0.5 min, it was taken out and placed in a constant temperature drying box at 50°C, and after 1 min, a crystallization-assisted high-flux nanofiltration membrane was obtained.

[0113] The dried crystallization-assisted high-flux nanofiltration membrane was taken out and sealed in a water environment for measurement. Under a pressure of 0.2 MPa, the performance of the prepared crystallization-assisted high-flux nanofiltration membrane was tested using pure water, a 2000 ppm Na2SO4 aqueous solution, and a 2000 ppm Na2SO4 aqueous solution, respectively. The test results showed that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane was 30.39 L·m-2h-1bar-1, and the rejection rate of the Na2SO4 aqueous solution was 95.08%.

[0114] Comparative Example 5

[0115] The nanofiltration membrane was prepared, and the following steps without temperature were carried out at room temperature.

[0116] (1) The polyethersulfone (PES) membrane with a size of 6 cm x 6 cm and a molecular weight cut-off of 100 KDa was immersed in deionized water for pretreatment, and the immersion time was 48 h, and the deionized water needed to be replaced every 12 h.

[0117] (2) Take 3g of sodium hypophosphite and mix with 97g of deionized water to prepare a salt solution with a concentration of 3wt% sodium hypophosphite.

[0118] (3) Take 0.2g of trans-2,5-dimethylpiperazine and mix with 99.8g of deionized water to prepare a trans-2,5-dimethylpiperazine solution with a concentration of 0.2wt%; mix the salt solution and the trans-2,5-dimethylpiperazine solution in equal proportions to prepare an aqueous phase solution with a concentration of 1.5wt% sodium hypophosphite and a concentration of 0.1wt% trans-2,5-dimethylpiperazine.

[0119] (4) Mix 0.3g of 1,3,5-benzene tricarbonyl chloride and 199.7g of n-hexane solvent to prepare an organic phase solution with a concentration of 0.15wt% 1,3,5-benzene tricarbonyl chloride.

[0120] (5) Adjust the temperature of the organic phase to 20℃; immerse the pretreated polyether sulfone membrane in the prepared aqueous phase solution, and take it out after 5min. Dry the residual water on the membrane surface with a rubber roller, and then place it in the organic phase solution for interfacial polymerization. Take it out after 0.5min, and place it in a constant temperature drying box at 20℃, and obtain the crystallization-assisted high-flux nanofiltration membrane after 1min.

[0121] Take out the dried crystallization-assisted high-flux nanofiltration membrane, seal it in a water environment, and use it for measurement. Under a pressure of 0.2Mpa, test the performance of the prepared crystallization-assisted high-flux nanofiltration membrane with pure water, a 2000ppm Na2SO4 aqueous solution, and a 2000ppm Na2SO4 aqueous solution, respectively. The test results show that the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane is 32.72L·m-2h-1bar-1, and the Na2SO4 aqueous solution rejection rate is 96.56%.

[0122] As can be seen from the above, the pure water permeability of the crystallization-assisted high-flux nanofiltration membrane prepared in Example 5 is 45.31L·m-2h-1bar-1, and the Na2SO4 aqueous solution rejection rate is 96.83%, which is significantly higher than that of the comparative example in terms of water flux and Na2SO4 aqueous solution rejection rate.

[0123] In the description, "an embodiment", "one embodiment”, etc. means that the described embodiment can include a specific feature, structure or property, but not necessarily every embodiment includes the specific feature, structure or property. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure or property is described in combination with an embodiment, it is within the knowledge of those skilled in the art to realize such feature, structure or property in combination with other embodiments that are explicitly or implicitly described.

[0124] It should be noted that, in this document, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a", "comprising", or "comprises" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0125] The preferred embodiments of the present disclosure have been described above with the intent to enable those skilled in the art to make and use it. Any modifications, equivalent replacements or improvements made without departing from the spirit and principles of the present disclosure shall fall within the scope of the present disclosure.

Claims

1. A method for preparing a crystallization-assisted high-flux nanofiltration membrane, characterized in that: The following steps are involved: Pretreatment of nanofiltration base membrane; Prepare a salt solution with sodium hypophosphite; Trans-2,5-dimethylpiperazine is prepared into a trans-2,5-dimethylpiperazine solution, and then the salt solution is mixed with the trans-2,5-dimethylpiperazine solution to prepare an aqueous phase solution; Mixing 1,3,5-benzenetricarboxylic acid chloride and n-hexane solvent to prepare an organic phase solution; The pretreated nanofiltration base membrane is placed in an aqueous solution, taken out, dried, and then placed in a low-temperature organic phase solution for low-temperature interfacial polymerization. After being taken out, it is dried again to obtain a crystallization-assisted high-flux nanofiltration membrane. The temperature of the organic phase solution is adjusted to -15°C-20°C.

2. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: The nanofiltration base membrane is made of polyethersulfone.

3. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: The membrane molecular weight cut-off of the nanofiltration base membrane is greater than 50 KDa and less than 150 KDa.

4. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: The pretreatment of the nanofiltration basement membrane comprises: The nanofiltration base membrane was immersed in deionized water at 15°C-30°C for 48 h-98 h, and the deionized water was replaced every 6 h-12 h.

5. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: The concentration of the sodium hypophosphite is 0.01 wt%-5.00 wt%.

6. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: The concentration of the trans-2,5-dimethylpiperazine is 0.05 wt%-1.00 wt%.

7. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: The concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution is 0.025 wt%-0.25 wt%.

8. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: In the step of placing the pretreated nanofiltration base membrane into the aqueous solution, the nanofiltration base membrane stays in the aqueous solution for 2 min-7 min, the interfacial polymerization reaction lasts for 20 s-120 s, and the drying is performed by rubber roller drying.

9. The method for preparing a crystallization-assisted high-flux nanofiltration membrane according to claim 1, wherein: After taking out, the membrane is dried again to obtain a crystallization-assisted high-flux nanofiltration membrane. The drying time is 0.5 min-2.5 min, and the drying temperature is 20° C.-80° C.

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