Highly selective nanofiltration composite membrane and method for its preparation

Abstract

The application discloses a kind of high selectivity nanofiltration composite membrane and preparation method thereof, belong to nanofiltration membrane related technical field.The application is in the form of in-situ polymerization with anhydride, ester group, amide group on membrane surface, the degree of hydrolysis of polyamide membrane is controlled by the cleaning of post-processing solution, to control the charge density of membrane surface, to improve or reduce the permeability of monovalent ion;By controlling the ratio of trimesoyl chloride and diacyl chloride monomer, the size of pore structure can be adjusted, further improving the permeability of monovalent salt;By adjusting the amount of hydrophilic pore-forming agent to improve the hydrophilic performance of ultrafiltration base film, the flux and monovalent salt permeability of nanofiltration composite membrane are improved.The high selectivity nanofiltration composite membrane prepared by the application has excellent divalent salt ion removal rate, lower monovalent salt removal rate, and higher water flux, suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane technology, specifically to a highly selective nanofiltration composite membrane and its preparation method. Background Technology

[0002] Nanofiltration is a novel membrane separation technology developed in the late 1980s, falling between ultrafiltration and reverse osmosis. Nanofiltration membranes have a porous structure with a pore size typically of 1-2 nm and a molecular weight cutoff of 200-1000 Da. Compared to ultrafiltration membranes, nanofiltration membranes possess a certain charge capacity and exhibit the Donnan effect for ions of different valence states. Compared to reverse osmosis membranes, in desalination, nanofiltration membranes retain the vast majority of divalent / polyvalent salts and some monovalent salts. Therefore, this technology has broad application prospects in fine salt separation, fruit juice concentration, pharmaceutical separation, and the removal of hardness and organic matter from groundwater.

[0003] With the deepening research into nanofiltration membrane applications, especially in recent years, zero-emission processes have placed higher demands on the performance of nanofiltration membranes, requiring high desalination selectivity, high flux, and antifouling properties. Currently, commercially available nanofiltration membranes are mainly prepared through classic interfacial polymerization. Existing polyamide-based nanofiltration membranes are primarily prepared using trimesoyl chloride (TMC) and piperazine (PIP) monomers, exhibiting a mixed aromatic and aliphatic structure. Current research focuses on two main directions: firstly, altering the pore structure through doping and blending novel reactive monomers; and secondly, modifying the surface charge density through organic / inorganic molecule grafting, ultimately aiming to improve the performance of nanofiltration membranes.

[0004] However, there are some problems with the existing technological improvements to nanofiltration membranes in terms of high selectivity and high flux. For example, when selecting and designing novel acyl chloride or amine monomers, some novel acyl chloride monomers have strong or weak reactivity, making it difficult to achieve industrial-scale production in terms of monomer stability storage and controlling the appropriate reaction time for interfacial polymerization. Grafting modification with some organic polymers may easily generate more defects on the membrane surface, which is not conducive to the long-term stable use of the membrane product. Furthermore, the grafting modification of novel reactive monomers and polymers also presents some challenges in industrial-scale production.

[0005] Therefore, there is an urgent need for a nanofiltration membrane material with moderate reactivity, suitable for industrial production, and possessing high selectivity and high flux. Summary of the Invention

[0006] To address the existing technical problems, this invention provides a method for preparing a highly selective nanofiltration composite membrane, comprising the following steps:

[0007] I. Preparation of ultrafiltration base membrane: Polysulfone and hydrophilic pore-forming agent are mixed and dissolved in an organic solvent. After mixing evenly, the mixture is heated and stirred to obtain a polysulfone solution. The polysulfone solution is uniformly coated on the surface of a nonwoven fabric. After cooling and solidification, an ultrafiltration base membrane is obtained.

[0008] II. Preparation of aqueous solution: Dissolve piperazine and charge modifier in deionized water, mix well, add alkaline acid adsorbent, and adjust the pH to 10-12 to form an aqueous solution;

[0009] III. Preparation of oil phase solution: Pyromellitic trimethylol chloride and diacyl chloride monomers are mixed and dissolved in solvent oil, and after being mixed evenly, an oil phase solution of acyl chloride is obtained;

[0010] IV. Preparation of nascent nanofiltration membrane: Immerse the ultrafiltration base membrane in the aqueous solution described in step II. After immersion, remove the excess aqueous solution from the surface of the ultrafiltration base membrane. Then, coat one side of the ultrafiltration base membrane with the oil solution described in step III. After leaching off the excess oil phase from the surface, dry the membrane to obtain the nascent nanofiltration membrane.

[0011] V. The nascent nanofiltration membrane is cleaned with a cleaning solution, and then rinsed with deionized water to obtain the highly selective nanofiltration composite membrane.

[0012] Preferably or optionally, the hydrophilic pore-forming agent in step I is one or more of PEG 1000, PEG 2000, PVP K30, PVPK60, and PVP K90.

[0013] Preferably or optionally, the alkaline acid-absorbing agent in step II is one or more of sodium hydroxide, triethylamine, trisodium phosphate, sodium dihydrogen phosphate, sodium bicarbonate, and sodium carbonate.

[0014] Preferably or optionally, the charge modifier in step II is an organic polyamine containing carboxyl groups and / or hydroxyl groups.

[0015] Preferably or optionally, the charge modifier is one or more of 2,4-diaminophenol, 3,5-diaminobenzoic acid, 1,2-cyclohexanediaminetetraacetic acid, and 2,5-diaminoterephthalic acid.

[0016] Preferably or optionally, the mass ratio of pyromellitic trimethylolpropionate chloride to diacyl chloride monomer in step III is 2 to 100; the diacyl chloride monomer is an aromatic diacyl chloride monomer including one or more of terephthaloyl chloride, isophthaloyl chloride, and orthophthaloyl chloride.

[0017] Preferably or optionally, the cleaning solution in step V is one or more of the following: deionized water, sodium bicarbonate aqueous solution with a concentration of 0.1-5%, sodium carbonate aqueous solution with a concentration of 0.1-5%, and sodium hydroxide aqueous solution with a concentration of 0.01-2%.

[0018] A highly selective nanofiltration composite membrane is prepared by any of the above-described methods for preparing highly selective nanofiltration composite membranes, wherein the highly selective nanofiltration composite membrane comprises a polysulfone nonwoven support layer and a polypiperazine amide desalination layer.

[0019] Beneficial Effects: The high-selectivity nanofiltration composite membrane provided by this invention introduces small-molecule charge modifiers with high electronegativity (carboxyl or hydroxyl groups) into the aqueous dispersion phase during its preparation. Simultaneously, the polypiperazine amide is moderately crosslinked. After in-situ interfacial polymerization, amide groups, anhydrides, and / or ester groups with different hydrolytic activities are inoculated onto the membrane surface. The degree of hydrolysis of the polyamide membrane can be controlled by cleaning with the post-treatment solution, thereby regulating the charge density on the membrane surface and increasing or decreasing the permeability of monovalent ions. Compared with existing graft polymerization methods that introduce highly electronegative polymer groups, the membrane prepared by in-situ polymerization in this invention exhibits higher long-term stability, is less prone to grafting defects, and has greater controllability in its production process, facilitating industrialization. Furthermore, the pore size can be adjusted by varying the ratio of trimesoyl chloride and diacyl chloride monomers in the oil phase solution, further improving the permeability of monovalent salts. To ensure the smooth and forward polymerization reaction, an alkaline acid-absorbing agent is added to neutralize the hydrochloric acid produced during the polymerization reaction. Meanwhile, by adjusting the amount of hydrophilic pore-forming agent during the preparation of the ultrafiltration base membrane, the contact angle of the ultrafiltration base membrane can be controlled. This improves the hydrophilicity of the ultrafiltration base membrane and reduces the concentration of amine monomers in the aqueous phase, thereby increasing the flux and monovalent salt permeability of the nanofiltration composite membrane. This avoids the problem of high crosslinking degree of the desalination layer and high monovalent salt removal rate caused by the addition of ionic surfactants. The highly selective nanofiltration composite membrane prepared by this invention exhibits excellent divalent salt ion removal rate and low monovalent salt removal rate, while also possessing high water flux, making it suitable for industrial production. Detailed Implementation

[0020] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0021] The present invention will be further described below with reference to the embodiments. These embodiments are intended to explain the invention and should not be construed as limiting it. Where specific techniques and reaction conditions are not specified in the embodiments, they can be performed according to the techniques or conditions described in the literature or product instructions in the art. All reagents, instruments, or equipment without a specified manufacturer are commercially available.

[0022] The high-selectivity nanofiltration composite membrane of the present invention is prepared by a method comprising:

[0023] ① Preparation of ultrafiltration membrane: A certain amount of polysulfone particles and a hydrophilic pore-forming agent are mixed and dissolved in an organic solvent. The temperature is raised to 60-100℃, and the mixture is stirred continuously for 4-8 hours to ensure complete dissolution and degassing. The resulting solution is then uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water for 30 seconds to 5 minutes to obtain the ultrafiltration membrane, which is then stored in deionized water for later use.

[0024] ② Dissolve piperazine and the charge modifier in deionized water, mix well, then add an alkaline acid adsorbent to adjust the pH to 10-12 to form a mixed solution of aqueous organic amines, and keep the temperature constant at 25℃±2℃.

[0025] ③ Mix trimesoyl chloride (TMC) and diacyl chloride monomers in an organic solvent in a specific ratio, mix thoroughly to obtain an oil phase solution of acyl chloride, and keep the temperature constant at 25℃±2℃.

[0026] ④ Immerse the ultrafiltration membrane in the aqueous solution in step ② for 10s to 4min, preferably 20 to 60s, to remove excess aqueous solution from the surface of the ultrafiltration membrane. Then, apply the oil solution in step ③ to one side of the ultrafiltration membrane surface, controlling the immersion time to 10 to 100s, preferably 10 to 30s, to remove excess oil from the surface, and dry to obtain the nascent nanofiltration membrane.

[0027] ⑤ The newly formed nanofiltration membrane is cleaned with a post-treatment solution at a certain temperature. The cleaning solution has a temperature range of 25 to 100°C and a cleaning time of 10 seconds to 5 minutes, preferably 1 to 2 minutes.

[0028] ⑥ Rinse the cleaned membrane with deionized water and place it in deionized water for later use.

[0029] In step ①, the ultrafiltration substrate of polysulfone or polyethersulfone is selected with a water contact angle range of 40–100°, more preferably 40–60°, and most preferably 50–60°. The hydrophilicity of the ultrafiltration membrane is adjusted by the amount of hydrophilic pore-forming agent added in the conventional polysulfone formulation. The hydrophilic pore-forming agent is at least one of PEG 1000, PEG 2000, PVP K30, PVP K60, and PVP K90, and the added content is 0.5–10%, preferably 1–8%.

[0030] In step ②, the charge modifier containing carboxyl or hydroxyl groups is a small organic polyamine molecule. The charge modifier is one of the following: 2,4-diaminophenol, 3,5-diaminobenzoic acid, 1,2-cyclohexanediaminetetraacetic acid, or 2,5-diaminoterephthalic acid. The addition amount is 0.005%–0.5%, preferably 0.01%–0.2%. The piperazine content is 0.5%–5%, preferably 0.5%–2.0%. The alkaline acid-absorbing agent includes NaOH, triethylamine, trisodium phosphate, sodium dihydrogen phosphate, sodium bicarbonate, sodium carbonate, etc., preferably sodium bicarbonate or sodium carbonate which is beneficial for increasing flux. The addition amount is 0.1%–1.0%, preferably 0.5%.

[0031] In step ③, TMC is selected and blended with aromatic diacyl chloride. Commonly used aromatic diacyl chlorides include terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride, with phthaloyl chloride (OPC) being preferred. The TMC:OPC ratio is in the range of 100:1 to 100:50, preferably 100:5 to 100:20. The total content of the acyl chloride monomer is 0.08% to 0.50%, preferably 0.08% to 0.30%.

[0032] In step ④, the ultrafiltration membrane is immersed in an aqueous organic amine solution for 10 seconds to 4 minutes, preferably 20 seconds to 60 seconds. Excess aqueous solution is removed from the surface using a squeeze roller made of flexible PVA or PU. Next, the oil phase solution from step ③ is coated onto one side of the ultrafiltration membrane surface, controlling the immersion temperature at 25℃±2℃ for 10 seconds to 100 seconds, preferably 10 to 30 seconds. Excess oil phase is then removed, and the membrane is completely dried in an 80℃ oven to obtain the nascent nanofiltration membrane.

[0033] The cleaning solution in step ⑤ is one of deionized water, sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, or sodium hydroxide aqueous solution, wherein the concentration of sodium bicarbonate is 0.1%–5%; the concentration of sodium carbonate is 0.1%–5%, preferably 0.1%–2%; and the concentration of sodium hydroxide is 0.1%–2%, preferably 0.01%–1%. The operating temperature of the cleaning solution is 25℃–100℃, preferably 50–90℃; and the cleaning time is 10s–5min, preferably 1–2min.

[0034] Example 1

[0035] 1) 40g of PEG1000 was dispersed in 780g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h until fully dissolved. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0036] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0037] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0038] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0039] 5) Immerse the oil phase acyl chloride solution from 3) onto the base film from 4), react for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven.

[0040] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0041] Example 2

[0042] 1) 40g of PEG1000 was dispersed in 780g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h until fully dissolved. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0043] 2) Dissolve 10g piperazine and 0.1g NaOH in 989.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.0%.

[0044] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0045] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0046] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0047] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0048] Example 3

[0049] 1) 40g of PEG1000 was dispersed in 780g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h until fully dissolved. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0050] 2) Dissolve 15g piperazine and 0.1g NaOH in 984.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.5%.

[0051] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0052] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0053] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0054] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0055] Example 4

[0056] 1) 40g of PEG1000 was dispersed in 780g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h until fully dissolved. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0057] 2) Dissolve 20g piperazine and 0.1g NaOH in 979.9g deionized water to prepare an aqueous amine solution with a mass concentration of 2.0%.

[0058] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0059] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0060] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0061] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0062] Example 5

[0063] 1) Disperse 50g of PEG1000 in 770g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and allow it to stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit-type coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0064] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0065] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0066] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0067] 5) Immerse the oil phase acyl chloride solution from 3) onto the base film from 4), react for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven.

[0068] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0069] Example 6

[0070] 1) Disperse 50g of PEG1000 in 770g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and allow it to stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit-type coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0071] 2) Dissolve 10g piperazine and 0.1g NaOH in 989.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.0%.

[0072] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0073] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0074] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0075] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0076] Example 7

[0077] 1) Disperse 50g of PEG1000 in 770g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and allow it to stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit-type coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0078] 2) Dissolve 15g piperazine and 0.1g NaOH in 984.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.5%.

[0079] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0080] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0081] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0082] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0083] Example 8

[0084] 1) Disperse 50g of PEG1000 in 770g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and allow it to stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit-type coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0085] 2) Dissolve 20g piperazine and 0.1g NaOH in 979.9g deionized water to prepare an aqueous amine solution with a mass concentration of 2.0%.

[0086] 3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0087] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0088] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0089] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0090] Example 9

[0091] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0092] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0093] 3) Dissolve 1.5g of TMC in 998.5g of ISOPAR-G solvent to obtain an oil-phase acyl chloride solution with a mass concentration of 0.15% TMC.

[0094] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0095] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0096] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0097] Example 10

[0098] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0099] 2) Dissolve 10g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.0%.

[0100] 3) Dissolve 1.5g of TMC in 998.5g of ISOPAR-G solvent to obtain an oil-phase acyl chloride solution with a mass concentration of 0.15% TMC.

[0101] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0102] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0103] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0104] Example 11

[0105] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0106] 2) Dissolve 15g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.5%.

[0107] 3) Dissolve 1.5g of TMC in 998.5g of ISOPAR-G solvent to obtain an oil-phase acyl chloride solution with a mass concentration of 0.15% TMC.

[0108] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0109] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0110] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0111] Example 12

[0112] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0113] 2) Dissolve 20g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 2.0%.

[0114] 3) Dissolve 1.5g of TMC in 998.5g of ISOPAR-G solvent to obtain an oil-phase acyl chloride solution with a mass concentration of 0.15% TMC.

[0115] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0116] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0117] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0118] Example 13

[0119] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0120] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0121] 3) Dissolve 1.5g TMC and 0.010g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.010% OPC.

[0122] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0123] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0124] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0125] Example 14

[0126] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0127] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0128] 3) Dissolve 1.5g TMC and 0.015g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0129] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0130] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0131] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0132] Example 15

[0133] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0134] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0135] 3) Dissolve 1.5g TMC and 0.030g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.030% OPC.

[0136] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0137] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0138] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0139] Example 16

[0140] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0141] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0142] 3) Dissolve 1.5g TMC and 0.045g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.045% OPC.

[0143] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0144] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0145] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0146] Example 17

[0147] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0148] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.05g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare a 0.8% aqueous amine solution.

[0149] 3) Dissolve 1.5g TMC and 0.15g OPC (phthaloyl chloride) in 998.35g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0150] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0151] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0152] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0153] Example 18

[0154] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0155] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.10g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0156] 3) Dissolve 1.5g TMC and 0.15g OPC (phthaloyl chloride) in 998.35g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0157] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0158] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0159] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0160] Example 19

[0161] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0162] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.20g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0163] 3) Dissolve 1.5g TMC and 0.15g OPC (phthaloyl chloride) in 998.35g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0164] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0165] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0166] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0167] Example 20

[0168] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0169] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.50g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0170] 3) Dissolve 1.5g TMC and 0.15g OPC (phthaloyl chloride) in 998.35g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0171] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0172] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0173] 6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 30 minutes to clean it, and set it aside for later use.

[0174] Example 21

[0175] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0176] 2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0177] 3) Dissolve 1.5g TMC and 0.015g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0178] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0179] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0180] 6) Place the newly formed nanofiltration membrane in deionized water at 80℃ for 2 minutes to clean it, and set it aside.

[0181] Example 22

[0182] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0183] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.20g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0184] 3) Dissolve 1.5g TMC and 0.015g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0185] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0186] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0187] 6) Wash the newly formed nanofiltration membrane in deionized water at 80°C for 2 minutes and set aside.

[0188] Example 23

[0189] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0190] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.20g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0191] 3) Dissolve 1.5g TMC and 0.015g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0192] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0193] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0194] 6) Wash the newly formed nanofiltration membrane in a 1% Na2CO3 solution at 80℃ for 2 minutes, and set aside for later use.

[0195] Example 24

[0196] 1) Disperse 70g of PEG1000 in 750g of N,N-dimethylacetamide and mechanically stir at 1000rpm for 30min. Then, disperse 180g of polysulfone in the solution, raise the temperature to 80℃, and continue stirring for 6h until fully dissolved. Then, place the solution in a vacuum drying oven and let it stand for 12h to remove bubbles. Coat the resulting solution evenly on the surface of a nonwoven fabric using a slit coating method and solidify it at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer is 50μm.

[0197] 2) Dissolve 8g piperazine, 0.1g NaOH, and 0.20g of 3,5-diaminobenzoic acid charge modifier in deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0198] 3) Dissolve 1.5g TMC and 0.015g OPC (phthalic acid chloride) in 998.49g of ISOPAR-G solvent to obtain an oil-phase blended acyl chloride solution with a mass concentration of 0.15% TMC: 0.015% OPC.

[0199] 4) Immerse the polysulfone ultrafiltration membrane prepared in 1) in an aqueous amine solution for 60 seconds, then remove and drain.

[0200] 5) Immerse the oil phase acyl chloride solution from 3) onto the base membrane from 4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven to obtain the nascent nanofiltration membrane.

[0201] 6) Wash the newly formed nanofiltration membrane in a 0.5% NaOH solution at 80℃ for 2 minutes, and set aside for later use.

[0202] Compare with Example 1

[0203] (1) 20g of PEG1000 was dispersed in 800g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h to fully dissolve the polysulfone. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0204] (2) Dissolve 8g piperazine and 0.1g NaOH in 991.9g deionized water to prepare an aqueous amine solution with a mass concentration of 0.8%.

[0205] (3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0206] (4) Immerse the polysulfone ultrafiltration membrane prepared in (1) in an aqueous amine (2) solution for 60s, then remove and drain.

[0207] (5) Immerse the oil phase acyl chloride solution from (3) onto the base film from (4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven.

[0208] (6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 2 minutes and store it in deionized water for later use.

[0209] Compare with Example 2

[0210] (1) 20g of PEG1000 was dispersed in 800g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h to fully dissolve the polysulfone. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0211] (2) Dissolve 10g piperazine and 0.1g NaOH in 989.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.0%.

[0212] (3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0213] (4) Immerse the polysulfone ultrafiltration membrane prepared in (1) in an aqueous amine (2) solution for 60s, then remove and drain.

[0214] (5) Immerse the oil phase acyl chloride solution from (3) onto the base film from (4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven.

[0215] (6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 2 minutes and store it in deionized water for later use.

[0216] Compare with Example 3

[0217] (1) 20g of PEG1000 was dispersed in 800g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h to fully dissolve the polysulfone. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0218] (2) Dissolve 15g piperazine and 0.1g NaOH in 984.9g deionized water to prepare an aqueous amine solution with a mass concentration of 1.5%.

[0219] (3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0220] (4) Immerse the polysulfone ultrafiltration membrane prepared in (1) in an aqueous amine (2) solution for 60s, then remove and drain.

[0221] (5) Immerse the oil phase acyl chloride solution from (3) onto the base film from (4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven.

[0222] (6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 2 minutes and store it in deionized water for later use.

[0223] Compare with Example 4

[0224] (1) 20g of PEG1000 was dispersed in 800g of N,N-dimethylacetamide and mechanically stirred at 1000rpm for 30min. Then, 180g of polysulfone was dispersed in the solution, the temperature was raised to 80℃, and stirring was continued for 6h to fully dissolve the polysulfone. The solution was then placed in a vacuum drying oven and allowed to stand for 12h to remove bubbles. The resulting solution was uniformly coated onto the surface of a nonwoven fabric using a slit-type coating method and solidified at 10℃ water temperature for 30s-5min. The thickness of the prepared ultrafiltration polysulfone layer was 50μm.

[0225] (2) Dissolve 20g piperazine and 0.1g NaOH in 979.9g deionized water to prepare an aqueous amine solution with a mass concentration of 2.0%.

[0226] (3) Dissolve 1.5g TMC in 998.5g of ISOPAR-G solvent to obtain an oil phase acyl chloride solution with a mass concentration of 0.15%.

[0227] (4) Immerse the polysulfone ultrafiltration membrane prepared in (1) in an aqueous amine (2) solution for 60s, then remove and drain.

[0228] (5) Immerse the oil phase acyl chloride solution from (3) onto the base film from (4) for 15 seconds, drain for 30 seconds, and then dry completely in an 80°C oven.

[0229] (6) Place the newly formed nanofiltration membrane in deionized water at 25°C for 2 minutes and store it in deionized water for later use.

[0230] Test method:

[0231] The separation performance of each composite nanofiltration membrane product is characterized by its flux F and salt removal rate R for MgSO4 aqueous solution and NaCl aqueous solution.

[0232] The separation performance of the products obtained in Examples 1-24 and Comparative Examples 1-4 was tested under the following operating conditions: the concentration of divalent salt MgSO4 was 2000 pppm, the concentration of monovalent salt NaCl was 2000 ppm, the pre-compression pressure was 0.69 MPa (100 psi), the pre-compression time was 30 min, and the solution pH was 7.0 ± 0.5.

[0233] Salt removal rate R (%) = [(C f -C p ) / C f ]*100%

[0234] Where C f C represents the salt concentration of the feed solution. p This represents the salt concentration of the permeate.

[0235] Flux F is the volume V of water passing through a unit area S per unit time t under a certain operating pressure, and its unit is LMH (m³). 3 m 2 h 1 bar 1 ), that is, F = V / St.

[0236] The separation performance of Comparative Examples 1-4 and Examples 1-24 is shown in the table below:

[0237] surface

[0238]

[0239]

[0240] Based on the table above and the data from each example and control example, the difference between Examples 1-4 lies in the amount of piperazine added, increasing from less to more. The removal rates of monovalent and divalent salts show an increasing trend, while the water flux gradually decreases. Examples 5-8 differ from Examples 1-4 in that in step 1, the PEG1000 content is adjusted to 50g and dispersed in 770g of N,N-dimethylacetamide. In Examples 5-8, the removal rates of monovalent and divalent salts both show an increasing trend, while the flux also shows a decreasing trend. A longitudinal comparison of Examples 5-8, 9-12, and Examples 1-4 shows that the increased hydrophilicity of the ultrafiltration membrane also leads to an increasing ion removal rate and a decreasing flux. The contact angle of the base membrane in Examples 13-24 was 55±5°. Examples 13-16, by selecting the proportion of diacyl chloride, reduced the removal rate of monovalent salts to a certain extent. Comparing Examples 17-20 with Examples 13-16, it was found that by optimizing the amount of charge modifier added, the slight decrease in the removal rate of divalent salts caused by the addition of diacyl chloride in Examples 13-16 was compensated for, and the removal rate of monovalent salts was kept at a low level. The post-treatment cleaning temperature in Examples 22-24 was 80°C, and the cleaning solution was an alkaline liquid rather than deionized water. The test results showed that, except for a higher removal rate of divalent salts, the removal rate of monovalent salts was relatively lower, while the water flux for both monovalent and divalent salts exceeded that of the other examples. In contrast, the ultrafiltration base membranes in Control Examples 1-4 had the lowest hydrophilic wettability, and their overall separation performance was generally average.

[0241] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A method for preparing a highly selective nanofiltration composite membrane, characterized in that, Includes the following steps: I. Preparation of ultrafiltration base membrane: Polysulfone and hydrophilic pore-forming agent are mixed and dissolved in an organic solvent. After mixing evenly, the mixture is heated and stirred to obtain a polysulfone solution. The polysulfone solution is uniformly coated on the surface of a nonwoven fabric. After cooling and solidification, an ultrafiltration base membrane is obtained. II. Preparation of aqueous solution: Dissolve piperazine and charge modifier in deionized water, mix well, add alkaline acid-binding agent, adjust pH to 10-12 to form aqueous solution; III. Preparation of oil phase solution: Pyromellitic trimethylol chloride and diacyl chloride monomers are mixed and dissolved in solvent oil, and after being mixed evenly, an oil phase solution of acyl chloride is obtained; IV. Preparation of nascent nanofiltration membrane: Immerse the ultrafiltration base membrane in the aqueous solution described in step II. After immersion, remove the excess aqueous solution from the surface of the ultrafiltration base membrane. Then, coat one side of the ultrafiltration base membrane with the oil solution described in step III. After leaching off the excess oil phase from the surface, dry the membrane to obtain the nascent nanofiltration membrane. V. The nascent nanofiltration membrane is cleaned with a cleaning solution and then rinsed with deionized water to obtain the high-selectivity nanofiltration composite membrane. The high-selectivity nanofiltration composite membrane has excellent divalent salt ion removal rate and low monovalent salt removal rate. In step I, the water contact angle of the polysulfone ultrafiltration membrane ranges from 40° to 100°. The charge modifier in step II is one or more of 2,4-diaminophenol, 3,5-diaminobenzoic acid, 1,2-cyclohexanediaminetetraacetic acid, and 2,5-diaminoterephthalic acid, with an addition amount of 0.005%~0.5%; the piperazine content is 0.5%~5%; the alkaline acid-binding agent is NaOH, triethylamine, trisodium phosphate, sodium dihydrogen phosphate, sodium bicarbonate, or sodium carbonate, with an addition amount of 0.1%~1.0%. In step V, the cleaning solution is one or more of the following: a sodium bicarbonate aqueous solution with a concentration of 0.1-5%, a sodium carbonate aqueous solution with a concentration of 0.1-5%, and a sodium hydroxide aqueous solution with a concentration of 0.01-2%.

2. The method for preparing the highly selective nanofiltration composite membrane according to claim 1, characterized in that, In step III, the mass ratio of pyromellitic trichloroisocyanurate to diacyl chloride monomer is 2-100; the diacyl chloride monomer is one or more of terephthaloyl chloride, isophthaloyl chloride, and orthophthaloyl chloride.

3. A highly selective nanofiltration composite membrane, characterized in that, It is prepared by the method of preparing the high-selectivity nanofiltration composite membrane according to any one of claims 1 to 2.

4. The highly selective nanofiltration composite membrane according to claim 3, characterized in that, The highly selective nanofiltration composite membrane comprises a polysulfone nonwoven support layer and a polypiperazine amide desalination layer.

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