Polytetrafluoroethylene composite nanofiltration membrane and preparation method thereof

Abstract

The invention discloses a polytetrafluoroethylene composite nanofiltration membrane and a preparation method thereof, and relates to the technical field of nanofiltration membranes. According to the invention, polytetrafluoroethylene is taken as a base membrane, the surface of the polytetrafluoroethylene membrane is subjected to hydrophilic modification, and the surface of the polytetrafluoroethylene membrane is modified with perfluorohexyl ethyl sulfonamide propyl ethyl carboxyl betaine, so that the surface hydrophilicity of the polytetrafluoroethylene membrane can be effectively improved, and the water flux of the nanofiltration membrane is improved. The preparation method comprises the following steps: preparing a polytetrafluoroethylene membrane, co-depositing polydopamine to form a polydopamine anchoring layer, and immersing the polytetrafluoroethylene membrane into a water phase solution and an oil phase solution for interfacial polymerization reaction to form a polyamide surface layer, thereby preparing the polytetrafluoroethylene composite nanofiltration membrane, and the nanofiltration membrane not only has excellent acid and alkali resistance and pollution resistance, but also has excellent hydrophilicity. And the method can be widely applied to the fields of water treatment and the like.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membranes, in particular to a polytetrafluoroethylene composite nanofiltration membrane and a preparation method thereof. Background Art

[0002] Membrane separation technology is a high-tech technology that meets the needs of contemporary new industries. It has the advantages of energy saving, high efficiency, simple process, no phase change, and light pollution. It is widely used in water treatment, food, chemical industry, medicine, energy and other fields. Among them, the most concerned is nanofiltration membrane separation technology. The driving pressure of its separation process is between reverse osmosis and ultrafiltration, also known as "low-pressure reverse osmosis" or "loose reverse osmosis". The separation membrane with nanofiltration effect is called nanofiltration membrane.

[0003] The composite nanofiltration membrane is composed of a functional layer and a supporting layer (base membrane). Common base membranes include PS, PAN and PVDF, but the acid and alkali resistance of the above base membranes is poor, which will be limited in application. Polytetrafluoroethylene has good chemical stability, heat resistance, cold resistance, acid and alkali resistance and solvent resistance, and has excellent comprehensive performance. However, since polytetrafluoroethylene is a hydrophobic material, it cannot be directly used as the base membrane of the composite nanofiltration membrane. Therefore, in order to solve this technical problem, the present application discloses a polytetrafluoroethylene composite nanofiltration membrane and a preparation method thereof. Summary of the invention

[0004] The object of the present invention is to provide a polytetrafluoroethylene composite nanofiltration membrane and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing a polytetrafluoroethylene composite nanofiltration membrane comprises the following steps: Step 1: mixing perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water to obtain a surfactant solution; The polytetrafluoroethylene membrane is ultrasonically cleaned in anhydrous ethanol for 20-30 minutes, dried at 40-50°C, and then immersed in a surfactant solution for 2-5 hours. After being taken out, the membrane is immersed in a dopamine deposition solution and reacted at 25-30°C for 8-12 hours. The membrane is then washed with deionized water and vacuum dried to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, and disperse them by ultrasonic for 20-30 minutes, then add triethylamine and stir evenly to obtain an aqueous solution; Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution for 10 to 15 minutes, then taken out, the excess solution on the membrane surface was removed by aspiration, and then immersed in an oil phase solution, and the interfacial polymerization reaction was carried out for 1 to 2 minutes. The membrane was taken out and dried, and then transferred to 70 to 75°C for heat treatment for 10 to 15 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0006] In a more optimized scheme, in step 1, the preparation steps of the dopamine deposition solution are: adding dopamine and polyethyleneimine into Tris buffer, stirring evenly, then adding quercetin-ethanol solution, mixing evenly, to obtain the dopamine deposition solution.

[0007] In a more optimized solution, the concentration of the quercetin-ethanol solution is 1-2 g / L; the concentration of the dopamine deposition solution is 1.5-2 g / L; the mass ratio of dopamine, polyethyleneimine, and quercetin is 1:0.1:1; and the pH of the Tris buffer is 8.5.

[0008] In a more optimized solution, in step 1, the mass concentration of the surfactant solution is 1~2wt%.

[0009] In a more optimized solution, in the aqueous phase solution of step 2, the mass concentration of m-phenylenediamine is 1-1.5wt%, the mass concentration of triethylamine is 1-1.5wt%; and the mass concentration of trimesoyl chloride in the oil phase solution is 0.3-0.5wt%.

[0010] The most optimized solution is the preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethyl mercaptan at 100-110°C at a dropping rate of 2-3 drops / s, keep warm and react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 20-40°C, keep the temperature at room temperature for 3-4 hours, distill and recover triethylamine, discharge the material after cooling, and purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine.

[0011] In a more optimized solution, in step S11, the molar ratio of perfluorohexylethanethiol, sodium perchlorate and concentrated hydrochloric acid is (0.8-0.9):1:(1-1.1).

[0012] In a more optimized scheme, in step S12, the molar ratio of the N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is (1-1.5):1.

[0013] A more optimized solution is a polytetrafluoroethylene composite nanofiltration membrane prepared according to any of the preparation methods described above.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: The invention discloses a method for preparing a polytetrafluoroethylene composite nanofiltration membrane. The method uses polytetrafluoroethylene as a base membrane, hydrophilically modifies the surface of the polytetrafluoroethylene membrane, and then co-deposits polydopamine to form a polydopamine anchoring layer. The polytetrafluoroethylene membrane is then immersed in an aqueous solution and an oily solution for interfacial polymerization to form a polyamide surface layer, thereby preparing the polytetrafluoroethylene composite nanofiltration membrane. The nanofiltration membrane has not only excellent acid and alkali resistance and anti-pollution capabilities, but also excellent hydrophilicity and high water flux, and can be widely used in water treatment and other fields.

[0015] In this scheme, perfluorohexyl ethyl mercaptan, sodium perchlorate, concentrated hydrochloric acid and other raw materials are first reacted to obtain perfluorohexyl ethyl sulfonyl chloride, and then perfluorohexyl ethyl sulfonyl chloride is reacted with N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to obtain perfluorohexyl ethyl sulfonamidopropyl ethyl carboxy betaine, which is a carboxy betaine-type fluorocarbon surfactant. By modifying the surface of the polytetrafluoroethylene membrane with perfluorohexyl ethyl sulfonamidopropyl ethyl carboxy betaine, the surface hydrophilicity of the polytetrafluoroethylene membrane can be effectively improved, thereby increasing the water flux of the nanofiltration membrane.

[0016] However, in actual operation, it was found that simply immersing the polytetrafluoroethylene membrane in perfluorohexylethylsulfonamidopropylethylcarboxybetaine resulted in poor hydrophilic durability of the membrane layer, and the perfluorohexylethylsulfonamidopropylethylcarboxybetaine on the membrane surface was easily lost, resulting in a decrease in the water flux of the nanofiltration membrane. Therefore, in order to solve this technical problem, the present invention modified the surface of the polytetrafluoroethylene membrane with perfluorohexylethylsulfonamidopropylethylcarboxybetaine, and then co-deposited dopamine on its surface. In order to promote the deposition of dopamine, quercetin and polyethyleneimine were introduced into the scheme. The addition of quercetin and polyethyleneimine can promote Schiff base reaction and Michael addition reaction, effectively inhibit the self-polymerization reaction of dopamine, reduce the formation of aggregated particles and membrane pore blockage, and is beneficial to the improvement of permeability performance.

[0017] This scheme discloses a method for preparing a polytetrafluoroethylene composite nanofiltration membrane. The preparation process is simple, and the hierarchical structures and components are reasonably designed. The prepared composite nanofiltration membrane has excellent hydrophilicity, excellent anti-pollution and acid-base resistance, and high water flux and salt retention performance, and can be widely used in water treatment and other fields. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In this embodiment, the polyethyleneimine model is E107078, provided by Shanghai Aladdin; the average pore size of the polytetrafluoroethylene membrane is 0.1µm, the porosity is 73.55%, and the contact angle is 132.4°.

[0020] Embodiment 1: A method for preparing a polytetrafluoroethylene composite nanofiltration membrane, comprising the following steps: Step 1: The preparation step of dopamine deposition solution is as follows: 2g dopamine and polyethyleneimine are added to Tris buffer (pH 8.5), stirred evenly, and then quercetin-ethanol solution is added, mixed evenly, and dopamine deposition solution is obtained. The concentration of the quercetin-ethanol solution is 2g / L; the concentration of the dopamine deposition solution is 2g / L; the mass ratio of dopamine, polyethyleneimine, and quercetin is 1:0.1:1.

[0021] Perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water are mixed to obtain a surfactant solution; the mass concentration of the surfactant solution is 1wt%.

[0022] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 20 minutes, dried at 40°C, and then immersed in a surfactant solution for 4 hours. After being taken out, the membrane was immersed in a dopamine deposition solution and reacted at 25°C for 10 hours. The membrane was washed with deionized water and vacuum dried to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, perform ultrasonic dispersion for 20 minutes, add triethylamine, stir evenly, and obtain an aqueous phase solution; the mass concentration of m-phenylenediamine is 1.5wt%, and the mass concentration of triethylamine is 1.5wt%.

[0023] Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3wt%.

[0024] The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution, taken out after soaking for 10 minutes, the excess solution on the membrane surface was absorbed, and then immersed in an oil phase solution, interfacial polymerization reaction was carried out for 1 minute, taken out and dried, and then transferred to 70°C for heat treatment for 15 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0025] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 100° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0026] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 30°C, keep the temperature at normal pressure for 3 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0027] Embodiment 2: A method for preparing a polytetrafluoroethylene composite nanofiltration membrane, comprising the following steps: Step 1: The preparation step of dopamine deposition solution is as follows: 2g dopamine and polyethyleneimine are added to Tris buffer (pH 8.5), stirred evenly, and then quercetin-ethanol solution is added, mixed evenly, and dopamine deposition solution is obtained. The concentration of the quercetin-ethanol solution is 2g / L; the concentration of the dopamine deposition solution is 2g / L; the mass ratio of dopamine, polyethyleneimine, and quercetin is 1:0.1:1.

[0028] Perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water were mixed to obtain a surfactant solution; the mass concentration of the surfactant solution was 1.5wt%.

[0029] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 25 minutes, dried at 45°C, and then immersed in a surfactant solution for 4 hours. After being taken out, the membrane was immersed in a dopamine deposition solution and reacted at 25°C for 10 hours. The membrane was washed with deionized water and dried in a vacuum to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, perform ultrasonic dispersion for 25 minutes, add triethylamine, stir evenly, and obtain an aqueous phase solution; the mass concentration of m-phenylenediamine is 1.5wt%, and the mass concentration of triethylamine is 1.5wt%.

[0030] Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3wt%.

[0031] The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution, taken out after soaking for 10 minutes, the excess solution on the membrane surface was absorbed, and then immersed in an oil phase solution, interfacial polymerization reaction was carried out for 1 minute, taken out and dried, and then transferred to 75°C for heat treatment for 10 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0032] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 105° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0033] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 35°C, keep the temperature at room temperature for 3.5 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0034] Embodiment 3: A method for preparing a polytetrafluoroethylene composite nanofiltration membrane, comprising the following steps: Step 1: The preparation step of dopamine deposition solution is as follows: 2g dopamine and polyethyleneimine are added to Tris buffer (pH 8.5), stirred evenly, and then quercetin-ethanol solution is added, mixed evenly, and dopamine deposition solution is obtained. The concentration of the quercetin-ethanol solution is 2g / L; the concentration of the dopamine deposition solution is 2g / L; the mass ratio of dopamine, polyethyleneimine, and quercetin is 1:0.1:1.

[0035] Perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water were mixed to obtain a surfactant solution; the mass concentration of the surfactant solution was 2 wt %.

[0036] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 30 minutes, dried at 50°C, and then immersed in a surfactant solution for 4 hours. After being taken out, the membrane was immersed in a dopamine deposition solution and reacted at 25°C for 10 hours. The membrane was washed with deionized water and dried in a vacuum to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, perform ultrasonic dispersion for 30 minutes, add triethylamine, stir evenly, and obtain an aqueous phase solution; the mass concentration of m-phenylenediamine is 1.5wt%, and the mass concentration of triethylamine is 1.5wt%.

[0037] Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3wt%.

[0038] The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution, taken out after soaking for 10 minutes, the excess solution on the membrane surface was absorbed, and then immersed in an oil phase solution, interfacial polymerization reaction was carried out for 1 minute, taken out and dried, and then transferred to 75°C for heat treatment for 10 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0039] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 110° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0040] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 40°C, keep the temperature at normal pressure for 3 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0041] Comparative Example 1: Example 3 was used as the control group, and the mass concentration of the surfactant solution in Comparative Example 1 was adjusted to 3 wt %.

[0042] A method for preparing a polytetrafluoroethylene composite nanofiltration membrane comprises the following steps: Step 1: The preparation step of dopamine deposition solution is as follows: 2g dopamine and polyethyleneimine are added to Tris buffer (pH 8.5), stirred evenly, and then quercetin-ethanol solution is added, mixed evenly, and dopamine deposition solution is obtained. The concentration of the quercetin-ethanol solution is 2g / L; the concentration of the dopamine deposition solution is 2g / L; the mass ratio of dopamine, polyethyleneimine, and quercetin is 1:0.1:1.

[0043] Perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water were mixed to obtain a surfactant solution; the mass concentration of the surfactant solution was 3wt%.

[0044] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 30 minutes, dried at 50°C, and then immersed in a surfactant solution for 4 hours. After being taken out, the membrane was immersed in a dopamine deposition solution and reacted at 25°C for 10 hours. The membrane was washed with deionized water and dried in a vacuum to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, perform ultrasonic dispersion for 30 minutes, add triethylamine, stir evenly, and obtain an aqueous phase solution; the mass concentration of m-phenylenediamine is 1.5wt%, and the mass concentration of triethylamine is 1.5wt%.

[0045] Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3wt%.

[0046] The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution, taken out after soaking for 10 minutes, the excess solution on the membrane surface was absorbed, and then immersed in an oil phase solution, interfacial polymerization reaction was carried out for 1 minute, taken out and dried, and then transferred to 75°C for heat treatment for 10 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0047] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 110° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0048] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 40°C, keep the temperature at normal pressure for 3 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0049] Comparative Example 2: Example 3 was used as the control group, and no quercetin-ethanol solution was added to Comparative Example 2.

[0050] A method for preparing a polytetrafluoroethylene composite nanofiltration membrane comprises the following steps: Step 1: The preparation step of dopamine deposition solution is as follows: 2g dopamine and polyethyleneimine are added into Tris buffer (pH 8.5), stirred evenly, and a dopamine deposition solution is obtained. The concentration of the dopamine deposition solution is 2g / L; the mass ratio of dopamine to polyethyleneimine is 1:0.1.

[0051] Perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water were mixed to obtain a surfactant solution; the mass concentration of the surfactant solution was 2 wt %.

[0052] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 30 minutes, dried at 50°C, and then immersed in a surfactant solution for 4 hours. After being taken out, the membrane was immersed in a dopamine deposition solution and reacted at 25°C for 10 hours. The membrane was washed with deionized water and dried in a vacuum to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, perform ultrasonic dispersion for 30 minutes, add triethylamine, stir evenly, and obtain an aqueous phase solution; the mass concentration of m-phenylenediamine is 1.5wt%, and the mass concentration of triethylamine is 1.5wt%.

[0053] Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3wt%.

[0054] The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution, taken out after soaking for 10 minutes, the excess solution on the membrane surface was absorbed, and then immersed in an oil phase solution, interfacial polymerization reaction was carried out for 1 minute, taken out and dried, and then transferred to 75°C for heat treatment for 10 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0055] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 110° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0056] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 40°C, keep the temperature at normal pressure for 3 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0057] Comparative Example 3: Example 3 was used as a control group, and only dopamine deposition was used in Comparative Example 3.

[0058] A method for preparing a polytetrafluoroethylene composite nanofiltration membrane comprises the following steps: Step 1: The preparation step of dopamine deposition solution is as follows: 2 g of dopamine is added into Tris buffer (pH 8.5), and stirred evenly to obtain dopamine deposition solution. The concentration of the dopamine deposition solution is 2 g / L.

[0059] Perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water were mixed to obtain a surfactant solution; the mass concentration of the surfactant solution was 2 wt %.

[0060] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 30 minutes, dried at 50°C, and then immersed in a surfactant solution for 4 hours. After being taken out, the membrane was immersed in a dopamine deposition solution and reacted at 25°C for 10 hours. The membrane was washed with deionized water and dried in a vacuum to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, perform ultrasonic dispersion for 30 minutes, add triethylamine, stir evenly, and obtain an aqueous phase solution; the mass concentration of m-phenylenediamine is 1.5wt%, and the mass concentration of triethylamine is 1.5wt%.

[0061] Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3wt%.

[0062] The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution, taken out after soaking for 10 minutes, the excess solution on the membrane surface was absorbed, and then immersed in an oil phase solution, interfacial polymerization reaction was carried out for 1 minute, taken out and dried, and then transferred to 75°C for heat treatment for 10 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

[0063] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 110° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0064] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 40°C, keep the temperature at normal pressure for 3 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0065] Blank control group: Step 1: Mix perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water to obtain a surfactant solution; the mass concentration of the surfactant solution is 2wt%.

[0066] The polytetrafluoroethylene membrane was ultrasonically cleaned in anhydrous ethanol for 30 minutes, dried at 50°C, and then immersed in a surfactant solution for 4 hours. After being taken out, it was immersed in Tris buffer and soaked for 2 hours. It was washed with deionized water and vacuum dried to obtain a hydrophilic modified polytetrafluoroethylene membrane.

[0067] The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are as follows: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethanethiol at 110° C. at a dropping rate of 3 drops / s, keep warm to react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; the molar ratio of perfluorohexyl ethanethiol, sodium perchlorate and concentrated hydrochloric acid is 0.87:1:1.05.

[0068] S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 40°C, keep the temperature at normal pressure for 3 hours, distill and recover triethylamine, cool and discharge, purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine. The molar ratio of N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is 1.4:1.

[0069] Detection experiment: 1. According to the methods disclosed in Examples 1 to 3 and Comparative Examples 1 to 3, a hydrophilic modified polytetrafluoroethylene membrane was prepared. At the same time, according to the method disclosed in the blank control group, a blank control sample was taken and the water contact angle of the sample was tested respectively; the volume of the water droplet was 3 μL, and at least 5 measurements were made at different positions on the membrane surface during the test, and the average value was taken. " / " in the table means not tested.

[0070] 2. According to the methods disclosed in Examples 1 to 3 and Comparative Examples 1 to 3, a polytetrafluoroethylene composite nanofiltration membrane was prepared, and the salt retention rate of the nanofiltration membrane was tested. The test parameters were as follows: the feed liquid was sodium sulfate with a concentration of 1 g / L, and the test was performed after pre-pressing for 30 minutes. The test pressure was 0.5 MPa, the feed liquid temperature was 25, and the pH was 7.0.

[0071] 3. According to the methods disclosed in Examples 1 to 3 and Comparative Examples 1 to 3, a polytetrafluoroethylene composite nanofiltration membrane was prepared. The acid resistance of the nanofiltration membrane was tested. The pure water flux of the nanofiltration membrane was first tested. The test parameters were as follows: the feed liquid was deionized water, and the test was performed after pre-pressing for 30 minutes. The test pressure was 0.5 MPa, and the feed liquid temperature was 25°C. The nanofiltration membrane was then immersed in a hydrochloric acid solution (pH 1) for 7 days, the pure water flux of the nanofiltration membrane was retested, and the water flux retention rate was calculated.

[0072]

[0073] Conclusion: This scheme discloses a method for preparing a polytetrafluoroethylene composite nanofiltration membrane. The preparation process is simple, and the hierarchical structure and component design are reasonable. The prepared composite nanofiltration membrane has excellent hydrophilicity, excellent anti-pollution and acid-base resistance, and high water flux and salt retention performance, and can be widely used in water treatment and other fields.

[0074] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a polytetrafluoroethylene composite nanofiltration membrane, characterized in that: The following steps are involved: Step 1: mixing perfluorohexylethylsulfonamidopropylethylcarboxybetaine and deionized water to obtain a surfactant solution; The polytetrafluoroethylene membrane is ultrasonically cleaned in anhydrous ethanol for 20-30 minutes, dried at 40-50°C, and then immersed in a surfactant solution for 2-5 hours. After being taken out, the membrane is immersed in a dopamine deposition solution and reacted at 25-30°C for 8-12 hours. The membrane is then washed with deionized water and vacuum dried to obtain a hydrophilic modified polytetrafluoroethylene membrane. Step 2: Mix m-phenylenediamine and deionized water, and disperse them by ultrasonic for 20-30 minutes, then add triethylamine and stir evenly to obtain an aqueous solution; Dissolve trimesoyl chloride in n-hexane and stir evenly to obtain an oil phase solution; The hydrophilic modified polytetrafluoroethylene membrane was immersed in an aqueous solution for 10 to 15 minutes, then taken out, the excess solution on the membrane surface was removed by aspiration, and then immersed in an oil phase solution, and the interfacial polymerization reaction was carried out for 1 to 2 minutes. The membrane was taken out and dried, and then transferred to 70 to 75°C for heat treatment for 10 to 15 minutes to obtain a polytetrafluoroethylene composite nanofiltration membrane.

2. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 1, characterized in that: In step 1, the preparation steps of the dopamine deposition solution are: adding dopamine and polyethyleneimine into Tris buffer, stirring evenly, then adding quercetin-ethanol solution, mixing evenly, and obtaining the dopamine deposition solution.

3. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 2, characterized in that: The concentration of the quercetin-ethanol solution is 1-2 g / L; the concentration of the dopamine deposition solution is 1.5-2 g / L; and the mass ratio of dopamine, polyethyleneimine, and quercetin is 1:0.1:

1.

4. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 1, characterized in that: In step 1, the mass concentration of the surfactant solution is 1-2 wt%.

5. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 1, characterized in that: In the aqueous phase solution of step 2, the mass concentration of m-phenylenediamine is 1-1.5wt%, and the mass concentration of triethylamine is 1-1.5wt%; the mass concentration of trimesoyl chloride in the oil phase solution is 0.3-0.5wt%.

6. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 1, characterized in that: The preparation steps of perfluorohexylethylsulfonamidopropylethylcarboxy betaine are: S11: Add concentrated hydrochloric acid and sodium perchlorate into a reaction kettle, stir evenly, slowly add perfluorohexyl ethyl mercaptan at 100-110°C at a dropping rate of 2-3 drops / s, keep warm and react until the materials are completely added, stop the reaction, cool, collect the crude product, and purify it by distillation to obtain perfluorohexyl ethyl sulfonyl chloride; S12: Dissolve N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt in triethylamine, put it into a reaction kettle after it is completely dissolved, slowly add perfluorohexyl ethyl sulfonyl chloride at 20-40°C, keep the temperature at room temperature for 3-4 hours, distill and recover triethylamine, discharge the material after cooling, and purify to obtain perfluorohexyl ethyl sulfonamide propyl ethyl carboxy betaine.

7. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 6, characterized in that: In step S11, the molar ratio of perfluorohexylethanethiol, sodium perchlorate and concentrated hydrochloric acid is (0.8-0.9):1:(1-1.1).

8. The method for preparing a polytetrafluoroethylene composite nanofiltration membrane according to claim 6, characterized in that: In step S12, the molar ratio of the N,N-dimethyl-1,3-propylenediamine ethyl lactone quaternary ammonium salt to perfluorohexyl ethyl sulfonyl chloride is (1-1.5):

1.

9. A polytetrafluoroethylene composite nanofiltration membrane prepared according to the preparation method according to any one of claims 1 to 8.

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