Processing technology of high-performance nanofiltration membrane

Abstract

The invention relates to the technical field of nanofiltration membranes, in particular to a processing technology of a high-performance nanofiltration membrane, which comprises the following steps: adding 35-40 parts by weight of polytetrafluoroethylene, 6-10 parts by weight of kaolin-doped filling agent and 4-7 parts by weight of combined modifier into 30-35 parts by weight of xylene; and then adding 3-5 parts by weight of silicone oil and 2-4 parts by weight of sodium lignin sulfonate, and fully blending to obtain a membrane preparation solution. According to the nanofiltration membrane processing technology, a modified nanofiltration membrane is prepared from the membrane preparation liquid through the technologies of melt blending, extrusion by an extruder and the like, the retention rate, the water flux and the pollution resistance of the prepared nanofiltration membrane product are difficult to realize balanced and coordinated improvement through blending and synergistic effects of the kaolin-doped filling agent and the combined-effect modifier and through the co-matching and synergistic effects of the raw materials, and the water flux and the pollution resistance of the nanofiltration membrane product are greatly improved. And meanwhile, the product has remarkable high-temperature-resistant and washable stability effects.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membranes, and particularly to a processing technology for high-performance nanofiltration membranes. Background Art

[0002] As a new type of membrane separation technology, nanofiltration membranes have unique advantages in removing impurities, salts and harmful substances in water, and have received extensive attention. Nanofiltration membranes are a pressure-driven membrane separation process between ultrafiltration membranes and reverse osmosis membranes. Existing nanofiltration membranes have poor rejection rates for organic matter and sodium sulfate, as well as poor water flux and fouling resistance. It is very difficult to achieve balanced and coordinated improvement in rejection rate, water flux and fouling resistance. At the same time, the products have poor high-temperature resistance and washing stability, which limits the use efficiency of the products. Summary of the Invention

[0003] Aiming at the defects of the existing technology, the purpose of the present invention is to provide a processing technology for high-performance nanofiltration membranes to solve the problems raised in the above background art.

[0004] The present invention adopts the following technical solutions to solve the technical problems: The present invention provides a processing technology for high-performance nanofiltration membranes, including the following steps: Step 1: Add 1-2 parts by weight of silane coupling agent KH550 and 4-7 parts by weight of sodium alginate solution to 5-8 parts by weight of a chitosan solution with a mass fraction of 3-5%, and mix well to obtain a uniform coating solution; Step 2: Add 35-40 parts by weight of polytetrafluoroethylene, 6-10 parts by weight of a filler doped with kaolin, and 4-7 parts by weight of a synergistic modifier to 30-35 parts by weight of xylene, and then add 3-5 parts by weight of silicone oil and 2-4 parts by weight of sodium lignosulfonate, and mix well to obtain a membrane-forming solution; Melt and blend the membrane-forming solution, extrude it with an extruder, then cool and form, extract, biaxially stretch and sinter and cure at a high temperature of 340 °C for 15 min to prepare a modified nanofiltration membrane; Step 3: Wash the modified nanofiltration membrane with clean water and dry it until the moisture content is lower than 2%; Step 4: Uniformly coat the uniform coating solution on the surface of the membrane obtained in Step 3, perform negative pressure treatment, then crosslink it in an epoxy chloropropane solution with a mass fraction of 2% for 8-10 h, and finally dry it at 80 °C for 10 min to obtain a high-performance nanofiltration membrane.

[0005] Preferably, the mass fraction of the sodium alginate solution is 5-8%; the extrusion temperature of the extruder is 195 °C; the MD stretching rate of the biaxial stretching is 21% in the MD direction and 40% in the TD direction; The conditions for the negative pressure treatment are: negative pressure 0.8 MPa, treatment at a temperature of 55 °C for 2 h.

[0006] Preferably, the preparation method of the filler doped with kaolin is: S01: Stir the boron nitride in a sufficient amount of 5% potassium permanganate solution, then wash, filter and dry; 5-8 parts by weight of dry boron nitride, 2-4 parts by weight of wood cellulose and 3-6 parts by weight of 5% sodium dodecylbenzene sulfonate solution are uniformly mixed to obtain a boron nitride liquid; S02: 3-5 parts by weight of halloysite nanotubes, 5-8 parts by weight of dopamine hydrochloride solution and 2-3 parts by weight of lanthanum oxide are uniformly blended, and then 2-4 parts by weight of sodium stearate are added and blended sufficiently to obtain a halloysite nanotube solution; The boron nitride liquid and the halloysite nanotube liquid are mixed and stirred in a weight ratio of 3:5, and the stirring is completed to obtain a mixed modified liquid; S03: preheating kaolin at 60-65°C for 1 hour, stirring the preheated kaolin in a modified liquid that is 3-5 times the total weight of the kaolin, and completing the stirring to obtain a modified liquid doped with kaolin; S04: The modified liquid doped with kaolin and the filler are mixed in a weight ratio of 5:3 and ball-milled at a speed of 1000 r / min for 2 h. After the ball-milling is completed, the mixture is filtered and dried to obtain the filler doped with kaolin.

[0007] Preferably, the mass fraction of the dopamine hydrochloride solution is 4-7%; the stirring speed of the blending and stirring treatment in S02 is 750-800 r / min, and the stirring is for 2 hours.

[0008] Preferably, the preparation method of the filler is: Add 2-3 parts by weight of nano-bentonite and 3-5 parts by weight of silicon carbide whiskers to 5-8 parts by weight of sodium silicate solution, stir evenly, then add 2-4 parts by weight of urea solution and 1-3 parts by weight of titanium oxide, stir sufficiently, filter and dry to obtain a filler.

[0009] Preferably, the mass fraction of the sodium silicate solution is 5-7%; the mass fraction of the urea solution is 2-5%.

[0010] Preferably, the preparation method of the synergistic modifier is: S11: irradiating the silicon dioxide in a proton irradiation box for 1 hour at an irradiation power of 350-400W, and obtaining irradiated silicon dioxide after the irradiation is completed; The irradiated silicon dioxide is stirred fully in a sufficient amount of 5% by mass sulfuric acid solution, then washed with water, filtered and dried; S12: Ultrasonic treatment is performed on the dried silica and the synergistic liquid in a weight ratio of 3:5. After the ultrasonic treatment is completed, the mixture is filtered and dried to obtain a synergistic modifier.

[0011] Preferably, the ultrasonic treatment is performed at an ultrasonic power of 350-400 W for 1 hour.

[0012] Preferably, the preparation method of the synergistic liquid is: 2-5 parts by weight of β-cyclodextrin and 0.45-0.55 parts by weight of silane coupling agent KH560 are added to 15-20 parts by weight of ethanol solvent, and then 1-3 parts by weight of hydrotalcite and 2-5 parts by weight of nano-alumina are added, and stirred sufficiently to obtain a synergistic liquid.

[0013] Preferably, the average particle size of the nano-alumina is 20-100 nm, and the specific surface area is 200-500 m 2 / g.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. In the nanofiltration membrane processing technology of the present invention, the membrane-making liquid is used to form a modified nanofiltration membrane through melt blending, extrusion and other processes, and then the uniform coating liquid is used for uniform coating, and then the epichlorohydrin solution is used for cross-linking treatment. The chitosan solution, silane coupling agent KH550 and sodium alginate solution in the uniform coating liquid are coordinated to optimize the functional effect of the nanofiltration membrane. The membrane-making liquid uses polytetrafluoroethylene as a matrix, and is coordinated with raw materials such as silicone oil and sodium lignin sulfonate, and then the filler and the synergistic modifier doped with kaolin are used for coordination. Through the synergistic effect between the raw materials, the retention rate, water flux and anti-fouling property of the prepared nanofiltration membrane product are difficult to achieve balanced and coordinated improvement, and the product has remarkable high temperature resistance and washing stability; 2. The filler doped with kaolin is made of kaolin that has been preheated and then improved and optimized with a modified liquid. The modified liquid is improved by mixing and stirring a boron nitride liquid and a halloysite nanotube liquid. The boron nitride in the boron nitride liquid is used as a matrix, and cellulose and a 5% sodium dodecylbenzene sulfonate solution are blended. The halloysite nanotubes in the halloysite nanotube liquid are combined with a hydrochloric acid dopamine solution, lanthanum oxide, sodium stearate and other raw materials. Boron nitride is used as a matrix support structure, and the tubular structure of the halloysite nanotubes enhances the specific surface area, which is convenient for the contact area between the nanofiltration membrane and the sewage. Kaolin has an interlayer spacing channel, and the sewage can be immersed in the channel. In combination with raw materials such as boron nitride, the coordinated improvement of the rejection rate, water flux and anti-fouling performance of the nanofiltration membrane product is achieved. 3. The nano-bentonite in the filler has a layered structure, which, together with the whisker structure of silicon carbide whiskers and titanium oxide raw materials, further plays a synergistic effect. At the same time, the sodium silicate solution and urea solution in the filler are further blended into the system to enhance the system performance and optimize the system's performance coordination and stability. 4. The synergistic modifier is prepared by irradiating nano-silica with proton radiation and treating it with an acid solution to activate its activity. Then, it is further improved by the synergistic liquid. The hydrotalcite and nano-aluminum oxide in the synergistic liquid are used as the matrix, and β-cyclodextrin is added. β-cyclodextrin has amphiphilic effects, being hydrophilic to both organic and inorganic substances. When incorporated into the system, it optimizes the rejection rate of the system for organic substances and sodium sulfate. Through the co-compounding and synergistic effects of the raw materials, the synergistic effect between the obtained synergistic modifier and the filler doped with kaolin is further enhanced, thus further improving the performance of the product. Detailed implementation mode

[0015] The following combines specific embodiments to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0016] The processing technology of a high-performance nanofiltration membrane in this embodiment includes the following steps: Step 1: Add 1-2 parts by weight of silane coupling agent KH550 and 4-7 parts by weight of sodium alginate solution to 5-8 parts by weight of a chitosan solution with a mass fraction of 3-5%, and mix them thoroughly to obtain a uniform coating solution. Step 2: Add 35-40 parts by weight of polytetrafluoroethylene, 6-10 parts by weight of a filler doped with kaolin, and 4-7 parts by weight of a synergistic modifier to 30-35 parts by weight of xylene. Then, add 3-5 parts by weight of silicone oil and 2-4 parts by weight of sodium lignosulfonate and mix them thoroughly to obtain a membrane-forming solution. Melt-blend the membrane-forming solution, extrude it with an extruder, then cool and form, extract, biaxially stretch, and sinter and cure at a high temperature of 340 °C for 15 min to prepare a modified nanofiltration membrane. Step 3: Wash the modified nanofiltration membrane with clean water and dry it until the moisture content is lower than 2%. Step 4: Uniformly coat the uniform coating solution on the surface of the membrane obtained in Step 3, perform negative pressure treatment, then crosslink it in an epoxy chloropropane solution with a mass fraction of 2% for 8-10 h, and finally dry it at 80 °C for 10 min to obtain a high-performance nanofiltration membrane.

[0017] In this embodiment, the mass fraction of the sodium alginate solution is 5-8%; the extrusion temperature of the extruder is 195 °C; the MD stretching ratio in the biaxial stretching direction is 21%, and the TD direction is 40%. The conditions for negative pressure treatment are: negative pressure 0.8 MPa, treatment at a temperature of 55 °C for 2 h.

[0018] The preparation method of the filler doped with kaolin in this embodiment is: S01: Stir the boron nitride in a sufficient amount of 5% potassium permanganate solution, then wash, filter and dry; 5-8 parts by weight of dry boron nitride, 2-4 parts by weight of wood cellulose and 3-6 parts by weight of 5% sodium dodecylbenzene sulfonate solution are uniformly mixed to obtain a boron nitride liquid; S02: 3-5 parts by weight of halloysite nanotubes, 5-8 parts by weight of dopamine hydrochloride solution and 2-3 parts by weight of lanthanum oxide are uniformly blended, and then 2-4 parts by weight of sodium stearate are added and blended sufficiently to obtain a halloysite nanotube solution; The boron nitride liquid and the halloysite nanotube liquid are mixed and stirred in a weight ratio of 3:5, and the stirring is completed to obtain a mixed modified liquid; S03: preheating kaolin at 60-65°C for 1 hour, stirring the preheated kaolin in a modified liquid that is 3-5 times the total weight of the kaolin, and completing the stirring to obtain a modified liquid doped with kaolin; S04: The modified liquid doped with kaolin and the filler are mixed in a weight ratio of 5:3 and ball-milled at a speed of 1000 r / min for 2 h. After the ball-milling is completed, the mixture is filtered and dried to obtain the filler doped with kaolin.

[0019] The mass fraction of the dopamine hydrochloride solution in this embodiment is 4-7%; the stirring speed of the blending and stirring treatment in S02 is 750-800r / min, and the stirring is for 2h.

[0020] The preparation method of the filler of this embodiment is: Add 2-3 parts by weight of nano-bentonite and 3-5 parts by weight of silicon carbide whiskers to 5-8 parts by weight of sodium silicate solution, stir evenly, then add 2-4 parts by weight of urea solution and 1-3 parts by weight of titanium oxide, stir sufficiently, filter and dry to obtain a filler.

[0021] The mass fraction of the sodium silicate solution in this embodiment is 5-7%; the mass fraction of the urea solution is 2-5%.

[0022] The preparation method of the synergistic modifier of this embodiment is: S11: irradiating the silicon dioxide in a proton irradiation box for 1 hour at an irradiation power of 350-400W, and obtaining irradiated silicon dioxide after the irradiation is completed; The irradiated silicon dioxide is stirred fully in a sufficient amount of 5% by mass sulfuric acid solution, then washed with water, filtered and dried; S12: Ultrasonic treatment is performed on the dried silica and the synergistic liquid in a weight ratio of 3:5. After the ultrasonic treatment is completed, the mixture is filtered and dried to obtain a synergistic modifier.

[0023] The ultrasonic treatment in this embodiment has an ultrasonic power of 350-400 W and is carried out for 1 hour.

[0024] The preparation method of the synergistic liquid of this embodiment is: 2-5 parts by weight of β-cyclodextrin and 0.45-0.55 parts by weight of silane coupling agent KH560 are added to 15-20 parts by weight of ethanol solvent, and then 1-3 parts by weight of hydrotalcite and 2-5 parts by weight of nano-alumina are added, and stirred sufficiently to obtain a synergistic liquid.

[0025] The average particle size of the nano-alumina in this embodiment is 20-100nm, and the specific surface area is 200-500m 2 / g.

[0026] Example 1 A processing technology of a high-performance nanofiltration membrane in this embodiment includes the following steps: Step 1: Add 1 part by weight of silane coupling agent KH550 and 4 parts by weight of sodium alginate solution to 5 parts by weight of 3% chitosan solution and mix thoroughly to obtain a uniform coating solution; Step 2: adding 35 parts by weight of polytetrafluoroethylene, 6 parts by weight of a filler doped with kaolin and 4 parts by weight of a synergistic modifier to 30 parts by weight of xylene, and then adding 3 parts by weight of silicone oil and 2 parts by weight of sodium lignin sulfonate to fully blend to obtain a film-making solution; The membrane-making liquids were melt-blended, extruded by an extruder, and then cooled, formed, extracted, biaxially stretched, and sintered at a high temperature of 340° C. for 15 min to prepare a modified nanofiltration membrane; Step 3: Wash the modified nanofiltration membrane with clean water and dry it until the moisture content is less than 2%; Step 4: Evenly apply the coating liquid to the membrane surface of step 3, treat it under negative pressure, cross-link it in a 2% by mass epichlorohydrin solution for 8 hours, and finally dry it at 80°C for 10 minutes to obtain a high-performance nanofiltration membrane.

[0027] The mass fraction of the sodium alginate solution in this embodiment is 5%; the extrusion temperature of the extruder is 195°C; the stretching ratio of the biaxial stretching direction is 21% and the TD direction is 40%; The negative pressure treatment conditions are: negative pressure 0.8 MPa, temperature 55°C for 2 hours.

[0028] The preparation method of the filler doped with kaolin in this embodiment is: S01: Stir the boron nitride in a sufficient amount of 5% potassium permanganate solution, then wash, filter and dry; 5 parts by weight of dry boron nitride, 2 parts by weight of wood cellulose and 3 parts by weight of 5% sodium dodecylbenzene sulfonate solution are uniformly mixed to obtain a boron nitride liquid; S02: Blend 3 parts by weight of halloysite nanotubes, 5 parts by weight of dopamine hydrochloride solution, and 2 parts by weight of lanthanum oxide evenly, and then add 2 parts by weight of sodium stearate and blend well to obtain halloysite nanotube liquid; Blend the boron nitride liquid and the halloysite nanotube liquid according to a weight ratio of 3:5, stir and process, and after stirring ends, obtain the blended modified liquid; S03: Preheat kaolin at 60 °C for 1 h, and stir the preheated kaolin well in the blended modified liquid that is 3 times the total weight of kaolin. After stirring ends, obtain the modified liquid doped with kaolin; S04: Mix and ball-mill the modified liquid doped with kaolin and the filler according to a weight ratio of 5:3. The ball-milling speed is 1000 r / min, ball-mill for 2 h. After ball-milling ends, filter and dry to obtain the filler doped with kaolin.

[0029] The mass fraction of the dopamine hydrochloride solution in this example is 4%; the stirring speed of the blending and stirring treatment in S02 is 750 r / min, and stir for 2 h.

[0030] The preparation method of the filler in this example is: Add 2 parts by weight of nano-bentonite and 3 parts by weight of silicon carbide whiskers to 5 parts by weight of sodium silicate solution, stir evenly, then add 2 parts by weight of urea solution and 1 part by weight of titanium oxide, stir well, and then filter and dry to obtain the filler.

[0031] The mass fraction of the sodium silicate solution in this example is 5%; the mass fraction of the urea solution is 2%.

[0032] The preparation method of the synergistic modifier in this example is: S11: Irradiate silicon dioxide in a proton irradiation chamber for 1 h, and the irradiation power is 350 W. After irradiation ends, obtain the irradiated silicon dioxide; Stir the irradiated silicon dioxide well in a sulfuric acid solution with a mass fraction of 5% in sufficient quantity, then wash with water, filter, and dry; S12: Ultrasonically process the dried silicon dioxide and the synergistic liquid according to a weight ratio of 3:5. After ultrasonic treatment ends, filter and dry to obtain the synergistic modifier.

[0033] The ultrasonic power of the ultrasonic treatment in this example is 350 W, and ultrasonic for 1 h.

[0034] The preparation method of the synergistic liquid in this example is: Add 2 parts by weight of β-cyclodextrin and 0.45 parts by weight of silane coupling agent KH560 to 15 parts by weight of ethanol solvent, then add 1 part by weight of hydrotalcite and 2 parts by weight of nano-aluminum oxide, and stir well to obtain the synergistic liquid.

[0035] The average particle size of the nano-aluminum oxide in this embodiment is 20 nm, and the specific surface area is 200 m 2 / g.

[0036] Example 2 A processing technology for a high-performance nanofiltration membrane in this embodiment includes the following steps: Step 1: Add 2 parts by weight of silane coupling agent KH550 and 7 parts by weight of sodium alginate solution to 8 parts by weight of a 5% chitosan solution by mass, and mix well to obtain a uniform coating solution; Step 2: Add 40 parts by weight of polytetrafluoroethylene, 10 parts by weight of a filler doped with kaolin, and 7 parts by weight of a synergistic modifier to 35 parts by weight of xylene, then add 5 parts by weight of silicone oil and 4 parts by weight of sodium lignosulfonate, and mix well to obtain a membrane-making solution; Melt-blend the membrane-making solution, extrude it with an extruder, then cool and form, extract, biaxially stretch, and sinter and cure at a high temperature of 340 °C for 15 min to prepare a modified nanofiltration membrane; Step 3: Wash the modified nanofiltration membrane with clean water and dry it until the moisture content is lower than 2%; Step 4: Uniformly coat the uniform coating solution on the membrane surface obtained in Step 3, perform negative pressure treatment, then crosslink it in a 2% epichlorohydrin solution by mass for 10 h, and finally dry it at 80 °C for 10 min to obtain a high-performance nanofiltration membrane.

[0037] The mass fraction of the sodium alginate solution in this embodiment is 8%; the extrusion temperature of the extruder is 195 °C; the MD stretching rate direction of the biaxial stretching is 21%, and the TD direction is 40%; The conditions for the negative pressure treatment are: negative pressure of 0.8 MPa and treatment at a temperature of 55 °C for 2 h.

[0038] The preparation method of the filler doped with kaolin in this embodiment is: S01: Stir boron nitride sufficiently in a sufficient amount of 5% potassium permanganate solution by mass, then wash with water, filter by suction, and dry; Mix 8 parts by weight of dried boron nitride, 4 parts by weight of wood cellulose, and 6 parts by weight of a 5% sodium dodecylbenzenesulfonate solution by mass evenly to obtain a boron nitride solution; S02: Mix 5 parts by weight of halloysite nanotubes, 8 parts by weight of dopamine hydrochloride solution, and 3 parts by weight of lanthanum oxide evenly, and then add 4 parts by weight of sodium stearate and mix well to obtain a halloysite nanotube solution; Mix and stir the boron nitride solution and the halloysite nanotube solution according to a weight ratio of 3:5. After stirring, obtain a blended modified solution; S03: Preheat kaolin at 65 °C for 1 h, and stir the preheated kaolin sufficiently in a blended modified solution that is 5 times the total weight of the kaolin. After stirring, obtain a modified solution of kaolin doped with the modifier; S04: The modified liquid doped with kaolin and the filler are mixed in a weight ratio of 5:3 and ball-milled at a speed of 1000 r / min for 2 h. After the ball-milling is completed, the mixture is filtered and dried to obtain the filler doped with kaolin.

[0039] The mass fraction of the dopamine hydrochloride solution in this embodiment is 7%; the stirring speed of the blending and stirring treatment in S02 is 800r / min, and the stirring is for 2h.

[0040] The preparation method of the filler of this embodiment is: 3 parts by weight of nano-bentonite and 5 parts by weight of silicon carbide whiskers were added to 8 parts by weight of sodium silicate solution, and the mixture was stirred evenly. Then, 4 parts by weight of urea solution and 3 parts by weight of titanium oxide were added, and the mixture was stirred sufficiently. The mixture was filtered and dried to obtain a filler.

[0041] The mass fraction of the sodium silicate solution in this embodiment is 7%; the mass fraction of the urea solution is 5%.

[0042] The preparation method of the synergistic modifier of this embodiment is: S11: irradiating the silicon dioxide in a proton irradiation box for 1 hour at an irradiation power of 400 W, and obtaining irradiated silicon dioxide after the irradiation is completed; The irradiated silicon dioxide is stirred fully in a sufficient amount of 5% by mass sulfuric acid solution, then washed with water, filtered and dried; S12: Ultrasonic treatment is performed on the dried silica and the synergistic liquid in a weight ratio of 3:5. After the ultrasonic treatment is completed, the mixture is filtered and dried to obtain a synergistic modifier.

[0043] The ultrasonic treatment in this embodiment has an ultrasonic power of 400 W and is carried out for 1 hour.

[0044] The preparation method of the synergistic liquid of this embodiment is: 5 parts by weight of β-cyclodextrin and 0.55 parts by weight of silane coupling agent KH560 were added to 20 parts by weight of ethanol solvent, and then 3 parts by weight of hydrotalcite and 5 parts by weight of nano-alumina were added, and stirred sufficiently to obtain a synergistic liquid.

[0045] The average particle size of the nano-alumina in this example is 100 nm, and the specific surface area is 500 m 2 / g.

[0046] Example 3 A processing technology of a high-performance nanofiltration membrane in this embodiment includes the following steps: Step 1: Add 1.5 parts by weight of silane coupling agent KH550 and 5.5 parts by weight of sodium alginate solution to 6.5 parts by weight of 4% chitosan solution and mix thoroughly to obtain a uniform coating solution; Step 2: Add 37.5 parts by weight of polytetrafluoroethylene, 8 parts by weight of a filler doped with kaolin, and 5.5 parts by weight of a synergistic modifier to 32.5 parts by weight of xylene. Subsequently, add 4 parts by weight of silicone oil and 3 parts by weight of sodium lignosulfonate and blend them thoroughly to obtain a film-forming solution; Melt-blend the film-forming solution, extrude it through an extruder, then cool and form, extract, biaxially stretch, and sinter and cure at a high temperature of 340 °C for 15 min to prepare a modified nanofiltration membrane; Step 3: Wash the modified nanofiltration membrane with clean water and dry it until the moisture content is lower than 2%; Step 4: Uniformly coat the sizing solution onto the surface of the membrane obtained in Step 3, perform negative pressure treatment, then crosslink it in an epichlorohydrin solution with a mass fraction of 2% for 9 h, and finally dry it at 80 °C for 10 min to obtain a high-performance nanofiltration membrane.

[0047] In this example, the mass fraction of the sodium alginate solution is 6.5%; the extrusion temperature of the extruder is 195 °C; the MD draw ratio of the biaxial stretching is 21% in the direction and 40% in the TD direction; The conditions for the negative pressure treatment are: negative pressure of 0.8 MPa and treatment at a temperature of 55 °C for 2 h.

[0048] The preparation method of the filler doped with kaolin in this example is as follows: S01: Stir boron nitride sufficiently in a sufficient amount of a potassium permanganate solution with a mass fraction of 5%, then wash it with water, filter it by suction, and dry it; Blend 6.5 parts by weight of dried boron nitride, 3 parts by weight of wood cellulose, and 4.5 parts by weight of a sodium dodecylbenzenesulfonate solution with a mass fraction of 5% evenly to obtain a boron nitride solution; S02: Blend 4 parts by weight of halloysite nanotubes, 6.5 parts by weight of a dopamine hydrochloride solution, and 2.5 parts by weight of lanthanum oxide evenly, and then add 3 parts by weight of sodium stearate and blend them thoroughly to obtain a halloysite nanotube solution; Blend and stir the boron nitride solution and the halloysite nanotube solution according to a weight ratio of 3:5. After the stirring ends, obtain a blended modified solution; S03: Preheat kaolin at 62.5 °C for 1 h, and stir the preheated kaolin sufficiently in a blended modified solution that is 4 times the total weight of the kaolin. After the stirring ends, obtain a modified solution of kaolin doped with the blended modified solution; S04: Mix and ball-mill the modified solution of kaolin doped with the filler according to a weight ratio of 5:3. The ball-milling speed is 1000 r / min, and ball-mill for 2 h. After the ball-milling ends, filter it by suction and dry it to obtain a filler doped with kaolin.

[0049] In this example, the mass fraction of the dopamine hydrochloride solution is 5.5%; the stirring speed of the blending and stirring treatment in S02 is 780 r / min, and stir for 2 h.

[0050] The preparation method of the filler of this embodiment is: 2.5 parts by weight of nano-bentonite and 4 parts by weight of silicon carbide whiskers were added to 6.5 parts by weight of sodium silicate solution, and the mixture was stirred evenly. Then, 3 parts by weight of urea solution and 2 parts by weight of titanium oxide were added, and the mixture was stirred sufficiently. The mixture was filtered and dried to obtain a filler.

[0051] The mass fraction of the sodium silicate solution in this embodiment is 6%; the mass fraction of the urea solution is 3.5%.

[0052] The preparation method of the synergistic modifier of this embodiment is: S11: irradiating the silicon dioxide in a proton irradiation box for 1 hour at an irradiation power of 375 W, and obtaining irradiated silicon dioxide after the irradiation is completed; The irradiated silicon dioxide is stirred fully in a sufficient amount of 5% by mass sulfuric acid solution, then washed with water, filtered and dried; S12: Ultrasonic treatment is performed on the dried silica and the synergistic liquid in a weight ratio of 3:5. After the ultrasonic treatment is completed, the mixture is filtered and dried to obtain a synergistic modifier.

[0053] The ultrasonic treatment in this embodiment was performed with an ultrasonic power of 375 W and for 1 h.

[0054] The preparation method of the synergistic liquid of this embodiment is: 3.5 parts by weight of β-cyclodextrin and 0.50 parts by weight of silane coupling agent KH560 were added to 17.5 parts by weight of ethanol solvent, and then 2 parts by weight of hydrotalcite and 3.5 parts by weight of nano-alumina were added, and stirred sufficiently to obtain a synergistic liquid.

[0055] The average particle size of the nano-alumina in this example is 60nm, and the specific surface area is 350m 2 / g.

[0056] Comparative Example 1 The difference from Example 3 is that no filler doped with kaolin is added to the membrane-forming solution.

[0057] Comparative Example 2 The difference from Example 3 is that no kaolin-doped modifying liquid is added in the preparation of the kaolin-doped filler.

[0058] Comparative Example 3 The difference from Example 3 is that no preheated kaolin is added to the modified liquid doped with kaolin.

[0059] Comparative Example 4 The difference from Example 3 is that no boron nitride liquid is added to the mixed modified liquid.

[0060] Comparative Example 5 The difference from Example 3 is that the halloysite nanotube liquid is not added to the mixed modified liquid.

[0061] Comparative Example 6 The difference from Example 3 is that no filler was added during the preparation of the doped kaolin filler.

[0062] Comparative Example 7 The difference from Example 3 is that no nano-bentonite and silicon carbide whiskers were added to the filler.

[0063] Comparative Example 8 The difference from Example 3 is that no urea solution and titanium oxide were added to the filler.

[0064] Comparative Example 9 The difference from Example 3 is that no synergistic modifier was added.

[0065] Comparative Example 10 The difference from Example 3 is that no synergistic liquid was added to the synergistic modifier.

[0066] Comparative Example 11 The difference from Example 3 is that no hydrotalcite and nano-aluminum oxide were added to the synergistic liquid.

[0067] Comparative Example 12 The difference from Example 3 is that no β-cyclodextrin and silane coupling agent KH560 were added to the synergistic liquid.

[0068] The products of Examples 1-3 and Comparative Examples 1-12 were subjected to conventional performance tests, including testing the rejection rate, water flux, and anti-fouling performance. At the same time, the high-temperature resistance and washing stability were tested (the product was placed at 75 °C for 12 h, and then washed with a sodium hydroxide solution with a pH of 12 under a pressure of 2.5 bar for 1 h. The above was one cycle, and the cycle was repeated 10 times). The test results are shown in Table 1; Table 1 Performance Test Results

[0069] It can be seen from Comparative Examples 1-12 and Example 3 that under conventional conditions, the products of Example 3 can achieve coordinated improvement in the rejection rate, water flux, and anti-fouling performance of the products, and the high-temperature resistance and washing stability of the products are remarkable; At the same time, for the products of Comparative Examples 1-12 under high-temperature and washing conditions, the water channels of the products deteriorated significantly. Adopting the solution of Example 3 of the present invention, the performance stability of the products is remarkable; When one of the doped kaolin filler and the synergistic modifier is not added to the membrane-forming solution, the performance of the product deteriorates significantly. By using the synergistic combination of the two, the performance of the product is remarkable; In the preparation of the filler doped with kaolin, the modified liquid of the doped kaolin is not added, the preheated kaolin is not added to the modified liquid of the doped kaolin, the boron nitride liquid is not added to the blended modified liquid, the halloysite nanotube liquid is not added to the blended modified liquid, the filler is not added in the preparation of the filler doped with kaolin, the nano-bentonite and silicon carbide whiskers are not added to the filler, and the urea solution and titanium oxide are not added to the filler. The performance of the product shows a deteriorating trend to varying degrees. The filler doped with kaolin prepared by using the modified liquid of the doped kaolin obtained by the specific method of the present invention in combination with the filler has the most remarkable performance effect. Using other methods instead is not as obvious as the effect of the present invention; In the synergistic modifier, the synergistic liquid is not added, and hydrotalcite and nano-aluminum oxide are not added to the synergistic liquid. β-cyclodextrin and silane coupling agent KH560 are not added to the synergistic liquid. The performance of the product shows a deteriorating trend to varying degrees. The synergistic modifier improved by using the synergistic liquid obtained by the specific method of the present invention has the most remarkable performance effect.

[0070] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0071] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A processing technology for high-performance nanofiltration membrane, characterized in that: The following steps are involved: Step 1: Add 1-2 parts by weight of silane coupling agent KH550 and 4-7 parts by weight of sodium alginate solution to 5-8 parts by weight of chitosan solution with a mass fraction of 3-5%, and mix well to obtain a uniform coating solution; Step 2: adding 35-40 parts by weight of polytetrafluoroethylene, 6-10 parts by weight of a filler doped with kaolin and 4-7 parts by weight of a synergistic modifier to 30-35 parts by weight of xylene, and then adding 3-5 parts by weight of silicone oil and 2-4 parts by weight of sodium lignin sulfonate to fully blend to obtain a film-making solution; The membrane-making liquids were melt-blended, extruded by an extruder, and then cooled, formed, extracted, biaxially stretched, and sintered at a high temperature of 340° C. for 15 min to prepare a modified nanofiltration membrane; Step 3: Wash the modified nanofiltration membrane with clean water and dry it until the moisture content is less than 2%; Step 4: Evenly apply the coating liquid to the membrane surface of step 3, treat it under negative pressure, cross-link it in a 2% by mass epichlorohydrin solution for 8-10 hours, and finally dry it at 80°C for 10 minutes to obtain a high-performance nanofiltration membrane.

2. The processing technology of a high-performance nanofiltration membrane according to claim 1, characterized in that: The mass fraction of the sodium alginate solution is 5-8%; the extrusion temperature of the extruder is 195°C; the biaxial stretching stretching ratio is 21% in the MD direction and 40% in the TD direction; The negative pressure treatment conditions are: negative pressure 0.8 MPa, temperature 55°C for 2 hours.

3. The processing technology of a high-performance nanofiltration membrane according to claim 1, characterized in that: The preparation method of the filler doped with kaolin is: S01: Stir the boron nitride in a sufficient amount of 5% potassium permanganate solution, then wash, filter and dry; 5-8 parts by weight of dry boron nitride, 2-4 parts by weight of wood cellulose and 3-6 parts by weight of 5% sodium dodecylbenzene sulfonate solution are uniformly mixed to obtain a boron nitride liquid; S02: 3-5 parts by weight of halloysite nanotubes, 5-8 parts by weight of dopamine hydrochloride solution and 2-3 parts by weight of lanthanum oxide are uniformly blended, and then 2-4 parts by weight of sodium stearate are added and blended sufficiently to obtain a halloysite nanotube solution; The boron nitride liquid and the halloysite nanotube liquid are mixed and stirred in a weight ratio of 3:5, and the stirring is completed to obtain a mixed modified liquid; S03: preheating kaolin at 60-65°C for 1 hour, stirring the preheated kaolin in a modified liquid that is 3-5 times the total weight of the kaolin, and completing the stirring to obtain a modified liquid doped with kaolin; S04: The modified liquid doped with kaolin and the filler are mixed in a weight ratio of 5:3 and ball-milled at a speed of 1000 r / min for 2 h. After the ball-milling is completed, the mixture is filtered and dried to obtain the filler doped with kaolin.

4. A processing technology for a high-performance nanofiltration membrane according to claim 3, characterized in that: The mass fraction of the dopamine hydrochloride solution is 4-7%; the stirring speed of the blending and stirring treatment in S02 is 750-800r / min, and the stirring is for 2h.

5. The processing technology of a high-performance nanofiltration membrane according to claim 3, characterized in that: The preparation method of the filler is: Add 2-3 parts by weight of nano-bentonite and 3-5 parts by weight of silicon carbide whiskers to 5-8 parts by weight of sodium silicate solution, stir evenly, then add 2-4 parts by weight of urea solution and 1-3 parts by weight of titanium oxide, stir sufficiently, filter and dry to obtain a filler.

6. A high performance nanofiltration membrane processing technology according to claim 5, characterized in that: The mass fraction of the sodium silicate solution is 5-7%; the mass fraction of the urea solution is 2-5%.

7. The processing technology of a high-performance nanofiltration membrane according to claim 1, characterized in that: The preparation method of the synergistic modifier is: S11: irradiating the silicon dioxide in a proton irradiation box for 1 hour at an irradiation power of 350-400W, and obtaining irradiated silicon dioxide after the irradiation is completed; The irradiated silicon dioxide is stirred fully in a sufficient amount of 5% by mass sulfuric acid solution, then washed with water, filtered and dried; S12: Ultrasonic treatment is performed on the dried silica and the synergistic liquid in a weight ratio of 3:

5. After the ultrasonic treatment is completed, the mixture is filtered and dried to obtain a synergistic modifier.

8. The processing technology of a high-performance nanofiltration membrane according to claim 7, characterized in that: The ultrasonic treatment was performed at an ultrasonic power of 350-400 W for 1 hour.

9. The processing technology of a high-performance nanofiltration membrane according to claim 7, characterized in that: The preparation method of the synergistic liquid is: 2-5 parts by weight of β-cyclodextrin and 0.45-0.55 parts by weight of silane coupling agent KH560 are added to 15-20 parts by weight of ethanol solvent, and then 1-3 parts by weight of hydrotalcite and 2-5 parts by weight of nano-alumina are added, and stirred sufficiently to obtain a synergistic liquid.

10. A high performance nanofiltration membrane processing technology according to claim 9, characterized in that: The average particle size of the nano-alumina is 20-100nm, and the specific surface area is 200-500m 2 / g.

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