Reverse osmosis membrane for treating high-pollution wastewater and preparation method of reverse osmosis membrane

Abstract

The invention discloses a reverse osmosis membrane for treating high-pollution wastewater and a preparation method of the reverse osmosis membrane, and relates to the technical field of separation membranes. The reverse osmosis membrane is sequentially laminated and compounded into an enhanced non-woven fabric supporting layer, a nanofiber enhanced porous polymer middle supporting layer, a high-crosslinking-degree polyamide active separation layer and a protective layer from bottom to top. Through synergistic enhancement of a multi-layer structure, the mechanical strength, the chlorine oxidation resistance, the pollution resistance and the chemical cleaning recovery rate of the membrane are remarkably improved, and the membrane is suitable for reverse osmosis treatment of high-pollution water bodies such as landfill leachate and high-concentration industrial wastewater.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology, specifically to a reverse osmosis membrane for treating highly polluted wastewater and its preparation method. Background Technology

[0002] Disc reverse osmosis (DTRO) technology has become one of the core processes in the treatment of special wastewaters such as landfill leachate and high-concentration industrial wastewater due to its ability to withstand high-flux, high-salinity, and highly polluted feed water. As the core separation element of the DTRO system, the performance of the DT membrane directly determines the system's desalination rate, permeate flux, cleaning cycle, and service life.

[0003] Traditional DT reverse osmosis membranes typically employ a composite structure, consisting of a non-woven fabric support layer, a porous polymer intermediate support layer such as polysulfone, and a polyamide active separation layer, from bottom to top. However, when treating highly polluted industrial wastewater with complex and variable compositions, while conventional aromatic polyamide desalination layers possess excellent desalination performance, the amide bonds in their molecular structure and the acyl chloride groups that may remain after interfacial polymerization are susceptible to attack by active chlorine in the feed water, leading to chlorine substitution or amide bond degradation, resulting in a permanent and irreversible decrease in desalination rate. Furthermore, their long-term chemical stability faces severe challenges when dealing with frequent chemical cleaning, especially in strong acid or alkaline environments.

[0004] Polyamide separation layers typically exhibit a certain degree of roughness and negative charge on their surface. This makes them prone to adsorbing positively charged organic pollutants, colloidal particles, and microorganisms from wastewater through electrostatic interactions and physical trapping, forming a dense fouling layer, i.e., fouling. The physicochemical properties of their surface are not optimized for antifouling under extreme conditions, leading to rapid decline in membrane flux and increased operating pressure.

[0005] DTRO systems typically operate at pressures as high as 80-120 bar, with intense water flow impact. Traditional membrane support layers are prone to structural compaction or fatigue damage under long-term high pressure and turbulent impact, leading to an accelerated decline in permeate flux over time, and even membrane rupture in extreme cases, severely affecting system stability and membrane lifespan.

[0006] Once contamination occurs, contaminants easily embed themselves in the rough "peak-valley" structure of the polyamide layer, forming irreversible contamination that is difficult to remove. Conventional chemical cleaning is insufficient to completely remove these embedded contaminants, leading to a gradual decrease in the membrane's cleaning recovery rate and ultimately causing the membrane to fail to meet operational requirements and be prematurely scrapped.

[0007] Therefore, developing a DT reverse osmosis membrane that combines high desalination rate, excellent chemical stability, strong antifouling ability, and ultra-high mechanical strength is of great significance for promoting the advancement of high-difficulty wastewater treatment technology and reducing system operating costs and maintenance frequency. Summary of the Invention

[0008] The purpose of this invention is to provide a reverse osmosis membrane for treating highly polluted wastewater and its preparation method, so as to solve the problems existing in the prior art.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a reverse osmosis membrane for treating highly polluted wastewater, which is composed of a reinforced nonwoven support layer, a nanofiber-reinforced porous polymer intermediate support layer, a highly cross-linked polyamide active separation layer, and a protective layer stacked from bottom to top. The reinforced nonwoven support layer is made of polyester fiber, polypropylene terephthalate fiber, and reinforcing fiber combed into a fiber web, and then needle punched and hydroentangled. The addition of reinforcing fiber significantly improves the longitudinal and transverse tear strength of the membrane substrate, as well as its creep resistance. The protective layer is prepared by plasma treatment of a highly cross-linked polyamide active separation layer followed by sequential immersion in a silane solution and a modified solution.

[0010] Furthermore, the reinforcing fiber is obtained by extrusion, spinning, and traction of polypropylene and modified carbon nanotubes after melt mixing.

[0011] Furthermore, the polypropylene is selected from polypropylene resin with a melt index of 10-40 g / 10 min.

[0012] Furthermore, the modified carbon nanotubes are prepared by modifying carbon nanotubes with acrylic acid and methyl methacrylate.

[0013] Furthermore, the nanofiber-reinforced porous polymer intermediate support layer is a polysulfone porous membrane layer doped with silica nanofibers. The introduction of nanofibers forms a three-dimensional network framework, which greatly enhances the mechanical strength of the support layer, prevents structural compaction under high pressure, and provides a more uniform and stable interface for the formation of the upper polyamide layer.

[0014] Furthermore, the porosity of the nanofiber-reinforced porous polymer intermediate support layer is 60%-80%, and the average pore size is 10-50 nm.

[0015] Furthermore, the highly crosslinked polyamide active separation layer is a piperidinyl polyamide membrane layer. The introduction of piperidinyl replaces part of the m-phenylenediamine, and due to its steric hindrance effect and electron-donating properties, a polyamide network with higher crosslinking density and lower acyl chloride group residue is formed. This layer structure significantly improves the desalination layer's resistance to chlorine oxidation and its chemical stability.

[0016] Furthermore, the silane solution is a silane compound containing double bonds, and polyvinylpyrrolidone is prepared into an ethanol solution. This invention also incorporates polyvinylpyrrolidone, a hydrophilic polymer containing amide bonds, which can bond with the plasma-activated polyamide layer via hydrogen bonds, interpenetrating with the polymer. It can act as a sacrificial layer, preferentially consuming active chlorine instead of the polyamide layer, thereby improving the chlorine resistance of the reverse osmosis membrane.

[0017] Furthermore, the modified solution is prepared by adding terminal alkenyl polyethylene glycol ether and zwitterions containing double bonds to a mixed solvent of tetrahydrofuran and chloroform in a volume ratio of 1:1.

[0018] Furthermore, the silane compound containing double bonds comprises at least one of allyl dimethoxysilane, bis(trimethoxysilylmethyl)ethylene, methacryloyloxymethyltrimethoxysilane, and acryloyloxypropyltrimethoxysilane; the zwitterion containing double bonds.

[0019] Furthermore, the molar ratio of the terminal alkenyl polyethylene glycol ether, the zwitterion containing double bonds, the silane compound containing double bonds, and the polyvinylpyrrolidone is 3-5:1:0.5-1:1-3.

[0020] Furthermore, the molecular weight of the polyvinylpyrrolidone is 4000-5000.

[0021] Furthermore, the terminal alkenyl polyethylene glycol ether is allyl polyethylene glycol ether-600, allyl polyethylene glycol ether-1000, allyl polyethylene glycol ether-2000, allyl polyethylene glycol ether-3000, methyl allyl polyethylene glycol ether-600, methyl allyl polyethylene glycol ether-1000, methyl allyl polyethylene glycol ether-2000, methyl allyl polyethylene glycol ether-2400, methyl allyl... A mixture of one or more monomers selected from polyethylene glycol ether-3100, methyl allyl polyethylene glycol ether-4000, methyl allyl polyethylene glycol ether-5000, isopentenyl polyoxyethylene ether-1000, isopentenyl polyoxyethylene ether-2400, isopentenyl polyoxyethylene ether-3000, and isopentenyl polyoxyethylene ether-5000, or other terminal alkenyl polyoxyethylene ethers with a molecular weight of 600 to 6000.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) In this invention, the highly cross-linked polyamide active separation layer is pretreated by air plasma, oxygen-containing polar groups are introduced on its surface, and silane compounds containing double bonds are used as cross-linking agents to fix terminal alkenyl polyethylene glycol ether and zwitterionic polymers containing double bonds on the separation layer surface to form a protective layer. By adjusting the ratio of the three, the proportion of terminal alkenyl polyethylene glycol ether is maximized to ensure that the protective layer is still hydrophilic. Moreover, the hydrophilic polymer long chains of terminal alkenyl polyethylene glycol ether increase the disturbance on the membrane surface, further improving the fouling resistance of the reverse osmosis composite membrane. At the same time, the zwitterionic groups carry both positive and negative charges, have superhydrophilicity and strong hydration ability, and improve the fouling resistance. The presence of the protective layer not only reduces the attack sites of active chlorine, but also forms a three-dimensional polymer network structure with hydrophilic long chains as interpenetration and silane short chains as cross-linking, which is beneficial to form a chlorine-resistant and fouling-resistant protective layer without increasing the permeation resistance of the membrane surface.

[0023] (2) From the bottom fiber-reinforced nonwoven fabric to the middle support layer of nanofiber skeleton, the entire membrane structure of this invention can withstand higher operating pressure and more intense fluid shear force, effectively suppressing the membrane compaction effect under high pressure, ensuring long-term stability of water production flux, and reducing the attenuation rate by more than 30%. Since pollutants are difficult to adhere firmly to smooth, hydrophilic surfaces, even if contamination occurs, it is easier to remove them through conventional chemical cleaning. The membrane cleaning recovery rate of this invention can be stably maintained at more than 95%, which is much higher than the 80%-90% of traditional membranes. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 A reverse osmosis membrane for treating highly polluting wastewater has a four-layer composite structure stacked from bottom to top, specifically: a reinforced non-woven fabric support layer, a nanofiber-reinforced porous polymer intermediate support layer, a highly cross-linked polyamide active separation layer, and a protective layer. The method for preparing the reinforced nonwoven support layer is as follows: (1) Place 14 parts by mass of carbon nanotubes in a container, add 32 parts by mass of 15wt% sulfuric acid and 28 parts by mass of 15wt% nitric acid, sonicate at 20℃ for 2.5h, heat to 100℃ for 1h, filter to obtain solid, wash with deionized water 3 times, and dry in an oven at 45℃ for 10h to obtain hydroxylated carbon nanotubes. (2) Hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, and methyl methacrylate were added to N,N-dimethylformamide and ultrasonically dispersed evenly in an ice bath. Then, under a nitrogen atmosphere, polymerization was carried out at 50°C for 24 hours. After filtration, modified carbon nanotubes were obtained. The mass ratio of hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, methyl methacrylate, and N,N-dimethylformamide was 1:0.01:5:10:100. (3) Polypropylene and modified carbon nanotubes are melt-mixed at 170-200℃ in a mass ratio of 100:1 and then extruded and granulated to obtain modified polypropylene masterbatch. Then, spinning, winding and hot drawing are carried out. The spinning temperature is 200-250℃, the winding rate is 150m / min, and the hot drawing ratio is 3 times to obtain reinforcing fibers with a diameter of 3.5μm. (4) Polyester fibers with a diameter of 3.5 μm, polypropylene terephthalate fibers with a diameter of 3.5 μm, and reinforcing fibers are combed at a mass ratio of 10:10:5 to form a fiber web. The fiber web is needle-punched and then hydroentangled with a water pressure of 200 bar, with a basis weight of 150 g / m. 2 The thickness is 100 μm; in the needle-punching step, the needle is 500 ppsc (punch / cm). 2 The fiber web is needle-punched under the following conditions; in the hydroentangling step, the hydroentangling is performed while water is supplied to the fiber web through a nozzle with a diameter of 0.15 mm and a density of 15 ea / cm. The method for preparing the nanofiber-reinforced porous polymer intermediate support layer is as follows: (1) Add silica nanofibers, KH-550 and anhydrous ethanol to a beaker and let stand at 78°C for 5 hours to obtain modified silica nanofibers. The mass ratio of KH-550, silica nanofibers and anhydrous ethanol is 1:45:70. (2) 2% by weight of modified silica nanofibers were dispersed in dimethylformamide, 13% by weight of polysulfone was added, and the mixture was stirred until dissolved. Then, 0.5% by weight of polyethylene glycol was added, and the mixture was stirred evenly and allowed to stand and cool to form a casting solution. The cooled casting solution was uniformly coated onto the surface of the reinforced nonwoven fabric support layer with a coating thickness of 50 μm. After hydrogelation and rinsing, the intermediate support layer was prepared with a porosity of 60% and an average pore size of 50 nm. The preparation method of the highly cross-linked polyamide active separation layer is as follows: (1) Mix m-phenylenediamine, piperidine, sodium camphor sulfonate and water to prepare the aqueous phase solution; then immerse the polysulfone-based membrane in the aqueous phase solution for 2 minutes, then pour off the aqueous phase solution and remove the liquid remaining on the surface of the polysulfone-based membrane; the aqueous phase solution contains 2.5 wt% m-phenylenediamine and 3.0 wt% sodium camphor sulfonate; the molar ratio of piperidine to m-phenylenediamine is 1:3 to 1:1; (2) Dissolve pyromellitic chloride in ethylcyclohexane to prepare the oil phase liquid (pyromellitic chloride accounts for 0.15 wt% in the oil phase liquid); then place the polysulfone-based membrane in the oil phase liquid for 30 seconds of interfacial polymerization reaction. After the reaction, pour off the oil phase liquid and remove the residual liquid on the membrane surface. Then dry it in an oven at 50°C for 3 minutes. Finally, take out the membrane and wash it with water to obtain a highly crosslinked polyamide active separation layer. The method for preparing the protective layer: The highly cross-linked polyamide active separation layer was subjected to air plasma treatment for 20 seconds at a current of 0.1 A and a voltage of 20 V. Allyl dimethoxysilane was prepared into a 20% (w / w) ethanol solution, and polyvinylpyrrolidone was added. The highly cross-linked polyamide active separation layer was then impregnated in this solution, with ammonia added to a concentration of 0.2 wt%, and impregnated for 1 minute. Excess solution was discarded, and the layer was allowed to drain naturally. Allyl polyethylene glycol ether-600 and 2-methacryloyloxyethyl phosphate were then added. Choline was added to a mixed solvent of tetrahydrofuran and chloroform in a volume ratio of 1:1, and then 1 wt% of the total monomer weight of the initiator azobisisobutyronitrile was added. The highly cross-linked polyamide active separation layer was then impregnated in the mixture. The reaction was carried out at 75°C for 5 minutes under a nitrogen atmosphere. The excess solution was poured off, the mixture was allowed to drain naturally, and then dried in an oven at 50°C for 3 minutes. The molar ratio of allyl polyethylene glycol ether-600, 2-methacryloyloxyethyl phosphocholine, allyl dimethoxysilane, and polyvinylpyrrolidone was 3:1:1:3.

[0026] Example 2 A reverse osmosis membrane for treating highly polluting wastewater has a four-layer composite structure stacked from bottom to top, specifically: a reinforced non-woven fabric support layer, a nanofiber-reinforced porous polymer intermediate support layer, a highly cross-linked polyamide active separation layer, and a protective layer. The method for preparing the reinforced nonwoven support layer is as follows: (1) Place 22 parts by mass of carbon nanotubes in a container, add 50 parts by mass of 15wt% sulfuric acid and 46 parts by mass of 15wt% nitric acid, sonicate at 30℃ for 1.5h, heat to 80℃ for 3h, filter to obtain solid, wash with deionized water 3 times, and dry in an oven at 55℃ for 6h to obtain hydroxylated carbon nanotubes. (2) Hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, and methyl methacrylate were added to N,N-dimethylformamide and ultrasonically dispersed evenly in an ice bath. Then, under a nitrogen atmosphere, polymerization was carried out at 80°C for 6 hours. After filtration, modified carbon nanotubes were obtained. The mass ratio of hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, methyl methacrylate, and N,N-dimethylformamide was 5:0.05:10:20:100. (3) Polypropylene and modified carbon nanotubes are melt-mixed at 170-200℃ in a mass ratio of 100:5 and then extruded and granulated to obtain modified polypropylene masterbatch. Then, spinning, winding and hot drawing are carried out. The spinning temperature is 200-250℃, the winding rate is 150m / min, and the hot drawing ratio is 3 times to obtain reinforcing fibers with a diameter of 3.5μm. (4) Polyester fibers with a diameter of 5 μm, polypropylene terephthalate fibers with a diameter of 5 μm, and reinforcing fibers are combed at a mass ratio of 20:20:10 to form a fiber web. The fiber web is then needle-punched and hydroentangled with a water pressure of 200 bar, resulting in a basis weight of 150 g / m². 2 The thickness is 100 μm; in the needle-punching step, the needle is 500 ppsc (punch / cm). 2 The fiber web is needle-punched under the following conditions; in the hydroentangling step, the hydroentangling is performed while water is supplied to the fiber web through a nozzle with a diameter of 0.15 mm and a density of 15 ea / cm. The method for preparing the nanofiber-reinforced porous polymer intermediate support layer is as follows: (1) Silica nanofibers, KH-550 and anhydrous ethanol were added to a beaker and allowed to stand at 78°C for 5 hours to obtain modified silica nanofibers. The mass ratio of KH-550, silica nanofibers and anhydrous ethanol was 1:55:80. (2) 0.5% by weight of modified silica nanofibers were dispersed in dimethylformamide, 18% by weight of polysulfone was added, and the mixture was stirred until dissolved. Then, 0.1% by weight of polyvinylpyrrolidone was added, and the mixture was stirred evenly and allowed to stand and cool to form a casting solution. The cooled casting solution was uniformly coated onto the surface of the reinforced nonwoven fabric support layer with a coating thickness of 50 μm. After hydrogelation and rinsing, the intermediate support layer was prepared with a porosity of 60% and an average pore size of 50 nm. The preparation of the highly cross-linked polyamide active separation layer is the same as in Example 1; The method for preparing the protective layer: The highly cross-linked polyamide active separation layer was subjected to air plasma treatment for 1 second at a current of 5A and a voltage of 150V. A 30% (w / w) ethanol solution of methacryloyloxymethyltrimethoxysilane was prepared, and polyvinylpyrrolidone was added. The highly cross-linked polyamide active separation layer was then immersed in this solution, with ammonia added to a concentration of 0.2 wt%, and immersed for 5 minutes. Excess solution was discarded, and the layer was allowed to drain naturally. Then, methyl allyl polyethylene glycol ether-5000 and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide were added. Add the mixture to a 1:1 volume ratio of tetrahydrofuran and chloroform, then add 1 wt% of the total monomer weight of the initiator azobisisobutyronitrile (AIBN), and then impregnate the highly crosslinked polyamide active separation layer in it. React at 75°C for 1 min under a nitrogen atmosphere, pour off the excess solution, let it drain naturally, and dry it in an oven at 50°C for 3 min. The molar ratio of the methyl allyl polyethylene glycol ether-5000, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, methacryloyloxymethyltrimethoxysilane, and polyvinylpyrrolidone is 5:1:0.5:1.

[0027] Example 3 A reverse osmosis membrane for treating highly polluting wastewater has a four-layer composite structure stacked from bottom to top, specifically: a reinforced non-woven fabric support layer, a nanofiber-reinforced porous polymer intermediate support layer, a highly cross-linked polyamide active separation layer, and a protective layer. The method for preparing the reinforced nonwoven support layer is as follows: (1) Place 18 parts by mass of carbon nanotubes in a container, add 41 parts by mass of 15wt% sulfuric acid and 37 parts by mass of 15wt% nitric acid, sonicate at 25℃ for 2.0h, heat to 90℃ for 2h, filter to obtain solid, wash with deionized water 3 times, and dry in an oven at 50℃ for 8h to obtain hydroxylated carbon nanotubes. (2) Hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, and methyl methacrylate were added to N,N-dimethylformamide and ultrasonically dispersed evenly in an ice bath. Then, under a nitrogen atmosphere, polymerization was carried out at 65°C for 15 hours. After filtration, modified carbon nanotubes were obtained. The mass ratio of hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, methyl methacrylate, and N,N-dimethylformamide was 3:0.03:7:15:100. (3) Polypropylene and modified carbon nanotubes are melt-mixed at 170-200℃ in a mass ratio of 100:3 and then extruded and granulated to obtain modified polypropylene masterbatch. Then, spinning, winding and hot drawing are carried out. The spinning temperature is 200-250℃, the winding rate is 150m / min, and the hot drawing ratio is 3 times to obtain reinforcing fibers with a diameter of 3.5μm. (4) Polyester fibers with a diameter of 4.2 μm, polypropylene terephthalate fibers with a diameter of 4.2 μm, and reinforcing fibers are combed at a mass ratio of 15:15:7 to form a fiber web. The fiber web is needle-punched and then hydroentangled with a water pressure of 200 bar, with a basis weight of 150 g / m. 2 The thickness is 100 μm; in the needle-punching step, the needle is 500 ppsc (punch / cm). 2 The fiber web is needle-punched under the following conditions; in the hydroentangling step, the hydroentangling is performed while water is supplied to the fiber web through a nozzle with a diameter of 0.15 mm and a density of 15 ea / cm. The method for preparing the nanofiber-reinforced porous polymer intermediate support layer is as follows: (1) Add silica nanofibers, KH-550 and anhydrous ethanol to a beaker and let stand at 78°C for 5 hours to obtain modified silica nanofibers. The mass ratio of KH-550, silica nanofibers and anhydrous ethanol is 1:50:75. (2) 1.2% by weight of modified silica nanofibers were dispersed in dimethylformamide, 15% by weight of polysulfone was added, and the mixture was stirred until dissolved. Then, 0.3% by weight of lithium chloride was added, and the mixture was stirred evenly and allowed to stand and cool to form a casting solution. The cooled casting solution was uniformly coated onto the surface of the reinforced nonwoven fabric support layer with a coating thickness of 50 μm. After hydrogelation and rinsing, the intermediate support layer was prepared with a porosity of 60% and an average pore size of 50 nm. The preparation of the highly cross-linked polyamide active separation layer is the same as in Example 1; The method for preparing the protective layer: The highly cross-linked polyamide active separation layer was subjected to air plasma treatment for 12 seconds at a current of 2.5 A and a voltage of 80 V. Allyl dimethoxysilane was prepared into a 26% (w / w) ethanol solution, and polyvinylpyrrolidone was added. The highly cross-linked polyamide active separation layer was then impregnated in this solution, with ammonia added to a concentration of 0.2 wt%, and impregnated for 3 minutes. Excess solution was discarded, and the layer was allowed to drain naturally. Then, isopentenyl alcohol polyoxyethylene ether-3000 and 3-((3-acrylamidopropyl)dimethylammonium)propionic acid were added. The ester was added to a mixed solvent of tetrahydrofuran and chloroform in a volume ratio of 1:1, and then 1 wt% of the total monomer weight of the initiator azobisisobutyronitrile was added. The highly cross-linked polyamide active separation layer was then impregnated in the mixture. The reaction was carried out at 75°C for 3 minutes under a nitrogen atmosphere. The excess solution was then poured off, allowed to drain naturally, and dried in an oven at 50°C for 3 minutes. The molar ratio of isopentenyl alcohol polyoxyethylene ether-3000, 3-((3-acrylamidopropyl)dimethylammonium)propionate, allyl dimethoxysilane, and polyvinylpyrrolidone was 4:1:0.8:2.

[0028] Example 4 A reverse osmosis membrane for treating highly polluting wastewater has a four-layer composite structure stacked from bottom to top, specifically: a reinforced non-woven fabric support layer, a nanofiber-reinforced porous polymer intermediate support layer, a highly cross-linked polyamide active separation layer, and a protective layer. The method for preparing the reinforced nonwoven support layer is as follows: (1) Place 16 parts by mass of carbon nanotubes in a container, add 36 parts by mass of 15wt% sulfuric acid and 32 parts by mass of 15wt% nitric acid, sonicate at 22℃ for 2.2h, raise the temperature to 95℃ and react for 1.5h, filter to obtain solid, wash with deionized water 3 times, and dry in an oven at 48℃ for 9h to obtain hydroxylated carbon nanotubes. (2) Hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, and methyl methacrylate were added to N,N-dimethylformamide and ultrasonically dispersed evenly in an ice bath. Then, under a nitrogen atmosphere, polymerization was carried out at 55°C for 20 hours. After filtration, modified carbon nanotubes were obtained. The mass ratio of hydroxylated carbon nanotubes, ammonium persulfate, acrylic acid, methyl methacrylate, and N,N-dimethylformamide was 2:0.02:6:12:100. (3) Polypropylene and modified carbon nanotubes are melt-mixed at 170-200℃ in a mass ratio of 100:2 and then extruded and granulated to obtain modified polypropylene masterbatch. Then, spinning, winding and hot drawing are carried out. The spinning temperature is 200-250℃, the winding rate is 150m / min, and the hot drawing ratio is 3 times to obtain reinforcing fibers with a diameter of 3.5μm. (4) Polyester fibers with a diameter of 4.0 μm, polypropylene terephthalate fibers with a diameter of 4.0 μm, and reinforcing fibers are combed in a mass ratio of 12:12:6 to form a fiber web. The fiber web is needle-punched and then hydroentangled with a water pressure of 200 bar, with a basis weight of 150 g / m. 2 The thickness is 100 μm; in the needle-punching step, the needle is 500 ppsc (punch / cm). 2 The fiber web is needle-punched under the following conditions; in the hydroentangling step, the hydroentangling is performed while water is supplied to the fiber web through a nozzle with a diameter of 0.15 mm and a density of 15 ea / cm. The method for preparing the nanofiber-reinforced porous polymer intermediate support layer is as follows: (1) Silica nanofibers, KH-550 and anhydrous ethanol were added to a beaker and allowed to stand at 78°C for 5 hours to obtain modified silica nanofibers. The mass ratio of KH-550, silica nanofibers and anhydrous ethanol was 1:48:72. (2) 1.8% by weight of modified silica nanofibers were dispersed in dimethylformamide, 17% by weight of polysulfone was added, and the mixture was stirred until dissolved. Then, 0.4% by weight of polyethylene glycol was added, and the mixture was stirred evenly and allowed to stand and cool to form a casting solution. The cooled casting solution was uniformly coated onto the surface of the reinforced nonwoven fabric support layer with a coating thickness of 50 μm. After hydrogelation and rinsing, the intermediate support layer was prepared with a porosity of 60% and an average pore size of 50 nm. The preparation of the highly cross-linked polyamide active separation layer is the same as in Example 1; The method for preparing the protective layer: The highly cross-linked polyamide active separation layer was subjected to air plasma treatment for 5 seconds at a current of 1.2 A and a voltage of 90 V. A 22% (w / w) ethanol solution of bis(trimethoxysilylmethyl)ethylene was prepared, and polyvinylpyrrolidone was added. The highly cross-linked polyamide active separation layer was then impregnated in this solution, with ammonia added to a concentration of 0.2 wt%, and impregnated for 1 minute. Excess solution was discarded, and the layer was allowed to drain naturally. Then, methyl allyl polyethylene glycol ether-2000 and methacryloyloxyethyltrimethylammonium chloride were added... The mixture is added to a 1:1 volume ratio of tetrahydrofuran and chloroform, followed by 1 wt% of azobisisobutyronitrile (AIBN) as an initiator. The highly cross-linked polyamide active separation layer is then impregnated in the mixture. The reaction is carried out at 75°C for 4 minutes under a nitrogen atmosphere. Excess solution is discarded, the mixture is allowed to drain naturally, and then dried in an oven at 50°C for 3 minutes. The molar ratio of methyl allyl polyethylene glycol ether-2000, methacryloyloxyethyltrimethylammonium chloride, bis(trimethoxysilylmethyl)ethylene, and polyvinylpyrrolidone is 3:1:0.6:1.5.

[0029] Comparative Example 1 The difference between Comparative Example 1 and Example 4 is that no reinforcing fibers are added in the preparation of the reinforced nonwoven support layer, while the rest of the preparation methods are the same as in Example 4.

[0030] Comparative Example 2 The difference between Comparative Example 2 and Example 4 is that silica nanofibers are not added in the preparation of the protective layer, while the rest of the preparation method is the same as in Example 4.

[0031] Comparative Example 3 The difference between Comparative Example 3 and Example 4 is that no particulate nano-silica is added in the preparation of the nanofiber-reinforced porous polymer intermediate support layer; the rest of the preparation methods are the same as in Example 4.

[0032] Comparative Example 4 The difference between Comparative Example 4 and Example 4 is that piperidine is not added in the preparation of the highly cross-linked polyamide active separation layer, while the rest of the preparation method is the same as in Example 4.

[0033] Comparative Example 5 The difference between Comparative Example 5 and Example 4 is that air plasma pretreatment is not performed in the preparation of the protective layer, while the rest of the preparation method is the same as in Example 4.

[0034] Comparative Example 6 The difference between Comparative Example 6 and Example 4 is that no silane compound containing double bonds is added in the preparation of the protective layer, while the rest of the preparation method is the same as in Example 4.

[0035] Comparative Example 7 The difference between Comparative Example 7 and Example 4 is that polyvinylpyrrolidone is not added in the preparation of the protective layer, while the rest of the preparation method is the same as in Example 4.

[0036] Comparative Example 8 The difference between Comparative Example 8 and Example 4 is that no terminal alkenyl polyethylene glycol ether is added in the preparation of the protective layer, while the rest of the preparation method is the same as in Example 4.

[0037] Comparative Example 9 The difference between Comparative Example 9 and Example 4 is that no zwitterions containing double bonds are added in the preparation of the protective layer; the rest of the preparation method is the same as in Example 4.

[0038] Comparative Example 10 The difference between Comparative Example 10 and Example 4 is that the molar ratio of methyl allyl polyethylene glycol ether-2000, methacryloyloxyethyltrimethylammonium chloride, bis(trimethoxysilylmethyl)ethylene, and polyvinylpyrrolidone in the preparation of the protective layer is 3:1:3:1.5, while the rest of the preparation method is the same as in Example 4.

[0039] Performance testing (1) Chlorine resistance: The membrane was first subjected to static accelerated oxidation by contacting it with a 1000ppm sodium hypochlorite aqueous solution for 8 hours at a pH of 4.0 and a temperature of 25℃. The membrane was then rinsed with pure water and soaked in pure water for 48 hours. A cross-flow membrane testing station was used, with a 2000ppm sodium chloride aqueous solution as the inlet water, an operating pressure of 1.55MPa, a temperature of 25℃, and an inlet water pH of 7.0. The water flux and desalination rate of the membrane were tested, and the water flux decay rate and desalination rate decay rate were calculated. The calculation method is as follows: Chlorination-induced water flux decline rate = (1 - post-chlorination flux / initial flux) * 100%; Desalination rate decay rate = (1 - desalination rate after chlorination / initial desalination rate) * 100%.

[0040] (2) Antifouling: Under the same operating conditions as performance test (1), the test aqueous solution was replaced with a mixed solution of electronegative sodium dodecyl sulfate solution (50 g / L), electronegative dodecyltrimethylammonium bromide (50 g / L), and electronegative bovine serum albumin (100 g / L) for 30 min. The flux of the high-flux, high-desalination-rate antifouling polyamide reverse osmosis membrane after fouling was tested. After the fouling test was completed, the pressure was released, and the fouled membrane was cleaned with deionized water as feed liquid. Then, under the same operating conditions as performance test (1), a 2000 ppm sodium chloride aqueous solution was filtered for 30 min. The flux recovery rate and water flux decay rate after cleaning were calculated. The calculation method is as follows: Flux recovery rate after cleaning = (flux after cleaning / initial flux) * 100%; Post-contamination flux decline rate = (1 - Post-contamination flux / Initial flux) * 100% (3) Chemical cleaning resistance: The reverse osmosis membranes prepared in each example and comparative example were pre-pressurized with pure water at 5.0 MPa for 1 hour. Then, a mixed alkaline solution of 2% (W) ammonium tripolyphosphate and 0.25% (W) sodium dodecylbenzenesulfonate (pH 10) was prepared, and a hydrochloric acid solution of 0.5% (W) (pH 2.5) was prepared. The acid and alkaline solutions were circulated and rinsed for 10 hours. Then, the performance was tested (1). The pure water flux P2 and desalination rate R2 of the reverse osmosis membrane after chemical cleaning were tested, and the decrease in pure water flux and desalination rate were calculated. The calculation method is as follows: The decrease in pure water flux = (P1-P2) / P1×100%, The decrease in desalination rate = (R1-R2) / R1×100%.

[0041] (4) Hydrophilicity: The reverse osmosis membrane is laid flat on the sample stage of the contact angle analyzer with the protective layer facing upward. After adjusting the parameter settings of the contact angle analyzer, a small drop of pure water or salt water is dropped onto the sample. After the droplet is balanced on the membrane, a static image of the droplet can be obtained. The static image of the droplet and the contact angle are analyzed using droplet shape analysis software.

[0042] Table 1. Separation performance data of reverse osmosis membranes before and after chlorination. Table 2. Experimental data on contact angle and tensile strength of reverse osmosis membranes. 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 invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A reverse osmosis membrane for treating highly polluted wastewater, comprising, from bottom to top, a reinforced nonwoven fabric support layer, a nanofiber-reinforced porous polymer intermediate support layer, a highly cross-linked polyamide active separation layer, and a protective layer, characterized in that, The reinforced nonwoven support layer is made of polyester fiber, polypropylene terephthalate fiber, and reinforcing fiber combed into a web, and then needle punched and hydroentangled. The protective layer is prepared by plasma treatment of a highly cross-linked polyamide active separation layer followed by sequential immersion in a silane solution and a modified solution.

2. The reverse osmosis membrane for treating highly polluted wastewater according to claim 1, characterized in that, The reinforcing fiber is obtained by extrusion, spinning, and traction of polypropylene and modified carbon nanotubes after melt mixing.

3. The reverse osmosis membrane for treating highly polluted wastewater according to claim 2, characterized in that, The modified carbon nanotubes are prepared by modifying carbon nanotubes with acrylic acid and methyl methacrylate.

4. The reverse osmosis membrane for treating highly polluted wastewater according to claim 1, characterized in that, The nanofiber-reinforced porous polymer intermediate support layer is a polysulfone porous membrane layer doped with silica nanofibers.

5. The reverse osmosis membrane for treating highly polluted wastewater according to claim 4, characterized in that, The porosity of the nanofiber-reinforced porous polymer intermediate support layer is 60%-80%, and the average pore size is 10-50 nm.

6. The reverse osmosis membrane for treating highly polluted wastewater according to claim 1, characterized in that, The highly cross-linked polyamide active separation layer is a piperidinyl polyamide membrane layer.

7. The reverse osmosis membrane for treating highly polluted wastewater according to claim 1, characterized in that, The silane solution is a silane compound containing double bonds, prepared as an ethanol solution from polyvinylpyrrolidone.

8. The reverse osmosis membrane for treating highly polluted wastewater according to claim 1, characterized in that, The modified solution was prepared by adding terminal alkenyl polyethylene glycol ether and zwitterions containing double bonds to a mixed solvent of tetrahydrofuran and chloroform in a volume ratio of 1:

1.

9. A reverse osmosis membrane for treating highly polluted wastewater according to claim 7 or 8, characterized in that, The silane compound containing double bonds comprises at least one of allyl dimethoxysilane, bis(trimethoxysilylmethyl)ethylene, methacryloyloxymethyltrimethoxysilane, and acryloyloxypropyltrimethoxysilane; the zwitterion containing double bonds is at least one of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, methacryloyloxyethyltrimethylammonium chloride, 2-methacryloyloxyethylphosphocholine, or 3-((3-acrylamidopropyl)dimethylammonium)propionate.

10. A reverse osmosis membrane for treating highly polluted wastewater according to claim 7 or 8, characterized in that, The molar ratio of the terminal alkenyl polyethylene glycol ether, the zwitterionic compound containing double bonds, the silane compound containing double bonds, and the polyvinylpyrrolidone is 3-5:1:0.5-1:1-3.

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