An antioxidant polyamide reverse osmosis composite membrane and its preparation method

Abstract

The present invention belongs to the field of preparation of seawater desalination separation membranes, and specifically discloses an antioxidant polyamide reverse osmosis composite membrane and a preparation method thereof, comprising the following steps: (1) conventionally soaking and cleaning a flat ultrafiltration membrane; (2) on the ultrafiltration membrane, a common polyamine and N-monosubstituted hydroxylamine are mixed to prepare an aqueous phase solution, and an interfacial polymerization reaction is carried out with an organic solution of a polyacyl chloride monomer to form a reverse osmosis membrane; (3) the reverse osmosis membrane is immersed in an alcohol solution of N-disubstituted hydroxylamine compounds, and heat-treated, and finally the preparation of an antioxidant reverse osmosis membrane is completed. The method of the present invention has a simple process, and only hydroxylamine structure reaction monomers are used in the preparation and modification process to ensure that the hydroxylamine structure exists in the body and on the surface, the body hydroxylamine molecules form a stable chemical bond with the acyl chloride, and the hydroxylamine molecules on the membrane surface have low water solubility, and can be operated in cross-flow for a long time without failure, thereby achieving a double improvement in the antioxidant property of the membrane.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of seawater desalination separation membranes, relates to an anti-oxidation polyamide reverse osmosis composite membrane and a preparation method thereof, and belongs to a method for improving the anti-oxidation performance of a polyamide reverse osmosis separation membrane. Background Art

[0002] The current mainstream reverse osmosis uses polyamide (PA) materials as the key separation layer, but the amide bonds in the polyamide separation layer are prone to oxidative hydrolysis reactions with oxidative chlorine components in the water body. The continued chlorination reaction will greatly destroy the strong hydrogen bonding of the amide bonds, causing the molecular chain to hydrolyze and break and the separation performance to decay. Every year, a large number of membrane elements face replacement, elimination and abandonment due to oxidative degradation failure, which not only increases the environmental bearing pressure, but also causes huge economic losses. In view of the huge market demand for reverse osmosis membranes, the development of new antioxidant polyamide membrane materials is of great significance for expanding the application field of reverse osmosis technology and reducing the current operating costs of water treatment processes.

[0003] One of the effective methods for preparing antioxidant reverse osmosis membranes is to introduce antioxidant structures into the molecular chain skeleton or membrane surface area of ​​polyamide materials so that they react preferentially with oxidizing components in water, thereby alleviating the oxidative degradation problem of polyamide membranes. Currently, most reports use antioxidant structures containing phenolic hydroxyl groups, such as hindered phenols, tannic acid and other molecular compounds with a large number of phenolic hydroxyl groups. Although phenolic hydroxyl groups can effectively capture oxidizing components, their oxidation product quinone derivatives have a color reaction, causing the color of the membrane material to gradually darken during use, affecting the appearance of the membrane product. Therefore, it is necessary to develop new antioxidant structures and preparation methods for polyamide reverse osmosis membranes. Summary of the invention

[0004] In order to overcome the problem of insufficient oxidation resistance of polyamide membranes, the present invention provides a method for preparing an antioxidant polyamide membrane.

[0005] The technical solution adopted to achieve the purpose of the present invention is:

[0006] A method for preparing an oxidation-resistant polyamide reverse osmosis composite membrane comprises the following steps:

[0007] S1: A flat ultrafiltration membrane is used as a base membrane, the base membrane is immersed in a cleaning solution for a period of time to clean the organic solvent remaining in the base membrane, and then immersed in pure water for cleaning and left to stand for several hours for use;

[0008] S2: taking out the basement membrane from the pure water and removing the excess solution, then immersing the basement membrane in a mixed aqueous solution containing a mass concentration of 1-4% polyamine and 0.1-1% N-monosubstituted hydroxylamine, keeping for 1-5 minutes, then taking it out and hanging it vertically in the air for 1-10 minutes and removing the excess solution;

[0009] S3: immersing the base membrane again in an organic phase solution containing a polyacyl chloride monomer having a mass concentration of 0.1-1% for 1-10 minutes, then taking out the base membrane from the organic phase reaction solution, and washing the surface of the ultrafiltration membrane with a corresponding pure organic phase solvent to remove residual unreacted acyl chloride monomers, thereby obtaining a polyamide reverse osmosis composite membrane;

[0010] S4: Immerse the prepared polyamide reverse osmosis composite membrane in an alcohol solution containing 0.5-2% by mass concentration of N-disubstituted hydroxylamine compounds for 1-4 minutes, and finally put the membrane into a forced air drying oven for drying, and obtain an antioxidant polyamide reverse osmosis composite membrane after washing with water.

[0011] Furthermore, the material of the ultrafiltration membrane in step S1 is one of polysulfone, polyethersulfone, polyethylene, polypropylene, and polyvinylidene fluoride; the ultrafiltration membrane has a molecular weight cutoff of 40000-80000 Da, preferably 50000-60000 Da.

[0012] Furthermore, in step S1, the cleaning solution is a 30% by mass isopropanol aqueous solution, and the soaking treatment time is 6-8 hours.

[0013] Furthermore, in step S2, the polyamine is one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, and o-xylylenediamine, and the N-monosubstituted hydroxylamine is one of N-methylhydroxylamine, N-tert-butylhydroxylamine, N-isopropylhydroxylamine, N-benzylhydroxylamine, N-benzyloxycarbonylhydroxylamine, and N-cyclohexylhydroxylamine.

[0014] Furthermore, in step S3, the polyacyl chloride monomer is one of succinyl chloride, diphenyl diacetyl chloride, 4,4'-oxybis(benzoyl chloride), trimesoyl chloride or a mixture thereof, and the organic phase is one of pentane, hexane, cyclohexane, heptane or a mixture thereof.

[0015] Furthermore, in step S4, the N-disubstituted hydroxylamine compound is one of bis(octadecyl)hydroxylamine, N,N-diethylhydroxylamine, N,N-dimethylhydroxylamine salt, N,N-dibenzylhydroxylamine, and indolinehydroxylamine, and the alcohol is one of methanol, ethanol, isopropanol, and n-hexanol.

[0016] Furthermore, in step S2, the mass concentration of the polyamine in step 2) is 2-3%, and the mass concentration of the N-monosubstituted hydroxylamine is 0.3-0.8%; the immersion time of the base film in the aqueous solution is 2-4 minutes; and the drying time of the base film in the air is 3-6 minutes.

[0017] Furthermore, in step S3, the concentration of the polyacyl chloride monomer is 0.2%-0.5%; and the immersion time of the base film in the organic phase reaction solution is 2-5 minutes.

[0018] Furthermore, in step S4, the mass concentration of the N-disubstituted hydroxylamine compound is 1-1.5%; the composite film is immersed in the alcohol solution of hydroxylamine for 2-3 minutes; the oven temperature is 60-120°C, preferably 80-100°C, and the heat treatment time is 10-30 minutes, preferably 15-20 minutes.

[0019] The present invention also provides an anti-oxidation polyamide reverse osmosis composite membrane, which is prepared by the preparation method as described above.

[0020] In this application, in view of the defect of the existing polyamide membrane material being easily oxidized and degraded, regulation is carried out from two aspects: the intrinsic structure of the membrane material and the surface properties of the membrane. First, an N-monosubstituted hydroxylamine compound is added to the reverse osmosis membrane polymerization reaction system, thereby introducing a hydroxylamine structure (—N-OH) into the membrane molecular chain structure, and utilizing the characteristic of the hydroxylamine group to quickly capture oxidative free radicals, inhibiting the oxidative destruction of the polyamide membrane material by active chlorine components in the water, thereby improving the antioxidant capacity of the membrane. The surface of the polyamide membrane is further treated with an alcohol solution of an N-disubstituted hydroxylamine compound, so that the hydroxylamine structure is further enriched on the membrane surface, thereby enhancing the antioxidant capacity of the membrane. Compared with the existing methods for preparing antioxidant polyamide membranes (such as CN202211730161.7, CN202210924166.7, CN202111365685.6, CN201710615106.6, etc.), which generally use phenolic hydroxyl groups as antioxidant groups, the hydroxylamine groups used in this application will avoid the obvious color change caused by phenolic hydroxyl groups during the oxidation process. This characteristic makes hydroxylamine compounds widely used in the field of commercial antioxidants. Therefore, the polyamide reverse osmosis membrane prepared by this method has both good antioxidant properties and stable appearance properties.

[0021] As an illustration, the aqueous reaction solution in the present application uses a monosubstituted hydroxylamine molecule because it contains a secondary amine -NH-, which can react with the acyl chloride monomer to ensure that the hydroxylamine is fixed in the polyamide membrane molecular chain; the post-treatment liquid uses a disubstituted hydroxylamine molecule because the disubstituted molecule has low water solubility and can inhibit the loss of hydroxylamine molecules during membrane operation.

[0022] The present invention proposes a method for preparing a high-performance reverse osmosis membrane with both bulk anti-oxidation and membrane surface anti-oxidation by using a reaction monomer rich in hydroxylamine structure, wherein the anti-oxidation hydroxylamine structure-containing reagent includes a bulk reaction reagent A and a surface protection reagent B, wherein reagent A is an N-monosubstituted hydroxylamine and reagent B is an N-disubstituted hydroxylamine compound. The present invention discloses a method for preparing an anti-oxidation polyamide reverse osmosis membrane by using the above-mentioned hydroxylamine structure-rich monomer reagent, comprising the following steps: (1) conventionally soaking and cleaning a flat ultrafiltration membrane; (2) on the ultrafiltration membrane, preparing an aqueous phase solution by mixing a common polyamine and reagent A, and performing an interfacial polymerization reaction with an organic solution of a polyacyl chloride monomer to form a reverse osmosis membrane; (3) immersing the reverse osmosis membrane in an aqueous solution of reagent B and performing a heat treatment, and finally completing the preparation of an anti-oxidation reverse osmosis membrane. The method of the present invention has a simple process. Only hydroxylamine structure reaction monomers are used in the preparation and modification process to ensure that the hydroxylamine structure exists in the body and on the surface. The body hydroxylamine molecules form stable chemical bonds with the acyl chloride, and the hydroxylamine molecules on the membrane surface have low water solubility, so the membrane can be operated in cross-flow for a long time without failure, thereby achieving a double improvement in the membrane's antioxidant properties. DETAILED DESCRIPTION

[0023] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0024] In order to evaluate the effectiveness of the method, the present application also prepared three reverse osmosis membranes as comparative examples. The specific preparation process is shown in the comparative examples below.

[0025] The test method of the flux and salt rejection rate of the reverse osmosis membrane of the present invention is as follows:

[0026] Membrane separation performance test: The prepared membrane was pre-pressed with an electrolyte solution of 0.2% mass concentration of NaCl at 1.55 MPa for half an hour to test the desalination performance and water flux of the reverse osmosis membrane.

[0027] The calculation formula of water flux is shown in (1):

[0028] (1)

[0029] Where A is the effective membrane area, m 2 ; t - the time required to collect Q volume of produced liquid, h; Q - the volume of produced liquid collected within t time, L.

[0030] The calculation method of membrane desalination performance is shown in (2):

[0031] (2)

[0032] Among them, R is the desalination rate, C f - Conductivity of the stock solution, μS / cm; C p - Conductivity of produced water, μS / cm.

[0033] Chlorine resistance and oxidation resistance test: Sodium hypochlorite (a common oxidant in water) is used as a typical oxidant. 0.05% (mass concentration) sodium hypochlorite is added to the NaCl test solution and the system is run for 12 hours. The changes in membrane performance are recorded and examined to verify the compactness and integrity of the polyamide separation layer, thereby evaluating the membrane's resistance to chlorination.

[0034] Embodiment 1:

[0035] (1) A polysulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 40,000-80,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for use.

[0036] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in a mixed aqueous solution containing 1% (mass concentration) m-phenylenediamine and 0.1% (mass concentration) N-methylhydroxylamine for 1 minute, then take it out and hang it vertically in the air for 1 minute, and wipe off the excess solution with a paper towel;

[0037] (3) immersing the base membrane again in a 0.1% (mass concentration) succinyl chloride pentane solution for 1 minute, then taking out the membrane from the pentane reaction solution, washing the membrane surface with a pentane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0038] (4) The prepared polyamide composite membrane was immersed in a methanol solution containing 0.5% (mass concentration) of dioctadecylhydroxylamine for 1 minute. Finally, the membrane was placed in a forced air drying oven at 60°C for 10 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0039] Performance test: The initial reverse osmosis membrane desalination rate was 96.7%; the water flux was 29.0 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 95.2% and the water flux was 30.2 L / m 2 .h.

[0040] Embodiment 2:

[0041] (1) A polyethersulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 20,000-70,000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for use.

[0042] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in a mixed aqueous solution containing 4% (mass concentration) p-phenylenediamine and 1% (mass concentration) N-tert-butylhydroxylamine for 5 minutes, then take it out and hang it vertically in the air for 10 minutes, and wipe off the excess solution with a paper towel;

[0043] (3) immersing the base membrane again in a 1% (mass concentration) hexane solution of diphenyl diacetyl chloride for 10 minutes, then taking out the membrane from the hexane reaction solution, washing the membrane surface with a hexane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0044] (4) The prepared polyamide composite membrane was immersed in an ethanol solution containing 2% (mass concentration) N,N-diethylhydroxylamine for 4 minutes. Finally, the membrane was placed in a forced air drying oven at 120°C for 30 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0045] Performance test: The initial reverse osmosis membrane desalination rate was 96.4%; the water flux was 30.1 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 96.3% and the water flux was 34.4 L / m 2 .h.

[0046] Embodiment 3:

[0047] (1) A polypropylene flat ultrafiltration membrane (molecular weight cutoff ≈ 50,000-80,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for standby use.

[0048] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in a mixed aqueous solution containing 2% (mass concentration) o-phenylenediamine and 0.3% (mass concentration) N-isopropylhydroxylamine for 2 minutes, then take it out and hang it vertically in the air for 3 minutes, and wipe off the excess solution with a paper towel;

[0049] (3) immersing the base membrane again in a 0.2% (mass concentration) 4,4'-oxybis(benzoyl chloride) cyclohexane solution for 2 minutes, then taking the membrane out of the cyclohexane reaction solution, and washing the membrane surface with cyclohexane solvent to remove residual unreacted acyl chloride monomers, thereby obtaining a polyamide reverse osmosis composite membrane;

[0050] (4) The prepared polyamide composite membrane was immersed in an isopropanol solution containing 1% (mass concentration) N,N-dimethylhydroxylamine salt for 2 minutes. Finally, the membrane was placed in a forced air drying oven at 80°C for 15 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0051] Performance test: The initial reverse osmosis membrane desalination rate was 97.0%; the water flux was 34.5 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 96.4% and the water flux was 38.7 L / m 2 .h.

[0052] Embodiment 4:

[0053] (1) A polyvinylidene fluoride flat ultrafiltration membrane (molecular weight cutoff ≈ 80,000-100,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for standby use.

[0054] (2) The ultrafiltration base membrane was taken out from the pure water and the excess solution was wiped off with a paper towel. The membrane was then immersed in a mixed aqueous solution containing 3% (mass concentration) of o-xylylenediamine and 0.8% (mass concentration) of N-benzylhydroxylamine for 4 minutes. The membrane was then taken out and hung vertically in the air for 6 minutes, and the excess solution was wiped off with a paper towel.

[0055] (3) immersing the base membrane again in a 0.5% (mass concentration) heptane solution of trimesoyl chloride for 5 minutes, then taking out the membrane from the heptane reaction solution, washing the membrane surface with a heptane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0056] (4) The prepared polyamide composite membrane was immersed in a n-hexanol solution containing 1.5% (mass concentration) of N,N-dibenzylhydroxylamine for 3 minutes. Finally, the membrane was placed in a forced air drying oven at 100°C for 20 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0057] Performance test: The initial reverse osmosis membrane desalination rate was 96.4%; the water flux was 25.7L / m 2.h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 95.9% and the water flux was 30.3 L / m 2 .h.

[0058] Embodiment 5:

[0059] (1) A polyethersulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 20,000-70,000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for use.

[0060] (2) The ultrafiltration base membrane was taken out from the pure water and the excess solution was wiped off with a paper towel. The membrane was then immersed in a mixed aqueous solution containing 2% (mass concentration) of o-xylylenediamine and 0.6% (mass concentration) of N-benzyloxycarbonylhydroxylamine for 3 minutes. The membrane was then taken out and hung vertically in the air for 5 minutes, and the excess solution was wiped off with a paper towel.

[0061] (3) immersing the base membrane again in a 0.3% (mass concentration) hexane solution of diphenyl diacetyl chloride for 3 minutes, then taking out the membrane from the hexane reaction solution, washing the membrane surface with a hexane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0062] (4) The prepared polyamide composite membrane was immersed in a methanol solution containing 1.1% (mass concentration) of indolehydroxylamine for 4 minutes. Finally, the membrane was placed in a 90°C forced air drying oven for 17 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0063] Performance test: The initial reverse osmosis membrane desalination rate was 98.0%; the water flux was 34.4 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 97.4% and the water flux was 39.6 L / m 2 .h.

[0064] Embodiment 6:

[0065] (1) A polyethylene flat ultrafiltration membrane (molecular weight cutoff ≈ 30,000-60,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for standby use.

[0066] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in a mixed aqueous solution containing 1% (mass concentration) m-phenylenediamine and 0.7% (mass concentration) N-methylhydroxylamine for 4 minutes, then take it out and hang it vertically in the air for 5 minutes, and wipe off the excess solution with a paper towel;

[0067] (3) immersing the base membrane again in a 0.4% (mass concentration) succinyl chloride pentane solution for 4 minutes, then taking out the membrane from the pentane reaction solution, washing the membrane surface with a pentane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0068] (4) The prepared polyamide composite membrane was immersed in a methanol solution containing 1.3% (mass concentration) of dioctadecylhydroxylamine for 3 minutes. Finally, the membrane was placed in a forced air drying oven at 85°C for 16 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0069] Performance test: The initial reverse osmosis membrane desalination rate was 96.6%; the water flux was 27.6 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 95.7% and the water flux was 35.0L / m 2 .h.

[0070] Embodiment 7:

[0071] (1) A polysulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 40,000-80,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for use.

[0072] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in a mixed aqueous solution containing 3% (mass concentration) o-phenylenediamine and 0.5% (mass concentration) N-isopropylhydroxylamine for 3 minutes, then take it out and hang it vertically in the air for 5 minutes, and wipe off the excess solution with a paper towel;

[0073] (3) immersing the base membrane again in a 0.3% (mass concentration) 4,4'-oxybis(benzoyl chloride) cyclohexane solution for 5 minutes, then taking the membrane out of the cyclohexane reaction solution, and washing the membrane surface with cyclohexane solvent to remove residual unreacted acyl chloride monomers, thereby obtaining a polyamide reverse osmosis composite membrane;

[0074] (4) The prepared polyamide composite membrane was immersed in an isopropanol solution containing 1.4% (mass concentration) of N,N-dimethylhydroxylamine salt for 3 minutes. Finally, the membrane was placed in a 95°C forced air drying oven for 18 minutes. After washing with water, an antioxidant polyamide reverse osmosis composite membrane was obtained.

[0075] Performance test: The initial reverse osmosis membrane desalination rate was 95.7%; the water flux was 32.3 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 94.0% and the water flux was 39.5 L / m 2 .h.

[0076] Comparative Example 1:

[0077] (1) A polysulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 60,000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for use.

[0078] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in an aqueous solution containing 2% (mass concentration) m-phenylenediamine for 2 minutes, then take it out and hang it vertically in the air for 5 minutes, and wipe off the excess solution with a paper towel;

[0079] (3) immersing the base membrane again in a 0.15% (mass concentration) hexane organic phase solution of trimesoyl chloride for 1 minute, then taking out the membrane from the reaction solution, washing the membrane surface with a hexane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0080] (4) The prepared polyamide composite membrane was immersed in an ethanol solution for 2 minutes, and finally the membrane was placed in an 80°C forced air drying oven for 20 minutes, and then washed with water before testing.

[0081] Performance test: The initial reverse osmosis membrane desalination rate was 98.7%; the water flux was 28.1 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 88.2% and the water flux was 58.5 L / m 2 .h.

[0082] Comparative Example 2:

[0083] (1) A polysulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 60,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for standby use.

[0084] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in a mixed aqueous solution containing 2% (mass concentration) m-phenylenediamine and 0.5% (mass concentration) N-tert-butylhydroxylamine for 2 minutes, then take it out and hang it vertically in the air for 5 minutes, and wipe off the excess solution with a paper towel;

[0085] (3) immersing the base membrane again in a 0.15% (mass concentration) hexane solution of trimesoyl chloride for 1 minute, then taking the membrane out of the reaction solution, washing the membrane surface with a hexane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0086] (4) The prepared polyamide composite membrane was immersed in an ethanol solution for 2 minutes, and finally the membrane was placed in an 80°C forced air drying oven for 20 minutes, and then washed with water before testing.

[0087] Performance test: The initial reverse osmosis membrane desalination rate was 96.9%; the water flux was 36.5 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 93.7% and the water flux was 40.1 L / m 2 .h.

[0088] Comparative Example 3:

[0089] (1) A polysulfone flat ultrafiltration membrane (molecular weight cutoff ≈ 60,000 Da) was used as a base membrane. The ultrafiltration membrane was immersed in a cleaning solution (30% by mass isopropanol aqueous solution) for 6 hours to clean the organic solvent remaining in the base membrane. The membrane was then immersed in pure water for cleaning and allowed to stand for 6 hours for standby use.

[0090] (2) Take out the ultrafiltration base membrane from the pure water and wipe off the excess solution with a paper towel, then immerse the membrane in an aqueous solution containing 2% (mass concentration) m-phenylenediamine for 2 minutes, then take it out and hang it vertically in the air for 5 minutes, and wipe off the excess solution with a paper towel;

[0091] (3) immersing the base membrane again in a 0.15% (mass concentration) hexane solution of trimesoyl chloride for 1 minute, then taking the membrane out of the reaction solution, washing the membrane surface with a hexane solvent to remove residual unreacted acyl chloride monomers, and obtaining a polyamide reverse osmosis composite membrane;

[0092] (4) The prepared polyamide composite membrane was immersed in an ethanol solution containing 1% (mass concentration) of dioctadecylhydroxylamine for 2 minutes. Finally, the membrane was placed in a forced air drying oven at 80°C for 20 minutes and then washed with water before testing.

[0093] Performance test: The initial reverse osmosis membrane desalination rate was 98.2%; the water flux was 28.8 L / m 2 .h; After the reverse osmosis membrane was treated with hypochlorous acid for 12 hours, the measured desalination rate was 94.3% and the water flux was 42.6 L / m 2 .h.

[0094] Table 1 Differences in performance and stability of membranes in Examples and Comparative Examples

[0095]

[0096] As shown in Table 1, after the unmodified reverse osmosis membrane (Comparative Example 1) was treated with active chlorine oxidation, the desalination rate decreased from 98.7% to 88.2%, while after being cross-linked with a single-substituted hydroxylamine or a di-substituted hydroxylamine (Comparative Examples 2 and 3), the desalination rate decrease was significantly improved, proving that the introduction of the hydroxylamine reducing agent has a strengthening effect on the antioxidant properties of the polyamide membrane; and after being treated with two reducing compounds together (Examples 1-9), the desalination rate change before and after the oxidant treatment was basically <2%, further proving that the method described in the present application can be used to prepare a polyamide reverse osmosis membrane with significant antioxidant ability.

[0097] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing an antioxidant polyamide reverse osmosis composite membrane, characterized in that: The steps include: S1: A flat ultrafiltration membrane is used as a base membrane, the base membrane is immersed in a cleaning solution for a period of time to clean the organic solvent remaining in the base membrane, and then immersed in pure water for cleaning and left to stand for several hours for use; S2: taking out the basement membrane from the pure water and removing the excess solution, then immersing the basement membrane in a mixed aqueous solution containing a mass concentration of 1-4% polyamine and 0.1-1% N-monosubstituted hydroxylamine, keeping for 1-5 minutes, then taking it out and hanging it vertically in the air for 1-10 minutes and removing the excess solution; S3: immersing the base membrane again in an organic phase solution containing a polyacyl chloride monomer having a mass concentration of 0.1-1% for 1-10 minutes, then taking out the base membrane from the organic phase reaction solution, and washing the surface of the ultrafiltration membrane with a corresponding pure organic phase solvent to remove residual unreacted acyl chloride monomers, thereby obtaining a polyamide reverse osmosis composite membrane; S4: immersing the prepared polyamide reverse osmosis composite membrane into an alcohol solution containing an N-disubstituted hydroxylamine compound with a mass concentration of 0.5-2%, maintaining the solution for 1-4 minutes, and finally placing the membrane in a blast drying oven to dry it, and obtaining an antioxidant polyamide reverse osmosis composite membrane after washing with water; The N-monosubstituted hydroxylamine is one of N-methylhydroxylamine, N-tert-butylhydroxylamine, N-isopropylhydroxylamine, N-benzylhydroxylamine, N-benzyloxycarbonylhydroxylamine, and N-cyclohexylhydroxylamine; the N-disubstituted hydroxylamine compound is one of bis(octadecyl)hydroxylamine, N,N-diethylhydroxylamine, N,N-dimethylhydroxylamine salt, N,N-dibenzylhydroxylamine, and indolinehydroxylamine.

2. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: The material of the ultrafiltration membrane in step S1 is one of polysulfone, polyethersulfone, polyethylene, polypropylene, and polyvinylidene fluoride; and the molecular weight cutoff of the ultrafiltration membrane is 40000-80000 Da.

3. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step S1, the cleaning solution is a 30% by mass isopropanol aqueous solution, and the soaking treatment time is 6-8 hours.

4. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step S2, the polyamine is one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine and o-xylylenediamine.

5. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step S3, the polyacyl chloride monomer is one of succinyl chloride, diphenyl diacetyl chloride, 4,4'-oxybis(benzoyl chloride), trimesoyl chloride or a mixture thereof, and the organic phase is one of pentane, hexane, cyclohexane, heptane or a mixture thereof.

6. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: The alcohol in step S4 is one of methanol, ethanol, isopropanol and n-hexanol.

7. The method for preparing an oxidation-resistant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step S2, the mass concentration of the polyamine in step 2) is 2-3%, and the mass concentration of the N-monosubstituted hydroxylamine is 0.3-0.8%; the immersion time of the base film in the aqueous solution is 2-4 minutes; and the drying time of the base film in the air is 3-6 minutes.

8. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step S3, the concentration of the polyacyl chloride monomer is 0.2%-0.5%; the immersion time of the base film in the organic phase reaction solution is 2-5 minutes.

9. The method for preparing an antioxidant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step S4, the mass concentration of the N-disubstituted hydroxylamine compound is 1-1.5%; the composite membrane is immersed in the alcohol solution of hydroxylamine for 2-3 minutes; the oven temperature is 60-120° C., and the heat treatment time is 10-30 minutes.

10. An antioxidant polyamide reverse osmosis composite membrane, characterized in that: The method is prepared according to any one of claims 1 to 9.

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