High-stability, easily-stored low-pressure reverse osmosis membrane and preparation method thereof

Abstract

This application relates to the field of reverse osmosis membranes, specifically disclosing a highly stable, easily stored, low-pressure reverse osmosis membrane and its preparation method. The highly stable, easily stored, low-pressure reverse osmosis membrane comprises a polysulfone-based membrane and a polyamide functional layer. The polyamide functional layer is formed by an interfacial polycondensation reaction between an aqueous phase containing organic amines and an oil phase containing acyl chlorides. The aqueous phase also includes silane-modified aminopolyethylene glycol dopamine and an antioxidant. The reverse osmosis membrane of this application utilizes chemical crosslinking modification and the addition of antioxidants to avoid poor stability of the low-pressure reverse osmosis membrane during storage and performance degradation after the membrane is placed.

Description

Technical Field

[0001] This application relates to a reverse osmosis membrane, and more specifically, to a highly stable, easily stored, low-pressure reverse osmosis membrane and a method for preparing the same. Background Technology

[0002] Membrane separation technology has experienced rapid development in recent years due to its combined functions of separation, concentration, and purification, as well as its energy-saving, environmentally friendly, simple, and easy-to-control characteristics. Low-pressure reverse osmosis membranes, which operate at pressures below 2.0 MPa, consume less energy and are therefore highly popular in the market. Ultra-low pressure reverse osmosis membranes, in particular, operate at pressures between 0.5 and 1.0 MPa, consuming even less energy and further facilitating their promotion and application.

[0003] Currently, the preparation method for polyamide reverse osmosis membranes is interfacial polymerization. First, a layer of aqueous solution containing a certain proportion is uniformly spread on the surface of a polysulfone membrane, which serves as the support layer. After removing excess aqueous solution, an oil-phase solution is poured onto the membrane surface to carry out the interfacial polymerization reaction. After a period of reaction, the polyamide reverse osmosis membrane is obtained. In high-temperature and high-humidity environments, oxidizing and acidic substances in the air are more active, increasing the possibility of membrane instability. Simultaneously, the polyamide functional layer is also subject to physical damage during use, reducing its service life. Therefore, the storage and transportation conditions for membranes in actual production are extremely demanding, causing significant challenges to the product. Especially during the high-temperature and high-humidity conditions of summer, air leakage is easily caused when the membrane is rolled into membrane elements, leading to a decrease in desalination rate, poor storage stability, and in severe cases, failure to meet performance standards. How to significantly improve the strength of reverse osmosis membranes, enhance storage stability, and ensure the flux and desalination rate of reverse osmosis membranes under high-temperature and high-humidity conditions is an urgent problem to be solved. Summary of the Invention

[0004] To address the issue of maintaining high flux and high desalination rate performance of low-pressure reverse osmosis membranes when stored in high-temperature and high-humidity environments, this application provides a highly stable and easily stored low-pressure reverse osmosis membrane and its preparation method.

[0005] In a first aspect, this application provides a highly stable, easily stored, low-pressure reverse osmosis membrane, the highly stable, easily stored, low-pressure reverse osmosis membrane comprising a polysulfone-based membrane and a polyamide functional layer, the polysulfone-based membrane being made from a casting solution containing polysulfone, the polyamide functional layer being made from an aqueous solution containing an organic amine aqueous monomer and an oil solution containing an acyl chloride oil monomer, the aqueous solution further comprising silane coupling agent modified aminopolyethylene glycol dopamine.

[0006] By adopting the above scheme, using polysulfone as the base membrane, a polyamide functional layer is obtained on one side of the polysulfone base membrane through interfacial polycondensation between an aqueous phase containing organic amines and an oil phase containing acyl chlorides. After silane coupling agent-modified amino-polyethylene glycol dopamine is added to the reverse osmosis membrane, during the membrane formation process in the aqueous solution, the migration properties of the silane coupling agent promote the migration of the silane coupling agent-treated amino-polyethylene glycol dopamine phase membrane surface. At the same time, the regular long chains of polyethylene glycol freely extend in the system. When the aqueous phase diffuses to the oil phase, the silane coupling agent-treated amino-polyethylene glycol dopamine cross-links in the cross-linked structure, thereby improving the overall strength of the reverse osmosis membrane. In addition, the phenolic hydroxyl groups in the silane coupling agent-treated amino-polyethylene glycol dopamine can react with acyl chlorides and participate in interfacial polymerization, improving the compactness and overall strength of the reverse osmosis membrane, and further improving the separation performance and strength of the reverse osmosis membrane. The silane coupling agent-modified aminopolyethylene glycol dopamine that migrates to the base membrane retains some phenolic hydroxyl groups, thereby increasing the hydrophilicity of the reverse osmosis membrane and thus improving the water flux of the reverse osmosis membrane.

[0007] In one specific implementation, the polysulfone-based membrane of the high-stability, easily stored, low-pressure reverse osmosis membrane is further coated with a glycerol moisturizing layer on the side away from the polyamide functional layer, and a protective layer is further coated on the side of the polyamide functional layer away from the polysulfone-based membrane.

[0008] By adopting the above-mentioned solution, glycerin wets the pores of the polysulfone-based membrane, providing it with a long-lasting moisturizing effect. This prevents the porous structure from collapsing during subsequent oven drying, resulting in a more intact structure and better support for the polyamide functional layer in subsequent use. Simultaneously, it ensures high flux and uniform fluid distribution, preventing filtrate accumulation at the collapse points of the reverse osmosis membrane, reducing physical damage caused by filtrate pressure concentration, and preventing suspended solids in the filtrate from accumulating at the collapse points, thus extending service life and achieving more efficient separation. Furthermore, coating the side of the polyamide functional layer away from the polysulfone-based membrane with a protective coating... The protective layer provides protection for the polyamide functional layer. Instead of using glycerol to soak the entire reverse osmosis membrane, different moisturizing and protective layers are coated on the polysulfone-based membrane side and the polyamide functional layer side, respectively. This reduces the amount of excess glycerol droplets left on the reverse osmosis membrane due to surface tension during soaking, avoiding damage to the reverse osmosis membrane caused by excessive swelling of glycerol. Moderate swelling also makes the pores of the reverse osmosis membrane more uniform and the flux greater. The separate coating of moisturizing and protective layers on both sides is a differentiated setting based on the different strengths and hydrophilicities of the polysulfone-based membrane and the polyamide functional layer, further improving the performance of the reverse osmosis membrane.

[0009] In one specific embodiment, the glycerin moisturizing layer is formed by coating with a glycerin solution of 5-10% by mass; the associated protective layer is formed by coating with a polyvinyl alcohol solution containing trace amounts of glycerin, wherein the polyvinyl alcohol solution contains 2-5% by mass of polyvinyl alcohol and the degree of hydrolysis of the polyvinyl alcohol is 78-92%; the amount of trace amounts of glycerin added is 2-10% by mass of polyvinyl alcohol.

[0010] One side of the polyamide functional layer is coated with a polyvinyl alcohol solution containing trace amounts of glycerol as a protective layer. The polyvinyl alcohol is distributed on the surface of the polyamide functional layer. Its high molecular weight and cross-linking properties improve the strength of the polyamide functional layer, giving it a longer service life. It also improves the density of the polyamide functional layer, further enhancing its desalination capacity. By limiting the degree of alcoholysis, the polyvinyl alcohol forms a complete membrane layer based on the formulation of the reverse osmosis membrane in this application, while minimizing the impact on flux. The addition of trace amounts of glycerol improves the affinity between the polyvinyl alcohol and the polyamide functional layer, resulting in a more uniform distribution of polyvinyl alcohol in the polyamide functional layer, more stable performance, and a simpler processing process. At the same time, the trace amounts of glycerol also further improve the wettability of one side of the polyamide functional layer. Controlling the glycerol content ensures that the reverse osmosis membrane maintains good filtration performance in subsequent use.

[0011] In one specific implementation, the silane coupling agent is isocyanate-propyltrimethoxysilane, and the molar ratio of aminopolyethylene glycol dopamine to isocyanate-propyltrimethoxysilane is 1:(0.9-1.1).

[0012] By adopting the above scheme, amino-polyethylene glycol dopamine reacts with isocyanate-based propyltrimethoxysilane, and the silane-modified amino-polyethylene glycol dopamine migrates in the reverse osmosis membrane. The regular long chains of polyethylene glycol extend and interweave in the system, and the phenolic hydroxyl groups in the silane-modified amino-polyethylene glycol dopamine react with acyl chlorides. Through the combination of physical and chemical aspects, the various parts of the reverse osmosis membrane are more tightly bound, resulting in a reverse osmosis membrane with high overall strength. It is not easily damaged under large water flux, ensuring good filtration effect. The retention of some phenolic hydroxyl groups makes the reverse osmosis membrane more hydrophilic, and the water flux is further improved. By limiting the ratio of the two, the amino-polyethylene glycol dopamine in the system is fully modified, further improving the strength of the reverse osmosis membrane and enhancing its stability during long-term storage.

[0013] In one specific implementation, the preparation process of the silane coupling agent modified amino polyethylene glycol dopamine includes: adding the silane coupling agent and amino polyethylene glycol dopamine into an aqueous ethanol solution, mixing, stirring at 70-80°C for 15-20 minutes, filtering, and drying to obtain silane modified amino polyethylene glycol dopamine.

[0014] By adopting the above scheme, the preparation method is simple and the modification effect of amino-polyethylene glycol dopamine is good.

[0015] In one specific implementation, the polysulfone-based film contains nano-silica, and the weight percentage of the nano-silica is 2-3% based on the total weight of the casting solution.

[0016] By adopting the above-mentioned approach, filling the base membrane with nano-silica can improve the overall strength of the base membrane. Simultaneously, the numerous pores in the nano-silica provide ample channels for water, thereby increasing the water flux of the composite membrane. Furthermore, after the aminopolyethylene glycol dopamine treated with the silane coupling agent in the aqueous solution migrates to the membrane surface, during the membrane formation process in the aqueous solution, the silanol groups generated by the hydrolysis of the silane coupling agent will form chemical bonds with the hydroxyl groups on the silica surface. This tightly connects the base membrane and the functional layer membrane formed by the aqueous solution, further enhancing the overall strength of the reverse osmosis membrane. It also exhibits stronger resistance to oxidizing and acidic substances in the air, and its performance is more stable under high temperature and high humidity conditions. By controlling the weight percentage of added nano-silica, it is possible to maintain a high flux of the reverse osmosis membrane without significantly increasing its hardness.

[0017] In one specific embodiment, the aqueous solution further comprises an antioxidant, a surfactant, a pH adjuster, and an acid acceptor, wherein the hydrophilic aid includes dimethyl sulfoxide, the antioxidant includes sodium metabisulfite, the surfactant includes sodium dodecylbenzenesulfonate, the pH adjuster includes camphor sulfonic acid, and the acid acceptor includes sodium hydroxide.

[0018] By adopting the above-mentioned scheme, the addition of antioxidants prevents performance degradation caused by the degradation of the functional layer; the addition of surfactants helps the formation of the functional layer and also increases the hydrophilicity of the membrane, further improving the water flux of the reverse osmosis membrane; the addition of pH adjusters regulates the environmental pH value to promote the reaction; the addition of acid acceptors neutralizes the byproducts generated by interfacial polymerization, further promoting the forward progress of interfacial polymerization. The addition of sodium metabisulfite, an antioxidant, prevents the functional layer's aromatic polyamide from undergoing reactive degradation and performance degradation under high humidity and temperature conditions, as oxidants such as acidic substances in the air become more active. The addition of sodium dodecylbenzenesulfonate promotes the polymerization and uniform dispersion of the functional layer. It also improves the hydrophilicity of the base membrane, enhances the uniformity of the aqueous solution distribution on the base membrane, and further promotes the functional stability of the generated functional layer. The addition of camphor sulfonic acid regulates the environmental pH value to promote the reaction; the addition of sodium hydroxide neutralizes the byproducts generated by interfacial polymerization, further promoting the forward progress of interfacial polymerization.

[0019] Secondly, this application provides a method for preparing a highly stable, easily stored, low-pressure reverse osmosis membrane, the method comprising the following steps:

[0020] S1: Base film preparation: The casting solution is coated onto nonwoven fabric, left to stand, and cured in pure water to obtain a polysulfone base film;

[0021] S2: Aqueous phase coating: The aqueous phase solution is coated onto the polysulfone-based film obtained in S1 and dried to obtain an aqueous phase layer;

[0022] S3: Oil phase coating: The oil phase solution is coated onto the aqueous phase layer of S2 and dried to obtain a reverse osmosis membrane.

[0023] By adopting the above technical solution, the preparation process of the low-pressure reverse osmosis membrane is simple, and the prepared low-pressure reverse osmosis membrane has a good filtration effect.

[0024] In one specific feasible implementation, the preparation method further includes the following steps: S4: the reverse osmosis membrane obtained in S3 is washed with pure water, a glycerol moisturizing layer is coated on the side of the polysulfone-based membrane away from the polyamide functional layer, a protective layer is coated on the side of the polyamide functional layer away from the polysulfone-based membrane, and then dried.

[0025] By adopting the above technical solutions, the method of providing a moisturizing layer and a protective layer to the base membrane and functional layer of the reverse osmosis membrane is simple, and there is no excessive additional glycerin residue after wetting the reverse osmosis membrane.

[0026] In one specific implementation, the preparation process of the casting solution in S1 involves stirring and mixing solid polysulfone, a good solvent, a pore-forming agent, and nano-silica. The standing time is 5-15 minutes. The good solvent includes N,N-dimethylformamide, and the pore-forming agent includes ethylene glycol monomethyl ether. Based on the total mass of the casting solution, the mass percentage of polysulfone is 12-18%, the mass percentage of the good solvent is 75-85%, and the mass percentage of the pore-forming agent is 0.5-10%.

[0027] The drying temperature in S2 is 50-80℃, and the aqueous solution contains 2-10% by mass of organic amine aqueous monomers and 3-5% by mass of silane coupling agent-modified amino polyethylene glycol dopamine.

[0028] The drying temperature in S3 is 50-80℃, and the oil phase solution contains 0.1-1.0% by mass of acyl chloride oil phase monomers; the temperature of the pure water coagulated solution solidified in pure water in S1 is 10-15℃.

[0029] By adopting the above technical solutions, the reverse osmosis membrane prepared with the appropriate content of each component has good filtration effect, high strength, large flux, high desalination rate, and high stability under high temperature and high humidity environment.

[0030] In summary, this application has the following beneficial effects:

[0031] 1. This application uses glycerol as a humectant coated on one side of the polysulfone base membrane and a polyvinyl alcohol solution containing glycerol as a protective layer coated on the other side of the functional layer. The different coatings with different formulations provide differentiated reinforcement of the performance of the base membrane layer and the functional layer, without excessive glycerol residue beyond its wetting function. This improves the wettability of the reverse osmosis membrane and enhances its structural integrity after drying. At the same time, through physical barrier, it further protects the reverse osmosis membrane from the attack of acidic and oxidizing substances in the environment, maintaining high desalination capacity for a long time. By limiting the glycerol content, polyvinyl alcohol content, and degree of polyvinyl alcohol hydrolysis in the protective layer, it further provides sufficient protection for the reverse osmosis membrane while ensuring high flux.

[0032] 2. This application improves the strength and separation performance of the reverse osmosis membrane by adding silane-modified aminopolyethylene glycol dopamine to the aqueous phase of the reverse osmosis membrane. This is achieved by utilizing the cross-linking of the structure and the simultaneous participation of phenolic hydroxyl groups in polymerization. This makes the structure less susceptible to the effects of glycerol swelling, ensuring the structural stability of the reverse osmosis membrane under high temperature and high humidity conditions, facilitating storage. Furthermore, the phenolic hydroxyl groups on the aminopolyethylene glycol dopamine enhance the hydrophilicity of the reverse osmosis membrane, thereby increasing the water flux while simultaneously improving the strength and separation performance of the reverse osmosis membrane.

[0033] 3. This application enhances the strength of the polysulfone-based membrane by adding a certain amount of nano-silica, preventing the deformation caused by glycerol swelling of the polysulfone-based membrane from being transmitted to the polyamide functional layer. This further improves the stability of the reverse osmosis membrane under high temperature and high humidity conditions. The large number of pores contained in the nano-silica also further increases the water flux of the reverse osmosis membrane. At the same time, the silanol groups generated by the hydrolysis of the silane coupling agent form chemical bonds with the hydroxyl groups on the surface of the silica, thereby tightly connecting the base membrane and the membrane formed by the aqueous solution, further enhancing the overall strength of the composite membrane and reducing the possibility of swelling of the composite membrane during subsequent use. Detailed Implementation

[0034] The degree of hydrolysis of polyvinyl alcohol used in Example 4 was 92%, that used in Example 5 was 98%, that used in Example 6 was 70%, and that used in the other examples was 78%. Unless otherwise specified, the experimental reagents used in the preparation examples and examples were all from commercially available brands or obtained through conventional preparation processes.

[0035] Preparation Example

[0036] Preparation Example 1

[0037] 205.28g of isocyanate-based propyltrimethoxysilane and 5000g of amino polyethylene glycol dopamine were added to an 85% aqueous ethanol solution and mixed. The mixture was stirred at 70°C for 20 minutes, filtered, and dried in an oven at 70°C to obtain silane-modified amino polyethylene glycol dopamine.

[0038] Example

[0039] Example 1

[0040] S1: Base film preparation: Mix 16g of solid polysulfone, 80g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, stir for 30 minutes, let stand for 10 minutes to degas, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric, let stand for 10 seconds after coating, and place the film coated with casting solution into pure water coagulation solution at 10 degrees Celsius to obtain polysulfone base film.

[0041] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 86.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, 0.5g of sodium hydroxide, and 4g of amino polyethylene glycol dopamine modified with the silane coupling agent from Preparation Example 1 to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0042] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0043] Example 2

[0044] S1: Base film preparation: Mix 16g of solid polysulfone, 80g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, stir for 30 minutes, let stand for 10 minutes to degas, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric, let stand for 10 seconds after coating, and place the film coated with casting solution into pure water coagulation solution at 10 degrees Celsius to obtain polysulfone base film.

[0045] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 86.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, 0.5g of sodium hydroxide, and 4g of amino polyethylene glycol dopamine modified with the silane coupling agent from Preparation Example 1 to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0046] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a reverse osmosis membrane.

[0047] S4: Cleaning and wetting: Clean the reverse osmosis membrane twice with pure water at 60℃, dry it at 60℃, immerse the dried reverse osmosis membrane in an 8% glycerol aqueous solution, take it out, and dry it again in an oven at 60℃ to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0048] Example 3

[0049] S1: Base film preparation: Mix 16g of solid polysulfone, 80g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, stir for 30 minutes, let stand for 10 minutes to degas, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric, let stand for 10 seconds after coating, and place the film coated with casting solution into pure water coagulation solution at 10 degrees Celsius to obtain polysulfone base film.

[0050] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 86.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, 0.5g of sodium hydroxide, and 4g of amino polyethylene glycol dopamine modified with the silane coupling agent from Preparation Example 1 to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0051] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a reverse osmosis membrane.

[0052] S4: Cleaning, wetting, and surface modification: The reverse osmosis membrane was cleaned twice with 60°C pure water. 4g of polyvinyl alcohol and 0.3g of glycerol were added to 97.7g of pure water and stirred evenly to prepare a polyvinyl alcohol aqueous solution with trace amounts of glycerol. This solution was then coated onto the polyamide functional layer side of the reverse osmosis membrane until the polyamide functional layer side was fully wetted. Then, an 8% glycerol aqueous solution was coated onto the base membrane side of the reverse osmosis membrane until it was fully wetted. The reverse osmosis membrane was then dried again in an oven at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0053] Examples 4-6

[0054] The only difference between the preparation processes of Examples 4-6 and Example 3 is the degree of alcoholysis of the polyvinyl alcohol used.

[0055] Example 7

[0056] S1: Base film preparation: Mix 16g of solid polysulfone, 78g of N,N-dimethylformamide, 4g of ethylene glycol monomethyl ether, and 2g of nano-silica. Stir for 30 minutes, let stand for 10 minutes to remove bubbles, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric. After coating, let stand for 10 seconds. Place the film coated with casting solution into a pure water coagulation solution at 10 degrees Celsius to obtain a polysulfone base film.

[0057] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 86.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, and 0.5g of sodium hydroxide sequentially to prepare 4g of amino polyethylene glycol dopamine modified with the silane coupling agent in Example 1 to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0058] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a reverse osmosis membrane.

[0059] S4: Cleaning, wetting, and surface modification: The reverse osmosis membrane was cleaned twice with 60°C pure water. 4g of polyvinyl alcohol and 0.3g of glycerol were added to 97.7g of pure water and stirred evenly to prepare a polyvinyl alcohol-glycerol aqueous solution. This solution was then coated on the polyamide functional layer side of the reverse osmosis membrane until the polyamide functional layer side was fully wetted. Then, an 8% glycerol aqueous solution was coated on the base membrane side of the reverse osmosis membrane until it was fully wetted. The reverse osmosis membrane was then dried again in an oven at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0060] Example 8

[0061] S1: Base film preparation: Mix 16g of solid polysulfone, 77g of N,N-dimethylformamide, 4g of ethylene glycol monomethyl ether, and 3g of nano-silica. Stir for 30 minutes, let stand for 10 minutes to remove bubbles, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric. After coating, let stand for 10 seconds. Place the film coated with casting solution into a pure water coagulation solution at 10 degrees Celsius to obtain a polysulfone base film.

[0062] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 86.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, and 0.5g of sodium hydroxide sequentially to prepare 4g of amino polyethylene glycol dopamine modified with the silane coupling agent in Example 1 to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0063] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a reverse osmosis membrane.

[0064] S4: Cleaning, wetting, and surface modification: The reverse osmosis membrane was cleaned twice with 60°C pure water. 4g of polyvinyl alcohol and 0.3g of glycerol were added to 97.7g of pure water and stirred evenly to prepare a polyvinyl alcohol-glycerol aqueous solution. This solution was then coated on the polyamide functional layer side of the reverse osmosis membrane until the polyamide functional layer side was fully wetted. Then, an 8% glycerol aqueous solution was coated on the base membrane side of the reverse osmosis membrane until it was fully wetted. The reverse osmosis membrane was then dried again in an oven at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0065] Comparative Example

[0066] Comparative Example 1

[0067] S1: Base film preparation: Mix 16g of solid polysulfone, 80g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, stir for 30 minutes, let stand for 10 minutes to degas, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric, let stand for 10 seconds after coating, and place the film coated with casting solution into pure water coagulation solution at 10 degrees Celsius to obtain polysulfone base film.

[0068] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 86.35g of purified water to obtain an organic amine solution. Then, add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, 0.5g of sodium hydroxide, and 4g of aminopolyethylene glycol dopamine to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit onto the polysulfone-based membrane obtained in S1 and dry it at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0069] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0070] S4: Cleaning, wetting, and surface modification: The reverse osmosis membrane was cleaned twice with 60°C pure water. 4g of polyvinyl alcohol and 0.3g of glycerol were added to 97.7g of pure water and stirred evenly to prepare a polyvinyl alcohol-glycerol aqueous solution. This solution was then coated on the polyamide functional layer side of the reverse osmosis membrane until the polyamide functional layer side was fully wetted. Then, an 8% glycerol aqueous solution was coated on the base membrane side of the reverse osmosis membrane until it was fully wetted. The reverse osmosis membrane was then dried again in an oven at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0071] Comparative Example 2

[0072] S1: Base film preparation: Mix 16g of solid polysulfone, 80g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, stir for 30 minutes, let stand for 10 minutes to degas, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric, let stand for 10 seconds after coating, and place the film coated with casting solution into pure water coagulation solution at 10 degrees Celsius to obtain polysulfone base film.

[0073] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 90.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate and 0.5g of sodium hydroxide in sequence to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0074] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0075] S4: Cleaning, wetting, and surface modification: The reverse osmosis membrane was cleaned twice with 60°C pure water. 4g of polyvinyl alcohol and 0.3g of glycerol were added to 97.7g of pure water and stirred evenly to prepare a polyvinyl alcohol-glycerol aqueous solution. This solution was then coated on the polyamide functional layer side of the reverse osmosis membrane until the polyamide functional layer side was fully wetted. Then, an 8% glycerol aqueous solution was coated on the base membrane side of the reverse osmosis membrane until it was fully wetted. The reverse osmosis membrane was then dried again in an oven at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0076] Comparative Example 3

[0077] S1: Base film preparation: Mix 16g of solid polysulfone, 80g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, stir for 30 minutes, let stand for 10 minutes to degas, and obtain casting solution. Spray the casting solution evenly onto nonwoven fabric, let stand for 10 seconds after coating, and place the film coated with casting solution into pure water coagulation solution at 10 degrees Celsius to obtain polysulfone base film.

[0078] S2: Aqueous phase coating: Dissolve 6g of m-phenylenediamine in 90.35g of purified water to obtain an organic amine solution. Add 3g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate and 0.5g of sodium hydroxide in sequence to obtain an aqueous phase solution. Extrude the aqueous phase solution through a slit and coat it onto the polysulfone-based membrane obtained in S1. Dry at 60°C to obtain a polysulfone-based membrane coated with the aqueous phase solution.

[0079] S3: Oil phase coating: Dissolve 1g of trimesoyl chloride in 99g of isoalkanes to obtain an oil phase solution. Extrude the oil phase solution through a slit and coat it onto the polysulfone-based membrane coated with the aqueous phase solution prepared in S2. Let it stand for 50 minutes to obtain a polyamide functional layer. Dry it at 60°C to obtain a high-stability, easy-to-store, low-pressure reverse osmosis membrane.

[0080] Performance testing

[0081] Test 1: The reverse osmosis membranes prepared in Examples 1-8 and Comparative Examples 1-3 were pre-pressurized with pure water at 5.0 MPa for 1 hour, and then the flux was tested using pure water at a temperature controlled at 25°C and a pressure of 5.0 MPa. The test results are summarized in Table 1. The calculation method is as follows:

[0082]

[0083] Where P is the membrane permeation flux (L / (m²)). 2 ·h)), V is the volume of permeate collected during the test (L), and A is the membrane area (m²). 2 ), where t is the permeation time (h).

[0084] Test 2: A 2000 ppm MgSO4 solution was prepared as the test solution. The pH of the solution was adjusted to between 7 and 8, and the solution temperature was controlled at 25°C. The desalination rate of the reverse osmosis membranes prepared in Examples 1-8 and Comparative Examples 1-3 was tested under a pressure of 5.0 MPa. The test results are summarized in Table 1. The calculation method is as follows:

[0085]

[0086] Where R is the desalination rate of the membrane, and C f C represents the inorganic salt concentration (ppm) of the solution before filtration. t The concentration of inorganic salts in the filtered solution is shown in ppm.

[0087] Test 3: The reverse osmosis membranes prepared in Examples 1-8 and Comparative Examples 1-3 were placed at an ambient temperature of 35°C and an ambient humidity of 90%RH for 15 days. Then, the process of Test 1 was repeated to measure the flux after storage. The test results are summarized in Table 1.

[0088] Test 4: The reverse osmosis membranes prepared in Examples 1-8 and Comparative Examples 1-3 were placed at an ambient temperature of 35°C and an ambient humidity of 90% for 15 days. Then, the process of Test 2 was repeated to measure the desalination rate after storage. The test results are summarized in Table 1.

[0089] Table 1 Performance test data of Examples 1-8 and Comparative Examples 1-3

[0090]

[0091]

[0092] In conjunction with Examples 1-4 and Comparative Examples 1-3, this application adds silane-modified amino polyethylene glycol dopamine, which improves the long-term stability of the reverse osmosis membrane. After storage in a high temperature and high humidity environment, the decrease in water flux and desalination rate is not significant. Furthermore, by protecting the reverse osmosis membrane with glycerol and glycerol-containing polyvinyl alcohol, the performance stability of the reverse osmosis membrane is further improved.

[0093] As can be seen from Examples 4-6, by adjusting the degree of alcoholysis, polyvinyl alcohol can form a complete membrane layer based on the reverse osmosis membrane formulation of this application, while minimizing the impact on flux.

[0094] In conjunction with Examples 3 and 7-8, this application further improves the flux of the reverse osmosis membrane by adding nano-silica to the reverse osmosis membrane. At the same time, due to the combination of the hydroxyl groups on the surface of the nano-silica with the silanol groups generated by the hydrolysis of the silane coupling agent, the strength and density of the reverse osmosis membrane are further improved. While increasing the flux, the desalination rate is also very high, and the influence of glycerol swelling is reduced, further improving the performance stability of the reverse osmosis membrane in high temperature and high humidity environments.

[0095] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A highly stable, easily stored, low-pressure reverse osmosis membrane, characterized in that: The high-stability, easily stored, low-pressure reverse osmosis membrane comprises a polysulfone-based membrane and a polyamide functional layer. The polysulfone-based membrane is made from a casting solution containing polysulfone. The polyamide functional layer is made from an aqueous solution containing organic amine monomers and an oil solution containing acyl chloride monomers. The aqueous solution also includes aminopolyethylene glycol dopamine modified with a silane coupling agent.

2. The high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 1, characterized in that: The polysulfone-based membrane of the highly stable, easily stored, low-pressure reverse osmosis membrane is coated with a glycerol moisturizing layer on the side away from the polyamide functional layer, and a protective layer is coated on the side of the polyamide functional layer away from the polysulfone-based membrane.

3. The high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 2, characterized in that: The glycerin moisturizing layer is formed by coating with a glycerin solution of 5-10% by mass; the protective layer is formed by coating with a polyvinyl alcohol solution containing trace amounts of glycerin, wherein the polyvinyl alcohol solution contains 2-5% by mass of polyvinyl alcohol and the degree of alcoholysis of polyvinyl alcohol is 78-92%; the amount of trace amounts of glycerin added is 2-10% by mass of polyvinyl alcohol.

4. The high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 1, characterized in that: The silane coupling agent is isocyanate-based propyltrimethoxysilane, and the molar ratio of aminopolyethylene glycol dopamine to isocyanate-based propyltrimethoxysilane is 1:(0.9-1.1).

5. The high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 1, characterized in that: The preparation process of the silane coupling agent modified amino polyethylene glycol dopamine includes: adding the silane coupling agent and amino polyethylene glycol dopamine into an aqueous ethanol solution, mixing, stirring at 70-80℃ for 15-20 minutes, filtering, and drying to obtain the silane coupling agent modified amino polyethylene glycol dopamine.

6. The high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 1, characterized in that: The polysulfone-based film contains nano-silica, and the nano-silica accounts for 2-3% of the total mass of the casting solution.

7. The high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 1, characterized in that: The aqueous solution also contains antioxidants, surfactants, pH adjusters, and acid acceptors. The antioxidants include sodium metabisulfite, the surfactants include sodium dodecylbenzenesulfonate, the pH adjusters include camphor sulfonic acid, and the acid acceptors include sodium hydroxide.

8. A method for preparing a high-stability, easily stored, low-pressure reverse osmosis membrane according to any one of claims 1-7, characterized in that: The preparation method includes the following steps: S1: Base film preparation: The casting solution is coated onto nonwoven fabric, left to stand, and cured in pure water to obtain a polysulfone base film; S2: Aqueous phase coating: The aqueous phase solution is coated onto the polysulfone-based film obtained in S1 and dried to obtain an aqueous phase layer; S3: Oil phase coating: The oil phase solution is coated onto the aqueous phase layer obtained in S2, and then dried to obtain a reverse osmosis membrane.

9. The method for preparing a high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 8, characterized in that: The preparation method also includes the following steps: S4: The reverse osmosis membrane obtained in S3 is washed with pure water, a glycerol moisturizing layer is coated on the side of the polysulfone-based membrane away from the polyamide functional layer, a protective layer is coated on the side of the polyamide functional layer away from the polysulfone-based membrane, and then dried.

10. The method for preparing a high-stability, easily stored, low-pressure reverse osmosis membrane according to claim 8, characterized in that: The preparation process of the casting solution in S1 involves stirring and mixing solid polysulfone, a good solvent, a pore-forming agent, and nano-silica. The standing time is 5-15 minutes. The good solvent includes N,N-dimethylformamide, and the pore-forming agent includes ethylene glycol monomethyl ether. Based on the total mass of the casting solution, the mass percentage of polysulfone is 12-18%, the mass percentage of the good solvent is 75-85%, and the mass percentage of the pore-forming agent is 0.5-10%. The drying temperature in S2 is 50-80℃, and the aqueous solution contains 2-10% by mass of organic amine aqueous monomers and 3-5% by mass of silane coupling agent modified amino polyethylene glycol dopamine. The drying temperature in S3 is 50-80℃, and the oil phase solution contains 0.1-1.0% by mass of acyl chloride oil phase monomers; The temperature of the solidified pure water in S1 is 10-15℃.

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