Preparation method of large-flow reverse osmosis composite membrane based on finger structure base film and alginate nanotube separation layer

Abstract

The application relates to a preparation method of a high-flow reverse osmosis composite membrane based on a finger-shaped structure base membrane and an alginate nanotube separation layer, which comprises the following steps: S1, preparation of a casting solution: the casting solution comprises 15-18 wt% of solid polysulfone, 75-82 wt% of N, N-dimethylformamide and 0.5-9 wt% of a pore former, the above raw materials are uniformly mixed and placed, defoaming and filtration are carried out to obtain the casting solution; S2, uniformly spraying the casting solution on a base membrane and placing, placing the film in a water coagulation liquid to obtain a finger-shaped porous support polysulfone base membrane; S3, coating a binary amine aqueous solution on the finger-shaped porous support polysulfone base membrane obtained in the step S2 and drying; and S4, coating a multi-component acyl halide oil phase solution on the finger-shaped porous support polysulfone base membrane in the step S3 to prepare a composite membrane. The reverse osmosis composite membrane in the application can long-term improve and maintain water flux under the condition of ensuring a relatively optimal desalination rate, so as to improve membrane separation efficiency and reduce operation cost.

Description

Technical Field

[0001] This application relates to the field of reverse osmosis membranes, and in particular to a method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer. Background Technology

[0002] Many researchers are actively seeking methods to obtain fresh water through brackish water desalination and water reuse. Over the past three decades, membrane separation has rapidly developed into the main technology for water desalination, among which reverse osmosis membranes are widely used in water treatment due to their ultra-high monovalent salt rejection rate.

[0003] Reverse osmosis membranes generally consist of a nonwoven fabric layer, a porous support layer, and a separation layer. Currently, the porous support layer is mainly formed on the nonwoven fabric layer using a polysulfone casting solution via phase inversion, while the separation layer is mainly formed on the porous support layer using interfacial polymerization of m-phenylenediamine monomer and trimesoyl chloride monomer. The nonwoven fabric layer and porous support layer primarily provide mechanical strength, while the separation layer determines the separation performance of the composite membrane. The performance of the composite membrane can be improved by altering the structural properties of the nonwoven fabric layer and porous support layer. Researchers have tried many methods to improve the efficiency of reverse osmosis membranes, usually resulting in increased water flux at the cost of reduced desalination rate.

[0004] Therefore, the industrial goal of research in the field of reverse osmosis membranes is to increase or at least maintain water flux in the long term without reducing the degree of desalination, so as to improve membrane separation efficiency and reduce operating costs. Summary of the Invention

[0005] In order to effectively improve the separation efficiency of reverse osmosis membranes, that is, to increase or at least maintain the water flux in the long term without reducing the degree of desalination, this application provides a method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer.

[0006] The preparation method of a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer provided in this application adopts the following technical solution:

[0007] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0008] S1: Preparation of casting solution: The casting solution includes 15-18 wt% solid polysulfone, 75-82 wt% N,N-dimethylformamide and 0.5-9 wt% pore-forming agent. The above raw materials are mixed and allowed to stand, and then degassed and filtered to obtain the casting solution.

[0009] S2: Spray the casting solution evenly onto the base film and let it stand. Place the film after standing in the water coagulation solution to obtain a finger-shaped porous supported polysulfone film.

[0010] S3: Coat the finger-shaped porous supported polysulfone membrane obtained in step S2 with a diamine aqueous solution and dry it;

[0011] S4: A multi-acyl halide oil phase solution is coated onto the finger-shaped porous supported polysulfone membrane in step S3 to obtain a composite membrane.

[0012] By employing the above technical solution, the casting solution undergoes phase transformation in water to form a polysulfone-based membrane. Both N,N-dimethylformamide and the porogen are soluble in water. When the casting solution is immersed in water, N,N-dimethylformamide and the porogen escape from the polysulfone solution into the water. The escape rate of the porogen is much greater than that of N,N-dimethylformamide, thus sequentially generating a dense layer, a sponge-like layer, and a finger-like layer, obtaining a finger-type porous supported polysulfone-based membrane, which can reduce resistance during water mass transfer. A polyamide layer is formed through interfacial polymerization between a diamine aqueous solution and a polyacrylamide oil solution. By optimizing the physical properties of the porous support layer, the water flux of the composite membrane can be greatly improved, while ensuring the desalination rate of the composite membrane.

[0013] In one specific implementation, the porogen is ethylene glycol monomethyl ether.

[0014] By adopting the above technical solution and using ethylene glycol monomethyl ether as a pore-forming agent, the support layer of the present invention can generate a suitable finger-shaped pore structure, thereby improving the flux of the reverse osmosis membrane.

[0015] In one specific embodiment, the diamine aqueous solution comprises the following components by weight percentage: 2-10% diamine, 2.5-3% pH adjuster, 0.15%-0.5% surfactant, 0.5%-1.5% acid acceptor, 3-5% modifier, and 1-3% N,N-dimethylacetamide, with the balance being water.

[0016] By employing the above technical solution, diamines, as amine monomers, undergo cross-linking polymerization with polyacrylamide halides. pH adjusters are used to regulate the acidity or alkalinity of the liquid, promoting the chemical reaction. Surfactants reduce the interfacial tension between oil and water by adsorbing at the liquid interface, thereby affecting the polymerization rate at the interface and optimizing the performance of the composite membrane. Acid acceptors neutralize the acids generated during interfacial polymerization, reducing the corrosive effect of chloride ions and promoting the polymerization reaction. Modifiers hydrolyze and modify the surface of the support layer, resulting in a large number of active groups on the support layer surface. N,N-dimethylacetamide serves as a solvent or co-catalyst, ensuring the continuous and stable formation of the composite membrane.

[0017] In one specific feasible embodiment, the diamine is one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 4-chloro-1,3-phenylenediamine, and 6-chloro-1,3-phenylenediamine; the pH adjuster is one of camphor sulfonic acid, tartaric acid, and citric acid; the surfactant is one of sodium dodecyl sulfonate, sodium dioctyl succinate sulfonate, sodium dodecylbenzene sulfonate, and sodium glycocholate; the acid acceptor is sodium hydroxide; and the modifier is N-methylpyrrolidone.

[0018] By employing the above technical solutions and selecting specific diamines, the performance of the composite membrane can be improved, thereby increasing its desalination rate. pH adjusters lower the pH value of the liquid, which is beneficial for the smooth progress of the interfacial polymerization reaction. Surfactants can alter the dispersion rate of the diamine into the oil phase solution, thus affecting the interfacial polymerization rate and optimizing the performance of the composite membrane. Acid acceptors can absorb the acid generated during interfacial polymerization, promoting the polymerization reaction and facilitating the formation of the composite membrane.

[0019] In one specific feasible embodiment, the polyacrylamide halide oil phase solution comprises 0-5% by weight of alginate-coated carbon nanotubes, 0.5-3% by weight of polyacrylamide halide monomers, and 92-98% by weight of isoalkane oil phase solvent, wherein the polyacrylamide halide monomer is one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride, and the isoalkane is a methyl-substituted hydrocarbon with 5-12 carbon atoms.

[0020] By adopting the above technical solution, polyacryl halides are dissolved in isoalkanes. The multi-branched structure of isoalkanes reduces the intermolecular forces and improves solubility, which is conducive to the polymerization of polyacryl halides and aqueous solutions to form polyamide functional layers.

[0021] Alginate-coated carbon nanotubes filling the base membrane can significantly improve the water flux of the base membrane. Simultaneously, alginate has a strong ability to block bacteria and viruses, making it a key component of the coating material in this application. Furthermore, the one-dimensional porous structure of carbon nanotubes provides channels for water, thereby increasing the water flux of the composite membrane. Alginate, with its high viscosity and adhesiveness, can adhere to the polysulfone base membrane, ensuring the mechanical stability of both the polysulfone base membrane and the alginate-coated carbon nanotubes. Moreover, its good hydrophilicity can increase the water flux of the membrane in the initial stage of use, compensating for the hydrophobicity of the polysulfone base membrane. During long-term use, impurities may clog the channels in the composite membrane, affecting water flux. By adding alginate-coated carbon nanotubes to the base membrane, the alginate slowly hydrolyzes with use, exposing the carbon nanotubes. The porous structure of the carbon nanotubes provides new channels for water, thus enabling the composite membrane to maintain a sustained high flux effect.

[0022] In one specific feasible implementation, the method for preparing the alginate-coated carbon nanotubes includes the following steps:

[0023] Mix seaweed with sodium carbonate solution, stir at 55-100℃ for 1-6 hours, cool to room temperature, and centrifuge to obtain supernatant.

[0024] The obtained alginate solution was sprayed onto carbon nanotubes, granulated in a disc, and dried to obtain alginate-coated carbon nanotubes.

[0025] By employing the above technical solution and ensuring thorough stirring, the sodium alginate solution is guaranteed to possess the required viscosity and adhesion. Coating carbon nanotubes with sodium alginate effectively improves the adhesion between the alginate-coated carbon nanotubes and the polysulfone-based film, thereby enhancing the stability of the base film.

[0026] In one specific implementation scheme, the carbon nanotubes are modified carbon nanotubes. The carbon nanotubes are dispersed in an acidic aqueous solution with a pH of 1-3 and refluxed at 50℃-60℃ for 4 hours. The co-precipitate containing carbon nanotubes is washed several times with deionized water until the pH of the solution is between 5.6-7. The co-precipitate is separated, dehydrated and dried to obtain oxidized carbon nanotubes.

[0027] By employing the above-mentioned technical solution, acid oxidation treatment of carbon nanotubes increases the number of functional groups such as hydroxyl and carbonyl groups on the surface, leading to changes in the chemical and surface properties of the carbon nanotubes. This results in improved hydrophilicity, dispersibility, and higher reactivity. Therefore, it can effectively increase the water flux of subsequent reverse osmosis membranes.

[0028] In one specific implementation, the sodium carbonate solution is an aqueous sodium carbonate solution with a mass concentration of 15-25%, and the mass of the seaweed is 20-25% of the mass of the sodium carbonate solution.

[0029] By adopting the above technical solution and controlling a more suitable ratio and dosage, it is beneficial to generate a sodium alginate solution that meets the requirements.

[0030] In one specific implementation, the temperature range of the water-based coagulation solution is 10-15°C.

[0031] By adopting the above technical solution, it is beneficial for the casting solution to undergo phase transformation in water into a polysulfone-based membrane that meets the requirements.

[0032] In one specific implementation, the composite membrane obtained in step S4 is wetted with glycerin, then coated with PVA, and finally dried.

[0033] By adopting the above technical solution, the reverse osmosis membrane can have equivalent or better water purification function. Since the polyvinyl alcohol consumes the excess carboxyl groups of the polyamide layer and forms an antifouling layer on the surface of the polyamide layer, it can improve chlorine resistance. Therefore, the coating is not easy to peel off and can have good durability.

[0034] In summary, this application includes at least one of the following beneficial technical effects:

[0035] 1. By using ethylene glycol monomethyl ether as a pore-forming agent, the support layer of this invention can achieve a suitable finger-like pore structure. The casting solution undergoes phase transformation in water to form a polysulfone-based membrane. Both N,N-dimethylformamide and ethylene glycol monomethyl ether are soluble in water and escape from the polysulfone solution. The escape rate of ethylene glycol monomethyl ether is much greater than that of N,N-dimethylformamide, thereby sequentially generating a dense layer, a sponge-like layer, and a finger-like layer, resulting in a finger-shaped porous supported polysulfone-based membrane. This reduces resistance during water mass transfer. By optimizing the physical properties of the porous support layer, the water flux of the composite membrane can be significantly improved, while ensuring the desalination rate of the composite membrane.

[0036] 2. This application demonstrates that coating carbon nanotubes with sodium alginate effectively improves the adhesion between alginate-coated carbon nanotubes and polysulfone-based membranes, thereby enhancing the stability of the base membrane. Oxidation treatment of carbon nanotubes increases the number of functional groups such as hydroxyl and carbonyl groups on their surface, leading to changes in the chemical and surface properties of the carbon nanotubes, resulting in improved hydrophilicity, dispersibility, and higher reactivity. Therefore, it can effectively increase the water flux of subsequent reverse osmosis membranes.

[0037] 3. In this application, carbon nanotubes coated with alginate undergo slow and continuous hydrolysis during long-term reverse osmosis. Simultaneously, the modified carbon nanotubes exhibit hydrophilicity and higher reactivity, further enhancing the membrane's water flux. The slow and continuous hydrolysis of alginate also reduces the thickness of the composite membrane, alleviating system water supply pressure. This effectively mitigates the problem of impurities continuously precipitating, adhering, and clogging membrane pores, thus effectively solving the issues of increased system water supply pressure, flux decline, and reduced desalination rate.

[0038] 4. This application wets the reverse osmosis membrane with glycerin, then coats the surface of the composite membrane with PVA, and dries it. Polyvinyl alcohol forms an antifouling layer on the surface of the polyamide membrane, which makes the reverse osmosis membrane have a more stable chemical structure. Therefore, the coating is not easy to peel off and can have good durability. Detailed Implementation

[0039] Unless otherwise specified, all raw materials used in this application are from commercially available brands or obtained through conventional preparation processes.

[0040] Preparation Example

[0041] Preparation Example 1

[0042] First, soak the seaweed in water for 7 minutes, then wash it 4 times and pulverize it to obtain pulverized seaweed. Prepare a 15% sodium carbonate aqueous solution and mix the seaweed and sodium carbonate aqueous solution. The amount of seaweed added is 25% of the mass of sodium carbonate aqueous solution. Stir at 55°C and magnetic stirring speed of 150 r / min for 1 hour. Cool to room temperature and centrifuge to obtain alginate solution. Accurately weigh carbon nanotubes and spray the alginate solution evenly on the surface of carbon nanotubes. The mass ratio of carbon nanotubes to alginate solution is 1.3:5. Granulate in a disc and dry to obtain alginate-coated carbon nanotubes.

[0043] Preparation Example 2

[0044] First, soak the seaweed in water for 7 minutes, then wash it 4 times and pulverize it to obtain pulverized seaweed. Prepare a 25% sodium carbonate aqueous solution and mix the seaweed and sodium carbonate aqueous solution. The amount of seaweed added is 20% of the mass of sodium carbonate aqueous solution. Stir at 55℃ and magnetic stirring speed of 150 r / min for 6 hours. Cool to room temperature and centrifuge to obtain alginate solution. Accurately weigh carbon nanotubes and spray the alginate solution evenly on the surface of carbon nanotubes. The mass ratio of carbon nanotubes to alginate solution is 1.3:5. Granulate in a disc and dry to obtain alginate-coated carbon nanotubes.

[0045] Preparation Example 3

[0046] Carbon nanotubes were weighed into a round-bottom flask, and a mixed acid solution of concentrated H₂SO₄ and concentrated HNO₃ (volume ratio 3:1, mass ratio of carbon nanotubes to mixed acid 1:6) was added. The mixture was refluxed at 50°C for 4 hours. The co-precipitate containing carbon nanotubes was washed several times with deionized water until the pH of the solution reached 5.6, and then centrifuged at 8000 rpm for 30 minutes. The supernatant and precipitate were separated, and the oxidized carbon nanotubes were collected and dried in a vacuum oven at 60°C.

[0047] Soak the seaweed in water for 7 minutes, then wash it 4 times and crush it to obtain crushed seaweed. Prepare a sodium carbonate solution with a mass fraction of 25% and add seaweed at 20% of the mass of the sodium carbonate solution. Stir at 55°C and magnetic stirring speed of 150 r / min for 6 hours. Cool to room temperature and centrifuge to obtain alginate solution.

[0048] The alginate solution was uniformly sprayed onto the surface of the obtained carbon nanotubes, with a mass ratio of carbon nanotubes to alginate solution of 1.3:5. The nanotubes were then granulated in a disc and dried to obtain alginate-coated carbon nanotubes.

[0049] Preparation Example 4

[0050] Carbon nanotubes were weighed into a round-bottom flask, and a mixed acid solution of concentrated H₂SO₄ and concentrated HNO₃ (volume ratio 3:1, mass ratio of carbon nanotubes to mixed acid 1:6) was added. The mixture was refluxed at 60°C for 6 hours. The co-precipitate containing carbon nanotubes was washed several times with deionized water until the pH of the solution reached 6.8, and then centrifuged at 8000 rpm for 30 minutes. The supernatant and precipitate were separated, and the oxidized carbon nanotubes were collected and dried in a vacuum oven at 60°C.

[0051] Soak the seaweed in water for 7 minutes, then wash it 4 times and crush it to obtain crushed seaweed. Prepare a sodium carbonate solution with a mass fraction of 25% and add seaweed at 20% of the mass of the sodium carbonate solution. Stir at 55°C and magnetic stirring speed of 150 r / min for 6 hours. Cool to room temperature and centrifuge to obtain alginate solution.

[0052] The alginate solution was uniformly sprayed onto the surface of the obtained carbon nanotubes, with a mass ratio of carbon nanotubes to alginate solution of 1.3:5. The nanotubes were then granulated in a disc and dried to obtain alginate-coated carbon nanotubes.

[0053] Example 1

[0054] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0055] S1: Accurately weigh 17.5g of polysulfone, 82g of N,N-dimethylformamide and 0.5g of ethylene glycol monomethyl ether. Mix the above raw materials well and let stand. Then degas and filter to obtain casting solution for later use.

[0056] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0057] S3: Accurately weigh 2g of m-phenylenediamine, 2.5g of camphor sulfonic acid, 0.15g of sodium dodecyl sulfonate, 0.5g of sodium hydroxide, 3g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 89.85g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0058] S4: Accurately weigh 2g of trimesoyl chloride and 98g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0059] Example 2

[0060] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0061] S1: Accurately weigh 17g of polysulfone, 79g of N,N-dimethylformamide and 4g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use;

[0062] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the film after standing in a 15°C water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0063] S3: Accurately weigh 4g of m-phenylenediamine, 3g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 0.7g of sodium hydroxide, 4g of N-methylpyrrolidone, 1g of N,N-dimethylacetamide, and 87g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0064] S4: Accurately weigh 2g of trimesoyl chloride and 98g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0065] Example 3

[0066] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0067] S1: Accurately weigh 18g of polysulfone, 75g of N,N-dimethylformamide and 7g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0068] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 3 seconds. Place the standing film in a 10°C water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0069] S3: Accurately weigh 6g of p-phenylenediamine, 2.8g of tartaric acid, 0.5g of sodium dodecyl sulfonate, 1.5g of sodium hydroxide, 5g of N-methylpyrrolidone, 3g of N,N-dimethylacetamide, and 81.2g of water. Dissolve p-phenylenediamine in water, and then add tartaric acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0070] S4: Accurately weigh 2g of trimesoyl chloride and 98g of isoheptane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0071] Example 4

[0072] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0073] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0074] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0075] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0076] S4: Accurately weigh 3g of trimesoyl chloride and 97g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0077] Example 5

[0078] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0079] S1: Accurately weigh 15g of polysulfone, 76g of N,N-dimethylformamide and 9g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0080] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0081] S3: Accurately weigh 10g of m-phenylenediamine, 3g of camphor sulfonic acid, 0.3g of sodium dioctyl succinate sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 79.5g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0082] S4: Accurately weigh 3g of terephthaloyl chloride and 97g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0083] Example 6

[0084] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0085] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0086] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0087] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0088] S4: Accurately weigh 2g of pyromellitic methyl chloride, 0.5g of alginate-coated carbon nanotubes prepared in Example 1, and 97.5g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head for reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0089] Example 7

[0090] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0091] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0092] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0093] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0094] S4: Accurately weigh 2g of pyromellitic trimethylol chloride, 0.5g of alginate-coated carbon nanotubes prepared in Example 2, and 97.5g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head for reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0095] Example 8

[0096] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0097] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0098] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0099] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0100] S4: Accurately weigh 2g of alginate-coated carbon nanotubes, 0.5g of trimesoyl chloride, and 97.5g of isohexane obtained in Preparation Example 1, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head for reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0101] Example 9

[0102] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0103] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0104] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0105] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0106] S4: Accurately weigh 4.2g of alginate-coated carbon nanotubes, 2g of trimesoyl chloride and 93.8g of isohexane obtained in Preparation Example 1, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0107] Example 10

[0108] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0109] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0110] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0111] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0112] S4: Accurately weigh 5g of alginate-coated carbon nanotubes, 3g of trimesoyl chloride and 92g of isohexane obtained in Preparation Example 1, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0113] Example 11

[0114] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0115] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0116] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0117] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0118] S4: Accurately weigh 0.5g of alginate-coated carbon nanotubes, 2g of trimesoyl chloride and 97.5g of isohexane obtained in Preparation Example 3, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0119] Example 12

[0120] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0121] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0122] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0123] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0124] S4: Accurately weigh 0.5g of alginate-coated carbon nanotubes, 2g of trimesoyl chloride and 97.5g of isohexane obtained in Preparation Example 4, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0125] Example 13

[0126] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0127] S1: Accurately weigh 17g of polysulfone, 75g of N,N-dimethylformamide and 8g of ethylene glycol monomethyl ether, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use.

[0128] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0129] S3: Accurately weigh 2g of m-phenylenediamine, 2.8g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 1.2g of sodium hydroxide, 4g of N-methylpyrrolidone, 2g of N,N-dimethylacetamide, and 87.7g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0130] S4: Accurately weigh 0.5g of alginate-coated carbon nanotubes, 2g of trimesoyl chloride and 97.5g of isohexane obtained in Preparation Example 4, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50°C for 6 minutes to obtain a reverse osmosis composite membrane.

[0131] S5: The obtained composite membrane is moistened with glycerin and then coated with PVA. The composite membrane is brought into contact with PVA by dip coating for 60 seconds, followed by drying.

[0132] Comparative Example 1

[0133] A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer includes the following steps:

[0134] S1: Accurately weigh 18g of polysulfone and 82g of N,N-dimethylformamide, mix the above raw materials evenly and let stand, then degas and filter to obtain casting solution for later use;

[0135] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0136] S3: Accurately weigh 4g of m-phenylenediamine, 3g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 0.7g of sodium hydroxide, 4g of N-methylpyrrolidone, 1g of N,N-dimethylacetamide, and 87g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0137] S4: Accurately weigh 2g of trimesoyl chloride and 98g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0138] Comparative Example 2

[0139] Accurately weigh 17g of polysulfone, 73g of N,N-dimethylformamide, and 10g of ethylene glycol monomethyl ether. Mix the above raw materials thoroughly and let stand. Then degas and filter to obtain the casting solution for later use.

[0140] S2: Spray the casting solution evenly onto the nonwoven membrane and let it stand for 10 seconds. Place the standing film in a 10℃ water coagulation solution to obtain a finger-shaped porous supported polysulfone membrane.

[0141] S3: Accurately weigh 4g of m-phenylenediamine, 3g of camphor sulfonic acid, 0.3g of sodium dodecyl sulfonate, 0.7g of sodium hydroxide, 4g of N-methylpyrrolidone, 1g of N,N-dimethylacetamide, and 87g of water. Dissolve the m-phenylenediamine in water, and then add camphor sulfonic acid, sodium dodecyl sulfonate, sodium hydroxide, and N-methylpyrrolidone in sequence to obtain an aqueous solution. Apply the aqueous solution to the base film obtained in step S2 through a slit coating head and dry it.

[0142] S4: Accurately weigh 2g of trimesoyl chloride and 98g of isohexane, mix them to obtain an oil phase solution, coat the oil phase solution onto the membrane in step S3 through a slit coating head to carry out the reaction, and then place it in an oven to dry at 50℃ for 6min to obtain a reverse osmosis composite membrane.

[0143] Performance testing of the reverse osmosis composite membrane: The reverse osmosis membranes prepared in Examples 1-13 and Comparative Examples 1 and 2 were tested at room temperature using a cross-flow flat sheet membrane performance evaluation device. The pure water flux and the rejection rate of 500 ppm sodium chloride aqueous solution of the product membranes were tested respectively. The pH value of the test solution was adjusted to 8. The membrane to be tested was installed in the test cell of the membrane performance evaluation instrument. The test temperature was 25℃ and the test pressure was 15 bar. In addition, in order to test the reverse osmosis performance of the composite membrane during long-term use, and whether it can maintain a considerable water flux while maintaining a good desalination rate, the desalination rate and water flux of the composite membrane were tested again after three months of continuous operation using the above methods. The results are shown in Table 1.

[0144] Table 1. Water flux performance test results

[0145]

[0146] Referring to Examples 1-5 of this invention, the water flux of the high-flux reverse osmosis membrane obtained by this invention is 60-85.6 L / m³. 2 The desalination rate was 97.0-99.2% over h. Compared with Comparative Example 1 and Comparative Example 2, the flux was significantly improved while maintaining a high desalination rate. It is evident that this invention, by using ethylene glycol monomethyl ether as a porogen and leveraging the different escape rates of ethylene glycol monomethyl ether and N,N-dimethylformamide from polysulfone, creates a dense layer, a sponge-like layer, and a finger-like layer in the base membrane, resulting in a finger-type porous supported polysulfone base membrane. This effectively reduces resistance during water mass transfer and improves the water flux of the composite membrane.

[0147] In conjunction with Examples 4 and 6-10 of this invention, alginate-coated carbon nanotubes are used for interfacial polymerization. The hydrolyticity, hydrophilicity, and high adhesion of alginate are utilized to coat and modify polysulfone-based membranes with modified carbon nanotubes. This compensates for the insufficient hydrophilicity of the polysulfone-based membrane, which affects water flux and improves the stability of the membrane. The porous structure of the carbon nanotubes provides more flow paths for water, thereby increasing the water flux of the composite membrane.

[0148] In conjunction with Examples 6 and 11-12, the modification of carbon nanotubes is crucial. Oxidation treatment of carbon nanotubes increases the number of functional groups such as hydroxyl and carbonyl groups on their surface, leading to changes in the chemical and surface properties of the carbon nanotubes, resulting in improved hydrophilicity, dispersibility, and higher reactivity. The one-dimensional pore structure of the modified carbon nanotubes provides channels for water, thus effectively increasing the water flux of the subsequent reverse osmosis membrane and ensuring the desalination rate of the composite membrane.

[0149] Combining Examples 11 and 13, coating the surface of the composite membrane with polyvinyl alcohol consumes excess carboxyl groups in the polyamide layer and forms an antifouling layer on the surface of the polyamide layer. This can improve chlorine resistance and reduce the possibility of impurities adhering to the surface of the polyamide layer, thereby affecting water flux and rejection rate. This allows the composite membrane to have good durability while maintaining high flux and rejection rate.

[0150] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer, characterized in that, Includes the following steps: S1: Preparation of casting solution: The casting solution includes 15-18 wt% solid polysulfone, 75-82 wt% N,N-dimethylformamide, and 0.5-9 wt% pore-forming agent. The above raw materials are mixed and allowed to stand, then degassed and filtered to obtain the casting solution; S2: The casting solution is uniformly sprayed onto the substrate and allowed to stand. The film after standing is placed in an aqueous coagulation solution to obtain a finger-shaped porous supported polysulfone-based membrane; S3: A diamine aqueous solution is coated onto the finger-shaped porous supported polysulfone-based membrane obtained in step S2 and dried; S4: A polyacrylamide halide oil phase solution is coated onto the finger-shaped porous supported polysulfone-based membrane obtained in step S3 to obtain a composite membrane; The polyacrylamide halide oil phase solution comprises 0.5-5% by weight alginate-coated carbon nanotubes, 0.5-3% by weight polyacrylamide halide monomers, and 92-98% by weight isoalkane oil phase solvent. The polyacrylamide halide monomers are one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride. The isoalkane is a methyl-substituted hydrocarbon with 5-12 carbon atoms. The method for preparing alginate-coated carbon nanotubes includes the following steps: mixing seaweed with sodium carbonate solution, stirring at 55-100℃ for 1-6 hours, cooling to room temperature, and centrifuging to obtain the supernatant; spraying the obtained alginate solution onto carbon nanotubes, granulating on a disc, and drying to obtain alginate-coated carbon nanotubes.

2. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 1, characterized in that, The pore-forming agent is ethylene glycol monomethyl ether.

3. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 1, characterized in that, The diamine aqueous solution comprises the following components by weight percentage: 2-10% diamine, 2.5-3% pH adjuster, 0.15%-0.5% surfactant, 0.5%-1.5% acid acceptor, 3-5% modifier, and 1-3% N,N-dimethylacetamide, with the balance being water.

4. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 3, characterized in that, The diamine is one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 4-chloro-1,3-phenylenediamine, and 6-chloro-1,3-phenylenediamine; the pH adjuster is one of camphor sulfonic acid, tartaric acid, and citric acid; the surfactant is one of sodium dodecyl sulfonate, sodium dioctyl succinate sulfonate, sodium dodecylbenzene sulfonate, and sodium glycocholate; the acid acceptor is sodium hydroxide; and the modifier is N-methylpyrrolidone.

5. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 1, characterized in that: The carbon nanotubes are modified carbon nanotubes. The carbon nanotubes are dispersed in an acidic aqueous solution and refluxed at 50℃-60℃ for 4-6 hours. The coprecipitate containing carbon nanotubes in the acid solution is washed several times with deionized water until the pH of the solution is between 5.6 and 7. The coprecipitate is separated, dehydrated and dried to obtain oxidized carbon nanotubes.

6. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 1, characterized in that: The sodium carbonate solution is an aqueous sodium carbonate solution with a mass concentration of 15-25%, and the mass of the seaweed is 20-25% of the mass of the sodium carbonate solution.

7. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 1, characterized in that, The temperature range of the aqueous coagulation solution is 10-15℃.

8. The method for preparing a high-flow-rate reverse osmosis composite membrane based on a finger-structured base membrane and an alginate nanotube separation layer according to claim 1, characterized in that, The composite membrane obtained in step S4 is moistened with glycerin, then coated with PVA, and finally dried.

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