Preparation method of high-flux seawater desalination reverse osmosis membrane

Abstract

The invention discloses a preparation method of a high-flux seawater desalination reverse osmosis membrane. The high-flux seawater desalination reverse osmosis membrane prepared by the preparation method provided by the invention is high in desalination rate and high in water flux, is used for seawater filtration, and can improve the filtration efficiency and effect.

Description

Technical Field

[0001] The invention relates to the technical field of reverse osmosis membranes, and more specifically, to a method for preparing a high-flux seawater desalination reverse osmosis membrane. Background Art

[0002] Water shortage is one of the global challenges facing mankind today. It is predicted that by 2050, the global water demand will be about 540-6100 billion cubic meters, which cannot be met by current freshwater resources. Given the abundant reserves of seawater, seawater desalination can be an ideal way to solve the global freshwater resource crisis. Seawater desalination technology mainly includes two categories: thermal method and membrane method. Among them, membrane separation technology represented by reverse osmosis membrane technology can achieve efficient seawater desalination. Compared with thermal technology, it has the characteristics of simple operation, low cost, and environmental friendliness, showing unique advantages in the field of seawater desalination. However, the seawater desalination reverse osmosis membrane (SWRO), which is the core of the membrane desalination process, still needs to be improved in order to further reduce the cost of related infrastructure and system operation costs. According to modeling research, when the seawater desalination reverse osmosis membrane system has a given daily water production and recovery rate, increasing the SWRO permeation flux by more than double can reduce the number of pressure vessels and energy consumption of the membrane system by 44% and 15%, respectively. Therefore, under the premise of ensuring the high desalination and separation performance of the seawater desalination reverse osmosis membrane material, it is of great significance to further improve its permeation water flux.

[0003] Desalination reverse osmosis membranes are generally prepared by interfacial polymerization. They are composite membranes with three layers, including a non-woven fabric layer, a polysulfone layer, and a polyamide layer from bottom to top. The preparation methods of the polysulfone layer and the polyamide layer are as follows: a polysulfone solution is cast on a non-woven fabric layer, a polysulfone-based membrane is prepared by a phase inversion method, and then the polysulfone-based membrane is immersed in an aqueous solution containing amine monomers and other additives, and then taken out, and excess solution is removed by a vacuum pump, an air knife, etc., and then an oil phase solution containing an acyl chloride monomer and other additives is poured on the membrane surface to cause an interfacial polymerization reaction. The excess oil phase solution is removed by heating in an oven to obtain a polyamide layer, and then a complete desalination reverse osmosis membrane is obtained after rinsing and other post-treatment processes. Conventionally prepared desalination reverse osmosis membranes have the following shortcomings: 1. The desalination rate of seawater desalination reverse osmosis membrane is between 99.0% and 99.8%, and the low desalination rate limits its application.

[0004] 2. The water flux of seawater desalination reverse osmosis membrane is 30-60L / m 2 ・h, the low flux results in greater system energy consumption.

[0005] At present, in order to prepare high-throughput seawater desalination reverse osmosis membranes, most research work is focused on optimizing interfacial polymerization reaction conditions, developing new reaction monomers, adding porous nanomaterials, etc. to fine-tune the performance of the polyamide layer in order to further improve the permeate water flux of the membrane material.

[0006] Although the introduction of nanomaterials can improve the separation performance and water permeability of the membrane, nanomaterials are expensive and difficult to obtain, and have process defects such as "agglomeration", making them unsuitable for large-scale industrial production. Coating PVA on the membrane surface, chemically grafting PVA with polyamide on the membrane surface, or grafting PVA inside polyamide can protect the separation layer on the membrane surface, thereby improving the membrane's anti-pollution ability and desalination rate, but will reduce the water flux of the membrane.

[0007] In summary, how to prepare a seawater desalination reverse osmosis membrane with large membrane flux and high salt removal rate is a technical problem that needs to be solved by those skilled in the art. Summary of the invention

[0008] To solve the above technical problems, the present invention provides a method for preparing a high-flux seawater desalination reverse osmosis membrane. The prepared high-flux seawater desalination reverse osmosis membrane has high desalination rate and high water flux, and is used for filtering seawater to improve filtration efficiency and effect.

[0009] The technical solution provided by the present invention is as follows: A method for preparing a high-flux seawater desalination reverse osmosis membrane comprises the following steps: (1) A polysulfone-based membrane with a porous large pore size is prepared using a polysulfone solution containing lithium chloride; (2) coating the polyacrylamide solution on the back side of the polysulfone-based membrane, the back side, i.e., the side of the polysulfone-based membrane that contacts the non-woven fabric during the membrane-forming process, and drying the polysulfone-based membrane after the pores of the polysulfone-based membrane are fully infiltrated with the polyacrylamide solution to obtain a polysulfone-based membrane with partially macropores filled with polyacrylamide; (3) coating the polysulfone-based membrane obtained in step (2) with an aqueous solution and an oily solution in sequence, and then drying the membrane to obtain a primary seawater desalination reverse osmosis membrane; (4) The nascent reverse osmosis membrane is immersed in water to wash away the polyacrylamide, then immersed in a room temperature solution, and dried to obtain a high-flux seawater desalination reverse osmosis membrane.

[0010] Among them, a method for preparing a high-flux seawater desalination reverse osmosis membrane may include the following steps: (1) Casting a polysulfone solution containing lithium chloride onto a non-woven fabric, solidifying it into a membrane by phase conversion after soaking in deionized water, and then washing it with deionized water to obtain a porous large-pore polysulfone-based membrane; (2) coating the polyacrylamide solution on the back side of the polysulfone-based membrane, which is the side in contact with the non-woven fabric during the membrane formation process, and drying the polysulfone-based membrane after the pores of the polysulfone-based membrane are fully infiltrated with the polyacrylamide solution to obtain a polysulfone-based membrane with partially macropores filled with polyacrylamide; (3) coating the polysulfone-based membrane obtained in the above with an aqueous solution, removing excess solution on the surface with a low-pressure air knife, coating the polysulfone-based membrane with an oily solution, removing the oily solution on the surface with a low-pressure air knife, and then placing the membrane in an oven at 80° C. for 5 minutes to dry the oily solution and obtain a nascent seawater desalination reverse osmosis membrane; (4) The nascent reverse osmosis membrane is immersed in water to wash away the polyacrylamide, then immersed in a glycerol solution, and dried to obtain a high-flux seawater desalination reverse osmosis membrane.

[0011] The polysulfone solution is prepared by dissolving 150-190 parts by weight of polysulfone and 0.5-3 parts by weight of lithium chloride in 810-850 parts by weight of DMF solvent.

[0012] Preferably, the polysulfone solution is obtained by dissolving 160-180 parts by weight of polysulfone and 0.6-2 parts by weight of lithium chloride in 820-840 parts by weight of DMF solvent.

[0013] More preferably, the polysulfone solution is obtained by dissolving 170 parts by weight of polysulfone and 1 part by weight of lithium chloride in 830 parts by weight of DMF solvent.

[0014] The polyacrylamide solution is prepared by dissolving 0.5-3 parts by weight of polyacrylamide and 10-30 parts by weight of glycerol in 960-990 parts by weight of water.

[0015] Preferably, the polyacrylamide solution is prepared by dissolving 0.8-2.5 parts by weight of polyacrylamide and 15-25 parts by weight of glycerol in 960-990 parts by weight of water.

[0016] More preferably, the polyacrylamide solution is prepared by dissolving 1 part by weight of polyacrylamide and 20 parts by weight of glycerol in water.

[0017] The aqueous phase solution is prepared by dissolving 15-40 parts by weight of m-phenylenediamine, 1-4 parts by weight of sodium dodecylbenzenesulfonate and 10-40 parts by weight of N-methylpyrrolidone in 916-974 parts by weight of water, and adjusting the pH value to 7.5-8.0 with sodium hydroxide.

[0018] Preferably, the aqueous phase solution is prepared by dissolving 20-30 parts by weight of m-phenylenediamine, 2-3.5 parts by weight of sodium dodecylbenzenesulfonate and 15-30 parts by weight of N-methylpyrrolidone in 930-960 parts by weight of 15° C. pure water, and adjusting the pH value to 7.5-8.0 with sodium hydroxide.

[0019] More preferably, the aqueous phase solution is prepared by dissolving 25 parts by weight of m-phenylenediamine, 3 parts by weight of sodium dodecylbenzenesulfonate and 20 parts by weight of N-methylpyrrolidone in 952 parts by weight of pure water at 15° C. and adjusting the pH value to 7.5-8.0 with sodium hydroxide.

[0020] The oil phase solution is prepared by dissolving 1-4 parts by weight of trimesoyl chloride in 980-1000 parts by weight of Isopar G.

[0021] Preferably, the oil phase solution is prepared by dissolving 2-3 parts by weight of trimesoyl chloride in 960-998 parts by weight of Isopar G.

[0022] More preferably, the oil phase solution is prepared by dissolving 2.5 parts by weight of trimesoyl chloride in 997.5 parts by weight of Isopar G.

[0023] The polysulfone solution is prepared as follows: 810-850 parts by weight of DMF solvent is added to a beaker, 150-190 parts by weight of polysulfone is added under heating and stirring at 70°C-80°C, and after stirring until dissolved, 0.5-3 parts by weight of lithium chloride is added, and heating and stirring are continued at 70°C-80°C until a homogeneous solution is formed, and the homogeneous solution is allowed to stand and degas for 12-36 hours to obtain a polysulfone solution.

[0024] Preferably, the polysulfone solution is prepared as follows: 822-840 parts by weight of DMF solvent is added to a beaker, 160-180 parts by weight of polysulfone is added under heating and stirring at 70°C-80°C, and after stirring until dissolved, 0.6-2 parts by weight of lithium chloride is added, and heating and stirring are continued at 70°C-80°C to form a homogeneous solution, and the homogeneous solution is allowed to stand and degas for 12-36 hours to obtain a polysulfone solution.

[0025] More preferably, the polysulfone solution is prepared by adding 830 g of DMF solvent into a beaker, adding 170 g of polysulfone under heating and stirring at 75°C, stirring until dissolved, adding 1 g of lithium chloride, continuing heating and stirring at 75°C to form a homogeneous solution, and allowing the homogeneous solution to stand for 24 hours to degas, thereby obtaining a polysulfone solution.

[0026] The polyacrylamide solution is prepared by the following method: adding 0.5-3 parts by weight of polyacrylamide to 960-990 parts by weight of hot water at 45°C-55°C, stirring to dissolve, adding 10-30 parts by weight of glycerol, and cooling for later use.

[0027] Preferably, the polyacrylamide solution is prepared by the following method: adding 0.8-2.5 parts by weight of polyacrylamide to 965-985 parts by weight of hot water at 45° C.-55° C., stirring to dissolve, adding 15-25 parts by weight of glycerol, and cooling for standby use.

[0028] Preferably, the polyacrylamide solution is prepared by the following method: 1 g of polyacrylamide is added to 979 g of 50° C. hot water, stirred to dissolve, and then 20 g of glycerol is added, followed by cooling for later use.

[0029] The aqueous phase solution is prepared by the following method: 10-40 parts by weight of m-phenylenediamine, 1-4 parts by weight of sodium dodecylbenzenesulfonate, and 10-40 parts by weight of N-methylpyrrolidone are dissolved in 916-974 parts by weight of 15° C. pure water, and the pH value is adjusted to 7.5-8.0 with sodium hydroxide, and the aqueous phase solution is obtained after stirring evenly.

[0030] Preferably, the aqueous solution is prepared by the following method: 20-30 parts by weight of m-phenylenediamine, 2-3.5 parts by weight of sodium dodecylbenzenesulfonate, and 15-30 parts by weight of N-methylpyrrolidone are dissolved in 930-960 parts by weight of 15° C. pure water, the pH value is adjusted to 7.5-8.0 with sodium hydroxide, and the aqueous solution is obtained after uniform stirring.

[0031] More preferably, the aqueous phase solution is prepared by the following method: 25g of m-phenylenediamine, 3g of sodium dodecylbenzenesulfonate, and 20g of N-methylpyrrolidone are dissolved in 952g of 15°C pure water, and the pH value is adjusted to 7.5-8.0 with sodium hydroxide, and the aqueous phase solution is obtained after being stirred evenly. The low temperature of the aqueous phase solution coated on the surface of the base film can effectively prevent the polyacrylamide pore filling agent from being dissolved.

[0032] The oil phase solution is prepared by the following method: 1-4 parts by weight of trimesoyl chloride is dissolved in 980-1000 parts by weight of Isopar G, and the mixture is stirred evenly to obtain the oil phase solution.

[0033] Preferably, the oil phase solution is prepared by the following method: dissolving 2-3 parts by weight of trimesoyl chloride in 960-998 parts by weight of Isopar G, and stirring to obtain the oil phase solution.

[0034] Preferably, the oil phase solution is prepared by the following method: dissolving 2.5 g of trimesoyl chloride in 997.5 g of Isopar G, and stirring evenly to obtain the oil phase solution.

[0035] Specifically, step (1) comprises casting the polysulfone solution onto the non-woven fabric, soaking it in deionized water to solidify it into a membrane through phase conversion, and then washing it with deionized water to obtain a porous large-pore polysulfone-based membrane.

[0036] Among them, step (2) specifically comprises coating the polyacrylamide solution on the back side of the polysulfone-based membrane, that is, the side of the polysulfone-based membrane that contacts the non-woven fabric during the membrane formation process, and drying the polyacrylamide solution in an oven at 45°C-55°C for 2min-5min after the pores of the polysulfone-based membrane are fully infiltrated with the polyacrylamide solution, thereby obtaining a polysulfone-based membrane with some macropores filled with polyacrylamide.

[0037] Specifically, step (3) comprises coating an aqueous solution on the polysulfone-based membrane obtained in step (2), removing excess surface solution with a low-pressure air knife, coating an oily solution thereon, removing the surface oily solution with a low-pressure air knife, and drying the membrane in an oven at 75°C to 85°C for 2 minutes to obtain a nascent seawater desalination reverse osmosis membrane.

[0038] Specifically, step (4) comprises: immersing the nascent reverse osmosis membrane in pure water at 50°C-60°C for 5 minutes, so as to dissolve and remove the polyacrylamide filling the macropores of the base membrane and restore the macropores in the base membrane; then immersing the membrane in a glycerol solution at room temperature for 5 minutes; then draining the membrane and drying it in an oven at 60°C for 5 minutes to obtain a high-throughput seawater desalination reverse osmosis membrane.

[0039] Among them, the weight average molecular weight of polyacrylamide is more than 11 million; the weight average molecular weight of polysulfone is 60,000-100,000.

[0040] Compared with the prior art, the method for preparing a high-flux seawater desalination reverse osmosis membrane of the present invention comprises the following steps: (1) using a polysulfone solution containing lithium chloride to prepare a porous large-pore polysulfone-based membrane; (2) coating a polyacrylamide solution on the back side of the polysulfone-based membrane, i.e., the side of the polysulfone-based membrane that contacts the non-woven fabric during the membrane formation process, and then drying the membrane to obtain a polysulfone-based membrane whose macropores are partially filled with polyacrylamide; (3) coating an aqueous phase solution and an oil phase solution on the polysulfone-based membrane prepared in step (2), and then drying the membrane to obtain a nascent seawater desalination reverse osmosis membrane; and (4) immersing the nascent reverse osmosis membrane in water to wash away the polyacrylamide, and then immersing the membrane in a glycerol solution, and drying the membrane to obtain a high-flux seawater desalination reverse osmosis membrane.

[0041] In step (1) of the present invention, the pore-forming effect of lithium chloride in the polysulfone-based membrane is utilized to prepare a polysulfone-based membrane containing macropores, and then polyacrylamide is used to fill part of the macropores in the polysulfone-based membrane. When the polyamide separation layer is generated by interfacial polymerization in step (3), the disadvantage that the macroporous base membrane is not conducive to the preparation of a dense polyamide layer is compensated. Polyacrylamide is easily soluble in water and has good hydrophilicity. Temporarily filling polyacrylamide in part of the macropores of the polysulfone-based membrane can ensure the smooth progress of interfacial polymerization and generate a defect-free polyamide separation layer. At the same time, due to the hydrophilicity of polyacrylamide, the hydrophilicity of the surface of the polysulfone-based membrane is further improved. Therefore, the prepared polyamide separation layer has a dense cross-linking degree and a high desalination rate, and a thin effective thickness, so that the water flux is high. The moderately hydrophilic surface of the polysulfone-based membrane is conducive to the preparation of a dense and thin polyamide separation layer, that is, a high-flux seawater desalination reverse osmosis membrane. Furthermore, after the preparation of a dense and defect-free polyamide separation layer by interfacial polymerization, the "mission" of polyacrylamide is completed. The polyacrylamide filled in the large pores of the polysulfone-based membrane can be dissolved and removed by using hot water at a relatively low temperature, thereby restoring the large pores of the polysulfone-based membrane and further improving the flux of the seawater desalination reverse osmosis membrane.

[0042] The present invention skillfully realizes the preparation of a dense and defect-free seawater desalination reverse osmosis membrane polyamide separation layer on the surface of the macroporous base membrane by using polyacrylamide to fill the macropores of the polysulfone base membrane. At the same time, due to the characteristics of the thin polyamide and the large pore size of the polysulfone base membrane, the preparation of a high-flux seawater desalination reverse osmosis membrane is realized. This process is simple and easy to operate. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0044] The sources of materials used in the embodiments of the present invention are as follows: Polysulfone: BASF, S6010, weight average molecular weight: 60000-100000; Polyacrylamide: BASF manufacturer, zetag-8140, weight average molecular weight: 12 million; Polyvinyl alcohol: Sekisui Co., Ltd., PVA205, weight average molecular weight 10000-30000; The remaining materials were commercially available.

[0045] Example 1 1. Preparation of polysulfone solution: Add 830 g of DMF solvent into a beaker, add 170 g of polysulfone under heating and stirring at 75 °C, stir until dissolved, add 1 g of lithium chloride, continue heating and stirring at 75 °C to form a homogeneous solution, let the homogeneous solution stand for 24 h to degas, and obtain a polysulfone solution.

[0046] 2. Preparation of aqueous solution: add 25g of m-phenylenediamine, 3g of sodium dodecylbenzenesulfonate, and 20g of N-methylpyrrolidone and dissolve them in 952g of 15°C pure water, adjust the pH value to 7.5-8.0 with sodium hydroxide, and stir evenly to obtain an aqueous solution.

[0047] 3. Preparation of polyacrylamide solution: Add 1g polyacrylamide to 979g of 50℃ hot water, stir to dissolve, then add 20g glycerol and cool for later use.

[0048] 4. Prepare the oil phase solution: dissolve 2.5 g of trimesoyl chloride in 997.5 g of Isopar G and stir evenly to obtain the oil phase solution.

[0049] 5. Preparation of high-flux seawater desalination reverse osmosis membrane: (1) The polysulfone solution is cast onto a non-woven fabric, which is then soaked in deionized water to undergo phase inversion and solidified into a membrane, which is then washed with deionized water to obtain a porous, large-pore polysulfone-based membrane.

[0050] (2) The polyacrylamide solution is coated on the back side of the polysulfone-based membrane (i.e., the side in contact with the non-woven fabric during the membrane formation process). After the pores of the polysulfone-based membrane are fully infiltrated with the polyacrylamide solution, the membrane is dried in an oven at 50°C for 3 minutes to obtain a polysulfone-based membrane with partially macropores filled with polyacrylamide.

[0051] (3) The polysulfone-based membrane obtained in the above process is coated with an aqueous solution, and the excess solution on the surface is removed by a low-pressure air knife. An oil-phase solution is then coated thereon, and the oil-phase solution on the surface is removed by a low-pressure air knife until there is no obvious flowing liquid visible to the naked eye. The membrane is then placed in an oven at 80° C. for 5 minutes to dry the oil-phase liquid and obtain a primary desalination reverse osmosis membrane.

[0052] (4) The nascent reverse osmosis membrane was immersed in 50°C pure water for 5 min. The purpose of this was to dissolve and remove the polyacrylamide filling the macropores of the basement membrane and restore the macropores in the basement membrane. The membrane was then immersed in a glycerol solution at room temperature for 5 min. Glycerol can moisturize the membrane when it is dried in an oven, so that the polysulfone pores will not collapse. The membrane was then drained and dried in a 60°C oven for 5 min to obtain a high-throughput seawater desalination reverse osmosis membrane.

[0053] Example 2 Except for the different amount of polyacrylamide solution, the other steps and materials are the same as those in Example 1.

[0054] Preparation of polyacrylamide solution: Add 3g polyacrylamide to 977g of 50℃ hot water, stir to dissolve, then add 20g glycerol, and cool for later use.

[0055] Example 3 Except for the different amount of polyacrylamide solution, the other steps and materials are the same as those in Example 1.

[0056] Preparation of polyacrylamide solution: Add 5g polyacrylamide to 975g 50℃ hot water, stir to dissolve, then add 20g glycerol, and cool for later use.

[0057] Example 4 Except for the different amount of polyacrylamide solution, the other steps and materials are the same as those in Example 1.

[0058] Preparation of polyacrylamide solution: Add 7g polyacrylamide to 973g 50℃ hot water, stir to dissolve, then add 20g glycerol, and cool for later use.

[0059] Example 5 Except for the different amount of the polysulfone solution, the remaining steps and materials are the same as those in Example 1.

[0060] Preparation of polysulfone solution: Add 830 g of DMF solvent to a beaker, add 170 g of polysulfone under heating and stirring at 75 °C, stir until dissolved, add 3 g of lithium chloride, continue heating and stirring at 75 °C until a homogeneous solution is formed. The homogeneous solution is allowed to stand and degas for 24 hours to obtain a polysulfone solution.

[0061] Embodiment 6: Except for the different amount of the polysulfone solution, the remaining steps and materials are the same as those in Example 1.

[0062] Preparation of polysulfone solution: Add 830g of DMF solvent to a beaker, add 170g of polysulfone under heating and stirring at 75°C, stir until dissolved, add 5g of lithium chloride, continue heating and stirring at 60-80°C until a homogeneous solution is formed. The homogeneous solution is allowed to stand and degas for 24h to obtain a polysulfone solution.

[0063] Comparative Example 1 1. Preparation of polysulfone solution: Add 830 g of DMF solvent to a beaker, add 170 g of polysulfone under heating and stirring at 75 °C, and stir until dissolved to form a homogeneous solution. Let the homogeneous solution stand for 24 hours to degas, and obtain a polysulfone solution.

[0064] 2. Preparation of aqueous solution: add 25g of m-phenylenediamine, 3g of sodium dodecylbenzenesulfonate, and 20g of N-methylpyrrolidone and dissolve them in 952g of 15°C pure water, adjust the pH value to 7.5-8.0 with sodium hydroxide, and stir evenly to obtain an aqueous solution.

[0065] 3. Preparation of oil phase solution: Dissolve 2.5 g of trimesoyl chloride in 997.5 g of Isopar G and stir evenly to obtain an oil phase solution.

[0066] 4. Preparation of reverse osmosis membrane for seawater desalination: (1) The polysulfone solution is cast onto a non-woven fabric, which is then soaked in deionized water to undergo phase inversion and solidified into a membrane, which is then washed with deionized water to obtain a polysulfone-based membrane.

[0067] (2) Then, an aqueous solution is coated on the polysulfone base membrane, and the excess solution on the surface is removed with a low-pressure air knife. Then, the polysulfone base membrane adsorbed with the aqueous solution is passed through a closed space with a heating and exhaust system, and the internal temperature is controlled at 26°C and the relative humidity is 60% for 1 minute to allow the water on the membrane surface to evaporate further. After that, an oil phase solution is coated on it, and the surface oil phase solution is removed with a low-pressure air knife until there is no obvious flowing liquid visible to the naked eye, and then it is placed in an 80°C oven for 5 minutes to dry the oil phase liquid and form a polyamide primary ecological membrane.

[0068] (3) After subsequent deionized water washing and drying, a polyamide seawater desalination reverse osmosis membrane is obtained.

[0069] Comparative Example 2: Except for the different amount of the polysulfone solution, the rest is the same as Comparative Example 1.

[0070] Preparation of polysulfone solution: Add 830g of DMF solvent to a beaker, add 1g of polyacrylamide and 170g of polysulfone under heating and stirring at 75°C. After sufficient stirring and dissolution, a homogeneous solution is formed. The homogeneous solution is allowed to stand for 24 hours to degas, and a polysulfone solution is obtained.

[0071] Comparative Example 3 1. Preparation of polysulfone solution: same as in Example 1.

[0072] 2. Preparation of aqueous solution: same as in Example 1.

[0073] 3. Preparation of polyvinyl alcohol solution: Add 1g polyvinyl alcohol to 979g of 80℃ hot water, stir to dissolve, then add 20g glycerol, and cool for later use.

[0074] 4. Preparation of oil phase solution: same as in Example 1.

[0075] 5. Preparation of reverse osmosis membrane for seawater desalination: (1) The polysulfone solution is cast onto a non-woven fabric, which is then soaked in deionized water to undergo phase inversion and solidified into a membrane, which is then washed with deionized water to obtain a porous, large-pore polysulfone-based membrane.

[0076] (2) The polyvinyl alcohol solution is coated on the front side of the polysulfone base membrane (i.e., the side that is not in contact with the non-woven fabric during the membrane formation process), and then dried in an oven at 50° C. for 3 minutes to obtain a polysulfone base membrane with the surface coated with polyvinyl alcohol.

[0077] (3) The polysulfone-based membrane obtained in the above process is coated with an aqueous solution, and the excess solution on the surface is removed by a low-pressure air knife. An oil-phase solution is then coated thereon, and the oil-phase solution on the surface is removed by a low-pressure air knife until there is no obvious flowing liquid visible to the naked eye. The membrane is then placed in an oven at 80° C. for 5 minutes to dry the oil-phase liquid and obtain a primary desalination reverse osmosis membrane.

[0078] (4) The nascent reverse osmosis membrane was immersed in 80°C pure water for 5 minutes to remove the polyvinyl alcohol on the surface of the polysulfone, and then immersed in a room temperature glycerol solution for 5 minutes. Afterwards, it was drained and dried in a 60°C oven for 5 minutes. A seawater desalination reverse osmosis membrane was obtained.

[0079] Comparative Example 4 1. Preparation of polysulfone solution: same as in Example 1.

[0080] 2. Preparation of aqueous solution: same as in Example 1.

[0081] 3. Preparation of polyacrylamide solution: Add 1g polyacrylamide to 979g of 50℃ hot water, stir to dissolve, then add 20g glycerol and cool for later use.

[0082] 4. Preparation of oil phase solution: same as in Example 1.

[0083] 5. Preparation of seawater desalination reverse osmosis membrane: (1) The polysulfone solution is cast onto a non-woven fabric, which is then solidified into a membrane by phase conversion by soaking in deionized water, and then washed with deionized water to obtain a porous large-pore polysulfone-based membrane.

[0084] (2) The polyacrylamide liquid is coated on the front side of the polysulfone base membrane (i.e., the side that is not in contact with the non-woven fabric during the membrane formation process), and then dried in an oven at 50°C for 3 minutes to obtain a polysulfone base membrane with polyacrylamide coated on the surface.

[0085] (3) The polysulfone-based membrane obtained in the above process is coated with an aqueous solution, and the excess solution on the surface is removed by a low-pressure air knife. An oil-phase solution is then coated thereon, and the oil-phase solution on the surface is removed by a low-pressure air knife until there is no obvious flowing liquid visible to the naked eye. The membrane is then placed in an oven at 80° C. for 5 minutes to dry the oil-phase liquid and obtain a primary desalination reverse osmosis membrane.

[0086] (4) The nascent reverse osmosis membrane was immersed in 50°C pure water for 5 minutes to remove the polyacrylamide on the surface of the polysulfone, and then immersed in a room temperature glycerol solution for 5 minutes. Afterwards, it was drained and dried in a 60°C oven for 5 minutes. A seawater desalination reverse osmosis membrane was obtained.

[0087] Comparative Example 5 Except for the different amount of the polysulfone solution, the rest is the same as Comparative Example 1.

[0088] Preparation of polysulfone solution: Add 830 g of DMF solvent into a beaker, add 170 g of polysulfone under heating and stirring at 75 °C, stir until dissolved, add 1 g of lithium chloride, continue heating and stirring at 75 °C to form a homogeneous solution, let the above homogeneous solution stand for 24 h to degas, and obtain a polysulfone solution.

[0089] The seawater desalination reverse osmosis membranes in the above comparative examples and embodiments were subjected to performance tests under the following test conditions: 1. 32000ppm sodium chloride is used as the test solution, the applied pressure is 5.51MPa, the aqueous solution temperature is 25℃, and the pH is 7.0-8.0.

[0090]

[0091] The performance comparison is as follows: It can be seen from the above table that, compared with the seawater desalination reverse osmosis membrane of the comparative example, the membrane flux of the embodiment is significantly improved while ensuring the salt removal rate.

[0092] In the polysulfone solution of Comparative Example 1, lithium chloride is not added, and polyacrylamide is not needed to fill the macropores of the sulfone membrane. The pores of the prepared reverse osmosis membrane are small but the membrane flux is low.

[0093] Reasons for low performance of Comparative Example 2: Although the hydrophilicity of the base membrane is improved to a certain extent by blending polyacrylamide and polysulfone, which is beneficial to the improvement of the membrane desalination rate, most of the polyacrylamide will be dissolved and lost by water during the preparation and molding of the base membrane due to the high water solubility of polyacrylamide. Compared with Comparative Example 2, in Example 1, the polyacrylamide solution is coated on the back of the polysulfone base membrane, and the aqueous phase solution and the oil phase solution are coated at the same time. The polyacrylamide is temporarily filled in part of the macropores of the polysulfone base membrane to ensure the smooth progress of the subsequent interfacial polymerization reaction and generate a defect-free polyamide separation layer, which can significantly improve the membrane flux.

[0094] The reason why the performance of Comparative Example 3 is not significantly improved is that polyvinyl alcohol is coated on the front side of the polysulfone base membrane, which will cause the entire base membrane surface to be too hydrophilic, which is not conducive to the improvement of the membrane flux. In addition, the polyamide desalination layer generated by interfacial polymerization will wrap the entire polyvinyl alcohol, which is not conducive to the subsequent dissolution and removal of polyvinyl alcohol with hot water, which is also not conducive to the improvement of the membrane flux.

[0095] In Comparative Example 4, polyacrylamide is coated on the front side of the polysulfone-based membrane. Since the coating is performed from the front side of the polysulfone-based membrane, the polyacrylamide will not only fill the macropores of the polysulfone-based membrane, but also a layer of polyacrylamide will be coated on the front side of the polysulfone-based membrane, which will cause the entire surface of the base membrane to be too hydrophilic, which is not conducive to the improvement of the membrane flux. In addition, the polyamide desalination layer generated by interfacial polymerization will wrap the entire polyacrylamide, which is not conducive to the subsequent dissolution and removal of the polyacrylamide with hot water, which is also not conducive to the improvement of the membrane flux.

[0096] Comparative Example 5 is a common method for preparing ultrafiltration membranes. The role of lithium chloride in the preparation of polysulfone-based membranes is to form pores. However, in the preparation of seawater desalination reverse osmosis membranes, if the pore size of the polysulfone-based membrane is large, it is not conducive to interfacial polymerization to form a dense polyamide desalination layer, resulting in a low desalination rate of the seawater desalination reverse osmosis membrane.

[0097] The present invention uses lithium chloride to make pores and polyacrylamide to temporarily fill part of the macropores. After the subsequent interfacial polymerization reaction is completed, the polyacrylamide is removed, which can significantly improve the water flux while ensuring the salt removal rate.

[0098] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-flux seawater desalination reverse osmosis membrane, characterized in that: The following steps are involved: (1) A porous large-pore polysulfone-based membrane is prepared using a polysulfone solution containing lithium chloride; the polysulfone solution is prepared by dissolving 150-190 parts by weight of polysulfone and 0.5-3 parts by weight of lithium chloride in 810-850 parts by weight of DMF solvent; (2) coating the polyacrylamide solution on the back side of the polysulfone-based membrane, i.e., the side of the polysulfone-based membrane in contact with the non-woven fabric during the membrane formation process, and drying the polyacrylamide solution in an oven at 45° C. to 55° C. for 2 min to 5 min to obtain a polysulfone-based membrane with partially macropores filled with polyacrylamide, wherein the polyacrylamide solution is prepared by dissolving 0.5 to 3 parts by weight of polyacrylamide and 10 to 30 parts by weight of glycerol in 960 to 990 parts by weight of water; (3) coating the polysulfone-based membrane obtained in step (2) with an aqueous solution, removing excess surface solution with a low-pressure air knife, coating the polysulfone-based membrane with an oily solution, removing the surface oily solution with a low-pressure air knife, until no visible flowing liquid is left, and then placing the membrane in an oven at 75° C. to 85° C. for 2 min. to dry the oily solution and obtain a primary seawater desalination reverse osmosis membrane, wherein the aqueous solution is prepared by dissolving 15-40 parts by weight of m-phenylenediamine, 1-4 parts by weight of sodium dodecylbenzenesulfonate, and 10-40 parts by weight of N-methylpyrrolidone in 916-974 parts by weight of water and adjusting the pH value to 7.5-8.0 with sodium hydroxide, and the oily solution is prepared by dissolving 1-4 parts by weight of trimesoyl chloride in 980-1000 parts by weight of Isopar G; (4) The nascent reverse osmosis membrane is immersed in 50°C-60°C pure water for 2 min-10 min, and then immersed in a room temperature glycerol solution for 2 min-10 min. Thereafter, the membrane is drained and dried in a 55°C-65°C oven for 2 min-10 min to obtain a high-throughput seawater desalination reverse osmosis membrane.

2. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The polysulfone solution is prepared as follows: 810-850 parts by weight of DMF solvent is added into a beaker, 150-190 parts by weight of polysulfone is added under heating and stirring at 70° C.-80° C., and after stirring until dissolved, 0.5-3 parts by weight of lithium chloride is added, and heating and stirring are continued at 70° C.-80° C. until a homogeneous solution is formed, and the homogeneous solution is allowed to stand and degas for 12-36 hours to obtain a polysulfone solution.

3. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The polyacrylamide solution is prepared by the following method: adding 0.5-3 parts by weight of polyacrylamide to 960-990 parts by weight of hot water at 45° C.-55° C., stirring to dissolve, adding 10-30 parts by weight of glycerol, and cooling for later use.

4. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The aqueous phase solution is prepared by the following method: 10-40 parts by weight of m-phenylenediamine, 1-4 parts by weight of sodium dodecylbenzenesulfonate, and 10-40 parts by weight of N-methylpyrrolidone are dissolved in 916-974 parts by weight of 15° C. pure water, the pH value is adjusted to 7.5-8.0 with sodium hydroxide, and the aqueous phase solution is obtained after uniform stirring.

5. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The oil phase solution is prepared by the following method: 1-4 parts by weight of trimesoyl chloride is dissolved in 980-1000 parts by weight of Isopar G, and the mixture is stirred to obtain the oil phase solution.

6. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 1, characterized in that: Step (1) specifically comprises casting the polysulfone solution onto the non-woven fabric, soaking it in deionized water to solidify it into a membrane through phase conversion, and then washing it with deionized water to obtain a porous large-pore polysulfone-based membrane.

7. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 3, characterized in that: The weight average molecular weight of polyacrylamide is 11 million or more.

8. The method for preparing a high-flux seawater desalination reverse osmosis membrane according to claim 2, characterized in that: The weight average molecular weight of polysulfone is 60,000-100,000.

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