A method for preparing a high-throughput seawater desalination reverse osmosis membrane

Abstract

The present invention discloses a method for preparing a high-flux seawater desalination reverse osmosis membrane. The high-flux seawater desalination reverse osmosis membrane prepared by the preparation method provided by the present invention has a high desalination rate and high water flux, and can be used for filtering seawater to improve filtration efficiency and effect.

Description

Technical Field

[0001] The present 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 humanity today. It is projected that by 2050, global water demand will be approximately 540 billion to 610 billion cubic meters, a demand that cannot be met by current freshwater resources. Given the abundant seawater reserves, desalination offers an ideal solution to the global freshwater crisis. Desalination technologies primarily fall into two categories: thermal and membrane. Membrane separation technologies, represented by reverse osmosis (RO) membranes, enable efficient desalination. Compared to thermal technologies, RO membranes offer unique advantages in the desalination field, such as ease of operation, low cost, and environmental friendliness. However, the SWRO membranes at the core of membrane desalination processes still require improvement to further reduce the costs of associated infrastructure and system operation. Modeling studies predict that, for a seawater desalination reverse osmosis membrane system with a given daily water production and recovery rate, more than doubling the SWRO permeate flux can reduce the number of pressure vessels and energy consumption of the membrane system by 44% and 15%, respectively. Therefore, while ensuring the high desalination and separation performance of the seawater desalination reverse osmosis membrane material, further improving its permeate water flux is of great significance.

[0003] Desalination reverse osmosis membranes are generally prepared by interfacial polymerization. They are composite membranes with a three-layer structure, which consists of a non-woven fabric layer, a polysulfone layer, and a polyamide layer from bottom to top. The preparation method of the polysulfone layer and the polyamide layer is 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 an amine monomer and other additives, and then taken out. The 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. After rinsing and other post-processing processes, a complete desalination reverse osmosis membrane can be obtained. Conventionally prepared desalination reverse osmosis membranes have the following shortcomings:

[0004] 1. The desalination rate of seawater desalination reverse osmosis membrane is between 99.0% and 99.8%. The low desalination rate limits its application.

[0005] 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.

[0006] At present, in order to prepare high-flux seawater desalination reverse osmosis membranes, most research work focuses on optimizing interfacial polymerization reaction conditions, developing new reaction monomers, adding porous nanomaterials, etc. to fine-tune the performance of the polyamide layer, so as to further improve the permeate water flux of the membrane material.

[0007] 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 to polyamide on the membrane surface, or grafting PVA inside the 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.

[0008] 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

[0009] 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 a high desalination rate and high water flux, and can be used for filtering seawater to improve filtration efficiency and effect.

[0010] The technical solutions provided by the present invention are as follows:

[0011] A method for preparing a high-flux seawater desalination reverse osmosis membrane comprises the following steps:

[0012] (1) A polysulfone-based membrane with a porous large pore size is prepared using a polysulfone solution containing lithium chloride;

[0013] (2) coating the polyacrylamide solution on the back side of the polysulfone-based membrane, which is the side of the polysulfone-based membrane that contacts the non-woven fabric during the membrane formation process, and drying the polyacrylamide solution after the pores of the polysulfone-based membrane are fully infiltrated to obtain a polysulfone-based membrane with partially macropores filled with polyacrylamide;

[0014] (3) coating the polysulfone-based membrane prepared in step (2) with an aqueous solution and an oily solution in sequence, and then drying the membrane to obtain a nascent seawater desalination reverse osmosis membrane;

[0015] (4) The nascent reverse osmosis membrane is immersed in water to wash away the polyacrylamide, and then immersed in a room temperature solution and dried to obtain a high-flux seawater desalination reverse osmosis membrane.

[0016] Among them, a method for preparing a high-flux seawater desalination reverse osmosis membrane may include the following steps:

[0017] (1) A polysulfone solution containing lithium chloride is cast onto a non-woven fabric, which is then solidified into a membrane by phase conversion after being soaked in deionized water, and then washed with deionized water to obtain a porous polysulfone-based membrane with a large pore size;

[0018] (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 polyacrylamide solution after the pores of the polysulfone-based membrane are fully infiltrated to obtain a polysulfone-based membrane with partially macropores filled with polyacrylamide;

[0019] (3) coating the polysulfone-based membrane obtained in the above process with an aqueous solution, removing excess surface solution with a low-pressure air knife, and then coating the membrane with an oily solution. After removing the surface oily solution with a low-pressure air knife, the membrane was placed in an oven at 80°C for 5 minutes to dry the oily solution and obtain a nascent seawater desalination reverse osmosis membrane.

[0020] (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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] More preferably, the polyacrylamide solution is prepared by dissolving 1 part by weight of polyacrylamide and 20 parts by weight of glycerol in water.

[0027] 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.

[0028] Preferably, the aqueous 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 pure water at 15° C., and adjusting the pH value to 7.5-8.0 with sodium hydroxide.

[0029] More preferably, the aqueous 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 using sodium hydroxide.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 while heating and stirring at 70°C-80°C, and the mixture is stirred until dissolved. Then, 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. The homogeneous solution is allowed to stand and degas for 12-36 hours to obtain a polysulfone solution.

[0034] 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 while heating and stirring at 70°C-80°C, and stirred until dissolved, 0.6-2 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. The homogeneous solution is allowed to stand and degas for 12-36 hours to obtain a polysulfone solution.

[0035] More preferably, the polysulfone solution is prepared as follows: 830 g of DMF solvent is added to a beaker, 170 g of polysulfone is added under heating and stirring at 75 ° C, and stirred until dissolved, 1 g of lithium chloride is added, and heating and stirring are continued at 75 ° C until a homogeneous solution is formed, and the above homogeneous solution is allowed to stand and degas for 24 hours to obtain a polysulfone solution.

[0036] 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 45-55° C. hot water, stirring to dissolve, adding 10-30 parts by weight of glycerol, and cooling for later use.

[0037] 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 45° C.-55° C. hot water, stirring to dissolve, adding 15-25 parts by weight of glycerol, and cooling for later use.

[0038] Preferably, the polyacrylamide solution is prepared by the following method: adding 1 g of polyacrylamide to 979 g of 50° C. hot water, stirring to dissolve, adding 20 g of glycerol, and cooling for later use.

[0039] 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 pure water at 15° C., the pH value is adjusted to 7.5-8.0 with sodium hydroxide, and the aqueous phase solution is obtained after uniform stirring.

[0040] Preferably, the aqueous phase 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 phase solution is obtained after uniform stirring.

[0041] More preferably, the aqueous solution is prepared by dissolving 25 g of m-phenylenediamine, 3 g of sodium dodecylbenzenesulfonate, and 20 g of N-methylpyrrolidone in 952 g of 15°C pure water, adjusting the pH to 7.5-8.0 with sodium hydroxide, and stirring to obtain an aqueous solution. The low temperature of the aqueous solution applied to the surface of the base film effectively prevents dissolution of the polyacrylamide pore-filling agent.

[0042] The oil phase solution is prepared by the following method: dissolving 1-4 parts by weight of trimesoyl chloride in 980-1000 parts by weight of Isopar G, and stirring the mixture to obtain the oil phase solution.

[0043] 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 the mixture to obtain the oil phase solution.

[0044] 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 the mixture to obtain the oil phase solution.

[0045] Among them, step (1) specifically includes casting the polysulfone solution onto the non-woven fabric, soaking it in deionized water to phase-convert and solidify it into a membrane, and then washing it with deionized water to obtain a porous large-pore polysulfone-based membrane.

[0046] 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 to obtain a polysulfone-based membrane with some macropores filled with polyacrylamide.

[0047] Among them, step (3) specifically comprises coating the aqueous phase solution on the polysulfone-based membrane obtained in step (2), removing the excess solution on the surface with a low-pressure air knife, coating the oil phase solution thereon, removing the surface oil phase solution with a low-pressure air knife, until there is no obvious flowing liquid visible to the naked eye, and then entering into a 75°C-85°C oven for 2min-8min to dry the oil phase liquid and obtain a primary seawater desalination reverse osmosis membrane.

[0048] Among them, step (4) is specifically as follows: immersing the nascent reverse osmosis membrane in 50℃-60℃ pure water for 5 minutes, the purpose of which is to dissolve and remove the polyacrylamide filled in the macropores of the basement membrane and restore the macropores in the basement membrane, and then immersing it in a glycerol solution at room temperature for 5 minutes, then draining and drying it in a 60℃ oven for 5 minutes to obtain a high-throughput seawater desalination reverse osmosis membrane.

[0049] The weight average molecular weight of polyacrylamide is above 11 million; the weight average molecular weight of polysulfone is 60,000-100,000.

[0050] Compared with the prior art, the preparation method of the 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 with some large pores 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.

[0051] 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 of the macroporous base membrane being unfavorable for the preparation of a dense polyamide layer is compensated. Polyacrylamide is easily soluble in water and has good hydrophilicity. Temporarily filling polyacrylamide into 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 polysulfone-based membrane surface is further improved. Therefore, the prepared polyamide separation layer has a dense cross-linking degree and a high desalination rate. At the same time, the effective thickness is thin, thereby having a high water flux. The moderately hydrophilic surface of the polysulfone-based membrane is conducive to the preparation of a dense and thin polyamide separation layer, i.e., a high-flux seawater desalination reverse osmosis membrane. Furthermore, after the preparation of a dense and defect-free polyamide separation layer by interfacial polymerization is completed, 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 lower temperature, restoring the large pores of the polysulfone-based membrane, and further improving the flux of the seawater desalination reverse osmosis membrane.

[0052] The present invention cleverly achieves 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 thin polyamide and large pore size of the polysulfone base membrane, the preparation of a high-flux seawater desalination reverse osmosis membrane is achieved. This process is simple and easy to operate. DETAILED DESCRIPTION

[0053] To help those skilled in the art better understand the technical solutions of 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 them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0054] The sources of materials used in the embodiments of the present invention are as follows:

[0055] Polysulfone: BASF, S6010, weight average molecular weight: 60,000-100,000;

[0056] Polyacrylamide: BASF manufacturer, zetag-8140, weight average molecular weight: 12 million;

[0057] Polyvinyl alcohol: Sekisui Co., Ltd., PVA205, weight average molecular weight 10,000-30,000;

[0058] The remaining materials were commercially available.

[0059] Example 1

[0060] 1. Preparation of polysulfone solution: Add 830 g of DMF solvent to a beaker, add 170 g of polysulfone while heating and stirring at 75 °C, stir until dissolved, add 1 g of lithium chloride, continue heating and stirring at 75 °C until a homogeneous solution is formed, and let the homogeneous solution stand for 24 hours to degas.

[0061] 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. Use sodium hydroxide to adjust the pH value to 7.5-8.0. Stir well to obtain an aqueous solution.

[0062] 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.

[0063] 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.

[0064] 5. Preparation of high-flux seawater desalination reverse osmosis membrane:

[0065] (1) The polysulfone solution is cast onto a non-woven fabric, which is then solidified into a membrane by phase conversion after being soaked in deionized water. The membrane is then washed with deionized water to obtain a porous polysulfone-based membrane with a large pore size.

[0066] (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 some macropores filled with polyacrylamide.

[0067] (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 with a low-pressure air knife. An oily solution is then coated on the membrane, and the oily solution on the surface is removed with a low-pressure air knife until no visible flowing liquid is observed. The membrane is then placed in an 80°C oven for 5 minutes to dry the oily solution and obtain a nascent seawater desalination reverse osmosis membrane.

[0068] (4) The nascent reverse osmosis membrane was immersed in 50℃ pure water for 5 minutes. The purpose was to dissolve and remove the polyacrylamide filling the macropores of the basement membrane and restore the macropores in the basement membrane. Then, it was immersed in a glycerol solution at room temperature for 5 minutes. The glycerol can moisturize the basement membrane when it is dried in an oven, so that the polysulfone pores will not collapse. After that, it was drained and dried in a 60℃ oven for 5 minutes to obtain a high-flux seawater desalination reverse osmosis membrane.

[0069] Example 2

[0070] Except for the different amount of polyacrylamide solution, the remaining steps and materials are the same as those in Example 1.

[0071] 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.

[0072] Example 3

[0073] Except for the different amount of polyacrylamide solution, the remaining steps and materials are the same as those in Example 1.

[0074] Preparation of polyacrylamide solution: Add 5g polyacrylamide to 975g 50℃ hot water, stir to dissolve, then add 20g glycerol, cool and set aside.

[0075] Example 4

[0076] Except for the different amount of polyacrylamide solution, the remaining steps and materials are the same as those in Example 1.

[0077] Preparation of polyacrylamide solution: Add 7g polyacrylamide to 973g 50℃ hot water, stir to dissolve, then add 20g glycerol, and cool for later use.

[0078] Example 5

[0079] Except for the different amounts of the polysulfone solution, the remaining steps and materials are the same as those in Example 1.

[0080] Prepare the polysulfone solution by adding 830 g of DMF solvent to a beaker. Add 170 g of polysulfone while heating and stirring at 75°C. Stir until dissolved. Then add 3 g of lithium chloride. Continue heating and stirring at 75°C until a homogeneous solution forms. Allow the homogeneous solution to stand and degas for 24 hours to obtain a polysulfone solution.

[0081] Example 6:

[0082] Except for the different amounts of the polysulfone solution, the remaining steps and materials are the same as those in Example 1.

[0083] Prepare the polysulfone solution by adding 830 g of DMF solvent to a beaker. Add 170 g of polysulfone while heating and stirring at 75°C. Stir until dissolved. Then add 5 g of lithium chloride. Continue heating and stirring at 60-80°C until a homogeneous solution forms. Allow the homogeneous solution to stand and degas for 24 hours to obtain a polysulfone solution.

[0084] Comparative Example 1

[0085] 1. Preparation of polysulfone solution: Add 830 g of DMF solvent to a beaker. Add 170 g of polysulfone while heating and stirring at 75°C. Stir until dissolved to form a homogeneous solution. Allow the homogeneous solution to stand and degas for 24 hours to obtain a polysulfone solution.

[0086] 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. Use sodium hydroxide to adjust the pH value to 7.5-8.0. Stir well to obtain an aqueous solution.

[0087] 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.

[0088] 4. Preparation of seawater desalination reverse osmosis membrane:

[0089] (1) The polysulfone solution is cast onto a non-woven fabric, which is then solidified into a membrane by phase conversion after being soaked in deionized water, and then washed with deionized water to obtain a polysulfone-based membrane.

[0090] (2) Then, the polysulfone base membrane is coated with an aqueous solution, and the excess solution on the surface is removed with a low-pressure air knife. The polysulfone base membrane adsorbed with the aqueous solution is then passed through a closed space with a heating and exhaust system, where the internal temperature is controlled at 26°C and the relative humidity is 60% for 1 minute to allow the moisture on the membrane surface to evaporate further. After that, the 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 visible flowing liquid. Then, the membrane is placed in an 80°C oven for 5 minutes to dry the oil phase liquid and form a polyamide primary ecological membrane.

[0091] (3) After subsequent deionized water washing and drying, a polyamide seawater desalination reverse osmosis membrane is obtained.

[0092] Comparative Example 2:

[0093] Except for the different amount of the polysulfone solution, the rest is the same as that of Comparative Example 1.

[0094] Prepare the polysulfone solution: Add 830 g of DMF solvent to a beaker. Heat and stir at 75°C, then add 1 g of polyacrylamide and 170 g of polysulfone. Stir thoroughly to dissolve until a homogeneous solution forms. Allow the homogeneous solution to stand for 24 hours to degas. This yields the polysulfone solution.

[0095] Comparative Example 3

[0096] 1. Preparation of polysulfone solution: same as in Example 1.

[0097] 2. Preparation of aqueous solution: same as in Example 1.

[0098] 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.

[0099] 4. Preparation of oil phase solution: same as in Example 1.

[0100] 5. Preparation of reverse osmosis membrane for seawater desalination:

[0101] (1) The polysulfone solution is cast onto a non-woven fabric, which is then solidified into a membrane by phase conversion after being soaked in deionized water. The membrane is then washed with deionized water to obtain a porous polysulfone-based membrane with a large pore size.

[0102] (2) The polyvinyl alcohol solution was coated on the front side of the polysulfone-based membrane (i.e., the side that did not come into 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-based membrane with a surface coated with polyvinyl alcohol.

[0103] (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 with a low-pressure air knife. An oily solution is then coated on the membrane, and the oily solution on the surface is removed with a low-pressure air knife until no visible flowing liquid is observed. The membrane is then placed in an 80°C oven for 5 minutes to dry the oily solution and obtain a nascent seawater desalination reverse osmosis membrane.

[0104] (4) The nascent reverse osmosis membrane was immersed in 80°C pure water for 5 minutes to remove the polyvinyl alcohol on the polysulfone surface. The membrane was then immersed in a room-temperature glycerol solution for 5 minutes. The membrane was then drained and dried in a 60°C oven for 5 minutes. This resulted in a desalination reverse osmosis membrane.

[0105] Comparative Example 4

[0106] 1. Preparation of polysulfone solution: same as in Example 1.

[0107] 2. Preparation of aqueous solution: same as in Example 1.

[0108] 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.

[0109] 4. Preparation of oil phase solution: same as in Example 1.

[0110] 5. Preparation of reverse osmosis membrane for seawater desalination: (1) The polysulfone solution is cast onto non-woven fabric, which is then solidified into a membrane by phase conversion after being soaked in deionized water. The membrane is then washed with deionized water to obtain a porous polysulfone-based membrane with a large pore size.

[0111] (2) The polyacrylamide liquid is coated on the front side of the polysulfone-based membrane (i.e., the side that does not contact 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-based membrane with a surface coated with polyacrylamide.

[0112] (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 with a low-pressure air knife. An oily solution is then coated on the membrane, and the oily solution on the surface is removed with a low-pressure air knife until no visible flowing liquid is observed. The membrane is then placed in an 80°C oven for 5 minutes to dry the oily solution and obtain a nascent seawater desalination reverse osmosis membrane.

[0113] (4) The nascent reverse osmosis membrane was immersed in 50°C pure water for 5 minutes to remove the polyacrylamide on the polysulfone surface. The membrane was then immersed in a room-temperature glycerol solution for 5 minutes. The membrane was then drained and dried in a 60°C oven for 5 minutes. This resulted in a desalination reverse osmosis membrane.

[0114] Comparative Example 5

[0115] Except for the different amount of the polysulfone solution, the rest is the same as that of Comparative Example 1.

[0116] Preparation of polysulfone solution: Add 830 g of DMF solvent to a beaker, add 170 g of polysulfone while heating and stirring at 75 °C, stir until dissolved, add 1 g of lithium chloride, continue heating and stirring at 75 °C until a homogeneous solution is formed, and let the above homogeneous solution stand for 24 hours to degas. To obtain a polysulfone solution.

[0117] The seawater desalination reverse osmosis membranes in the comparative examples and examples were subjected to performance tests under the following test conditions:

[0118] 1. 32000ppm sodium chloride is used as the test solution, the external pressure is 5.51MPa, the aqueous solution temperature is 25℃, and the pH is 7.0-8.0.

[0119]

[0120] The performance comparison is as follows:

[0121] As can be seen from the above table, 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.

[0122] In the polysulfone solution of Comparative Example 1, lithium chloride was not added, and polyacrylamide was not needed to fill the macropores of the sulfone membrane. The pores of the prepared reverse osmosis membrane were small but the membrane flux was low.

[0123] The reason for the low performance of Comparative Example 2: Although the blend of polyacrylamide and polysulfone to prepare the base membrane improves the hydrophilicity of the base membrane to a certain extent, which is beneficial to the improvement of the membrane rejection rate, due to the high water solubility of polyacrylamide, most of the polyacrylamide will be dissolved and lost in the water during the preparation and molding process of the base membrane. Compared with Comparative Example 2, Example 1 coated the polyacrylamide solution on the back of the polysulfone base membrane, and then coated it with an aqueous phase solution and an oil phase solution. The polyacrylamide temporarily filled some of the macropores of the polysulfone base membrane, ensuring the smooth progress of the subsequent interfacial polymerization reaction, forming a defect-free polyamide separation layer, and significantly improving the membrane flux.

[0124] The reason why the performance of Comparative Example 3 is not significantly improved is that polyvinyl alcohol is coated on the front 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.

[0125] 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 large pores 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 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 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.

[0126] Comparative Example 5 is a commonly used 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.

[0127] The present invention uses lithium chloride to form pores while temporarily filling some of the large pores with polyacrylamide. After the subsequent interfacial polymerization reaction is completed, the polyacrylamide is removed, which can significantly improve water flux while maintaining the salt removal rate.

[0128] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform 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 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 2-5 minutes 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. 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; (3) coating the polysulfone-based membrane obtained in step (2) with an aqueous solution, removing excess surface solution with a low-pressure air knife, and then coating the polysulfone-based membrane with an oily solution. After removing the surface oily solution with a low-pressure air knife, the membrane is dried until no visible flowing liquid is observed. The membrane is then placed in an oven at 75°C-85°C for 2-8 minutes to dry the oily solution and obtain a nascent seawater desalination reverse osmosis membrane. 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. 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 pure water at 50°C-60°C for 2 min-10 min, and then immersed in a glycerol solution at room temperature for 2 min-10 min. After that, it is drained and dried in an oven at 55°C-65°C 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, wherein: The polysulfone solution is prepared by adding 810-850 parts by weight of DMF solvent into a beaker, adding 150-190 parts by weight of polysulfone while heating and stirring at 70° C.-80° C., stirring until dissolved, adding 0.5-3 parts by weight of lithium chloride, continuing heating and stirring at 70° C.-80° C. until a homogeneous solution is formed, and allowing the homogeneous solution 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, wherein: 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 45-55° C. hot water, 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, wherein: 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 pure water at 15° C., 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, wherein: 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, wherein: 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, wherein: 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, wherein: The weight average molecular weight of polysulfone is 60,000-100,000.

Images