Forward osmosis membrane and its manufacturing method

Abstract

A forward osmosis membrane and its manufacturing method. The forward osmosis membrane has a modified membrane structure including a hydrophilic support grid and a hydrophilic polymer film layer mixed with an antioxidant. The support grid is a nonwoven fabric or a polyester screen.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Chinese Patent Application No. 202111056457.0, filed on September 9, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the technical field of polymer separation membranes and their manufacturing, and more particularly to an oxidation-resistant forward osmosis membrane and its manufacturing method. [Background technology]

[0003] The forward osmosis (FO) process is a process in which water is automatically diffused from the low osmotic pressure raw water side to the high osmotic pressure draw liquid side through a selectively permeable membrane, driven by the osmotic pressure difference between the draw liquid and the feed liquid. This process does not require external force or energy.

[0004] Unlike pressure-driven membrane separation processes such as ultrafiltration, nanofiltration, and reverse osmosis, forward osmosis can be operated at low or no pressure, resulting in low operating energy consumption. Low-pressure operation is characterized by the absence of pressure-induced cake formation and low membrane fouling. With sufficient osmotic pressure differential, high water recovery rates unattainable with conventional separation membranes can be achieved.

[0005] Based on the above characteristics of forward osmosis, forward osmosis technology has developed rapidly in recent years as a new membrane separation technology, attracting attention from researchers both at home and abroad. It is used in fields such as food, medicine, and energy, and is particularly expected to be applied in many fields such as seawater desalination, drinking water treatment, and wastewater treatment.

[0006] An ideal forward osmosis membrane should simultaneously possess properties such as good permeability, high permeation flux, high salt rejection, and good anti-fouling properties. These are the research directions that have attracted attention in this field in recent years. Currently, the technical field generally believes that cellulose acetate forward osmosis membranes are more resistant to acidification than aromatic polyamide composite membranes, and the use of cellulose acetate as a membrane material for forward osmosis membranes has become the mainstream of research and commercialization in this field. For example, Chinese Patent Application No. 201410050442.7 discloses an asymmetric forward osmosis cellulose acetate membrane that aims to reduce internal concentration polarization and improve forward permeation flux and chlorine resistance. These technical studies all aim to improve permeation flux and salt rejection, reduce internal concentration differences, etc., but do not disclose or improve the oxidation resistance of the membrane.

[0007] However, in actual use, membrane damage may occur during operation, especially when the wastewater after the catalytic oxidation process section is highly oxidative. Meanwhile, the traditional method of adding a reducing agent at the front end cannot guarantee the absolute safety of the membrane system at the rear end due to fluctuations in water quality and quantity. Currently, there is a lack of forward osmosis membranes with strong oxidation resistance to address this issue. For example, the membranes manufactured in the aforementioned Chinese Patent Application No. 201410050442.7 cannot be effectively used for highly oxidative wastewater treatment or other raw waters. The membranes are damaged by the oxidative nature of the raw water environment, shortening their service life and increasing the overall cost of the membrane system. Summary of the Invention

[0008] An object of the present invention is to provide a highly oxidation-resistant forward osmosis membrane that can be used safely and stably even under strongly oxidizing conditions.

[0009] Another object of the present invention is to provide a method for producing an oxidation-resistant forward osmosis membrane that can be used safely and stably under strong oxidizing conditions.

[0010] In order to achieve the above object, the present invention employs the following technical means. The present invention relates to a forward osmosis membrane. The provided forward osmosis membrane includes a modified hydrophilic polymer film layer. The hydrophilic polymer film layer includes a hydrophilic polymer and an antioxidant. The hydrophilic polymer film layer is manufactured by a process in which a hydrophilic polymer material is mixed with a solvent system containing the antioxidant to obtain a casting solution, the casting solution is formed into a membrane, and the solvent is removed.

[0011] In a preferred embodiment of the present invention, the hydrophilic polymer material constituting the hydrophilic polymer film layer includes at least one selected from polyacrylonitrile, polyacrylate, polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate. The antioxidant is a sterically hindered phenol-based antioxidant. The antioxidant preferably includes at least one selected from 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetra(3,5-di-tert-butyl-4-hydroxyl)phenylpropionate, and 1,3,5-tri(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1h,3h,5h)-trione.

[0012] In another preferred embodiment of the present invention, the mass ratio of the hydrophilic polymer to the antioxidant in the casting liquid is 8-15:0.1-1, preferably 9-14:0.2-0.9, further preferably 10-13:0.2-0.7, and even more preferably 8:0.2, or 13:0.5, 13:0.2, or 11:0.3.

[0013] In another preferred embodiment of the present invention, the system further includes a support grid made of a hydrophilic polyester screen or nonwoven fabric. The hydrophilic polymer film layer is laminated to the support grid. When the support grid is a polyester screen, it has a thickness of 30 μm-80 μm and a pore size of 100-200 mesh, preferably 30 μm, 50 μm, 60 μm, 70 μm, or 80 μm, and a pore size of 100 mesh, 120 mesh, or 150 mesh. The forward osmosis membrane has a thickness of 30 μm-150 μm, preferably 30 μm-100 μm, more preferably 30 μm-80 μm, and even more preferably 30 μm, 50 μm, 60 μm, or 70 μm.

[0014] In another preferred embodiment of the present invention, the mass fractions of the respective components in the casting liquid are 8-15 wt.% hydrophilic polymer, 0.1-1 wt.% antioxidant, and the solvent system contains 5-20 wt.% acetone, 5-10 wt.% methanol, and 6-8 wt.% lactic acid, with the remainder being 1,4-dioxane; preferably, the hydrophilic polymer is 9-14 wt.% hydrophilic polymer, 0.2-0.9 wt.% antioxidant, and the solvent system contains 7-20 wt.% acetone, 5-8 wt.% methanol, and 6-8 wt.% lactic acid, with the remainder being 1,4-dioxane. More preferably, the hydrophilic polymer is 10-13 wt.%, the antioxidant is 0.3-0.7 wt.%, and the solvent system comprises 10-20 wt.% acetone, 6-8 wt.% methanol, and 6-8 wt.% lactic acid, with the balance being 1,4-dioxane. More preferably, the hydrophilic polymer is 13 wt.% cellulose triacetate, the mass percentage of 1,4-dioxane is 53.5 wt.%, the mass percentage of acetone is 19 wt.%, the mass percentage of methanol is 8 wt.%, the mass percentage of 2,6-di-tert-butyl-4-methylphenol is 0.5 wt.%, and the mass percentage of lactic acid is 6 wt.%; even more preferably, the hydrophilic polymer is 13 wt.% cellulose triacetate, the mass percentage of 1,4-dioxane is 53.8 wt.%, the mass percentage of acetone is 19 wt.%, the mass percentage of methanol is 8 wt.%, the mass percentage of 2,6-di-tert-butyl-4-methylphenol is 0.2 wt.%, and the mass percentage of lactic acid is 6 wt.%. Alternatively, more preferably, the hydrophilic polymer is 11 wt.% cellulose triacetate, the mass percentage of 1,4-dioxane is 55.7 wt.%, the mass percentage of acetone is 19 wt.%, the mass percentage of methanol is 8 wt.%, the mass percentage of 2,6-di-tert-butyl-4-methylphenol is 0.3 wt.%, and the mass percentage of lactic acid is 6 wt.%.

[0015] Another object of the present invention is to provide a method for manufacturing a forward osmosis membrane, said membrane comprising a modified hydrophilic polymer film layer, said method comprising: (a) preparing a casting liquid: mixing a hydrophilic polymer material, an antioxidant, and a water-soluble organic solvent system to obtain a casting liquid; (b) applying the casting liquid to a glass plate or a glass plate on which a hydrophilic support grid is placed to obtain an initial forward osmosis membrane; (c) treating the outer layer of the initial forward osmosis membrane to remove the solvent and form a dense skin layer on the outer layer of the initial forward osmosis membrane to obtain a second initial forward osmosis membrane; (d) forming a phase separation membrane or an interface membrane on the second initial forward osmosis membrane to obtain the forward osmosis membrane; Includes:

[0016] The method further includes the following steps: (a-1) The casting liquid obtained in step (a) is degassed. In step (b), the casting liquid degassed in step (a-1) is further poured onto a glass plate or an optical glass plate on which a hydrophilic support grid is laid, and an initial forward osmosis membrane having a specific thickness is produced using a film applicator. In the outer layer treatment and solvent removal step (c), the obtained initial forward osmosis membrane is left standing in air to volatilize the solvent and form a dense skin layer on the outer layer. In the step (d), the second initial forward osmosis membrane is immersed in deionized water to gel, causing phase separation and forming a membrane. (e) The forward osmosis membrane obtained in step (d) is immersed in deionized water to remove residual organic solvents. (f) Remove the forward osmosis membrane, rinse with deionized water, and store in a solution of sodium metabisulfite until use.

[0017] The hydrophilic support grid is made of polyester screen or nonwoven fabric. If it is a polyester screen, its thickness is 30 μm-80 μm and its pore size is 100-200 mesh, preferably 30 μm, 50 μm, 60 μm, or 70 μm, and its pore size is 100 mesh, 120 mesh, or 150 mesh. The hydrophilic polymer material is at least one selected from polyacrylonitrile, polyacrylate, polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate. The antioxidant is a sterically hindered phenol-based antioxidant. The solvent system is a mixture of 1,4-dioxane, acetone, methanol, and lactic acid. The sterically hindered phenolic antioxidant is at least one selected from 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetra(3,5-di-tert-butyl-4-hydroxyl)phenylpropionate, and 1,3,5-tri(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1h,3h,5h)-trione.

[0018] Here, the mass fraction of the hydrophilic polymer in the casting liquid is 8-15 wt.%, and the mass fraction of the antioxidant is 0.1-1 wt.%. Preferably, the mass fraction of the hydrophilic polymer in the casting liquid is 9-14 wt.%, and the mass fraction of the antioxidant is 0.2-0.9 wt.%. Even more preferably, the mass fraction of the hydrophilic polymer in the casting liquid is 10-13 wt.%, and the mass fraction of the antioxidant is 0.2-0.7 wt.%. More preferably, the mass fraction of the hydrophilic polymer is 8 wt.%, and the mass fraction of the antioxidant is 0.2 wt.%. Alternatively, the mass fraction of the hydrophilic polymer is 13 wt.%, and the mass fraction of the antioxidant is 0.5 wt.% or 0.2 wt.%. Alternatively, the mass fraction of the hydrophilic polymer is 11 wt.%, and the mass fraction of the antioxidant is 0.3 wt.%.

[0019] Here, the mass percentages of the components of the solvent system and the casting liquid are as follows: acetone mass percentage is 5-20 wt.%, methanol mass percentage is 5-10 wt.%, lactic acid mass percentage is 6-8 wt.%, and the remainder is 1,4-dioxane; preferably, acetone mass percentage is 7-20 wt.%, methanol mass percentage is 5-8 wt.%, lactic acid mass percentage is 6-8 wt.%, and the remainder is 1,4-dioxane; more preferably, acetone mass percentage is 10-20 wt.%, methanol mass percentage is 6-8 wt.%, lactic acid mass percentage is 6-8 wt.%, and the remainder is 1,4-dioxane; and even more preferably, acetone mass percentage is 19 wt.%, methanol mass percentage is 8 wt.%, lactic acid mass percentage is 6%, and the remainder is 1,4-dioxane.

[0020] The hydrophilic support grid is a polyester screen with a thickness of 30 μm, 50 μm, or 70 μm and a pore size of 100 mesh, 120 mesh, or 150 mesh. It is pre-washed before use. In the pre-washing step, the polyester screen is immersed in 10% sodium hydroxide or 2% hydrochloric acid for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored. The initial forward osmosis membrane fabricated with a film applicator has a thickness of 30 μm-150 μm, preferably 30 μm-100 μm, more preferably 30 μm-80 μm, and even more preferably 30 μm, 50 μm, 60 μm, or 70 μm.

[0021] In step (a) of the manufacturing method, the mixing conditions are 30-50°C for 12-48 hours of stirring to achieve uniform mixing, preferably 40-50°C for 12-32 hours, more preferably 40°C for 24 hours. The degassing method is to leave the mixture to stand for 12-36 hours to fully degas, or to use ultrasonic degassing assistance, preferably 24 hours. The conditions for leaving the mixture to stand in air are to leave it to stand for 30-90 seconds in an environment at a temperature of 25°C or below and a humidity of 90% or above to form a dense cortex, preferably 25°C and 90% humidity for 30-60 seconds.

[0022] In step (e) of the method, the membrane is heat-treated in a 40-50°C water bath for 5-20 minutes before being immersed in deionized water, and then immersed in deionized water for 12-36 hours to remove residual organic solvents. Preferably, the membrane is heat-treated in a 50°C water bath for 15 minutes before being immersed in deionized water for 24 hours. The concentration of sodium metabisulfite in step (f) of the method is 0.5-2%.

[0023] The forward osmosis membrane provided by the present invention can be used for the treatment of strongly acidic wastewater, water purification, and filtration and purification of food and pharmaceuticals.

[0024] In the forward osmosis membrane and manufacturing method thereof provided by the present invention, the invented forward osmosis membrane is a modified membrane, and by mixing an antioxidant, particularly a sterically hindered phenolic antioxidant, into the hydrophilic polymer layer to obtain a high oxidation resistance effect, an oxidation-resistant forward osmosis membrane that can be used safely and stably even under strong oxidative conditions can be manufactured.

[0025] In another embodiment of the present invention, by forming a highly hydrophilic hydrophilic polymer layer on a nonwoven fabric or polyester screen, it is possible to improve the water permeability, water permeation flux, and salt rejection rate. The use of an antioxidant in the hydrophilic polymer film layer, particularly a sterically hindered phenolic antioxidant (e.g., 2,6-di-tert-butyl-4-methylphenol), ensures the oxidation resistance and chemical resistance of the forward osmosis membrane, effectively reducing the oxidative limitation of the raw water, reducing the input of pretreatment reducing agents, reducing operation costs, improving the operational stability of the forward osmosis membrane, improving the efficiency of water purification and separation, extending the service life of the forward osmosis membrane, and reducing the operating costs of the entire osmosis membrane system.

[0026] The method for producing a forward osmosis membrane of the present invention involves forming an oxidation-resistant hydrophilic polymer film layer under optimized conditions, which has high membrane permeation flux, high salt rejection, and high oxidation resistance, thereby reducing the oxidation limitation of the raw water entering the membrane, improving the operational stability of the forward osmosis membrane, improving the efficiency of water purification and separation, extending the service life of the forward osmosis membrane, and reducing the operating costs of the entire osmosis membrane system. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flowchart of a manufacturing process for a forward osmosis membrane of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to further explain the technical means and effects for achieving the objectives of the present invention, the forward osmosis membrane and its manufacturing method of the present invention, as well as its specific embodiments, structure, manufacturing method, features and functions, will be described below with reference to the drawings and preferred examples. The present invention will be further described herein with reference to the following examples, which are merely for the purpose of illustrating the present invention and are not intended to limit the present invention.

[0029] FIG. 1 shows a flow chart of the manufacturing process of the forward osmosis membrane of the present invention, and the specific process is as follows: (1) Preparation of the support grid: Remove impurities from the polyester screen, rinse, dry and store. Prepare the polyester screen as needed. (2) Preparation of the casting liquid: A hydrophilic polymer material, an antioxidant, and an organic solvent are mixed uniformly. In the present invention, a hydrophilic polymer material and a sterically hindered phenolic antioxidant are further added to the mixture of the water-soluble organic solvent, and the mixture is stirred at 30-50°C for 12-48 hours to obtain a uniform casting liquid. (3) Defoaming: The cast liquid obtained in step 2 is allowed to stand for 12-36 hours and degassed thoroughly or assisted by ultrasonic degassing. (4) Preparation of initial forward osmosis membrane: The completely degassed casting liquid is poured onto a glass plate covered with a pre-treated polyester screen or poured directly onto a light glass plate, and an initial forward osmosis membrane with a specific thickness is produced using a film applicator. (5) Film formation: The film obtained in step 4 is left to stand in air at a predetermined temperature and humidity for several seconds to form a dense skin layer, and then immersed in deionized water to gel and undergo phase separation to form a film. In the present invention, the film is preferably left to stand in air at a temperature of 25°C or less and a humidity of 90% or more for 30 to 90 seconds. (6) Optimization treatment: The membrane obtained in step 5 is placed in a water bath at 40-50°C for 5-20 minutes for heat treatment, and then immersed in deionized water for 24 hours to remove residual organic solvents, resulting in a further optimized forward osmosis membrane. (7) Storage until use: Remove the forward osmosis membrane, rinse with deionized water, and then place it in a 0.5-2% sodium metabisulfite solution and store until use. Decide whether to store it until use as needed.

[0030] Example 1 (1) A 30 μm thick, 200 mesh polyester screen was immersed in 2% hydrochloric acid and 10% sodium hydroxide for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored until use. (2) Cellulose triacetate (13 wt. %) was added to a mixture of 1,4-dioxane (53.5 wt. %), acetone (19 wt. %), methanol (8 wt. %), 2,6-di-tert-butyl-4-methylphenol (0.5 wt. %), and lactic acid (6 wt. %). The mixture was stirred at 40°C for 24 hours, yielding a uniform casting liquid. (3) The casting liquid obtained in step 2 was left to stand for 24 hours and thoroughly degassed, or degassing was assisted by ultrasonic waves. (4) The completely degassed casting liquid was poured onto a glass plate covered with a polyester screen (thickness: 30 μm), and an initial forward osmosis membrane with a thickness of 50 μm was produced using a film applicator. (5) The membrane obtained in step 4 is left to stand in air for 60 seconds in an environment of 25°C and 90% humidity to form a dense skin layer, and then immersed in deionized water to cause gelation, phase separation, and the formation of a membrane. (6) The membrane obtained in step 5 was placed in a water bath at 40-50°C for heat treatment for 5-15 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0031] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 50 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate with an ORP value of +800 mV and hydrogen peroxide were used as the draw and feed liquids, respectively, the membrane permeation flux was 11.5 L / (m 2 The membrane performance was also not deteriorated even after 30 days of immersion under conditions where the ORP value simulated with hydrogen peroxide was +800mV. Specific performance tests are shown in Table 1.

[0032] Example 2 (1) Cellulose triacetate (13 wt. %) was added to a mixture of 1,4-dioxane (53.8 wt. %), acetone (19 wt. %), methanol (8 wt. %), 2,6-di-tert-butyl-4-methylphenol (0.2 wt. %), and lactic acid (6 wt. %). The mixture was stirred at 40°C for 24 hours, yielding a uniform casting liquid. (2) The casting liquid obtained in step 1 was left to stand for 24 hours and thoroughly degassed, or degassing was assisted by ultrasonic waves. (3) The completely degassed casting liquid was poured onto a glass plate, and an initial forward osmosis membrane with a thickness of 50 μm was produced using a film applicator. (4) The membrane obtained in step 3 is left to stand in air for 60 seconds in an environment with a temperature of 25°C and humidity of 90% to form a dense skin layer, and then immersed in deionized water to cause gelation, phase separation, and the formation of a membrane. (5) The membrane obtained in step 4 was placed in a water bath at 40-50°C for heat treatment for 5-15 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0033] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 50 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate with an ORP value of +800 mV and added hydrogen peroxide are used as the draw and feed liquids, respectively, the membrane permeation flux is 11.2 L / (m 2 The membrane performance was also not deteriorated even after 30 days of immersion under conditions where the ORP value simulated with hydrogen peroxide was +800mV. Specific performance tests are shown in Table 1.

[0034] Example 3 (1) Cellulose triacetate (13 wt. %) was added to a mixture of 1,4-dioxane (53.8 wt. %), acetone (19 wt. %), methanol (8 wt. %), pentaerythritol tetra(3,5-di-tert-butyl-4-hydroxyl)phenylpropionate (0.2 wt. %), and lactic acid (6 wt. %). The mixture was stirred at 40°C for 24 hours, yielding a uniform cast liquid. (2) The casting liquid obtained in step 1 was left to stand for 24 hours and thoroughly degassed, or degassing was assisted by ultrasonic waves. (3) The completely degassed casting liquid was poured onto a glass plate, and an initial forward osmosis membrane with a thickness of 50 μm was produced using a film applicator. (4) The membrane obtained in step 3 is left to stand in air for 60 seconds in an environment with a temperature of 25°C and humidity of 90% to form a dense skin layer, and then immersed in deionized water to cause gelation, phase separation, and the formation of a membrane. (5) The membrane obtained in step 4 was placed in a water bath at 40-50°C for heat treatment for 5-15 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0035] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 50 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate with an ORP value of +800 mV and hydrogen peroxide were used as the draw and feed liquids, respectively, the membrane permeation flux was 11.3 L / (m 2 The membrane performance was also not deteriorated even after 30 days of immersion under conditions where the ORP value simulated with hydrogen peroxide was +800mV. Specific performance tests are shown in Table 1.

[0036] Example 4 (1) Cellulose triacetate (mass percentage: 11 wt.%) was added to a mixture of 1,4-dioxane (mass percentage: 55.7 wt.%), acetone (mass percentage: 19 wt.%), methanol (mass percentage: 8 wt.%), 2,6-di-tert-butyl-4-methylphenol (mass percentage: 0.3 wt.%), and lactic acid (mass percentage: 6%). The mixture was stirred at 40°C for 24 hours, and a uniform cast liquid was obtained. (2) The casting liquid obtained in step 1 was left to stand for 24 hours and thoroughly degassed, or degassing was assisted by ultrasonic waves. (3) The completely degassed casting liquid was poured onto a glass plate, and an initial forward osmosis membrane with a thickness of 70 μm was produced using a film applicator. (4) The membrane obtained in step 2 is left to stand in air for 60 seconds in an environment with a temperature of 25°C and humidity of 90% to form a dense skin layer, and then immersed in deionized water to cause gelation, phase separation, and the formation of a membrane. (5) The membrane obtained in step 4 was placed in a water bath at 50°C for 15 minutes for heat treatment, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0037] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 70 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate with an ORP value of +800 mV and added hydrogen peroxide are used as the draw and feed liquids, respectively, the membrane permeation flux is 12.5 L / (m 2The membrane performance was also not deteriorated even after 30 days of immersion under conditions where the ORP value simulated with hydrogen peroxide was +800mV. Specific performance tests are shown in Table 1.

[0038] Table 1: Performance evaluation of membranes using 0.5 mol / L sodium chloride extract and 0.01 mol / L magnesium sulfate feed with added hydrogen peroxide and an ORP value of +800 mV.

[0039] [Table 1]

[0040] As can be seen from Table 1, the forward osmosis membrane of the present invention to which an antioxidant was added had high oxidation resistance, and the membrane performance was not affected even when immersed in water with a high oxygen potential for 30 days. Conventional forward osmosis membranes made of cellulose triacetate and forward osmosis membranes of conventional products have low oxidation resistance, and membrane performance deteriorates significantly with immersion time.

[0041] In the examples of the present invention, the concentrations of sodium hydroxide, hydrochloric acid and sodium metabisulfite are calculated by mass ratio.

[0042] In the forward osmosis membrane and manufacturing method thereof provided by the present invention, the invented forward osmosis membrane is a modified membrane, and an antioxidant, particularly a sterically hindered phenolic antioxidant, is added to and mixed with the hydrophilic polymer layer to obtain a high oxidation resistance effect, thereby obtaining an oxidation-resistant forward osmosis membrane that can be used safely and stably even under strong oxidative conditions.

[0043] While the invention has been described herein with reference to specific embodiments, it will be apparent that various modifications and changes can be made thereto without departing from the spirit and scope of the invention. Accordingly, the present specification and drawings are to be regarded as illustrative rather than restrictive.

Claims

1. A method for manufacturing a forward osmosis membrane, comprising: the forward osmosis membrane comprises a modified hydrophilic polymer film layer; The manufacturing method includes: (a) preparing a casting liquid: mixing a hydrophilic polymer material, an antioxidant, and a water-soluble organic solvent system to obtain a casting liquid; (b) applying the casting liquid to a glass plate or an optical glass plate on which a hydrophilic support grid is laid to obtain an initial forward osmosis membrane; (c) treating the outer layer of the initial forward osmosis membrane to remove the solvent and form a dense skin layer on the outer layer of the initial forward osmosis membrane to obtain a second initial forward osmosis membrane; (d) forming a phase separation membrane or an interface membrane on the second initial forward osmosis membrane to obtain the forward osmosis membrane; Including, The hydrophilic polymer in the casting liquid is cellulose triacetate, and its mass fraction is 11-13 wt. %, and the antioxidant is the sterically hindered phenolic antioxidant 2,6-di-tert-butyl-4-methylphenol, and its mass fraction is 0.2-0.7 wt. %.

2. The method further comprises the steps of: (a-1) degassing the cast liquid obtained in step (a); In the step (b), the casting liquid after degassing in the step (a-1) is poured onto a glass plate or an optical glass plate on which a hydrophilic support grid is laid, and an initial forward osmosis membrane having a specific thickness is produced using a film applicator; The outer layer treatment and solvent removal in step (c) are carried out by leaving the obtained initial forward osmosis membrane in air to volatilize the solvent and form a dense skin layer on the outer layer; In the step (d), the second initial forward osmosis membrane is immersed in deionized water to gel, and phase separation occurs to form a membrane; (e) immersing the forward osmosis membrane obtained in step (d) in deionized water to remove residual organic solvent; (f) removing the forward osmosis membrane, rinsing it with deionized water, and storing it in a solution of sodium metabisulfite until use;

3. the material of the hydrophilic support grid is a polyester screen or nonwoven fabric; If it is a polyester screen, its thickness is 30 μm-80 μm, and the pore size is 100 mesh-200 mesh; 3. The method according to claim 2, wherein the water-soluble organic solvent system is a mixture of 1,4-dioxane, acetone, methanol, and lactic acid.

4. 2. The method according to claim 1, wherein the mass fraction of the antioxidant is 0.3-0.5 wt. %.

5. The production method according to claim 1, wherein the casting liquid contains a solvent system with a mass percentage of acetone of 5-20 wt. %, a methanol of 5-10 wt. %, a lactic acid of 6-8 wt. %, and the remainder of 1,4-dioxane.

6. the hydrophilic support grid is a polyester screen, the thickness of which is 30 μm, 50 μm, 60 μm or 70 μm, the pore size of which is 100 mesh or 150 mesh, and which is used after being pre-washed; In the pre-cleaning step, the polyester screen was immersed in 10% sodium hydroxide and 2% hydrochloric acid for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored until use. The method according to claim 3, wherein the initial thickness of the forward osmosis membrane produced using the film applicator is 30 μm-150 μm.

7. In step (a) of the preparation method, the mixing conditions are: stirring at a temperature of 30-50°C for 12-48 hours to mix uniformly; The degassing method is to leave the mixture to stand for 12-36 hours and then degas it thoroughly or by using ultrasonic waves to assist the degassing. The method according to claim 2, wherein the conditions for leaving the powder in the air are a temperature of 25°C or less and a humidity of 90% or more for 30 to 90 seconds to form a dense skin layer.

8. In step (e) of the preparation method, before the membrane is immersed in deionized water, the membrane is first heat-treated in a water bath at 50°C for 15 minutes, and then immersed in deionized water for 12-36 hours to remove residual organic solvents; 2. The method of claim 1, wherein the concentration of sodium metabisulfite in step (f) of the method is 0.5-2%.

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