A high-porosity ultrafiltration membrane with low filtration resistance and a preparation method thereof

Abstract

The application relates to a high-porosity ultrafiltration membrane with low filtration resistance and a preparation method thereof, and belongs to the technical field of ultrafiltration membranes. The ultrafiltration membrane is formed by extruding casting liquid through a spinneret, entering a coagulation bath after an air section to form a porous silk membrane structure, and then being protected to obtain the ultrafiltration membrane. According to mass percentage, the preparation raw materials of the casting liquid include 10-25% PVDF resin, 70-80% N,N-dimethylacetamide, 8-12% polyvinylpyrrolidone, 1-2% lithium chloride and 0.5-1% plant extract. PVDF is used as a main film-forming material, polyvinylpyrrolidone, lithium chloride and compounded plant extract are compounded, and a core liquid and a coagulation bath system with a specific proportion are matched. In the phase inversion process, a porous structure with good connectivity and uniform distribution can be formed, the opening rate is greatly improved while the integrity of the membrane silk structure is ensured, the water permeation resistance is effectively reduced, the pure water flux of the ultrafiltration membrane is higher, and the filtering operation energy consumption is lower.

Description

Technical Field

[0001] This invention belongs to the field of ultrafiltration membrane technology, specifically relating to an ultrafiltration membrane with high porosity and low filtration resistance and its preparation method. Background Technology

[0002] Fiber ultrafiltration is a membrane separation technology based on polymer separation membranes. The core component is a hollow fiber ultrafiltration membrane, whose micropores can retain substances with molecular weights ranging from several thousand to hundreds of thousands. This technology achieves dynamic filtration through external or internal pressure-driven flow, and features low-pressure operation, high flux, and low energy consumption. It is widely used in water treatment, biopharmaceuticals, food and beverage purification, and other fields.

[0003] However, traditional ultrafiltration membranes generally have significant deficiencies in antioxidant and aging resistance. During the manufacturing process, traditional processes typically do not perform targeted antioxidant treatment on the ultrafiltration membrane, nor do they introduce effective antioxidant components and post-treatment processes. This results in weak resistance of the membrane fibers to environmental erosion. When the ultrafiltration membrane is under actual water treatment conditions for a long time, it will continuously come into contact with oxidizing substances in the water. At the same time, it will be affected by external factors such as temperature fluctuations and water quality changes. The molecular structure of the membrane fibers is easily damaged, leading to obvious aging phenomena. Specifically, the surface of the membrane fibers gradually turns yellow and darkens in color, the material becomes brittle, the toughness decreases, and even micro-cracks appear. Ultimately, this causes the ultrafiltration membrane to be unable to maintain stable filtration accuracy and operating efficiency for a long time, significantly shortening its service life and increasing the maintenance cost and replacement frequency of the water treatment system. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrafiltration membrane with high porosity and low filtration resistance, and a method for preparing the same, in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions: This invention provides an ultrafiltration membrane with high porosity and low filtration resistance. The ultrafiltration membrane is obtained by extruding casting liquid through a spinneret, passing through an air section, and then entering a coagulation bath to form a porous filament membrane structure, followed by a protective treatment. The raw materials for preparing the casting solution, by weight percentage, include 10-25% PVDF resin, 70-80% N,N-dimethylacetamide, 8-12% polyvinylpyrrolidone, 1-2% lithium chloride, and 0.5-1% plant extracts.

[0006] As a further optimization of the present invention, a hollow spinneret is used to simultaneously extrude casting liquid and core liquid, wherein the casting liquid serves as the outer wall liquid and the core liquid serves as the support for the hollow inner hole; the inner diameter of the spinneret channel is 0.5-0.8 mm and the outer diameter is 1.2-1.5 mm. The raw materials for preparing the core fluid, by mass percentage, include 85-90% pure water and 10-15% N,N-dimethylacetamide.

[0007] As a further optimization of the present invention, the preparation process of the casting solution is as follows: N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 10-15 min. Polyvinylpyrrolidone, lithium chloride and plant extract are added, and the mixture is stirred at 135 r / min for 10-15 min. PVDF resin is added, the temperature is raised to 50-60℃, and the mixture is stirred at 135 r / min for 4-6 h. After stirring, the mixture is degassed at a gauge pressure of -0.08~-0.09 MPa for 2-3 h, and then allowed to stand at room temperature for 12-24 h to obtain the casting solution.

[0008] As a further optimization of the present invention, the preparation process of the core liquid is as follows: N,N-dimethylacetamide is added to pure water, stirred at 125 r / min for 10-15 min at room temperature, and after being mixed evenly, it is filtered through a 0.22 μm filter membrane to obtain the core liquid. The temperature is maintained at 35-40℃ for later use.

[0009] As a further optimization of the present invention, the preparation process of the plant extract is as follows: (i) Cut the paulownia flowers, paulownia bark, whole mint plant and whole artemisia plant into sections and place them in a pulverizer. Control the rotation speed at 2000-2500 rpm and crush them to a particle size of 0.1-0.2 mm. Collect the pulverized material. (ii) Add 75% ethanol aqueous solution to the pulverized material. The material-liquid mass ratio is 1:12-15. Extract at 60℃ for 2 hours. Stir once every 20 minutes for 3-5 minutes each time. Let it stand and precipitate for 45 minutes. Take the supernatant. (iii) Centrifuge the supernatant at 3000 rpm for 20 minutes. Concentrate it under reduced pressure to 1 / 5 of the original volume. After vacuum drying, grind it into powder and filter it through a 200-mesh sieve to obtain the plant extract.

[0010] As a further optimization of the present invention, the paulownia flowers, paulownia bark, whole mint plant and whole artemisia plant are all made from fresh and unspoiled raw materials, and the mass ratio of the paulownia flowers, paulownia bark, whole mint plant and whole artemisia plant is 1:1.2:0.3:0.8.

[0011] This invention also provides a method for preparing an ultrafiltration membrane with high porosity and low filtration resistance, comprising the following steps: S1, Dual-flow liquid extrusion: Using a hollow spinneret, the outer channel extrudes the casting liquid, and the central channel extrudes the core liquid. The casting liquid temperature is controlled at 45-55℃, and the extrusion speed is 4-6mL / min. The core liquid temperature is controlled at 35-40℃, and the extrusion speed is 3-5mL / min. S2, Air Section: The freshly extruded membrane filaments travel in the air, with a length of 20-35cm and a dwell time of 1-3s; Air section environment: temperature 25-30℃, humidity 50-60%; S3, Coagulation Bath: The membrane fibers coming out of the air section directly enter the coagulation bath. The coagulation bath temperature is 20-25℃, and the fiber feeding speed is 1-1.5m / min. S4, Protective treatment: The membrane fibers from the coagulation bath are washed three times with water for 5 minutes each time at a temperature of 25-30°C. After washing, they are immersed in the prepared antioxidant solution at a constant temperature of 35-40°C for 10-15 minutes. They are then removed and dried to obtain the ultrafiltration membrane.

[0012] As a further optimization of the present invention, the coagulation bath is a mixed coagulation bath of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.1-0.25:1.

[0013] As a further optimization of the present invention, the raw materials for preparing the antioxidant liquid include: tea polyphenols, deionized water, potassium sorbate and glycerin, wherein the mass ratio of tea polyphenols, deionized water, potassium sorbate and glycerin is 0.02:1:0.01:0.02.

[0014] As a further optimization of the present invention, the preparation method of the antioxidant solution is as follows: tea polyphenols, potassium sorbate and glycerol are added to deionized water, heated to 45-50℃, stirred at 40r / min for 20-25min, cooled to room temperature and filtered through a 0.45μm filter membrane to obtain the antioxidant solution.

[0015] The beneficial effects of this invention are as follows: This invention uses PVDF as the main membrane-forming material, compounded with polyvinylpyrrolidone, lithium chloride, and compounded plant extracts, and combined with a specific ratio of core liquid and coagulation bath system. During the phase transformation process, a porous structure with good connectivity and uniform distribution can be formed. While ensuring the integrity of the membrane fiber structure, the porosity is greatly improved, effectively reducing water permeation resistance, resulting in higher pure water flux and lower energy consumption for filtration operation of the ultrafiltration membrane. The use of natural plant extracts such as paulownia flower, peppermint, and artemisia annua, along with the introduction of an antioxidant liquid containing components such as tea polyphenols and glycerol during the post-treatment process, can significantly improve the antioxidant and aging resistance of the ultrafiltration membrane, effectively inhibiting yellowing, brittleness, and performance degradation of the membrane fibers, ensuring that it can maintain stable flux and mechanical properties under long-term water treatment conditions. The preparation process is green and mild, without adding toxic or harmful additives, and the resulting ultrafiltration membrane can be used in scenarios with high requirements for hygiene and safety, such as drinking water treatment. Detailed Implementation

[0016] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0017] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0018] Example 1 The preparation process of the plant extract is as follows: (I) Cut the paulownia flowers, paulownia bark, whole mint and whole artemisia into sections and place them in a pulverizer. Control the speed at 2000 rpm and crush them to a particle size of 0.1 mm. Collect the pulverized material. (II) Add 75% ethanol aqueous solution to the pulverized material. The material-to-liquid mass ratio is 1:12. Extract at 60℃ for 2 hours. Stir once every 20 minutes for 3 minutes each time. Let it stand and settle for 45 minutes. Take the supernatant. (III) Centrifuge the supernatant at 3000 rpm for 20 minutes. Concentrate under reduced pressure to 1 / 5 of the original volume. After vacuum drying, grind it into powder and filter it through a 200-mesh sieve to obtain the plant extract (the paulownia flowers, paulownia bark, whole mint and whole artemisia are all fresh and unspoiled raw materials. The mass ratio of paulownia flowers, paulownia bark, whole mint and whole artemisia is 1:1.2:0.3:0.8). The preparation process of the casting solution is as follows: 70% N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 10 min. 8% polyvinylpyrrolidone, 1% lithium chloride and 0.5% plant extract are added, and the mixture is stirred at 135 r / min for 10 min. 20.5% PVDF resin is added, the temperature is raised to 50℃, and the mixture is stirred at 135 r / min for 4 h. After stirring, the mixture is degassed at a gauge pressure of -0.08 MPa for 2 h, and then allowed to stand at room temperature for 12 h to mature, thus obtaining the casting solution. The preparation process of the core solution is as follows: 10% N,N-dimethylacetamide is added to 90% pure water, stirred at 125 r / min for 10 min at room temperature, and after being mixed evenly, it is filtered through a 0.22 μm filter membrane to obtain the core solution. The temperature is maintained at 35℃ for later use. The coagulation bath is a mixture of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.1:1. The preparation method of the antioxidant solution is as follows: tea polyphenols, potassium sorbate and glycerol are added to deionized water, heated to 45℃, stirred at 40r / min for 20min, cooled to room temperature and filtered through a 0.45μm filter membrane to obtain the antioxidant solution (the mass ratio of tea polyphenols, deionized water, potassium sorbate and glycerol is 0.02:1:0.01:0.02). Dual-flow liquid extrusion: A hollow spinneret is used, with the outer channel extruding casting liquid and the central channel extruding core liquid. The casting liquid serves as the outer wall liquid, and the core liquid serves as the support for the hollow inner hole. The inner diameter of the spinneret channel is 0.5 mm and the outer diameter is 1.2 mm. The casting liquid temperature is controlled at 45°C, and the extrusion speed is 4 mL / min. The core liquid temperature is controlled at 35°C, and the extrusion speed is 3 mL / min. Air section: The freshly extruded membrane filaments travel in the air, with a length of 20cm and a dwell time of 1 second; Air section environment: temperature 25℃, humidity 50%; Coagulation bath: The membrane fibers coming out of the air section directly enter the coagulation bath. The coagulation bath temperature is 20℃ and the fiber feeding speed is 1m / min. Protective treatment: The membrane fibers extracted from the coagulation bath were washed three times with water for 5 minutes each time at a temperature of 25°C. After washing, they were immersed in a prepared antioxidant solution at a constant temperature of 35°C for 10 minutes. They were then removed and dried to obtain the ultrafiltration membrane.

[0019] Example 2 The preparation process of the plant extract is as follows: (I) Cut the paulownia flowers, paulownia bark, whole mint and whole artemisia into sections and place them in a pulverizer. Control the speed at 2300 rpm and crush them to a particle size of 0.1 mm. Collect the crushed material. (II) Add 75% ethanol aqueous solution to the crushed material. The material-to-liquid mass ratio is 1:14. Extract at 60℃ for 2 hours. Stir once every 20 minutes for 4 minutes each time. Let it stand and settle for 45 minutes. Take the supernatant. (III) Centrifuge the supernatant at 3000 rpm for 20 minutes. Concentrate under reduced pressure to 1 / 5 of the original volume. After vacuum drying, grind it into powder and filter it through a 200-mesh sieve to obtain the plant extract (the paulownia flowers, paulownia bark, whole mint and whole artemisia are all fresh and unspoiled raw materials. The mass ratio of paulownia flowers, paulownia bark, whole mint and whole artemisia is 1:1.2:0.3:0.8). The preparation process of the casting solution is as follows: 75% N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 12 min. 10% polyvinylpyrrolidone, 2% lithium chloride and 0.8% plant extract are added, and the mixture is stirred at 135 r / min for 12 min. 12.2% PVDF resin is added, the temperature is raised to 55℃, and the mixture is stirred at 135 r / min for 5 h. After stirring, the mixture is degassed at a gauge pressure of -0.08 MPa for 2.5 h, and then allowed to stand at room temperature for 18 h to mature, thus obtaining the casting solution. The preparation process of the core solution is as follows: 12% N,N-dimethylacetamide is added to 88% pure water, stirred at 125 r / min for 12 min at room temperature, and after being mixed evenly, it is filtered through a 0.22 μm filter membrane to obtain the core solution. The temperature is maintained at 37℃ for later use. The coagulation bath is a mixture of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.2:1. The preparation method of the antioxidant solution is as follows: tea polyphenols, potassium sorbate and glycerol are added to deionized water, heated to 46℃, stirred at 40 r / min for 22 min, cooled to room temperature and filtered through a 0.45 μm filter membrane to obtain the antioxidant solution (the mass ratio of tea polyphenols, deionized water, potassium sorbate and glycerol is 0.02:1:0.01:0.02). Dual-flow liquid extrusion: A hollow spinneret is used, with the outer channel extruding casting liquid and the central channel extruding core liquid. The casting liquid serves as the outer wall liquid, and the core liquid serves as the support for the hollow inner hole. The inner diameter of the spinneret channel is 0.6 mm and the outer diameter is 1.3 mm. The casting liquid temperature is controlled at 50°C, and the extrusion speed is 5 mL / min. The core liquid temperature is controlled at 37°C, and the extrusion speed is 4 mL / min. Air section: The freshly extruded membrane filaments travel in the air, with a length of 30cm and a dwell time of 2s; Air section environment: temperature 27℃, humidity 55%; Coagulation bath: The membrane fibers coming out of the air section directly enter the coagulation bath. The coagulation bath temperature is 22℃ and the fiber feeding speed is 1.2m / min. Protective treatment: The membrane fibers extracted from the coagulation bath were washed three times with water for 5 minutes each time at a temperature of 27°C. After washing, they were immersed in a prepared antioxidant solution at a constant temperature of 38°C for 12 minutes. They were then removed and dried to obtain the ultrafiltration membrane.

[0020] Example 3 The preparation process of the plant extract is as follows: (I) Cut the paulownia flowers, paulownia bark, whole mint and whole artemisia into sections and place them in a pulverizer. Control the speed at 2500 rpm and crush them to a particle size of 0.2 mm. Collect the pulverized material. (II) Add 75% ethanol aqueous solution to the pulverized material. The material-to-liquid mass ratio is 1:15. Extract at 60℃ for 2 hours. Stir once every 20 minutes for 5 minutes each time. Let it stand and settle for 45 minutes. Take the supernatant. (III) Centrifuge the supernatant at 3000 rpm for 20 minutes. Concentrate under reduced pressure to 1 / 5 of the original volume. After vacuum drying, grind it into powder and filter it through a 200-mesh sieve to obtain the plant extract (the paulownia flowers, paulownia bark, whole mint and whole artemisia are all fresh and unspoiled raw materials. The mass ratio of paulownia flowers, paulownia bark, whole mint and whole artemisia is 1:1.2:0.3:0.8). The preparation process of the casting solution is as follows: 79.5% N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 15 min. 8% polyvinylpyrrolidone, 2% lithium chloride and 0.5% plant extract are added, and the mixture is stirred at 135 r / min for 15 min. 10% PVDF resin is added, the temperature is raised to 60℃, and the mixture is stirred at 135 r / min for 6 h. After stirring, the mixture is degassed by a gauge pressure of -0.09 MPa for 3 h, and then allowed to stand at room temperature for 24 h to mature, thus obtaining the casting solution. The preparation process of the core solution is as follows: 15% N,N-dimethylacetamide is added to 85% pure water, stirred at 125 r / min for 15 min at room temperature, and after being mixed evenly, it is filtered through a 0.22 μm filter membrane to obtain the core solution. The temperature is maintained at 40℃ for later use. The coagulation bath is a mixture of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.25:1. The preparation method of the antioxidant solution is as follows: tea polyphenols, potassium sorbate and glycerol are added to deionized water, heated to 50℃, stirred at 40r / min for 25min, cooled to room temperature and filtered through a 0.45μm filter membrane to obtain the antioxidant solution (the mass ratio of tea polyphenols, deionized water, potassium sorbate and glycerol is 0.02:1:0.01:0.02). Dual-flow liquid extrusion: A hollow spinneret is used, with the outer channel extruding casting liquid and the central channel extruding core liquid. The casting liquid serves as the outer wall liquid, and the core liquid serves as the support for the hollow inner hole. The inner diameter of the spinneret channel is 0.8 mm and the outer diameter is 1.5 mm. The casting liquid temperature is controlled at 55°C, and the extrusion speed is 6 mL / min. The core liquid temperature is controlled at 40°C, and the extrusion speed is 5 mL / min. Air section: The freshly extruded membrane filaments travel in the air, with a length of 35cm and a dwell time of 3 seconds; Air section environment: temperature 30℃, humidity 60%; Coagulation bath: The membrane fibers exiting the air section directly enter the coagulation bath. The coagulation bath temperature is 25℃ and the fiber feeding speed is 1.5m / min. Protective treatment: The membrane fibers extracted from the coagulation bath were washed three times with water for 5 minutes each time at a temperature of 30°C. After washing, they were immersed in a prepared antioxidant solution at a constant temperature of 40°C for 15 minutes. After drying, the ultrafiltration membrane was obtained.

[0021] Comparative Example 1 The preparation process of the casting solution is as follows: 75% N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 12 min. 10% polyvinylpyrrolidone and 2% lithium chloride are added, and the mixture is stirred at 135 r / min for 12 min. 13% PVDF resin is added, the temperature is raised to 55℃, and the mixture is stirred at 135 r / min for 5 h. After stirring, the mixture is degassed at a gauge pressure of -0.08 MPa for 2.5 h, and then allowed to stand at room temperature for 18 h to mature, thus obtaining the casting solution. The preparation process of the core solution is as follows: 12% N,N-dimethylacetamide is added to 88% pure water, stirred at 125 r / min for 12 min at room temperature, and after being mixed evenly, it is filtered through a 0.22 μm filter membrane to obtain the core solution. The temperature is maintained at 37℃ for later use. The coagulation bath is a mixture of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.2:1. The preparation method of the antioxidant solution is as follows: tea polyphenols, potassium sorbate and glycerol are added to deionized water, heated to 46℃, stirred at 40 r / min for 22 min, cooled to room temperature and filtered through a 0.45 μm filter membrane to obtain the antioxidant solution (the mass ratio of tea polyphenols, deionized water, potassium sorbate and glycerol is 0.02:1:0.01:0.02). Dual-flow liquid extrusion: A hollow spinneret is used, with the outer channel extruding casting liquid and the central channel extruding core liquid. The casting liquid serves as the outer wall liquid, and the core liquid serves as the support for the hollow inner hole. The inner diameter of the spinneret channel is 0.6 mm and the outer diameter is 1.3 mm. The casting liquid temperature is controlled at 50°C, and the extrusion speed is 5 mL / min. The core liquid temperature is controlled at 37°C, and the extrusion speed is 4 mL / min. Air section: The freshly extruded membrane filaments travel in the air, with a length of 30cm and a dwell time of 2s; Air section environment: temperature 27℃, humidity 55%; Coagulation bath: The membrane fibers coming out of the air section directly enter the coagulation bath. The coagulation bath temperature is 22℃ and the fiber feeding speed is 1.2m / min. Protective treatment: The membrane fibers extracted from the coagulation bath were washed three times with water for 5 minutes each time at a temperature of 27°C. After washing, they were immersed in a prepared antioxidant solution at a constant temperature of 38°C for 12 minutes. They were then removed and dried to obtain the ultrafiltration membrane.

[0022] Comparative Example 2 The preparation process of the plant extract is as follows: (I) Cut the paulownia flowers, paulownia bark, whole mint and whole artemisia into sections and place them in a pulverizer. Control the speed at 2300 rpm and crush them to a particle size of 0.1 mm. Collect the crushed material. (II) Add 75% ethanol aqueous solution to the crushed material. The material-to-liquid mass ratio is 1:14. Extract at 60℃ for 2 hours. Stir once every 20 minutes for 4 minutes each time. Let it stand and settle for 45 minutes. Take the supernatant. (III) Centrifuge the supernatant at 3000 rpm for 20 minutes. Concentrate under reduced pressure to 1 / 5 of the original volume. After vacuum drying, grind it into powder and filter it through a 200-mesh sieve to obtain the plant extract (the paulownia flowers, paulownia bark, whole mint and whole artemisia are all fresh and unspoiled raw materials. The mass ratio of paulownia flowers, paulownia bark, whole mint and whole artemisia is 1:1.2:0.3:0.8). The preparation process of the casting solution is as follows: 75% N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 12 min. 10% polyvinylpyrrolidone, 2% lithium chloride and 0.8% plant extract are added, and the mixture is stirred at 135 r / min for 12 min. 12.2% PVDF resin is added, the temperature is raised to 55℃, and the mixture is stirred at 135 r / min for 5 h. After stirring, the mixture is degassed at a gauge pressure of -0.08 MPa for 2.5 h, and then allowed to stand at room temperature for 18 h to mature, thus obtaining the casting solution. The preparation process of the core solution is as follows: 12% N,N-dimethylacetamide is added to 88% pure water, stirred at 125 r / min for 12 min at room temperature, and after being mixed evenly, it is filtered through a 0.22 μm filter membrane to obtain the core solution. The temperature is maintained at 37℃ for later use. The coagulation bath is a mixture of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.2:1. The preparation method of the antioxidant solution is as follows: tea polyphenols and glycerol are added to deionized water, heated to 46℃, stirred at 40r / min for 22min, cooled to room temperature, and filtered through a 0.45μm filter membrane to obtain the antioxidant solution (the mass ratio of tea polyphenols, deionized water and glycerol is 0.02:1:0.02). Dual-flow liquid extrusion: A hollow spinneret is used, with the outer channel extruding casting liquid and the central channel extruding core liquid. The casting liquid serves as the outer wall liquid, and the core liquid serves as the support for the hollow inner hole. The inner diameter of the spinneret channel is 0.6 mm and the outer diameter is 1.3 mm. The casting liquid temperature is controlled at 50°C, and the extrusion speed is 5 mL / min. The core liquid temperature is controlled at 37°C, and the extrusion speed is 4 mL / min. Air section: The freshly extruded membrane filaments travel in the air, with a length of 30cm and a dwell time of 2s; Air section environment: temperature 27℃, humidity 55%; Coagulation bath: The membrane fibers coming out of the air section directly enter the coagulation bath. The coagulation bath temperature is 22℃ and the fiber feeding speed is 1.2m / min. Protective treatment: The membrane fibers extracted from the coagulation bath were washed three times with water for 5 minutes each time at a temperature of 27°C. After washing, they were immersed in a prepared antioxidant solution at a constant temperature of 38°C for 12 minutes. They were then removed and dried to obtain the ultrafiltration membrane.

[0023] Performance testing (i) The tensile strength and elongation at break of the ultrafiltration membranes prepared by the methods of Examples 1-3 and the ultrafiltration membranes prepared by the methods of Comparative Examples 1-2 were tested according to HY / T213-2016 "Method for Determination of Tensile Strength of Hollow Fiber Ultrafiltration / Microfiltration Membranes". The test results are shown in Table 1.

[0024] Table 1 As can be seen from Table 1, the tensile strength at break of Examples 1-3 is 118cN, 122cN, and 121cN, respectively, and is generally stable in the range of 118-122cN, with an average of about 120.33cN. Among them, Example 2 has the best mechanical strength; Comparative Examples 1 and 2 are only 112cN and 114cN, respectively, which are significantly lower than those of the Examples. Examples 1-3 showed elongation at break of 34%-36%, with an average of about 35%, demonstrating a balance between toughness and ductility; Comparative Examples 1 and 2 showed elongation at break of 31% and 33% respectively, both lower than the levels of the examples. The ultrafiltration membranes prepared in Examples 1-3 are superior to those in Comparative Examples 1-2 in terms of tensile strength and elongation at break. This indicates that the preparation process of the present invention can simultaneously improve the mechanical strength and toughness of the membrane fibers, making the products more resistant to stretching and breakage during use, and providing greater advantages in service life and operational stability.

[0025] (ii) The bubble point pressure of the ultrafiltration membranes prepared by the methods of Examples 1-3 and Comparative Examples 1-2 was tested in accordance with GB / T36137-2018 "Integrity Test Method for Hollow Fiber Ultrafiltration Membranes and Microfiltration Membrane Modules". (III) The ultrafiltration membranes prepared by the methods of Examples 1-3 and Comparative Examples 1-2 were tested for pure water flux in accordance with GB / T32360-2015 "Test Methods for Ultrafiltration Membranes". The pure water flux test conditions were: 25℃±0.5℃, 0.1MPa±0.005MPa, and 1L / min circulation.

[0026] Table 2 As can be seen from Table 2, the bubble point pressure of Examples 1 and 3 is 0.4 MPa, while that of Example 2 reaches 0.5 MPa, which is better than that of the comparative examples. The bubble point pressure of Comparative Examples 1 and 2 is 0.3 MPa, which is lower than that of Examples 2 and 3. The pure water fluxes of Examples 1-3 were 1531, 1560, and 1520 L / (m²·h·kPa), respectively, and remained stable in the range of 1520-1560. The pure water fluxes of Comparative Examples 1 and 2 were 1486 and 1490 L / (m²·h·kPa), respectively, which were significantly lower than those of Examples 1-3. The ultrafiltration membranes prepared in Examples 1-3 are superior to those in Comparative Examples 1-2 in terms of bubble point pressure and pure water flux. They achieve simultaneous improvement in membrane integrity, separation accuracy and water permeate flux, resulting in better overall filtration performance and meeting the requirements of efficient and stable water treatment applications.

[0027] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. An ultrafiltration membrane with high porosity and low filtration resistance, characterized in that, The ultrafiltration membrane is obtained by extruding the casting solution through a spinneret, passing through an air section, and then entering a coagulation bath to form a porous filament membrane structure, followed by a protective treatment. The raw materials for preparing the casting solution, by weight percentage, include 10-25% PVDF resin, 70-80% N,N-dimethylacetamide, 8-12% polyvinylpyrrolidone, 1-2% lithium chloride, and 0.5-1% plant extracts.

2. The ultrafiltration membrane with high porosity and low filtration resistance according to claim 1, characterized in that, The spinneret is a hollow spinneret, which simultaneously extrudes casting liquid and core liquid. The casting liquid serves as the outer wall liquid, and the core liquid serves as the support for the hollow inner hole. The inner diameter of the spinneret channel is 0.5-0.8 mm, and the outer diameter is 1.2-1.5 mm. The raw materials for preparing the core fluid, by mass percentage, include 85-90% pure water and 10-15% N,N-dimethylacetamide.

3. The ultrafiltration membrane with high porosity and low filtration resistance according to claim 1, characterized in that, The preparation process of the casting solution is as follows: N,N-dimethylacetamide is added to a stirred tank, nitrogen gas is introduced for protection, and the mixture is stirred at 65 r / min for 10-15 min. Polyvinylpyrrolidone, lithium chloride and plant extract are added, and the mixture is stirred at 135 r / min for 10-15 min. PVDF resin is added, the temperature is raised to 50-60℃, and the mixture is stirred at 135 r / min for 4-6 h. After stirring, the mixture is degassed at a gauge pressure of -0.08~-0.09 MPa for 2-3 h, and then allowed to stand at room temperature for 12-24 h to obtain the casting solution.

4. The ultrafiltration membrane with high porosity and low filtration resistance according to claim 1, characterized in that, The preparation process of the core liquid is as follows: N,N-dimethylacetamide is added to pure water and stirred at 125 r / min for 10-15 min at room temperature. After mixing evenly, the mixture is filtered through a 0.22 μm filter membrane to obtain the core liquid. The temperature is maintained at 35-40℃ for later use.

5. The ultrafiltration membrane with high porosity and low filtration resistance according to claim 1, characterized in that, The preparation process of the plant extract is as follows: (i) Cut the paulownia flowers, paulownia bark, whole mint plant and whole artemisia plant into sections and place them in a pulverizer. Control the speed at 2000-2500 rpm and crush them to a particle size of 0.1-0.2 mm. Collect the pulverized material. (ii) Add 75% ethanol aqueous solution to the pulverized material. The material-liquid mass ratio is 1:12-15. Extract at 60℃ for 2 hours. Stir once every 20 minutes for 3-5 minutes each time. Let it stand and precipitate for 45 minutes. Take the supernatant. (iii) Centrifuge the supernatant at 3000 rpm for 20 minutes. Concentrate it under reduced pressure to 1 / 5 of the original volume. After vacuum drying, grind it into powder and filter it through a 200-mesh sieve to obtain the plant extract.

6. The ultrafiltration membrane with high porosity and low filtration resistance according to claim 5, characterized in that, The paulownia flowers, paulownia bark, whole mint plant, and whole artemisia plant are all made from fresh, unspoiled raw materials, and the mass ratio of the paulownia flowers, paulownia bark, whole mint plant, and whole artemisia plant is 1:1.2:0.3:0.

8.

7. A method for preparing an ultrafiltration membrane with high porosity and low filtration resistance as described in any one of claims 1-6, characterized in that, Includes the following steps: S1, Dual-flow liquid extrusion: Using a hollow spinneret, the outer channel extrudes the casting liquid, and the central channel extrudes the core liquid. The casting liquid temperature is controlled at 45-55℃, and the extrusion speed is 4-6mL / min. The core liquid temperature is controlled at 35-40℃, and the extrusion speed is 3-5mL / min. S2, Air Section: The freshly extruded membrane filaments travel in the air, with a length of 20-35cm and a dwell time of 1-3s; Air section environment: temperature 25-30℃, humidity 50-60%; S3, Coagulation Bath: The membrane fibers coming out of the air section directly enter the coagulation bath. The coagulation bath temperature is 20-25℃, and the fiber feeding speed is 1-1.5m / min. S4, Protective treatment: The membrane fibers from the coagulation bath are washed three times with water for 5 minutes each time at a temperature of 25-30°C. After washing, they are immersed in the prepared antioxidant solution at a constant temperature of 35-40°C for 10-15 minutes. They are then removed and dried to obtain the ultrafiltration membrane.

8. The method for preparing an ultrafiltration membrane with high porosity and low filtration resistance according to claim 7, characterized in that, The coagulation bath is a mixed coagulation bath of N,N-dimethylacetamide and pure water; the mass ratio of N,N-dimethylacetamide to pure water is 0.1-0.25:

1.

9. The method for preparing an ultrafiltration membrane with high porosity and low filtration resistance according to claim 8, characterized in that, The raw materials for preparing the antioxidant liquid include: tea polyphenols, deionized water, potassium sorbate and glycerin, wherein the mass ratio of tea polyphenols, deionized water, potassium sorbate and glycerin is 0.02:1:0.01:0.

02.

10. The method for preparing an ultrafiltration membrane with high porosity and low filtration resistance according to claim 9, characterized in that, The antioxidant solution is prepared by adding tea polyphenols, potassium sorbate and glycerol to deionized water, heating to 45-50℃, stirring at 40r / min for 20-25min, cooling to room temperature and filtering with a 0.45μm filter membrane to obtain the antioxidant solution.

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