Preparation process of virus-removing hollow fiber membrane

Abstract

The invention belongs to the technical field of membrane treatment, and relates to a preparation process of a virus-removing hollow fiber membrane, which comprises the following steps: S1, preparation of a membrane casting solution: dissolving 25wt% of PVDF in benzophenone, adding 6wt% of silver-loaded molecular sieve (the silver content is 9.7%), heating to 220 DEG C, uniformly mixing, and standing to obtain the membrane casting solution; and S2, extrusion of the hollow fiber membrane: carrying out further high-temperature shearing, melting and mixing on the membrane casting solution through a double-screw extruder, finally converging the membrane casting solution with the inner core solution and the outer layer spray at a three-layer spinning nozzle, and extruding one path through the spinning nozzle to form a hollow fiber-shaped homogeneous-phase high-temperature membrane casting solution of which the inner cavity contains the high-temperature core solution and the outer part is surrounded by a low-temperature spray layer. The hollow fiber membrane is of a three-layer structure and comprises a membrane outer layer, a membrane middle layer and a membrane inner layer, the membrane outer layer is formed by compounding PVDF and a silver-loaded molecular sieve, and the membrane surface of the prepared hollow fiber membrane is modified through a quaternary ammonium salt polymer, so that the hollow fiber membrane can well inhibit bacterium breeding and reduce virus deposition through surface charge adsorption; and the membrane life is prolonged by more than 35%.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane treatment, and more particularly to a preparation process of a virus-removing hollow fiber membrane. Background Art

[0002] Pathogenic microorganisms refer to pathogenic bacteria, viruses, and protozoa (protozoa and worms) that are widely present in water bodies and can cause a variety of diseases such as gastroenteritis, diarrhea, dysentery, hepatitis, cholera, and typhoid. Therefore, controlling the risk of pathogenic microorganisms in drinking water is a top priority for drinking water safety. Among all pathogenic microorganisms, viruses tend to cause more serious consequences, but due to their smaller size, ranging from approximately 20-300nm, they are also more difficult to treat. Drinking water quality standards in countries such as the United States and Canada stipulate that the removal / inactivation rate of viruses must be no less than 99.99%. Although my country's drinking water hygiene standards do not include virus indicators, they stipulate that domestic drinking water should be disinfected and include specific control requirements for disinfection, and also stipulate turbidity limits. Compared to flat membranes, hollow fiber membranes offer significant advantages. They have a larger specific surface area, lower pressure loss, lower pretreatment requirements, and a wider range of applications. They are simple in structure, easy to install, and highly operable in practical applications. Separation devices are simple to use, easy to control, clean, and maintain. Furthermore, hollow fiber membrane modules exhibit excellent anti-fouling properties, preventing contaminants from adhering to the membrane surface, thereby extending the life of the modules. Publication number CN1269741C describes a membrane bioprocessing device and method for removing viruses from water. This invention treats contaminated wastewater from hospitals and other sources, or domestic sewage from residential areas, through membrane bioprocessing to meet discharge standards. The purified water can then be reused for applications such as landscaping, road spraying, toilet flushing, or landscape water. In this invention, bacteria are easily deposited on the surface of the membrane, which increases the contamination of the membrane surface and cannot effectively inhibit the growth of bacteria. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides a preparation process of a virus-removing hollow fiber membrane.

[0004] A preparation process for a virus-removing hollow fiber membrane comprises the following steps: S1. Preparation of casting solution: 25 wt% PVDF was dissolved in benzophenone, 6 wt% silver-loaded molecular sieve (silver content 9.7%) was added, the mixture was heated to 220°C and mixed evenly, and the mixture was allowed to stand to obtain a casting solution; S2. Extrusion of hollow fiber membranes: The casting solution is further sheared and melt-mixed at high temperature through a twin-screw extruder, and finally merged with the inner core solution and outer spray layer at a three-layer spinneret. The solution is extruded through the spinneret together to form a hollow fiber-shaped homogeneous high-temperature casting solution with a high-temperature core solution in the inner cavity and a low-temperature spray layer surrounding the outer surface. S21. Outer layer spray solvent exchange to form the outer layer of the membrane: a hollow fiber-shaped homogeneous high-temperature solution incorporating silver molecular sieve is coexisted with the spray for 0.01-0.05 seconds, and the surface diluent undergoes solvent exchange with a small amount of ethanol in the spray, forming a dense outer surface with extremely small openings. At the same time, the casting liquid with a thickness of 5-10 μm below the outer surface is affected by the low temperature of the spray, and the PVDF in the casting liquid undergoes phase separation from the diluent and rapidly solidifies, forming a dense layer with a very small closed cellular pore structure. The outer surface and the shallow cellular dense layer together form the outer layer, which is composited with PVDF and the silver-loaded molecular sieve; S22, Intermediate layer low temperature phase separation film forming intermediate layer: the area 10-50μm below the outer surface of the casting liquid is also affected by the low temperature of the spray, PVDF and diluent phase separation occurs for a longer time, the pore structure is significantly enlarged, and low permeability closed cell-like pores are formed to form the intermediate layer; S23, inner layer low temperature phase separation membrane inner layer: after the hollow fiber-shaped homogeneous high temperature casting liquid is cooled by spraying, it is directly immersed in a water bath 30-50°C higher than the spray temperature for cooling. After staying for 1-2 seconds, the PVDF and diluent undergo typical thermally induced phase separation. The PVDF and diluent phases fully coarsen and grow before solidification to form a double continuous through-hole structure. The casting liquid is completely solidified and stopped, forming the inner layer; S3. Membrane surface modification: S31, pre-treating the membrane: soaking the obtained membrane in acetone for 1 hour to remove surface grease, and drying; S32, initiator treatment: immerse in 0.1-1% potassium persulfate solution at 60°C for 30 minutes to 1 hour to induce surface free radicals; S33, graft polymerization treatment: soak the initiator-treated membrane in a phosphate buffer solution containing 0.1-1.0% polyethylene glycol, add a quaternary ammonium salt polymer, adjust the pH to neutral, and react at 70-80°C for 2-4 hours under nitrogen protection; S34. Post-treatment: repeatedly washing with ethanol and deionized water to remove ungrafted monomers, and drying to obtain a hollow fiber membrane.

[0005] Preferably, the PVDF in step S1 is 20-30 wt %, and the silver-loaded molecular sieve is 5-10 wt %.

[0006] Preferably, the outer layer spray in step S2 is aqueous ethanol, and the inner core liquid is glycerol.

[0007] Preferably, the outer layer in step S21 has a thickness of 5-10 μm and an average pore size of 20-50 nm, the middle layer in step S22 has a thickness of 10-50 μm and an average pore size of 50-100 nm, and the inner layer in step S23 has a thickness of 100-200 μm and an average pore size of 1-5 μm.

[0008] In summary, the present invention includes at least one of the following beneficial technical effects: 1. The hollow fiber membrane in the present invention has a three-layer structure, which is the outer layer, the middle layer and the inner layer. The outer layer is composed of PVDF and silver-loaded molecular sieve. After the hollow fiber membrane is manufactured, the surface of the membrane is modified by quaternary ammonium salt polymer, so that the hollow fiber membrane can effectively inhibit bacterial growth, reduce virus deposition by surface charge adsorption, and extend the membrane life by more than 35%; 2. The three-layer membrane structure of the present invention works synergistically, with a retention rate of ≥99.999% for bacteriophages (22-24nm), thereby improving the retention rate for viruses. DETAILED DESCRIPTION

[0009] The present invention is described in further detail.

[0010] Example 1 S1. Preparation of casting solution: 25 wt% PVDF was dissolved in benzophenone, 6 wt% silver-loaded molecular sieve was added, the mixture was heated to 220°C and mixed evenly, and the mixture was allowed to stand to obtain a casting solution; S2. Extrusion of hollow fiber membranes: The casting solution is further sheared and melt-mixed at high temperature through a twin-screw extruder, and finally merged with the inner core solution and outer spray layer at a three-layer spinneret. The solution is extruded through the spinneret together to form a hollow fiber-shaped homogeneous high-temperature casting solution with a high-temperature core solution in the inner cavity and a low-temperature spray layer surrounding the outer surface. S21. Outer layer spray solvent exchange to form the outer layer of the membrane: a hollow fiber-shaped homogeneous high-temperature solution incorporating silver molecular sieves is coexisted with the spray for 0.04 seconds, and the surface diluent undergoes solvent exchange with a small amount of ethanol in the spray, forming a dense outer surface with extremely small openings. At the same time, the casting liquid with a thickness of 5-10 μm below the outer surface is affected by the low temperature of the spray, causing the PVDF in the casting liquid to phase separate from the diluent and rapidly solidify, forming a dense layer with a very small closed cellular pore structure. The outer surface and the shallow cellular dense layer together form the outer layer, which is composited with PVDF and the silver-loaded molecular sieve; S22, Intermediate layer low temperature phase separation film forming intermediate layer: the area 10-50μm below the outer surface of the casting liquid is also affected by the low temperature of the spray, PVDF and diluent phase separation occurs for a longer time, the pore structure is significantly enlarged, and low permeability closed cell-like pores are formed to form the intermediate layer; S23, inner layer low temperature phase separation membrane inner layer: after the hollow fiber-shaped homogeneous high temperature casting liquid is cooled by spraying, it is directly immersed in a water bath 40°C higher than the spray temperature for cooling. After staying for 1 second, the PVDF and diluent undergo typical thermally induced phase separation. The PVDF and diluent phases fully coarsen and grow before solidification to form a double continuous through-hole structure. The inner layer is formed until the casting liquid is completely solidified. S3. Membrane surface modification: S31, pre-treating the membrane: soaking the obtained membrane in acetone for 1 hour to remove surface grease, and drying; S32, initiator treatment: immerse in 0.5% potassium persulfate solution at 60°C for 0.5 h to induce surface free radicals; S33, graft polymerization treatment: soak the initiator-treated membrane in phosphate buffer containing 0.5% polyethylene glycol, add quaternary ammonium salt polymer, adjust the pH to neutral, and react at 75°C for 3 hours under nitrogen protection; S34, post-treatment: rinse repeatedly with ethanol and deionized water to remove ungrafted monomers, dry, and obtain a hollow fiber membrane The prepared hollow fiber membrane performance: membrane surface fouling: ATP: 300RLU; pure water flux: 1664 L / m²・h・bar; phage retention rate ≥99.99%.

[0011] Comparative Example 1 S1. Preparation of casting solution: dissolve 25 wt% PVDF in benzophenone, heat to 220°C, mix well, and allow to stand to obtain casting solution; S2. Extrusion of hollow fiber membranes: The casting solution is further sheared and melt-mixed at high temperature through a twin-screw extruder, and finally merged with the inner core solution and outer spray layer at a three-layer spinneret. The solution is extruded through the spinneret together to form a hollow fiber-shaped homogeneous high-temperature casting solution with a high-temperature core solution in the inner cavity and a low-temperature spray layer surrounding the outer surface. S21. Outer layer spray solvent exchange to form the outer layer of the membrane: a hollow fiber-shaped homogeneous high-temperature solution incorporating silver molecular sieves is coexisted with the spray for 0.04 seconds, and the surface diluent undergoes solvent exchange with a small amount of ethanol in the spray, forming a dense outer surface with extremely small openings. At the same time, the casting liquid with a thickness of 5-10 μm below the outer surface is affected by the low temperature of the spray, causing the PVDF in the casting liquid to phase separate from the diluent and rapidly solidify, forming a dense layer with a very small closed cellular pore structure. The outer surface and the shallow cellular dense layer together form the outer layer, which is composited with PVDF and the silver-loaded molecular sieve; S22, Intermediate layer low temperature phase separation film forming intermediate layer: the area 10-50μm below the outer surface of the casting liquid is also affected by the low temperature of the spray, PVDF and diluent phase separation occurs for a longer time, the pore structure is significantly enlarged, and low permeability closed cell-like pores are formed to form the intermediate layer; S23, inner layer low temperature phase separation membrane inner layer: after the hollow fiber-shaped homogeneous high temperature casting liquid is cooled by spraying, it is directly immersed in a water bath 40°C higher than the spray temperature for cooling. After staying for 1 second, the PVDF and diluent undergo typical thermally induced phase separation. The PVDF and diluent phases fully coarsen and grow before solidification to form a double continuous through-hole structure. The inner layer is formed until the casting liquid is completely solidified. S3. Membrane surface modification: S31, pre-treating the membrane: soaking the obtained membrane in acetone for 1 hour to remove surface grease, and drying; S32, initiator treatment: immerse in 0.5% potassium persulfate solution at 60°C for 0.5 h to induce surface free radicals; S33, graft polymerization treatment: soak the initiator-treated membrane in phosphate buffer containing 0.5% polyethylene glycol, add quaternary ammonium salt polymer, adjust the pH to neutral, and react at 75°C for 3 hours under nitrogen protection; S34, post-treatment: rinse repeatedly with ethanol and deionized water to remove ungrafted monomers, dry, and obtain a hollow fiber membrane The prepared hollow fiber membrane performance: membrane surface fouling: ATP: 420RLU; pure water flux: 1530 L / m²・h・bar; phage retention rate ≥99.9%.

[0012] Comparative Example 2 S1. Preparation of casting solution: 25 wt% PVDF was dissolved in benzophenone, 6 wt% silver-loaded molecular sieve was added, the mixture was heated to 220°C and mixed evenly, and the mixture was allowed to stand to obtain a casting solution; S2. Extrusion of hollow fiber membranes: The casting solution is further sheared and melt-mixed at high temperature through a twin-screw extruder, and finally merged with the inner core solution and outer spray layer at a three-layer spinneret. The solution is extruded through the spinneret together to form a hollow fiber-shaped homogeneous high-temperature casting solution with a high-temperature core solution in the inner cavity and a low-temperature spray layer surrounding the outer surface. S21. Outer layer spray solvent exchange to form the outer layer of the membrane: a hollow fiber-shaped homogeneous high-temperature solution incorporating silver molecular sieves is coexisted with the spray for 0.04 seconds, and the surface diluent undergoes solvent exchange with a small amount of ethanol in the spray, forming a dense outer surface with extremely small openings. At the same time, the casting liquid with a thickness of 5-10 μm below the outer surface is affected by the low temperature of the spray, causing the PVDF in the casting liquid to phase separate from the diluent and rapidly solidify, forming a dense layer with a very small closed cellular pore structure. The outer surface and the shallow cellular dense layer together form the outer layer, which is composited with PVDF and the silver-loaded molecular sieve; S22, Intermediate layer low temperature phase separation film forming intermediate layer: the area 10-50μm below the outer surface of the casting liquid is also affected by the low temperature of the spray, PVDF and diluent phase separation occurs for a longer time, the pore structure is significantly enlarged, and low permeability closed cell-like pores are formed to form the intermediate layer; S23. Inner layer low-temperature phase separation membrane inner layer: After the hollow fiber-shaped homogeneous high-temperature casting liquid is cooled by spraying, it is directly immersed in a water bath 40°C higher than the spray temperature for cooling. It stays for 1 second, and PVDF and the diluent undergo typical thermally induced phase separation. The PVDF and diluent phases are fully coarsened and grown before solidification to form a double continuous through-hole structure. The inner layer is formed until the casting liquid is completely solidified and stops.

[0013] The prepared hollow fiber membrane performance: membrane surface fouling: ATP: 400RLU; pure water flux: 1600 L / m²・h・bar; phage retention rate ≥99.9%.

[0014] Comparative Example 3 S1. Preparation of casting solution: dissolve 25 wt% PVDF in benzophenone, heat to 220°C, mix well, and allow to stand to obtain casting solution; S2. Extrusion of hollow fiber membranes: The casting solution is further sheared and melt-mixed at high temperature through a twin-screw extruder, and finally merged with the inner core solution and outer spray layer at a three-layer spinneret. The solution is extruded through the spinneret together to form a hollow fiber-shaped homogeneous high-temperature casting solution with a high-temperature core solution in the inner cavity and a low-temperature spray layer surrounding the outer surface. S21. Outer layer spray solvent exchange to form the outer layer of the membrane: a hollow fiber-shaped homogeneous high-temperature solution incorporating silver molecular sieves is coexisted with the spray for 0.04 seconds, and the surface diluent undergoes solvent exchange with a small amount of ethanol in the spray, forming a dense outer surface with extremely small openings. At the same time, the casting liquid with a thickness of 5-10 μm below the outer surface is affected by the low temperature of the spray, causing the PVDF in the casting liquid to phase separate from the diluent and rapidly solidify, forming a dense layer with a very small closed cellular pore structure. The outer surface and the shallow cellular dense layer together form the outer layer, which is composited with PVDF and the silver-loaded molecular sieve; S22, Intermediate layer low temperature phase separation film forming intermediate layer: the area 10-50μm below the outer surface of the casting liquid is also affected by the low temperature of the spray, PVDF and diluent phase separation occurs for a longer time, the pore structure is significantly enlarged, and low permeability closed cell-like pores are formed to form the intermediate layer; S23. Inner layer low-temperature phase separation membrane inner layer: After the hollow fiber-shaped homogeneous high-temperature casting liquid is cooled by spraying, it is directly immersed in a water bath 40°C higher than the spray temperature for cooling. It stays for 1 second, and PVDF and the diluent undergo typical thermally induced phase separation. The PVDF and diluent phases are fully coarsened and grown before solidification to form a double continuous through-hole structure. The inner layer is formed until the casting liquid is completely solidified and stops.

[0015] The prepared hollow fiber membrane performance: membrane surface fouling: ATP: 450RLU; pure water flux: 1750 L / m²・h・bar; phage retention rate ≥99.9%.

[0016] It can be seen from the data between Example 1 and Comparative Examples 1, 2 and 3 that the outer membrane of the hollow fiber membrane composed of PVDF and silver-loaded molecular sieve, and the hollow fiber membrane modified by adding quaternary ammonium salt polymer, can effectively inhibit the growth of bacteria on the membrane surface, and the surface charge adsorption reduces bacterial deposition.

[0017] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made according to the principles, components, ratios, and methods of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing a virus-removing hollow fiber membrane, characterized in that: The steps are as follows: S1. Preparation of casting solution: 25 wt% PVDF was dissolved in benzophenone, 6 wt% silver-loaded molecular sieve (silver content 9.7%) was added, the mixture was heated to 220°C and mixed evenly, and the mixture was allowed to stand to obtain a casting solution; S2. Extrusion of hollow fiber membranes: The casting solution is further sheared and melt-mixed at high temperature through a twin-screw extruder, and finally merged with the inner core solution and outer spray layer at a three-layer spinneret. The solution is extruded through the spinneret together to form a hollow fiber-shaped homogeneous high-temperature casting solution with a high-temperature core solution in the inner cavity and a low-temperature spray layer surrounding the outer surface. S21. Outer layer spray solvent exchange to form the outer layer of the membrane: a hollow fiber-shaped homogeneous high-temperature solution incorporating silver molecular sieve is coexisted with the spray for 0.01-0.05 seconds, and the surface diluent undergoes solvent exchange with a small amount of ethanol in the spray, forming a dense outer surface with extremely small openings. At the same time, the casting liquid with a thickness of 5-10 μm below the outer surface is affected by the low temperature of the spray, and the PVDF in the casting liquid undergoes phase separation from the diluent and rapidly solidifies, forming a dense layer with a very small closed cellular pore structure. The outer surface and the shallow cellular dense layer together form the outer layer, which is composited with PVDF and the silver-loaded molecular sieve; S22, Intermediate layer low temperature phase separation film forming intermediate layer: the area 10-50μm below the outer surface of the casting liquid is also affected by the low temperature of the spray, PVDF and diluent phase separation occurs for a longer time, the pore structure is significantly enlarged, and low permeability closed cell-like pores are formed to form the intermediate layer; S23, inner layer low temperature phase separation membrane inner layer: after the hollow fiber-shaped homogeneous high temperature casting liquid is cooled by spraying, it is directly immersed in a water bath 30-50°C higher than the spray temperature for cooling. After staying for 1-2 seconds, the PVDF and diluent undergo typical thermally induced phase separation. The PVDF and diluent phases fully coarsen and grow before solidification to form a double continuous through-hole structure. The casting liquid is completely solidified and stopped, forming the inner layer; S3. Membrane surface modification: S31, pre-treating the membrane: soaking the obtained membrane in acetone for 1 hour to remove surface grease, and drying; S32, initiator treatment: immerse in 0.1-1% potassium persulfate solution at 60°C for 30 minutes to 1 hour to induce surface free radicals; S33, graft polymerization treatment: soak the initiator-treated membrane in a phosphate buffer solution containing 0.1-1.0% polyethylene glycol, add a quaternary ammonium salt polymer, adjust the pH to neutral, and react at 70-80°C for 2-4 hours under nitrogen protection; S34. Post-treatment: repeatedly washing with ethanol and deionized water to remove ungrafted monomers, and drying to obtain a hollow fiber membrane.

2. The process for preparing a virus-removing hollow fiber membrane according to claim 1, wherein: In step S1, the PVDF is 20-30 wt%, and the silver-loaded molecular sieve is 5-10 wt%.

3. The process for preparing a virus-removing hollow fiber membrane according to claim 1, characterized in that: The outer layer spray in step S2 is aqueous ethanol, and the inner core liquid is glycerol.

4. The process for preparing a virus-removing hollow fiber membrane according to claim 1, wherein: The outer layer in step S21 has a thickness of 5-10 μm and an average pore size of 20-50 nm, the middle layer in step S22 has a thickness of 10-50 μm and an average pore size of 50-100 nm, and the inner layer in step S23 has a thickness of 100-200 μm and an average pore size of 1-5 μm.