Charge-modified polyether sulfone hollow fiber membrane with variable-diameter pore structure and preparation method of charge-modified polyether sulfone hollow fiber membrane

Abstract

The invention discloses a charge-modified polyether sulfone hollow fiber membrane with a variable-diameter pore structure and a preparation method thereof. The preparation method comprises the following steps: (1) mixing polyether sulfone resin, sulfonated polyether sulfone, a pore-forming agent, polyethylene glycol and an organic solvent to prepare a membrane casting solution; (2) extruding the membrane casting liquid and the core liquid from a single-layer spinneret plate from outside to inside, immersing the membrane casting liquid and the core liquid into a coagulating bath through an air gap to generate primary membrane filaments, introducing the primary membrane filaments into a rinsing bath for rinsing through a filament guide roller, winding and collecting the primary membrane filaments through a filament collecting roller, and then soaking the collected membrane filaments in pure water to obtain a sulfonated polyethersulfone modified hollow fiber membrane; and (3) soaking the sulfonated polyethersulfone modified hollow fiber membrane in a sulfomethyl water-soluble phenolic resin aqueous solution, and cleaning with pure water. The polyethersulfone hollow fiber membrane obtained by the invention comprises the compact layer and the microporous layer from inside to outside, and has the advantages of higher protein yield, excellent pure water flux and high filtering efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of hollow fiber membranes, and in particular to a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane and a preparation method thereof. Background Art

[0002] Hollow fiber membrane is a high-performance separation membrane material, which is similar to a slender fiber in shape and has a hollow tubular structure inside. Hollow fiber membrane has extremely high specific surface area and permeation flux. During the separation process, the feed liquid flows on the outside or inside of the membrane, and the separated substances penetrate through the membrane wall to the other side, thereby achieving the separation and purification of the substances. It has high separation efficiency, simple operation, easy production, and good antioxidant, high temperature resistance, corrosion resistance and other characteristics.

[0003] Polyethersulfone (PESU) is a commonly used hollow fiber membrane material with excellent film-forming properties. Compared with other materials, it has the advantages of stable chemical properties, high corrosion resistance and heat resistance. After film formation, it has excellent physical strength and has broad application prospects in industrial water treatment, seawater desalination, chemical separation and purification, and biomedicine.

[0004] At present, polyethersulfone hollow fiber membranes are often used for protein purification. Hollow fiber membranes can allow small molecules such as water and salts to pass through, but prevent protein macromolecules from passing through. However, polyethersulfone (PES) hollow fiber membranes have a certain hydrophobicity during protein purification, which easily leads to protein adsorption on the membrane surface and in the membrane pores, forming membrane pollution, resulting in a significant decrease in membrane filtration flux during separation operations, affecting the separation efficiency of the membrane and shortening the service life of the membrane. Therefore, it is necessary to enhance the hydrophilicity of polyethersulfone hollow fiber membranes and reduce the adsorption of proteins by the membrane.

[0005] The invention patent with application number 202410030232.5 discloses a polyethersulfone hollow fiber ultrafiltration membrane and its preparation method and application. The polyethersulfone hollow fiber ultrafiltration membrane has an asymmetric sponge-like pore structure, including a support layer, and an inner surface layer and an outer surface layer covered on the support layer; the preparation method comprises the following steps: heating and stirring the polyethersulfone, solvent and additive to dissolve, vacuum degassing, and standing degassing to obtain a casting solution; the casting solution is transported from the spinning kettle to the outer hole of the spinneret through a filter, and the core liquid is transported into the inner hole of the spinneret through a metering pump to obtain a hollow fiber; the hollow fiber enters the coagulation bath after passing through the air area to form; step four, the formed hollow fiber is pulled to the wire collection drum for winding and drying to obtain a hollow fiber ultrafiltration membrane. When the polyethersulfone hollow fiber ultrafiltration membrane is applied to protein purification, it has a high retention effect on protein and can obtain a high protein yield, but its pure water flux is low, which makes the polyethersulfone hollow fiber ultrafiltration membrane may take a long time to process a large amount of protein solution, and the overall filtration efficiency is relatively low. Summary of the invention

[0006] The purpose of the present invention is to provide a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane and a preparation method, so that the obtained polyethersulfone hollow fiber membrane has both high protein yield and excellent pure water flux and high filtration efficiency.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for preparing a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane comprises the following steps: (1) A casting solution is prepared by mixing polyethersulfone resin, sulfonated polyethersulfone, a pore former, polyethylene glycol and an organic solvent; a core solution is prepared by mixing a small molecule alcohol additive, water and an organic solvent; (2) extruding the casting liquid and the core liquid from the single-layer spinneret in order from the outside to the inside, immersing them in a coagulation bath through an air gap to generate primary membrane filaments, and then introducing them into a water washing tank for water washing by a guide roller, and then winding them up by a collection drum, and then soaking the collected membrane filaments in pure water to obtain a sulfonated polyethersulfone modified hollow fiber membrane; (3) Soaking the sulfonated polyethersulfone modified hollow fiber membrane in an aqueous solution of sulfomethyl water-soluble phenolic resin with a mass fraction of 1.5-3.5 wt % and a temperature of 50-55° C. for 6-12 hours, washing with pure water after soaking, and then storing in a glycerol solution.

[0008] The present invention uses sulfomethyl water-soluble phenolic resin aqueous solution to soak the membrane to graft negative charges, so that the membrane has load-bearing properties, and ultimately improves the hydrophilicity of the membrane and reduces the adsorption of proteins. The purpose of using glycerol aqueous solution for storage is to keep the average pore size of the membrane unchanged.

[0009] Preferably, in step (1), the casting solution comprises the following components in weight percentage: 12-16 wt% of polyethersulfone resin, 0.8-1.3 wt% of sulfonated polyethersulfone, 11-13 wt% of pore former, 9-12 wt% of polyethylene glycol, and the balance is an organic solvent; the core liquid comprises the following components in weight percentage: 9-12 wt% of small molecule alcohol additive, 28-33 wt% of water, and the balance is an organic solvent.

[0010] Preferably, in step (1), the method for preparing the casting solution comprises the following steps: stirring, mixing and dissolving polyethersulfone resin, sulfonated polyethersulfone, pore-forming agent, polyethylene glycol and organic solvent at 75-85° C. for 10-15 hours, and then vacuum degassing to obtain the casting solution.

[0011] Preferably, in step (2), the temperatures of the casting liquid and the core liquid are 45-55°C; the height of the air gap is 200-250 mm, and the relative humidity of the air gap is 65-70%; the temperature of the coagulation bath is 75-85°C; the temperature of the water washing is 70-75°C; the speed of the membrane winding is 15-25 m / min; the temperature of the pure water immersion is 55-65°C, and the time is 20-30 h.

[0012] The present invention reasonably controls the components of the casting solution and optimizes and controls various process parameters in the wet spinning process, so that the obtained sulfonated polyethersulfone modified hollow fiber membrane with a variable diameter pore structure includes a dense layer and a microporous layer from the inside to the outside.

[0013] Preferably, in step (3), the method for preparing the aqueous solution of sulfomethyl water-soluble phenolic resin comprises the following steps: S1. preparing a sulfomethylating agent using formaldehyde aqueous solution, sodium bisulfite and deionized water as raw materials; S2, add phenol to the reactor, heat and melt, add sodium hydroxide aqueous solution, and heat to 70-75 ° C, then simultaneously add sulfomethylating agent and formaldehyde aqueous solution, after the dropwise addition is complete, continue isothermal reaction for 30-60 min, then heat to 85-90 ° C isothermal reaction for 2-3 h, and cool to room temperature to obtain sulfomethyl water-soluble phenolic resin; S3, adding the sulfomethyl water-soluble phenolic resin into deionized water, heating to 50-55° C., and preparing a sulfomethyl water-soluble phenolic resin aqueous solution with a mass fraction of 1.5-3.5wt% after fully dissolving.

[0014] Preferably, in step S1, the mass ratio of the sodium bisulfite to the deionized water is 1:1-1.2; the molar ratio of formaldehyde to sodium bisulfite in the formaldehyde aqueous solution is 1.1-1.2:1; In step S2, the amount of the sulfomethylating agent added is 15-20% of the mass of phenol, the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution used is 1:2-2.1; the molar concentration of the sodium hydroxide aqueous solution is 8-10 mol / L, and the molar ratio of sodium hydroxide to phenol in the sodium hydroxide aqueous solution used is 0.23-0.25:1.

[0015] Preferably, the weight average molecular weight of the polyethersulfone resin is 60,000 to 90,000; the weight average molecular weight of the sulfonated polyethersulfone is 60,000 to 90,000; The pore-forming agent is at least one of polyvinyl pyrrolidone K30, polyvinyl pyrrolidone K60, polyvinyl pyrrolidone K90, polyvinyl alcohol and LiCl; The polyethylene glycol is at least one of polyethylene glycol 200 and polyethylene glycol 400; The small molecule alcohol additive is at least one of ethylene glycol, propylene glycol, n-butanol, diethylene glycol, and triethylene glycol; The organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N-methylpyrrolidone and .

[0016] As a general inventive concept, the present invention provides a charge-modified polyethersulfone hollow fiber membrane with a variable pore structure prepared by the above-mentioned preparation method.

[0017] Preferably, the charged modified variable pore structure polyethersulfone hollow fiber membrane comprises a dense layer and a microporous layer from the inside to the outside; the average pore size of the dense layer is 0.005~0.02μm, the thickness of the dense layer is 20~50μm, and the porosity is 40~60%; the average pore size of the microporous layer is 0.1~0.4μm, the thickness of the microporous layer is 40~80μm, and the porosity is 60~80%.

[0018] Preferably, the structures of the dense layer and the microporous layer are both sponge pore structures.

[0019] The beneficial effects of the present invention are: (1) After the polyethersulfone membrane is sulfonated and modified in the present invention, the hydrophilicity of the membrane is enhanced. On this basis, the polyethersulfone hollow fiber membrane is further modified by using a negatively charged sulfomethyl water-soluble phenolic resin, so that the negative charge loaded on the polyethersulfone hollow fiber membrane is increased, thereby improving the performance of the membrane. When purifying negatively charged proteins, since both the polyethersulfone hollow fiber membrane and the protein are negatively charged, the two repel each other, thereby reducing the adsorption of the membrane to the protein and improving the product yield. At the same time, the polyethersulfone hollow fiber membrane prepared by the method of the present invention also has excellent pure water flux, so the overall filtration efficiency is high.

[0020] (2) The cross-section of the hollow fiber membrane prepared by the present invention has a gradient change in average pore size from the inside to the outside, including a microporous layer with a larger average pore size and a dense layer with a smaller average pore size. When the hollow fiber membrane is used for protein purification, the dense layer is near the inner surface of the cross-section, and the microporous layer is near the outer surface. This structure can effectively ensure the yield of the target protein and increase the loading capacity. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the following examples and comparative examples, the weight average molecular weight of the polyethersulfone (PES) resin used is 66000. The weight average molecular weight of the sulfonated polyethersulfone is 80000.

[0023] Embodiment 1: A method for preparing a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane comprises the following steps: (1) Stirring and dissolving polyethersulfone resin, sulfonated polyethersulfone, polyvinyl pyrrolidone K30, polyethylene glycol 400, and N-methyl pyrrolidone at 80° C. for 12 hours, and then vacuum degassing for 12 hours to obtain the casting solution; the casting solution comprises the following components in weight percentage: polyethersulfone resin 13wt%, sulfonated polyethersulfone 1.1wt%, polyvinyl pyrrolidone K30 11.5wt%, polyethylene glycol 400 11wt%, and the balance N-methyl pyrrolidone; Ethylene glycol, water and N-methylpyrrolidone are stirred uniformly at room temperature to obtain a core liquid; the core liquid comprises the following components in weight percentage: 10wt% ethylene glycol, 30wt% water and the balance N-methylpyrrolidone.

[0024] (2) Under a pressure of 0.1 MPa, the casting liquid and the core liquid at a temperature of 50°C were extruded from a single-layer spinneret in order from the outside to the inside, and immersed in a coagulation bath at 80°C through an air gap with a height of 200 mm and a relative humidity of 67% to generate primary membrane filaments, which were then introduced into a water washing tank by a guide roller and washed with water at 75°C. The membrane filaments were then wound up by a winding drum at a speed of 25 m / min, and the collected membrane filaments were then immersed in pure water at 60°C for 25 h to obtain sulfonated polyethersulfone modified hollow fiber membranes.

[0025] (3) The sulfonated polyethersulfone modified hollow fiber membrane is immersed in a 3 wt % sulfomethyl water-soluble phenolic resin aqueous solution at a temperature of 50° C. for 10 h. After the immersion, it is washed with pure water and then stored in a glycerol solution for later use.

[0026] Wherein, the preparation method of sulfomethyl water-soluble phenolic resin aqueous solution comprises the following steps: S1, firstly mix sodium bisulfite and deionized water in a mass ratio of 1:1, then heat to 50°C, dropwise add formaldehyde aqueous solution, the molar ratio of formaldehyde to sodium bisulfite used is 1.2:1; after the dropwise addition is completed, react at a constant temperature for 5 hours to obtain the sulfomethylating agent; S2, add phenol to the reactor, heat and melt, add sodium hydroxide aqueous solution, the molar concentration of the sodium hydroxide aqueous solution is 8 mol / L, and the molar ratio of sodium hydroxide to phenol in the sodium hydroxide aqueous solution is 0.25:1; heat to 75°C, and then simultaneously add formaldehyde aqueous solution and 15% sulfomethylating agent by mass of phenol, the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution used is 1:2; after the addition is complete, continue the isothermal reaction for 30 minutes, then heat to 90°C and react at this temperature for 2 hours, and cool to room temperature to obtain sulfomethyl water-soluble phenolic resin; S3. Add sulfomethyl water-soluble phenolic resin into deionized water, raise the temperature to 50° C., and after fully dissolving, prepare a sulfomethyl water-soluble phenolic resin aqueous solution with a mass fraction of 3 wt%.

[0027] The charged modified variable pore structure polyethersulfone hollow fiber membrane prepared in this embodiment includes a dense layer and a microporous layer from the inside to the outside; after testing, the average pore size of the dense layer is 0.012μm, the thickness of the dense layer is 32μm, and the porosity is 45%; the average pore size of the microporous layer is 0.2μm, the thickness of the microporous layer is 60μm, and the porosity is 68%; the structures of the dense layer and the microporous layer are both sponge pore structures.

[0028] Embodiment 2: A method for preparing a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane comprises the following steps: (1) A polyethersulfone resin, a sulfonated polyethersulfone, a polyvinyl pyrrolidone K60, a polyethylene glycol 400, and a N-methylpyrrolidone are stirred and mixed and dissolved at 80° C. The stirring and mixing dissolution time is 12 hours, and then vacuum degassing is performed for 12 hours to obtain a casting solution; the casting solution comprises the following components in weight percentage: a polyethersulfone resin of 12wt%, a sulfonated polyethersulfone of 1wt%, a polyvinyl pyrrolidone K60 of 11.5wt%, a polyethylene glycol 400 of 12wt%, and the balance of N-methylpyrrolidone; Ethylene glycol, water and N-methylpyrrolidone are mixed and stirred at room temperature to obtain a core liquid; the core liquid comprises the following components in weight percentage: 12wt% ethylene glycol, 30wt% water, and the balance N-methylpyrrolidone.

[0029] (2) Under a pressure of 0.1 MPa, the casting liquid and the core liquid at a temperature of 55°C were extruded from a single-layer spinneret in order from the outside to the inside, and immersed in a coagulation bath at 85°C through an air gap with a height of 250 mm and a relative humidity of 70% to generate primary membrane filaments, which were then introduced into a water washing tank by a guide roller and washed with water at 75°C. The membrane filaments were then wound up by a winding drum at a speed of 20 m / min, and the collected membrane filaments were then immersed in pure water at 60°C for 30 h to obtain sulfonated polyethersulfone modified hollow fiber membranes.

[0030] (3) The sulfonated polyethersulfone modified hollow fiber membrane is immersed in a 2.5 wt% sulfomethyl water-soluble phenolic resin aqueous solution at a temperature of 52° C. for 10 h. After the immersion, it is washed with pure water and then stored in a glycerol solution for later use.

[0031] Wherein, the preparation method of sulfomethyl water-soluble phenolic resin aqueous solution comprises the following steps: S1, firstly mix sodium bisulfite and deionized water in a mass ratio of 1:1.2, then heat to 50°C, dropwise add formaldehyde aqueous solution, the molar ratio of formaldehyde to sodium bisulfite used is 1.1:1; after the dropwise addition is completed, the reaction is continued at a constant temperature for 5 hours to obtain the sulfomethylating agent; S2, add phenol to the reactor, heat and melt, add sodium hydroxide aqueous solution, the molar concentration of the sodium hydroxide aqueous solution is 10 mol / L, and the molar ratio of sodium hydroxide to phenol in the sodium hydroxide aqueous solution is 0.23:1; heat to 70 ° C, and then dropwise add formaldehyde aqueous solution and 20% sulfomethylating agent of phenol mass, the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution is 1:2.1; after the addition is completed, continue the isothermal reaction for 60 minutes, then heat to 85 ° C and react at this temperature for 3 hours, and cool to room temperature to obtain sulfomethyl water-soluble phenolic resin; S3. Add sulfomethyl water-soluble phenolic resin to deionized water, raise the temperature to 55° C., and after fully dissolving, prepare a sulfomethyl water-soluble phenolic resin aqueous solution with a mass fraction of 2.5 wt%.

[0032] Embodiment 3: A method for preparing a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane comprises the following steps: (1) A polyethersulfone resin, a sulfonated polyethersulfone, a polyvinyl pyrrolidone K30, a polyethylene glycol 200, and a N-methylpyrrolidone are stirred and mixed to dissolve at 75° C. The stirring and mixing dissolving time is 10 hours, and then vacuum degassing is performed for 12 hours to obtain a casting solution; the casting solution comprises the following components in weight percentage: a polyethersulfone resin of 16wt%, a sulfonated polyethersulfone of 1.3wt%, a polyvinyl pyrrolidone K30 of 11wt%, a polyethylene glycol 200 of 10wt%, and the balance of N-methylpyrrolidone; Ethylene glycol, water and N-methylpyrrolidone are stirred uniformly at room temperature to obtain a core liquid; the core liquid comprises the following components in weight percentage: 9wt% ethylene glycol, 28wt% water and the balance N-methylpyrrolidone.

[0033] (2) Under a pressure of 0.1 MPa, the casting liquid and the core liquid at a temperature of 45°C were extruded from a single-layer spinneret in order from the outside to the inside, and immersed in a coagulation bath at 75°C through an air gap with a height of 250 mm and a relative humidity of 65% to generate primary membrane filaments, which were then introduced into a water washing tank by a guide roller and washed with water at 70°C. The membrane filaments were then wound up by a winding drum at a speed of 15 m / min, and then the collected membrane filaments were immersed in pure water at 55°C for 20 h to obtain sulfonated polyethersulfone modified hollow fiber membranes.

[0034] (3) The sulfonated polyethersulfone modified hollow fiber membrane is immersed in a 1.5 wt% sulfomethyl water-soluble phenolic resin aqueous solution at a temperature of 50° C. for 12 hours. After the immersion, it is washed with pure water and then stored in a glycerol solution for later use.

[0035] Wherein, the preparation method of the sulfomethyl water-soluble phenolic resin aqueous solution is referred to Example 1.

[0036] Embodiment 4: A method for preparing a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane comprises the following steps: (1) A polyethersulfone resin, a sulfonated polyethersulfone, a polyvinyl pyrrolidone K60, a polyethylene glycol 200, and a N-methylpyrrolidone are stirred and mixed and dissolved at 85° C. The stirring and mixing dissolution time is 15 hours, and then vacuum degassing is performed for 12 hours to obtain a casting solution; the casting solution comprises the following components in weight percentage: a polyethersulfone resin of 15wt%, a sulfonated polyethersulfone of 0.8wt%, a pore former of 13wt%, a polyethylene glycol 200 of 9wt%, and the balance of N-methylpyrrolidone; Ethylene glycol, water and N-methylpyrrolidone are stirred uniformly at room temperature to obtain a core liquid; the core liquid comprises the following components in weight percentage: 10wt% ethylene glycol, 33wt% water and the balance N-methylpyrrolidone.

[0037] (2) Under a pressure of 0.1 MPa, the casting liquid and the core liquid at a temperature of 50 °C were extruded from a single-layer spinneret in order from the outside to the inside, and immersed in a coagulation bath at 80 °C through an air gap with a height of 200 mm and a relative humidity of 65% to generate primary membrane filaments, which were then introduced into a water washing tank by a guide roller and washed with water at 75 °C. The membrane filaments were then wound up by a winding drum at a speed of 25 m / min, and the collected membrane filaments were then immersed in pure water at 65 °C for 25 h to obtain sulfonated polyethersulfone modified hollow fiber membranes.

[0038] (3) The sulfonated polyethersulfone modified hollow fiber membrane is immersed in a 3.5 wt% sulfomethyl water-soluble phenolic resin aqueous solution at a temperature of 55° C. for 6 hours. After the immersion, it is washed with pure water and then stored in a glycerol solution for later use.

[0039] Wherein, the preparation method of the sulfomethyl water-soluble phenolic resin aqueous solution is referred to Example 2.

[0040] Comparative Example 1: The difference from Example 1 is that the casting solution includes the following components in weight percentage: 14.1wt% polyethersulfone resin, 11.5wt% polyvinylpyrrolidone K30, 11wt% polyethylene glycol 400, and the balance is N-methylpyrrolidone. Step (3) is not performed. The remaining process steps are basically the same as those in Example 1.

[0041] Comparative Example 2: The difference from Example 1 is that step (3) is not performed. The remaining process steps are basically the same as those in Example 1.

[0042] Comparative Example 3: The difference from Example 1 is that the casting solution includes the following components in weight percentage: 14.1wt% polyethersulfone resin, 11.5wt% polyvinylpyrrolidone K30, 11wt% polyethylene glycol 400, and the balance is N-methylpyrrolidone. The remaining process steps are basically the same as those in Example 1.

[0043] Data detection: The pure water flux, protein yield, water contact angle, and pure water flux recovery rate after protein filtration of the polyethersulfone hollow fiber membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested. The specific test results are shown in Table 1.

[0044] Table 1: Pure water flux (LMH) Protein yield (%) Water contact angle (°) Pure water flux recovery rate after protein filtration (%) Example 1 770 97 61 95 Example 2 750 98 62 95 Example 3 830 99 57 97 Example 4 800 97 54 96 Comparative Example 1 350 80 95 68 Comparative Example 2 610 89 77 85 Comparative Example 3 560 82 82 80 As shown in Table 1, after modification with sulfonated polyethersulfone and sulfomethyl water-soluble phenolic resin aqueous solution, the pure water flux of the obtained polyethersulfone hollow fiber membrane is greatly improved, the hydrophilicity is improved, and the protein yield and the pure water flux recovery rate after protein filtration are significantly improved.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane, characterized in that: The following steps are involved: (1) A casting solution is prepared by mixing polyethersulfone resin, sulfonated polyethersulfone, a pore former, polyethylene glycol and an organic solvent; a core solution is prepared by mixing a small molecule alcohol additive, water and an organic solvent; (2) extruding the casting liquid and the core liquid from the single-layer spinneret in order from the outside to the inside, immersing them in a coagulation bath through an air gap to generate primary membrane filaments, and then introducing them into a water washing tank for water washing by a guide roller, and then winding them up by a collection drum, and then soaking the collected membrane filaments in pure water to obtain a sulfonated polyethersulfone modified hollow fiber membrane; (3) Soaking the sulfonated polyethersulfone modified hollow fiber membrane in an aqueous solution of sulfomethyl water-soluble phenolic resin with a mass fraction of 1.5-3.5 wt % and a temperature of 50-55° C. for 6-12 hours, washing with pure water after soaking, and then storing in a glycerol solution.

2. The preparation method according to claim 1, characterized in that In step (1), the casting solution comprises the following components in weight percentage: 12-16 wt% of polyethersulfone resin, 0.8-1.3 wt% of sulfonated polyethersulfone, 11-13 wt% of pore former, 9-12 wt% of polyethylene glycol, and the balance is an organic solvent; the core liquid comprises the following components in weight percentage: 9-12 wt% of small molecule alcohol additive, 28-33 wt% of water, and the balance is an organic solvent.

3. The preparation method according to claim 1, characterized in that: In step (1), the method for preparing the casting solution comprises the following steps: stirring, mixing and dissolving polyethersulfone resin, sulfonated polyethersulfone, pore-forming agent, polyethylene glycol and organic solvent at 75-85° C. for 10-15 hours, and then vacuum degassing to obtain the casting solution.

4. The preparation method according to claim 1, characterized in that: In step (2), the temperatures of the casting liquid and the core liquid are 45-55°C; the height of the air gap is 200-250 mm, and the relative humidity of the air gap is 65-70%; the temperature of the coagulation bath is 75-85°C; the temperature of the water washing is 70-75°C; the speed of the membrane winding is 15-25 m / min; the temperature of the pure water immersion is 55-65°C, and the time is 20-30 h.

5. The preparation method according to claim 1, characterized in that: In step (3), the method for preparing the aqueous solution of sulfomethyl water-soluble phenolic resin comprises the following steps: S1. preparing a sulfomethylating agent using formaldehyde aqueous solution, sodium bisulfite and deionized water as raw materials; S2, add phenol to the reactor, heat and melt, add sodium hydroxide aqueous solution, and heat to 70-75 ° C, then simultaneously add sulfomethylating agent and formaldehyde aqueous solution, after the dropwise addition is complete, continue isothermal reaction for 30-60 min, then heat to 85-90 ° C isothermal reaction for 2-3 h, and cool to room temperature to obtain sulfomethyl water-soluble phenolic resin; S3, adding the sulfomethyl water-soluble phenolic resin into deionized water, heating to 50-55° C., and preparing a sulfomethyl water-soluble phenolic resin aqueous solution with a mass fraction of 1.5-3.5wt% after fully dissolving.

6. The preparation method according to claim 5, characterized in that: In step S1, the mass ratio of sodium bisulfite to deionized water is 1:1-1.2; the molar ratio of formaldehyde to sodium bisulfite in the formaldehyde aqueous solution is 1.1-1.2:1; In step S2, the amount of the sulfomethylating agent added is 15-20% of the mass of phenol, the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution used is 1:2-2.1; the molar concentration of the sodium hydroxide aqueous solution is 8-10 mol / L, and the molar ratio of sodium hydroxide to phenol in the sodium hydroxide aqueous solution used is 0.23-0.25:

1.

7. The preparation method according to claim 1, characterized in that: The weight average molecular weight of the polyethersulfone resin is 60,000 to 90,000; the weight average molecular weight of the sulfonated polyethersulfone is 60,000 to 90,000; The pore-forming agent is at least one of polyvinyl pyrrolidone K30, polyvinyl pyrrolidone K60, polyvinyl pyrrolidone K90, polyvinyl alcohol and LiCl; The polyethylene glycol is at least one of polyethylene glycol 200 and polyethylene glycol 400; The small molecule alcohol additive is at least one of ethylene glycol, propylene glycol, n-butanol, diethylene glycol, and triethylene glycol; The organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N-methylpyrrolidone and .

8. A charge-modified polyethersulfone hollow fiber membrane with a variable pore structure prepared by the preparation method according to any one of claims 1 to 7.

9. The charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane according to claim 8, characterized in that: The charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane comprises a dense layer and a microporous layer from the inside to the outside; the average pore size of the dense layer is 0.005-0.02 μm, the thickness of the dense layer is 20-50 μm, and the porosity is 40-60%; the average pore size of the microporous layer is 0.1-0.4 μm, the thickness of the microporous layer is 40-80 μm, and the porosity is 60-80%.

10. The charge-modified variable-diameter pore structure polyethersulfone hollow fiber membrane according to claim 9, characterized in that: The structures of the dense layer and the microporous layer are both sponge pore structures.