A small-pore high-flux ultrafiltration membrane, a preparation method and application thereof

Abstract

The application belongs to the technical field of membrane separation, and particularly relates to a small-aperture high-flux ultrafiltration membrane and a preparation method and application thereof. Polymer material, an additive and an organic solvent are mixed, constant-temperature stirring and standing defoaming are performed to obtain a casting solution, and then a non-solvent phase separation method is used to prepare the ultrafiltration membrane. The polymer material comprises polyethersulfone and sulfonated polyphenylsulfone with a mass ratio of 95:5-80:20, and the additive is polyethylene glycol. The rejection rate of the ultrafiltration membrane to bovine serum albumin (BSA) is above 99%, the rejection rate of direct red 23 and coomassie brilliant blue and other dyes can be above 96%, and the pure water permeability is 310 L·m ‑2 ·h ‑1 ·bar ‑1 , which has a wide application prospect in the fields of antibody protein purification and concentration, dye desalination and nanoscale pollutant treatment in wastewater.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and relates to a small-pore high-flux ultrafiltration membrane, its preparation method and application, particularly a small-pore high-flux ultrafiltration membrane for antibody protein purification and concentration, dye desalination and removal of nanoscale pollutants in wastewater and its preparation method. Background Technology

[0002] Compared to traditional separation and filtration technologies, membrane separation technology offers numerous advantages, including high separation efficiency, low energy consumption, no phase change, and mild operating conditions. In the biopharmaceutical field, especially in the production of large molecule biopharmaceuticals such as monoclonal antibodies, antibody concentration is a core step in downstream purification. This process requires separation and purification methods that can almost completely retain the target antibody molecules (typically 10-20 nm in size) while efficiently permeating water, salt, and even smaller impurities. Therefore, an ideal membrane must possess both extremely high selective separation precision and excellent permeation flux to ensure product activity and yield, while controlling production costs and time.

[0003] Meanwhile, in the dyeing and textile industry, the treatment and resource recovery of dye wastewater are urgent needs for sustainable development. The key technology lies in achieving efficient separation of dye molecules and inorganic salts to achieve wastewater discharge standards, dye reuse, and salt recovery. This places very similar requirements on membranes: the ability to stably maintain high flux in high-concentration, highly polluting feed solutions, while simultaneously achieving high retention of dye molecules and high permeability of salts.

[0004] Small-pore ultrafiltration membranes, with pore sizes ranging from 2 to 20 nm, effectively concentrate antibody molecules and retain dye molecules while allowing small molecules such as water and salts to pass through, maintaining high permeability. Compared to nanofiltration membranes, small-pore ultrafiltration membranes have a molecular weight cutoff (MWCO) ranging from 300 Da to 20,000 Da, effectively removing soluble pollutants from industrial wastewater while operating at lower pressures. Compared to traditional ultrafiltration membranes, small-pore ultrafiltration membranes exhibit superior retention capacity for low molecular weight compounds that traditional ultrafiltration membranes cannot effectively remove, such as textile dyes and humic compounds. These advantages make small-pore ultrafiltration membranes highly promising for development. Therefore, developing a simple-to-prepare, high-flux, small-pore ultrafiltration membrane is of great significance.

[0005] Currently, various technologies have been explored to prepare ultrafiltration membranes with both high rejection rates and high flux. For example, Chinese patent CN109847587A discloses a method for preparing a low molecular weight rejection ultrafiltration membrane. This method uses a casting solution composed of polyethersulfone, sulfonated polysulfone, and polyethylene glycol, and prepares the ultrafiltration membrane via a phase inversion method, achieving a rejection rate of over 95% for polyethylene glycol with a molecular weight of 10,000. However, the sulfonated polysulfone used in this technical solution is a common bisphenol A type polysulfone, whose molecular chain lacks a rigid biphenyl structure. This makes it difficult to form a highly ordered, close-packed structure during membrane formation, resulting in a wide pore size distribution and a lower pure water flux (the highest flux in its examples is approximately 168 L·m). -2 ·h -1 ·bar -1 Furthermore, its application is mainly aimed at the retention of low molecular weight polyethylene glycol, and does not involve the concentration of antibody proteins or the treatment of dye wastewater. It lacks targeted optimization for the specific needs of the biopharmaceutical and dyeing wastewater treatment fields (such as high BSA retention, high dye retention and high throughput).

[0006] Therefore, it is of great significance to develop a small-pore ultrafiltration membrane that is easy to prepare, can ensure high rejection rate (especially for proteins and dyes) while also having high permeation flux, and is suitable for antibody concentration and dye removal. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a small-pore-size high-flux ultrafiltration membrane, its preparation method, and its applications. The casting solution for this ultrafiltration membrane is composed of a hydrophilic polymer material, alcohol additives, and organic solvents, and is prepared in one step using a non-solvent-induced phase separation (NIPS) method. The prepared small-pore-size ultrafiltration membrane achieves a retention rate of over 99% for bovine serum albumin (BSA) and over 96% for dyes with a molecular weight of over 800 Da, while maintaining an inorganic salt retention rate of less than 7% and a pure water permeability as high as 310 L·m⁻¹. -2 ·h -1 ·bar -1 It exhibits excellent performance in antibody and protein purification and concentration, dye desalination, and the treatment of nanoscale pollutants in wastewater.

[0008] The specific technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a small-pore-size high-flux ultrafiltration membrane, comprising the following steps: (1) The polymer material, additives and organic solvent are mixed and stirred at a constant temperature to obtain a uniform mixed solution. After stirring is stopped, the mixture is heated and allowed to stand to remove bubbles to obtain a casting solution. The polymer material accounts for 15-25 wt% of the casting solution by weight, and the organic solvent and additives together account for 75-85 wt% of the casting solution by weight, with a total weight of 100 wt%. The polymer material includes polyethersulfone (PES) and sulfonated polyphenylene sulfone (SPPSU) in a mass ratio of 95:5-80:20. (2) A small-pore-size high-flux ultrafiltration membrane was prepared by using the non-solvent induced phase separation method (NIPS) to prepare the casting solution.

[0009] Furthermore, the degree of sulfonation of the sulfonated polyphenylsulfone is 10%-30%.

[0010] Furthermore, the polymer material accounts for 21 wt% of the casting solution by weight, and the solvent and additives together account for 79 wt% of the casting solution by weight, for a total of 100 wt%.

[0011] Further, let it stand to remove bubbles for 40-60 minutes.

[0012] Further, step (2) specifically involves: wiping the glass plate clean, using a film scraper to spread the casting solution evenly and at a uniform speed on the glass plate, then quickly immersing the glass plate in a constant-temperature coagulation bath, waiting for the phase transformation process to form a membrane, and then storing the membrane at room temperature in deionized water to obtain an ultrafiltration membrane. The coagulation bath is deionized water, and the temperature of the coagulation bath is controlled at 25 ± 1℃.

[0013] Further, the polyethylene glycol accounts for 2-12 wt% of the casting solution. The additive is polyethylene glycol with a molecular weight of 200-4000. Polyethylene glycol is hydrophilic, which is beneficial for controlling the membrane structure and improving membrane performance, enabling the ultrafiltration membrane to maintain high target filtrate retention while improving pure water permeability. Polyethylene glycol-400 (PEG-400) is further preferred.

[0014] Furthermore, the organic solvent is one or more of dimethylformamide, dimethyl sulfoxide, dimethylacetamide, and N-methylpyrrolidone (NMP).

[0015] Furthermore, the temperature of the constant-temperature stirring is 60℃-80℃, and the stirring time is 6-9 h.

[0016] A second aspect of the present invention provides a small-pore-size high-flux ultrafiltration membrane obtained by the above preparation method.

[0017] The third aspect of this invention provides the application of a small-pore-size high-flux ultrafiltration membrane in antibody protein purification and concentration, dye desalting, and removal of nanoscale pollutants from wastewater.

[0018] Advantages and beneficial effects of the present invention: 1. This invention modifies PES ultrafiltration membranes by adding the hydrophilic polymer sulfonated polyphenylene sulfone (SPPSU) and the hydrophilic additive polyethylene glycol to the casting solution. In non-solvent-induced phase separation (NIPS) processes, it is difficult to prepare ultrafiltration membranes with antifouling properties, small pore size, and compact structure using a single PES casting solution. Therefore, this invention introduces SPPSU. The SPPSU molecular structure contains a biphenyl conjugated structure with two linked benzene rings in its main chain. Compared with other polysulfones, the biphenyl groups tend to be closely arranged during membrane formation, resulting in a more ordered molecular chain arrangement of SPPSU, leading to small pore size (average pore size (diameter) range of 3.0-8.0 nm) and narrow distribution. Simultaneously, the hydroxyl groups (-OH) in the polyethylene glycol molecule and the sulfonic acid groups (-SO3) in the SPPSU molecular structure... - Hydrogen bonds exist between PES and SPPSU polymer chains, which restrict the migration of these chains, causing delayed phase separation during the phase inversion process and inhibiting the formation of large pores. The hydrophilic sulfonic acid groups (-SO3) - The presence of ) can also improve the hydrophilicity of the ultrafiltration membrane surface, which is beneficial for obtaining high-flux small-pore ultrafiltration membranes.

[0019] 2. This invention can be applied to antibody protein purification and concentration, dye desalting, and the removal of nanoscale pollutants from wastewater. The polymers and additives used are inexpensive, safe, and non-toxic. It achieves a retention rate of over 99% for bovine serum albumin (BSA) and over 96% for dyes such as Direct Red 23 and Coomassie Brilliant Blue. Simultaneously, the pure water flux reaches 310 L·m³. -2 ·h -1 ·bar -1 It shows excellent application prospects in antibody protein purification and concentration, dye desalting, and removal of nanoscale pollutants in wastewater.

[0020] 3. The preparation process of this invention is efficient and easy to operate, and has excellent scale-up effect and promotion potential, which can quickly realize industrial mass production. Attached Figure Description

[0021] Figure 1 The charge characteristic curves are for small-pore ultrafiltration membranes prepared by blending different mass ratios of PES and SPPSU in Examples 1-3 and Comparative Example 1.

[0022] Figure 2 The retention performance curve and pore size distribution curve of the ultrafiltration membrane prepared for Comparative Example 1 are shown, where A corresponds to the retention performance curve and B corresponds to the pore size distribution curve.

[0023] Figure 3The curves show the retention performance and pore size distribution of the ultrafiltration membrane prepared in Example 2, where A corresponds to the retention performance curve and B corresponds to the pore size distribution curve.

[0024] Figure 4 The curves show the retention performance and pore size distribution of the ultrafiltration membrane prepared in Example 3, where A corresponds to the retention performance curve and B corresponds to the pore size distribution curve. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments. The following description is for illustrative purposes only and does not limit the scope of the invention.

[0026] Example 1 A method for preparing a small-pore-size high-flux ultrafiltration membrane, comprising the following steps: (1) Polyethylene glycol-400 (PEG-400) additive was dissolved in NMP organic solvent at 70°C. After stirring at 70°C for 0.5 h, polymer material was added. The polymer material contained PES and SPPSU (sulfonated polyphenylene sulfone) in a mass ratio of 90:10, the degree of sulfonation of SPPSU was 20%, the polymer material accounted for 21 wt% of the casting solution by weight, PEG-400 accounted for 4 wt% of the casting solution by weight, and the total amount of polymer material, additive and organic solvent was 100 wt%. The mixture was stirred at 70°C for 8 h. After stirring was stopped, the mixture was heated at 70°C and allowed to stand for 60 min to remove bubbles, thus obtaining a homogeneous casting solution. (2) Clean the glass plate with deionized water in advance to ensure that it is dry and free of water droplets. Then, use a 250μm thick film scraper to spread the casting solution evenly and uniformly on the glass plate. Then quickly immerse it in a pre-prepared deionized water coagulation bath with the temperature controlled at 25℃. After the phase transformation process is completed and the film is formed, transfer it to another clean deionized water coagulation bath and soak it for at least 24 hours to remove residual solvent and obtain an ultrafiltration membrane, which can be used as a test sample.

[0027] Example 2 A method for preparing a small-pore-size high-flux ultrafiltration membrane is provided. The preparation steps are the same as in Example 1, except that the mass ratio of PES to SPPSU in the polymer material is 88:12.

[0028] Example 3 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as those in Example 1, the only difference being that the mass ratio of PES to SPPSU in the polymer material is 86:14.

[0029] Example 4 A method for preparing a small-pore-size high-flux ultrafiltration membrane is provided. The preparation steps are the same as in Example 2, except that the degree of sulfonation of the SPPSU (sulfonated polyphenylene sulfone) used is 10%.

[0030] Example 5 A method for preparing a small-pore-size high-flux ultrafiltration membrane is provided. The preparation steps are the same as in Example 2, except that the degree of sulfonation of the SPPSU (sulfonated polyphenylene sulfone) used is 15%.

[0031] Example 6 A method for preparing a small-pore-size high-flux ultrafiltration membrane is provided. The preparation steps are the same as in Example 2, except that the degree of sulfonation of the SPPSU (sulfonated polyphenylene sulfone) used is 30%.

[0032] Comparative Example 1 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as those in Example 1, the only difference being that the mass ratio of PES to SPPSU in the polymer material is 100:0.

[0033] Comparative Example 2 A method for preparing a small-pore-size high-flux ultrafiltration membrane is described. The preparation steps are the same as in Example 2, except that step (1) does not contain PEG-400. After stirring in NMP organic solvent at 70°C for 0.5 h, polymer material is added. The polymer material contains PES and SPPSU (sulfonated polyphenylene sulfone) in a mass ratio of 88:12, the degree of sulfonation of SPPSU is 20 wt%, the polymer material accounts for 21 wt% of the casting solution by weight, PEG-400 accounts for 0 wt% of the casting solution by weight, and the total amount of polymer material, additives, and organic solvent is 100 wt%. The mixture is stirred continuously at 70°C for 8 h. After stirring is stopped, the temperature is maintained at 70°C, and the mixture is allowed to stand for 60 min to remove air bubbles, thereby obtaining a homogeneous casting solution.

[0034] Example 7 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as in Example 2, the only difference being that the content of PEG-400 is 2 wt%.

[0035] Example 8 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as those in Example 2, the only difference being that the content of PEG-400 is 3 wt%.

[0036] Example 9 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as in Example 2, the only difference being that the content of PEG-400 is 5 wt%.

[0037] Example 10 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as in Example 2, the only difference being that the content of PEG-400 is 6 wt%.

[0038] Example 11 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as in Example 2, the only difference being that the content of PEG-400 is 8 wt%.

[0039] Example 12 A method for preparing a small-pore-size high-flux ultrafiltration membrane, the preparation method steps are the same as in Example 2, the only difference being that the content of PEG-400 is 12 wt%.

[0040] Comparative Example 3 The complete formulation and process of Example 2 of this application are used, but SPPSU is replaced with ordinary sulfonated polysulfone (SPSf, bisphenol A type, sulfonation degree 20%) used in patent CN109847587A.

[0041] Comparative Example 4 Using the complete formulation and process of Example 2 of this application, PEG-400 is replaced with PEG-800 used in patent CN109847587A.

[0042] Comparative Example 5 The formulation and process are completely based on Example 1 of patent CN109847587A, except that ordinary SPSf is replaced with SPPSU (20% sulfonation) of this application.

[0043] The separation performance of the ultrafiltration membranes prepared in Examples 1-12 and Comparative Examples 1-5 was tested using a membrane performance evaluation instrument. The test conditions were: room temperature; feed pressure 1 bar; inorganic salt concentration: 1 g / L; dye concentration: 0.1 g / L; bovine serum albumin concentration: 1 g / L.

[0044] Table 1. Separation performance test results of the ultrafiltration membranes prepared in Examples 1-6.

[0045] As shown in Table 1, Comparative Example 1 and Examples 1-3 illustrate the effect of polymer blending ratio on ultrafiltration membrane performance. Comparative Example 1 and Examples 1-3 are ultrafiltration membranes blended with different mass ratios of PES and SPPSU, numbered Control, M-10S, M-12S, and M-14S respectively. The retention rates of bovine serum albumin (BSA) in Comparative Example 1 and Examples 1-3 are all above 99%. Compared to Comparative Example 1, Examples 1-3 show significant improvements in dye retention rates and pure water flux. In particular, Example 2, prepared with a PES:SPPSU mass ratio of 88:12, exhibits a small-pore, high-flux ultrafiltration membrane with a retention rate of over 96% for Direct Red 23 and Coomassie Brilliant Blue dyes, a retention rate of over 99% for BSA, and a pure water permeability of 310.53 L·m⁻¹. -2 ·h -1 ·bar -1 This demonstrates that introducing the hydrophilic polymer sulfonated polyphenylsulfone into the casting solution can improve the hydrophilicity and membrane structure of the ultrafiltration membrane, while simultaneously increasing the sulfonic acid groups (-SO3) - The presence of [agents] also enhances the negative charge on the ultrafiltration membrane surface, which is beneficial for strengthening the repulsion of dye molecules on the membrane surface. By ensuring a bovine serum albumin rejection rate of over 99%, a dye rejection rate of over 96%, and an inorganic rejection rate of less than 7%, the permeation performance of the ultrafiltration membrane is maintained at a high level.

[0046] As shown in Table 1, Examples 2 and 4-6 above illustrate the effect of different degrees of sulfonation of polyphenylene sulfone (SPPSU) on the performance of ultrafiltration membranes. It can be seen that with the increase of SPPSU sulfonation degree, the prepared ultrafiltration membrane exhibits higher retention rates for bovine serum albumin and both dyes. The large number of sulfonic acid groups present on the membrane surface and in the pores increases the membrane's hydrophilicity and water flux. However, when the sulfonation degree reaches 30%, with the continuous exchange between solvent and non-solvent, severe gelation occurs after phase inversion, the polymer chain structure cannot completely detach from the solvent, resulting in an imperfect pore structure and a decrease in water flux. Compared to Examples 4-6, the ultrafiltration membrane prepared in Example 2 maintains a high level of pure water permeability while retaining high dye and antibody protein retention and low inorganic salt retention.

[0047] The charge properties of the ultrafiltration membranes prepared in Comparative Example 1 and Examples 1-3 are as follows: Figure 1 As shown, the electronegativity of the ultrafiltration membrane surface gradually increases with the increase of the sulfonated polyphenylene sulfone (SPPSU) ratio. This is because with the increase of the SPPSU ratio, more SPPSU migrates to the membrane surface during phase separation, forming a dense skin layer, and the sulfonic acid groups (-SO3) on the membrane surface... - The increased content of ) enhances the negative charge on the surface of the ultrafiltration membrane.

[0048] The retention performance curves and pore size distribution curves of the ultrafiltration membranes prepared in Comparative Examples 1, 2, and 3 are shown below. Figure 2-4 As shown. A cross-flow filtration device was used to measure the membrane's response to PEO solutions (100 mg) of different molecular weights (40, 100, 300, 400, 500 kDa). L -1 The retention performance of the membrane was assessed, and the pore size, pore size distribution, and molecular weight cutoff (MWCO) were calculated. Compared with ultrafiltration membranes prepared by adding only polyethersulfone (SPPSU), the ultrafiltration membrane prepared by adding sulfonated polyphenylsulfone (SPPSU) had a smaller pore size. This is because the SPPSU molecular structure contains a conjugated structure of biphenyl groups in its main chain. During membrane formation, the biphenyl groups tend to be closely packed, resulting in a more ordered arrangement of SPPSU molecular chains, leading to smaller pore sizes and a narrower distribution range, which is beneficial for preparing small-pore ultrafiltration membranes.

[0049] Table 2. Results of test on the effect of PEG-400 content on the separation performance of ultrafiltration membranes.

[0050] Table 2 shows the effect of PEG-400 additive on the performance of polyethersulfone / sulfonated polyphenylsulfone ultrafiltration membranes. The addition of the additive helps control the membrane structure and improve the membrane's permeability. As can be seen from Examples 2 and 7-12, compared with the membrane without PEG-400, the ultrafiltration membrane with added PEG-400 showed improved retention of various dyes, while the retention of bovine serum albumin remained largely unchanged; the pure water permeability decreased, and the overall trend of pure water flux was first decreasing, then increasing, and then decreasing again. This is because the hydroxyl groups (-OH) in the PEG-400 molecule and the sulfonic acid groups (-SO3) in the SPPSU molecule... - Hydrogen bonds exist between the polymer chains, enhancing their interaction and entanglement, leading to delayed phase separation during phase inversion and inhibiting the formation of large pores, thus reducing membrane flux. PEG-400, a hydrophilic additive, exhibits hydrogen bonding with sulfonic acid groups as its content increases, while another portion acts as a pore-forming agent, accelerating phase separation and increasing the pure water flux. However, excessive PEG-400 significantly affects the viscosity of the casting solution, prioritizing its role in slowing phase separation. This results in a denser membrane layer and thicker membrane, increasing mass transfer resistance and reducing pure water flux. This indicates that adding an appropriate amount of PEG-400 can improve the permeation performance of ultrafiltration membranes while achieving high antibody and dye rejection rates.

[0051] Table 3. Separation performance test results of the ultrafiltration membranes prepared in the comparative example.

[0052] Table 3 shows the test results of the comparative experiment. The pure water flux and dye rejection rate of Comparative Example 3 are lower than those of Example 2 (310.53 L·m). -2 ·h -1 ·bar -1 The results, along with the dye rejection rate (over 96%), demonstrate that even if the formulation and process of this application are completely replicated, simply replacing SPPSU with the ordinary SPSf used in patent CN109847587A results in a significant performance decrease. This indicates that the core breakthrough of this application lies not in selecting a specific ratio, but in identifying and selecting SPPSU, a specific polymer material with a biphenyl structure. The strength of the hydrogen bonding between PEG-400 and SPPSU varies with molecular weight; in Comparative Example 4, the pure water flux decreased to 276.45 L·m. -2 ·h -1 ·bar -1 This demonstrates that there is an optimal hydrogen bonding synergistic effect (regulating phase separation kinetics) between the PEG-400 selected in this application and SPPSU. Not all molecular weights of polyethylene glycol can achieve optimal performance with SPPSU. The pure water flux of Comparative Example 5 was 87.78 L·m⁻¹. -2 ·h -1 ·bar -1 The BSA rejection rate was 99.79%. Comparative Example 5 demonstrates that simply replacing SPSf with SPPSU without changing other conditions cannot achieve the high throughput of this application. This indicates that SPPSU itself cannot enable ultrafiltration membranes to achieve high throughput; high throughput requires SPPSU to be compatible with the specific system described in this application.

[0053] As can be seen from Examples 1-12 and Comparative Examples 1-5, small-pore high-flux ultrafiltration membranes can be prepared by adjusting the blending ratio of PES and SPPSU, the degree of SPPSU sulfonation, and the hydrophilic additive PEG-400 in the polymer material. The small-pore high-flux ultrafiltration membrane of this invention can be used for antibody protein purification and concentration, dye desalination, and the removal of nanoscale pollutants from wastewater. This method is simple to operate, requires no additional steps, and can effectively regulate the membrane performance and structure, thereby preparing small-pore ultrafiltration membranes with high separation efficiency.

[0054] Although the description of the invention has been quite detailed and particularly of several described embodiments, it is not intended to limit it to any of these details or embodiments or any particular embodiment, but should be considered as providing a broad possible interpretation of the claims by referring to the appended claims and taking into account the prior art, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

Claims

1. A method for preparing a small-pore-size, high-flux ultrafiltration membrane, characterized in that: Includes the following steps: (1) The polymer material, additives, and organic solvent are mixed and stirred at a constant temperature to obtain a uniform mixed solution. After stirring is stopped, the mixture is heated and allowed to stand to remove bubbles, thus obtaining a casting solution. The polymer material accounts for 15-25 wt% of the casting solution by weight, and the organic solvent and additives together account for 75-85 wt% of the casting solution by weight, with a total weight of 100 wt%. The polymer material includes polyethersulfone and sulfonated polyphenylsulfone in a mass ratio of 95:5-80:

20. The additive is polyethylene glycol. (2) A small-pore-size high-flux ultrafiltration membrane was prepared by using a non-solvent phase separation method to prepare the casting solution.

2. The preparation method according to claim 1, characterized in that: The degree of sulfonation of the sulfonated polyphenylsulfone is 10%-30%.

3. The preparation method according to claim 1, characterized in that: The polyethylene glycol accounts for 2-12 wt% of the casting solution.

4. The preparation method according to claim 1, characterized in that: The polyethylene glycol is polyethylene glycol-400.

5. The preparation method according to claim 1, characterized in that: The organic solvent is one or more of dimethylformamide, dimethyl sulfoxide, dimethylacetamide, and N-methylpyrrolidone.

6. The preparation method according to claim 1, characterized in that: The temperature for constant temperature stirring is 60℃-80℃, and the stirring time is 6-9 hours.

7. The preparation method according to claim 1, characterized in that: Step (2) is as follows: wipe the glass plate clean, use a scraper to spread the casting solution evenly and uniformly on the glass plate, then quickly immerse the glass plate in a constant temperature coagulation bath, wait for the phase transformation process to form a membrane, and then store the membrane at room temperature in deionized water to obtain an ultrafiltration membrane.

8. The preparation method according to claim 7, characterized in that: The solvent in the coagulation bath is deionized water, and the temperature of the coagulation bath is controlled at 25±1℃.

9. A small-pore-size high-flux ultrafiltration membrane obtained by the preparation method according to any one of claims 1-8.

10. The application of the small-pore-size high-flux ultrafiltration membrane as described in claim 9 in antibody protein purification and concentration, dye desalting, and removal of nanoscale pollutants from wastewater.

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