A high-flux ultrafiltration membrane preparation method based on phase inversion method

Abstract

The application relates to the field of membrane separation material preparation and discloses a high-flux ultrafiltration membrane preparation method based on a phase inversion method; the method comprises the following steps: preparing casting solution containing a main film-forming polymer, a sacrificial pore-forming agent, an amphiphilic pore-wall regulating agent and a film-forming solvent; coating the casting solution to form a wet film and performing surface pre-gel treatment in a wet air environment containing film-forming solvent vapor; placing the wet film into a first coagulation bath containing water, a film-forming solvent and a monovalent inorganic salt to perform limited solvent exchange, and the concentration of divalent metal ions in the first coagulation bath is less than 0.005 mol / L; when the mass of the wet film is reduced by 8% to 20%, the wet film is transferred into a second coagulation bath containing water, a film-forming solvent and a divalent metal salt, so that the divalent metal ions are combined with structural units containing carboxylate groups to form fixed structures in the pore wall of the membrane; and then the ultrafiltration membrane is obtained through water washing and sacrificial pore-forming agent elution.

Description

Technical Field

[0001] This invention relates to the field of membrane separation material preparation, and specifically to a method for preparing a high-throughput ultrafiltration membrane based on phase inversion. Background Technology

[0002] Ultrafiltration membranes are commonly used in water treatment, material separation, and solution purification. Among them, ultrafiltration membranes prepared from polymeric materials such as polyethersulfone via phase inversion are widely used. The phase inversion method typically involves preparing a casting solution from the membrane-forming polymer, pore-forming agent, and solvent, followed by membrane coating, pre-evaporation, or coagulation bath treatment to form the membrane pore structure. This process is relatively mature and facilitates continuous preparation.

[0003] In the preparation of existing high-flux ultrafiltration membranes, the membrane pore structure and hydrophilicity are often improved by increasing the content of pore-forming agent, adding hydrophilic modifiers, and adjusting the salt or solvent ratio in the coagulation bath. There are also methods that introduce metal ions or crosslinking agents into the system to reduce the loss of hydrophilic components during water washing or use.

[0004] However, the above methods often fail to accurately distinguish between the pore formation stage and the hydrophilic component fixation stage during phase transformation. If solidification is too rapid, the membrane surface layer is prone to excessive shrinkage and the formation of a thick, dense layer; if the hydrophilic component is fixed too early, the fixed structure is prone to concentrate on the membrane surface layer or be randomly distributed inside the membrane; if fixation is insufficient, the hydrophilic component is prone to be lost during solidification and washing, making it difficult to coordinate flux, retention stability, and pore wall hydrophilicity retention. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing high-throughput ultrafiltration membranes based on phase inversion, thereby solving the technical problems existing in the prior art.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for preparing a high-flux ultrafiltration membrane based on phase inversion includes the following steps: S1: Prepare the casting solution, which includes a main film-forming polymer, a sacrificial pore-forming agent, an amphiphilic pore wall regulator, and a film-forming solvent. The amphiphilic pore wall regulator includes aromatic structural units containing benzene rings and structural units containing carboxyl groups. S2: The casting solution is scraped to form a wet film, and the wet film is subjected to surface pregelation treatment in a humid air environment containing film-forming solvent vapor; S3: The wet film that has completed the surface pregelation treatment is placed in the first coagulation bath for restricted solvent exchange. The first coagulation bath includes water, film-forming solvent and monovalent inorganic salt, and the concentration of divalent metal ions in the first coagulation bath is greater than or equal to 0 mol / L and less than 0.005 mol / L. S4: When the wet film mass decreases by 8% to 20% relative to before entering the first coagulation bath, the wet film is transferred from the first coagulation bath to the second coagulation bath. The second coagulation bath includes water, film-forming solvent and divalent metal salt. The mass fraction of the film-forming solvent in the second coagulation bath is 5% to 15%. The divalent metal ions provided by the divalent metal salt combine with the structural units containing carboxylate groups to form a fixed structure on the membrane pore wall. S5: The membrane after the second coagulation bath is washed with water and eluted with a sacrificial pore-forming agent to obtain an ultrafiltration membrane.

[0007] Preferably, the main film-forming polymer is polyethersulfone, the sacrificial pore-forming agent is polyvinylpyrrolidone, the film-forming solvent is N-methylpyrrolidone or N,N-dimethylacetamide, and the amphiphilic pore wall regulator is a partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer.

[0008] Preferably, the casting solution comprises, by weight, the following components: 12 to 18 parts polyethersulfone, 4 to 10 parts polyvinylpyrrolidone, 0.5 to 3 parts partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer, and 70 to 83.5 parts N-methylpyrrolidone or N,N-dimethylacetamide.

[0009] Preferably, in the partially hydrolyzed sodium salt of the styrene-maleic anhydride copolymer, the ring-opening hydrolysis ratio of the maleic anhydride structural unit is 40% to 80%.

[0010] Preferably, when preparing the casting solution, the main film-forming polymer, the sacrificial pore-forming agent and the amphiphilic pore wall regulator are added to the film-forming solvent, stirred at 50°C to 70°C for 6 to 12 hours, and then allowed to stand at 40°C to 60°C for 2 to 6 hours to degas.

[0011] Preferably, the conditions for the surface pregel treatment are: a humid air environment with a temperature of 25°C to 40°C, a relative humidity of 50% to 80%, a treatment time of 10 to 60 seconds, and the humid air environment containing the same film-forming solvent vapor as the casting solution.

[0012] Preferably, the first coagulation bath comprises, by weight, 65 to 80 parts water, 15 to 25 parts film-forming solvent, and 3 to 8 parts monovalent inorganic salt, wherein the monovalent inorganic salt is sodium chloride or sodium sulfate, and the pH of the first coagulation bath is 6.5 to 8.0.

[0013] Preferably, the wet film quality reduction rate is determined by a follow-up sample, which is prepared from the same casting solution and the same coating thickness as the wet film, and enters the first coagulation bath simultaneously with the wet film; When the mass reduction rate of the accompanying sample is 8% to 20%, and the mass fraction of the film-forming solvent in the first coagulation bath sampling solution is 3% to 12%, the wet film is transferred to the second coagulation bath.

[0014] Preferably, the divalent metal salt is calcium chloride, calcium acetate, or magnesium chloride, the concentration of divalent metal ions in the second coagulation bath is 0.02 mol / L to 0.12 mol / L, the pH of the second coagulation bath is 6.0 to 7.5, and the processing time is 3 to 15 minutes.

[0015] Preferably, the water washing and sacrificial pore-forming agent elution includes: immersing the membrane treated in a second coagulation bath in deionized water for 12 to 24 hours, then treating it in a 0.01 mol / L to 0.05 mol / L sodium bicarbonate aqueous solution for 5 to 20 minutes, and then washing it with deionized water until the pH of the final wash solution is 6.5 to 7.5.

[0016] In summary, the present invention has the following main beneficial effects: This application employs a surface pre-gelation treatment containing film-forming solvent vapor before the wet membrane enters the coagulation bath. In the first coagulation bath, water, the film-forming solvent, and a monovalent inorganic salt are used to create a confined solvent exchange environment. This achieves the effects of controlling the surface gelation rate of the wet membrane, reducing instantaneous surface shrinkage, and promoting the gradual formation of the membrane pore structure. Compared to directly immersing the wet membrane in a pure water coagulation bath, this treatment process allows for a continuous transition between the surface pre-gelation and subsequent phase transformation, reducing the problems of excessive surface density and pore unevenness caused by rapid phase separation. This provides a stable pore foundation for the subsequent formation of the membrane pore wall fixation structure.

[0017] This application achieves the effect of separating the restricted solvent exchange stage from the divalent metal ion fixation stage by controlling the concentration of divalent metal ions in the first coagulation bath to be greater than or equal to 0 mol / L and less than 0.005 mol / L, and using the wet film mass reduction rate of 8% to 20% and the mass fraction of film-forming solvent in the first coagulation bath sampling solution as the criteria for bath transfer. This method avoids divalent metal ions from prematurely combining with carboxylate-containing structural units before the wet film has formed stable initial pores, thereby reducing the situation where the fixed structure is concentrated on the membrane surface or randomly distributed inside the membrane. This ensures that the wet film entering the second coagulation bath is in a state where the membrane pore structure has been initially formed but not yet fully solidified, improving the consistency of bath transfer timing in different batches of membrane fabrication.

[0018] This application achieves the effect of forming a fixed structure on the membrane pore wall and reducing the loss of the amphiphilic pore wall regulator by retaining 5% to 15% of the film-forming solvent in the second coagulation bath and adding a divalent metal salt. This allows the divalent metal ions to combine with the carboxylate-containing structural units in the amphiphilic pore wall regulator during the continued solidification of the membrane pore structure, thus reducing the loss of the amphiphilic pore wall regulator. Simultaneously, subsequent water washing and gentle sodium bicarbonate elution remove residual film-forming solvent and unfixed sacrificial pore-forming agent, enabling the formation of a pore structure suitable for ultrafiltration separation while maintaining the stability of the polyethersulfone main membrane structure. This creates a continuous coordination between the membrane pore wall fixation structure, pore formation, and post-treatment elution. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 refer to Figure 1 A method for preparing a high-flux ultrafiltration membrane based on phase inversion includes the following steps: S1: Prepare the casting solution, which includes a main film-forming polymer, a sacrificial pore-forming agent, an amphiphilic pore wall regulator, and a film-forming solvent. The amphiphilic pore wall regulator includes aromatic structural units containing benzene rings and structural units containing carboxyl groups. S2: The casting solution is scraped to form a wet film, and the wet film is subjected to surface pregelation treatment in a humid air environment containing film-forming solvent vapor; S3: The wet film that has completed the surface pregelation treatment is placed in the first coagulation bath for restricted solvent exchange. The first coagulation bath includes water, film-forming solvent and monovalent inorganic salt, and the concentration of divalent metal ions in the first coagulation bath is greater than or equal to 0 mol / L and less than 0.005 mol / L. S4: When the wet film mass decreases by 8% to 20% relative to before entering the first coagulation bath, the wet film is transferred from the first coagulation bath to the second coagulation bath. The second coagulation bath includes water, film-forming solvent and divalent metal salt. The mass fraction of the film-forming solvent in the second coagulation bath is 5% to 15%. The divalent metal ions provided by the divalent metal salt combine with the structural units containing carboxylate groups to form a fixed structure on the membrane pore wall. S5: The membrane after the second coagulation bath is washed with water and eluted with a sacrificial pore-forming agent to obtain an ultrafiltration membrane.

[0022] The preparation method of this application focuses on the phase transformation process through staged control. Instead of directly mixing hydrophilic additives, inorganic salts, or metal salts into the casting solution and then solidifying them into a single film, the method first involves restricted solvent exchange in a first coagulation bath, followed by a second coagulation bath after the transfer conditions are met. This allows divalent metal ions to bind to carboxylate-containing structural units at the membrane pore wall positions. This sequential control ensures that the first coagulation bath primarily forms the restricted exchange environment, while the second coagulation bath primarily forms the fixed structure of the membrane pore walls.

[0023] In this embodiment, polyethersulfone (PES) is selected as the primary film-forming polymer. PES possesses heat resistance and film-forming stability, making it suitable for preparing ultrafiltration membranes via solvent-inducible phase inversion. Polyvinylpyrrolidone (PVP) is selected as the sacrificial pore-forming agent. PSP can partially migrate from the membrane during coagulation and subsequent water washing, thus regulating the membrane pore structure. N-methylpyrrolidone (NMP) or N,N-dimethylacetamide (NDM) is selected as the film-forming solvent, as these solvents can dissolve PES and form a uniform casting solution.

[0024] The amphiphilic pore wall regulator is a partially hydrolyzed sodium salt of a styrene-maleic anhydride copolymer. In this substance, the styrene structural unit, as an aromatic structural unit containing a benzene ring, is compatible with the polyethersulfone segment; the maleic anhydride structural unit, after partial ring-opening hydrolysis, forms a structural unit containing a carboxylate group, which can bind to divalent metal ions in the second coagulation bath. Because the amphiphilic pore wall regulator possesses both aromatic and carboxylate-containing structural units, it is not completely lost with the aqueous phase during phase inversion but can be distributed near the pore wall during membrane pore formation.

[0025] The partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer can be obtained from commercially available products or by partial hydrolysis of the copolymer in sodium hydroxide solution. During hydrolysis, the amount of sodium hydroxide added is controlled based on the molar amount of the maleic anhydride structural unit, ensuring that the ring-opening hydrolysis ratio of the maleic anhydride structural unit is between 40% and 80%. The hydrolysis ratio can be determined by acid-base titration or confirmed by observing changes in the characteristic peaks of the anhydride and carboxylate in Fourier transform infrared spectroscopy.

[0026] In one embodiment, 15 parts by weight of polyethersulfone, 7 parts by weight of polyvinylpyrrolidone, 1.5 parts by weight of partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer, and 76.5 parts by weight of N-methylpyrrolidone are weighed. The above proportions fall within the range of 12 to 18 parts by weight of polyethersulfone, 4 to 10 parts by weight of polyvinylpyrrolidone, 0.5 to 3 parts by weight of partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer, and 70 to 83.5 parts by weight of N-methylpyrrolidone or N,N-dimethylacetamide.

[0027] In preparation, N-methylpyrrolidone is first added to a container equipped with a stirrer, followed by the sequential addition of polyvinylpyrrolidone, partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer, and polyethersulfone. The mixture is stirred at 60°C for 8 hours to ensure complete dissolution of all components and the formation of a homogeneous casting solution. After stirring, the casting solution is allowed to stand at 50°C for 4 hours to degas. After degassing, no visible air bubbles should remain in the casting solution to avoid pinholes or localized defects after film scraping.

[0028] When N,N-dimethylacetamide is selected as the film-forming solvent, the temperature and time for preparing the casting solution can be maintained in the range of 50℃ to 70℃ and 6 hours to 12 hours, and the temperature and time for standing degassing can be maintained in the range of 40℃ to 60℃ and 2 hours to 6 hours.

[0029] The degassed casting solution is poured onto a clean glass plate or continuous film-forming substrate, and a wet film is formed by coating with a film scraper. The thickness of the wet film can be determined according to the target film thickness; for flat sheet membrane preparation, a thickness of 150 μm to 250 μm can be used. Immediately after coating, the wet film is placed in a humid air environment containing film-forming solvent vapor for surface pre-gelation treatment.

[0030] The surface pregelation treatment is carried out in a closed or semi-closed environment. The temperature in this environment is 25°C to 40°C, the relative humidity is 50% to 80%, and the treatment time is 10 to 60 seconds. A film-forming solvent vapor source is provided in a humid air environment; this film-forming solvent is the same as that in the casting solution. When N-methylpyrrolidone is used as the film-forming solvent, an N-methylpyrrolidone vapor source is provided in the humid air environment; when N,N-dimethylacetamide is used as the film-forming solvent, an N,N-dimethylacetamide vapor source is provided in the humid air environment.

[0031] The purpose of the surface pregelation treatment is to allow the wet membrane surface to enter a controlled pregelation state, preventing excessively rapid surface shrinkage when the wet membrane is directly exposed to a strong non-solvent environment. This treatment is not the final coagulation step; the wet membrane still needs to enter the first and second coagulation baths to complete phase transformation and membrane pore wall fixation.

[0032] After the surface pre-gelation treatment is completed, the wet film is placed in the first coagulation bath for restricted solvent exchange. The first coagulation bath includes water, film-forming solvent, and monovalent inorganic salt. By weight, the first coagulation bath includes 65 to 80 parts of water, 15 to 25 parts of film-forming solvent, and 3 to 8 parts of monovalent inorganic salt, which is sodium chloride or sodium sulfate. The pH of the first coagulation bath is 6.5 to 8.0.

[0033] In one embodiment, the first coagulation bath consists of 72 parts water, 20 parts N-methylpyrrolidone, and 8 parts sodium chloride, with the pH adjusted to 7.0 to 7.3. No calcium chloride, calcium acetate, magnesium chloride, or other divalent metal salts are actively added to the first coagulation bath. To prevent divalent metal ions from prematurely binding to structural units containing carboxyl groups, the concentration of divalent metal ions in the first coagulation bath is controlled to be greater than or equal to 0 mol / L and less than 0.005 mol / L. This concentration can be controlled by the amount of water used in preparation and the inorganic salt raw materials, or it can be confirmed by detecting the first coagulation bath using inductively coupled plasma atomic emission spectrometry or ion chromatography.

[0034] A certain mass fraction of film-forming solvent is retained in the first coagulation bath to reduce the non-solvent strength of the wet film after it enters the coagulation bath, thus keeping the rate of solvent diffusion and water entry into the wet film within a controllable range. Monovalent inorganic salts are used to adjust the ionic strength of the bath solution and the phase separation environment, but are not used to fix divalent ions with structural units containing carboxyl groups.

[0035] The endpoint of the wet film treatment in the first coagulation bath is controlled by the wet film quality reduction rate. For ease of detection during continuous or batch film production, a follow-up sample is used to determine the wet film quality reduction rate. The follow-up sample is prepared from the same casting solution and has the same coating thickness as the wet film, and enters the first coagulation bath simultaneously with the wet film. The follow-up sample can be cut to 20mm × 20mm or other fixed areas, as long as the area is consistent within the same batch.

[0036] The wet film quality reduction rate is calculated using the following formula: ; In the formula, The wet film quality reduction rate is expressed in % %. The mass of the accompanying sample before the first solidification is expressed in grams. The accompanying sample was processed during the first solidification to a time. The mass after removal and removal of the surface solution is expressed in grams. The processing time of the accompanying sample during the first solidification is expressed in seconds or minutes.

[0037] During the measurement, the accompanying sample was weighed before entering the first coagulation bath. After processing for the predetermined time, remove the accompanying sample. Gently touch the edges and back of the sample with clean filter paper to remove the bath liquid adhering to the surface, without squeezing the membrane surface, and then weigh it. When the wet membrane mass decreases by 8% to 20% relative to before entering the first coagulation bath, transfer the wet membrane to the second coagulation bath.

[0038] In a further embodiment, the mass fraction of the film-forming solvent in the first coagulation bath sampling solution is simultaneously detected. When the mass reduction rate of the accompanying sample is 8% to 20%, and the mass fraction of the film-forming solvent in the first coagulation bath sampling solution is 3% to 12%, the wet film is transferred to the second coagulation bath. This dual criterion is used to reduce the timing deviation of the bath transfer caused by different film thicknesses, different ambient humidity, or different bath liquid volumes.

[0039] The mass fraction of the film-forming solvent in the first coagulation bath sample solution is calculated using the following formula: ; In the formula, The mass fraction of the film-forming solvent in the first coagulation bath sample solution, expressed as %. The mass of the film-forming solvent in the sample solution is expressed in grams. The total mass of the sample solution is expressed in grams.

[0040] The content of film-forming solvent in the sample solution can be detected by gas chromatography, high-performance liquid chromatography, or a calibrated refractive index method. When using chromatography, a standard curve is first established using an aqueous solution of the film-forming solvent with a known mass fraction. Then, the sample solution from the first coagulation bath is tested, and the concentration is calculated based on the standard curve. or .

[0041] Once the wet film meets the transfer conditions, it is transferred from the first coagulation bath to the second coagulation bath. The second coagulation bath consists of water, a film-forming solvent, and a divalent metal salt. The mass fraction of the film-forming solvent in the second coagulation bath is 5% to 15%, and this solvent is the same as that in the casting solution. The divalent metal salt in the second coagulation bath is calcium chloride, calcium acetate, or magnesium chloride, with a concentration of 0.02 mol / L to 0.12 mol / L. The pH of the second coagulation bath is 6.0 to 7.5, and the treatment time is 3 to 15 minutes.

[0042] In one embodiment, the second coagulation bath is an aqueous solution containing 10% N-methylpyrrolidone and 0.06 mol / L calcium chloride, with a pH of 6.8, and a treatment time of 10 minutes. Because the second coagulation bath retains 5% to 15% of the film-forming solvent, the wet membrane is not subjected to a sudden shock from a pure water environment when transferred from the first to the second coagulation bath. Divalent metal ions can enter the pore wall region during the continued solidification of the membrane pore structure and bind to the carboxylate-containing structural units in the amphiphilic pore wall regulator.

[0043] In this application, the divalent metal ions in the second coagulation bath are not added to the casting solution beforehand, nor are they added to the first coagulation bath for pre-fixation. Instead, they are introduced after the wet membrane has completed the limited solvent exchange in the first coagulation bath and reached the bath transfer conditions. This treatment sequence allows the structural units containing carboxylate groups to distribute to the vicinity of the membrane pore wall during the membrane pore formation process in the first coagulation bath, and then combine with the divalent metal ions in the second coagulation bath, thereby forming a fixed structure on the membrane pore wall. This fixed structure differs from the random cross-linked structure formed by directly mixing metal salts into the casting solution, and also differs from the treatment method that simultaneously completes phase separation and fixation in a single coagulation bath.

[0044] The binding of divalent metal ions to structural units containing carboxylate groups can be confirmed by X-ray photoelectron spectroscopy, energy dispersive spectroscopy (EDS), or Fourier transform infrared spectroscopy (FTIR). X-ray photoelectron spectroscopy can detect calcium or magnesium signals on or near the membrane surface. EDS can observe the distribution of divalent metal elements near the membrane pore walls in the membrane cross-section. FTIR can observe the changes in carboxylate-related absorption peaks before and after the binding of divalent metal ions. These detections are used to verify the formation of the fixed structure on the membrane pore walls and are not considered necessary limitations of the preparation steps.

[0045] After the second coagulation bath treatment, the membrane is removed and immersed in deionized water for 12 to 24 hours to remove residual film-forming solvent, unfixed water-soluble components, and migratable polyvinylpyrrolidone. Subsequently, the membrane is treated in a 0.01 mol / L to 0.05 mol / L sodium bicarbonate aqueous solution for 5 to 20 minutes, and then washed with deionized water until the pH of the final wash solution is 6.5 to 7.5.

[0046] In one embodiment, the membrane is immersed in deionized water for 18 hours, with the deionized water being replaced every 6 hours; it is then treated in a 0.03 mol / L sodium bicarbonate aqueous solution for 10 minutes, and then washed with deionized water until the pH of the final wash solution is 7.0 to 7.2. The sodium bicarbonate aqueous solution is used to promote the removal of unfixed water-soluble components and sacrificial pore-forming agents; the concentration used is low, the treatment time is short, and it does not damage the polyethersulfone host membrane structure.

[0047] After the above treatment, an ultrafiltration membrane is obtained. The membrane pore structure of this ultrafiltration membrane is formed by a phase transformation process, and the membrane pore walls consist of a fixed structure formed by the combination of divalent metal ions and structural units containing carboxylate groups.

[0048] In another embodiment, the casting solution comprises, by weight, 12 parts polyethersulfone, 4 parts polyvinylpyrrolidone, 0.5 parts partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer, and 83.5 parts N,N-dimethylacetamide. The above components are stirred at 55°C for 10 hours and then allowed to stand at 45°C for 5 hours to remove bubbles.

[0049] After coating, the wet film is placed in a humid air environment containing N,N-dimethylacetamide vapor at 30℃ and 60% relative humidity for 30 seconds. It is then placed in the first coagulation bath, which consists of 75 parts water, 20 parts N,N-dimethylacetamide, and 5 parts sodium sulfate by weight, with a pH of 7.2 and a divalent metal ion concentration of less than 0.005 mol / L.

[0050] The wet membrane mass reduction rate was determined using accompanying sample samples. When the mass reduction rate of the accompanying sample samples reached 12%, and the mass fraction of N,N-dimethylacetamide in the first coagulation bath sample solution was 6%, the wet membrane was transferred to the second coagulation bath. The second coagulation bath was an aqueous solution containing 8% N,N-dimethylacetamide and 0.05 mol / L magnesium chloride, with a pH of 6.8, and a treatment time of 8 minutes. Subsequently, the membrane was soaked in deionized water, treated with sodium bicarbonate aqueous solution, and washed with deionized water to obtain the ultrafiltration membrane.

[0051] This embodiment illustrates that the process of this application is applicable not only to the N-methylpyrrolidone system but also to the N,N-dimethylacetamide system; and not only to the calcium chloride system but also to the magnesium chloride system. In different systems, the first coagulation bath still serves as a limited solvent exchange bath, and the second coagulation bath still serves as a binding and fixation bath for divalent metal ions.

[0052] To illustrate the differences between this application and existing conventional phase inversion film-forming methods, the following comparative implementation method can be set up. The film preparation steps, casting solution composition, film thickness, and post-treatment methods in the comparative implementation method are consistent with those in the example, with only the corresponding steps changed.

[0053] No first coagulation bath is used. After the wet membrane completes the surface pre-gelation treatment, it directly enters the second coagulation bath containing divalent metal salts. This method lacks the restricted solvent exchange process in the first coagulation bath. Divalent metal ions directly enter the membrane surface before the wet membrane has completed the controlled phase transformation, which can easily cause structural units containing carboxylate groups to bind prematurely on the surface.

[0054] A divalent metal salt is added to the first coagulation bath. This method replaces the first coagulation bath with a bath containing divalent metal ions, causing the divalent metal ions to bind in the early stages of phase transformation. This method differs from the setting in this application, where the concentration of divalent metal ions in the first coagulation bath is controlled to be greater than or equal to 0 mol / L and less than 0.005 mol / L, and therefore cannot achieve the separation of the migration and fixation stages.

[0055] No second coagulation bath is used. After treatment in the first coagulation bath, the wet membrane is directly washed with water and eluted with a sacrificial pore-forming agent. Although this method involves limited solvent exchange, it lacks the process of divalent metal ions combining with structural units containing carboxylate groups, and therefore cannot form the membrane pore wall fixation structure described in this application.

[0056] The method involves directly adding divalent metal salts to the casting solution. This method introduces divalent metal salts during the casting solution preparation stage, allowing the divalent metal ions to bind with carboxylate-containing structural units within the casting solution. This differs from the process described in this application, which involves introducing divalent metal ions post-in the second coagulation bath. This approach can easily cause premature changes in the viscosity and local binding state of the casting solution, making it difficult to control the pore formation process through the first coagulation bath.

[0057] A fixed-time transfer bath method is used. This method does not measure the wet film quality reduction rate, nor does it detect the mass fraction of film-forming solvent in the first coagulation bath sample solution; it simply transfers the wet film from the first coagulation bath to the second coagulation bath at fixed intervals. This method cannot confirm the phase inversion process based on the casting solution, film thickness, and coagulation bath state within the same batch, and inconsistencies in the timing of bath transfers between batches are likely to occur.

[0058] The above comparative embodiments are for illustrative purposes. This application does not simply employ hydrophilic additives, inorganic salt coagulation baths, or metal ion fixation. Instead, it achieves limited solvent exchange, bath transfer control, and membrane pore wall fixation at different stages through the sequential division of labor between the first and second coagulation baths. This process sequence is a key technical difference between this application and conventional blending modification, internal crosslinking with metal salts, and ordinary two-stage coagulation bath treatment.

[0059] To evaluate the structure and performance of the prepared ultrafiltration membrane, the following testing methods can be used. The obtained values ​​should be based on actual test results and should not be entered into fixed performance data before testing.

[0060] Pure water flux is calculated using the following formula: ; In the formula, Pure water flux, unit: ; The volume of water passing through is expressed in units of 1. ; Effective filtration area, in units of ; Filtering time, in units of ; Transmembrane pressure, unit: .

[0061] The retention rate can be tested using bovine serum albumin aqueous solution and calculated using the following formula: ; In the formula, Retention rate, unit: ; The mass concentration of bovine serum albumin in the permeate is expressed in units of... ; This represents the mass concentration of bovine serum albumin in the feed solution, in units of... .

[0062] The flux recovery rate after contamination cleaning is calculated using the following formula: ; In the formula, Flux recovery rate, in units of ; The pure water flux before contamination, in units of ; The pure water flux after contamination and cleaning, in units of .

[0063] The hydrophilicity of the membrane surface can be measured by the water contact angle. The pore structure of the membrane cross-section can be observed using a scanning electron microscope. The fixed structure formed by the combination of divalent metal ions and structural units containing carboxylate groups can be verified by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, or energy dispersive spectroscopy. Changes in the water contact angle and pure water flux after continuous immersion can be used to evaluate the stability of the fixed structure of the membrane pore wall.

[0064] Through the above embodiments, those skilled in the art can clearly obtain the following: the selection and proportioning of each component in the casting solution; the environmental conditions for surface pre-gelling; the composition of the first coagulation bath, the limitation of divalent metal ion concentration, and the restricted solvent exchange method; the determination method of wet film mass reduction rate and the mass fraction of film-forming solvent in the first coagulation bath sampling solution; the mass fraction of divalent metal salt, film-forming solvent, pH, and treatment time in the second coagulation bath; and the conditions for water washing and sacrificial pore-forming agent elution. The technical features in the claims can all be found in the corresponding descriptions in the above embodiments or directly determined by the above embodiments.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-throughput ultrafiltration membrane based on phase inversion, characterized in that, Includes the following steps: S1: Prepare the casting solution, which includes a main film-forming polymer, a sacrificial pore-forming agent, an amphiphilic pore wall regulator, and a film-forming solvent. The amphiphilic pore wall regulator includes aromatic structural units containing benzene rings and structural units containing carboxyl groups. S2: The casting solution is scraped to form a wet film, and the wet film is subjected to surface pregelation treatment in a humid air environment containing film-forming solvent vapor; S3: The wet film that has completed the surface pregelation treatment is placed in the first coagulation bath for restricted solvent exchange. The first coagulation bath includes water, film-forming solvent and monovalent inorganic salt, and the concentration of divalent metal ions in the first coagulation bath is greater than or equal to 0 mol / L and less than 0.005 mol / L. S4: When the wet film mass decreases by 8% to 20% relative to before entering the first coagulation bath, the wet film is transferred from the first coagulation bath to the second coagulation bath. The second coagulation bath includes water, film-forming solvent and divalent metal salt. The mass fraction of the film-forming solvent in the second coagulation bath is 5% to 15%. The divalent metal ions provided by the divalent metal salt combine with the structural units containing carboxylate groups to form a fixed structure on the membrane pore wall. S5: The membrane after the second coagulation bath is washed with water and eluted with a sacrificial pore-forming agent to obtain an ultrafiltration membrane.

2. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 1, characterized in that, The main film-forming polymer is polyethersulfone, the sacrificial pore-forming agent is polyvinylpyrrolidone, the film-forming solvent is N-methylpyrrolidone or N,N-dimethylacetamide, and the amphiphilic pore wall regulator is a partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer.

3. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 2, characterized in that, The casting solution is composed of the following components by weight: 12 to 18 parts polyethersulfone, 4 to 10 parts polyvinylpyrrolidone, 0.5 to 3 parts partially hydrolyzed sodium salt of styrene-maleic anhydride copolymer, and 70 to 83.5 parts N-methylpyrrolidone or N,N-dimethylacetamide.

4. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 3, characterized in that, In the partially hydrolyzed sodium salt of the styrene-maleic anhydride copolymer, the ring-opening hydrolysis ratio of the maleic anhydride structural unit is 40% to 80%.

5. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 4, characterized in that, When preparing the casting solution, the main film-forming polymer, sacrificial pore-forming agent and amphiphilic pore wall regulator are added to the film-forming solvent and stirred at 50°C to 70°C for 6 to 12 hours, followed by standing at 40°C to 60°C for degassing for 2 to 6 hours.

6. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 5, characterized in that, The conditions for the surface pregel treatment are: a humid air environment with a temperature of 25°C to 40°C, a relative humidity of 50% to 80%, a treatment time of 10 to 60 seconds, and the humid air environment containing the same film-forming solvent vapor as the casting solution.

7. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 6, characterized in that, The first coagulation bath comprises, by weight, 65 to 80 parts water, 15 to 25 parts film-forming solvent, and 3 to 8 parts monovalent inorganic salt, wherein the monovalent inorganic salt is sodium chloride or sodium sulfate, and the pH of the first coagulation bath is 6.5 to 8.

0.

8. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 7, characterized in that, The wet film quality reduction rate was determined by a follow-up sample, which was prepared from the same casting solution and the same coating thickness as the wet film, and entered the first coagulation bath simultaneously with the wet film. When the mass reduction rate of the accompanying sample is 8% to 20%, and the mass fraction of the film-forming solvent in the first coagulation bath sampling solution is 3% to 12%, the wet film is transferred to the second coagulation bath.

9. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 8, characterized in that, The divalent metal salt is calcium chloride, calcium acetate, or magnesium chloride. The concentration of divalent metal ions in the second coagulation bath is 0.02 mol / L to 0.12 mol / L, the pH of the second coagulation bath is 6.0 to 7.5, and the processing time is 3 to 15 minutes.

10. The method for preparing a high-throughput ultrafiltration membrane based on phase inversion according to claim 9, characterized in that, The water washing and sacrificial pore-forming agent elution include: immersing the membrane, after treatment in the second coagulation bath, in deionized water for 12 to 24 hours, then treating it in a 0.01 mol / L to 0.05 mol / L sodium bicarbonate aqueous solution for 5 to 20 minutes, and then washing it with deionized water until the pH of the final wash solution is 6.5 to 7.5.

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