A method for preparing high-performance small-pore precision separation membrane

Abstract

This invention discloses a method for preparing a small-pore precision separation membrane. A reactive porogen is added to the casting solution, and a reaction occurs during the heating process of the casting solution and / or the phase transformation process in the coagulation bath and / or subsequent membrane treatment. This generates uniformly sized and evenly distributed molecular-level nanobubbles in situ. These nanobubbles are used as porogens to modulate the membrane pore structure, thereby preparing a high-performance small-pore precision separation membrane. The method of this invention eliminates the need for conventional hydrophilic porogens that are prone to residue and precipitation.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and specifically relates to a method for preparing a high-performance small-pore precision separation membrane. Background Technology

[0002] Small-pore precision separation membranes are separation membranes with pore sizes between ultrafiltration and nanofiltration membranes, typically ranging from 1 to 10 nm. Compared to traditional polyamide nanofiltration membranes (which typically have pore sizes less than 1 nm), they have larger adjustable pore sizes and can be used for the separation of small organic molecules of different molecular weights, as well as the separation of small organic molecules from salts. They retain small organic molecules to a certain extent while having very low retention of inorganic salts. Therefore, they have wide applications in biopharmaceutical separation, high-salt dye wastewater treatment, food processing, electronic ultrapure water preparation, municipal drinking water, and industrial wastewater treatment.

[0003] Currently, the main methods for preparing small-pore precision separation membranes include interfacial polymerization, chemical cross-linking, self-assembly, and non-solvent-induced phase separation (NIPS). Among these, NIPS is one of the most effective methods for preparing separation membranes due to its simple process, high membrane formation efficiency, and low cost. The NIPS membrane formation process mainly includes preparing the casting solution, degassing, membrane formation, and immersion in a coagulation bath to prepare the membrane material. During the immersion process in the coagulation bath, the solvent exits from the solution membrane and enters the coagulation bath, while the non-solvent in the coagulation bath enters the solution membrane, causing it to solidify and take shape. Some of the added pore-forming agents dissolve from the casting solution and enter the coagulation bath during the phase inversion process, while some pore-forming agents are retained in the final membrane structure. Since porogens are typically hydrophilic materials, although retaining them in the membrane structure can improve the membrane's hydrophilicity and antifouling properties, these porogens will slowly precipitate out during membrane use, entering the permeate along with the material and affecting its composition and quality. This self-precipitation phenomenon should be avoided as much as possible in applications with special requirements (such as biopharmaceutical separation, food separation, water purification, electronic-grade ultrapure water, and electronic-grade reagents). Furthermore, small-pore precision separation membranes prepared by the NIPS method usually have a wide pore size distribution and low porosity, leading to decreased separation efficiency and permeate flux, making it difficult to prepare high-performance small-pore precision separation membranes.

[0004] CN113769586A discloses a double-layer polyvinylidene fluoride hollow fiber microporous precision separation membrane for dye desalination. The neutral molecular weight (MWCO) of the microporous precision separation membrane is 1530 Da, and the average pore size is 1.21 nm. Although it has a high rejection rate of almost 100% for the low molecular weight dye Eriochrome Black T (Mn=461 Da) and a high NaCl permeability of 96.8%, its pure water permeability is very low, only 14.2 L / (m²·h·bar).

[0005] To address the problems existing in the prior art, this invention provides a novel method for preparing a small-pore precision separation membrane. By using in-situ generated nanobubbles as porogens to modulate the membrane pore structure, the method eliminates the need to add conventional hydrophilic porogens that are prone to residue and precipitation. The resulting high-performance small-pore precision separation membrane has significant application prospects in fields such as biopharmaceutical separation, food separation, healthy water, electronic-grade ultrapure water, and electronic-grade reagent preparation. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a small-pore precision separation membrane. By adding a reactive pore-forming agent to the casting solution, a reaction can occur in situ during the heating process of the casting solution and / or the phase transformation process in the coagulation bath and / or the subsequent membrane treatment to generate molecular-level nanobubbles with uniform size and distribution. This method regulates the phase transformation process, modulates the membrane pore structure, and prepares a high-performance small-pore precision separation membrane.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a precision separation membrane with small pores includes the following steps:

[0009] (1) Add the film-forming polymer and additives to the solvent, dissolve them at 20-70°C, and allow them to cool naturally to below 60°C. At this temperature, perform vacuum degassing to form solution 1. The vacuum degassing time can be 7-9 hours, preferably 7.5-8.5 hours.

[0010] The reactive porogen is added to the same solvent and stirred to dissolve at 20-40°C. Vacuum degassing is performed at this temperature to form solution 2. The vacuum degassing time can be 3.5-5 hours, preferably 3.5-4 hours.

[0011] Slowly pour solution 2 into solution 1 and keep it at 40-60°C for a period of time to form a casting solution. The holding time can be, for example, 3-5 hours, preferably 3.5-4 hours.

[0012] The solvent ratio in solution 1 and solution 2 is 4:1, the content of film-forming polymer is 12%-30%, the content of reactive porogen is 2%-14%, and the content of additives is 0-10%, based on the total weight of the casting solution.

[0013] (2) Prepare a solution film with a thickness of 100-500 micrometers from the casting solution obtained in step (1);

[0014] (3) Immerse the solution membrane from step (2) in a coagulation bath with a pH of 7-14 and let it stand in the coagulation bath for no less than 30 seconds to obtain a fine separation membrane with small pores.

[0015] (4) Immerse the small-pore precision separation membrane obtained in step (3) in an aqueous solution of a certain temperature and a certain pH value for 0.5-48 hours to allow the unreacted reactive porogen in step (3) to react completely.

[0016] (5) The small-hole precision separation membrane treated in step (4) is washed with distilled water, and then treated with distilled water or glycerol solution before storage.

[0017] In step (1), the film-forming polymer is a polymer material that can be used to form a film, preferably one or two of the following materials: polysulfone (PSf), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), and polyimide (PI).

[0018] The solvent is a solvent that can dissolve the film-forming polymer, preferably one or more of the following solvents: N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0019] The reactive porogen refers to a substance that can be dissolved or uniformly dispersed in the casting solution and can decompose to generate gas under certain conditions. Preferably, one or more of the following are used as reactive porogens: azobisisobutyronitrile, diisopropyl azodicarbonate, diethyl azodicarbonate, azodicarbonamide, sodium borohydride, and p-toluenesulfonyl hydrazine.

[0020] The aforementioned additives refer to small molecule solvents that can promote the dissolution of reactive pore-forming agents or regulate the phase state of the casting liquid, preferably one or more of water, tetrahydrofuran, methanol, ethanol, glycerol, etc.

[0021] In step (2), the solution-state membrane coating can be performed by any conventional and suitable method, including but not limited to blade coating, brush coating, spray coating, etc. Alternatively, a supported or self-supporting hollow fiber membrane can be used to form the membrane.

[0022] In step (3), during the immersion process in the coagulation bath, the casting solution undergoes a phase transformation with the coagulation bath. At the same time, the reactive pore-forming agent reacts with the coagulation bath to generate nanobubbles. The hydrophobic and oleophobic properties of the generated nanobubbles are used to adjust the phase transformation rate and thus regulate the membrane pore structure.

[0023] The coagulation bath is an aqueous medium that can react with reactive porogens to generate nanobubbles. It can be adjusted to different pH values ​​using acid or alkali, typically between pH 7 and 14, for example, pH 7.0, 7.5, 8.5, 9.0, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, etc. The temperature of the coagulation bath is from room temperature to 70°C. The acid used to adjust the pH can be selected from hydrochloric acid or sulfuric acid solution, and the alkali can be selected from sodium hydroxide or potassium hydroxide solution.

[0024] In step (4), the aqueous solution with a certain pH value is an aqueous solution with a pH value adjusted to 7-14 by acid or alkali. The pH value is the same as the pH value of the coagulation bath in step (3). The soaking time is 0.5 to 48 h, and the temperature of the coagulation bath is room temperature to 70°C. The unreacted reactive porogen in step (3) reacts in it to generate nanobubbles.

[0025] The process of generating nanobubbles through the decomposition of the reactive porogen can occur in steps (1) to (4), or steps (1) to (3), or in step (3). In step (1), the nanobubbles generated are generated by the self-decomposition of the reactive porogen at a certain temperature. The bubbles generated in steps (2) to (4) are mainly generated by the reaction of the reactive porogen with a weak acid or a strong base, and also include some nanobubbles generated by the self-decomposition of the reactive porogen due to heating.

[0026] According to the method of the present invention, the reactive pore-forming agent can undergo a chemical reaction in three stages: the heating process of the casting solution, the phase transformation process of the coagulation bath, or the subsequent membrane treatment process, to generate nanobubbles of uniform size and distribution. The generation of nanobubbles can be regulated in all three stages, with the following advantages: In the first stage, in the casting solution (for steps (1) and (2) above), the generated nanobubbles affect the viscosity of the casting solution, thereby affecting the phase transformation process and ultimately affecting the membrane pore structure. Therefore, the viscosity of the casting solution can be regulated by treating it at a certain temperature, thereby controlling the membrane pore size. In the second stage, during the phase transformation process, the generated nanobubbles directly regulate the phase transformation process, promoting the uniformity of the phase transformation process and making the surface pore structure of the prepared separation membrane more uniform (corresponding to step (3) above). Therefore, the generation rate of nanobubbles can be regulated by controlling the concentration of alkali in the coagulation bath, thereby controlling the phase transformation process and ultimately controlling the membrane pore size and surface porosity. In the third stage, nanobubbles are generated during the post-treatment process, which is beneficial for pore formation, improving the overall porosity, and further improving the membrane permeation flux (corresponding to step (4) above). Therefore, the amount of the remaining material in the third stage can be controlled by adjusting the amount of reactive porogen added, thereby ultimately controlling the overall porosity of the membrane. Not every one of the three stages necessarily produces nanobubbles. For example, nanobubbles may be produced in the first, second, and third stages; nanobubbles may be produced only in the first and second stages; or nanobubbles may be produced only in the second stage.

[0027] The present invention further relates to a small-pore precision separation membrane prepared by the method of the present invention, wherein the small-pore precision separation membrane may be a flat sheet membrane, or various membrane forms such as a hollow fiber membrane, an inner-lined membrane, and a tubular membrane.

[0028] The permeation separation performance of the obtained small-pore precision separation membrane was tested using the following method: a cross-flow filtration device was used to test the permeation separation performance of the small-pore precision separation membrane, wherein the effective membrane area used for testing was 7.1 cm². 2 The test pressure was 1 bar, and the test temperature was 25±0.5℃.

[0029] The formula for calculating water flux is as follows (1):

[0030] (1)

[0031] in J The water flux of the membrane (L·m) 2 ·h), V The volume of water that permeates through the membrane (L), A The effective area of ​​the membrane (m²) 2 ), △t The infiltration time is in hours (h).

[0032] in J The water flux of the membrane (L·m) 2 ·h), V The volume of water that permeates through the membrane (L), A The effective area of ​​the membrane (m²) 2 ), △t The infiltration time is in hours (h).

[0033] The microporous precision separation membrane obtained by the method of this invention has a uniform pore structure, small pore size, and narrow distribution, with an average pore diameter in the range of 1-8 nm and a high surface porosity, reaching up to 15%. This membrane exhibits excellent selective separation, ensuring highly efficient retention (up to 99.9%) of small molecule dyes while maintaining low retention rates for inorganic salts such as Na₂SO₄, CaSO₄, and NaCl; for example, the retention rate for sodium chloride solution is less than 5%. Simultaneously, the pure water flux can reach up to 600 L / (m²·h), demonstrating superior separation performance. Compared with existing membrane products of the same pore size, the pure water permeation flux is significantly improved, and the separation precision is higher. The overall permeation and separation performance is superior to existing microporous separation membranes. Furthermore, the obtained microporous precision separation membrane maintains good mechanical properties; for example, its tensile strength can reach 8 MPa.

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] 1. The method of this invention uses a reactive porogen, which has good dispersibility in the casting solution and can achieve molecular-level dissolution and dispersion in the casting solution. During the phase transformation and film formation process, molecular-level nanobubbles are generated in situ through heating or acid-base catalytic reaction. The molecular-level nanobubbles are used as porogens, and the membrane pore structure is controlled by the ultra-high stability, self-pressurizing solubility, and oleophobic and hydrophobic properties of the molecular-level nanobubbles. The uniform dispersion of the reactive porogen in the casting solution makes the generated nanobubbles more uniform in size, smaller in size, and more stable, which is more conducive to the preparation of small-pore precision separation membranes with uniform pore size.

[0036] 2. The nanobubbles generated by the reactive porogen possess a "double-phobic" characteristic, being both repellent to organic solvents (casting solution solvent) and hydrophobic to water (coagulation bath). During the phase transition, once the casting solution comes into contact with the coagulation bath, the reactive porogen in the casting solution reacts with the acid-base medium in the coagulation bath to generate nanobubbles. The presence of these nanobubbles prevents the dual diffusion process between the solvent in the casting solution and the non-solvent in the coagulation bath, thus altering the exchange process between the solvent in the solution-state membrane and the solvent in the coagulation bath during the phase transition. This regulates the diffusion rate of both, thereby controlling the film formation kinetics and enabling independent control of the surface pore structure and distribution. This results in a small-pore precision separation membrane with both high separation accuracy and high throughput. This differs from the uncontrollable kinetics of solvent-non-solvent dual diffusion in the traditional NIPS method. Although small-pore (<10nm) separation membranes can also be obtained using the traditional NIPS method, they generally have fewer pores, lower surface porosity, and a wider pore distribution, leading to low water flux (typically around 100L / (m²)). 2 It has the disadvantages of low separation accuracy (below h).

[0037] 3. The good solubility and dispersibility of reactive porogens in casting solution allow for the adjustment of membrane porosity by changing the amount of reactive porogen added.

[0038] 4. Reactive porogens can decompose to generate nanobubbles in various ways, such as through heating, acid / base reactions, etc., which provides more possibilities for the controllability of the process.

[0039] 5. Reactive porogens have low molecular weights, and their decomposition products are usually gas molecules (such as CO2, O2, H2 and / or small molecule alkanes and alkenes), which can easily overflow directly after post-processing and membrane drying, leaving almost no porogen residue. This results in very few precipitates during membrane use, thereby reducing the pollution and damage to the separated products caused by precipitates. Unlike the traditional NIPS method, which uses hydrophilic macromolecules as porogens and suffers from porogen residue and difficulty in cleaning, this method is of great significance for applications in biopharmaceutical separation, food and beverage separation, healthy water, electronic ultrapure water, and electronic-grade reagent preparation.

[0040] 6. In addition to the reactive porogen, no other conventional hydrophilic porogens that are prone to residue and precipitation are added in this invention. The reactive porogens used are completely removed during phase inversion and post-treatment, leaving no residue. This significantly improves the problem of organic matter precipitation in the separation membrane, avoids the problem of high organic matter content in the coagulation bath caused by the entry of macromolecular porogens into the coagulation bath during the traditional NIPS method, simplifies the organic solvent recovery process in the coagulation bath, greatly reduces the cost of organic solvent recovery, and improves economic efficiency. Attached Figure Description

[0041] Figure 1This is a scanning electron microscope image of the precision separation membrane with small orifices obtained in Example 1.

[0042] Figure 2 This is a scanning electron microscope image of the separation membrane obtained in Comparative Example 1.

[0043] Figure 3 The graphs show the pore size distribution of the membranes obtained in Example 1 and Comparative Example 1.

[0044] Figure 4 The graphs show the pore size distribution of the membranes obtained in Examples 2 and 4. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific examples. The embodiments described are for illustrative purposes only and do not constitute a limitation. Any modifications and improvements made by those skilled in the art without departing from the concept and technology involved in the present invention are within the scope of protection of the present invention.

[0046] The reagents and raw materials used in the embodiments of this invention are not subject to any special restrictions and are all commercially available. Example

[0047] 12 g of polyethersulfone and 2 g of tetrahydrofuran were added to 59.2 g of N,N-dimethylformamide solvent. The mixture was stirred at 70 °C for 8 h, then transferred to a vacuum oven for degassing for 1 h and cooled to 40 °C, designated as solution 1. 12 g of azobisisobutyronitrile (AIBN) was added to 14.8 g of N,N-dimethylformamide solvent, dissolved at 40 °C, and degassed under vacuum to form solution 2. Solution 2 was then slowly poured into solution 1 and heated to 60 °C for 4 h to form a casting solution. The casting solution was uniformly coated onto a glass plate using an automatic coating machine at a speed of 1500 mm / min, controlling the film thickness to 100 µm. The plate was then immediately placed in a coagulation bath at pH 8 and 70 °C for phase inversion to form a membrane for 30 minutes. The membrane was then immersed in the above solution for 24 h to remove residual solvent and reactive porogens. Finally, the membrane was immersed in a 50% glycerol aqueous solution for 2 h and then naturally dried to obtain a small-pore precision separation membrane. The resulting membrane has a pore size of 8.2 nm, with a maximum pore size distribution ranging from 3 to 20 nm (pore size and pore size distribution are shown in the figure). Figure 1 and Figure 3 As shown), the permeation flux is 600.9 L / (m²). 2 The membrane has a rejection rate of less than 5% for inorganic salts such as sodium sulfate, calcium sulfate, and sodium chloride, and a membrane strength of 3.5 MPa.

[0048] Depend on Figure 1 As can be seen from the scanning electron microscope images, the membrane surface of this embodiment has a large number of pores with relatively uniform pore size. Therefore, the membrane can achieve high-throughput and precise separation. Figure 3As can be seen from the curve, the membrane surface of this embodiment has a high concentration of pore size, uniform pore diameter, and narrow pore diameter distribution. Example

[0049] 30 g of polysulfone and 2 g of ethanol were dissolved in 48 g of N,N-dimethylformamide / dimethyl sulfoxide (mass ratio 3:1) solvent. The solution was stirred at 70 °C for 8 h, then transferred to a vacuum oven for degassing for 1 h and cooled to 40 °C, designated as solution 1. 8 g of azodicarbonamide was added to 12 g of N,N-dimethylformamide / dimethyl sulfoxide (mass ratio 3:1) and dissolved at 60 °C, followed by vacuum degassing to form solution 2. Solution 2 was then slowly poured into solution 1 and heated to 60 °C for 4 h to form a casting solution. An automatic coating machine was used to uniformly coat the solution onto a glass plate at a speed of 1500 mm / min, controlling the film thickness to 500 µm. The film was then immediately placed in a coagulation bath at pH 14 and 60 °C for phase inversion to form a membrane for 30 minutes. The membrane was then immersed in an aqueous solution at pH 14 and 20 °C for 24 h to remove residual solvent and reactive porogens. Finally, the membrane was immersed in a 50% glycerol aqueous solution for 2 hours. The resulting membrane had a significantly smaller pore size of 1.3 nm, and a narrower maximum pore size distribution width of only 0.4-3 nm (pore size and pore size distribution are shown in Figure 1). Figure 4 As shown), the membrane permeation flux is 100.8 L / (m²). 2 (·h), which facilitates the separation of small molecules from salts, with a sodium chloride rejection of less than 5% and a membrane strength of 8.5 MPa. (By...) Figure 4 As can be seen from the curve, the membrane in Example 2 has a narrower pore size distribution and a more uniform pore size. Example

[0050] 30 g of polyethersulfone and 1 g of tetrahydrofuran were dissolved in 48.8 g of N,N-dimethylformamide solvent. The solution was stirred at 70 °C for 8 h, then transferred to a vacuum oven for degassing for 1 h and cooled to 60 °C, designated as solution 1. 8 g of sodium borohydride was added to 12.2 g of N,N-dimethylformamide and dissolved at 60 °C, followed by vacuum degassing to form solution 2. Solution 2 was then slowly poured into solution 1 and heated to 60 °C for 4 h to form a casting solution. An automatic coating machine was used to uniformly coat the solution onto a glass plate at a speed of 1500 mm / min, controlling the film thickness to 200 µm. The film was then immediately placed in a coagulation bath at pH 6 and 20 °C for phase inversion to form a membrane for 30 minutes. The membrane was then immersed in an aqueous solution at pH 7 and 20 °C for 24 h to remove residual solvent and reactive porogens. Finally, the membrane was immersed in a 50% glycerol aqueous solution for 24 h. The resulting membrane has a pore size of 3.8 nm and a permeation flux of 180.5 L / (m²). 2 The tensile strength of the membrane can reach 8.3 MPa (·h). Example

[0051] This embodiment repeats embodiment 2, except that no additives are added.

[0052] 30 g of polysulfone was dissolved in 48 g of N,N-dimethylformamide / dimethyl sulfoxide (mass ratio 3:1) solvent. The solution was stirred at 70 °C for 8 h, then transferred to a vacuum oven for degassing for 1 h and cooled to 40 °C, designated as solution 1. 8 g of azodicarbonamide was added to 12 g of N,N-dimethylformamide / dimethyl sulfoxide (mass ratio 3:1) and dissolved at 60 °C, followed by vacuum degassing to form solution 2. Solution 2 was then slowly poured into solution 1 and heated to 60 °C for 4 h to form a casting solution. An automatic coating machine was used to uniformly coat the solution onto a glass plate at a speed of 1500 mm / min, controlling the film thickness to 500 µm. The film was then immediately placed in a coagulation bath at pH 14 and 60 °C for phase inversion to form a membrane for 30 minutes. The membrane was then immersed in an aqueous solution at pH 14 and 20 °C for 24 h to remove residual solvent and reactive porogens. Finally, the membrane was immersed in a 50% glycerol aqueous solution for 2 hours. The resulting membrane had a pore size of 2.9 nm and a pore size distribution width of 1-10 nm (pore size and pore size distribution are shown in Figure 1). Figure 4 As shown), the membrane permeation flux is 70 L / (m²). 2 ·h). By Figure 4 As can be seen from the curve, compared with Example 2, the membrane pore size distribution of Example 4 is wider and the pore size is larger, indicating that the additive has a good regulatory effect on the pore size and distribution of the microporous membrane. Example

[0053] 30 g of polysulfone was dissolved in 48 g of N,N-dimethylformamide solvent and stirred at 70 °C for 8 h. The solution was then transferred to a vacuum oven for degassing for 1 h and cooled to 40 °C, and this solution was designated as solution 1. 8 g of sodium borohydride was added to 12 g of N,N-dimethylformamide and dissolved at 60 °C, followed by vacuum degassing to form solution 2. Solution 2 was then slowly poured into solution 1 and heated to 60 °C for 4 h to form a casting solution. An automatic coating machine was used to uniformly coat the solution onto a glass plate at a speed of 1500 mm / min, controlling the film thickness to 200 µm. The film was then immediately placed in a coagulation bath at pH 7 and 25 °C for phase inversion to form a membrane for 30 minutes. The membrane was then immersed in an aqueous solution at pH 7 and 20 °C for 24 h to allow the remaining reactive porogen to continue reacting and to remove residual solvent. Finally, the membrane was immersed in a 50% glycerol aqueous solution for 2 h. The resulting membrane has a pore size of 3.3 nm, a narrow maximum pore size distribution (only 1-8 nm), and a membrane permeation flux of 180.7 L / (m²). 2·h), which is beneficial for separating small molecules from salt, with a sodium chloride rejection of less than 5% and a membrane strength of 8.5 MPa.

[0054] Comparative Example 1

[0055] Comparative Example 1 is a repeat of Example 1, except that no reactive porogen is added.

[0056] 12 g of polyethersulfone and 2 g of tetrahydrofuran were added to 59.2 g of N,N-dimethylformamide solvent. The mixture was stirred at 70 °C for 8 h, then transferred to a vacuum oven for degassing for 1 h and cooled to 40 °C, designated as solution 1. Next, 14.8 g of N,N-dimethylformamide solvent was added to this solution, dissolved at 40 °C, and degassed under vacuum to obtain solution 2. Solution 2 was then slowly poured into solution 1 and heated to 60 °C for 4 h to form a casting solution. This solution was then uniformly coated onto a glass plate using an automatic coating machine at a speed of 1500 mm / min, controlling the film thickness to 100 µm. The film was immediately placed in a coagulation bath at pH 8 and 70 °C for phase inversion to form a membrane for 30 minutes. The membrane was then immersed in the above solution for 24 h to remove residual solvent and reactive porogens. Finally, the membrane was immersed in a 50% glycerol aqueous solution for 2 h and allowed to air dry to obtain a small-pore precision separation membrane. The resulting membrane has a pore size of 20 nm and a wide distribution (10-65 nm) (pore size and pore size distribution are shown in Figures 1-2). Figure 2 and Figure 3 (As shown), but the membrane permeation flux is very low (i.e., very few surface pores), only 15 L / (m²). 2 ·h).

[0057] Depend on Figure 2 The scanning electron microscope images show that the membrane surface in this comparative example has fewer pores and the pore sizes are uneven. Figure 3 As can be seen from the curve, the membrane has a wide pore size distribution and a low concentration of pore size on the surface. Therefore, the membrane is difficult to use for high-throughput precision separation.

Claims

1. A method for preparing a small-pore precision separation membrane, comprising the following steps: (1) The film-forming polymer and the additives are added to the solvent and dissolved at 20-70°C. The mixture is then allowed to cool naturally to below 60°C. Vacuum degassing is performed at this temperature to form solution 1. The additives are selected from one or more of water, tetrahydrofuran, methanol, ethanol, and glycerol. The reactive porogen is added to the same solvent and stirred to dissolve at 20-40°C. The solution is then degassed under vacuum at this temperature to form solution 2. The reactive porogen is one or more of azobisisobutyronitrile, diisopropyl azodicarbonate, diethyl azodicarbonate, azodicarbonamide, sodium borohydride, and p-toluenesulfonyl hydrazine. Slowly pour solution 2 into solution 1 and keep it at 40-60℃ for a period of time to form a casting solution; (2) Prepare a solution film with a thickness of 100-500 micrometers from the casting solution obtained in step (1); (3) Immerse the solution membrane from step (2) in a coagulation bath with a pH of 7-14 and let it stand in the coagulation bath for no less than 30 seconds to obtain a fine separation membrane with small pores. (4) Immerse the small-pore precision separation membrane obtained in step (3) into an aqueous solution with a pH value of 7-14 at room temperature to 70°C for 0.5-48 hours to allow the unreacted reactive porogen in step (3) to react completely. (5) The small-hole precision separation membrane treated in step (4) is washed with distilled water, and then treated with distilled water or glycerol solution before storage.

2. The method for preparing a precision separation membrane with small pores according to claim 1, wherein in step (1), the membrane-forming polymer is one or two of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyphenylene sulfide, and polyimide; and the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

3. The method for preparing a precision separation membrane with small pores according to claim 1, wherein in step (1), the solvent ratio in solution 1 and solution 2 is 4:1, the content of the film-forming polymer is 12%-30%, the content of the reactive pore-forming agent is 2%-14%, and the content of the auxiliary agent is 0-10%, based on the total weight of the casting solution.

4. The method for preparing a precision separation membrane with small pores according to claim 1, wherein in step (3), the temperature of the coagulation bath is room temperature to 70°C.

5. The method for preparing a precision separation membrane with small pores according to claim 1, wherein the pH value of the aqueous solution is the same as the pH value of the coagulation bath in step (3).

6. The method for preparing a precision separation membrane with small pores according to claim 1, wherein the process of generating nanobubbles by decomposing the reactive porogen occurs in steps (1) to (4), or steps (1) to (3), or in step (3).

7. A precision separation membrane with small pores prepared according to any one of claims 1-6.

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