A method for preparing separation membrane using small molecule monomers

Abstract

The invention discloses a method for preparing a separation membrane using a small molecule monomer, specifically comprising the following steps: (1) in an inert gas atmosphere, a monomer, a salt, a solvent and an entrainer are added to a reactor, the system is first heated to 100-150°C, dehydrated for 1-12h, and then the entrainer is removed; the system is then heated to 150-300°C, and the isothermal reaction is carried out for 0.5-20h; finally, the system is temperature-controlled at 100-300°C, and an end-capping agent is added, and the isothermal reaction is carried out for 0.5-10h; (2) filtering; (3) adding a porogen and / or a diluting solvent and stirring evenly; (4) film-making is carried out after degassing, and the obtained film is obtained. The inventive method starts from a monomer and directly prepares a high-performance polymer film, realizes the integration of membrane material synthesis and film-making process, shortens the production cycle, and solves the problems of organic solvent waste, energy consumption and environmental pollution in traditional processes.

Description

Technical Field

[0001] The invention relates to the technical field of membrane material synthesis, and more specifically to a method for preparing a separation membrane using small molecule monomers. Background Art

[0002] Membrane separation technology is a new field that is the result of the cross-integration and mutual penetration of many disciplines such as materials science and process engineering science. As a highly efficient separation technology, membrane separation technology has now been widely used in the fields of chemical industry, environmental protection, electronics, light industry, textile, petroleum, food, medicine, biotechnology and energy engineering. Membrane separation technology has received widespread attention in solving the water resource crisis due to its advantages of continuous separation, low energy consumption and easy combination with other separation processes. Most of the separation membranes currently used are organic membranes made of organic polymers as raw materials.

[0003] Common membrane materials are polysulfone, polyethersulfone, polyetheretherketone and amphiphilic block copolymers. The synthesis of these polymer materials is usually accompanied by lengthy post-processing processes, such as sedimentation, washing, purification and drying. These processes not only extend the production cycle of materials and increase manufacturing costs, but also consume a lot of water and generate a lot of wastewater and waste liquid, which easily cause environmental pollution.

[0004] In addition, in the traditional membrane making process, the preparation of the casting solution requires the consumption of a large amount of organic solvents, the dissolution process of the polymer is often accompanied by heating and the dissolution process takes a long time.

[0005] Comparing the post-processing process of polymer material synthesis and the traditional membrane preparation method, a lot of solvents, water resources and time are wasted during the process. If the two processes can be combined, the reaction products can be directly used for membrane preparation, eliminating the cumbersome operation process in between, and realizing an integrated process from small molecule monomers to membrane preparation, it can effectively solve the problems of environmental pollution and resource waste.

[0006] Therefore, how to develop a method for preparing separation membranes using small molecule monomers is an urgent problem that technicians in this field need to solve. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a method for preparing separation membranes using small molecule monomers, which integrates membrane material synthesis and membrane making process, can reduce the amount of organic solvents used, reduce energy consumption, reduce process steps, reduce wastewater and waste liquid, etc.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] The method for preparing a separation membrane using a small molecule monomer specifically comprises the following steps:

[0010] (1) Under an inert gas atmosphere, a monomer, a salt, a solvent and an azeotropic agent are added to a reaction kettle, the system is first heated to 100-150° C., dehydrated for 1-12 hours, and then the azeotropic agent is removed; the system is then heated to 150-300° C., and the reaction is carried out at a constant temperature for 0.5-20 hours; finally, the system is temperature-controlled at 100-300° C., and a capping agent is added, and the reaction is carried out at a constant temperature for 0.5-10 hours to obtain a reaction liquid;

[0011] (2) filtering the reaction solution to obtain a clarified solution;

[0012] (3) adding a porogen and / or a diluent solvent to the clarified solution and stirring the solution to obtain a casting solution;

[0013] (4) Degassing the casting solution and then forming a membrane to obtain a separation membrane.

[0014] Furthermore, in the above step (1), the monomers include monomer A and monomer B, and the molar ratio of monomer A to monomer B is (0.95-1.10):1, or the film is formed by the monomers alone; wherein monomer A is one or more aromatic diols or aromatic diol salt compounds, with the general formula HO-R-OH, wherein R is any derivative containing a benzene ring; monomer B is one or more aromatic monohalogen, dihalogen, trihalogen or tetrahalogenated compounds, with the general formula HRH`, wherein H is any halogen atom, H` is a halogen atom, a thiol group or a hydroxyl group, and R is any derivative containing a benzene ring.

[0015] Furthermore, the monomer A includes, but is not limited to, bisphenol A, bisphenol S, biphenol, hydroquinone, 4,4'-dihydroxydiphenyl sulfone, 2,2'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfide, 3,3'-dihydroxydiphenylamine, 2,2'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxybenzophenone, 1,4'-dihydroxynaphthalene, 1,5'-dihydroxynaphthalene, 1,6'-dihydroxynaphthalene, 2,6' -dihydroxynaphthalene and 2,7'-dihydroxynaphthalene; Monomer B includes, but is not limited to, p-fluorodiphenyl sulfone, p-chlorodiphenyl sulfone, p-bromodiphenyl sulfone, 4,4'-difluorodiphenyl sulfone, 4,4'-dichlorodiphenyl sulfone, 3-fluoro-4-chlorobenzophenone, 3-chloro-4-fluorobenzophenone, 4,4'-difluorobenzophenone, 3,4'-difluorobenzophenone, 3,4'-dichlorobenzophenone, 4,4'-dichlorobenzophenone, halogenated thiophenol, dichlorobenzene, 3,3,4,4'-tetrachlorodiphenyl sulfone and 3,3,4,4'-tetrafluorodiphenyl sulfone.

[0016] The beneficial effect of adopting the above further technical solution is that the present invention can control the molecular structure and performance generated in the feed solution by adjusting the types and proportions of monomer A and monomer B, and then adjust the separation performance of the formed membrane.

[0017] Furthermore, in the above step (1), the mass ratio of the salt to the monomer A is (1-5):1, specifically at least one of potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, sodium phosphate, potassium phosphate, sodium sulfide and sulfur; the mass of the solvent is 40%-90% of the total mass of the reaction system, specifically at least one of dimethyl sulfoxide, dimethyl sulfone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, cyclopentane sulfone and N-ethylpyrrolidone; the mass of the entrainer is 3%-50% of the mass of the solvent, specifically at least one of toluene, xylene, trimethylbenzene, tetramethylbenzene, chlorobenzene, ethylbenzene, diethylbenzene and diethylidene.

[0018] The beneficial effect of adopting the above further technical scheme is that the salt selected by the present invention is used as a catalyst for the reaction to promote the generation of high molecular weight products; the solvent selected by the present invention is used to dissolve the monomer and the reaction product, and the high boiling point solvent helps the reaction to proceed at a high temperature; the entrainer selected by the present invention is mainly used to remove the reaction byproduct water to promote the generation of high molecular weight products. Therefore, the present invention can control the molecular weight of the molecules in the generated feed liquid by adjusting the types and addition amounts of salt, entrainer and solvent, and then adjust the separation performance of the formed membrane.

[0019] Furthermore, in the above step (1), the end-capping agent is any one or more small molecules and polymer materials that can react with phenolic hydroxyl groups or aromatic halides, and the structure is linear, comb-shaped, cyclic or hyperbranched, and the molar ratio of the end-capping agent to the monomer is (0-5):100.

[0020] Furthermore, the above-mentioned end-capping agent includes, but is not limited to, polyethylene glycol, hyperbranched polyglycerol ether, polypropylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, cyclodextrin, polyethylene glycol methacrylate, polymethacrylic acid, polyvinyl alcohol, polypropylene alcohol, dextran, chitosan, polyacrylic acid, cyclodextrin, polyethyleneimine, glucose, glycerol, 4,4'-dichlorodiphenyl sulfone, 4-chlorodiphenyl sulfone, benzoyl chloride, bisphenol S, bisphenol A, phenol, p-cresol, p-methoxyphenol, methyldichlorosilane, methyl chloride, phenylethyldichlorosilane, phenoxytitanium trichloride, ethoxytitanium trichloride, 3,4'-dihalobenzophenone, 3-fluoro-4-chlorobenzophenone, 3-chloro-4-fluorobenzophenone, 3,4'-difluorobenzophenone, 3,4'-dichlorobenzophenone, aromatic polyphenols and polyhydroxyadamantane derivatives.

[0021] The beneficial effect of adopting the above further technical scheme is that the capping agent selected in the present invention can improve the stability and functionality of the product, and the structure, performance and molecular weight of the molecules in the generated feed liquid can be controlled by adjusting the type and addition amount of the capping agent, thereby adjusting the separation performance of the formed membrane.

[0022] Furthermore, in the above step (3), the porogen includes but is not limited to polymer porogens, small molecule organic matter and inorganic salt porogens and nano material porogens, and the mass thereof is 0-40% of the mass of the casting solution.

[0023] Furthermore, the above-mentioned polymer porogen is at least one of polyvinyl pyrrolidone, cyclodextrin, hyperbranched polyglycerol ether, polyoxypropylene, polyvinyl alcohol, polypropylene alcohol, dextran, polyethylene glycol, polypropylene glycol, chitosan, polymethacrylic acid, polymethacrylate and polyoxyethylene polyoxypropylene ether block copolymer (poloxamer); the small molecule organic and inorganic salt porogen is at least one of sodium dodecyl sulfate, camphorsulfonic acid, dopamine, glycerol, Tween, Span, tannic acid, zinc chloride, calcium carbonate, lithium nitrate, lithium chloride, sodium chloride, potassium chloride and lithium perchlorate; the nanomaterial porogen is at least one of graphene oxide, modified carbon nanotubes, modified silicon dioxide nanoparticles, modified titanium dioxide nanoparticles, modified montmorillonite, modified halloysite and modified calcium carbonate nanoparticles.

[0024] The beneficial effect of adopting the above further technical solution is that the porogen selected by the present invention can improve the porosity of the prepared membrane, thereby improving the water permeability of the membrane. By adjusting the type and amount of the porogen, the viscosity and properties of the generated feed liquid can be controlled, and then the separation performance of the formed membrane can be adjusted.

[0025] Furthermore, in the above step (3), the mass of the dilution solvent is 0-40% of the mass of the casting solution, and is at least one of methanol, ethanol, diethylene glycol, ethylene glycol, isopropanol, methyl ethyl ketone, N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, dioxane, ethyl acetate, methyl acetate, N,N-dimethylacetamide, dimethyl sulfoxide, sulfolane and tetramethyl sulfoxide.

[0026] The beneficial effect of adopting the above further technical solution is that the present invention can adjust the viscosity of the generated feed liquid, the state and properties of the casting liquid by adding different types of diluents, and then adjust the separation performance of the formed membrane.

[0027] Furthermore, in the above step (4), the film forming method is phase inversion, spin coating, spray coating, electrospinning or casting; wherein the phase inversion method is solvent evaporation phase inversion, vapor phase inversion, thermal phase inversion or immersion precipitation phase inversion; the coagulation bath used in the immersion precipitation phase inversion method is water or a mixed solvent of water and an organic solvent; further, the organic solvent is at least one of methanol, ethanol, isopropanol, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tetramethyl sulfoxide, cyclopentane sulfone and diphenyl sulfone.

[0028] The beneficial effect of adopting the above-mentioned further technical scheme is that the present invention can control the structure of the prepared membrane by adjusting the membrane making method and related membrane making parameters (such as the rotation speed used in the spin coating method, the distance used in the spray coating method, the voltage used in the electrospinning method, the type of coagulation bath used in the phase inversion method, etc.), and then adjust the separation performance of the formed membrane.

[0029] Furthermore, in the above step (4), the separation membrane is a flat membrane or a hollow fiber with or without a support layer, and the pore size range of the separation membrane is -50μm, used for gas or liquid separation; further, the supporting layer is a polymer porous material, a ceramic porous material or a metal porous material.

[0030] The beneficial effect of adopting the above-mentioned further technical solution is that the present invention can select whether a support layer is needed and the type of support layer in the membrane making process according to the requirements of the use environment. The support layer is mainly used to improve the strength and mechanical stability of the membrane; according to the separation accuracy requirements, a separation membrane with a suitable pore size can be selected to achieve an efficient separation process.

[0031] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. The present invention adds the monomers required for polymerization into the reactor, removes the by-products and impurities of the reaction by filtering after the polymerization, and the obtained filtrate is directly used for membrane preparation, thereby realizing the efficient coupling and integration of material synthesis and membrane preparation process, reducing the use of organic solvents, reducing the generation of wastewater and waste liquid, and reducing the waste of energy resources.

[0033] 2. The method of the present invention directly prepares high-performance polymer membranes from monomers, realizes the integration of membrane material synthesis and membrane making process, shortens the production cycle, and solves the problems of organic solvent waste, energy consumption and environmental pollution in traditional processes.

[0034] 3. The method of the present invention can be widely used to prepare membrane products such as flat membranes and hollow fibers.

[0035] 4. The method of the present invention has clear ideas and remarkable effects, and is the first of its kind in China and abroad. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] The method for preparing a (polyethersulfone) separation membrane using a small molecule monomer specifically comprises the following steps:

[0039] (1) Under an inert gas atmosphere, 2.0 mol of bisphenol S, 2.04 mol of 4,4'-dichlorodiphenyl sulfone and 8 mol of potassium carbonate were added to a 5 L reactor. After the oxygen in the reaction system was removed by using the Schlenk technique, 3 L of cyclopentane sulfone and 0.5 L of toluene were added. The system was first heated to 140° C. for dehydration treatment for 12 h to remove the water in the system; then the system was heated to 210° C. for constant temperature reaction for 8 h to obtain polyethersulfone with a number average molecular weight of 30,000 Da (wherein PDI=1.52);

[0040] (2) adding polyethersulfone to an online filter and filtering using a polytetrafluoroethylene membrane with an average pore size of 5 μm to remove salt particles and obtain a clear solution;

[0041] (3) adding 5% of the total mass of the casting solution of polyvinyl pyrrolidone (PVP-K50) to the clarified solution and stirring evenly to obtain a casting solution;

[0042] (4) The casting solution is ultrasonically degassed for 2 h, then coated on a PET non-woven fabric using a coating machine, placed in a coagulation bath to solidify into a film, then washed with water and soaked in glycerol to obtain a polyethersulfone flat membrane.

[0043] Example 2

[0044] The method for preparing a (polysulfone) separation membrane using a small molecule monomer specifically comprises the following steps:

[0045] (1) Under an inert gas atmosphere, 4.0 mol of bisphenol A, 4.08 mol of 4,4'-dichlorodiphenyl sulfone and 16 mol of potassium carbonate were added to a 10 L reactor. After removing oxygen from the reaction system using the Schlenk technique, 6 L of N,N-dimethylacetamide and 1.5 L of toluene were added. The system was first heated to 150° C. for dehydration treatment for 12 h to remove water from the system; the system was then heated to 165° C. for constant temperature reaction for 8 h to obtain a polysulfone with a number average molecular weight of 40,000 Da (wherein PDI=1.40);

[0046] (2) using 200-mesh diatomaceous earth filled in a chromatography column to filter the polysulfone to remove salt particles and obtain a clear solution;

[0047] (3) adding 10% of the total mass of the casting solution and polyethylene glycol (PEG2000) with a molecular weight of 2000 Da to the clarified solution and stirring evenly to obtain a casting solution;

[0048] (4) The casting solution is allowed to stand for degassing, and then coated on a PP non-woven fabric using a coating machine, placed in a coagulation bath to solidify into a film, and then washed with water and soaked in glycerol to obtain a polysulfone flat membrane.

[0049] Example 3

[0050] The method for preparing a (PSf-b-PEG block copolymer) separation membrane using a small molecule monomer specifically comprises the following steps:

[0051] (1) Under an inert gas atmosphere, 1.5 mol of bisphenol A, 1.5 mol of 4,4'-dichlorodiphenyl sulfone and 6 mol of potassium carbonate were added to a 5 L reactor. After the oxygen in the reaction system was removed by Schlenk technique, 2.5 L of N,N-dimethylacetamide and 1 L of toluene were added. The system was first heated to 150° C. for dehydration for 12 h to remove the water in the system; then the system was heated to 165° C. for constant temperature reaction for 8 h; finally, the system was controlled at 165° C., and 26.4 g of polyethylene glycol with a molecular weight of 400 Da was added, and the reaction was carried out at a constant temperature for 4 h to obtain a PSf-b-PEG block copolymer with a PEG content of 13 wt% (wherein Mn=42000 Da, PDI=1.65);

[0052] (2) filtering the PSf-b-PEG block copolymer using a 3 μm stainless steel filter to remove salt particles and obtain a clear solution;

[0053] (3) adding 40% of tetrahydrofuran by weight of the total mass of the casting solution to the clarified solution and stirring the mixture to obtain a casting solution;

[0054] (4) The casting solution was allowed to stand for degassing, and then coated on a PE non-woven fabric using a coating machine. After being placed in an air bath for 60 seconds, the solution was placed in a coagulation bath to solidify into a film, and then washed with water and soaked in glycerol to obtain a PSf-b-PEG flat membrane.

[0055] Example 4

[0056] The method for preparing a (PSf-b-hPG block copolymer) separation membrane using a small molecule monomer specifically comprises the following steps:

[0057] (1) Under an inert gas atmosphere, 2.0 mol of bisphenol A, 2.04 mol of 4,4'-dichlorodiphenyl sulfone and 8 mol of potassium carbonate were added to a 5 L reactor. After the oxygen in the reaction system was removed by Schlenk technology, 2.5 L of N,N-dimethylacetamide and 0.5 L of toluene were added. The system was first heated to 150° C. for dehydration for 12 h to remove the water in the system; then the system was heated to 165° C. for constant temperature reaction for 9 h; finally, the system was controlled at 165° C., and 66 g of hPG with a molecular weight of 2000 Da was added, and the reaction was carried out at a constant temperature for 4 h to obtain a PSf-b-hPG block copolymer with an hPG content of 5 wt% (wherein Mn=39000 Da, PDI=1.86);

[0058] (2) using a 3 μm stainless steel filter to perform online filtration on the PSf-b-hPG block copolymer to remove salt particles and obtain a clear solution;

[0059] (3) adding 40% of tetrahydrofuran by weight of the total mass of the casting solution to the clarified solution and stirring the mixture to obtain a casting solution;

[0060] (4) The casting solution is allowed to stand for degassing, and then coated on a metal porous substrate using a coating machine, placed in a coagulation bath to solidify into a film, and then washed with water and soaked in glycerol to obtain a PSf-b-hPG flat membrane.

[0061] Example 5

[0062] The method for preparing a (PEG-b-PSf-b-PEG block copolymer) separation membrane using a small molecule monomer specifically comprises the following steps:

[0063] (1) Under an inert gas atmosphere, 1.50 mol of bisphenol A, 1.53 mol of 4,4'-dichlorodiphenyl sulfone and 6 mol of potassium carbonate were added to a 5 L reactor. After removing oxygen from the reaction system using the Schlenk technique, 2.3 L of N,N-dimethylacetamide and 1 L of toluene were added. The system was first heated to 150° C. for dehydration for 12 h to remove water from the system; the system was then heated to 165° C. for constant temperature reaction for 8 h; finally, the system was controlled at 165° C., and 360 g of polyethylene glycol with a molecular weight of 6000 Da was added, and the reaction was continued at constant temperature for 5 h to obtain a PEG-b-PSf-b-PEG block copolymer with a PEG content of 23 wt% (wherein Mn=46000 Da, PDI=1.74);

[0064] (2) filtering the PEG-b-PSf-b-PEG block copolymer using a 7 μm ceramic membrane to remove salt particles and obtain a clear solution;

[0065] (3) adding 40% of tetrahydrofuran by weight of the total mass of the casting solution to the clarified solution and stirring the mixture to obtain a casting solution;

[0066] (4) The casting solution is allowed to stand for degassing, and then coated on a metal porous substrate using a coating machine, placed in a coagulation bath to solidify into a film, and then washed with water and soaked in glycerol to obtain a PEG-b-PSf-b-PEG flat membrane.

[0067] Performance Testing

[0068] 1. Separation performance test

[0069] The separation membranes prepared in Examples 1-5 were respectively tested for pure water flux, Congo red or bovine serum albumin retention rate and average pore size at a pressure of 3 bar using a cross-flow device. The results are shown in Table 1.

[0070] Table 1 Test results of separation membrane performance of Examples 1-5

[0071]

[0072] As can be seen from Table 1, Examples 1-5 of the present invention adjust the molecular structure of the product and the membrane-forming parameters to achieve the adjustment of the pore size of the formed membrane, thereby meeting different use environments and separation requirements.

[0073] 2. Energy consumption analysis

[0074] The preparation method of Example 1 and the traditional process production of 1m 2 The resources required for the membrane (water, electricity, organic solvent and time) were calculated, and the resource savings during the operation of the preparation method of Example 1 were calculated compared with the traditional membrane making process. The results are shown in Table 2.

[0075] Table 2 Example 1 Preparation method Production 1m 2 Summary of resources saved by membrane

[0076] project Save energy Water consumption in polymer purification and washing processes 5L water Power consumption of polymer drying process 2.5kWh Solvent consumption during polymer re-dissolution 0.2kg organic solvent Time consumed from material synthesis to membrane preparation 48h

[0077] It can be seen from Table 2 that, compared with the traditional process, the integrated separation membrane preparation process adopted in the present invention can significantly improve the production efficiency, achieve the maximum savings in water, organic solvents and electrical energy, and significantly reduce the generation of waste liquid.

[0078] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a separation membrane using a small molecule monomer, characterized in that: The specific steps include: (1) In an inert gas atmosphere, monomers, salts, solvents and entrainers are added to a reactor, the system is first heated to 100-150° C., dehydrated for 1-12 hours, and then the entrainer is removed; the system is then heated to 150-300° C., and the reaction is carried out at a constant temperature for 0.5-20 hours; finally, the system is temperature-controlled at 100-300° C., and a capping agent is added, and the reaction is carried out at a constant temperature for 0.5-10 hours to obtain a reaction liquid; wherein the monomers include monomer A and monomer B, and the molar ratio of monomer A to monomer B is (0.95-1.10):1, or the monomers are used to form a film alone; The end-capping agent includes, but is not limited to, polyethylene glycol, hyperbranched polyglycerol ether, polypropylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, cyclodextrin, polyethylene glycol methacrylate, polymethacrylic acid, polyvinyl alcohol, polypropylene alcohol, dextran, chitosan, polyacrylic acid, cyclodextrin, polyethylene imine, glucose, glycerol, 4,4′-dichlorodiphenyl sulfone, 4-chlorodiphenyl sulfone, benzoyl chloride, bisphenol S, bisphenol A, phenol, p-cresol, p-methoxyphenol, methyldichlorosilane, chloromethane, phenylethyldichlorosilane, phenoxytitanium trichloride, ethoxytitanium trichloride, 3,4′-dihalobenzophenone, 3-fluoro-4-chlorobenzophenone, 3-chloro-4-fluorobenzophenone, 3,4′-difluorobenzophenone, 3,4′-dichlorobenzophenone, aromatic polyphenols, and polyhydroxyadamantane derivatives; (2) filtering the reaction solution to obtain a clarified solution; (3) adding a porogen and / or a diluent solvent to the clarified solution and stirring the solution to obtain a casting solution; (4) degassing the casting solution and then forming a membrane to obtain the separation membrane; In step (1), the mass ratio of the salt to monomer A is (1-5): 1, and the salt is at least one of potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, sodium phosphate, potassium phosphate, sodium sulfide and sulfur; The mass of the solvent is 40%-90% of the total mass of the reaction system, and the solvent is at least one of dimethyl sulfoxide, dimethyl sulfone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, cyclopentane and N-ethylpyrrolidone; The mass of the entrainer is 3%-50% of the mass of the solvent, and the entrainer is at least one of toluene, xylene, trimethylbenzene, tetramethylbenzene, chlorobenzene, ethylbenzene, diethylbenzene and diethylidene benzene; In step (1), the molar ratio of the end-capping agent to the monomer is (0-5):100; In step (3), the porogen includes but is not limited to polymer porogens, small molecule organic matter and inorganic salt porogens and nano material porogens; the mass of the porogen is 0-40% of the mass of the casting solution.

2. A method for preparing a separation membrane using small molecule monomers according to claim 1, characterized in that: In step (1), the monomer A is one or more aromatic diols or aromatic diol salt compounds, with the general formula HO-R-OH, wherein R is any derivative containing a benzene ring; The monomer B is one or more aromatic monohalogen, dihalogen, trihalogen or tetrahalogen compounds, with the general formula HRH', wherein H is any halogen atom, H' is a halogen atom, a thiol group or a hydroxyl group, and R is any derivative containing a benzene ring.

3. A method for preparing a separation membrane using small molecule monomers according to claim 2, characterized in that: The monomer A includes but is not limited to bisphenol A, bisphenol S, biphenol, hydroquinone, 4,4′-dihydroxydiphenyl sulfone, 2,2′-dihydroxybiphenyl, 4,4′-dihydroxybiphenyl, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenyl sulfide, 3,3′-dihydroxydiphenylamine, 2,2′-dihydroxydiphenylmethane, 4,4′-dihydroxydiphenylmethane, 4,4′-dihydroxybenzophenone, 1,4′-dihydroxynaphthalene, 1,5′-dihydroxynaphthalene, 1,6′-dihydroxynaphthalene, 2,6′-dihydroxynaphthalene and 2v7′-dihydroxynaphthalene; The monomer B includes, but is not limited to, p-fluorodiphenyl sulfone, p-chlorodiphenyl sulfone, p-bromodiphenyl sulfone, 4,4′-difluorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone, 3-fluoro-4-chlorobenzophenone, 3-chloro-4-fluorobenzophenone, 4,4′-difluorobenzophenone, 3,4′-difluorobenzophenone, 3,4′-dichlorobenzophenone, 4v4′-dichlorobenzophenone, halogenated thiophenol, dichlorobenzene, 3,3,4,4′-tetrachlorodiphenyl sulfone and 3,3,4,4′-tetrafluorodiphenyl sulfone.

4. The method for preparing a separation membrane using small molecule monomers according to claim 1, characterized in that: The polymer porogen is at least one of polyvinyl pyrrolidone, cyclodextrin, hyperbranched polyglycerol ether, polyoxypropylene, polyvinyl alcohol, polypropylene alcohol, dextran, polyethylene glycol, polypropylene glycol, chitosan, polymethacrylic acid, polymethacrylate and polyoxyethylene polyoxypropylene ether block copolymer; The small molecule organic matter and inorganic salt porogen is at least one of sodium dodecyl sulfate, camphorsulfonic acid, dopamine, glycerol, Tween, Span, tannic acid, zinc chloride, calcium carbonate, lithium nitrate, lithium chloride, sodium chloride, potassium chloride and lithium perchlorate; the nano material porogen is at least one of graphene oxide, modified carbon nanotubes, modified silicon dioxide nanoparticles, modified titanium dioxide nanoparticles, modified montmorillonite, modified halloysite and modified calcium carbonate nanoparticles.

5. The method for preparing a separation membrane using small molecule monomers according to claim 1, characterized in that: In step (3), the mass of the dilution solvent is 0-40% of the mass of the casting solution; The diluting solvent is at least one of methanol, ethanol, diethylene glycol, ethylene glycol, isopropanol, methyl ethyl ketone, N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, dioxane, ethyl acetate, methyl acetate, N,N-dimethylacetamide, dimethyl sulfoxide, sulfolane and tetramethyl sulfoxide.

6. The method for preparing a separation membrane using small molecule monomers according to claim 1, characterized in that: In step (4), the film forming method is phase inversion, spin coating, spray coating, electrospinning or casting; The phase inversion method is a solvent evaporation phase inversion method, a vapor phase inversion method, a thermally induced phase inversion method or an immersion precipitation phase inversion method; The coagulation bath used in the immersion precipitation phase conversion method is water or a mixed solvent of water and an organic solvent; The organic solvent is at least one of methanol, ethanol, isopropanol, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tetramethyl sulfoxide, sulfolane and diphenyl sulfone.

7. The method for preparing a separation membrane using small molecule monomers according to claim 1, characterized in that: In step (4), the separation membrane is a flat membrane or a hollow fiber with or without a support layer, and the pore size range of the separation membrane is The support layer is a polymer porous material, a ceramic porous material or a metal porous material.

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