Preparation method of asymmetric polyether sulfone microporous filter membrane and microporous filter membrane

Abstract

The application provides a preparation method of an asymmetric polyether sulfone microporous filter membrane, polyether sulfone is dissolved in a solvent and an additive and a pore-forming agent are added, uniform mixing is carried out to obtain a casting solution, the casting solution is subjected to high-temperature blade casting after vacuum treatment, then is subjected to low-temperature cold roller induction treatment, and then is sent to a constant-temperature and constant-humidity environment for steam induction treatment, and finally is subjected to water bath solidification to form a wet membrane; the wet membrane is soaked in an ethanol aqueous solution and is dried to obtain the asymmetric polyether sulfone microporous filter membrane. In the method, a temperature difference is formed by high-temperature blade casting and low-temperature cold roller induction, the relative viscosity of the casting solution is regulated through the temperature difference, the viscosity of the casting solution at the bottom of the membrane is increased, phase separation is difficult, the viscosity of the upper and lower surfaces of the liquid membrane is different, the phase separation rate of the liquid membrane in the steam induction stage is controlled, the controllability of non-solvent movement is achieved, and thus an integrated asymmetric microporous filter membrane structure is formed, the surface has high porosity, the pollution capacity is increased, and the service life is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microporous membrane, in particular to a preparation method of asymmetric polyether sulfone microporous filter membrane. BACKGROUND

[0002] As a kind of polymer membrane material with excellent comprehensive performance, polyether sulfone (PES) has superior blood compatibility, corrosion resistance, heat resistance and other properties. Because the structure of the membrane prepared from polyether sulfone material is very sensitive to various film-forming conditions in the film-forming process, it is difficult to obtain high-precision PES asymmetric membrane by phase inversion method through the formulation, temperature and environmental conditions of the film-forming solution and coagulation bath. Therefore, the existing phase inversion process must be significantly improved.

[0003] For example, patent No. CN1759924B discloses a kind of multilayer composite asymmetric ultrafiltration membrane, which is prepared by co-casting at least two different casting solutions through a coating machine, forming a layered structure that is not integrally formed. The adhesion between layers is required to be high, otherwise the layers are easy to separate, affecting the filtration effect. Moreover, the preparation process requires the co-configuration of multiple casting solutions, which is relatively complicated to operate. At the same time, the composite process is complex, resulting in high economic cost. Therefore, the market urgently needs to develop a simpler preparation process that can prepare high-precision, integrally structured asymmetric PES membranes. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to:

[0005] In a first aspect, a preparation method of asymmetric polyether sulfone microporous filter membrane is provided, which is characterized by the following steps:

[0006] S1, dissolve polyether sulfone in a solvent and add additives and pore-forming agents, mix uniformly to obtain a casting solution, the additives include one of polyethylene glycol, glycolic acid and 2-pyrrolidone and polyhydric alcohol, the mass ratio of polyethylene glycol, glycolic acid or 2-pyrrolidone to polyhydric alcohol is (1-7):1;

[0007] S2, after vacuum treatment, the casting solution is scraped by high temperature of 50-80℃, then induced by low temperature cold roller of-10-20℃, and then sent to a constant temperature and humidity environment for steam induction treatment, and finally water bath solidification to form a wet film;

[0008] S3, after the wet film is soaked in ethanol aqueous solution, it is dried to obtain an asymmetric polyether sulfone microporous filter membrane.

[0009] In combination with the first aspect, in one implementation, the mass ratio of the additives to the polyether sulfone is (1-4):1.

[0010] In combination with the first aspect, in an implementation form, the vacuumizing process in step S2 is performed for 20-40 minutes.

[0011] In combination with the first aspect, in an implementation form, the high-temperature blade coating in step S2 is performed in a constant-temperature environment, the thickness of the blade coating is 100-120 um, and the pulling speed of the blade coating is 1-4 m / s.

[0012] In combination with the first aspect, in an implementation form, the low-temperature cold roller induction in step S2 is performed for 5-30 seconds.

[0013] In combination with the first aspect, in an implementation form, the constant-temperature and constant-humidity environment in step S2 has a temperature of 20-45℃ and a relative humidity of 40-90 RH%.

[0014] In combination with the first aspect, in an implementation form, the steam induction in step S2 has a steam temperature of 20-45℃ and a steam induction time of 5-60 seconds, and / or the water bath solidification has a temperature of 25-45℃.

[0015] In combination with the first aspect, in an implementation form, the solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, the mass ratio of the solvent to the polyether sulfone is (3-7):1; the porogen includes polyvinylpyrrolidone with a weight average molecular weight of 30000-58000 Da, and the mass ratio of the porogen to the polyether sulfone is 1:(5-15).

[0016] The second aspect also provides a microporous filter membrane, which is prepared by the preparation method of the asymmetric polyether sulfone microporous filter membrane in any implementation form of the first aspect. The microporous filter membrane includes a first porous layer, an intermediate porous layer and a second porous layer stacked along a thickness direction. The pore size of the microporous filter membrane decreases along the thickness direction from one side to the other side, and the pore size of the first porous layer decreases along the thickness direction. The average pore size of the first porous layer is 460-3500 nm, and the average pore size of the second porous layer is 135-325 nm.

[0017] In combination with the second aspect, in an implementation form, the pore size of the intermediate porous layer decreases along the thickness direction, and the pore size of the second porous layer decreases along the thickness direction.

[0018] As described above, the preparation method of the asymmetric polyether sulfone microporous filter membrane and the microporous filter membrane of the present application at least have the following beneficial effects: high-temperature blade casting and low-temperature cold roller induction form a temperature difference, the relative viscosity of the casting solution is regulated by the temperature difference, the viscosity of the casting solution at the bottom of the membrane is increased, the phase separation is difficult, the viscosity difference between the upper and lower surfaces of the liquid film is caused, thereby facilitating the formation of the asymmetric microporous filter membrane structure, and the high precision of the interception can be ensured; and by controlling the phase separation rate of the liquid film in the vapor induction stage, the controllability of the non-solvent movement is achieved, further assisting the formation of the gradient and integrated asymmetric microporous filter membrane structure, the surface has high porosity, the pollution capacity is increased, and the service life is increased. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 1 of the present application.

[0020] Fig. 2 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 2 of the present application.

[0021] Fig. 3 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 3 of the present application.

[0022] Fig. 4 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 4 of the present application.

[0023] Fig. 5 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 5 of the present application.

[0024] Fig. 6 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 6 of the present application.

[0025] Fig. 7 It is a cross-sectional electron microscope photo of the asymmetric polyether sulfone microporous filter membrane of the embodiment 7 of the present application. DETAILED DESCRIPTION

[0026] The embodiments of the present application are described below by way of specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure. The present application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the present application. It should be understood that the preferred embodiments are only for illustrating the present application, and are not intended to limit the protection scope of the present application.

[0027] It should be noted that the raw materials used in the technical scheme of the present application: polyether sulfone (PES for short), polyol, polyethylene glycol, glycolic acid, 2-pyrrolidone, N,N-dimethylacetamide (DMAC for short), N,N-dimethylformamide (DMF for short), N-methyl pyrrolidone (NMP for short), dimethyl sulfoxide, polyvinylpyrrolidone, etc. are all commercially available products.

[0028] The polyol is one of glycerol, triethylene glycol, diethylene glycol and ethylene glycol.

[0029] Firstly, the technical scheme of the present application provides a preparation method of asymmetric polyether sulfone microporous filter membrane, which is prepared according to the following steps:

[0030] S1, polyether sulfone is dissolved in a solvent and additives and pore-forming agents are added, and the mixture is uniformly mixed to obtain a casting solution, the additives include one of polyethylene glycol, glycolic acid and 2-pyrrolidone and polyol, the mass ratio of the polyethylene glycol, glycolic acid or 2-pyrrolidone to the polyol is (1-7):1; two additives form a composite additive system, and the additives have different migration rates in the vapor induction stage due to their different hydrophilic and hydrophobic properties, so that the microporous filter membrane with gradient distribution of pore size is more easily obtained. In addition, in order to ensure that the temperature of the film casting solution can quickly reach the ideal temperature, the raw materials are preheated synchronously during the mixing process.

[0031] S2, after vacuum treatment, the casting solution is high-temperature film casting at 50-80 DEG C, and then low-temperature cold roll induction treatment at-10-20 DEG C, and then sent to a constant temperature and humidity environment for vapor induction treatment, and finally water bath curing to form a wet film. The temperature is constant during the high-temperature film casting process, so that the overall temperature of the casting solution is constant. When the casting solution is cooled by the cooling roll for low-temperature cold roll induction, the temperature of one side of the casting solution drops rapidly, and a temperature difference is formed between the upper and lower surfaces of the film. The viscosity of the side with lower temperature increases and it is difficult to separate the phases, so that the viscosities of the upper and lower surfaces of the film are different, which is beneficial to the formation of asymmetric PES microporous filter membrane. In addition, during the vapor induction process, the phase separation rate is controlled in combination with the above-mentioned additives, the controllability of non-solvent movement is realized, and the one-piece forming of the asymmetric PES microporous filter membrane is further improved.

[0032] S3, the wet film is soaked in an ethanol aqueous solution and then dried to obtain an asymmetric polyether sulfone microporous filter membrane. The temperature of the ethanol aqueous solution is controlled at about 30 DEG C, the drying speed is controlled at 1.5 m / s, and the drying temperature is controlled at about 70 DEG C.

[0033] In some embodiments, the mass ratio of the additive to the polyether sulfone is (1-4):1.

[0034] In some embodiments, the vacuum treatment time in step S2 is 20-40 minutes. The formation of pores in the casting solution is reduced.

[0035] In some embodiments, in the step S2, the high-temperature blade coating is in a constant-temperature environment, the thickness of the blade coating is 100-120 um, and the pulling speed of the blade coating is 1-4 m / s.

[0036] In some embodiments, in the step S2, the low-temperature cold roll induction time is 5-30 seconds. The low-temperature cold roll induction time of the film is ensured in combination with the speed of the blade coating.

[0037] In some embodiments, in the step S2, the temperature of the constant-temperature and constant-humidity environment is 20-45℃, and the relative humidity is 40RH%-90RH%. The quality of the film forming environment is ensured.

[0038] In some embodiments, in the step S2, the steam temperature of the steam induction treatment is 20-45℃, the steam induction time is 5-60 seconds, and / or the temperature of the water bath curing is 25-45℃.

[0039] In some embodiments, the solvent comprises one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, the mass ratio of the solvent to the polyether sulfone is (3-7):1; the pore-forming agent comprises polyvinylpyrrolidone with a weight average molecular weight of 30000-58000 Da, and the mass ratio of the pore-forming agent to the polyether sulfone is 1:(5-15).

[0040] Secondly, a microporous filter membrane is also provided, which is prepared by the preparation method of the asymmetric polyether sulfone microporous filter membrane in any of the above embodiments. The microporous filter membrane comprises a first porous layer, an intermediate porous layer and a second porous layer stacked along the thickness direction. The pore size of the microporous filter membrane decreases along the thickness direction from one side to the other side, and the pore size of the first porous layer decreases along the thickness direction. The average pore size of the first porous layer is 460-3500 nm, and the average pore size of the second porous layer is 135-325 nm.

[0041] In some embodiments, the pore size of the intermediate porous layer decreases along the thickness direction, and the pore size of the second porous layer decreases along the thickness direction.

[0042] The application will be described in detail below by specific examples. It should also be understood that the following examples are only used to specifically describe the application, and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the application all belong to the protection scope of the application. The following examples of specific process parameters are only one example in the appropriate range, i.e. those skilled in the art can make appropriate selection within the range according to the description herein, and are not limited to the specific values of the following examples.

[0043] Example 1

[0044] The additive was prepared in a mass ratio of triethylene glycol and polyethylene glycol of 1:1, then 52 g of N-methyl pyrrolidone and 30 g of the additive were weighed into a stirred tank, respectively, followed by adding 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone into the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6 h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumed for 0.5 h, then placed in an 80°C constant temperature box, the film thickness was controlled at 110 um, the pulling speed was 2.5 m / s, after inducing for 20 s through a cold roller at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out for 20 s using 40°C steam, and the film was formed by solidification in a 30°C water bath; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5 m / s, and the film was dried at a roller temperature of 70°C.

[0045] Example 2

[0046] The additive was prepared in a mass ratio of ethylene glycol and polyethylene glycol of 1:1, then 60 g of N-methyl pyrrolidone and 16 g of the additive were weighed into a stirred tank, respectively, followed by adding 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone into the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6 h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumed for 0.5 h, then placed in an 80°C constant temperature box, the film thickness was controlled at 110 um, the pulling speed was 2.5 m / s, after inducing for 20 s through a cold roller at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out for 20 s using 40°C steam, and the film was formed by solidification in a 30°C water bath; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5 m / s, and the film was dried at a roller temperature of 70°C.

[0047] Example 3

[0048] The additive was prepared according to the mass ratio of triethylene glycol and polyethylene glycol of 1:7, then 45 g of N-methyl pyrrolidone and 60 g of the additive were weighed into a stirring kettle respectively, then 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone were added into the stirring kettle respectively, and the casting solution was stirred at 50°C for 6 h. After the stirring of the casting solution was completed, it was poured into a pressure container, vacuumized for 0.5 h, then placed into a 50°C constant temperature box, the film thickness was controlled at 100 um, the pulling speed was 1 m / s, after being induced by a cold roller at -10°C for 5 s, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out at 20°C for 60 s, and the film was solidified by a water bath at 30°C.

[0049] Example 4

[0050] The additive was prepared according to the mass ratio of triethylene glycol and polyethylene glycol of 1:5, then 105 g of N-methyl pyrrolidone and 15 g of the additive were weighed into a stirring kettle respectively, then 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone were added into the stirring kettle respectively, and the casting solution was stirred at 70°C for 6 h. After the stirring of the casting solution was completed, it was poured into a pressure container, vacuumized for 0.5 h, then placed into a 70°C constant temperature box, the film thickness was controlled at 120 um, the pulling speed was 4 m / s, after being induced by a cold roller at 20°C for 20 s, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out at 45°C for 30 s, and the film was solidified by a water bath at 30°C.

[0051] Example 5

[0052] The additive was prepared according to the mass ratio of triethylene glycol and polyethylene glycol of 1:3, then 52 g of N-methyl pyrrolidone and 30 g of the additive were weighed into a stirring kettle respectively, then 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone were added into the stirring kettle respectively, and the casting solution was stirred at 80°C for 6 h. After the stirring of the casting solution was completed, it was poured into a pressure container, vacuumized for 0.5 h, then placed into an 80°C constant temperature box, the film thickness was controlled at 110 um, the pulling speed was 1 m / s, after being induced by a cold roller at 0°C for 40 s, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out at 30°C for 5 s, and the film was solidified by a water bath at 30°C.

[0053] Example 6

[0054] The additive was prepared according to the mass ratio of glycerol and glycolic acid of 1:1, then 52 g of N,N-dimethylacetamide and 30 g of the additive were weighed in a stirred tank, respectively, followed by adding 15 g of polyether sulfone and 3 g of polyvinylpyrrolidone to the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6 h. After the complete stirring of the casting solution, it was poured into a pressure vessel, vacuumed for 0.5 h, and then placed in an 80°C thermostat, with the thickness of the cast film controlled at 110 um and the pulling speed at 2.5 m / s, and after inducing for 20 s by a cold roller at 0°C, the humidity in the thermostat was adjusted to 80%, steam induction was carried out for 20 s by using steam at 40°C, and the film was formed by solidification in a water bath at 30°C; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5 m / s, and the film was dried at a roller temperature of 70°C.

[0055] Example 7

[0056] The additive was prepared according to the mass ratio of diethylene glycol and 2-pyrrolidone of 1:1, then 52 g of dimethyl sulfoxide and 30 g of the additive were weighed in a stirred tank, respectively, followed by adding 15 g of polyether sulfone and 3 g of polyvinylpyrrolidone to the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6 h. After the complete stirring of the casting solution, it was poured into a pressure vessel, vacuumed for 0.5 h, and then placed in an 80°C thermostat, with the thickness of the cast film controlled at 110 um and the pulling speed at 2.5 m / s, and after inducing for 20 s by a cold roller at 0°C, the humidity in the thermostat was adjusted to 80%, steam induction was carried out for 20 s by using steam at 40°C, and the film was formed by solidification in a water bath at 30°C; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5 m / s, and the film was dried at a roller temperature of 70°C.

[0057] Example 8

[0058] The final products of Examples 1-7 were detected: 1, the scanning electron microscope images were shown in FIGS. 1-7, respectively, 2, the detection results of the pure water flux, the first bubble point pressure and the pollution capacity of the membrane at 0.7 MPa were shown in Table 1. Figs. 1-7

[0059] Table 1 is the detection data of the PES microporous filter membrane in Examples 1-7

[0060]

[0061]

[0062] Comparative Example 1

[0063] ​The additive was prepared according to the mass ratio of triethylene glycol and polyethylene glycol of 2:1, then 52g of N-methyl pyrrolidone and 30g of the additive were weighed into a stirred tank, respectively, followed by adding 15g of polyether sulfone and 3g of polyvinyl pyrrolidone into the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumed for 0.5h, then placed into a 80°C constant temperature box, the film thickness was controlled between 110um, the pulling speed was 2.5m / s, after inducing for 20s through a cold roller of 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out for 20s using steam of 40°C, and the film was formed through a water bath solidification of 30°C; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the film was dried at a roller temperature of 70°C. It was detected that the prepared polyether sulfone microporous filter membrane had a pore size of 0.22μm, and the pure water flux of the polyether sulfone microporous filter membrane was 14ml / cm 2 ·min, the first bubble point pressure was 0.42MPa, and the contamination capacity was 80g.

[0064] Analysis: Compared with Example 1, the difference between Comparative Example 1 and Example 1 is that the mass ratio of triethylene glycol and polyethylene glycol in the additive is different, and other steps are the same. The method of this comparative example can form an asymmetric PES microporous filter membrane, but the pure water flux of the membrane is slightly lower, and the contamination capacity also cannot meet the standard. Reason: The molecular weight of triethylene glycol is relatively small, and its proportion is relatively large, which leads to a large amount of retention in the membrane after induction, and the overall pore size of the formed membrane is small.

[0065] Comparative Example 2

[0066] The additive was prepared according to the mass ratio of triethylene glycol and polyethylene glycol of 1:1, then 52g of N-methyl pyrrolidone and 30g of the additive were weighed into a stirred tank, respectively, followed by adding 15g of polyether sulfone and 3g of polyvinyl pyrrolidone into the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumed for 0.5h, then placed into a 80°C constant temperature box, the film thickness was controlled between 110um, the pulling speed was 2.5m / s, after inducing for 20s through a cold roller of 30°C, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out for 20s using steam of 40°C, and the film was formed through a water bath solidification of 30°C; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the film was dried at a roller temperature of 70°C. It was detected that the prepared polyether sulfone microporous filter membrane had a pore size of 0.22μm, and the pure water flux of the polyether sulfone microporous filter membrane was 17ml / cm 2 ·min, the first bubble point pressure was 0.38MPa, and the contamination capacity was 110g.

[0067] Analysis: Compared with Example 1, the difference between Comparative Example 2 and Example 1 is the temperature induced by the cold roller, and other steps are the same. The method of this comparative example can form an asymmetric PES microporous filter membrane, and the pure water flux of the membrane is barely qualified, but the pollutant capacity of the membrane does not meet the standard. Reason: The temperature of the cold roller is larger, and a larger viscosity difference cannot be formed on both sides of the liquid film, resulting in smaller lower aperture and poorer performance.

[0068] Comparative Example 3

[0069] The additive was prepared in a mass ratio of triethylene glycol to polyethylene glycol of 1:1. Then 52g of N-methyl pyrrolidone and 30g of the additive were weighed into a stirred tank, respectively. Then 15g of polyether sulfone and 3g of polyvinyl pyrrolidone were added to the stirred tank, respectively, so that the casting solution was stirred at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumized for 0.5h, and then placed in an 80°C constant temperature box. The thickness of the blade was controlled between 110um, the pulling speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was carried out at 40°C for 90s. The film was solidified in a 30°C water bath; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the film was dried at a roller temperature of 70°C. After detection, the prepared polyether sulfone microporous filter membrane had a pore size of 0.22μm, a pure water flux of 11ml / cm 2 ·min at 0.7MPa, a first bubble point pressure of 0.52MPa, and a pollutant capacity of 45g.

[0070] Analysis: Compared with Example 1, the difference between Comparative Example 3 and Example 1 is the time of steam induction, and other steps are the same. The method of this comparative example can form an asymmetric PES microporous filter membrane, but the pure water flux of the membrane is too low, and the pollutant capacity far fails to meet the standard. Reason: The steam induction time is too long, resulting in a large amount of non-solvent migration, thereby forming a symmetric structure.

[0071] Comparative Example 4

[0072] The additive was prepared in a mass ratio of triethylene glycol and polyethylene glycol of 1:1, then 52 g of N-methyl pyrrolidone and 30 g of the additive were weighed into a stirred tank, respectively, followed by adding 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone to the stirred tank, and the casting solution was stirred at 80°C for 6 h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumed for 0.5 h, and then placed in an 80°C constant temperature box, the casting thickness was controlled between 110 um, the pulling speed was 2.5 m / s, after inducing for 20 s through a cold roller of 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out for 20 s using steam of 50°C, and the film was formed through a water bath solidification of 30°C; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5 m / s, and the film was dried at a roller temperature of 70°C. The prepared polyether sulfone microporous filter membrane has a pore size of 0.22 μm, and the pure water flux of the polyether sulfone microporous filter membrane is 16 ml / cm 2 ·min, the first bubble point pressure is 0.48 MPa, and the pollution capacity is 105 g.

[0073] Analysis: Compared with Example 1, the difference between Comparative Example 4 and Example 1 is the steam temperature during steam induction, and the other steps are the same. The method of this comparative example can form an asymmetric PES microporous filter membrane, but the pure water flux and pollution capacity cannot meet the standard. Reason: The induction temperature is too high, which leads to the accelerated migration speed of the non-solvent, thereby forming a symmetric structure.

[0074] Comparative Example 5

[0075] The additive was prepared in a mass ratio of triethylene glycol and polyacrylate of 1:1, then 52 g of N-methyl pyrrolidone and 30 g of the additive were weighed into a stirred tank, respectively, followed by adding 15 g of polyether sulfone and 3 g of polyvinyl pyrrolidone to the stirred tank, and the casting solution was stirred at 80°C for 6 h. After the casting solution was completely stirred, it was poured into a pressure container, vacuumed for 0.5 h, and then placed in an 80°C constant temperature box, the casting thickness was controlled between 110 um, the pulling speed was 2.5 m / s, after inducing for 20 s through a cold roller of 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, steam induction was carried out for 20 s using steam of 40°C, and the film was formed through a water bath solidification of 30°C; the prepared wet film was soaked in a 25% ethanol aqueous solution, the solution temperature was controlled at 30°C, the drying speed was 1.5 m / s, and the film was dried at a roller temperature of 70°C. The prepared polyether sulfone microporous filter membrane has a pore size of 0.22 μm, and the pure water flux of the polyether sulfone microporous filter membrane is 8 ml / cm 2 ·min, the first bubble point pressure is 0.58 MPa, and the pollution capacity is 17 g.

[0076] Analysis: Compared with Example 1, the difference of Comparative Example 5 is that the additive raw material is different, and other steps are the same. The method of this comparative example can form an asymmetric PES microporous filter membrane, but the pure water flux and the nanofiltration capacity cannot reach the standard. Reason: the liquid membrane phase separation speed is slow in the induction stage, the surface opening rate is low, which leads to low flow rate and high bubble point.

[0077] The above examples only illustrate the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical concept disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for preparing asymmetric polyether sulfone microfiltration membranes, characterized in that Prepared according to the following steps: S1, dissolve the polyether sulfone in a solvent and add additives and pore-forming agents, mix uniformly to obtain a casting solution, the additives include one of polyethylene glycol, glycolic acid and 2-pyrrolidone and polyol, the mass ratio of polyethylene glycol, glycolic acid or 2-pyrrolidone to polyol is (1~7):1; the polyol is one of glycerol, triethylene glycol, diethylene glycol and ethylene glycol; S2, after vacuum treatment, the casting solution is high temperature blade casting at 50~80℃, then induced by low temperature cold roller at-10~20℃, then sent to a constant temperature and humidity environment for steam induction treatment, and finally water bath curing to form a wet film; S3, the wet film is soaked in an ethanol aqueous solution and dried to obtain an asymmetric polyether sulfone microporous filter membrane.

2. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1, characterized in that: The mass ratio of the additive to the polyether sulfone is (1~4):

1.

3. The process for the preparation of asymmetric polyethersulfone microporous membranes according to claim 1 or 2, characterized in that: In step S2, the vacuum treatment time is 20~40 minutes.

4. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In step S2, the high temperature blade casting is in a constant temperature environment, the thickness of the blade casting is 100~120um, and the pulling speed of the blade casting is 1~4m / s.

5. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In step S2, the low temperature cold roller induction time is 5~30 seconds.

6. The method of claim 1 or 2, wherein the asymmetric polyethersulfone microfiltration membrane is prepared by the steps of: In step S2, the temperature of the constant temperature and humidity environment is 20℃~45℃, and the relative humidity is 40 RH%~90 RH%.

7. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In step S2, the steam temperature of the steam induction treatment is 20-45℃, the steam induction time is 5~60 seconds, and / or the temperature of the water bath curing is 25~45℃.

8. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: The solvent includes one of N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, the mass ratio of the solvent to the polyether sulfone is (3~7):1; the pore-forming agent includes polyvinylpyrrolidone with a weight average molecular weight of 30000-58000Da, and the mass ratio of the pore-forming agent to the polyether sulfone is 1:(5~15).

9. A microporous filtration membrane characterized by: Prepared by the preparation method of the asymmetric polyether sulfone microporous filter membrane according to any one of claims 1~8, the microporous filter membrane includes a first porous layer, an intermediate porous layer and a second porous layer stacked along the thickness direction, the pore size of the microporous filter membrane decreases along the thickness direction from one side to the other side, and the pore size of the first porous layer decreases along the thickness direction; the average pore size of the first porous layer is 460~3500nm, and the average pore size of the second porous layer is 135~325nm.

10. The micro-porous filter membrane of claim 9, wherein: The pore size of the intermediate porous layer decreases along the thickness direction, and the pore size of the second porous layer decreases along the thickness direction.

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