CN114130202B - Microporous filter membrane and preparation method thereof - Google Patents

Abstract

The invention provides a microporous filter membrane and a preparation method thereof, belonging to the technical field of microporous filter membranes. Mixing a polymer, a thickening agent and a solvent, stirring for 1-12 h at 50-100 ℃ for dissolving, adding a pore-forming agent, stirring, cooling to room temperature, defoaming in vacuum, and standing to obtain a casting solution of a high-molecular organic membrane; scraping the casting solution into a nascent-state membrane, and staying in a first air bath; then entering a second air bath for staying; and finally, placing the organic membrane in a gel bath for solidification and solvent exchange to obtain the microporous filter membrane. The surface structure is adjusted, so that the prepared microporous filter membrane has a higher specific surface area, the hydrophilicity and the pollution resistance of the filter membrane are improved, and meanwhile, the microporous filter membrane has an hourglass-shaped structure, so that the dirt holding capacity and the mechanical damage resistance of the filter membrane can be improved.

Description

A kind of microporous filter membrane and preparation method thereof

technical field

The invention belongs to the technical field of microporous membranes, and in particular relates to a microporous membrane and a preparation method thereof.

Background technique

Due to the superior performance of the membrane separation technology itself, the membrane separation process has received widespread attention from all over the world, and has been widely used in petroleum, chemical, pharmaceutical, chemical, electronic energy and other fields. With the gradual improvement of membrane technology, it has gradually replaced or improved traditional separation and purification processes. The core of the membrane separation process is the membrane with separation ability. The separation membrane is divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane according to the pore size.

According to the types of materials, microfiltration membranes can be divided into two categories: organic polymer membranes and inorganic membranes. Although inorganic membranes have the characteristics of high temperature resistance, good hydrophilicity, and low pollution, due to their high preparation costs, many processes , more inclined to organic polymer microporous membranes. The preparation method of organic polymer membranes (the microporous membranes described later are all referred to as such membranes) is mainly a phase inversion method. The prepared microporous membranes can be divided into symmetrical membranes and asymmetric membranes. Due to the symmetrical structure of the symmetrical membrane, the flux of the membrane decays faster during use, and the cost of use is higher. Therefore, the vast majority of microporous membranes in use are asymmetric membranes, which can be further divided into traditional asymmetric microporous membranes. The separation layer of this type of microporous membrane is on the upper surface of the membrane; the other One is a microporous membrane with an "hourglass" structure. The separation layer of this type of microporous membrane is between the upper and lower surfaces of the membrane. At the same time, the upper and lower surfaces are porous and have low surface roughness. The pore size distribution of the membrane is from large to small, and then from small to large. Since the filtrate passes through the large-diameter filter layer before contacting the separation layer of the membrane, large-size particles can be removed, reducing the risk of large-size particles clogging the separation layer of the membrane.

Microporous membranes can also be divided into two types: hydrophilic and hydrophobic in terms of surface properties. Once the surface of the former comes into contact with water, water can immediately wet the surface of the microporous membrane and diffuse to the whole inside of the membrane under extremely low pressure or without additional pressure. The latter is the exact opposite of the former. In the existing preparation method, it is mainly realized by adding hydrophilic additives in the casting solution (such as Chinese patent CN100337730C/CN 103055724A, CN 1748847A), or by post-treatment method (such as Chinese patent CN101992034A), while Chinese patent CN105268335A In this paper, by changing the surface structure of the microporous membrane, a microporous membrane with a high specific surface area is prepared, which improves the hydrophilicity of the microporous membrane. At the same time, the rough surface structure can reduce the protein adsorption capacity of the microporous membrane. Increase the anti-pollution performance of the microporous membrane.

In order to improve the performance of microporous membranes, suitable hydrophilic and hydrophobic properties, suitable symmetrical or asymmetrical structures, anti-pollution properties, etc. will be prepared according to different process conditions. The preparation methods mentioned in CN 103055724A, CN 1748847A and other patents prepare microporous membranes. The separation layer of the membrane is distributed on the upper surface of the membrane, which is a traditional asymmetric structure. The cost of the microporous membrane prepared by this method is relatively low. US4933081 firstly proposed the preparation method of microporous membrane with "hourglass structure", but in this patent, the prepared microporous membrane is hydrophobic, and the application field of separation process is less. In US8728136B2, it is mentioned that adding a hydrophilic polymer sulfonated polysulfone to prepare a "hourglass" structure microporous membrane with hydrophilic properties, specifically, the separation layer of the microporous membrane is between the upper and lower surfaces of the membrane. It can increase the mechanical damage resistance and dirt-holding capacity of the membrane and the hydrophilicity of the membrane, but the surface opening rate of the microporous membrane prepared by this method is low.

In the application process, microporous membranes are mostly prepared in the form of folded filter elements to complete the separation purpose. In the process of preparing a pleated filter element, it will cause dangers such as scratches and punctures on the membrane surface. Therefore, the microporous filter membranes used should have an "hourglass" structure. At the same time, in order to change the hydrophilic performance of the microporous membrane, a large amount of hydrophilic additives are usually added, but the addition of a large amount of hydrophilic additives will reduce the acid and alkali resistance and mechanical strength of the microporous membrane, and with the increase of hydrophilic The loss of non-toxic additives will lead to the disappearance of the hydrophilic property of the microporous membrane. By adjusting the surface structure of the membrane, a microporous membrane with a high specific surface area can be prepared, which can change the influence of a large number of hydrophilic additives and reduce the cost of hydrophilic modification.

The method mentioned in the aforementioned article is mainly one-step steam induction and one-step gel method to prepare microporous membrane. CN1748847A discloses a method for preparing a structurally symmetrical polyethersulfone hydrophilic microporous membrane. The method prepares the microporous membrane through a secondary gel method. CN 1627983A, the United States Cuo Nuo Company, discloses a method for preparing a multilayer microporous membrane. In the existing literature reports, it has not been disclosed that a microporous filter membrane with a specific structure has been prepared by a two-step air-induced method.

The two-step air-induced process can prepare a new type of microporous membrane by changing the phase separation speed and phase separation path of the nascent membrane. This type of membrane has a high specific surface and an "hourglass" structure. The microporous membrane has the characteristics of high porosity, high water flux, uniform pore size distribution, and high resistance to mechanical damage. The high specific surface area endows the filter membrane with a higher contact area than conventional filter membranes, making the filter membrane more hydrophilic, reducing the need for microporous membranes for hydrophilic groups in membrane materials, and reducing the cost of microporous membranes.

Contents of the invention

The invention provides a microporous filter membrane and a preparation method thereof. The microporous filter membrane has the characteristics of high specific surface area, mechanical damage resistance with a separation layer in the middle of the section, and extremely high anti-pollution ability.

The present invention at first provides a kind of preparation method of microporous filter membrane, and this method comprises:

Step 1: Mix the polymer, thickener and solvent, stir at 50-100°C for 1-12 hours to dissolve, add porogen and stir, cool to room temperature, vacuum defoam, and obtain a polymer organic film after standing casting solution;

Step 2: Scrape the casting solution of the polymeric organic membrane obtained in step 1 into a nascent eco-film, and stay in the first air bath;

Step 3: Enter the film in step 2 into the second air bath to stay;

Step 4: placing the organic polymer membrane prepared in Step 3 in a gel bath for curing and solvent exchange to obtain a microporous membrane.

Preferably, the polymer is selected from one of polysulfone, polyarylethersulfone, polyolefins, polyetherketone, polyimide sulfonated polysulfone, sulfonated polyethersulfone and polyetherimide one or more species.

Preferably, the solvent is selected from one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, caprolactam, and 1,4-dioxane.

Preferably, the thickener is selected from one or more of polyvinylpyrrolidone, glycerin, and high molecular weight polyethylene glycol.

Preferably, the porogen is selected from one or more of low molecular weight polyethylene glycol, triethylene glycol, diethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol dimethyl ether.

Preferably, the mass ratio of the polymer, solvent, thickener and porogen is 8-15:18-89:1-20:10-80.

Preferably, the residence temperature of the first air bath is 20-35°C, the humidity is 30%-80%, and the time is 3s-30s.

Preferably, the dwelling temperature of the second air bath is 30-50°C, the humidity is 35%-85%, and the dwelling time is 2s-50s.

Preferably, the curing temperature is 30-80°C, and the curing time is 0.5-3h.

The present invention also provides the microporous membrane obtained by the above preparation method, and the microporous membrane has an hourglass structure.

Beneficial effects of the present invention

The invention provides a high specific surface area microporous filter membrane and a preparation method thereof. The method adopts two-step air bath induction preparation, and the prepared composite membrane has a high specific surface area and a high anti-pollution ability. The microporous filter membrane of the present invention The membrane has an "hourglass" structure with a high specific surface area, and the separation layer is between the upper and lower surfaces. This type of membrane has the ability to resist mechanical damage such as puncture and scratches. At the same time, this type of membrane has a high surface porosity, high Water flux and other characteristics. This type of membrane can be made into a flat membrane or a hollow fiber membrane, and the prepared hollow fiber membrane can have a rough inner surface, or a rough outer surface or a rough inner and outer surface.

Description of drawings

Fig. 1 is the scanning electron microscope picture of the microporous membrane rough surface that the embodiment of the present invention 1 prepares;

Fig. 2 is the scanning electron microscope picture of the overall cross-section of the microporous membrane prepared in Example 1 of the present invention;

Fig. 3 is the scanning electron microscope picture of the membrane surface prepared by comparative example 1 of the present invention;

Fig. 4 is the scanning electron microscope picture of the film section prepared by comparative example 1 of the present invention;

Fig. 5 is the scanning electron microscope picture of the microporous membrane cross-section prepared by the embodiment of the present invention 6;

Fig. 6 is a scanning electron microscope picture of the surface of the microporous membrane prepared in Example 6 of the present invention.

Detailed ways

The present invention at first provides a kind of preparation method of microporous filter membrane, and this method comprises:

Step 1: Mix the polymer, thickener and solvent, stir at 50-100°C for 1-12 hours to dissolve, then add the porogen and stir, the temperature is preferably 80°C, and the stirring time is preferably 0.5-5h , cooled to room temperature, vacuum defoaming, the defoaming time is preferably 0.5-3h, and after standing, the casting solution of the polymer organic film is obtained; the standing time is preferably 1-24h;

The polymer is preferably selected from one or more of polysulfone, polyarylethersulfone, polyolefins, polyetherketone, polyimide sulfonated polysulfone, sulfonated polyethersulfone and polyetherimide kind;

The solvent is preferably selected from one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, caprolactam, and 1,4-dioxane;

The thickener is preferably selected from one or more of polyvinylpyrrolidone, glycerin, and high molecular weight polyethylene glycol;

The porogen is preferably selected from one or more of low molecular weight polyethylene glycol, triethylene glycol, diethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol dimethyl ether;

The mass ratio of the polymer, solvent, thickener and porogen is preferably 8-15:18-89:1-20:10-80, more preferably 12-15:18-38:10:40 -60.

Step 2: Scrape the casting solution of the polymeric organic film obtained in step 1 into a nascent film, preferably scrape the casting solution on a stainless steel strip or polypropylene resin with a 200-350 μm thickness scraper, and in the first air Stay in the bath; the stay temperature in the first air bath is preferably 20-35°C, the humidity is preferably 30% to 80%, and the time is preferably 3s-30s;

Step 3: Put the film in step 2 into the second air bath to stay. The temperature of the second air bath stay is preferably 30-50°C, and the humidity is preferably 35%-85%.

Step 4: Place the polymeric organic membrane prepared in step 3 in a gel bath for solidification and solvent exchange to obtain a microporous membrane. The coagulation bath is preferably selected from water or a mixture of water and alcohols. The alcohols are preferably methanol or ethanol, more preferably water; the curing temperature is preferably 30-80°C, and the curing time is preferably 1min-3h.

The present invention also provides the microporous membrane obtained by the above preparation method, and the microporous membrane has an hourglass structure.

The present invention will be further described below in conjunction with the examples and accompanying drawings. The examples are only to help better understand the present invention, but the present invention is not limited to the following examples.

Example 1 Preparation of "hourglass" structure polyethersulfone microporous membrane with high specific surface area

According to the mass ratio of polyethersulfone resin (PES): polyvinylpyrrolidone: diethylene glycol: dimethylformamide = 15:10:45:30, add PES, polyvinylpyrrolidone, dimethylformamide to the melting pot Diethylene glycol was added into the porogen after stirring at 80°C for 4 hours, and the stirring was continued for 1 hour to prepare a stable and uniform viscous solution. The temperature was lowered to 25°C for 1 hour of defoaming, and then stood still for 8 hours to obtain a feed solution.

Scrape the feed liquid with a constant feed temperature of 25°C on a stainless steel strip or polypropylene resin with a 350 μm thick scraper, place it in humid air with a temperature of 25°C and a relative humidity of 60% for 10 seconds, and then place it at a temperature of 35 ℃, relative humidity of 70% in an air bath for 20s, then immersed in 50℃ coagulation bath water for 8 minutes, and dried at 100℃. The bubble point pressure of water measured by PMI-1500A gas-liquid method pore size tester is 650KPa-670KPa, the average The pore size is 0.1 μm. The flux is 9.5cc·min ^-1 ·cm ^-2 @70Kpa. The membrane has a structure with a high specific surface area and a separation layer between the upper and lower surfaces. Bovine serum albumin adsorption was 0.5% (bovine serum albumin solution 1.6 μg/5ml water).

The microporous filter membrane prepared in Example 1 has a rough surface scanning electron microscope picture shown in Figure 1, and a cross-sectional scanning electron microscope picture shown in Figure 2.

Comparative example 1

Referring to the composition and treatment method of the polymer solution in Example 1, the difference is that the temperature is 20°C and the relative humidity is 75% humid air for 30 seconds by means of a single air bath condition control method, and then immersed in a solidification solution at 50°C. Soak in bath water for 8 minutes, and dry in dry air at 100°C. The measured bubble point pressure is 630Kpa-650Kpa, the average pore size is 0.11μm, and the flux is 5cc·min ^-1 ·cm ^-2 @70Kpa. The microporous membrane prepared by the method has a smooth surface, and the separation layer is on the upper surface of the microporous membrane. Bovine serum albumin adsorption was 5.3%.

Compared with comparative example 1, compared with the smooth microporous membrane prepared, the flux of the microporous membrane of the present invention is promoted by 20%, and the adsorption of bovine serum albumin is reduced from 5.3% to 0.5%, which confirms the process of passing through the multi-step air bath. The microporous membrane with high specific surface area prepared by this method has better anti-protein adsorption ability.

The SEM pictures of the surface and the cross-section of the film prepared in Comparative Example 1 are shown in Figures 3 and 4, respectively.

Example 2

Prepare the solution according to the formula in Example 1, scrape the feed liquid with a constant feed liquid temperature of 25°C on the stainless steel strip or polypropylene resin with a 350 μm thickness scraper, and place it in a wet room with a temperature of 25°C and a relative humidity of 50%. In the air for 10s, then placed in an air bath with a temperature of 30°C and a relative humidity of 70% for 25s, then immersed in 50°C coagulation bath water for 8 minutes, and dried at 100°C, the measured bubble point pressure of water was 400Kpa-420KPa, and the pore size was 0.2μm, the measured pure water flux at 25°C is 28cc·min ^-1 ·cm ^-2 @70Kpa. The membrane has a structure with a high specific surface area and a separation layer between the upper and lower surfaces. Bovine serum albumin adsorption was 0.4% (bovine serum albumin solution 1.6 μg/5ml water).

Example 3

According to the mass ratio of polyethersulfone resin (PES): polyvinylpyrrolidone: diethylene glycol: N-methylpyrrolidone = 12:10:40:38, add PES, polyvinylpyrrolidone After dissolving alkanone and dimethylformamide at 80°C and stirring for 4 hours, add a porogen and continue stirring for 1 hour to prepare a stable and uniform viscous solution. Lower the temperature to 25°C for 1 hour of defoaming, and then let stand for 8 hours to obtain the material liquid.

Scrape the feed liquid with a constant feed temperature of 25°C on a stainless steel strip or polypropylene resin with a 350 μm thick scraper, place it in humid air with a temperature of 25°C and a relative humidity of 60% for 5 seconds, and then place it at a temperature of 35°C. ℃, relative humidity of 70% in an air bath for 20s, then immersed in 50℃ coagulation bath water for 8 minutes, and dried at 100℃. The measured bubble point pressure of water is 250Kpa-260Kpa, the pore size is 0.44μm, and the flux is 51cc·min ^-1 cm ^-2 @70Kpa. The membrane has a structure with a high specific surface area and a separation layer between the upper and lower surfaces. The bovine serum albumin adsorption was 0.6% (bovine serum albumin solution 1.6 μg/5ml water).

Example 4

According to the mass ratio of polyethersulfone resin (PES): polyvinylpyrrolidone: polyethylene glycol 600: N-methylpyrrolidone = 12:10:43:35, add PES, polyvinylpyrrolidone After the alkanone and dimethylformamide were dissolved and stirred at 80°C for 4 hours, the porogen polyethylene glycol 600 was added, and the stirring was continued for 1 hour to prepare a stable and uniform viscous solution. Set for 8h to obtain feed liquid.

Scrape the feed liquid with a constant feed liquid temperature of 25°C on a stainless steel strip or polypropylene resin with a 350 μm thick scraper, place it in humid air with a temperature of 25°C and a relative humidity of 60% for 20 seconds, and then place it at a temperature of 35°C. ℃, relative humidity of 70% air bath for 15s, then immersed in coagulation bath water at 50℃ for 8min, and dried at 100℃, the bubble point pressure of water was measured to be 170Kpa-195Kpa, the pore size was 0.62μm, and the flux was 65cc·min ^-1 cm ^-2 @70Kpa. The membrane has a structure with a high specific surface area and a separation layer between the upper and lower surfaces. Bovine serum albumin adsorption was 0.5% (bovine serum albumin solution 1.6 μg/5ml water).

Example 5 Preparation of polysulfone microporous membrane with "hourglass" structure with high specific surface area

According to mass ratio polysulfone resin (PSF): polyvinylpyrrolidone: triethylene glycol: N-methylpyrrolidone=12:10:40:38, add PES, polyvinylpyrrolidone, After dimethylformamide was dissolved and stirred at 80°C for 4 hours, the porogen triethylene glycol was added, and the stirring was continued for 1 hour to prepare a stable and uniform viscous solution. The temperature was lowered to 25°C for defoaming for 1 hour, and then stood for 8 hours to obtain the material liquid.

Scrape the feed liquid with a constant feed temperature of 25°C on a stainless steel strip or polypropylene resin with a 200 μm thick scraper, place it in humid air with a temperature of 25°C and a relative humidity of 40% for 10 seconds, and then place it at a temperature of 40 ℃, relative humidity of 70% in an air bath for 20s, then immersed in 50℃ coagulation bath water for 8 minutes, and dried at 100℃. The measured bubble point pressure of water is 260Kpa-287Kpa, the pore size is 0.45μm, and the flux is 48cc·min ^-1 cm ^-2 @70Kpa. The membrane has a structure with a high specific surface area and a separation layer between the upper and lower surfaces. Bovine serum albumin adsorption was 0.7% (bovine serum albumin solution 1.6 μg/5ml water).

Example 6 Preparation of Conventional "Hourglass" Structure Polyethersulfone Microporous Membrane

According to the mass ratio of polyethersulfone resin (PES): polyvinylpyrrolidone: polyethylene glycol 400: N-methylpyrrolidone = 12:10:50:28, add PES, polyethylene After pyrrolidone and dimethylformamide were dissolved and stirred at 80°C for 4 hours, the porogen polyethylene glycol 400 was added and stirred for 1 hour to prepare a stable and uniform viscous solution, and the temperature was lowered to 25°C for 1 hour of defoaming. Then stand still for 8h to obtain feed liquid.

Scrape the feed liquid with a constant feed temperature of 25°C on a stainless steel strip or polypropylene resin with a 200 μm thick scraper, place it in humid air with a temperature of 25°C and a relative humidity of 55% for 18 seconds, and then place it at a temperature of 40 ℃, relative humidity 80% air bath for 12s, then immersed in coagulation bath water at 50℃ for 8min, and dried at 100℃. The measured bubble point pressure of water is 260Kpa-287Kpa, the pore size is 0.45μm, and the flux is 40cc·min ^-1 cm ^-2 @70Kpa. The scanning electron microscope pictures and the surface scanning electron microscope pictures are shown in Figures 5 and 6, respectively. The film has a smooth surface, but the separation layer is between the upper and lower surfaces. The bovine serum albumin adsorption was 2.5% (bovine serum albumin solution 1.6 μg/5ml water).

Example 7

According to the mass ratio of polyethersulfone resin (PES): polyvinylpyrrolidone: polyethylene glycol 200: N-methylpyrrolidone = 12:10:60:18, add PES, polyvinylpyrrolidone After the alkanone and dimethylformamide were dissolved and stirred at 80°C for 4 hours, the porogen polyethylene glycol 200 was added, and the stirring was continued for 1 hour to prepare a stable and uniform viscous solution. Set for 8h to obtain feed liquid.

Scrape the feed liquid with a constant feed liquid temperature of 25°C on a stainless steel strip or polypropylene resin with a 200 μm thick scraper, place it in humid air with a temperature of 25°C and a relative humidity of 55% for 8 seconds, and then place it at a temperature of 40 ℃, relative humidity 80% air bath for 15 seconds, then immersed in 50 ℃ coagulation bath water for 8 minutes, and dried at 100 ℃, the measured bubble point pressure of water is 320Kpa-350Kpa, the pore size is 0.22μm, and the flux is 25cc·min ^-1 cm ^-2 @70Kpa. The structure is similar to that of Figure 6, the film has a smooth surface, but the separation layer is between the upper and lower surfaces. The bovine serum albumin adsorption was 2.9% (bovine serum albumin solution 1.6 μg/5ml water).

Table 1 shows the performance data of microporous membranes prepared under different conditions, which can be visually seen and compared:

It can be seen from the data in Table 1 that the microporous membrane with high specific surface area prepared by two-step air bath induced phase separation has a high flow rate, and at the same time, this type of membrane has extremely high anti-BSA adsorption performance .

Claims (2)

1. A method of making a microporous filtration membrane, the method comprising:

the method comprises the following steps: polyether sulfone resin according to mass ratio: polyvinylpyrrolidone: diethylene glycol: dimethylformamide =15:10:45, adding polyether sulfone resin, polyvinylpyrrolidone and dimethylformamide into a dissolving kettle, dissolving and stirring at 80 ℃ for 4h, adding pore-forming agent diethylene glycol, continuously stirring for 1h to prepare a stable and uniform viscous solution, reducing the temperature to 25 ℃ for defoaming for 1h, and then standing for 8h to obtain a feed liquid;

step two: scraping the feed liquid with the constant feed liquid temperature of 25 ℃ obtained in the step one on a stainless steel band or polypropylene resin by using a scraper with the thickness of 350 mu m, and placing the feed liquid in wet air with the temperature of 25 ℃ and the relative humidity of 60% for 10s;

step three: placing the film in the second step in an air bath with the temperature of 35 ℃ and the relative humidity of 70% for 20s;

step four: and (3) immersing the polymer organic membrane prepared in the step three in water at 50 ℃ for 8min for curing and solvent exchange, and drying at 100 ℃ to obtain the polyether sulfone microporous filter membrane with the hourglass-shaped structure and high specific surface area.

2. The microfiltration membrane according to claim 1 having an hourglass-shaped configuration with a high specific surface area.

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