Preparation method of high-porosity and high-flux asymmetric membrane

Abstract

The invention relates to a preparation method of a high-porosity and high-flux asymmetric membrane, and belongs to the technical field of membrane separation. A preparation method of a high-porosity and high-flux asymmetric membrane comprises the following steps: uniformly dissolving a polymer and a hydrophilic additive in an organic solvent to prepare a homogeneous membrane casting solution; preparing a primary membrane from the membrane casting solution, then carrying out atomization pretreatment on the primary membrane, rapidly cooling after treatment, then immersing the primary membrane in a gel bath to form an asymmetric membrane, and washing and soaking the asymmetric membrane in normal-temperature deionized water for multiple times to obtain the high-porosity and high-flux asymmetric membrane. According to the asymmetric membrane, a non-solvent atomization technology is combined with cooling induced crystallization, non-solvent atomization is introduced into the surface of a primary membrane, the temperature is accurately controlled, so that a solution is rapidly saturated, crystal formation is triggered, large-aperture pores are formed, and the porosity and flux of the membrane are improved. The surface layer of the obtained asymmetric membrane is provided with a large-aperture network, the supporting layer is finger-shaped holes, the porosity is 75%-85%, the pure water flux is greatly improved, and the efficient separation requirement is met.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-porosity and high-flux asymmetric membrane, belonging to the technical field of membrane separation. Background Art

[0002] As an efficient and environmentally friendly water treatment technology, membrane water purification technology has been widely used in laboratory research and industrial practice. By controlling the membrane pore size, this technology can achieve accurate separation of substances of different sizes and molecular weights at room temperature. Among them, asymmetric (UF) membranes, as an important part of membrane water purification technology, have shown broad application prospects in many fields such as food, pharmaceuticals, drinking water production and industrial wastewater treatment due to their good separation performance, simple operation and easy maintenance.

[0003] However, traditional asymmetric membranes often have problems such as insufficient porosity, uneven pore size distribution, and low flux during the preparation process, which limits their separation efficiency and processing capacity. The asymmetric membrane is an asymmetric structure as a whole, with a thin epidermis and a more open internal structure. Although this structure provides the necessary mechanical strength for the membrane, it also affects its permeability to a certain extent. In order to improve the porosity and flux of asymmetric membranes, researchers have tried a variety of methods. However, while these methods improve membrane performance, they also bring problems such as high preparation cost, complex process, and low production efficiency. Summary of the invention

[0004] The present invention provides a method for preparing a high-porosity and high-flux asymmetric membrane. The method has the advantages of simple preparation process, easy acquisition of raw materials, and low cost. It is easy to produce separation membranes continuously and on a large scale, and is convenient for industrial application. The method adopts a preparation strategy of non-solvent atomization combined with cooling-induced crystallization technology, which opens up a new way for the production of high-porosity and high-flux asymmetric membranes. This method not only significantly reduces the operating cost, but is also environmentally friendly. Its unique process advantages indicate that the technology has great application potential and is expected to achieve large-scale production in the future.

[0005] A method for preparing a high-porosity and high-flux asymmetric membrane comprises the steps of uniformly dissolving a polymer and a hydrophilic additive in an organic solvent to prepare a homogeneous membrane casting solution; preparing a primary membrane from the membrane casting solution, then atomizing the primary membrane for pretreatment, rapidly cooling the primary membrane after treatment, and then immersing the membrane in a gel bath to form an asymmetric membrane; and rinsing and immersing the asymmetric membrane in deionized water at room temperature for multiple times to obtain an asymmetric membrane with high porosity and high flux.

[0006] Among them, the atomization pretreatment is as follows: at a certain distance from the surface of the primary membrane, an inorganic salt aqueous solution with a mass fraction of 60% to 95% of the saturated concentration of the corresponding inorganic salt is evenly sprayed on the surface of the primary membrane in an atomized form for a certain period of time. Among them, the inorganic salt is at least one of sodium chloride, calcium chloride, magnesium sulfate, potassium chloride, ammonium sulfate, calcium nitrate, and sodium carbonate.

[0007] In the above technical solution, the concentration of the inorganic salt aqueous solution used in the present invention is 60 to 95% of the saturated concentration of the inorganic salt aqueous solution at the corresponding temperature.

[0008] Preferably, at a distance of 3 cm to 20 cm from the surface of the primary membrane, an inorganic salt aqueous solution at a temperature of 30°C to 70°C is evenly sprayed on the surface of the primary membrane in an atomized form for 5 s to 120 s, and the spray amount is 50 ml / h to 350 ml / h.

[0009] Preferably, the atomization method is one of pressure atomization, rotary atomization, ultrasonic atomization, and thermal energy atomization.

[0010] Preferably, the mass fraction of the polymer in the casting solution is 4% to 22%, the mass fraction of the hydrophilic additive is 2% to 18%, and the balance is an organic solvent.

[0011] Preferably, the polymer is selected from at least one of polyvinyl chloride, polysulfone, polyethersulfone, sulfonated polyethersulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polyimide, polyacrylic acid, polylactic acid, polyamide, chitosan, polyetherimide, polystyrene, polyolefin, polyester, polychlorotrifluoroethylene, silicone resin, and acrylonitrile-styrene copolymer.

[0012] Preferably, the hydrophilic additive is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, fluoropolymer, polyoxyethylene, and polyoxypropylene ether block copolymer.

[0013] Preferably, the organic solvent is at least one of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N-vinylpyrrolidone (NVP).

[0014] Preferably, the thickness of the primary membrane is 100 to 500 μm.

[0015] Preferably, the preparation method of the primary membrane is scraping or drawing.

[0016] Preferably, the primary membrane is of a flat plate type or a composite support type structure.

[0017] The preparation method is scraping or drawing; the membrane is of a flat plate type or a composite support type structure.

[0018] Preferably, the rapid cooling is as follows: the cooling time is 5 s to 60 s, and the temperature is reduced to 0 °C to 20 °C.

[0019] Preferably, the gel bath is one of deionized water, methanol, ethanol, glycerol, isopropanol, ethylene glycol, n-butanol, and acetone.

[0020] Furthermore, the temperature of the gel bath is 10 °C to 20 °C.

[0021] Another object of the present invention is to provide a high-porosity and high-flux asymmetric membrane prepared by the above method. The surface layer of the asymmetric membrane has a network-like pore structure, and the support layer is a finger-like pore, with a porosity of 75% to 85%.

[0022] The beneficial effects of the present invention are as follows: The preparation method of the asymmetric support membrane of the present invention adopts the non-solvent atomization technology combined with cooling-induced crystallization. The non-solvent atomization is introduced onto the surface of the nascent membrane, and the temperature is precisely controlled to quickly saturate the solution, triggering crystal formation, forming large-pore pores, and improving the membrane porosity and flux. The obtained asymmetric membrane has a large-pore network on the surface layer and a finger-like pore on the support layer, with a porosity of 75% to 85%, and the pure water flux is greatly improved, meeting the requirements of efficient separation. The present invention is an innovation based on the traditional non-solvent induced phase inversion method preparation process, and only needs to add atomization pretreatment and cooling-induced crystallization. This innovative method not only simplifies the preparation process, but also the raw materials used are easy to obtain and cost-effective. More importantly, this method supports continuous large-scale production of separation membrane materials and is very suitable for industrial application. Therefore, in many aspects such as water treatment, biotechnology, pharmaceutical industry, and energy field, the present invention shows broad application potential and excellent application prospects. Description of the Drawings

[0023] Figure 1 is the electron microscope photograph of the surface of the asymmetric membrane prepared in Example 1;

[0024] Figure 2 is the electron microscope photograph of the cross-section of the asymmetric membrane prepared in Example 1;

[0025] Figure 3 is the electron microscope photograph of the surface of the asymmetric membrane prepared in Comparative Example 1;

[0026] From Figure 1 and Figure 2 it can be seen that the surface layer of the asymmetric membrane treated by the method of the present invention has a large-pore network-like pore structure, and the support layer has a finger-like pore structure. For the convenience of comparison, from Figure 3 it can be seen that the surface layer of the asymmetric membrane untreated by this method is a dense sponge-like pore structure. Detailed Embodiments

[0027] The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0028] In the test methods described in the following examples, unless otherwise specified, they are all conventional methods; the reagents and materials, unless otherwise specified, can all be obtained from commercial sources.

[0029] One specific implementation method: a method for preparing a high-porosity and high-flux asymmetric membrane, dissolving a polymer and a hydrophilic additive in an organic solvent, stirring them evenly, and vacuum degassing to prepare a homogeneous casting solution, casting the casting solution to form a primary membrane; subsequently, performing atomization pretreatment on the primary membrane, immediately entering a cooling device for rapid cooling induction crystallization after treatment for a period of time, and then immersing it in a gel bath to form an asymmetric membrane, and rinsing and soaking the asymmetric membrane in deionized water at room temperature multiple times to obtain the high-porosity and high-flux asymmetric membrane.

[0030] Example 1

[0031] Dissolve 12 g of polyacrylonitrile and 16 g of polyethylene glycol 400 in 72 g of DMF, stir them evenly, and vacuum degas to prepare a homogeneous casting solution. Cast and scrape the casting solution into a flat primary membrane with a thickness of 200 μm. Immediately use ultrasonic atomization to evenly spray a calcium chloride solution with a mass fraction of 40% and a temperature of 70 °C on the surface of the primary membrane at a rated atomization rate of 350 ml / h for 30 s at a distance of 5 cm from the surface of the primary membrane, and then immediately enter a cooling device and cool down to 5 °C in 20 s for rapid cooling induction crystallization, and then immerse it in deionized water at 15 °C to form an asymmetric membrane. Rinse and soak the asymmetric membrane in deionized water at room temperature multiple times to obtain the high-porosity and high-flux asymmetric membrane. The surface microstructure of this membrane is as Figure 1 described, and the porosity and pure water flux are shown in Table 1.

[0032] Comparative Example 1

[0033] For convenient comparison, according to the experimental method of Example 1, the difference from Example 1 is that an ultrafiltration membrane is prepared without the processes of atomization pretreatment and low-temperature induction crystallization. The surface microtopography of this membrane is as Figure 3 shown, and the porosity and pure water flux are shown in Table 1.

[0034] Table 1

[0035]

[0036] Examples 2 to 18

[0037] According to the experimental method of Example 1, but different from Example 1 in that the type of polymer and the mass fraction of the polymer are changed. The polymers are polyvinyl chloride, polysulfone, polyethersulfone, sulfonated polyethersulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polyimide, polyacrylic acid, polylactic acid, polyamide, chitosan, polyetherimide, polystyrene, polyolefin, polyester, polychlorotrifluoroethylene, silicone resin; the mass fraction of the polymer is 4% - 22%. The porosity and pure water flux of the prepared asymmetric membranes are shown in Table 2.

[0038] Table 2

[0039]

[0040]

[0041] Example 19

[0042] Dissolve 14 g of polyaryletherketone and 14 g of polyethylene glycol 1000 in 72 g of DMAc, stir evenly, and degas under vacuum to prepare a homogeneous casting solution. Cast and scrape the casting solution into a flat primary membrane with a thickness of 300 μm. Immediately, use a rotary atomization method to spray a sodium chloride solution with a mass fraction of 20% and a temperature of 70 °C evenly on the surface of the primary membrane at a rated atomization rate of 300 ml / h for 20 s at a distance of 8 cm from the surface of the primary membrane. Then immediately enter a cooling device and cool down to 5 °C in 10 s for rapid cooling-induced crystallization. Then immerse it in deionized water at 20 °C to form an asymmetric membrane. Rinse and soak the asymmetric membrane in deionized water at room temperature multiple times to obtain an asymmetric membrane with a porosity of 83% and a pure water flux of 4106 L / (m 2 ·h·bar).

[0043] Examples 20 - 22

[0044] According to the experimental method of Example 19, but different from Example 19 in that the type and mass fraction of the hydrophilic additive are changed. The hydrophilic additives are polyvinylpyrrolidone, polyethylene glycol, fluorine-containing polymer, polyoxyethylene; the mass fractions are 2% - 18% respectively. The porosity and pure water flux of the prepared asymmetric membranes are shown in Table 3.

[0045] Table 3

[0046]

[0047] Example 23

[0048] Dissolve 16 g of polyimide and 8 g of polyvinylpyrrolidone K30 in 76 g of DMAc, stir it evenly, and degas it under vacuum to prepare a homogeneous casting solution. Cast and scrape the casting solution into a flat primary film with a thickness of 250 μm. Immediately, use a pressure atomization method to evenly spray a magnesium sulfate solution with a mass fraction of 30% and a temperature of 70 °C at a rated atomization rate of 250 ml / h on the surface of the primary film at a distance of 12 cm for 15 s. Then, immediately enter a cooling device and cool it to 5 °C in 10 s for rapid cooling-induced crystallization. Then, immerse it in ethanol at 25 °C to form an asymmetric membrane. Rinse and soak the asymmetric membrane in deionized water at room temperature multiple times to obtain an asymmetric membrane with a porosity of 80% and a pure water flux of 4026 L / (m 2 ·h·bar).

[0049] Examples 24 - 26

[0050] According to the experimental method of Example 23, but the difference from Example 23 is the type of organic solvent. The organic solvents are N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N-vinylpyrrolidone (NVP) respectively. The porosities and pure water fluxes of the prepared asymmetric membranes are shown in Table 4.

[0051] Table 4

[0052]

[0053] Example 27

[0054] Dissolve 10 g of polyolefin and 10 g of polyoxyethylene in 80 g of DMAc, stir it evenly, and degas it under vacuum to prepare a homogeneous casting solution. Cast and scrape the casting solution into a flat primary film with a thickness of 180 μm. Immediately, use a thermal atomization method to evenly spray a magnesium sulfate solution with a mass fraction of 30% and a temperature of 70 °C at a rated atomization rate of 250 ml / h on the surface of the primary film at a distance of 11 cm for 15 s. Then, immediately enter a cooling device and cool it to 5 °C in 10 s for rapid cooling-induced crystallization. Then, immerse it in ethanol at 25 °C to form an asymmetric membrane. Rinse and soak the asymmetric membrane in deionized water at room temperature multiple times to obtain an asymmetric membrane with a porosity of 80% and a pure water flux of 4026 L / (m 2 ·h·bar).

[0055] Examples 28 - 33

[0056] According to the experimental method of Example 27, but the difference from Example 27 is the type and mass fraction of the inorganic salt aqueous solution. The types of inorganic salt aqueous solutions are sodium chloride, calcium chloride, potassium chloride, ammonium sulfate, calcium nitrate, and sodium carbonate aqueous solutions respectively. The porosities and pure water fluxes of the prepared asymmetric membranes are shown in Table 5.

[0057] Table 5

[0058]

[0059] Examples 34 to 36

[0060] According to the experimental method of Example 27, but different from Example 27 in that the atomization methods are different. The atomization methods are pressure atomization, rotary atomization, and ultrasonic atomization respectively. The porosity and pure water flux of the prepared asymmetric membranes are shown in Table 6.

[0061] Table 6

[0062]

Claims

1. A method for preparing a high-porosity and high-flux asymmetric membrane, characterized in that, The polymer and the hydrophilic additive are uniformly dissolved in an organic solvent to form a homogeneous casting solution; the casting solution is made into a nascent membrane, and then the nascent membrane is subjected to atomization pretreatment. After the treatment, the temperature is rapidly decreased, and then it is immersed in a gel bath to form an asymmetric membrane. The asymmetric membrane is rinsed and soaked in deionized water at room temperature for multiple times to obtain an asymmetric membrane with high porosity and high flux. Among them, the atomization pretreatment is as follows: at a certain distance from the surface of the nascent membrane, an inorganic salt aqueous solution with a mass fraction of 60% - 95% of the saturated concentration of the corresponding inorganic salt is uniformly sprayed on the surface of the nascent membrane in an atomized form for a period of time. Among them, the inorganic salt is at least one of sodium chloride, calcium chloride, magnesium sulfate, potassium chloride, ammonium sulfate, calcium nitrate, and sodium carbonate.

2. The method according to claim 1, wherein At a distance of 3 cm - 20 cm from the surface of the nascent membrane, an inorganic salt aqueous solution with a temperature of 30°C - 70°C is uniformly sprayed on the surface of the nascent membrane in an atomized form for 5 s - 120 s, and the spray rate is 50 ml / h - 350 ml / h.

3. The method according to claim 1, wherein The atomization method is one of pressure atomization, rotary atomization, ultrasonic atomization, and thermal energy atomization.

4. The method according to claim 1, wherein In the casting solution, the mass fraction of the polymer is 4% - 22%, the mass fraction of the hydrophilic additive is 2% - 18%, and the balance is an organic solvent.

5. The method according to claim 1, characterized in that, The polymer is selected from at least one of polyvinyl chloride, polysulfone, polyethersulfone, sulfonated polyethersulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polyimide, polyacrylic acid, polylactic acid, polyamide, chitosan, polyetherimide, polystyrene, polyolefin, polyester, polychlorotrifluoroethylene, silicone resin, and acrylonitrile-styrene copolymer; the hydrophilic additive is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, fluoropolymer, polyoxyethylene, and polyoxypropylene ether block copolymer; the organic solvent is at least one of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N-vinylpyrrolidone (NVP).

6. The method according to claim 1, wherein The thickness of the nascent membrane is 100 - 500 μm.

7. The method according to claim 1, wherein The preparation method of the nascent membrane is scraping or drawing; the nascent membrane is in a flat or composite support structure.

8. The method according to claim 1, wherein The rapid cooling is as follows: the cooling time is 5 s - 60 s, and the temperature is cooled to 0°C - 20°C.

9. The method according to claim 1, wherein The gel bath is one of deionized water, methanol, ethanol, glycerol, isopropanol, ethylene glycol, n-butanol, and acetone, and the temperature is 10°C - 20°C.

10. A method for preparing a highly porous and high-flux asymmetric membrane prepared by the method according to any one of claims 1 to 9, characterized in that, The surface layer of the asymmetric membrane has a network-like pore structure, the support layer has finger-like pores, and the porosity is 75% - 85%.

Images