Preparation method and application of asymmetric ultrafiltration membrane with high flux, high interception and controllable structure

Abstract

The invention discloses a preparation method and application of a high-flux, high-interception and structure-controllable asymmetric ultrafiltration membrane, and belongs to the technical field of ultrafiltration membranes. The preparation method of the asymmetric ultrafiltration membrane comprises the following steps: mixing 20-30 parts by weight of an ethylene-vinyl acetate copolymer, 40-70 parts by weight of a good solvent, 4-20 parts by weight of a pore-foaming agent, 10-25 parts by weight of a cosolvent and 0-10 parts by weight of a plasticizer, heating and stirring, standing and defoaming to obtain a homogeneous membrane casting solution; coating a substrate with the membrane casting solution and then carrying out pre-evaporation treatment; and immersing the pre-evaporated material into a coagulating bath to carry out phase separation and solvent exchange for curing, and washing to obtain the ultrafiltration membrane. Effective preparation of the asymmetric ultrafiltration membrane with high flux, high interception and controllable structure is realized, and the preparation method is simple to operate, clear in process, high in practicability and beneficial to product industrialization.

Description

Technical Field

[0001] This invention relates to the field of ultrafiltration membrane technology, and more specifically, to a method for preparing a high-flux, high-retention, and structurally controllable asymmetric ultrafiltration membrane and its application. Background Technology

[0002] Ultrafiltration is a pressure-driven process that uses porous membranes to separate large molecules from small molecules and water in a solution. It effectively removes proteins, large organic molecules, and microorganisms from water. Therefore, ultrafiltration technology is widely used in food, pharmaceutical, chemical, and water treatment industries.

[0003] Ultrafiltration membranes primarily rely on a dense separation layer for separation. While this dense layer results in a high rejection rate, it also increases the membrane's mass transfer resistance, leading to a decrease in permeate flux. In other words, current ultrafiltration membranes often cannot simultaneously achieve both high rejection rate and high flow rate. To obtain ultrafiltration membranes with high flux and high rejection rate, asymmetric ultrafiltration membranes with a dense surface and a porous bottom are currently a key research focus.

[0004] Chinese patent CN102179187A discloses a polyvinylidene fluoride (PVDF) ultrafiltration membrane and its preparation method, wherein modified nano-CaCO3 particles are used as a pore-forming agent; the bulk porosity of the ultrafiltration membrane is increased from 69% to 72%, and the pure water flux is increased from 450 L / (m³). 2 The concentration of ·h·Aar) was increased to 520 L / (m 2 The increased flux (·h·Aar) is due to the addition of calcium carbonate, which, after being dissolved by acid, leaves numerous pores, increasing the bulk porosity and thus enhancing the membrane's permeation flux. However, the membrane's separation performance is mainly related to its surface porosity and pore size; increasing the bulk porosity does not significantly affect the membrane's permeation flux and may even reduce the ultrafiltration membrane's retention performance and strength. Chinese patent CN114272772A discloses an asymmetric polyethersulfone porous membrane and its preparation method. This porous membrane comprises a first porous surface, a second porous surface, and a main body located between the first and second porous surfaces. This asymmetric polyethersulfone membrane improves its hydrophilicity and optimizes its structure by adding hydrophilic additives such as polyvinylpyrrolidone, 2-[[tris(hydroxymethyl)methyl]amino]ethanesulfonic acid, and 3-aminothiophene-2-carboxamide. However, the hydrophilic additives are expensive, offering no price advantage, and their separation performance is not significantly improved compared to other processes. Therefore, there is an urgent need to develop a method for preparing asymmetric polyethersulfone ultrafiltration membranes with excellent comprehensive performance in order to solve the problems existing in the current technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a high-flux, high-retention, and structurally controllable asymmetric ultrafiltration membrane and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a high-flux, high-retention, and structurally controllable asymmetric ultrafiltration membrane includes the following steps:

[0008] A1. Mix 20-30 parts by weight of ethylene-vinyl acetate copolymer, 40-70 parts by weight of good solvent, 4-20 parts by weight of pore-forming agent, 10-25 parts by weight of co-solvent, and 0-10 parts by weight of plasticizer, heat and stir, and let stand to degas to obtain homogeneous casting solution.

[0009] A2. After coating the casting solution onto the substrate, perform a pre-evaporation treatment;

[0010] A3. The pre-evaporated material is immersed in a coagulation bath to solidify by phase separation and solvent exchange, and then washed to obtain an ultrafiltration membrane.

[0011] The present invention is further configured such that, in step A1, the good solvent is one or more of N-methyl-2-pyrrolidone, acetoethyl ketone, tetrahydrofuran, ethyl acetate, and ethylene glycol dimethyl ether.

[0012] 3. The method for preparing a high-flux, high-retention, and structurally controllable asymmetric ultrafiltration membrane according to claim 1, characterized in that, in step A1, the co-solvent is one or more of 1,2-dichloroethane, isopropanol, hexanol, n-hexane, acetone, and sodium dodecyl sulfate.

[0013] The present invention is further configured such that, in step A1, the pore-forming agent is one or more of gelatin, polyvinyl alcohol, hydroxypropyl cellulose, and lithium chloride.

[0014] The present invention is further configured such that, in step A1, the plasticizer is one or more of sorbitol, xylitol, glycerol, propylene glycol, ethylene glycol, diethylene glycol, and triethylene glycol.

[0015] The present invention is further configured such that the obtained ultrafiltration membrane comprises a dense separation layer, a support layer and a bottom layer, wherein the thickness of the dense separation layer is 5-20 micrometers, the thickness of the support layer is 10-30 micrometers, and the thickness of the bottom layer is 10-20 micrometers.

[0016] The present invention is further configured such that the thickness of the support layer is 20%-60% of the total thickness of the ultrafiltration membrane.

[0017] The present invention is further configured such that the coagulation bath is a pure water or an aqueous ethanol solution.

[0018] Application of a high-flux, high-retention, and structurally controllable asymmetric ultrafiltration membrane in the field of ultrafiltration.

[0019] In summary, the present invention has the following beneficial effects:

[0020] This application rationally configures the film-forming components, controls the phase separation rate by adjusting the solvent type, ratio, and film-forming process, and regulates the structure and morphology of the ultrafiltration membrane by controlling the casting solution cooling time, substrate material, coating speed, coagulation bath temperature, and liquid film thickness. This enables the asymmetric ultrafiltration membrane to achieve high throughput and high retention in separation performance (the dense surface separation layer is responsible for retaining large molecules but allows liquid to pass through; the filtration accuracy is controlled by regulating the dense separation layer; at the same time, the dense surface separation layer is connected to the porous support layer and the bottom layer; as the pore size increases, the resistance of the liquid after passing through the surface layer will be greatly reduced; the filtration rate is controlled by regulating the support layer). The preparation method is simple to operate, has a clear process, and is highly practical, which is conducive to the industrialization of the product. Attached Figure Description

[0021] Figure 1 This is a cross-sectional scanning electron microscope image of the high-throughput, high-retention, and structurally controllable asymmetric ultrafiltration membrane of Example 1.

[0022] Figure 2 This is a cross-sectional scanning electron microscope image of the high-throughput, high-retention, and structurally controllable asymmetric ultrafiltration membrane of Example 2.

[0023] Figure 3 This is a cross-sectional scanning electron microscope image of the high-throughput, high-retention, and structurally controllable asymmetric ultrafiltration membrane of Example 3.

[0024] Figure 4 This is a cross-sectional scanning electron microscope image of the high-throughput, high-retention, and structurally controllable asymmetric ultrafiltration membrane of Example 4.

[0025] Figure 5 This is a cross-sectional scanning electron microscope image of the high-throughput, high-retention, and structurally controllable asymmetric ultrafiltration membrane of Example 5. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The high-flux, high-retention, and structurally controllable asymmetric ultrafiltration membrane of this invention comprises a dense separation layer, a support layer, and a bottom layer. The thickness of the dense separation layer is 5-20 micrometers, the thickness of the support layer is 10-30 micrometers, and the thickness of the bottom layer is 10-20 micrometers; the thickness of the support layer is 20%-60% of the total thickness of the ultrafiltration membrane. It is prepared through the following steps:

[0028] A1. Mix 20-30 parts by weight of ethylene-vinyl acetate copolymer (molecular weight of 40,000-60,000D, vinyl acetate content of 15-25%), 40-70 parts by weight of good solvent, 4-20 parts by weight of pore-forming agent, 10-25 parts by weight of co-solvent, and 0-10 parts by weight of plasticizer, heat and stir, and let stand to degas to obtain homogeneous casting solution.

[0029] The good solvent is one or more of N-methyl-2-pyrrolidone, acetoethyl ketone, tetrahydrofuran, ethyl acetate, and ethylene glycol dimethyl ether; the co-solvent is one or more of 1,2-dichloroethane, isopropanol, hexanol, n-hexane, acetone, and sodium dodecyl sulfate. The pore-forming agent is one or more of gelatin, polyvinyl alcohol, hydroxypropyl cellulose, and lithium chloride; the plasticizer is one or more of sorbitol, xylitol, glycerin, propylene glycol, ethylene glycol, diethylene glycol, and triethylene glycol.

[0030] A2. After coating the casting solution onto the substrate (such as non-woven fabric), perform a pre-evaporation treatment;

[0031] A3. The pre-evaporated material is immersed in a coagulation bath (pure water or ethanol aqueous solution) to solidify it by phase separation and solvent exchange, and then washed to obtain an ultrafiltration membrane.

[0032] The preferred embodiments are as follows (in each embodiment, the molecular weight of the ethylene-vinyl acetate copolymer is 50,000D, the vinyl acetate content is 20%, and the molecular weight of polyvinyl alcohol is 10,000D):

[0033] Example 1

[0034] A1: Preparation of casting solution; 19 parts by weight of ethylene-vinyl acetate copolymer and 43 parts by weight of ethyl acetate were mechanically stirred and mixed at 50°C, and then 23 parts by weight of 1,2-dichloroethane, 7 parts by weight of polyvinyl alcohol, 3 parts by weight of lithium chloride and 5 parts by weight of ethylene glycol were added and mechanically stirred and mixed at 60°C; the mixture was allowed to stand for 24 hours and degassed under vacuum to obtain a homogeneous casting solution.

[0035] A2: The degassed casting liquid is coated onto the nonwoven fabric at a speed of 3 m / min to obtain a liquid film; then the substrate coated with the liquid film is placed in the air medium for pre-evaporation for 10 s. The air medium conditions are: temperature 25℃ and air humidity 50%.

[0036] A3: Immerse the pre-evaporated liquid film along with the substrate in the coagulation bath for 60 seconds (the liquid film undergoes solvent exchange in the coagulation bath, inducing phase separation of the polymer solution and then solidifying into a phase); the coagulation bath is pure water, and the coagulation bath temperature is 25 ℃.

[0037] A4: Rinse the material obtained in step A3 with pure water for 3 hours and store it in a 20% glycerol aqueous solution.

[0038] Example 2

[0039] A1: Preparation of casting solution; 20 parts by weight of ethylene-vinyl acetate copolymer and 47 parts by weight of ethyl acetate were mechanically stirred and mixed at 50°C, and then 24 parts by weight of 1,2-dichloroethane, 3 parts by weight of polyvinyl alcohol, 3 parts by weight of lithium chloride and 3 parts by weight of ethylene glycol were added and mechanically stirred and mixed at 60°C; the mixture was allowed to stand for 24 hours and degassed under vacuum to obtain a homogeneous casting solution.

[0040] A2: The degassed casting liquid is coated onto the nonwoven fabric at a speed of 3 m / min to obtain a liquid film; then the substrate coated with the liquid film is placed in the air medium for pre-evaporation for 10 s. The air medium conditions are: temperature 25℃ and air humidity 50%.

[0041] A3: Immerse the pre-evaporated liquid film along with the substrate in the coagulation bath for 60 seconds (the liquid film undergoes solvent exchange in the coagulation bath, inducing phase separation of the polymer solution and then solidifying into a phase); the coagulation bath is pure water, and the coagulation bath temperature is 25 ℃.

[0042] A4: The material obtained in step A3 is rinsed with pure water for 3 hours to obtain an ultrafiltration membrane, which is then stored in a 20% glycerol aqueous solution.

[0043] Example 3

[0044] A1: Preparation of casting solution; 22 parts by weight of ethylene-vinyl acetate copolymer and 45 parts by weight of N-methyl-2-pyrrolidone were mechanically mixed at 50°C, and then 24 parts by weight of acetone, 3 parts by weight of polyvinyl alcohol, 3 parts by weight of lithium chloride and 3 parts by weight of ethylene glycol were added and mechanically mixed at 60°C; the mixture was allowed to stand for 24 hours and then degassed under vacuum to obtain a homogeneous casting solution.

[0045] A2: The degassed casting liquid is coated onto the nonwoven fabric at a speed of 3 m / min to obtain a liquid film; then the substrate coated with the liquid film is placed in the air medium for pre-evaporation for 10 s. The air medium conditions are: temperature 25℃ and air humidity 50%.

[0046] A3: Immerse the pre-evaporated liquid film along with the substrate in the coagulation bath for 120 seconds (the liquid film undergoes solvent exchange in the coagulation bath, inducing phase separation of the polymer solution and then solidifying into a phase); the coagulation bath is pure water, and the coagulation bath temperature is 25 ℃.

[0047] A4: Rinse the material obtained in step A3 with pure water for 3 hours and store it in a 20% glycerol aqueous solution.

[0048] Example 4

[0049] A1: Preparation of casting solution; 25 parts by weight of ethylene-vinyl acetate copolymer and 50 parts by weight of acetoethyl ketone were mechanically mixed at 50°C, and then 19 parts by weight of acetone, 2 parts by weight of polyvinyl alcohol, 2 parts by weight of lithium chloride and 2 parts by weight of ethylene glycol were added and mechanically mixed at 60°C; the mixture was allowed to stand for 24 hours and degassed under vacuum to obtain a homogeneous casting solution.

[0050] A2: The degassed casting liquid is coated onto the nonwoven fabric at a speed of 3 m / min to obtain a liquid film; then the substrate coated with the liquid film is placed in the air medium for pre-evaporation for 10 s. The air medium conditions are: temperature 25℃ and air humidity 50%.

[0051] A3: Immerse the pre-evaporated liquid film along with the substrate in the coagulation bath for 60 seconds (the liquid film undergoes solvent exchange in the coagulation bath, inducing phase separation of the polymer solution and then solidifying into a phase); the coagulation bath is pure water, and the coagulation bath temperature is 25 ℃.

[0052] A4: Rinse the material obtained in step A3 with pure water for 3 hours and store it in a 20% glycerol aqueous solution.

[0053] Example 5

[0054] A1: Preparation of casting solution; 26 parts by weight of ethylene-vinyl acetate and 50 parts by weight of N-methyl-2-pyrrolidone were mechanically mixed at 50°C, and then 15 parts by weight of isopropanol, 3 parts by weight of polyvinyl alcohol, 3 parts by weight of lithium chloride and 3 parts by weight of ethylene glycol were added and mechanically mixed at 60°C; the mixture was allowed to stand for 24 hours and then degassed under vacuum to obtain a homogeneous casting solution.

[0055] A2: The degassed casting liquid is coated onto the nonwoven fabric at a speed of 3 m / min to obtain a liquid film; then the substrate coated with the liquid film is placed in the air medium for pre-evaporation for 10 s. The air medium conditions are: temperature 25℃ and air humidity 50%.

[0056] A3: Immerse the pre-evaporated liquid film along with the substrate in the coagulation bath for 60 seconds (the liquid film undergoes solvent exchange in the coagulation bath, inducing phase separation of the polymer solution and then solidifying into a phase); the coagulation bath is pure water, and the coagulation bath temperature is 25 ℃.

[0057] A4: Rinse the material obtained in step A3 with pure water for 3 hours and store it in a 20% glycerol aqueous solution.

[0058] The performance of the ultrafiltration membranes prepared in Examples 1 to 5 is shown in Table 1. The methods for testing the pure water flux and BSA rejection rate are as follows:

[0059] 1. Pretreatment: Cut the membrane and place it in a flux cup, immerse it in deionized water, and pre-compress it at 0.15 MPa for 10 minutes. The purpose is to remove air from the membrane, fully wet the membrane pores, and achieve osmotic equilibrium.

[0060] 2. Constant pressure operation: Adjust the pressure of the flow cup system to the target test pressure of 0.1 MPa.

[0061] 3. Data Acquisition: Record the water flow rate after stable operation. Perform continuous testing for 30 minutes and take the average value to eliminate transient effects.

[0062] 4. Then, the separation performance was tested using BSA (concentration of 1000 ppm) at a pressure of 0.1 MPa. The test was repeated three times, and the average value was recorded.

[0063] Pure water flux (F) is the volume of water that permeates through the membrane per unit time, expressed in L / (m²). 2 The calculation formula is: F = V / (At). Where A is the effective membrane area through which water passes, in meters. 2 t is the running time in hours (h); V is the volume of the permeate in a given time in liters (L).

[0064] The formula for calculating the BSA rejection rate (R) is: R = (1 - C p / C f )×100%. Where R is the ultrafiltration membrane rejection rate, in units of %; C p C represents the absorbance of the permeate BSA; f This represents the initial BSA absorbance.

[0065] Table 1

[0066]

[0067] As shown in Table 1, the pure water flux of the asymmetric ultrafiltration membrane prepared in this application is much higher than that of existing ultrafiltration membranes, while the rejection rate is above 96%.

[0068] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-flux, high-rejection and structure-controllable asymmetric ultrafiltration membrane, characterized in that, The method comprises the following steps: A1, 20-30 parts by weight of ethylene-vinyl acetate copolymer, 40-70 parts by weight of a good solvent, 4-20 parts by weight of a pore-forming agent, 10-25 parts by weight of a cosolvent, and 0-10 parts by weight of a plasticizer are mixed and heated and stirred, and then a homogeneous casting solution is obtained after standing and defoaming; A2, the casting solution is coated on a substrate and then subjected to pre-evaporation treatment; A3, the material after pre-evaporation is immersed in a coagulation bath to cause phase separation and solvent exchange for solidification, and then an ultrafiltration membrane is obtained after washing.

2. The method of claim 1, wherein the asymmetric ultrafiltration membrane has a high flux, a high rejection, and a controllable structure. In step A1, the good solvent is one or more of N-methyl-2-pyrrolidone, acetylacetone, tetrahydrofuran, ethyl acetate, and ethylene glycol dimethyl ether.

3. The method of claim 1, wherein the asymmetric ultrafiltration membrane has a high flux, a high rejection, and a controllable structure. In step A1, the cosolvent is one or more of 1,2-dichloroethane, isopropyl alcohol, hexanol, n-hexane, acetone, and sodium dodecyl sulfate.

4. The method of claim 1, wherein the asymmetric ultrafiltration membrane has a high flux, a high rejection, and a controllable structure. In step A1, the pore-forming agent is one or more of gelatin, polyvinyl alcohol, hydroxypropyl cellulose, and lithium chloride.

5. The method of claim 1, wherein the asymmetric ultrafiltration membrane has a high flux, a high rejection, and a controllable structure. In step A1, the plasticizer is one or more of sorbitol, xylitol, glycerol, propylene glycol, ethylene glycol, diethylene glycol, and triethylene glycol.

6. The method of claim 1, wherein the asymmetric ultrafiltration membrane has a high flux, a high rejection, and a controllable structure. The obtained ultrafiltration membrane comprises a dense separation layer, a support layer, and a bottom layer, the thickness of the dense separation layer is 5-20 microns, the thickness of the support layer is 10-30 microns, and the thickness of the bottom layer is 10-20 microns.

7. The method according to claim 6, wherein the asymmetric ultrafiltration membrane is prepared by the steps of: (1) dissolving the polymer in a solvent to form a solution; (2) adding the additive to the solution; (3) casting the solution on a substrate to form a membrane; (4) drying the membrane; and (5) washing the membrane with water. The thickness of the support layer is 20%-60% of the total thickness of the ultrafiltration membrane.

8. The method of claim 1, wherein the asymmetric ultrafiltration membrane has a high flux, a high rejection, and a controllable structure. The coagulation bath is pure water or an ethanol aqueous solution.

9. Use of a high-flux high-rejection and structure-controllable asymmetric ultrafiltration membrane prepared by the method of any one of claims 1-7 in the field of ultrafiltration.

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