A microfiltration membrane and its preparation method

Abstract

The present invention discloses a microfiltration membrane and a preparation method thereof, belonging to the technical field of polymer materials. By utilizing the characteristic that the porous structure support layer can permeate the atmosphere, the upper and lower surfaces of the porous structure support layer coated with the casting liquid membrane are simultaneously subjected to steam-induced forming, greatly shortening the pre-film formation time. At the same time, by adjusting parameters such as the composition and temperature of the atmosphere in the upper and lower parts of the porous structure support layer, synchronous control of the pore sizes on the upper and lower surfaces of the pre-film can be achieved, so that the microfiltration membrane has the advantages of high porosity and controllable pore sizes on both the upper and lower surfaces.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a microfiltration membrane and a preparation method thereof. Background Art

[0002] Membrane technology is a new technology for efficient separation in contemporary times. Compared with traditional distillation and rectification technologies, it has the advantages of high separation efficiency, low energy consumption, and small footprint. The core of membrane separation technology is the separation membrane. Among them, polymer filter membrane is a type of separation membrane made of organic high molecular polymers as raw materials according to a certain process. According to the different types of high molecular polymers, polymer filter membranes can be subdivided into cellulose polymer filter membranes, polyamide polymer filter membranes, sulfone polymer filter membranes, polytetrafluoroethylene polymer filter membranes, etc. In addition, according to the pore size of the membrane, it can be divided into microfiltration membranes, ultrafiltration membranes, nanofiltration membranes and reverse osmosis membranes.

[0003] Microfiltration membranes can intercept particles between 0.1 and 1 micron, allowing macromolecules and soluble solids (inorganic salts) to pass through, but will intercept suspended matter, bacteria, and high molecular weight colloids. At present, microfiltration membranes are mainly used for filtration and sterilization in the pharmaceutical industry, including the production of sterile liquids, separation of biological preparations, preparation of ultrapure water, air filtration, biological and microbial detection and analysis, etc. The operating pressure of microfiltration membranes is generally 0.3-7bar. Microfiltration membrane filtration is the earliest membrane technology developed and applied in the world, using natural or synthetic polymer compounds as membrane materials. For microfiltration membranes, the separation mechanism is mainly screening and interception. In order to develop microfiltration membranes with higher porosity and water flux, common methods include non-solvent induced phase separation (NIPS), vapor induced phase separation (VIPS), and atomization pretreatment induced phase separation.

[0004] Traditional steam-induced phase separation, such as patent CN1170620C, can significantly improve the porosity of the membrane and increase the water flux of the membrane, but generally requires a long time (more than 30 minutes) in high-temperature steam (greater than 100°C). The method of combining atomization pretreatment and non-solvent induced phase separation, such as CN112973451B and CN114797484B, can solve the problem of high temperature and long processing time during traditional steam-induced phase separation to a certain extent, but the pre-atomization process will produce obvious liquid droplets, and the droplets will fall during the long-term batch film formation process and contaminate the membrane surface. At the same time, both methods involve the diffusion of steam or liquid droplets from the surface of the casting liquid to the bottom layer, which will result in a large difference in the pore size morphology between the surface and the bottom layer, and the controllability of the bottom layer pore size is poor.

[0005] Therefore, there is an urgent need to develop a microfiltration membrane with high porosity and controllable pore sizes on the upper and lower surfaces. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a microfiltration membrane and a preparation method thereof. The microfiltration membrane has the advantages of high porosity and controllable pore sizes on both the upper and lower surfaces.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for preparing a microfiltration membrane, comprising the following steps:

[0009] In a closed space, the support layer divides the space into upper and lower parts. By inducing simultaneous formation on the upper and lower surfaces of the support layer through different atmospheres in the upper and lower spaces, a preformed membrane is obtained, and then phase separation forming is carried out to prepare a microfiltration membrane.

[0010] Preferably, the support layer is a porous structure support layer coated with a casting solution.

[0011] Preferably in the present invention, the support layer is placed on a rubber ring, and the rubber ring is in a hollow shape.

[0012] The hollow rubber ring is beneficial to the simultaneous induction and formation of the upper and lower surfaces of the porous structure support layer coated with the casting solution by the atmospheres in the upper and lower spaces.

[0013] The above preparation method controls the pore sizes formed on the upper and lower surfaces of the membrane by controlling the composition and temperature of the atmospheres in the upper and lower parts of the space.

[0014] Preferably in the present invention, the atmosphere is selected from one or more of air, water vapor, ethanol vapor, ethylene glycol vapor, vapor of polar aprotic solvents, salt solution vapor, acid solution vapor, and alkali solution vapor; more preferably, the atmosphere is selected from one or more of air, water vapor, and ethanol vapor.

[0015] Preferably, the temperature of the upper and lower spaces is 5°C to 125°C; more preferably 30°C to 125°C.

[0016] In some specific embodiments of the present invention, the atmosphere is preferably one or more of 60°C air with 70% humidity, 30°C air with 30% humidity, 125°C water vapor, and a 60°C mixed gas of water and ethanol with a mass ratio of 1:1.

[0017] Preferably in the present invention, the forming time of the preformed membrane is 10 to 600 s; more preferably 50 to 300 s; further preferably 100 to 200 s. In some specific embodiments of the present invention, the forming time of the preformed membrane of the microfiltration membrane is 120 s or 180 s.

[0018] Preferably in the present invention, the casting solution is selected from solutions containing polymers;

[0019] Preferably, the polymer is selected from one or more of polysulfone, polyethersulfone, polyvinylidene fluoride, cellulose acetate, polyethylene oxide, polyacrylonitrile, polyamide, and polyimide; more preferably polyethersulfone or polyvinylidene fluoride.

[0020] Preferably, the solution contains a pore-forming additive, a good solvent and / or a poor solvent for the polymer.

[0021] Preferably, the pore-forming additive is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, zinc chloride, and lithium chloride.

[0022] Preferably, the good solvent for the polymer is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tetramethyl sulfoxide, tetrahydrofuran, dioxane, acetonitrile, chloroform, and tetramethyl sulfoxide; more preferably N,N-dimethylacetamide or N-methyl-2-pyrrolidone.

[0023] Preferably, the poor solvent for the polymer is selected from water or an alcohol solvent.

[0024] The alcohol solvent is preferably a small molecule alcohol, specifically including but not limited to one or more of methanol, ethanol, benzyl alcohol, and isopropanol.

[0025] Preferably, in the present invention, the solid content of the casting solution is 6 wt% to 30 wt%; more preferably 10 wt% to 25 wt%. In some specific embodiments of the present invention, the solid content of the casting solution is 19 wt%.

[0026] Preferably, the thickness of the casting solution on the porous structure support layer is 50 to 500 μm; more preferably 75 to 300 μm; further preferably 100 to 150 μm. In some specific embodiments of the present invention, the thickness of the casting solution on the porous support material is 100 μm or 110 μm.

[0027] The present invention does not particularly limit the stirring time and temperature of the above casting solution. The stirring time is preferably 24 to 48 h, and the stirring temperature is preferably 60°C to 100°C.

[0028] In the above preparation method, the porous structure support layer (porous membrane) includes but is not limited to porous structure support materials such as non-woven fabric, woven fabric, and porous ceramic.

[0029] In the present invention, in order to fully carry out steam induction, preferably, a partition is first used to divide the closed space into upper and lower parts. After the atmospheres of the upper and lower parts are stable, the partition is quickly replaced with a porous membrane coated with the casting solution, so that the atmospheres of the upper and lower parts simultaneously perform steam-induced forming on the porous membrane coated with the casting solution to obtain a preformed membrane.

[0030] Before the above-mentioned steam-induced forming, the partition plate is placed on the hollow rubber ring.

[0031] In the present invention, the phase separation forming is preferably carried out by the non-solvent induced phase separation method.

[0032] The above-mentioned non-solvent induced phase separation method specifically is to soak the preformed film prepared above in the non-solvent of the polymer for a period of time and then form and prepare a microfiltration membrane, and use the solvent in the preformed film and the non-solvent of the polymer for physical exchange to cause phase separation of the preformed film.

[0033] The non-solvent of the polymer includes but is not limited to single-component solvents such as water, ethanol, ethylene glycol, aqueous sodium hydroxide solution, or a mixed solution of water and a polar aprotic solvent, or a mixed solution of water and other solvents.

[0034] When the preformed film undergoes phase separation, the temperature is preferably 10°C to 80°C, the time is preferably 1 to 60 minutes, and more preferably 3 to 10 minutes;

[0035] In the present invention, the casting solution is coated on the porous structure support layer substrate by a doctor blade or casting technique, and steam-induced phase separation is carried out by controlling the atmosphere composition and temperature on the upper and lower sides of the porous structure support layer to complete the preparation of the preformed film, and then the preformed film is immersed in a non-solvent bath to further complete the phase separation, thereby obtaining a microfiltration membrane with a high porosity and controllable pore diameters on both the upper and lower surfaces.

[0036] The preparation method of the microfiltration membrane described in the present invention specifically includes the following steps:

[0037] 1) In a closed space, place the partition plate on the hollow rubber ring to divide the space into upper and lower layers, introduce atmosphere into the upper and lower layers, and simultaneously control the temperatures of the upper and lower partitions;

[0038] 2) Remove the partition plate, place the porous structure support layer coated with the casting solution on the gasket, and induce forming simultaneously through the atmosphere in the upper and lower layers to prepare the preformed film;

[0039] 3) Carry out phase separation forming on the preformed film to prepare a microfiltration membrane.

[0040] In the above-mentioned preparation method, after completing the phase separation forming in step 3), soak the completely formed porous membrane in deionized water for a certain period of time to remove the residual solvent, and dry it to prepare the microfiltration membrane described in the present invention.

[0041] The soaking time in deionized water is preferably 24 to 48 hours, and the soaking temperature is preferably 30 to 80°C.

[0042] The present invention does not particularly limit the above drying method, which can be methods well-known to those skilled in the art such as ordinary heating and drying, vacuum drying, etc. In the present invention, the heating and drying method is preferably adopted, and the temperature of the heating and drying is preferably 60°C to 120°C, and the time of the heating and drying is preferably 24 to 48 h.

[0043] The present invention also provides a microfiltration membrane prepared by the above preparation method.

[0044] Preferably, the interior of the microfiltration membrane has a sponge pore structure.

[0045] The present invention simultaneously induces the formation of the upper and lower surfaces of the porous structure support layer of the coated casting solution film by means of steam induction, greatly shortening the pre-film formation time.

[0046] Compared with the prior art, the microfiltration membrane provided by the present invention utilizes the characteristic that the porous structure support layer can permeate the atmosphere, and simultaneously performs steam-induced formation on the upper and lower surfaces of the porous structure support layer of the coated casting solution film, greatly shortening the pre-film formation time. At the same time, by adjusting parameters such as the composition and temperature of the atmosphere in the upper and lower parts of the porous structure support layer, synchronous control of the pore diameters of the upper and lower surfaces of the pre-film can be achieved, so that the microfiltration membrane has the advantages of high porosity and controllable pore diameters on both the upper and lower surfaces. Description of the Drawings

[0047] Figure 1 It is a schematic diagram of the preparation process of the microfiltration membrane;

[0048] Figure 2 It is the cross-section of the microfiltration membrane in Example 1, a is the longitudinal section, b is the upper surface, and c is the lower surface;

[0049] Figure 3 It is the cross-section of the microfiltration membrane in Example 2, d is the longitudinal section, e is the upper surface, and f is the lower surface. Detailed Embodiments

[0050] In order to further illustrate the present invention, the microfiltration membrane and its preparation method provided by the present invention will be described in detail below in conjunction with embodiments.

[0051] Example 1

[0052] First step: Place the partition on the hollow rubber ring to separate the space into upper and lower layers. Inject air with a humidity of 70% and a temperature of 60°C into the upper layer as atmosphere A, and inject air with a humidity of 30% and a temperature of 30°C into the lower layer as atmosphere B, and wait for the atmosphere composition and temperature of the upper and lower layers to stabilize;

[0053] Second step: Dissolve 12 g of polyethersulfone and 4 g of polyvinylpyrrolidone in 84 g of N,N-dimethylacetamide, and stir at 60°C for 24 h to obtain a uniform casting solution;

[0054] Step 3: Coating the obtained casting solution on the porous ceramic by the blade coating technique, and controlling the coating thickness to be 100 μm;

[0055] Step 4: Quickly remove the partition plate, and then place the porous ceramic coated with the casting solution between atmosphere A and atmosphere B. The upper layer of the casting solution is affected by the upper atmosphere A, and the lower layer is affected by the lower atmosphere B, and steam-induced phase separation is carried out simultaneously. Control the time to be 2 min to obtain a preformed membrane;

[0056] Step 5: Immerse the preformed membrane in a 40% DMAc solution and soak for 7 min to further carry out phase separation and forming;

[0057] Step 6: Immerse the fully formed porous membrane in deionized water at 30 °C for 24 h to remove the residual solvent, and dry it at 80 °C for 24 h to obtain a microfiltration membrane.

[0058] Example 2

[0059] Step 1: Place the partition plate on the hollow rubber ring to separate the space into upper and lower layers. Inject 125 °C water vapor into the upper layer as atmosphere A, and inject a mixed gas of 60 °C water: ethanol of 100 g: 100 g into the lower layer as atmosphere B, and wait for the atmosphere composition and temperature of the upper and lower layers to stabilize;

[0060] Step 2: Dissolve 10 g of polyvinylidene fluoride and 6 g of polyvinylpyrrolidone in 84 g of N-methylpyrrolidone, and stir at 80 °C for 24 h to obtain a uniform casting solution;

[0061] Step 3: Coating the obtained casting solution on the non-woven fabric by the blade coating technique, and controlling the coating thickness to be 110 μm;

[0062] Step 4: Quickly remove the partition plate, and then place the non-woven fabric coated with the casting solution between atmosphere A and atmosphere B. The upper layer of the casting solution is affected by the upper atmosphere A, and the lower layer is affected by the lower atmosphere B, and steam-induced phase separation is carried out simultaneously. Control the time to be 3 min to obtain a preformed membrane;

[0063] Step 5: Immerse the preformed membrane in a 30% DMAc solution and soak for 3 min to further carry out phase separation and forming;

[0064] Step 6: Immerse the fully formed porous membrane in deionized water at 60 °C for 24 h to remove the residual solvent, and dry it at 60 °C for 36 h to obtain a microfiltration membrane.

[0065] The following relevant tests were carried out on the microfiltration membranes prepared in the above examples, and the specific data are shown in Table 1.

[0066] 1) Scanning electron microscope test

[0067] Use Hitachi SU3800 to scan and count the pore sizes of the upper and lower surfaces of the microfiltration membrane to obtain the average pore sizes of the upper and lower surfaces. SeeFigure 2 (Microfiltration membrane prepared in Example 1) Figure 3 (Microfiltration membrane prepared in Example 2).

[0068] 2) Water flux test

[0069] Water flux is the volume or mass of water passing through a unit membrane area per unit time, which is an important index for evaluating membrane separation efficiency and one of the key indexes for measuring the performance of microfiltration membranes. The larger the water flux, the higher the separation efficiency of the membrane and the more permeable the internal pores of the membrane. The microfiltration membranes prepared in Examples 1 and 2 have a relatively high water flux. The test is carried out with reference to the standard of GB / T 34242-2017.

[0070] 3) Most probable pore size

[0071] The most probable pore size refers to the pore size that is most likely to occur, that is, the pore size with the largest number of pores. It is an important index for evaluating membrane separation effect and one of the key indexes for measuring the performance of microfiltration membranes. The most probable pore size determines the size of the particles separated by the membrane. Table 1 shows that the microfiltration membranes prepared in Examples 1 and 2 have excellent separation performance. The test is carried out with reference to the standard of GB / T 5249-2013.

[0072] 4) Porosity

[0073] Porosity is the ratio of the total volume of interconnected tiny voids in a porous medium to the external volume of the porous medium. Generally speaking, the higher the porosity, the more permeable the inside of the membrane and the higher the separation efficiency. When the porosity is greater than 80%, it belongs to high porosity. The test is carried out with reference to the standard of GB / T 33052-2016.

[0074] Table 1 Water flux, pore size and porosity of the examples

[0075]

[0076] From the data in Table 1, combined with Figure 2 and Figure 3 it can be seen that by changing the composition and temperature of the upper and lower atmospheres, the present invention controls the pore sizes on the upper and lower surfaces of the preformed membrane. The prepared microfiltration membrane has a sponge-like pore structure inside, and has excellent separation performance and high porosity. Moreover, the preparation method of the microfiltration membrane of the present invention can prepare microfiltration membranes with different pore sizes and adjustable pore sizes on the upper and lower surfaces according to needs, and has strong practical applicability; in addition, the preparation method has a simple process, and the use of simultaneous steam induction on the upper and lower surfaces greatly shortens the preformed membrane time, which can meet different industrial production needs and has a broad market application prospect.

[0077] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a microfiltration membrane, characterized in that, it comprises the following steps: In a closed space, the support layer divides the space into upper and lower parts. A preformed membrane is obtained by simultaneously inducing the formation on the upper and lower surfaces of the support layer with different atmospheres in the upper and lower spaces, and then phase separation forming is carried out to prepare a microfiltration membrane; The support layer is a porous structure support layer coated with a casting solution.

2. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the support layer is placed on a rubber ring, and the rubber ring is in a hollow shape.

3. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the atmosphere is selected from one or more of air, water vapor, ethanol vapor, ethylene glycol vapor, vapor of a polar aprotic solvent, vapor of a salt solution, vapor of an acid solution, and vapor of an alkali solution.

4. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the temperature of the upper and lower spaces is 5°C to 125°C.

5. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the forming time of the preformed membrane is 10 to 600 s.

6. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the casting solution is selected from solutions containing polymers; the polymers are selected from one or more of polysulfone, polyethersulfone, polyvinylidene fluoride, cellulose acetate, polyethylene oxide, polyacrylonitrile, polyamide, and polyimide; the solution contains a pore-forming additive, a good solvent and / or a poor solvent of the polymer; the pore-forming additive is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, zinc chloride, and lithium chloride; the good solvent of the polymer is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tetramethyl sulfoxide, tetrahydrofuran, dioxane, acetonitrile, and chloroform; the poor solvent of the polymer is selected from water or an alcohol solvent.

7. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the solid content of the casting solution is 6 wt% to 30 wt%.

8. The method for preparing a microfiltration membrane according to claim 1, characterized in that, the thickness of the casting solution on the porous structure support layer is 50 to 500 μm.

9. A microfiltration membrane, characterized in that, it is prepared by the preparation method according to any one of claims 1 to 8.

10. The microfiltration membrane according to claim 9, characterized in that, the interior of the microfiltration membrane has a sponge pore structure.

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