Microfiltration membrane and its manufacturing method

Abstract

A microfiltration membrane and a method for manufacturing the same, in which the method uses a first atmosphere in the upper space and a second atmosphere in the lower space to simultaneously perform steam-induced molding on the upper and lower surfaces of a porous structure support layer coated with a casting liquid, significantly shortening the pre-membrane formation time. At the same time, by adjusting the composition and temperature of the first atmosphere in the upper space and the second atmosphere in the lower space of the porous structure support layer, synchronous control of the pore sizes on the upper and lower surfaces of the pre-membrane is achieved, resulting in a microfiltration membrane with high porosity and controllable pore sizes on both the upper and lower surfaces.

Description

[Technical Field]

[0001] This application claims priority to a Chinese patent application bearing application number CN202310691553.5 and entitled "Microfiltration membrane and manufacturing method thereof," filed with the State Intellectual Property Office on June 12, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the technical field of polymeric materials, in particular to microfiltration membranes and methods for producing the same. [Background technology]

[0003] Membrane technology is a modern, new, highly efficient separation technology. Compared to traditional technologies such as distillation and rectification, it offers advantages such as higher separation efficiency, lower energy consumption, and smaller site footprint. The core of membrane separation technology is the separation membrane. Polymer filtration membranes are separation membranes made from organic polymers and manufactured according to a specific process. Polymer filtration membranes are classified according to the type of polymer, including cellulose-based polymer filtration membranes, polyamide-based polymer filtration membranes, sulfone-based polymer filtration membranes, and polytetrafluoroethylene-based polymer filtration membranes. Furthermore, according to the pore size of the membrane, they are classified into microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes.

[0004] Microfiltration membranes can block particles between 0.1 and 1 μm in size, allowing polymers and dissolved solids (inorganic salts) to pass through while blocking suspended solids, bacteria, and high-molecular-weight colloids. Currently, microfiltration membranes are primarily used for filtration and sterilization in the pharmaceutical industry, including the production of sterile liquids, the separation of biological products, the production of ultrapure water, air filtration, and biological and microbiological detection and analysis. The operating pressure of microfiltration membranes is generally 0.3 to 7 bar. Filtration through microfiltration membranes is the world's earliest membrane technology, using natural or synthetic polymers as membrane materials. The separation mechanism of microfiltration membranes is primarily screening and blocking. Common methods for developing microfiltration membranes with higher porosity and water flux include nonsolvent-induced phase separation (NIPS), vapor-induced phase separation (VIPS), and atomization pretreatment-induced phase separation.

[0005] Conventional vapor-induced phase separation techniques, such as those described in Patent CN1170620C (Patent Document 1), can significantly increase membrane porosity and water flux, but typically require prolonged exposure to high-temperature steam (above 100°C) for longer periods (over 30 minutes). Methods combining atomization pretreatment with non-solvent-induced phase separation, such as those described in Patent Documents CN112973451B (Patent Document 2) and CN114797484B (Patent Document 3), can partially address the high temperature and long processing time issues associated with conventional vapor-induced phase separation. However, significant droplets are generated during the atomization pretreatment process, and droplets fall and contaminate the membrane surface during long-term batch membrane formation. At the same time, both of these methods result in the diffusion of vapor or droplets from the surface to the bottom layer of the casting liquid, resulting in significant differences in pore size morphology between the surface and bottom layers, resulting in poor control of the pore size of the bottom layer.

[0006] Therefore, it is necessary to develop a microfiltration membrane with high porosity and controllable pore sizes on both the upper and lower surfaces. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Chinese Patent Application Publication No. 1170620 [Patent Document 2] Chinese Patent Application Publication No. 112973451 [Patent Document 3] Chinese Patent Application Publication No. 114797484 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of this, the technical problem to be solved by the present application is to provide a microfiltration membrane and a method for manufacturing the same. The microfiltration membrane has the advantages of high porosity and the pore sizes of both the upper and lower surfaces can be controlled. [Means for solving the problem]

[0009] To achieve the above objectives, the present application adopts the following technical solutions:

[0010] The present application provides a method for producing a microfiltration membrane, In a sealed space, a support layer divides the space into an upper space and a lower space, and simultaneously performs induced molding on the upper and lower surfaces of the support layer using a first atmosphere in the upper space and a second atmosphere in the lower space to obtain a pre-formed membrane, and then performs phase separation molding to produce a microfiltration membrane, wherein the first atmosphere and the second atmosphere are different, and the support layer is a porous structure support layer coated with a casting liquid.

[0011] Preferably, the support layer is disposed on a rubber ring, and the rubber ring is hollow.

[0012] The hollow rubber ring is advantageous in that the atmospheres in the upper and lower spaces simultaneously induce molding on the upper and lower surfaces of the porous structure support layer coated with the casting liquid.

[0013] The above manufacturing method further controls the pore size at the upper and lower surfaces of the membrane by controlling the composition and temperature of the atmosphere in the upper and lower spaces.

[0014] Preferably, the first atmosphere and the second atmosphere are independently selected from one or more of air, water vapor, ethanol vapor, ethylene glycol vapor, polar aprotic solvent vapor, salt solution vapor, acid solution vapor, and alkaline solution vapor, and more preferably, the atmosphere is selected from one or more of air, water vapor, and ethanol vapor.

[0015] Preferably, the temperatures of the upper space and the lower space are independently 5°C to 125°C, more preferably 30°C to 125°C.

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

[0017] Preferably, the pre-forming time is 10 to 600 seconds, more preferably 50 to 300 seconds, and even more preferably 100 to 200 seconds. In some specific examples of the present application, the pre-forming time for the microfiltration membrane is 120 seconds or 180 seconds.

[0018] Preferably, the casting liquid is a solution containing a polymer, Preferably, the polymer is selected from one or more of polysulfone, polyethersulfone, polyvinylidene fluoride, cellulose acetate, polyethylene oxide, polyacrylonitrile, polyamide and polyimide, more preferably selected from polyethersulfone or polyvinylidene fluoride.

[0019] Preferably, the solution containing the polymer also contains a pore-forming additive and a solvent for the polymer; the solvent for the polymer is a good solvent for the polymer and / or a poor solvent for the polymer, The pore-forming additive is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, zinc chloride, and lithium chloride.

[0020] 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, and more preferably selected from N,N-dimethylacetamide or N-methyl-2-pyrrolidone.

[0021] Preferably, the poor solvent for the polymer is selected from water or an alcohol solvent.

[0022] The alcohol solvent is preferably a low molecular weight alcohol, specifically including, but not limited to, one or more of methanol, ethanol, benzyl alcohol, and isopropanol.

[0023] Preferably, the solid content of the casting liquid is 6 to 30 wt%, more preferably 10 to 25 wt%. In some specific examples of the present application, the solid content of the casting liquid is 19 wt%.

[0024] Preferably, the thickness of the casting liquid on the porous structure support layer is 50 to 500 μm, more preferably 75 to 300 μm, and even more preferably 100 to 150 μm. In some specific examples of the present application, the thickness of the casting liquid on the porous support material is 100 μm or 110 μm.

[0025] In the present application, the stirring time and temperature of the casting liquid are not particularly limited, but the stirring time is preferably 24 to 48 hours, and the stirring temperature is preferably 60 to 100°C.

[0026] In the above manufacturing method, the porous structure support layer (porous membrane) includes, but is not limited to, porous structure support materials such as nonwoven fabric, woven fabric, and porous ceramic.

[0027] In the present application, in order to sufficiently perform the steam induction, it is preferable to first divide the sealed space into an upper space and a lower space with a partition plate, and after the atmospheres in the upper space and the lower space have stabilized, quickly replace the partition plate with a porous membrane whose surface is coated with the casting liquid, so that the atmospheres in the upper space and the lower space simultaneously perform steam-induced molding on the porous membrane whose surface is coated with the casting liquid, thereby obtaining a pre-formed membrane.

[0028] Prior to the steam-induced molding, the partition plate is placed in a hollow rubber ring.

[0029] In the present application, the phase separation molding is preferably carried out by a non-solvent induced phase separation method.

[0030] Specifically, the non-solvent-induced phase separation method involves immersing the pre-formed membrane produced as described above in a non-solvent for the polymer for a certain period of time, and then molding the membrane to produce a microfiltration membrane, thereby physically exchanging the solvent in the pre-formed membrane with the non-solvent for the polymer, thereby causing phase separation of the pre-formed membrane.

[0031] Non-solvents for the polymer include, but are not limited to, single component solvents such as water, ethanol, ethylene glycol, aqueous sodium hydroxide, or mixtures of water with polar aprotic solvents, or mixtures of water with other solvents.

[0032] When the pre-formed membrane is subjected to phase separation, the temperature is preferably 10 to 80°C, and the time is preferably 1 to 60 minutes, more preferably 3 to 10 minutes. In this application, a casting liquid is coated onto the base of a porous structure support layer by blade coating or casting technology, and the production of a pre-formed membrane is completed by performing vapor-induced phase separation by controlling the composition and temperature of the atmosphere above and below the porous structure support layer.The pre-formed membrane is then immersed in a non-solvent bath to further complete the phase separation, thereby obtaining a microfiltration membrane with a high porosity and controllable pore sizes on both the upper and lower surfaces.

[0033] Specifically, the method for producing a microfiltration membrane described in the present application includes: 1) in a sealed space, a partition plate is disposed in a hollow rubber ring to divide the space into an upper space and a lower space, and an atmosphere is introduced into the upper space and the lower space, and simultaneously the temperatures of the upper space and the lower space are separately controlled; 2) remove the partition plate, place the porous structure support layer coated with the casting liquid on the gasket, and simultaneously perform induced molding by the atmosphere in the upper space and the lower space to manufacture a pre-formed membrane; 3) performing phase separation molding on the pre-formed membrane to produce a microfiltration membrane.

[0034] In the above manufacturing method, after the phase separation molding in step 3) is completed, the fully molded porous membrane is immersed in deionized water for a certain period of time to remove residual solvent, and then dried to produce the microfiltration membrane described in the present application.

[0035] The immersion time in the deionized water is preferably 24 to 48 hours, and the immersion temperature is preferably 30 to 80°C.

[0036] In the present application, the drying method is not particularly limited, and may be a method well known to those skilled in the art, such as general heat drying, vacuum drying, etc. In the present application, it is preferable to use a heat drying method, and the heat drying temperature is preferably 60 to 120°C, and the heat drying time is preferably 24 to 48 hours.

[0037] The present application further provides a microfiltration membrane produced by the above production method.

[0038] Preferably, the inside of the microfiltration membrane has a sponge-like pore structure.

[0039] The present application uses a vapor-induced method to simultaneously perform induced molding on the upper and lower surfaces of a porous structure support layer coated with a casting liquid, thereby significantly shortening the pre-deposition time.

[0040] Compared with the prior art, the microfiltration membrane provided by the present application utilizes the atmosphere-permeable property of the porous structure support layer to simultaneously perform steam-induced molding on the upper and lower surfaces of the porous structure support layer coated with a casting liquid using a first atmosphere in the upper space and a second atmosphere in the lower space, thereby significantly shortening the pre-membrane formation time. At the same time, by adjusting the composition and temperature of the first atmosphere in the upper space and the second atmosphere in the lower space of the porous structure support layer, synchronous control of the pore sizes on the upper and lower surfaces of the pre-membrane is achieved, resulting in the microfiltration membrane having the advantages of high porosity and controllable pore sizes on both the upper and lower surfaces. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a schematic diagram of a manufacturing process for a microfiltration membrane. [Figure 2] 1 is a cross section of the microfiltration membrane in Example 1, where a is a longitudinal section, b is an upper surface, and c is a lower surface. [Figure 3] 1 is a cross section of the microfiltration membrane in Example 2, where d is a longitudinal section, e is an upper surface, and f is a lower surface. DETAILED DESCRIPTION OF THE INVENTION

[0042] To further illustrate the present application, the microfiltration membrane and the manufacturing method thereof provided by the present application will be described in detail below with reference to examples.

[0043] Example 1 First step: A partition plate was placed on the hollow rubber ring to divide the space into an upper space and a lower space. Air at 60°C and 70% humidity was injected into the upper space as atmosphere A, and air at 30°C and 30% humidity was injected into the lower space as atmosphere B. The atmosphere composition and temperature of the upper and lower spaces were then allowed to stabilize. Second step: 12 g of polyethersulfone and 4 g of polyvinylpyrrolidone were dissolved in 84 g of N,N-dimethylacetamide, and the solution was stirred at 60° C. for 24 hours to obtain a uniform casting liquid. Third step: the obtained casting liquid was coated onto the porous ceramic by blade coating technique, and the coating thickness was controlled to 100 μm. Fourth step: After the partition plate was quickly removed, the porous ceramic coated with the casting liquid was placed between atmosphere A and atmosphere B, so that the upper layer of the casting liquid was affected by atmosphere A in the upper space, and the lower layer was affected by atmosphere B in the lower space, and simultaneously, vapor-induced phase separation was carried out, and a preliminary film was obtained with a control time of 2 min. Fifth step: The pre-formed membrane was immersed in a 40% DMAc solution for 7 minutes to further perform phase separation molding. Sixth step: The fully formed porous membrane was immersed in deionized water at 30°C for 24 hours to remove residual solvent, and then dried at 80°C for 24 hours to obtain a microfiltration membrane.

[0044] Example 2 First step: A partition plate was placed on a hollow rubber ring to divide the space into an upper space and a lower space. Water vapor at 125°C was injected into the upper space as atmosphere A, and a mixed gas of 100g water:100g ethanol at 60°C was injected into the lower space as atmosphere B. The atmosphere composition and temperature of the upper and lower spaces were then allowed to stabilize. Second step: 10 g of polyvinylidene fluoride and 6 g of polyvinylpyrrolidone were dissolved in 84 g of N-methylpyrrolidone, and the solution was stirred at 80° C. for 24 hours to obtain a uniform casting liquid. Third step: The obtained casting liquid was coated onto the nonwoven fabric by blade coating technique, and the coating thickness was controlled to 110 μm. The fourth step: After the partition plate was quickly removed, the nonwoven fabric coated with the casting liquid was placed between atmosphere A and atmosphere B. The upper layer of the casting liquid was affected by atmosphere A in the upper space, and the lower layer was affected by atmosphere B in the lower space. Simultaneously, vapor-induced phase separation was carried out, and a preliminary membrane was obtained with a control time of 3 min. Fifth step: The pre-formed membrane was immersed in a 30% DMAc solution for 3 minutes to further perform phase separation molding. Sixth step: The fully formed porous membrane was immersed in deionized water at 60°C for 24 h to remove residual solvent, and then dried at 60°C for 36 h to obtain a microfiltration membrane.

[0045] The microfiltration membranes manufactured in the above examples were subjected to the following related tests, and the specific data are shown in Table 1.

[0046] 1) Scanning electron microscope examination The pore sizes on the upper and lower surfaces of the microfiltration membrane were scanned and analyzed using a Hitachi SU3800 to obtain the average pore sizes on the upper and lower surfaces. For details, see Figure 2 (microfiltration membrane prepared in Example 1) and Figure 3 (microfiltration membrane prepared in Example 2).

[0047] 2) Water flux test Water flux is the volume or mass of water passing through a unit membrane area per unit time. It is an important index for evaluating the separation efficiency of a membrane and is also one of the important indexes for measuring the performance of a microfiltration membrane. A higher water flux indicates a higher separation efficiency of the membrane and higher permeability of the voids inside the membrane. The microfiltration membranes produced in Examples 1 and 2 have a high water flux. Tests were conducted in accordance with GB / T 34242-2017.

[0048] 3) Most frequent pore diameter The most frequent pore size refers to the pore size most likely to appear, i.e., the pore size with the most pores. It is an important index for evaluating the separation effect of a membrane and is also one of the important indexes for evaluating the performance of a microfiltration membrane. The most frequent pore size determines the particle size of the membrane separation material. Table 1 shows that the microfiltration membranes produced in Examples 1 and 2 have excellent separation performance. Tests were conducted in accordance with GB / T 5249-2013.

[0049] 4) Porosity Porosity is the ratio of the total volume of interconnected micropores within a porous medium to the apparent volume of the porous medium. Generally, the higher the porosity, the higher the internal permeability of the membrane and the higher the separation efficiency. A porosity of over 80% is considered high. Tests were conducted in accordance with GB / T 33052-2016.

[0050] [Table 1]

[0051] Combining the data in Table 1 with Figures 2 and 3, the present application controls the pore size of the upper and lower surfaces of the pre-formed membrane by varying the atmosphere composition and temperature in the upper and lower spaces. The resulting microfiltration membrane exhibits a sponge-like pore structure, with excellent separation performance and high porosity. The microfiltration membrane manufacturing method described in the present application can produce microfiltration membranes with different pore sizes and adjustable pore sizes on the upper and lower surfaces as needed, making it highly practical. Furthermore, the manufacturing process is simple, and simultaneous steam induction on the upper and lower surfaces significantly reduces the pre-formation time, meeting various industrial production needs and demonstrating broad market prospects.

[0052] The above description of the embodiments is only to help understand the method and core idea of ​​the present application. It should be noted that a person skilled in the art can make some improvements and modifications to the present application without departing from the principle of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A method for producing a microfiltration membrane, comprising: In the enclosed space, a support layer divides the space into an upper space and a lower space, and an upper surface and a lower surface of the support layer are simultaneously induced to undergo molding by a first atmosphere in the upper space and a second atmosphere in the lower space to obtain a pre-formed membrane, and then a phase separation molding is performed to manufacture a microfiltration membrane, wherein the first atmosphere and the second atmosphere are different, The method for producing a microfiltration membrane, wherein the support layer is a porous support layer coated with a casting liquid.

2. 2. The manufacturing method according to claim 1, wherein the support layer is disposed on a rubber ring, and the rubber ring is hollow.

3. 2. The manufacturing method of claim 1, wherein the first atmosphere and the second atmosphere are independently selected from one or more of air, water vapor, ethanol vapor, ethylene glycol vapor, polar aprotic solvent vapor, salt solution vapor, acid solution vapor, and alkali solution vapor.

4. The method for producing a microfiltration membrane according to claim 1, wherein the temperatures of the upper space and the lower space are independently 5 to 125°C.

5. The method according to any one of claims 1 to 4, wherein the phase separation molding time is 10 to 600 seconds.

6. the casting liquid is a solution containing a polymer, the polymer is selected from one or more of polysulfone, polyethersulfone, polyvinylidene fluoride, cellulose acetate, polyethylene oxide, polyacrylonitrile, polyamide, and polyimide; the polymer-containing solution also includes a pore-forming additive and a solvent for the polymer; the solvent for the polymer is a good solvent for the polymer and / or a poor solvent for the polymer, the pore-forming additive is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, zinc chloride, and lithium chloride; 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; 2. The method according to claim 1, wherein the poor solvent for the polymer is selected from water and alcohol solvents.

7. 7. The method according to claim 1, wherein the solid content of the casting liquid is 6 to 30 wt %.

8. 10. The method according to claim 1, wherein the thickness of the casting liquid on the porous structure support layer is 50 to 500 μm.

9. 5. The manufacturing method according to claim 3, wherein the first atmosphere and the second atmosphere are independently selected from one or more of air at 60°C and 70% humidity, air at 30°C and 30% humidity, water vapor at 125°C, and a mixed gas of water and ethanol at a mass ratio of 1:1 at 60°C.

10. The alcohol solvent is a low molecular weight alcohol, 7. The method according to claim 6, wherein the low molecular weight alcohol includes at least one of methanol, ethanol, benzyl alcohol, and isopropanol.

11. the porous structure support layer comprises a porous structure support material; The method according to claim 1, wherein the porous structural support material is at least one of a nonwoven fabric, a woven fabric, and a porous ceramic.

12. After the phase separation molding, the obtained fully formed porous membrane is immersed in deionized water to remove residual solvent, and then dried to obtain a microfiltration membrane; 2. The method according to claim 1, wherein the immersion time in the deionized water is 24 to 48 hours, and the temperature is 30 to 80°C.

13. A microfiltration membrane, characterized in that it is produced by the production method according to any one of claims 1 to 4.

14. The microfiltration membrane according to claim 13, wherein the interior of the microfiltration membrane has a sponge-like pore structure.

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