Method for realizing cross-layer preparation of asymmetric ceramic membrane based on interface phase separation

Abstract

The invention discloses a method for realizing cross-layer preparation of an asymmetric ceramic membrane based on interface phase separation. The preparation method comprises the following steps: preparing homogeneous coating liquid from small-particle ceramic, an organic polymer and N-methyl pyrrolidone as raw materials; and immersing the macroporous ceramic support body into deionized water, taking out the macroporous ceramic support body, wiping the surface with a tissue to remove excessive water, immediately spraying the coating liquid onto the surface of the support body to construct a membrane layer, and drying and sintering to obtain the asymmetric ceramic membrane with the cross-layer structure. And the membrane preparation liquid is subjected to interface phase separation at the moment of contacting with moisture in the pore channel of the support body and is cured and formed, so that membrane layer particles are effectively inhibited from infiltrating, the membrane layer integrity is ensured, the requirement on a transition layer in the traditional asymmetric ceramic membrane preparation process is broken through, and the method has the innovative advantages of simple process and low cost. The organic polymer in the raw materials can be decomposed at high temperature, does not block pore channels, and has no adverse effect on flux. The method provides reference for efficient cross-layer preparation of the ceramic membrane with high flux and high filtration precision.

Description

Technical Field

[0001] This invention relates to a method for preparing asymmetric ceramic membranes across layers based on interfacial phase separation, belonging to the field of membrane material preparation. Background Technology

[0002] Ceramic membranes possess advantages such as high temperature resistance, acid and alkali corrosion resistance, thermal shock resistance, high mechanical strength, and long service life, making them promising for applications in high-temperature flue gas treatment, oil-water separation, and seawater desalination. Ceramic membranes are generally asymmetric structures, consisting of a support and a membrane layer. The support, made of large particles, provides mechanical strength, while the membrane layer, composed of small particles, performs the separation function. However, the pore sizes of the membrane layer particles and the support need to be matched; excessive differences can lead to severe infiltration, resulting in membrane defects, pore blockage, and reduced flux. Therefore, high-precision asymmetric ceramic membranes are often prepared by adding an intermediate layer. However, this layered approach increases manufacturing costs, and the multi-layered structure also increases filtration resistance and reduces flux. Thus, a trade-off effect exists between ceramic membrane flux and filtration precision, making the efficient preparation of high-performance ceramic membranes a research hotspot.

[0003] The key to preparing high-performance ceramic membranes lies in finding new strategies to suppress particle infiltration. Using whiskers or fiber materials as intermediate layers to suppress particle infiltration has become an effective method. Wei et al. [Journal of Membrane Science, 2017, 540: 381-390] sequentially sprayed silicon carbide whisker layers and membrane layers onto the surface of a silicon carbide support, preparing a silicon carbide ceramic membrane with a pore size of 2.31 μm and a gas flux of 105 m³ / h. 3 ·m -2 ·h -1 ·kPa -1 However, silicon carbide whiskers are expensive, which is not conducive to industrial applications. Gao et al. [Separation and Purification Technology, 2023, 305:122400] constructed a sandwich-structured ceramic fiber composite membrane using mullite fibers as the intermediate layer. The average pore size was approximately 120 nm, and the pure water flux was 4235 L·m. -2 ·h -1 ·bar -1The three-dimensional network structure composed of fibers can effectively suppress infiltration; however, this intermediate layer still has a certain negative impact on the flux of ceramic membranes. Based on this, a sacrificial intermediate layer method was proposed to further improve the performance of ceramic membranes. Qiao et al. [Journal of Membrane Science, 2020, 594: 117464] proposed spraying Al-DTPA (aluminum-diethylenetriaminepentaacetic acid) onto a silicon carbide support to suppress infiltration of membrane particles, and then preparing a high-flux silicon carbide ceramic membrane after calcination. Al-DTPA decomposes at high temperature without affecting the flux, and the resulting silicon carbide ceramic membrane has a pore size range of 2-5 μm and a gas flux range of 240-277 m³ / h. 3 ·m -2 ·h -1 ·kPa -1 Ni et al. [Journal of Membrane Science, 2024, 695: 122496] used polyvinyl butyral (PVB) as a prefiller to block the pores of the support to completely inhibit infiltration. After coating and sintering, they successfully prepared asymmetric ceramic membranes across multiple layers. The resulting ceramic membranes had an average pore size of 1.93 μm and a gas flux of 149.3 m³. 3 ·m -2 ·h -1 ·kPa -1 These methods effectively avoid the negative impact of the interlayer on the flux of ceramic membranes; however, their process complexity still limits their widespread application. Specifically, the sacrificial interlayer needs to completely fill the pores of the support to prevent infiltration of membrane particles; at the same time, the sacrificial layer should not be too thick to avoid insufficient adhesion between the ceramic membrane and the substrate after sintering, leading to membrane detachment. In addition, the process of constructing the sacrificial interlayer still incurs certain raw material costs, and the combustion products such as carbon dioxide generated by the decomposition of the sacrificial layer may have adverse environmental impacts. Therefore, there is an urgent need to develop a simpler and more efficient method for preparing high-performance translayer ceramic membranes.

[0004] In the traditional asymmetric ceramic membrane preparation process, the fundamental cause of particle infiltration is the flowability of the slurry. Therefore, it can be inferred that if the slurry solidifies instantly upon contact with the support, the particle infiltration problem can be effectively avoided. Phase separation technology refers to the process of inducing a ceramic slurry containing a large amount of polymer solution to transform from a liquid to a solid state through wet or dry methods. In the application of phase separation in ceramic membrane preparation, a common method is to first form the slurry by casting or extrusion, and then immerse it in a non-solvent phase (usually water) to achieve rapid phase separation, simultaneously generating a high-porosity finger-like pore structure, ultimately forming high-performance planar and hollow fiber ceramic membranes [Journal of Membrane Science, 2024, 709: 123104]. It is noteworthy that the slurry undergoes phase separation and solidifies instantly upon contact with the non-solvent phase. However, no researchers have yet applied this characteristic to solve the slurry infiltration problem during the multi-layer preparation of asymmetric ceramic membranes. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high-efficiency, low-cost, multilayer fabrication method for high-performance asymmetric ceramic membranes using an interfacial phase separation process. Unlike traditional pore-blocking methods, in this invention, water, as a non-solvent phase, is drawn into the pores of the support and then comes into contact with the coating liquid. At the contact interface, a rapid solvent-non-solvent exchange occurs, causing organic matter to precipitate as a solid—this is the "interfacial phase separation" process. This allows the membrane layer to rapidly solidify and form at the interface, effectively inhibiting particle infiltration. Furthermore, the organic matter in the membrane layer decomposes at high temperatures without negatively impacting flux, thus enabling the one-step fabrication of an asymmetric ceramic membrane that combines high flux and high filtration accuracy.

[0006] The technical solution of this invention is as follows: a method for preparing asymmetric ceramic membranes across layers based on interfacial phase separation, the specific steps of which are as follows: A. Small-diameter ceramic particles, organic polymers, and N-methylpyrrolidone (NMP) are mixed in a certain proportion, and after ball milling and ultrasonic degassing for a certain time, a homogeneous coating liquid is obtained; B. A macroporous ceramic support is placed in deionized water until it is completely submerged and wetted, and after being taken out, the surface is wiped with a paper towel to remove excess water. Then, the coating liquid is immediately sprayed onto the wetted support surface, and an asymmetric ceramic membrane is prepared through drying and sintering processes.

[0007] Preferably, the small-diameter ceramic particles are one or more of silicon carbide, alumina, mullite, and zirconium oxide, with a particle size range of 1 μm-50 μm; the organic polymer is one of polyvinylidene fluoride (PVDF), polysulfone (PSF), and polyethersulfone (PES); the mass ratio of small-diameter ceramic particles: organic polymer: NMP is (4-10):1:(6-20).

[0008] Preferably, the ball milling time is 2-12 h, the rotation speed is 300-800 r / min, and the ultrasonic degassing time is 0.5-2 h.

[0009] Preferably, the macroporous ceramic support material is one or more of silicon carbide, alumina, mullite fiber, and zirconium oxide, with a pore size range of 20 μm-500 μm.

[0010] The preferred spraying time is 2-8 seconds.

[0011] Preferably, the drying temperature is 25-60 ℃ and the drying time is 6-24 h; the sintering process involves calcining the green blank at 1150-1600 ℃, controlling the heating and cooling rates at 0.5-3 ℃ / min, and holding for 1-3 h.

[0012] The ceramic membranes prepared by this invention have an average pore size of 0.39-14.93 μm and a gas permeability of 49.8-1008.9 μm. 3 ·m -2 ·h -1 ·kPa -1 . Beneficial effects

[0013] This invention innovatively utilizes an interfacial phase separation process to achieve low-cost, multi-layer fabrication of high-performance asymmetric ceramic membranes. The key lies in the rapid solvent-non-solvent phase exchange process that occurs when the coating solution comes into contact with the aqueous phase, enabling the membrane to solidify quickly and effectively suppress particle infiltration. This ensures membrane integrity and enhances flux. Multi-layer ceramic membrane fabrication can be achieved without adding an intermediate layer or modifying the support structure. This innovative approach offers advantages such as simplicity, efficiency, low cost, and wide applicability, providing a reference for the fabrication of high-performance (high-flux, high-precision) asymmetric ceramic membranes. Attached Figure Description

[0014] Figure 1 These are electron microscope images of the surface (a) and cross-section (b) of the silicon carbide support in Example 3.

[0015] Figure 2 These are three-dimensional surface morphology images of the silicon carbide support in Example 3 before (a) wetting and after (b) wetting.

[0016] Figure 3 These are electron microscope images (a) of the surface and (b) of the silicon carbide ceramic film prepared in Example 3.

[0017] Figure 4 This is a pore size distribution diagram of the silicon carbide ceramic membrane prepared in Example 3.

[0018] Figure 5This is a comparison graph showing the relationship between Darcy permeability, pore size, and porosity of the silicon carbide ceramic membrane prepared in Example 3 and ceramic membranes prepared in other studies. Detailed Implementation Example 1

[0019] First, zirconia particles with an average particle size of 1 μm, PVDF, and NMP were mixed at a mass ratio of 10:1:20 and ball-milled at 400 r / min for 8 h. After ultrasonic degassing for 1 h, a homogeneous coating solution was obtained. A zirconia support with an average pore size of 50 μm was completely immersed in deionized water. After removal, the surface was wiped with a paper towel to remove excess moisture. Immediately afterwards, the coating solution was sprayed onto the wetted support surface for 5 s. The solution was then dried at 40 ℃ for 12 h, followed by heating to 1150 ℃ in air at a rate of 2 ℃ / min and holding for 3 h. The resulting ceramic membrane had an average pore size of 0.39 μm and a gas permeability of 49.8 μm. 3 ·m -2 ·h -1 ·kPa -1 . Example 2

[0020] First, alumina particles with an average particle size of 3 μm, PSF, and NMP were mixed at a mass ratio of 4:1:6 and ball-milled at 300 r / min for 12 h. After ultrasonic degassing for 0.5 h, a homogeneous coating solution was obtained. An alumina support with an average pore size of 20 μm was completely immersed in deionized water. After removal, the surface was wiped with a paper towel to remove excess moisture. Immediately afterwards, the coating solution was sprayed onto the wetted support surface for 8 s. The solution was then dried at 60 ℃ for 8 h, followed by heating to 1400 ℃ in air at a rate of 0.5 ℃ / min and holding for 2 h. The resulting ceramic membrane had an average pore size of 1.16 μm and a gas permeability of 188.7 μm. 3 ·m -2 ·h -1 ·kPa -1 . Example 3

[0021] First, silicon carbide particles with an average particle size of 5 μm, PVDF, and NMP were mixed at a mass ratio of 6:1:10 and ball-milled at 500 r / min for 6 h. After ultrasonic degassing for 1.5 h, a homogeneous coating solution was obtained. A silicon carbide support with an average pore size of 30 μm was completely immersed in deionized water. After removal, the surface was wiped with a paper towel to remove excess moisture. Immediately afterwards, the coating solution was sprayed onto the wetted support surface for 2 s. The solution was then dried at 25 ℃ for 24 h, followed by heating to 1200 ℃ in air at a rate of 2 ℃ / min and holding for 2 h. The resulting ceramic membrane had an average pore size of 2.46 μm and a gas permeability of 268.7 μm. 3 ·m -2 ·h -1 ·kPa -1 .

[0022] Table 1 compares the performance of the ceramic membrane prepared in this example with that of the ceramic membrane in the literature. It can be seen that the asymmetric ceramic membrane prepared by the interfacial phase separation process has a significant high-throughput advantage. Figure 1 These are SEM images of the surface and cross-section of the silicon carbide support used in this example. They show that it is well-sintered, possesses certain mechanical properties, and has numerous through-holes. Figure 2 (a) and (b) are three-dimensional morphology images of the support surface before and after wetting, respectively. It can be seen that before and after wetting, due to the water filling the pores, the surface roughness value (Sa) of the support decreases from 19.32 μm to 13.52 μm. Figure 3 These are electron microscope images of the surface and cross-section of the silicon carbide ceramic membrane prepared in this example. It can be seen that the membrane surface is smooth and without defects, the membrane structure is uniform (thickness is about 100 μm), the membrane substrate is well bonded and there is no particle infiltration. Figure 4 This is a pore size distribution diagram of the silicon carbide ceramic membrane prepared in this example. Its average pore size is 2.46 μm, and it can be seen that the ceramic membrane prepared by the interface phase separation method has the advantage of concentrated pore size distribution. Figure 5 This is a comparison of the Darcy permeability with pore size and porosity of the silicon carbide ceramic membrane prepared in this example and ceramic membranes prepared in other studies. It can be seen that the air permeability of the ceramic membrane prepared in this work is better than the average level. Example 4

[0023] First, mullite particles with an average particle size of 50 μm, PVDF, and NMP were mixed at a mass ratio of 8:1:15 and ball-milled at 800 r / min for 2 h. After ultrasonic degassing for 2 h, a homogeneous coating solution was obtained. A mullite support with an average pore size of 500 μm was completely immersed in deionized water. After removal, the surface was wiped with a paper towel to remove excess moisture. The coating solution was then immediately sprayed onto the wetted support surface for 6 s. The solution was subsequently dried at 60 ℃ for 6 h, and then heated to 1600 ℃ in air at a rate of 3 ℃ / min and held for 1 h. The resulting ceramic membrane had an average pore size of 14.93 μm and a gas permeability of 1008.9 μm. 3 ·m -2 ·h -1 ·kPa -1 .

[0024] Table 1. Performance comparison of the ceramic membrane prepared in Example 3 with that of the ceramic membrane in the literature. Material Pore ​​diameter μm <![CDATA[Gas permeability m 3 ·m -2 ·h -1 ·kPa -1 > References silicon carbide 0.12 4.5 Ceram. Int., 2021(47): 17161-17166 Mullite 14.8 673 Sep. Purif. Technol. 2022(292): 120967 Mullite 2.7 106 J. Membr. Sci. 2023(668): 121143 Mullite / alumina 0.12 2.96 Sep. Purif. Technol. 2023(305): 122400 silicon carbide 2.31 105 J. Membr. Sci., 2017(540): 381-390 silicon carbide 3.9 246.3 J. Membr. Sci., 2024(692): 122265 silicon carbide 2.46 268.7 Example 3

Claims

1. A method for preparing asymmetric ceramic films across multiple layers based on interfacial phase separation, characterized in that, The specific steps are as follows: A. Small-diameter ceramic particles, organic polymer, and N-methylpyrrolidone are ball-milled and mixed in a certain proportion, and then ultrasonically degassed for a certain time to obtain a homogeneous coating liquid; wherein, the small-diameter ceramic particles are one or more of silicon carbide, alumina, mullite, and zirconium oxide, with a particle size range of 1 μm-50 μm; the organic polymer is one of polyvinylidene fluoride, polysulfone, and polyethersulfone; the mass ratio of small-diameter ceramic particles: organic polymer: N-methylpyrrolidone is (4-10):1:(6-20). B. Immerse the macroporous ceramic support in deionized water until it is completely wetted. After removing it, wipe the surface with a paper towel to remove excess water. Then immediately spray the coating liquid obtained in step A onto the wetted support surface. After drying and sintering, an asymmetric ceramic film is prepared.

2. The method for preparing asymmetric ceramic membranes across layers based on interfacial phase separation according to claim 1, characterized in that: The ball milling time in step A is 2-12 h, and the rotation speed is 300-800 r / min; the ultrasonic degassing time is 0.5-2 h.

3. The method for preparing asymmetric ceramic films across layers based on interfacial phase separation according to claim 1, characterized in that: The macroporous ceramic support material mentioned in step B is one or more of silicon carbide, alumina, mullite fiber, and zirconium oxide, with a pore size range of 20 μm-500 μm.

4. The method for preparing asymmetric ceramic films across layers based on interfacial phase separation according to claim 1, characterized in that: The spraying time mentioned in step B is 2-8 seconds.

5. The method for preparing asymmetric ceramic films across layers based on interfacial phase separation according to claim 1, characterized in that: The drying temperature in step B is 25-60 ℃, and the drying time is 6-24 h; the sintering process involves calcining the green blank at 1150-1600 ℃, controlling the heating and cooling rates at 0.5-3 ℃ / min, and holding for 1-3 h.

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