Preparation method of silicon carbide film for constructing hollow interface based on wettability difference

Abstract

The invention discloses a preparation method of a silicon carbide film for constructing a hollow interface based on wettability difference induction. According to the method, a carbon powder pore-forming agent having wettability difference with silicon carbide particles is introduced into a support body green body, and slurry is preferentially spread in a hydrophilic region and locally detained in a hydrophobic region in a dip-coating process, so that an ordered hollow channel structure is formed on a membrane-support interface through induction. In the co-sintering process, the structure can effectively inhibit membrane slurry from permeating into macropores of the supporting body, the integrity of the membrane layer is enhanced, and the interface mass transfer resistance is remarkably reduced. The obtained membrane layer has a surface structure with adjustable and controllable pore diameter and high continuity, the gas flux and dust filtering performance are remarkably improved compared with a traditional membrane, and meanwhile, the preparation period is shortened and the sintering energy consumption is reduced. The method is suitable for construction of various asymmetric film structures, has good expandability and process compatibility, and provides a new way for realizing large-scale preparation of low-cost and high-performance silicon carbide films.

Description

Technical Field

[0001] The invention relates to a method for preparing a silicon carbide membrane with a hollow interface constructed based on wettability differences, and belongs to the field of preparation of ceramic membrane materials. Background Art

[0002] Efficient high-temperature flue gas purification is a key link in achieving energy conservation and pollutant emission reduction. It is particularly suitable for high-energy-consuming industries such as chemical, petrochemical and metallurgical industries. It can achieve waste heat recovery while removing fine particulate matter, which has important economic and environmental significance. Among the many gas separation membrane materials, silicon carbide (SiC) has become a very promising choice for industrial gas-solid separation due to its excellent thermal stability, chemical inertness and mechanical strength. Despite the superior performance of silicon carbide membranes, their actual engineering applications are still subject to the dual constraints of high preparation costs and low gas flux. Especially in large-flow flue gas treatment scenarios, low membrane flux will significantly increase the equipment size and investment costs, limiting its promotion in large-scale fields.

[0003] At present, traditional SiC membrane structures mostly adopt a multilayer configuration of three or more layers to take into account separation accuracy while suppressing the membrane slurry from penetrating into the support structure. However, this strategy requires multiple dip-coating and sintering, which is not only complex in process, long in cycle, and high in energy consumption, but also leads to increased preparation costs. In addition, the multilayer structure will bring more membrane-membrane or membrane-support interfaces, and the risk of slurry penetrating into the lower structure will increase, thereby increasing the interface resistance and reducing the overall membrane permeability. Studies have shown that up to 40% of the total pressure drop of ceramic membranes comes from the interface area between the membrane layer and the support [Ceram. Int., 2021, 47(9): 12357–12365]. Therefore, interface structure design has become one of the key directions for improving membrane flux and overall performance.

[0004] A more effective strategy is to construct a SiC membrane structure without an intermediate layer, that is, to deposit the membrane layer directly onto the surface of a macroporous support through a single dip coating. This method reduces the number of process steps and reduces costs to a certain extent, but it still faces problems such as slurry penetration, membrane sintering defects, and insufficient membrane-substrate bonding. To alleviate these problems, some literature has attempted to pre-fill the support with organic / inorganic barrier agents such as polyvinyl alcohol (PVA) and butyraldehyde resin (PVB) to block the macropores and reduce the risk of slurry infiltration [J. Membr. Sci., 2024, 695, 122496]. However, the close bonding between the membrane layer and the support skeleton still leads to a large interfacial resistance, which is difficult to fundamentally overcome with conventional methods. To further optimize the interface structure, researchers have proposed constructing a porous interlayer [Sep. Purif. Technol., 2023, 305: 122400] or introducing sacrificial pore-forming agents [Chinese Invention Patent CN201910668952.3]. However, these methods often introduce randomly distributed or oversized interlayer voids, which are detrimental to interfacial bonding. Therefore, there is an urgent need to construct interfacial cavity structures with clear directionality and controllable size to effectively reduce interfacial resistance while ensuring bonding strength.

[0005] In contrast, co-sintering the membrane directly onto the green support is a more efficient construction route [Sep. Purif. Technol. 2024;338:126441]. This method eliminates the need for intermediate layers and multiple sintering steps. The burnout of the pore-forming agent allows the formation of local cavities at the membrane-support interface. This directionally distributed hollow structure provides preferential gas pathways, significantly alleviating interfacial mass transfer limitations while reducing local stress, helping to maintain membrane structural integrity and maintaining excellent interfacial bonding properties while improving membrane flux.

[0006] The present invention proposes a new method for constructing asymmetric silicon carbide membranes based on a wettability induction strategy. The core of the method is to achieve directional construction of interfacial hollow channels by driving differential wettability. Specifically, polyvinyl alcohol (PVA) and citric acid (CA) are used to construct a cross-linking system so that the surface of the support exhibits heterogeneous wettability characteristics, which not only enhances the selectivity of the membrane slurry distribution, but also improves the mechanical strength of the green body. During the dip-coating process, the wettability difference between SiC particles and activated carbon pore-forming agents is utilized to achieve preferential spreading of the slurry in the hydrophilic area and local blockage in the hydrophobic area, thereby inducing the formation of a directional hollow interface structure and effectively reducing the interfacial resistance. Combined with a one-step co-firing process, this method has the advantages of low cost, stable structure, and easy scale-up, providing a high-performance, scalable new solution for industrial gas-solid separation under high-temperature conditions. Summary of the Invention

[0007] The present invention provides a hollow interface construction method driven by wettability difference. By introducing a region with significant wettability difference between the surface and the capillary pore structure into the silicon carbide support green body, the membrane slurry is induced to undergo orderly redistribution during the film formation process, and a directional cavity structure is formed at the interface between the membrane layer and the support body, thereby effectively reducing the interface mass transfer resistance and improving the flux performance and structural stability of the membrane material under high-temperature gas-solid separation conditions.

[0008] The technical solution of the present invention is: A method for preparing a silicon carbide film with a hollow interface constructed based on wettability differences, the specific steps of which are as follows: Preparation of the support green body: Polyvinyl alcohol (PVA) and citric acid (CA) are uniformly mixed in a set ratio at a set speed to form a green body binder; silicon carbide powder is uniformly mixed with a sintering aid, an activated carbon pore-forming agent, and the binder, and then a cold isostatic pressing process is used to prepare the support green body; heat treatment is performed at a set crosslinking temperature and time to obtain a structurally stable support green body; Preparation of membrane slurry and film formation: Silicon carbide membrane powder and sintering aid are dispersed in methyl cellulose (MC) aqueous solution, and a defoaming agent is added. After adding an appropriate amount of defoaming agent, vacuum stirring and degassing treatment are performed to obtain a stable membrane slurry; the membrane slurry is evenly coated on the surface of the support green body with set dipping parameters (immersion rate, pulling rate, holding time), and after drying and high-temperature co-sintering, a silicon carbide ceramic membrane with an asymmetric structure and hollow interface characteristics is obtained.

[0009] Preferably, the binder is a water-soluble system prepared with pure water as solvent, comprising 5-25 wt% PVA and 0-20 wt% CA, with a crosslinking temperature of 25-170°C and a crosslinking time of 4-24 h.

[0010] Preferably, the average particle size of the silicon carbide powder in the membrane slurry is 10-40 μm, and the proportion is 30 wt%.

[0011] Preferably, the amount of MC added to the membrane slurry is 0.25-1.75 wt%, preferably 1.0 wt%.

[0012] Preferably, the dipping parameters include an immersion rate of 500-2000 μm / s, a pulling rate of 125-2000 μm / s, and a dipping time of 20-160 s.

[0013] Preferably, the co-sintering temperature is 1250-1450° C., and the holding time is 1-4 h.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The asymmetric silicon carbide ceramic membrane prepared by the present invention has a directional interface hollow channel structure, which can effectively overcome the "separation accuracy and flux" trade-off effect caused by the increase in the number of traditional membrane layers. By utilizing the heterogeneous wettability characteristics of the green structure, the membrane slurry is induced to selectively spread and locally block during the film formation process, achieving the effect of orderly distribution of particles and retention of cavities in the carbon powder area. During the sintering process, the cavity structure is further developed, significantly reducing the contact area of the membrane-support interface, thereby reducing the mass transfer resistance. In addition, the membrane layer structure forms a complete and dense top structure and a low-resistance intermediate cavity transition layer under the regulation of high MC content, and inhibits the slurry from penetrating into the interior of the support. Compared with traditional multi-layer structures, this method, combined with a one-step co-firing process, significantly shortens the preparation cycle, reduces energy consumption and material consumption, and has the advantages of high flux, low cost, and easy scalability. It is suitable for large-scale promotion in industrial scenarios such as high-temperature flue gas filtration, particle capture, and heat recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an electron microscope image of the surface of the support green body prepared in Example 3.

[0016] Figure 2 This is an electron microscope image of the surface of the ceramic membrane prepared in Example 3.

[0017] Figure 3 This is an electron microscope image of the cross section of the ceramic membrane prepared in Example 3.

[0018] Figure 4 This is the pore size distribution diagram of the ceramic membrane prepared in Example 3.

[0019] Figure 5 is the air permeability of the ceramic membrane prepared in Example 3.

[0020] Figure 6 The air permeability of the ceramic membrane prepared in Example 3 is compared with that of other research works. DETAILED DESCRIPTION Example 1

[0021] A support was prepared using a PVA and CA binder system with a ratio of 5 wt% PVA to 0 wt% CA. The mixture was then stirred at 150 rpm for 2 h. 200 μm SiC, CaO, ZrO₂, 3Al₂O⋅2SiO₂, an activated carbon pore former, and a binder were uniformly mixed in a mass ratio of 49:0.6:0.6:1.2:9:4.5. The green support was then cold isostatically pressed at 10 MPa and allowed to crosslink at 25°C for 12 h. A membrane powder was prepared by mixing 40 μm silicon carbide with CaO, ZrO₂, and mullite whiskers in a mass ratio of 96:1:1:2. The membrane powder was then mixed with a 0.25 wt% aqueous solution of MC in a ratio of 3:7 and stirred at 150 rpm for 4 h (vacuum level -0.1 MPa) to form a homogeneous membrane slurry. The support was fixed in a dipping device, and the coating was performed at a rate of 3000 μm / s for 10 s and a pulling rate of 3000 μm / s. After drying at room temperature for 12 h, the support was sintered at 1450 °C for 4 h and then cooled naturally.

[0022] The green strength of the silicon carbide support was 1.19 MPa, the average pore size of the silicon carbide membrane was 14.4 μm, and the gas permeation flux was 676.2 m 3 ·m -2 ·h -1 kPa. Example 2

[0023] PVA 10 wt% and CA 5 wt% were used as binders, stirred at 300 rpm for 2 h; the green body cross-linking heat treatment temperature before sintering was 90 ℃ for 4 h. 20μm SiC was used as the membrane powder, and the ratio with the sintering aid remained unchanged. The MC addition amount was 0.5 wt%, the degassing time was 6 h, the dip coating parameters were immersion 2000μm / s, holding 40s, pulling 500μm / s, drying 2h, and sintering at 1450 ℃ for 1 h. After testing, the green body strength of the obtained silicon carbide support was 2.48 MPa, the average pore size of the silicon carbide membrane was 9.70 μm, and the gas permeation flux was 553.5 m 3 ·m -2 ·h -1 kPa. Example 3

[0024] PVA 15 wt% and CA 10 wt% were used as binders, and the mixture was stirred for 4 h (300 rpm). The green body was cross-linked and heat treated at 110°C for 12 h. The membrane powder was 20 μm SiC with an MC content of 1.0 wt%, and the membrane was degassed for 12 h. The dip coating was set to immerse at 2000 μm / s, hold for 20 seconds, pull at 125 μm / s, dry for 4 h, and sinter at 1450°C for 4 h. The green body strength of the silicon carbide support was 4.39 MPa, the average pore size of the silicon carbide membrane was 7.5 μm, and the gas permeation flux was 521.8 m 3 ·m -2 ·h -1 kPa.

[0025] Figure 1 This is an electron microscope image of the surface of the support green body prepared in Example 3. Figure 2 This is an electron microscope image of the surface of the ceramic membrane prepared in Example 3. Figure 3 This is an electron microscope image of the cross section of the ceramic membrane prepared in Example 3. Figure 4 This is the pore size distribution diagram of the ceramic membrane prepared in Example 3. Figure 5 is the air permeability of the ceramic membrane prepared in Example 3. Figure 6 The air permeability of the ceramic membrane prepared in Example 3 is compared with that of other research works. Example 4

[0026] Using PVA 25wt% and CA 20wt% as binders, the green body was cross-linked and heat treated at 170°C for 24 hours. The membrane powder particle size was 10μm, the MC concentration was 1.5wt%, the rotation speed was 150 rpm, and the degassing time was 12 hours. The dip coating parameters were immersion at 2000μm / s, holding for 20s, and a pull rate of 31.25μm / s. The membrane was dried for 4 hours and sintered at 1250°C for 4 hours. The green body strength of the silicon carbide support was 2.24 MPa, the average pore size of the silicon carbide membrane was 4.6 μm, and the gas permeation flux was 291.0 m 3 ·m -2 ·h -1 kPa.

Claims

1. A method for preparing a silicon carbide film with a hollow interface based on wettability difference, characterized in that: The specific steps are as follows: (1) Preparation of a support green body: polyvinyl alcohol and citric acid are mixed in proportion to prepare a binder, and the support silicon carbide powder is evenly mixed with a sintering aid, a carbon powder pore-forming agent, and the binder. After cold isostatic pressing, heat treatment is performed at a set cross-linking temperature and time to obtain a structurally stable support green body; (2) Membrane slurry preparation and film formation: Add silicon carbide powder with a certain solid content and sintering aids to a certain concentration of methyl cellulose aqueous solution, mix them evenly, add an appropriate amount of defoaming agent, continue stirring to fully disperse them, and then vacuum degas to obtain a homogeneous membrane slurry; the membrane slurry is evenly dipped onto the surface of the support green body, and after a drying process, it is co-sintered at high temperature to obtain an asymmetric silicon carbide membrane with hollow interface characteristics.

2. The method for preparing a silicon carbide film by inducing a hollow interface based on wettability difference according to claim 1, characterized in that: The binder is a water-soluble system prepared with pure water as a solvent, comprising 5-25 wt% of polyvinyl alcohol and 0-20 wt% of citric acid, with a cross-linking temperature of 25-170°C and a cross-linking time of 4-24 h.

3. The method for preparing a silicon carbide film by inducing a hollow interface based on wettability difference according to claim 1, characterized in that: The average particle size of the silicon carbide powder in the membrane slurry is 10-40 μm, and the added amount is 20-40 wt%.

4. The method for preparing a silicon carbide film by inducing a hollow interface based on wettability difference according to claim 1, characterized in that: The amount of methylcellulose added to the membrane slurry is 0.25-1.75 wt%.

5. The method for preparing a silicon carbide film by inducing a hollow interface based on wettability difference according to claim 1, characterized in that: During the dipping process, the immersion rate is 500-2000 μm / s, the pulling rate is 31.25-8000 μm / s, and the dipping time is 0-640 s.

6. The method for preparing a silicon carbide film by inducing a hollow interface based on wettability difference according to claim 1, characterized in that: The co-sintering temperature is 1250-1450° C., and the holding time is 1-4 h.

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