Method for preparing high-porosity gas-solid separation ceramic membrane based on direct foaming method

Abstract

Disclosed is a method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method. Ceramic powder is mixed with water to prepare a ceramic suspension and the pH value is adjusted, a surfactant is added and stirring is carried out to form wet foam, the wet foam is then injected into a mold, drying and demolding are carried out, and then calcination is carried out to obtain a high-porosity ceramic membrane. The method achieves a simple process and a low preparation cost. By controlling the type of the ceramic powder, the particle size of the ceramic powder, the concentration of the suspension, the pH value, and the amount of the added surfactant, the pore size and porosity of the ceramic membrane can be adjusted, and the ceramic membrane having high porosity, high gas permeability, and high dust filtering performance is prepared, thereby providing reference for preparation of the high-porosity ceramic membrane applicable to the field of gas-solid separation.

Description

A method for preparing high-porosity gas-solid separation ceramic membrane based on direct foaming method Technical Field

[0001] The invention relates to a method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method, and belongs to the field of preparation of ceramic membrane materials. Background Art

[0002] Large amounts of high-temperature dusty flue gas are generated in industrial processes such as metallurgy, petroleum, chemical industry, and electric power. These flue gases often contain harmful gases such as nitrogen oxides, sulfur oxides, and dioxins. Direct emission of these gases can cause serious environmental pollution and requires dust removal before they can be removed using processes such as catalytic oxidation. Porous ceramic membranes have broad application prospects in the field of gas-solid separation due to their excellent chemical stability, mechanical strength, and thermal shock resistance. High porosity is an important characteristic of porous ceramic membrane materials. Generally, the higher the porosity, the better the gas permeability. At the same time, high porosity can provide a larger specific surface area, thereby enhancing the material's adsorption capacity and reaction rate.

[0003] Traditional ceramic membranes are prepared using a layer-by-layer stacking method, generally consisting of a support layer, a transition layer, and a separation layer. The support layer increases the mechanical strength of the membrane, and the transition layer has a smaller pore size than the support layer to prevent particles from penetrating into the porous support layer during membrane preparation. The pore size distribution of the entire membrane gradually decreases from the support layer to the membrane layer, forming an asymmetric structural distribution. Fan Yiqun et al. [Chemical Industry and Engineering Journal, 2013, 64(01):107-115] described how layer-by-layer preparation of ceramic membranes can achieve a denser structure. However, the preparation process is cumbersome and costly, and the resulting ceramic membranes have a relatively low porosity, typically 30%-35%, which limits their application in some fields.

[0004] In order to improve the porosity of ceramic membranes, researchers have adopted a variety of improved methods to further optimize the membrane preparation process. The currently mature preparation methods mainly include the addition of pore-forming agents and the sacrificial template method. However, there are usually problems such as high equipment requirements, difficult to control the cost of pore-forming agent materials, long organic matter pyrolysis time, and high energy consumption. Wei et al. [J Membr Sci, 2017, 540: 381-390] used activated carbon as a pore-forming agent to prepare a macroporous silicon carbide carrier, and sprayed a silicon carbide whisker layer-modified silicon carbide membrane on it for sintering. The results showed that the average pore size of the ceramic membrane sintered at 1500 ° C was 2.31 μm, the porosity was 40%, and the gas permeability was 105.2 m 3 m -2 h -1 kPa -1, the dust removal efficiency for dust with a diameter of less than 0.3μm is 99.95%. Qiao et al. [J Membr Sci, 2020, 594, 117464] used ultrafine Al-DTPA fibers as sacrificial intermediate layers to prepare asymmetric, transition-layer-free high-porosity ceramic membranes with an average pore size of 2-5μm and a gas permeability of 240-277m 3 m -2 h -1 kPa -1 The dust removal efficiency for dust with a diameter less than 0.5μm is 99.8%.

[0005] To address these deficiencies, the present invention discloses a method for preparing high-porosity gas-solid separation ceramic membranes based on a direct foaming process. Gas is introduced into a ceramic suspension through rapid stirring to produce a dense and stable foam. Driven by interfacial tension, the ceramic powder self-assembles at the gas-liquid interface. After drying and sintering, a stable and porous ceramic membrane material is obtained. Its simplicity, efficiency, and low cost can effectively reduce the economic burden of the preparation process and promote the large-scale preparation and application of high-porosity ceramic membrane materials in the field of gas-solid separation.

[0006] Summary of the Invention

[0007] The present invention aims to improve the shortcomings of existing technologies by proposing a method for preparing high-porosity ceramic membranes based on a direct foaming process, simplifying the preparation process and reducing costs. Furthermore, by controlling the type and particle size of the ceramic powder, the concentration and pH value of the suspension, and the amount of surfactant added, the porosity of the ceramic membrane can be adjusted for application in gas-solid separation.

[0008] The technical solution of the present invention is: a method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method, the specific steps of which are as follows: A. At room temperature and pressure, ceramic powder of a certain particle size is mixed with water in a mass ratio of (0.3-0.6):1 and stirred uniformly to prepare a ceramic suspension, the pH value of the ceramic suspension is adjusted to 8-11, a surfactant cetyltrimethylammonium bromide (CTAB) is added at a mass ratio of 0.03%-0.15% of the mass of the ceramic suspension, and stirred for a certain period of time to form a wet foam. B. The wet foam is injected into a ring-shaped injection mold, dried at room temperature for 4-12 hours, then placed in an environment of 40°C to 100°C to dry for 6-24 hours, and after demolding, a high-porosity ceramic membrane is obtained through a calcination process.

[0009] Preferably, the ceramic powder is one or more of Al2O3, TiO2, Y2O3, ZrO2, SiO2, SiC, Si3N4 or mullite.

[0010] Preferably, the particle size of the ceramic powder is 0.5-10 μm.

[0011] Preferably, the solution for adjusting the pH value of the ceramic suspension is a NaOH solution.

[0012] Preferably, the stirring speed of the membrane-forming liquid is 1500-3000 rpm, and the stirring time is 5-25 min.

[0013] Preferably, the calcination process is as follows: calcining the green body at 1200-1800° C., controlling the heating rate and cooling rate at 0.5-3° C. / min, and holding time at a temperature of 1-3 hours.

[0014] The average pore size of the interconnected through holes of the ceramic membrane prepared by the present invention is 78-183 μm, the average pore size of the small holes with gas-solid separation function is 2-10 μm, the porosity is 81.9%-89.6%, and the gas permeability is 1007.4-1283.6 μm. 3 m -2 h -1 kPa -1 The filtration effect for dust with a diameter less than 0.3μm is 95.62-99.97%. Beneficial effects:

[0015] The present invention provides a method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method. The method has the advantages of simple process and low preparation cost.

[0016] The porosity and pore size of ceramic membranes are closely related to the particle size of ceramic powder, suspension concentration, pH value and the amount of surfactant added. Generally speaking, the smaller the particle size of ceramic powder, the smaller the pore size of the ceramic membrane obtained. However, too small a particle size of ceramic powder will make the formed wet foam unstable, and the ceramic powder will easily desorb from the interface, resulting in the formation of fine cracks during the drying and shrinkage process. Secondly, the higher the suspension concentration, the lower the porosity of the ceramic membrane, but the more complete the honeycomb structure and the higher the bending strength. An appropriate suspension concentration can make the prepared ceramic membrane have both more suitable porosity and bending strength, and at the same time have a complete honeycomb structure and more interconnected pores. In addition, the wet foam formed based on the direct foaming method has poor stability in acidic solutions, but can remain stable in alkaline solutions. The appropriate pH value can maintain a good dispersion state of the ceramic powder in the suspension. Finally, when the amount of surfactant added is too low, the ceramic membrane is basically closed-pore. Increasing the amount of surfactant added can increase the foaming volume of wet foam and the proportion of gas phase, thereby increasing the contact points between bubbles, causing the ceramic membrane to gradually transform from closed pores to interconnected pores, and increasing the pore size of the ceramic membrane.

[0017] By controlling the type of ceramic powder, ceramic powder particle size, suspension concentration, pH value and the amount of surfactant added, the pore size and porosity of the ceramic membrane can be adjusted to prepare a ceramic membrane with high porosity, high gas permeability and high dust filtration performance, providing a reference for the preparation of high-porosity ceramic membranes for the field of gas-solid separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a macroscopic morphology of the ceramic membrane prepared in Example 3 after drying.

[0019] FIG2 is a macroscopic morphology of the ceramic membrane prepared in Example 3 after calcination.

[0020] FIG3 is a SEM image of a cross section of the ceramic membrane prepared in Example 3. DETAILED DESCRIPTION

[0021] Example 1

[0022] First, at room temperature and pressure, 0.5μm ZrO2 powder was placed in water and stirred and dispersed, so that the mass ratio of ZrO2 powder to water was 0.3:1 to obtain a ceramic suspension. NaOH solution was added to adjust the pH value of the suspension to 8, and 0.03% of the total mass of the ceramic suspension was added with surfactant CTAB. The mixture was stirred at 1500rpm for 5min to form wet foam and then injected into a ring injection mold. The foam was dried at room temperature for 4h and then dried in a 40℃ environment for 6h. After demolding, the mixture was heated to 1200℃ at a rate of 0.5℃ / min in an air atmosphere and kept warm for 1h. The average pore size of the interconnected through holes of the prepared ceramic membrane was 183μm, the average pore size of the small holes with gas-solid separation function was 10μm, the porosity was 81.9%, and the gas permeability was 1007.4m 3 m -2 h -1 kPa -1 The filtration effect for dust with a diameter less than 0.3μm is 95.62%.

[0023] Example 2

[0024] First, at room temperature and pressure, 2μm TiO2 and ZrO2 powders were placed in water for stirring and dispersion, and the mass ratio of TiO2, ZrO2 powders to water was 0.3:0.1:1 to obtain a ceramic suspension. NaOH solution was added to adjust the pH value of the suspension to 9, and 0.06% of the total mass of the ceramic suspension was added with surfactant CTAB. The mixture was stirred at a speed of 2000rpm for 10min, and after forming wet foam, it was injected into a ring injection mold, dried at room temperature for 6h, and then placed in a 60℃ environment for drying for 12h. After demolding, the mixture was heated to 1500℃ at a rate of 1℃ / min in an air atmosphere and kept warm for 1.5h. The average pore size of the interconnected through holes of the prepared ceramic membrane was 147μm, the average pore size of the small holes with gas-solid separation function was 7μm, the porosity was 85.2%, and the gas permeability was 1135.9m 3 m -2 h -1 kPa -1 The filtration effect for dust with a diameter less than 0.3μm is 97.54%.

[0025] Example 3

[0026] First, at room temperature and pressure, 5μm SiC powder was placed in water for stirring and dispersion, and the mass ratio of SiC powder to water was 0.5:1 to prepare a ceramic suspension. NaOH solution was added to adjust the pH value of the suspension to 10, and 0.10% of the total mass of the ceramic suspension was added with surfactant CTAB. The mixture was stirred at 2500rpm for 20min, and then injected into a ring injection mold after forming wet foam. The foam was dried at room temperature for 8h and then dried at 80℃ for 18h. After demolding, the temperature was raised to 1250℃ at a rate of 2℃ / min in an air atmosphere and kept warm for 2h. The average pore size of the interconnected through holes of the prepared ceramic membrane was 107μm, the average pore size of the small holes with gas-solid separation function was 2μm, the porosity was 89.6%, and the gas permeability was 1283.6m 3 m -2 h -1 kPa -1 The filtration effect for dust with a diameter less than 0.3μm is 99.97%.

[0027] Table 1 compares the performance of the ceramic membrane prepared by the direct foaming method in Example 3 with that reported in the literature. Figure 1 is a macroscopic image of the dried ceramic membrane prepared in Example 3. Figure 2 is a macroscopic image of the calcined ceramic membrane prepared in Example 3. Figure 3 is a SEM image of a cross-section of the ceramic membrane prepared in Example 3.

[0028] Example 4

[0029] First, at room temperature and pressure, 10μm Al2O3 and TiO2 powders were placed in water for stirring and dispersion, and the mass ratio of Al2O3, TiO2 powders and water was 0.5:0.1:1 to prepare a ceramic suspension. NaOH solution was added to adjust the pH value of the suspension to 11, and 0.15% of the total mass of the ceramic suspension was added with surfactant CTAB. The mixture was stirred at 3000rpm for 25min, and then injected into a ring injection mold after forming wet foam. The foam was dried at room temperature for 12h and then dried in a 100℃ environment for 24h. After demolding, the temperature was raised to 1800℃ at a rate of 3℃ / min in an air atmosphere and kept warm for 3h. The average pore size of the interconnected through holes of the prepared ceramic membrane was 78μm, the average pore size of the small holes with gas-solid separation function was 5μm, the porosity was 85.02%, and the gas permeability was 1240.1m 3 m -2 h -1 kPa -1 The filtration effect for dust with a diameter less than 0.3μm is 99.03%.

[0030] Table 1 is a comparison of the performance of the ceramic membrane prepared in Example 3 and the literature

Claims

1. A method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method, characterized in that: The specific steps are as follows: A. Under normal temperature and pressure, ceramic powder of a certain particle size is mixed with water in a mass ratio of (0.3-0.6):1 and stirred evenly to obtain a ceramic suspension, the pH value of the ceramic suspension is adjusted to 8-11, and a surfactant cetyltrimethylammonium bromide (CTAB) is added at 0.03%-0.15% of the mass of the ceramic suspension, and stirred for a certain period of time to form wet foam; B. Inject the wet foam into a ring-shaped injection mold, dry it at room temperature for 4-12 hours, and then place it in a 40°C to 100°C environment to dry it for 6-24 hours. After demolding, a high-porosity ceramic membrane is obtained through a calcination process.

2. The method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method according to claim 1, characterized in that: The type of the ceramic powder in step A is one or more of Al2O3, TiO2, Y2O3, ZrO2, SiO2, SiC, Si3N4 or mullite.

3. The method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method according to claim 1, characterized in that: The particle size of the ceramic powder in step A is 0.5-10 μm.

4. The method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method according to claim 1, characterized in that: The solution for adjusting the pH value of the ceramic suspension in step A is a NaOH solution.

5. The method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method according to claim 1, characterized in that: The stirring speed of the membrane-making liquid in step A is 1500-3000 rpm, and the stirring time is 5-25 min.

6. The method for preparing a high-porosity gas-solid separation ceramic membrane based on a direct foaming method according to claim 1, characterized in that: The calcination process is to calcine the green body at 1200-1800°C, control the heating rate and cooling rate at 0.5-3°C / min, and keep the temperature for 1-3h.

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