Catalytic ceramic membrane and preparation method and application thereof

Abstract

This invention discloses a catalytic ceramic membrane, its preparation method, and its applications, belonging to the technical field of inorganic functional ceramic microfiltration membranes and their preparation. This invention solves the problems of limited specific surface area, insufficient number of active sites, easy loss of loaded active components, and poor stability of existing catalytic ceramic membranes. By combining in-situ hydrothermal synthesis and plasma-assisted sintering technology, this invention combines thermally unstable molecular sieves with a ceramic matrix, obtaining uniformly distributed molecular sieves in the ceramic membrane, thus achieving a simultaneous improvement in the catalytic activity and permeation flux of the ceramic membrane.

Description

Technical Field

[0001] This invention relates to a catalytic ceramic membrane, its preparation method and application, belonging to the technical field of inorganic functional ceramic microfiltration membranes and their preparation. Background Technology

[0002] Catalytic ceramic membranes, possessing both separation and catalytic functions, have significant application value in the energy and environmental fields. Traditional catalytic ceramic membranes often use alumina, silica, or titanium dioxide as supports, loading active components via impregnation. However, these membranes generally suffer from limited specific surface area, insufficient number of active sites, easy loss of loaded active components, and poor stability. Molecular sieves, with their regular pore structure and abundant acid / redox sites, are ideal catalytic materials, but their poor thermal stability leads to framework collapse and decreased crystallinity during conventional high-temperature sintering at 1200–1400℃, making stable composite formation with ceramic membrane substrates difficult. Therefore, providing a molecular sieve composite catalytic ceramic membrane and its preparation method is essential. Summary of the Invention

[0003] This invention addresses the problems of limited specific surface area, insufficient number of active sites, easy loss of loaded active components, and poor stability of existing catalytic ceramic membranes by providing a catalytic ceramic membrane, its preparation method, and its application.

[0004] The technical solution of the present invention: One objective of this invention is to provide a method for preparing a catalytic ceramic membrane, specifically comprising the following steps: (1) Aluminum source, silicon source, iron source, molecular sieve structure guiding agent and water are ball-milled to obtain the first slurry; (2) Add binder and pore-forming agent to the first slurry and perform secondary ball milling. After thorough mixing, dry and sieve to obtain pre-pressed powder. Place the pre-pressed powder in a mold and press it to form a green body. (3) The green blank is placed in a plasma-assisted sintering device for sintering and cooling to obtain a catalytic ceramic film.

[0005] Further specifying, (1) the aluminum source is alumina powder and / or boehmite, the silicon source is silica sol or tetraethyl orthosilicate, the iron source is iron oxide powder, ferric nitrate and / or ferric sulfate, and the molecular sieve structure directing agent is tetrapropylammonium hydroxide or tetraethylammonium bromide.

[0006] Furthermore, the particle size of the alumina powder is specified to be 150~1000nm.

[0007] Furthermore, the particle size of the iron oxide powder is specified to be 30~500nm.

[0008] Further specified, (1) the molar ratio of aluminum source, silicon source and iron source in the first slurry is 1:(0.5~3):(0.01~0.1), and the molar ratio of molecular sieve structure directing agent to silicon source is (0.1~0.5):1.

[0009] Further specified, the ball milling time in (1) is 0.5~24h.

[0010] Further specified, (2) the binder is polyethylene glycol and / or polyvinyl alcohol; the added mass of the binder is 1 to 5% of the total mass of the green embryo.

[0011] Further specified, (2) the pore-forming agent is one or more of corn starch, nano carbon, yellow dextrin, cyclodextrin, calcium carbonate, melamine, PMMA microspheres; the added mass of the pore-forming agent is 10~30% of the total mass of the embryo.

[0012] Further specified, (2) the drying temperature is 40~100℃ and the time is 0.5~12h.

[0013] Further specifying, the sieve size in (2) is 40~400 mesh.

[0014] Further specified, the molding pressure in (3) is 2~60MPa.

[0015] Further specified, (3) the thickness of the green blank is 0.5~2.5mm.

[0016] Further specifying, in (4), the sintering conditions are: under vacuum or inert atmosphere, using a pulsed DC power supply, with a pulse frequency of 50~1000Hz and a current density of 10~50A / cm. 2 The voltage is 5~20V, and the pulse duty cycle is 10~50%. Apply a pressure of 20~40MPa to the green billet, heat it to 900~1100℃ at a heating rate of 100~200℃ / min, hold it for 5~15min, and then cool it to room temperature at a rate of 2~10℃ / min after holding.

[0017] The second objective of this invention is to provide a catalytic ceramic membrane prepared by the above method.

[0018] Further specifying, the catalytic ceramic membrane contains molecular sieves with uniformly distributed grain sizes of 50~500nm.

[0019] A third objective of this invention is to provide an application of the above-mentioned catalytic ceramic membrane, specifically for the catalytic oxidation of toluene.

[0020] Beneficial effects: This invention combines in-situ hydrothermal synthesis and plasma-assisted sintering techniques to integrate thermally unstable molecular sieves with a ceramic matrix, resulting in a uniformly distributed molecular sieve within the ceramic membrane. This achieves a simultaneous improvement in the catalytic activity and permeation flux of the ceramic membrane. Compared with existing technologies, this application also has the following advantages: (1) This invention enables the in-situ nucleation and growth of molecular sieves on the surface and in the pores of ceramic particles, forming chemical bonds and strong physical interlocking with the ceramic matrix. The interfacial bonding is strong and the sieves are not easily detached, effectively improving the catalytic activity of the ceramic membrane. Furthermore, the in-situ synthesized molecular sieves are uniformly dispersed and have small particle sizes, significantly increasing the specific surface area of ​​the ceramic membrane. At the same time, the introduction of molecular sieves further broadens the catalytic reaction application range of the ceramic membrane.

[0021] (2) The present invention uses plasma-assisted sintering technology to achieve the integrity of molecular sieve structure while inhibiting excessive grain growth and retaining more pores. Under the same thickness conditions, the permeation flux is significantly higher than that of traditional high-temperature sintered membranes. Attached Figure Description

[0022] Figure 1 The diagram shows a comparison of the pore size distribution of the catalytic ceramic membranes prepared in Examples 1-2 and Comparative Examples 1-3. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials, reagents, methods, and instruments used are conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art. Furthermore, all solid and liquid reagents used are of analytical grade.

[0027] Example 1 The process for preparing the catalytic ceramic membrane in this embodiment is as follows: (1) Mix 20g of boehmite, 25g of silica sol, 0.5g of iron oxide powder, 5g of tetrapropylammonium hydroxide and 50mL of deionized water, and ball mill for 4h to obtain the first slurry; The SiO2 content in the silica sol is 20 wt%. (2) Add 8g PMMA microspheres and 1g polyvinyl alcohol to the first slurry, continue ball milling for 2h, mix thoroughly, dry at 80℃, pass through a 100-mesh sieve to obtain pre-pressed powder, place the pre-pressed powder in a mold, press at 10MPa for 3min to obtain a green body with a thickness of 2mm. (3) The green body is placed in a plasma-assisted sintering apparatus, using a pulsed DC power supply with a pulse frequency of 200 Hz and a current density of 25 A / cm². 2 The voltage was 10V, the pulse duty cycle was 30%, the vacuum degree was ≤5Pa, the temperature was increased to 400℃ at 80℃ / min and held for 3min; then the temperature was increased to 1000℃ at 150℃ / min and held for 10min, while applying an axial pressure of 30MPa; after sintering, the temperature was cooled to 150℃ at 80℃ / min and cooled to room temperature with the furnace to obtain the catalytic ceramic membrane.

[0028] Example 2 The difference between this embodiment and Example 1 is that tetraethylammonium bromide is used to replace tetrapropylammonium hydroxide in step (1), and the sintering temperature in (3) is 950°C and the time is 15 min. The remaining process steps and parameter settings are the same as in Example 1, and a catalytic ceramic membrane is obtained.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that: step (3) involves placing the green blank in a box-type resistance furnace, heating it to 1400°C at 5°C / min, holding it at that temperature for 2 hours, and then cooling it to room temperature with the furnace to obtain a catalytic ceramic film.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that the amount of tetrapropylammonium hydroxide used is 7.2g, while the remaining process steps and parameter settings are the same as in Example 1, resulting in a catalytic ceramic membrane.

[0031] Comparative Example 3 The difference between this comparative example and Example 1 is that the amount of tetrapropylammonium hydroxide used is 0.6g, while the remaining process steps and parameter settings are the same as in Example 1, resulting in a catalytic ceramic membrane.

[0032] Example of effect (1) The pure water flux of the catalytic ceramic membranes prepared in Examples 1-2 and Comparative Examples 1-3 was tested using an ultrafiltration cup in dead-end filtration mode at 25°C and a transmembrane pressure difference of 0.1 MPa. The test results showed that the pure water flux of the catalytic ceramic membranes prepared in Examples 1-2 and Comparative Examples 1-3 was 150 L·m⁻¹, respectively. -2 ·h -1 ·bar -1 130L·m -2 ·h -1 ·bar -1 50L·m -2 ·h -1 ·bar -1 80L·m -2 ·h -1 ·bar -1 and 40 L·m -2 ·h -1 ·bar -1 The comparison shows that the catalytic ceramic membrane prepared in Example 1 has the highest pure water flux. This is because the conventional high-temperature sintering method in Comparative Example 1 caused pore collapse, resulting in a decrease in pure water flux. In Comparative Example 2, due to excessive structure-directing agent, some pores were closed or occupied by carbon deposits, further reducing the pure water flux. In Comparative Example 3, due to insufficient structure-directing agent and poor pore development, the flux was the lowest, only 40 L·m. -2 ·h -1 ·bar -1 .

[0033] (2) The pore size distribution of the catalytic ceramic membranes prepared in Examples 1-2 and Comparative Examples 1-3 was tested, and the test results are as follows: Figure 1 As shown, by Figure 1 It can be seen that Example 1 exhibits a distinct mesoporous peak at 2-5 nm and a macroporous plateau at 1-5 μm, presenting a typical hierarchical porous structure, while the mesopores in Example 2 shift towards 3-6 nm. In Comparative Example 1, the mesoporous peak is broadened and its intensity is significantly reduced, and the macroporous plateau is noticeably weakened, indicating that conventional high-temperature sintering leads to pore collapse. In Comparative Example 2, both the mesoporous peak height and peak area are reduced, and the macroporous plateau is partially absent, reflecting that excessive structure-directing agent leads to partial pore blockage. In Comparative Example 3, the mesoporous peak is the weakest, and the macroporous plateau is almost invisible, indicating poor pore development when the structure-directing agent is insufficient. Furthermore, the above pore size distribution characteristics are consistent with the variation law of pure water flux, further demonstrating that the hierarchical porous structure constructed in this invention has advantages in improving permeation flux.

[0034] (3) The catalytic performance of the catalytic ceramic membranes prepared in Examples 1-2 and Comparative Examples 1-3 was characterized. Specifically, a tube furnace was used as the reactor. The quartz tube filled with the catalytic ceramic membrane was placed in the tube furnace. Air with a toluene volume concentration of 1000 ppm was used as the pollutant air. After reacting for 30 min under heating conditions, the toluene concentration was detected and the toluene conversion rate was calculated. The catalytic performance is shown in Table 1 below.

[0035] Table 1 As shown in Table 1 above, the catalytic ceramic membrane prepared in Example 1 achieved a toluene conversion rate as high as 90% at 260°C. This indicates that the catalytic ceramic membrane prepared using the in-situ hydrothermal synthesis of molecular sieves and plasma-assisted low-temperature short-time sintering technology employed in this application achieves high-throughput catalysis while maintaining high activity. The catalytic ceramic membrane prepared in Example 2 achieved a conversion rate of 87% under the same catalytic conditions as Example 1, slightly lower than Example 1 but higher than Comparative Examples 1-3. This demonstrates that the method provided in this application is applicable to the introduction of various molecular sieves, and that different molecular sieves have an impact on the catalytic performance of the ceramic membrane. Comparative Example 1, using conventional high-temperature sintering at a sintering temperature of 1400°C, achieved a conversion rate of only 70% due to the destruction of the molecular sieve framework. Comparative Examples 2 and 3, due to excessively high or low amounts of molecular sieve structure-directing agents, resulted in changes in the pore structure, leading to significantly lower conversion rates than Example 1.

[0036] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a catalytic ceramic membrane, characterized in that, include: (1) Aluminum source, silicon source, iron source, molecular sieve structure guiding agent and water are ball-milled to obtain the first slurry; (2) Add binder and pore-forming agent to the first slurry and perform secondary ball milling. After thorough mixing, dry and sieve to obtain pre-pressed powder. Place the pre-pressed powder in a mold and press it to form a green body. (3) The green blank is placed in a plasma-assisted sintering device for sintering and cooling to obtain a catalytic ceramic film.

2. The preparation method according to claim 1, characterized in that, (1) The aluminum source is alumina powder and / or boehmite, the silicon source is silica sol or tetraethyl orthosilicate, the iron source is iron oxide powder, ferric nitrate and / or ferric sulfate, and the molecular sieve structure directing agent is tetrapropylammonium hydroxide or tetraethylammonium bromide.

3. The preparation method according to claim 1, characterized in that, (1) The molar ratio of aluminum source, silicon source and iron source in the first slurry is 1:(0.5~3):(0.01~0.1), and the molar ratio of molecular sieve structure directing agent to silicon source is (0.1~0.5):

1.

4. The preparation method according to claim 1, characterized in that, (1) The ball milling treatment time is 0.5~24h.

5. The preparation method according to claim 1, characterized in that, (2) The binder is polyethylene glycol and / or polyvinyl alcohol; the amount of binder added is 1 to 5% of the total mass of the green embryo.

6. The preparation method according to claim 1, characterized in that, (2) The pore-forming agent is one or more of corn starch, nano carbon, yellow dextrin, cyclodextrin, calcium carbonate, melamine, and PMMA microspheres; the mass of the pore-forming agent added is 10-5% of the total mass of the embryo.

7. The preparation method according to claim 1, characterized in that, (2) The thickness of the green billet is 0.5~2.5mm.

8. The preparation method according to claim 1, characterized in that, (4) The sintering conditions are as follows: under vacuum or inert atmosphere, a pulsed DC power supply is used, with a pulse frequency of 50~1000Hz and a current density of 10~50A / cm. 2 The voltage is 5~20V, and the pulse duty cycle is 10~50%. Apply a pressure of 20~40MPa to the green billet, heat it to 900~1100℃ at a heating rate of 100~200℃ / min, hold it for 5~15min, and then cool it to room temperature at a rate of 2~10℃ / min after holding.

9. A catalytic ceramic membrane prepared by the method according to any one of claims 1 to 8.

10. An application of the catalytic ceramic membrane described in claim 9, characterized in that, Used for the catalytic oxidation of toluene.

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