A method for preparing a high-flux SiC filter of a rhinoid structure

Abstract

The application discloses a preparation method of a high-flux SiC filter with a nasal cavity-like structure. A polycarbosilane precursor solution is prepared by using xylene as a solvent, polycarbosilane as a precursor and introducing a small amount of ferrocene, and then polyurethane foam is impregnated, dried and calcined, a three-dimensional interconnected macro-porous framework is constructed in situ by using a template removal method, and the polycarbosilane is converted into SiC. During the heat treatment process, ferrocene is decomposed to generate iron nanoparticles, the nanoparticles catalyze the growth of nanowires on the pore wall and surface, and a complex nanostructure similar to a 'nasal cavity' is formed. The filter has high porosity, continuous through-pore channels and rich particle capture sites, can significantly enhance the mechanical interception capacity for oily particles while maintaining a low flow resistance. Due to the above structural characteristics, the filter has excellent high-flux filtering performance and is especially suitable for the fields of high-temperature oily flue gas purification and particle pollution control.

Description

Technical Field

[0001] This invention belongs to the field of air pollution control, specifically relating to a method for preparing a high-flux SiC filter with a nasal cavity-like structure. Background Technology

[0002] Silicon carbide (SiC) filters are widely used in high-temperature flue gas filtration due to their excellent chemical stability, high-temperature resistance, and mechanical properties. The traditional organic foam rigid template method is a common process for preparing porous silicon carbide ceramic filters. However, this method is limited by the porosity characteristics of the template itself, resulting in a relatively large skeleton, wide pore size distribution, smooth pore walls, and limited specific surface area in the obtained SiC filter. This leads to insufficient filtration efficiency for nanoscale dust particles, making it difficult to meet the requirements for high filtration precision.

[0003] To overcome the aforementioned structural limitations, a catalyst-assisted in-situ nanostructure generation technique was used to prepare SiC filters. This technique first utilizes an organic foam template method to construct a SiC filter with a three-dimensional interconnected macroporous framework, ensuring high permeability and low flow resistance. Subsequently, ferrocene was introduced as a catalyst on the surface of the foam framework and inside the pores, and the precursor pyrolysis process was controlled to grow high-density SiC nanowires in situ. This significantly increases the specific surface area of ​​the filter, effectively trapping nanoscale dust particles and greatly improving filtration accuracy.

[0004] In existing technologies, precursor conversion methods provide an important approach for the controllable preparation of SiC nanowires. For example, CN109607541B discloses a bamboo-like SiC nanowire and its preparation method, using polycarbosilane (PCS) and activated carbon as raw materials, ferrocene as a catalyst, and a dual-temperature zone tube furnace at 900~1250℃ to achieve precursor pyrolysis conversion, thus preparing bamboo-like SiC nanowires with periodically fluctuating diameters, solving the problems of complex processes, high growth temperatures, and low purity in traditional methods. However, the nanowires obtained by this method are loose powder products, lacking a macroscopic three-dimensional support structure, making it difficult to directly use them as filter materials in the field of gas-solid separation. On the other hand, to introduce in-situ grown nanowires into composite material systems to exert a reinforcing effect, CN103553616B proposes a method for preparing in-situ grown SiC nanowire-reinforced SiC composite materials. This method first involves ball milling PCS with catalysts such as ferrocene to form a slurry. Then, the slurry is impregnated under vacuum and high pressure to fully penetrate the carbon fiber preform. After cross-linking and curing, the preform is subjected to high-temperature pyrolysis at 1000–1300°C under a protective atmosphere. During the PCS pyrolysis process, uniformly sized and distributed SiC nanowires are grown in situ under the action of a metal catalyst, thereby reinforcing the SiC composite material. However, this technical route primarily serves the mechanical reinforcement of dense composite materials. Its impregnation process easily leads to dense pore filling, lacking the high-permeability pore structure required for filters.

[0005] In summary, there is an urgent need in this field for an innovative method that can systematically integrate PCS precursor conversion, catalyst-assisted in-situ nanowire growth, and porous filter support to prepare novel SiC filters that combine high permeability and high filtration accuracy. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a high-flux SiC filter with a nasal cavity-like structure. This method involves introducing ferrocene into a precursor solution, followed by high-temperature calcination, and then combining this with an in-situ nanostructure growth method to prepare a silicon carbide filter with a nanowire structure. This successfully solves the problem of low porosity and difficulty in achieving high filtration accuracy in the traditional organic foam rigid template method, realizing the integrated preparation of a complex structure, high airflow, and high filtration accuracy SiC filter.

[0007] The technical solution of the present invention is as follows: A method for preparing a nasal cavity-like high-flux SiC filter, characterized by comprising the following steps: A. Weigh out polycarbosilane powder and xylene in a certain proportion. Under stirring conditions, slowly and in small batches add the polycarbosilane powder to the xylene solvent and stir until completely dissolved. Then add a certain amount of ferrocene and continue stirring until completely dissolved to obtain the precursor solution.

[0008] B. Cut polyurethane foam into circular slices of different thicknesses using a cutting machine. Immerse the slices in the prepared precursor solution, and after uniform impregnation, remove them and dry them. Then, heat the solution to cause the polycarbosilane to undergo oxidative self-crosslinking.

[0009] C. Place the disc obtained in step B into a tube furnace, set the heating rate and holding time for the calcination process, and cool it with the furnace after calcination to obtain a SiC filter; Preferably, the polycarbosilane powder content is 25-50 wt% of the precursor solution, the xylene content is 50-75 wt% of the precursor solution, and the ferrocene content is 0-20 wt% of the polycarbosilane powder.

[0010] Preferably, the polyurethane foam has a specification of 60, 90, or 120 PPI and an internal structure that is three-dimensionally interconnected.

[0011] Preferably, the circular slice has a diameter of approximately 40 mm and a thickness of 3, 5, or 10 mm.

[0012] Preferably, the drying temperature is 80~120℃, the drying time is 12~24h, the oxidation self-crosslinking temperature is 180~220℃, and the oxidation self-crosslinking time is 2~6h.

[0013] In the preferred calcination process, the nitrogen pretreatment temperature is 200℃, the heating rate is 2~5℃ / min, and the holding time is 2~6h; the pyrolysis temperature is 1100℃, the heating rate is 2~5℃ / min, and the holding time is 2~6h; the sintering temperature is 1500℃, the heating rate is 2~5℃ / min, and the holding time is 2~6h; then the temperature is slowly lowered to 900℃ at a cooling rate of 2~5℃ / min, and finally allowed to cool naturally.

[0014] The present invention provides a nasal cavity-like high-flux SiC filter that can be used for high-temperature oily flue gas purification and particulate pollution control.

[0015] The beneficial effects of this invention are: 1. This invention achieves a dual combination of high-throughput structure and high filtration precision. Based on a three-dimensional interconnected macroporous SiC framework constructed using an organic foam template method, high-density SiC nanowires are grown in situ on the framework surface and inside the pores during high-temperature pyrolysis by introducing ferrocene into the precursor solution. This overcomes the problems of traditional organic foam rigid template methods in preparing SiC filter frameworks, such as large size, low porosity, wide pore size distribution, and insufficient filtration precision for nanoscale particles.

[0016] 2. The in-situ grown nanowires, with diameters ranging from tens to hundreds of nanometers, are stacked in an interlaced manner to form a three-dimensional nanoscale nanonetwork structure, which has a highly efficient physical interception and inertial collision effect on nanoscale oily particles. At the same time, the oily particles themselves are highly viscous, and once they come into contact with the surface of the nanowires, they will adhere firmly due to van der Waals forces and liquid bridging forces, making them difficult to be blown off by airflow.

[0017] 3. Unlike traditional methods that often lead to a sharp increase in pressure drop and reduced flux when trying to improve filtration accuracy by reducing pore size or increasing membrane thickness, the nanowires grown with the help of ferrocene are only present on the surface of the pore walls of the macroporous framework and do not block the original three-dimensional interconnected macroporous channels, thus preserving the high-flux structure of the silicon carbide support.

[0018] 4. Crucially, the in-situ grown SiC nanowires are not simply uniformly covered, but rather interwoven and stacked on the pore wall surface, forming a unique nasal cavity-like microstructure—the nanowires cross-link to form nanoscale channels with constricted openings. This configuration allows nanoscale oily particles to be effectively captured at the constricted openings and within the channels due to inertial collisions and physical interception when dust-laden airflow passes through, while gas molecules can smoothly bypass them. This significantly improves filtration efficiency while maintaining low flow resistance. This structure, in conjunction with a three-dimensional interconnected macroporous framework, truly achieves high-precision interception and high-throughput transmission, making it particularly suitable for industrial filtration scenarios involving highly viscous particles such as high-temperature oily fumes. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the three-dimensional interconnected macroporous filter material prepared in Example 3.

[0020] Figure 2 This is a SEM image of the cross-section of the pores in the three-dimensional interconnected macroporous filter material prepared in Example 3.

[0021] Figure 3 The graph shows the gas flux test results of the three-dimensional interconnected macroporous filter materials prepared in Examples 1-5.

[0022] Figure 4 The diagram shows the oil fume removal efficiency of the three-dimensional interconnected macroporous filter materials prepared in Examples 1-5. Detailed Implementation

[0023] The present invention will be further explained in detail below with reference to the embodiments. The following embodiments are only for illustrating the present invention, but the implementation of the present invention is not limited thereto. Example 1

[0024] A method for fabricating a nasal cavity-like high-flux SiC filter, the specific steps of which are as follows: The PCS powder content was 45 wt% of the precursor solution, the xylene content was 55 wt% of the precursor solution, and the ferrocene content was 0 wt% of the PCS powder. The PCS powder was added to the xylene solvent and stirred until completely dissolved. 60 PPI polyurethane foam was used and cut into circular slices with a diameter of 40 mm and a thickness of 3 mm. The circular slices were placed in the prepared precursor solution and uniformly impregnated. After removal, they were vertically placed in an 80℃ oven and dried for 12 hours, followed by oxidative self-crosslinking in a 180℃ oven for 2 hours. The SiC filter was calcined in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200℃ at a rate of 2℃ / min and held for 2 hours for nitrogen pretreatment. Then, the temperature was increased to 1100℃ at a rate of 2℃ / min and held for 2 hours for pyrolysis. Next, the temperature was increased to 1500℃ at a rate of 2℃ / min and held for 2 hours for sintering. Immediately afterwards, the temperature was slowly decreased to 900℃ at a rate of 2℃ / min, and finally allowed to cool naturally to room temperature. The resulting SiC filter had an average diameter of 30 mm and a gas permeability of 3800 μm. 3 / (m 2 The oil fume removal efficiency is 30% (·h·kPa). Example 2

[0025] The PCS powder content was 35wt% of the precursor solution, the xylene content was 65wt% of the precursor solution, and the ferrocene content was 5wt% of the PCS powder. The PCS powder was added to the xylene solvent and stirred until completely dissolved. Then, the ferrocene was added and stirred until a homogeneous precursor solution was formed. 90PPI polyurethane foam was used and cut into circular slices with a diameter of 40mm and a thickness of 5mm. The circular slices were placed in the prepared precursor solution and uniformly impregnated. After being removed, they were vertically placed in a 100℃ oven to air dry for 18 hours, followed by oxidation and self-crosslinking in a 200℃ oven for 3 hours. The SiC filter was calcined in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200℃ at a rate of 3℃ / min and held for 4 hours for nitrogen pretreatment. Then, the temperature was increased to 1100℃ at a rate of 3℃ / min and held for 4 hours for pyrolysis. Next, the temperature was increased to 1500℃ at a rate of 3℃ / min and held for 4 hours for sintering. Immediately afterwards, the temperature was slowly decreased to 900℃ at a rate of 3℃ / min, and finally allowed to cool naturally to room temperature. The resulting SiC filter had an average diameter of 32 mm and a gas permeability of 3500 μm. 3 / (m 2 The oil fume removal efficiency is 44.6% (·h·kPa). Example 3

[0026] The PCS powder content is 40wt%, xylene content is 60wt%, and ferrocene content is 10wt% of the PCS powder. These components are added to the solvent and stirred until completely dissolved. Then, ferrocene is added and stirred until a homogeneous precursor solution is formed. 120PPI polyurethane foam is used and cut into circular slices with a diameter of 40mm and a thickness of 10mm. The circular slices are placed in the prepared precursor solution and uniformly impregnated. After removal, they are vertically placed in a 120℃ oven to air dry for 24 hours, followed by oxidative self-crosslinking in a 220℃ oven for 4 hours. The SiC filter was calcined in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200°C at a rate of 5°C / min and held for 6 hours for nitrogen pretreatment. Then, the temperature was increased to 1100°C at a rate of 5°C / min and held for 6 hours for pyrolysis. Next, the temperature was increased to 1500°C at a rate of 5°C / min and held for 6 hours for sintering. The temperature was then slowly reduced to 900°C and finally allowed to cool naturally to room temperature. The resulting SiC filter had an average diameter of 31 mm and a gas permeability of 3200 μm. 3 / (m 2 The oil fume removal efficiency is 58.9% (·h·kPa).

[0027] Figure 2This describes the microstructure within the pores of the three-dimensional interconnected macroporous filter fabricated in this embodiment. A significant increase in catalyst content is clearly observed, resulting in denser SiC nanowire growth. The in-situ grown SiC nanowires do not simply provide a uniform coverage; instead, they intertwine and stack on the pore wall surface, forming a unique nasal cavity-like structure. This significantly improves filtration accuracy, while slightly reducing gas permeability but still maintaining a high level.

[0028] Figure 1 This is the X-ray diffraction (XRD) pattern of the SiC filter prepared in this embodiment. Analysis shows that the diffraction peaks located near 2θ≈35.6°, 41.4°, 60.0°, 71.8°, and 75.5° correspond to the (111), (200), (220), (311), and (222) crystal planes of β-SiC, respectively, confirming that the PCS precursor was successfully transformed into the well-crystallized β-SiC phase. In addition, diffraction peaks of Fe3Si alloy were detected near 2θ≈44.7° and 65.0°, indicating that the iron nanoparticles generated by the decomposition of ferrocene reacted with the silicon species released by the cracking of PCS to form the Fe-Si alloy phase. This alloy phase, as the catalyst active center of the VLS growth mechanism, effectively induced the in-situ growth of SiC nanowires. At the same time, no obvious diffraction peaks of free iron or graphitic carbon were observed in the pattern, indicating that the catalyst utilization rate was high and no obvious catalyst agglomeration or excessive carbon deposition occurred. Example 4

[0029] The PCS powder content is 25wt%, xylene content is 75wt%, and ferrocene content is 15wt% of the PCS powder. These are added to the solvent and stirred until completely dissolved. Then, ferrocene is added and stirred until a homogeneous precursor solution is formed. 120PPI polyurethane foam is used and cut into circular slices with a diameter of 40mm and a thickness of 10mm. The circular slices are placed in the prepared precursor solution and uniformly impregnated. After removal, they are vertically placed in a 90℃ oven to air dry for 15 hours, followed by oxidation and self-crosslinking in a 190℃ oven for 5 hours. The SiC filter was calcined in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200°C at a rate of 4°C / min and held for 3 hours for nitrogen pretreatment. Then, the temperature was increased to 1100°C at a rate of 4°C / min and held for 3 hours for pyrolysis. Next, the temperature was increased to 1500°C at a rate of 4°C / min and held for 3 hours for sintering. The temperature was then slowly decreased to 900°C and finally allowed to cool naturally to room temperature. The resulting SiC filter had an average diameter of 29 mm and a gas permeability of 3600 μm. 3 / (m 2 The oil fume removal efficiency is 49.9% (·h·kPa). Example 5

[0030] The PCS powder content is 50wt%, the xylene content is 50wt%, and the ferrocene content is 20wt% of the PCS powder. These are added to the solvent and stirred until completely dissolved. Then, ferrocene is added and stirred until a homogeneous precursor solution is formed. 120PPI polyurethane foam is used and cut into circular slices with a diameter of 40mm and a thickness of 10mm. The circular slices are placed in the prepared precursor solution and uniformly impregnated. After removal, they are vertically placed in an oven at 110℃ to air dry for 21 hours, followed by oxidative self-crosslinking in an oven at 210℃ for 6 hours. The SiC filter was calcined in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200°C at a rate of 5°C / min and held for 5 hours for nitrogen pretreatment. Then, the temperature was increased to 1100°C at a rate of 5°C / min and held for 5 hours for pyrolysis. Next, the temperature was increased to 1500°C at a rate of 5°C / min and held for 5 hours for sintering. The temperature was then slowly decreased to 900°C and finally allowed to cool naturally to room temperature. The resulting SiC filter had an average diameter of 28 mm and a gas permeability of 3500 μm. 3 / (m 2 The oil fume removal efficiency is 41.5% (·h·kPa).

Claims

1. A method for preparing a high-flux SiC filter with a nasal cavity-like structure, characterized in that, Includes the following steps: A. Weigh out polycarbosilane powder and xylene in a certain proportion. Under stirring conditions, slowly and in small batches add the polycarbosilane powder to the xylene solvent and stir until completely dissolved. Then add a certain amount of ferrocene and continue stirring until completely dissolved to obtain the precursor solution. B. Use a cutting machine to cut polyurethane foam into circular slices of different thicknesses, immerse the slices in the prepared precursor solution, remove them after uniform impregnation, dry them, and then heat them to cause polycarbosilane to undergo oxidative self-crosslinking. C. Place the discs obtained in step B into a tube furnace for calcination. After calcination, cool the discs with the furnace to obtain a SiC filter.

2. The method for preparing a nasal cavity-like high-flux SiC filter according to claim 1, characterized in that, In step A, the polycarbosilane content is 25-50 wt% of the precursor solution, the xylene content is 50-75 wt% of the precursor solution, and the ferrocene content is 0-20 wt% of the polycarbosilane powder.

3. The method for preparing a nasal cavity-like high-flux SiC filter according to claim 1, characterized in that, In step B, the polyurethane foam specifications are 60, 90, and 120 PPI, and the internal structure of the polyurethane foam is a three-dimensional interconnected structure.

4. The method for preparing a nasal cavity-like high-flux SiC filter according to claim 1, characterized in that, In step B, the diameter of the circular slice is approximately 40 mm, and the thickness is 3, 5, and 10 mm.

5. The method for preparing a nasal cavity-like high-flux SiC filter according to claim 1, characterized in that, In step B, the drying temperature is 80~120℃, the drying time is 12~24h, the oxidation self-crosslinking temperature is 180~220℃, and the oxidation self-crosslinking time is 2~6h.

6. The method for preparing a nasal cavity-like high-flux SiC filter according to claim 1, characterized in that, In step C, the calcination process is divided into nitrogen pretreatment, pyrolysis, and sintering. The nitrogen pretreatment process is carried out at a temperature of 200℃, a heating rate of 2~5℃ / min, and a holding time of 2~6h. The pyrolysis process is carried out at a temperature of 1100℃, a heating rate of 2~5℃ / min, and a holding time of 2~6h. The sintering process is carried out at a temperature of 1500℃, a heating rate of 2~5℃ / min, and a holding time of 2~6h. Then, the temperature is slowly reduced to 900℃ at a cooling rate of 2~5℃ / min, and finally, the temperature is allowed to cool naturally.

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