A method for preparing a titanium dioxide modified silicon carbide ceramic fiber membrane

Abstract

The application discloses a preparation method of a titanium dioxide modified silicon carbide ceramic fiber membrane. By means of a solvothermal reaction and calcination growth of TiO2 nanocones on the surface of a silicon carbide support body, the roughness of the surface of the support body can be increased, so that the contact sites between the membrane layer fibers and the support body are increased, and the membrane-base bonding force of the membrane is increased. A silicon carbide fiber membrane liquid is sprayed on the support body, and then, programmed sintering is carried out, so that a complete and defect-free silicon carbide fiber membrane is prepared. The prepared silicon carbide fiber membrane has high gas permeability and good blowback stability.

Description

Technical Field

[0001] This invention relates to a titanium dioxide-modified silicon carbide ceramic fiber membrane and its preparation method, belonging to the field of porous ceramic separation membrane preparation. Background Technology

[0002] Porous ceramic membranes are an important material for high-temperature gas dust removal. To improve separation accuracy, a granular membrane layer is typically prepared on a ceramic support layer. However, ceramic membranes prepared using this method often have low porosity (below 35%) in the separation layer, resulting in low gas permeability, which limits their widespread application.

[0003] Silicon carbide fibers possess characteristics such as high temperature resistance, high strength, and good chemical stability. Constructing membrane layers using fibers can significantly increase membrane porosity, thereby improving the gas permeability of the membrane material. However, the inter-fiber bonding strength is relatively weak. This can be strengthened by adding sintering aids to the fiber aggregate to promote the formation of neck connections between fibers at high temperatures.

[0004] Cuo et al. (Ceramics International, 2018, 44: 11778-11782) successfully prepared homogeneous porous mullite fiber ceramics using a template agent method. This ceramic material exhibited high porosity, but its flexural strength was only 1.19 MPa. Ke et al. (J. Phys. Chem. B, 2008, 112: 5000-5006) constructed a layered separation layer on a porous ceramic support using titanate nanofibers and boehmite nanofibers. This membrane exhibited relatively high water flux and good integrity. To improve the bonding strength between fibers, small particles and sintering aids are often doped into the fiber material to react at high temperatures, promoting the formation of neck connections between fibers and enhancing the bonding strength. Pall Corporation's (Fuel, 2013, 108:19-23) Dia-Schumalith series filter tubes feature a support structure composed of large-diameter silicon carbide particles bonded together with high-temperature creep-resistant aluminosilicate, while the membrane layer consists of fine-diameter particles and mullite fibers. This filter is suitable for high-temperature flue gas purification and exhibits particularly excellent thermal shock resistance. However, efficiently improving the bonding strength between the fiber membrane layer and the particle support layer, thereby enhancing the membrane's backflushing stability, remains a major challenge in the field of ceramic fiber membranes. Summary of the Invention

[0005] The purpose of this invention is to improve the low gas permeability and poor backflush stability of existing ceramic separation membranes by proposing a method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane.

[0006] The technical solution of this invention is as follows: a method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane, the specific steps of which are as follows: A. Anhydrous ethanol, tetrabutyl titanate, and polyethylene glycol 600 are mixed and magnetically stirred at a molar ratio of (3-5):1:1 to obtain a clear and transparent titanium sol. The silicon carbide support is immersed in the above titanium sol and sonicated for 2-10 min. Then, it is lifted and vertically placed into a beaker and placed in an oven at 80-150 ℃ for 10-60 min to obtain silicon carbide support a. Glycerol and tetrabutyl titanate are mixed and stirred at a volume ratio of (10-20):1 and poured into a polytetrafluoroethylene liner. The silicon carbide support a is vertically placed into the polytetrafluoroethylene liner. The silicon carbide support b is obtained by hydrothermal treatment at 150-210 ℃ for 18-26 h, followed by washing with anhydrous ethanol 1-5 times. The silicon carbide support b is placed on a ceramic firing platform and held in a muffle furnace at 300-600 ℃ for 1-3 h to obtain a support c with anatase crystals. A certain amount of silicon carbide fiber and nano-zirconia are added to a pre-prepared 0.5-2wt% methylcellulose solution at a mass ratio of (8-20):1 to obtain a film-forming solution with a solid content of 4-8wt%. The film-forming solution is sprayed onto the silicon carbide support c, dried in a constant temperature drying oven, and finally sintered in a high-temperature furnace to obtain a silicon carbide fiber membrane.

[0007] The magnetic stirring speed in step (1) is 400-600 r / min, and the stirring time is 1-3 min.

[0008] The magnetic stirring speed in step (2) is 400-600 r / min, and the stirring time is 10-50 min.

[0009] The calcination procedure for the support b described in step (3) is to heat it to 300-600 ℃ at a rate of 4-6 ℃ / min at room temperature, hold it at 300-600 ℃ for 1-3 h, and then let it cool naturally to room temperature.

[0010] The silicon carbide fiber described in step (4) has an average diameter of 0.5-2 μm and an aspect ratio of 10-25, and the nano-zirconia has an average particle size of about 400-600 nm.

[0011] The film-forming liquid in step (5) is sprayed 2-4 times, with each spraying time being 0.5-2 s, the spraying pressure being 0.4-0.6 MPa, the spraying distance being 15-25 cm, the wet film drying temperature being 40-80 ℃, and the drying time being 5-12 h.

[0012] The sintering procedure for the silicon carbide fiber membrane in step (5) is as follows: at room temperature, the temperature is increased to 90-110 ℃ at a heating rate of 0.5-2 ℃ / min, then increased to 600-800 ℃ at a heating rate of 1-3 ℃ / min, then increased to 1100-1200 ℃ at a heating rate of 0.5-2 ℃ / min, held at 1100-1200 ℃ for 1-3 h, and then naturally cooled to room temperature.

[0013] The silicon carbide ceramic membrane prepared by this invention has a membrane thickness of 90-240 μm, an average pore size of 4.8-13 μm, and a gas permeability of 308-616 μm. 3 ·m -2 ·h -1 ·kPa -1

[0014] Beneficial effects:

[0015] This invention increases the surface roughness of a silicon carbide support by using a solvent hydrothermal reaction and calcination to grow TiO2 nanocones, thereby increasing the contact sites between the film fibers and the support and enhancing the film-substrate adhesion. A silicon carbide fiber film-forming solution is then sprayed onto the support, followed by programmed sintering to prepare a complete and defect-free silicon carbide fiber membrane. The prepared silicon carbide fiber membrane exhibits both high gas permeability and good backflush stability. Attached Figure Description

[0016] Figure 1 This is a surface morphology diagram of the support c with anatase crystals grown in Example 2.

[0017] Figure 2 The image shows the XRD pattern of the support c with anatase crystal structure grown in Example 2.

[0018] Figure 3 This is a pore size distribution diagram of the support c with anatase crystal structure grown in Example 2.

[0019] Figure 4 This is a cross-sectional morphology diagram of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2.

[0020] Figure 5 This is a surface morphology diagram of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2.

[0021] Figure 6 This is a pore size distribution diagram of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2.

[0022] Figure 7 The graph shows the dust filtration performance of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2.

[0023] Figure 8 This is a comparison chart of the Darcy permeability of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2 with relevant literature. Detailed Implementation

[0024] Example 1

[0025] Anhydrous ethanol, tetrabutyl titanate, and polyethylene glycol 600 were mixed in a molar ratio of 3:1:1 and magnetically stirred until homogeneous, yielding a clear and transparent titanium sol. A silicon carbide support was immersed in this titanium sol and sonicated for 2 minutes. It was then lifted and vertically placed into a beaker and placed in an 80 °C oven for 30 minutes, yielding silicon carbide support a. Glycerol and tetrabutyl titanate were mixed in a volume ratio of 15:1 and stirred until homogeneous. This mixture was poured into a polytetrafluoroethylene (PTFE) liner, and silicon carbide support a was vertically placed into the PTFE liner. The silicon carbide support b was obtained by hydrothermal treatment at 150℃ for 16 h, followed by washing three times with anhydrous ethanol. Support b was then placed on a ceramic firing platform and held in a muffle furnace at 400℃ for 2 h to obtain support c with anatase crystals. A certain amount of silicon carbide fiber and nano-zirconia were added to a pre-prepared 0.5wt% methylcellulose solution at a mass ratio of 8:1 to obtain a film-forming solution with a solid content of 4wt%. The film-forming solution was sprayed onto silicon carbide support c twice, with each spraying lasting 1 s, at a pressure of 0.4 MPa and a distance of 20 cm. The substrate was then dried in a constant-temperature drying oven to obtain a coated substrate d. The coated substrate d was then sintered in a high-temperature furnace at 1150℃ in air to obtain a silicon carbide fiber membrane.

[0026] The titanium dioxide-modified silicon carbide ceramic fiber membrane was tested and found to have an average pore size of 13 μm and a gas permeability of 616 μm. 3 ·m -2 ·h -1 ·kPa -1 After 30 backflushing cycles at 0.5 MPa, its morphology, pore size distribution, and gas permeability showed no significant changes.

[0027] Example 2

[0028] Anhydrous ethanol, tetrabutyl titanate, and polyethylene glycol 600 were mixed in a molar ratio of 4:1:1 and magnetically stirred until homogeneous, yielding a clear and transparent titanium sol. A silicon carbide support was immersed in this titanium sol and sonicated for 5 min. It was then lifted and vertically placed into a beaker and placed in an oven at 120 ℃ for 30 min, resulting in silicon carbide support a. Glycerol and tetrabutyl titanate were mixed in a volume ratio of 15:1 and stirred until homogeneous. This mixture was poured into a polytetrafluoroethylene (PTFE) liner, and silicon carbide support a was vertically placed into the PTFE liner. The silicon carbide support b was obtained by hydrothermal treatment at 180℃ for 24 h, followed by washing three times with anhydrous ethanol. Support b was placed on a ceramic firing platform and held in a muffle furnace at 450℃ for 2 h to obtain support c with anatase crystals. A certain amount of silicon carbide fiber and nano-zirconia were added to a pre-prepared 1wt% methylcellulose solution at a mass ratio of 10:1 to obtain a film-forming solution with a solid content of 6wt%. The film-forming solution was sprayed onto silicon carbide support c twice, with each spraying lasting 1 s, a spraying pressure of 0.5 MPa, and a spraying distance of 20 cm. It was then dried in a constant temperature drying oven to obtain a coated substrate d. The coated substrate d was sintered in a high-temperature furnace at 1150℃ in air to obtain a silicon carbide fiber membrane.

[0029] The titanium dioxide-modified silicon carbide ceramic fiber membrane was tested and found to have an average pore size of 6.8 μm and a gas permeability of 440 μm. 3 ·m -2 ·h -1 ·kPa -1 After 30 backflushing cycles at 0.5 MPa, its morphology, pore size distribution, and gas permeability showed no significant changes.

[0030] Figure 1 This is a surface morphology diagram of the support c with anatase crystal structure grown in Example 2, where titanium dioxide nanocones are uniformly covered on the surface of the support. Figure 2 The image shows the XRD pattern of the support c with anatase crystal structure grown in Example 2. It can be seen from the image that the support has anatase TiO2 diffraction peaks at 2θ=24° and 2θ=55°. Figure 3 This is a pore size distribution diagram of the support c with anatase crystal structure grown in Example 2. It can be seen from the figure that the support exhibits a single-peak distribution with an average pore size of 35.7 μm. Figure 4 This is a cross-sectional morphology diagram of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2. As can be seen from the figure, the membrane thickness is about 120 μm, and the bonding between the membrane fiber and the support is strong. Figure 5 This is a surface morphology diagram of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2. It can be seen from the figure that the fibers on the membrane surface are interwoven to form a three-dimensional mesh-like interconnected pore structure. Figure 6This is a pore size distribution diagram of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2. The diagram shows that the fiber membrane exhibits a single-peak distribution with an average pore size of 6.8 μm. Figure 7 This is a graph showing the dust filtration performance of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2. The membrane's dust retention rate remained above 99.93%, and the filtration pressure drop was 0.82 kPa after filtration for 80 minutes and four backflushing cycles. Throughout each backflushing cycle, the pressure drop consistently showed a trend of first increasing and then stabilizing, indicating that the membrane exhibits good backflushing stability. Figure 8 This is a comparison graph of the Darcy permeability of the titanium dioxide-modified silicon carbide ceramic fiber membrane in Example 2 with relevant literature. The Darcy permeability coefficient of this fiber membrane is higher than that of filters with similar porosity and pore size, therefore, this fiber membrane has relatively lower gas permeation resistance than filters with similar porosity and pore size.

[0031] Example 3

[0032] Anhydrous ethanol, tetrabutyl titanate, and polyethylene glycol 600 were mixed in a molar ratio of 5:1:1 and magnetically stirred until homogeneous, yielding a clear and transparent titanium sol. A silicon carbide support was immersed in this titanium sol and sonicated for 10 min. It was then lifted and vertically placed into a beaker and placed in an oven at 150 ℃ for 60 min, resulting in silicon carbide support a. Glycerol and tetrabutyl titanate were mixed in a volume ratio of 20:1 and stirred until homogeneous. This mixture was poured into a polytetrafluoroethylene (PTFE) liner, and silicon carbide support a was vertically placed into the PTFE liner. The silicon carbide support b was obtained by hydrothermal treatment at 210 ℃ for 26 h, followed by washing five times with anhydrous ethanol. Support b was then placed on a ceramic firing platform and held in a muffle furnace at 500 ℃ for 2 h to obtain support c with anatase crystals. A certain amount of silicon carbide fiber and nano-zirconia were added to a pre-prepared 1.5 wt% methylcellulose solution at a mass ratio of 12:1 to obtain a film-forming solution with a solid content of 8 wt%. The film-forming solution was sprayed onto silicon carbide support c twice, with each spraying lasting 2 s, at a pressure of 0.6 MPa and a distance of 25 cm. The substrate was then dried in a constant temperature drying oven to obtain a coated substrate d. The coated substrate d was then sintered in a high-temperature furnace at 1200 ℃ in air to obtain a silicon carbide fiber membrane.

[0033] The titanium dioxide-modified silicon carbide ceramic fiber membrane was tested and found to have an average pore size of 4.8 μm and a gas permeability of 308 μm. 3 ·m -2 ·h -1 ·kPa -1 After 30 backflushing cycles at 0.5 MPa, its morphology, pore size distribution, and gas permeability showed no significant changes.

[0034] Example 4

[0035] Anhydrous ethanol, tetrabutyl titanate, and polyethylene glycol 600 were mixed in a molar ratio of 3:1:1 and magnetically stirred until homogeneous, yielding a clear and transparent titanium sol. A silicon carbide support was immersed in this titanium sol and sonicated for 5 min. It was then lifted and vertically placed into a beaker and placed in an 80 ℃ oven for 40 min, resulting in silicon carbide support a. Glycerol and tetrabutyl titanate were mixed in a volume ratio of 10:1 and stirred until homogeneous. This mixture was poured into a polytetrafluoroethylene (PTFE) liner, and silicon carbide support a was vertically placed into the PTFE liner. The silicon carbide support b was obtained by hydrothermal treatment at 150℃ for 18 h, followed by washing with anhydrous ethanol. Support b was then placed on a ceramic firing platform and held in a muffle furnace at 550℃ for 2 h to obtain support c with anatase crystals. A certain amount of silicon carbide fiber and nano-zirconia were added to a pre-prepared 2wt% methylcellulose solution at a mass ratio of 16:1 to obtain a film-forming solution with a solid content of 6wt%. The film-forming solution was sprayed onto the silicon carbide support c three times, with each spraying lasting 0.5 s, at a pressure of 0.4 MPa, and a distance of 15 cm. The substrate was then dried in a constant temperature drying oven to obtain a coated substrate d. The coated substrate d was then sintered in a high-temperature furnace at 1100℃ in air to obtain a silicon carbide fiber membrane.

[0036] The titanium dioxide-modified silicon carbide ceramic fiber membrane was tested and found to have an average pore size of 6.3 μm and a gas permeability of 308 μm. 3 ·m -2 ·h -1 ·kPa -1 After 30 backflushing cycles at 0.5 MPa, its morphology, pore size distribution, and gas permeability showed no significant changes.

[0037] Example 5

[0038] Anhydrous ethanol, tetrabutyl titanate, and polyethylene glycol 600 were mixed in a molar ratio of 4:1:1 and magnetically stirred until homogeneous, yielding a clear and transparent titanium sol. A silicon carbide support was immersed in this titanium sol and sonicated for 5 min. It was then lifted and vertically placed into a beaker and placed in an oven at 120 ℃ for 60 min, resulting in silicon carbide support a. Glycerol and tetrabutyl titanate were mixed in a volume ratio of 15:1 and stirred until homogeneous. This mixture was poured into a polytetrafluoroethylene (PTFE) liner, and silicon carbide support a was vertically placed into the PTFE liner. The silicon carbide support b was obtained by hydrothermal treatment at 180℃ for 24 h, followed by washing three times with anhydrous ethanol. Support b was placed on a ceramic firing platform and held in a muffle furnace at 600℃ for 2 h to obtain support c with anatase crystals. A certain amount of silicon carbide fiber and nano-zirconia were added to a pre-prepared 2.5wt% methylcellulose solution at a mass ratio of 20:1 to obtain a film-forming solution with a solid content of 6wt%. The film-forming solution was sprayed onto silicon carbide support c four times, with each spraying lasting 2 s, a spraying pressure of 0.5 MPa, and a spraying distance of 25 cm. The substrate was then dried in a constant temperature drying oven to obtain a coated substrate d. The coated substrate d was sintered in a high-temperature furnace at 1200℃ in air to obtain a silicon carbide fiber membrane.

[0039] The titanium dioxide-modified silicon carbide ceramic fiber membrane was tested and found to have an average pore size of 5.5 μm and a gas permeability of 336 μm. 3 ·m -2 ·h -1 ·kPa -1 After 30 backflushing cycles at 0.5 MPa, its morphology, pore size distribution, and gas permeability showed no significant changes.

[0040] Table 1 compares the membrane prepared in Example 2 with that in the literature. As shown in the table, the membrane prepared by this method (average pore size approximately 6.8 μm) exhibits higher gas permeability, higher dust rejection rate, and lower pressure drop compared to the membrane in the literature. (Pore size unit: μm, gas permeability unit: m) 3 ·m -2 ·h -1 ·kPa -1 Dust retention rate (unit: %), pressure drop (unit: kPa).

[0041] Table 1. Comparison of the properties of the membranes prepared in Example 2 and those reported in the literature.

[0042]

Claims

1. A method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane, characterized in that, The specific steps are as follows: (1) Mix anhydrous ethanol, tetrabutyl titanate and polyethylene glycol 600 in a molar ratio of (3-5):1:1 and stir magnetically until homogeneous to obtain a clear and transparent titanium sol. Immerse the silicon carbide support in the above titanium sol and sonicate for 2-10 min. Then lift it up and place it vertically into a beaker and place it in an oven at 80-150 ℃ for 10-60 min to obtain silicon carbide support a. (2) Mix glycerol and tetrabutyl titanate in a volume ratio of (10-20):1 and stir magnetically until uniform. Pour into a polytetrafluoroethylene liner. Place silicon carbide support a vertically into the polytetrafluoroethylene liner and hydrothermally heat at 150 ℃-210 ℃ for 18-26 h. After removal, wash with anhydrous ethanol 1-5 times to obtain silicon carbide support b. (3) Place silicon carbide support b on a ceramic firing platform and heat it in a muffle furnace at 300-600 ℃ for 1-3 h to obtain support c with anatase crystal structure. (4) A certain amount of silicon carbide fiber and nano-zirconia are added to a pre-prepared 0.5-2wt% methylcellulose solution at a mass ratio of (8-20):1 to obtain a film-forming solution with a solid content of 4-8wt%. (5) Spray the film-forming solution onto the silicon carbide support c, then dry it in a constant temperature drying oven, and finally sinter it in a high temperature furnace to obtain a silicon carbide fiber membrane.

2. The method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane according to claim 1, characterized in that, The magnetic stirring speed in step (1) is 400-600 r / min, and the stirring time is 1-3 min.

3. The method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane according to claim 1, characterized in that, The magnetic stirring speed in step (2) is 400-600 r / min, and the stirring time is 10-50 min.

4. The method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane according to claim 1, characterized in that, The calcination procedure for the support b described in step (3) is to heat it to 300-600℃ at a rate of 4-6℃ / min at room temperature, hold it at 300-600℃ for 1-3 hours, and then let it cool naturally to room temperature.

5. The method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane according to claim 1, characterized in that, The silicon carbide fiber described in step (4) has an average diameter of 0.5-2 μm and an aspect ratio of 10-25, and the nano-zirconia has an average particle size of 400-600 nm.

6. The method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane according to claim 1, characterized in that, The film-forming liquid in step (5) is sprayed 2-4 times, with each spraying time being 0.5-2 s, the spraying pressure being 0.4-0.6 MPa, the spraying distance being 15-25 cm, the wet film drying temperature being 40-80 ℃, and the drying time being 5-12 h.

7. The method for preparing a titanium dioxide-modified silicon carbide ceramic fiber membrane according to claim 1, characterized in that, The sintering procedure for the silicon carbide fiber membrane in step (5) is as follows: at room temperature, the temperature is increased to 90-110 ℃ at a heating rate of 0.5-2 ℃ / min, then increased to 600-800 ℃ at a heating rate of 1-3 ℃ / min, then increased to 1100-1200 ℃ at a heating rate of 0.5-2 ℃ / min, held at 1100-1200 ℃ for 1-3 h, and then naturally cooled to room temperature.

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