Preparation method of fly ash-silane coupling agent composite ceramic membrane
The method for preparing composite ceramic membranes using fly ash and silane coupling agents solves the problems of high cost and performance control of traditional ceramic membranes, enabling the large-scale production of low-cost, high-performance ceramic membranes suitable for industrial separation applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUIZHOU NORMAL UNIVERSITY
- Filing Date
- 2025-10-09
- Publication Date
- 2026-07-21
AI Technical Summary
Traditional ceramic membranes are expensive to prepare, energy-intensive, and have difficult-to-control surface properties of fly ash, which limits their application in high-performance separation.
By combining fly ash with a silane coupling agent, a dense covalent network is prepared through multi-stage pretreatment, wet spinning, and high-temperature gradient sintering combined with silane coupling agent modification, thereby achieving hydrophilicity control and uniform modification.
It reduces the production cost of ceramic membranes, improves mechanical strength and separation performance, is suitable for industrial-scale production, and achieves high throughput and high stability.
Smart Images
Figure CN121244012B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of composite ceramic membrane technology, and in particular to a method for preparing a fly ash-silane coupling agent composite ceramic membrane. Background Technology
[0002] In the field of oily wastewater treatment, ceramic membranes have shown significant advantages in the field of separation membrane technology due to their excellent chemical stability, high temperature resistance, acid and alkali resistance and high mechanical strength. Especially when dealing with complex working conditions such as the performance degradation of organic membranes due to factors such as excessive chemical oxygen demand (COD), drastic pH fluctuations and temperature changes, the fly ash-silane coupling agent composite ceramic membrane provided in this application shows more outstanding separation efficiency and long-term operational stability. The preparation of traditional ceramic membranes has three major technical bottlenecks: (1) the raw materials rely on high-cost raw materials such as alumina (Al2O3) and zirconium dioxide (ZrO2), and the production cost is about 5-8 times that of organic membranes; (2) sintering is required at high temperatures of over 1600℃, which consumes a lot of energy and limits large-scale application; (3) when fly ash is used as a substitute raw material in the prior art, its original particle surface characteristics are difficult to control, and the hydrophilic / hydrophobic properties cannot meet the requirements of membrane separation performance. The core technical problem addressed in this application is overcoming the high cost limitation of traditional ceramic membranes. By utilizing fly ash resources (solid waste utilization rate ≥85%) and combining it with silane coupling agent surface modification technology, this application achieves the large-scale preparation of low-cost (raw material cost reduction of 60-70%), high-performance (pure water flux 300-500 L / m²·h·bar) ceramic membranes. Based on this, this application proposes a method for preparing a fly ash-silane coupling agent composite ceramic membrane.
[0003] Currently, while plasma treatment is an effective method for modifying ceramic membranes, it relies on specialized equipment, posing challenges for large-scale industrial application. Although electroless nickel plating offers good wear and corrosion resistance, it suffers from poor adhesion when treating fly ash ceramic membranes, and the stability of the plating solution is difficult to control, easily leading to uneven coating and affecting membrane performance. Therefore, developing a highly stable and low-cost fly ash-silane coupling agent composite ceramic membrane is of great significance. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing a powder / coal ash-silane coupling agent composite ceramic membrane, so as to solve the problems existing in the prior art.
[0005] To achieve the above objectives, the present invention is implemented according to the following technical solution: On one hand, the present invention includes the following steps: 1) Fly ash is pretreated to obtain fly ash powder. The pretreatment operation includes sequential multi-stage screening, sedimentation separation, alkaline washing, neutralization washing, acid treatment, drying after neutralization washing again, grinding and ball milling. 2) Take 55g of the fly ash powder and mix it with 80mL of N-methylpyrrolidone (NMP), 2g of polyvinylpyrrolidone (PVP), and 20g of polyethersulfone (PES), and then ball mill for 24h to obtain fly ash slurry with a mass fraction of 60%. 3) The fly ash slurry is transferred to a spinning kettle and wet-spun in a dry-wet spinning device. The extruded ceramic membrane fiber preform is transferred to an exchange solution of anhydrous ethanol and deionized water for phase inversion. After drying at room temperature, a ceramic membrane green body is obtained. 4) The ceramic membrane green body is placed in a muffle furnace and subjected to a high-temperature gradient sintering process. After cooling, it is cleaned and ultrasonically treated to obtain a fly ash ceramic membrane support. 5) The fly ash ceramic membrane support is vertically immersed in the silane coupling agent modified solution. After soaking for 20 minutes, the ceramic membrane support is slowly lifted out of the silane coupling agent modified solution, hung to dry, and then slowly lifted out of the silane coupling agent modified solution for coating. After curing at room temperature, it is treated in an 80℃ oven for 24 hours. After cooling, the fly ash-silane coupling agent composite ceramic membrane is obtained. Furthermore, during the ball milling process, the binder is 10% polyethersulfone by mass, and the dispersant is 1% polyvinylpyrrolidone by mass and 40% N-methylpyrrolidone by mass.
[0006] Furthermore, in the wet spinning process, the wet spinning pressure is 0.2 MPa, the core liquid flow rate is 70 mL / min, and the distance between the spinning head and the exchange liquid is 17 cm.
[0007] Further, the preparation method of the silane coupling agent modified solution includes adding hydrochloric acid to 50 ml of ethanol solution to adjust the pH to 4.5, adding 1.5 g of polyvinylpyrrolidone (PVP), and stirring at 300-500 rpm for 30 min; slowly adding 1 mL of silane coupling agent KH560 to the solution, controlling the dropping rate to 0.5 mL / min; continuing to stir the reaction at 400-600 rpm for 1 h, and allowing it to stand at room temperature for 24 h to obtain 50 mL of silane coupling agent modified solution, wherein the mass-volume ratio of silane coupling agent KH560, anhydrous ethanol, deionized water and polyvinylpyrrolidone is 1 g:41 mL:5 mL:3 g.
[0008] Furthermore, during the high-temperature gradient sintering process, the sintering temperatures are as follows: 0℃~200℃, the sintering rate is 2~5℃ / min, and the degreasing and holding time is 80min; 200℃~600℃, the sintering rate is 2~5℃ / min, and the pre-firing and holding time is 170min; 600℃~1050℃, the sintering rate is 3~5℃ / min, and the final firing and holding time is 122min.
[0009] Furthermore, during cleaning, the sample is immersed in a mixed solution of anhydrous ethanol and deionized water, sonicated for 30 minutes, and then cleaned with deionized water. The volume ratio of anhydrous ethanol to deionized water is 3:7.
[0010] Furthermore, the coating time during the dip coating process is 10 minutes, with a uniform dip speed of 0.5 mm / s. A second dip should be performed after the initial dip drying to improve the bonding strength between the modified layer and the ceramic film support through uniform dip and multiple dips.
[0011] Furthermore, the multi-stage sieving first uses a 2mm aperture sieve for preliminary sieving, and then uses a 0.5mm aperture sieve for fine sieving; the sedimentation separation involves placing fly ash in deionized water, stirring for 10 minutes, and then letting it stand for 20 minutes to separate and remove the supernatant; the alkaline washing treatment involves placing fly ash in a 5wt.% potassium hydroxide solution with a solid-liquid ratio of 1:4 and stirring for 1.5 hours; the acid treatment involves soaking fly ash in a 4wt.% phosphoric acid solution at room temperature with a solid-liquid ratio of 1:3 and stirring for 1 hour; the drying is carried out in an 80℃ oven; the grinding time is 30 minutes; and the ball milling treatment time is 48 hours.
[0012] On the other hand, a fly ash-silane coupling agent composite ceramic membrane prepared by the aforementioned method has an average pore size of 0.34 μm to 1.89 μm and a water flux of 12.6 × 10³ L / m³. 2 / h, with a film thickness of 1mm.
[0013] The beneficial effects of this invention are: This invention relates to a method for preparing a fly ash-silane coupling agent composite ceramic membrane. Compared with the prior art, this invention has the following technical advantages: (1) This invention achieves directional control of hydrophilicity by forming a dense covalent network through hydrolysis and condensation, significantly improving the separation performance of oil-water emulsions, reducing thermal stress, and enhancing the mechanical strength and antifouling ability of ceramic membranes. The use of the dip-coating method ensures uniform distribution and reaction of the silane coupling agent on the ceramic membrane surface, avoiding localized accumulation or incomplete coverage. Multiple dip-coating processes can reduce defects such as pinholes and cracks on the membrane surface, improving the structural integrity of the membrane. (2) This invention uses fly ash as raw material to realize the reuse of solid waste. After the silane molecules are hydrolyzed to generate silanol, they can form stable Si-O-Si or Si-O-Al covalent bonds with the abundant hydroxyl groups (-OH) on the surface of the fly ash ceramic membrane through dehydration condensation reaction, thus achieving precise interfacial chemical bonding. The active functional groups at the end of the molecules can directionally regulate the hydrophilicity / hydrophobicity of the membrane surface, and have high oil rejection rate, high flux and high stability, which significantly improves the filtration performance of the support, reduces the production cost of ceramic membrane, and is suitable for industrial-scale production. Attached Figure Description
[0014] Figure 1 Comparison of particle size distribution of fly ash, the raw material for composite ceramic membranes provided in this invention, after two ball milling processes. Figure 1 a is a particle size distribution diagram of fly ash, the raw material for the composite ceramic membrane provided by the present invention, after 48 hours of initial ball milling; Figure 1 b is the particle size distribution diagram of fly ash, the raw material for the composite ceramic membrane provided by this invention, after secondary ball milling for 24 hours. Figure 2 A comparison chart of oil removal rates before and after modification of the composite ceramic membrane provided by this invention; Figure 3 A comparison chart of water flux before and after modification of the composite ceramic membrane provided by this invention; Figure 4 A comparison diagram of the water contact angle of the ceramic membrane support before and after modification provided by the present invention; Figure 4 a is a water contact angle diagram of the unmodified ceramic membrane support provided by the present invention; Figure 4 b is a water contact angle diagram of the modified ceramic membrane support provided by the present invention; Figure 5 Electron micrographs of fly ash ceramic films in different states; Figure 5 a is an electron microscope image of the surface of the green compact; Figure 5 c is the electron micrograph of the unmodified surface; Figure 5 e is an electron microscope image of the modified surface; Figure 5 b is a partial cross-sectional electron microscope image of the green billet; Figure 5 d is an electron micrograph of the unmodified local cross-section; Figure 5 f is a cross-sectional electron microscope image of the modified section. Detailed Implementation
[0015] The present invention will be further described below through specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention. Example
[0016] Fly ash pretreatment The pretreatment of fly ash should include the following steps: multi-stage sieving (first, use a 2mm sieve to pre-screen the fly ash, then use a 0.5mm sieve for fine screening) → sedimentation separation (place the fly ash in deionized water, stir for 10 minutes, let stand for 20 minutes, separate and remove the supernatant) → alkaline washing treatment (place the fly ash in a 5wt.% potassium hydroxide (KOH) solution (solid-liquid ratio of 1:4), stir for 1.5 hours) → neutralization washing (wash with deionized water until the pH value reaches neutral) → acid treatment (soak the fly ash in a 4wt.% phosphoric acid (H3PO4) solution at room temperature (solid-liquid ratio of 1:3), stir for 1 hour) → deionized water (wash until the pH value is neutral). The washed fly ash is transferred to an 80℃ oven to dry thoroughly, then transferred to a mortar and ground for 30 minutes. After adding deionized water for weighting, it is ball-milled for 48 hours. After drying, the pretreated fly ash is obtained.
[0017] Preparation of ceramic membrane support 55g of pretreated fly ash was mixed with 80mL of N-methylpyrrolidone (NMP), 2g of polyvinylpyrrolidone (PVP), and 20g of polyethersulfone (PES) and transferred to a ball mill jar. After balancing, the mixture was ball milled for 24 hours to obtain a 60% (mass fraction) homogeneous slurry. The slurry was transferred to a spinning kettle and wet-spinned in a dry-wet spinning apparatus (0.2MPa pressure extrusion, core liquid (deionized water) flow rate 70mL / min). The extruded ceramic membrane fiber preform was transferred to an exchange solution of 30%:70% anhydrous ethanol and water (17cm distance between the spinneret and the exchange solution) and allowed to stand for 24 hours. After drying at room temperature, a ceramic membrane green body was obtained. The ceramic membrane green body is then transferred to a muffle furnace and subjected to a high-temperature gradient sintering process. The sintering temperatures are: 0℃~200℃, sintering rate of 2~5℃ / min, holding time of 80min (degreasing); 200℃~600℃, sintering rate of 2~5℃ / min, holding time of 170min (pre-firing); 600℃~1100℃, sintering rate of 3~5℃ / min, holding time of 122min (final firing). After cooling, the fly ash ceramic membrane support is obtained.
[0018] Fly ash-silane coupling agent composite ceramic membrane Measure 41 mL of anhydrous ethanol and 5 mL of deionized water and mix them. Add 0.1 mol / L hydrochloric acid solution to adjust the pH to 4.5. Add 1.5 g of polyvinylpyrrolidone (PVP) and stir for 30 min. Slowly add 2 mL of silane coupling agent (KH560) dropwise to the mixed solution (following the volume ratio of silane coupling agent (KH560): anhydrous ethanol: deionized water: polyvinylpyrrolidone (PVP) = 2:41:4:3). Stir to dissolve for 1 h. After aging, prepare 50 mL of silane coupling agent modified solution. Vertically immerse the fly ash ceramic membrane support in the silane coupling agent modified solution. After soaking for 20 minutes, the ceramic membrane support was slowly lifted from the silane coupling agent modified solution, hung to dry, and then slowly lifted from the silane coupling agent modified solution again. Finally, after aging at room temperature, it was treated in an 80℃ oven for 24 hours and cooled to obtain a fly ash-silane coupling agent composite ceramic membrane.
[0019] Performance testing The composite ceramic membrane prepared in this example was used to filter an oil-water emulsion with a transmembrane pressure difference of 0.3 MPa. The oil concentrations of the raw solution and the permeate were measured using an infrared oil analyzer to determine the oil retention effect of the composite ceramic membrane. The retention rate was calculated using the following formula: R = (1 - C1 / C0) × 100%, where R is the oil retention rate, C1 is the permeate oil concentration, and C0 is the raw solution oil concentration (mg·L⁻¹). The permeation flux was determined using a laboratory-made pressure osmosis device. The permeation flux (J, L·m⁻²·h⁻¹) was calculated using the following formula: Where V is the permeate volume (L) over a certain period of time, A is the effective membrane filtration area (m2), and ∆t is the test time (h).
[0020] Technical results: The water flux of the composite ceramic membrane is 12.21×103L·m-2·h-1, and the oil rejection rate reaches 96.1%, which is 55.4% higher than that of the unmodified fly ash ceramic membrane support. Example
[0021] Fly ash pretreatment The pretreatment of fly ash should include the following steps: multi-stage sieving (first, use a 2mm sieve to pre-screen the fly ash, then use a 0.5mm sieve for fine screening) → sedimentation separation (place the fly ash in deionized water, stir for 10 minutes, let stand for 20 minutes, separate and remove the supernatant) → alkaline washing treatment (place the fly ash in a 5wt.% potassium hydroxide (KOH) solution (solid-liquid ratio of 1:4), stir for 1.5 hours) → neutralization washing (wash with deionized water until the pH value reaches neutral) → acid treatment (soak the fly ash in a 4wt.% phosphoric acid (H3PO4) solution at room temperature (solid-liquid ratio of 1:3), stir for 1 hour) → deionized water (wash until the pH value is neutral). The washed fly ash is transferred to an 80℃ oven to dry thoroughly, then transferred to a mortar and ground for 30 minutes. After adding deionized water for weighting, it is ball-milled for 48 hours. After drying, the pretreated fly ash is obtained.
[0022] Preparation of ceramic membrane support 55g of pretreated fly ash was mixed with 80mL of N-methylpyrrolidone (NMP), 2g of polyvinylpyrrolidone (PVP), and 20g of polyethersulfone (PES) and transferred to a ball mill jar. After balancing, the mixture was ball milled for 24 hours to obtain a 60% (mass fraction) homogeneous slurry. The slurry was transferred to a spinning kettle and wet-spinned in a dry-wet spinning apparatus (0.2MPa pressure extrusion, core liquid (deionized water) flow rate 70mL / min). The extruded ceramic membrane fiber preform was transferred to an exchange solution of 30%:70% anhydrous ethanol and water (17cm distance between the spinneret and the exchange solution) and allowed to stand for 24 hours. After drying at room temperature, a ceramic membrane green body was obtained. The ceramic membrane green body is then transferred to a muffle furnace and subjected to a high-temperature gradient sintering process. The sintering temperatures are: 0℃~200℃, sintering rate of 2~5℃ / min, holding time of 80min (degreasing); 200℃~600℃, sintering rate of 2~5℃ / min, holding time of 170min (pre-firing); 600℃~1100℃, sintering rate of 3~5℃ / min, holding time of 122min (final firing). After cooling, the fly ash ceramic membrane support is obtained.
[0023] Fly ash-silane coupling agent composite ceramic membrane Measure 41 mL of anhydrous ethanol and 5 mL of deionized water and mix them. Add 0.1 mol / L hydrochloric acid solution to adjust the pH to 4.5. Add 1.5 g of polyvinylpyrrolidone (PVP) and stir for 30 min. Slowly add 1 mL of silane coupling agent (KH560) dropwise to the mixed solution (following the volume ratio of silane coupling agent (KH560): anhydrous ethanol: deionized water: polyvinylpyrrolidone (PVP) = 1:41:5:3). After ultrasonic treatment for 30 min, stir to dissolve for 2 h. After aging, prepare 50 mL of silane coupling agent modified solution. Vertically immerse the fly ash ceramic membrane support in the silane coupling agent modified solution. After soaking for 20 minutes, the ceramic membrane support was slowly lifted from the silane coupling agent modified solution, hung to dry, and then slowly lifted from the silane coupling agent modified solution again. Finally, after aging at room temperature, it was treated in an 80℃ oven for 24 hours and cooled to obtain a fly ash-silane coupling agent composite ceramic membrane.
[0024] The composite ceramic membrane prepared in this example was used to filter an oil-water emulsion with a transmembrane pressure difference of 0.3 MPa. The oil concentrations of the raw solution and the permeate were measured using an infrared oil analyzer to determine the oil retention effect of the composite ceramic membrane. The oil retention rate was calculated using the following formula: R = (1 - C1 / C0) × 100%, where R is the oil retention rate, C1 is the permeate oil concentration, and C0 is the raw solution oil concentration (mg·L⁻¹). The permeation flux (J, L·m⁻²·h⁻¹) was measured using a laboratory-made pressure osmosis device. The calculation formula is as follows:
[0025] Where V is the volume of permeate (L) within a certain time, A is the effective membrane filtration area (m2), ∆t is the test time (h), the water flux of the composite ceramic membrane is 13.6×103L·m-2·h-1, and the oil rejection rate reaches 95.6%, which is 54.9% higher than that of the unmodified fly ash ceramic membrane support.
[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation, characterized in that, 1) Fly ash is pretreated to obtain fly ash powder. The pretreatment operation includes sequential multi-stage screening, sedimentation separation, alkaline washing, neutralization washing, acid treatment, drying after neutralization washing again, grinding and ball milling. 2) Take 55g of the fly ash powder and mix it with 80mL of N-methylpyrrolidone (NMP), 2g of polyvinylpyrrolidone (PVP), and 20g of polyethersulfone (PES), and then ball mill for 24h to obtain fly ash slurry with a mass fraction of 60%. 3) The fly ash slurry is transferred to a spinning kettle and wet-spun in a dry-wet spinning device. The extruded ceramic membrane fiber preform is transferred to an exchange solution of anhydrous ethanol and deionized water for phase inversion. After drying at room temperature, a ceramic membrane green body is obtained. 4) The ceramic membrane green body is placed in a muffle furnace and subjected to a high-temperature gradient sintering process. After cooling, it is cleaned and ultrasonically treated to obtain a fly ash ceramic membrane support. 5) The fly ash ceramic membrane support is vertically immersed in the silane coupling agent modified solution. After soaking for 20 minutes, the ceramic membrane support is slowly lifted out of the silane coupling agent modified solution, hung to dry, and then slowly lifted out of the silane coupling agent modified solution for coating. After curing at room temperature, it is treated in an 80℃ oven for 24 hours. After cooling, the fly ash-silane coupling agent composite ceramic membrane is obtained. The preparation method of the silane coupling agent modified solution includes adjusting the pH to 4.5 by adding hydrochloric acid to 50 mL of ethanol solution, adding 1.5 g of polyvinylpyrrolidone (PVP), and stirring at 300-500 rpm for 30 min; slowly adding 1 mL of silane coupling agent KH560 dropwise to the solution, controlling the dropping rate to 0.5 mL / min; continuing to stir the reaction at 400-600 rpm for 1 h, and allowing it to stand at room temperature for 24 h to obtain 50 mL of silane coupling agent modified solution. The mass-volume ratio of silane coupling agent KH560, anhydrous ethanol, deionized water and polyvinylpyrrolidone is 1 g:41 mL:5 mL:3 g.
2. The method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to claim 1, characterized in that, During the ball milling process, the binder is 10% polyethersulfone by mass, and the dispersant is 1% polyvinylpyrrolidone by mass and 40% N-methylpyrrolidone by mass.
3. The method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to claim 1, characterized in that, In wet spinning, the wet spinning pressure is 0.2 MPa, the core liquid flow rate is 70 mL / min, and the distance between the spinning head and the exchange liquid is 17 cm.
4. The method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to claim 1, characterized in that, During the high-temperature gradient sintering process, the sintering temperatures are as follows: 0℃~200℃, the sintering rate is 2~5℃ / min, and the degreasing and holding time is 80min; 200℃~600℃, the sintering rate is 2~5℃ / min, and the pre-firing and holding time is 170min; 600℃~1050℃, the sintering rate is 3~5℃ / min, and the final firing and holding time is 122min.
5. The method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to claim 1, characterized in that, During cleaning, the sample is immersed in a mixed solution of anhydrous ethanol and deionized water, sonicated for 30 minutes, and then rinsed with deionized water. The volume ratio of anhydrous ethanol to deionized water is 3:
7.
6. The method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to claim 1, characterized in that, The coating time during the dip coating process is 10 minutes, with a uniform dip speed of 0.5 mm / s. A second dip should be performed after the initial dip drying to improve the bonding strength between the modified layer and the ceramic film support through uniform dip and multiple dips.
7. The method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to claim 1, characterized in that, The multi-stage sieving process first uses a 2mm aperture sieve for preliminary sieving, followed by a 0.5mm aperture sieve for fine sieving; the sedimentation separation involves placing fly ash in deionized water, stirring for 10 minutes, and then letting it stand for 20 minutes to separate and remove the supernatant; the alkaline washing treatment involves placing fly ash in a 5wt.% potassium hydroxide solution with a solid-liquid ratio of 1:4 and stirring for 1.5 hours; the acid treatment involves soaking fly ash in a 4wt.% phosphoric acid solution at room temperature with a solid-liquid ratio of 1:3 and stirring for 1 hour; the drying is carried out in an 80℃ oven; the grinding time is 30 minutes; and the ball milling treatment time is 48 hours.
8. A fly ash-silane coupling agent composite ceramic membrane prepared by the method for preparing a fly ash-silane coupling agent composite ceramic membrane for oil-water separation according to any one of claims 1-7, characterized in that, The fly ash-silane coupling agent composite ceramic membrane has an average pore size of 0.34 μm to 1.89 μm and a water flux of 12.6 × 10³ L / m³. 2 / h, with a film thickness of 1mm.