Preparation method of high-alumina fly ash-high clay composite ceramic membrane

Abstract

This invention discloses a method for preparing a high-alumina fly ash-kaolin composite ceramic membrane. The method utilizes high-alumina fly ash to prepare a support, and then sprays a kaolin filter layer onto the support. Specifically, alumina fly ash, a pore-forming agent, and a first binder are mixed, and deionized water is added to obtain a slurry. This slurry is then sintered at 1250–1300℃ for 1–2.5 hours. A coating solution containing kaolin, a second binder, a dispersant, and deionized water is then sprayed onto the support, and sintered at 950–1100℃, ultimately yielding a water flux of 1165–4080 L / h·m. 2 A high-alumina fly ash-kaolin composite ceramic membrane with an average pore size of 127–401 nm (bar). This invention effectively improves the filtration accuracy of ceramic membranes while reducing their cost.

Description

Technical Field

[0001] This invention relates to the field of ceramic membrane technology, specifically to a method for preparing a high-alumina fly ash-kaolin composite ceramic membrane. Background Technology

[0002] Membrane separation technology has received increasing attention in the water treatment field compared to traditional separation methods. Currently, membrane separation is mainly classified into inorganic membranes and organic membranes based on materials. Organic membranes are limited in the complex industrial water treatment field due to factors such as COD and pH. In contrast, inorganic ceramic membranes not only have high chemical stability but also possess advantages such as high temperature resistance, corrosion resistance, and high mechanical strength, leading to their widespread application in recent years. Common raw materials for ceramic membrane production include Al2O3, ZrO2, and TiO2, but their high price and high sintering temperature keep the cost of ceramic membranes high. Fly ash, a solid waste generated during coal combustion, contains a large amount of alumina and silicon dioxide, which can form mullite with good mechanical strength at high temperatures, making it an inexpensive material for preparing ceramic membranes. Applying it to the ceramic membrane field can not only reduce the manufacturing cost of ceramic membranes but also turn fly ash into a valuable resource.

[0003] Chinese patent CN116375453B discloses a method for preparing a high-alumina fly ash ceramic support. The resulting low-cost support possesses catalytic self-cleaning properties, but its water flux is low (only 1800–4100 L / h·m). 2 The water flux will be further reduced if a composite filter layer is added (MPa). Chinese patent CN109173748A discloses a method for preparing a fly ash ceramic membrane, using fly ash of different particle sizes as raw materials to prepare an asymmetric ceramic membrane with a support, transition layer, and separation layer. Multiple coating processes make the preparation process cumbersome, and the prepared separation membrane has a large pore size (1-2.2 μm) and low filtration accuracy. Chinese patent CN109126482B discloses a method for preparing a fly ash-alumina double-layer composite microfiltration ceramic membrane, using an impregnation method to coat an alumina microfiltration membrane onto a fly ash carrier, obtaining a composite ceramic membrane with a pore size of 0.1-0.3 μm, improving separation accuracy; however, the addition of alumina significantly increases the cost. To address the problems of high production cost, low water flux, and large filter layer pore size, a low-cost, high-water-flux, and small-pore-size high-alumina fly ash-kaolin composite ceramic membrane has been invented. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of current technologies by providing a method for preparing a high-alumina fly ash-kaolin composite ceramic membrane. This method uses high-alumina fly ash as a raw material to prepare the support structure. By extending the heat preservation time, the porosity and water flux of the support structure are increased while the compressive strength still meets technical requirements. Simultaneously, inexpensive kaolin is used as a raw material to prepare the filter layer, reducing the cumbersome coating process with a single-stage coating. This invention improves the filtration accuracy of the ceramic membrane while reducing costs.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a high-alumina fly ash-kaolin composite ceramic membrane, the method comprising the following steps:

[0007] (1) Preparation of the support

[0008] High-alumina fly ash, pore-forming agent, and first binder are dry-mixed for 1-2 hours to obtain a mixture. Then, 40-60% of deionized water by mass of the mixture is added, and the mixture is stirred and kneaded at a constant temperature of 90-100℃ for 1-2 hours to obtain a clay material. After aging the clay material at room temperature for 12-24 hours, 2.45-2.55g of the clay material is weighed and placed into a mold, and extruded under a pressure of 10-12MPa. The green body is sintered at 1250-1300℃ with a heating rate of 5-10℃ / min and a holding time of 1-2.5 hours to obtain a ceramic support with an average pore size of 0.74-1.26μm.

[0009] The mass percentages of each component in the mixture are as follows: high-alumina fly ash 89.3-96.3%, pore-forming agent 3.5-8.5%, and first binder 0.2-2.2%.

[0010] The moisture content of the mud is 16%–18%;

[0011] The high-alumina fly ash is high-alumina fly ash that has passed through a 500-2500 mesh sieve, resulting in particles with a particle size concentrated in the range of 0.71 to 33.4 μm; the pore-forming agent is starch, and the binder is methylcellulose;

[0012] (2) Preparation of coating solution

[0013] Kaolin, dispersant and deionized water are mixed in a ball mill at a speed of 500-700 r / min for 1-6 h; then a second binder is added and the mixture is further mixed in a ball mill at a speed of 100-200 r / min for 30-60 min to obtain the coating solution.

[0014] The coating solution contains 5-20 wt% kaolin, 0.2-2 wt% secondary binder, 0.3-2.7 wt% dispersant, and the remainder is water; the dispersant is polyethylene glycol, and the secondary binder is polyvinyl alcohol.

[0015] (3) Preparation of filter layer

[0016] The coating solution was sprayed onto the surface of the support by spraying, and after drying for 12-24 hours, it was sintered to obtain a high-alumina fly ash-kaolin composite ceramic membrane with an average pore size of 127-401 nm.

[0017] The drying temperature is 25℃~100℃; the sintering temperature is 950~1100℃; the holding time is 0~3h; and the heating rate is 2~8℃ / min.

[0018] Spray the coating on the support surface for 20–80 seconds for every 314–490 square millimeters, with a spray flow rate of 0.6–1.5 mL / min.

[0019] The composition and mass fraction of the high-alumina fly ash include:

[0020] Al2O3: 60% to 65%, SiO2: 20% to 25%, CaO: 3% to 5%, Fe2O3: 2% to 5%, TiO2: 2% to 5%.

[0021] The composition and mass fraction of the kaolin mentioned include:

[0022] Al2O3: 45% to 50%, SiO2: 50% to 55%, Fe2O3: 0.5% to 1%, TiO2: 1 to 2%.

[0023] Furthermore, the application of the method for preparing high-alumina fly ash-kaolin composite ceramic membranes includes the following steps:

[0024] Industrial wastewater with a particle concentration of 3–5 g / L was filtered using a composite ceramic membrane at a pressure of 0.1–0.2 MPa.

[0025] The particle size range is 44–500 nm.

[0026] The essential features of this invention are:

[0027] (1) In the current technology (patent CN116375453B), increasing the sintering temperature can improve the compressive strength of the support, but it will significantly reduce its porosity and water flux. The present invention does not increase the sintering temperature, but extends the holding time, which improves the porosity and water flux of the support while ensuring that its compressive strength meets the technical requirements.

[0028] (2) Kaolin is selected as the raw material. Its low cost and hydrophilic properties are utilized to prepare a low-cost, high-performance composite ceramic membrane, which improves the filtration accuracy while reducing the cost of ceramic membrane preparation.

[0029] (3) The filter is prepared by spraying, which effectively avoids the transmission of defects on the support. At the same time, the filter layer is micro-permeable into the support, which ensures the bonding between the filter layer and the support without clogging the pores.

[0030] The beneficial effects of this invention are:

[0031] (1) A ceramic support was prepared using high-alumina fly ash, an industrial waste, as raw material. Its porosity was 35–43%, the average pore size was 0.74–1.26 μm, the flexural strength was 16–32 MPa, and the water flux was 7941–14716 L / h·m. 2 • bar. Compared to the support structure in patent CN116375453B, which has a bending strength of 7 MPa to 28 MPa and a water flow rate of 1800 to 4100 L / h·m, this is significantly different. 2 • MPa, representing a significant improvement.

[0032] (2) Using inexpensive kaolin as the filter layer material, a high-alumina fly ash-kaolin composite ceramic membrane was prepared, with a water flux of 1165~4080 L / h·m. 2 The average pore size is 127–401 nm. It achieves a 99.2–99.6% rejection rate for industrial wastewater with an average particle size of 200 nm. This is significantly higher than the fly ash-alumina bilayer composite ceramic membrane in patent CN109126482B, which has an average pore size of 100–300 nm and a water flux of 400–2500 L / h·m. 2 The present invention has a high water flux and uses inexpensive raw materials, resulting in low preparation costs.

[0033] (3) The filter layer is prepared by spraying, which effectively avoids the transmission of defects on the support. At the same time, the filter layer micro-penetrates into the support, ensuring the interfacial bonding strength between the filter layer and the support. After multiple forward and reverse rinsing, the pore size change of the composite membrane is <5%. Attached Figure Description

[0034] Figure 1 Images of the support structure and composite ceramic membrane;

[0035] Figure 2 The images show SEM images of the surface of the support under different heat preservation times as described in Examples 1-4.

[0036] Figure 3 The XRD patterns of the supports under different heat preservation times described in Examples 1-4 are shown below.

[0037] Figure 4This illustrates the effect of insulation time on the bending strength of the support structure as described in Examples 1-4.

[0038] Figure 5 The images show surface SEM images of the composite ceramic films at different sintering temperatures described in Examples 9 and 15-17.

[0039] Figure 6 The effect of spraying time on the water flux of composite ceramic membranes as described in Examples 9 and 18-20;

[0040] Figure 7 This is a schematic diagram of a water flux testing device. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should be protected by this invention.

[0042] The high-alumina fly ash and kaolin involved in this invention are known materials. The composition and mass fraction of the high-alumina fly ash are as follows: Al2O3: 63.4%, SiO2: 24.8%, CaO: 3.68%, Fe2O3: 2.61%, TiO2: 2.53%. After passing through a 500-2500 mesh sieve, high-alumina fly ash particles with a particle size concentrated in the range of 0.71 to 33.4 μm are obtained.

[0043] The composition and mass fraction of kaolin are as follows: Al2O3: 45.8%, SiO2: 50.7%, Fe2O3: 0.7%, TiO2: 1.31%, but it is not limited to these.

[0044] Example 1

[0045] This embodiment provides a method for preparing ceramic supports from high-alumina fly ash, the method comprising the following steps:

[0046] The materials were added according to the following mass ratio: 93.3% fly ash, 6% starch (pore-forming agent), and 0.7% methylcellulose (binder). The materials were dry-mixed at room temperature for 2 hours. Distilled water (50% by mass of the mixture) was added to the uniformly mixed materials, and the mixture was stirred at 100℃ for 1.5 hours to refine the clay. The final moisture content (by mass) of the clay was controlled at 17%. 2.5g of clay was weighed and placed into a mold, then extruded at 10MPa. The green body was aged at room temperature for 12 hours and then sintered in a muffle furnace. The heat treatment process for the support was as follows: heating from room temperature to 300℃ at 10℃ / min and holding for 1.5 hours; heating from 300℃ to 650℃ at 10℃ / min and holding for 1.5 hours; heating from 650℃ to 1300℃ at 5℃ / min and holding for 1.5 hours. The fabricated support had an average pore size of 918 nm, a porosity of 40.54%, a flexural strength of 24.9 MPa, and a water flux of 9561.3 L / h·m. 2 ·bar.

[0047] Examples 2-8

[0048] The other steps are the same as in Example 1, and the differences are shown in Table 1.

[0049] Table 1

[0050] Example No. Pore-forming agent addition amount (%) Adhesive addition amount (%) Insulation time (h) 2 6 0.7 1 3 6 0.7 2 4 6 0.7 2.5 5 8.5 0.7 1.5 6 3.5 0.7 1.5 7 3.5 1.2 1.5 8 3.5 2.2 1.5

[0051] from Figure 2 As the heat preservation time increases, the mullite in the support gradually grows, from a vague cluster to a slender needle.

[0052] from Figure 3 As can be seen, the intensity of the diffraction peak of mullite in the support powder gradually increases with the increase of heat preservation time.

[0053] from Figure 4 As can be seen, with the increase of heat preservation time, the compressive strength of the support increases from 23MPa to 32MPa. This is consistent with the gradual growth of mullite and the increase of mullite diffraction peak intensity mentioned earlier. Increasing the heat preservation time can effectively improve the compressive strength of the support.

[0054] Example 9

[0055] This embodiment provides a method for preparing a high-alumina fly ash-kaolin composite ceramic membrane, the method comprising the following steps;

[0056] Kaolin, polyethylene glycol (PEG) dispersant, and deionized water were ball-milled at 600 rpm for 3 hours, maintaining a total mass of 90 g. Then, polyvinyl alcohol (PVA) binder was added, maintaining a total mass of 180 g. The mixture was further mixed at 200 rpm for 30 minutes to obtain the coating solution. The mass ratio of kaolin, dispersant, and binder was 5%:2.5%:1.5%. The coating solution was sprayed onto the surface of a 22 mm diameter support prepared in Example 1 using a spraying method. The spraying flow rate was 0.9 mL / min, and the spraying time was 40 s. The heat treatment process for the composite ceramic membrane was as follows: the green body was dried at 40 °C for 12 hours. The temperature was then increased from room temperature to 1000 °C at a rate of 2 °C / min and held for 2 hours. The resulting composite ceramic membrane had a thickness of 7.39 μm, an average pore size of 135 nm, and a water flux of 1990.6 L / h·m. 2 ·bar.

[0057] The porosity of the support was tested according to the "Test Method for Apparent Porosity of Porous Ceramics (GB / T1966-1996)" and the flexural strength of the support was tested according to the "Test Method for Flexural Strength of Porous Ceramics (GB / T1965-1996)". The average pore size of the support and the composite ceramic membrane was measured using a BSD-PB-1526 membrane pore size analyzer from Beijing Best Instrument Technology Co., Ltd., and the water flux was measured using a self-made laboratory device. Figure 7 As shown.

[0058] The high-alumina fly ash-kaolin composite ceramic membrane prepared in this embodiment was used to filter industrial wastewater. The transmembrane pressure difference was 0.1 MPa. By testing the turbidity of the feed liquid and the permeate, the composite ceramic membrane achieved a rejection rate of 99.6% for industrial wastewater with an average particle size of 200 nm.

[0059] The turbidity of the solution was measured using the LH-NTU2M portable turbidity meter from Beijing Lianhua Yongxing Technology Development Co., Ltd.

[0060] Table 2 compares the performance of the composite ceramic membrane prepared in this embodiment with that of the alumina ceramic membrane reported in the literature (where the average pore size is in nm and the water flux is in L / h·m). 2 • bar, sintering temperature is ℃). It can be seen that the self-made composite ceramic membrane effectively reduces costs while maintaining excellent performance.

[0061] Table 2

[0062] membrane Average aperture water flux Sintering temperature Refs. <![CDATA[Al2O3]]> 75-93 1450-1730 1300 Ma(J.Water Process.Eng,2024,58:104739) <![CDATA[Al2O3]]> 100 460 - Yang(Sep.Purif.Technol.2022,300:121862) <![CDATA[Al2O3]]> 120 850 1350 Qin(Ceram Int,2020,46(9):13189-13197) <![CDATA[Al2O3]]> 260 1468±81 1300 Qin (RSC Advances, 2020, 10) <![CDATA[Al2O3]]> 130 550 1200 Song(RSC Advances,2017,43(13):10502-10507) Kaolin 135 1990.6 1000 Example 9

[0063] Examples 10-25

[0064] The other steps are the same as in Example 9, with the differences shown in Tables 3 and 4.

[0065] Table 3

[0066] Example No. Kaolin addition amount (%) Adhesive addition amount (%) Dispersant addition amount (%) 10 10 1.5 2.5 11 20 1.5 2.5 12 5 0.2 0.3 13 5 1 1 14 5 2 2.7

[0067] Table 4

[0068] Example No. Spraying time (s) Sintering temperature (°C) Insulation time (h) Heating rate (°C / min) 15 40 950 2 2 16 40 1050 2 2 17 40 1100 2 2 18 20 1000 2 2 19 60 1000 2 2 20 80 1000 2 2 21 40 1000 0 2 22 40 1000 1 2 23 40 1000 3 2 24 40 1000 2 4 25 40 1000 2 8

[0069] from Figure 5 As the sintering temperature increases, the interaction between kaolin particles intensifies, leading to particle migration and bonding, forming sintering necks. With further increases in temperature, the membrane surface becomes more compact as the sintering necks grow, and the membrane pores gradually enlarge.

[0070] from Figure 6 As can be seen, the membrane water flux gradually decreases with increasing spraying time, from 4080 L / h·m 2 • bar drops to 1165 L / h·m 2 ·bar.

[0071] The above are merely a few specific embodiments of the present invention. The present invention is not limited to the above embodiments. Any modifications, substitutions, improvements, etc., made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

[0072] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a high-alumina fly ash-kaolin composite ceramic membrane, characterized in that, The method includes the following steps: (1) Preparation of the support High-alumina fly ash, pore-forming agent, and first binder are dry-mixed for 1-2 hours to obtain a mixture. Then, 40-60% of deionized water by mass of the mixture is added, and the mixture is stirred and kneaded at a constant temperature of 90-100℃ for 1-2 hours to obtain a clay material. After aging the clay material at room temperature for 12-24 hours, 2.45-2.55g of the clay material is weighed and placed into a mold, and extruded under a pressure of 10-12MPa. The green body is sintered at 1250-1300℃ with a heating rate of 5-10℃ / min and a holding time of 1-2.5 hours to finally obtain a ceramic support with an average pore size of 0.74-1.26μm. The mass percentages of each component in the mixture are as follows: high-alumina fly ash 89.3%~96.3%, pore-forming agent 3.5%~8.5%, and first binder 0.2%~2.2%. The moisture content of the clay is 16%~18%; the pore-forming agent is starch, and the first binder is methylcellulose; (2) Preparation of coating solution Kaolin, dispersant and deionized water are mixed in a ball mill at a speed of 500-700 r / min for 1-6 h; then a second binder is added and the mixture is further mixed in a ball mill at a speed of 100-200 r / min for 30-60 min to obtain the coating solution. The coating solution contains 5-20 wt% kaolin, 0.2-2 wt% secondary binder, 0.3-2.7 wt% dispersant, and the remainder is water; the dispersant is polyethylene glycol, and the secondary binder is polyvinyl alcohol. (3) Preparation of filter layer The coating solution was sprayed onto the surface of the support by spraying, and after drying for 12-24 hours, it was sintered to obtain a high-alumina fly ash-kaolin composite ceramic membrane with an average pore size of 127-401 nm. The drying temperature is 25℃~100℃; the sintering temperature is 950~1100℃; the holding time is 0~3h; and the heating rate is 2~8℃ / min. The composition and mass fraction of the high-alumina fly ash include: Al2O3: 60%~65%, SiO2: 20%~25%, CaO: 3%~5%, Fe2O3: 2%~5%, TiO2: 2%~5%; The composition and mass fraction of the kaolin mentioned include: Al2O3: 45%~50%, SiO2: 50%~55%, Fe2O3: 0.5%~1%, TiO2: 1~2%.

2. The preparation method of the high-alumina fly ash-kaolin composite ceramic membrane as described in claim 1, characterized in that, High-alumina fly ash is high-alumina fly ash that passes through a 500-2500 mesh sieve, resulting in particles with a particle size concentrated in the range of 0.71~33.4μm.

3. The preparation method of the high-alumina fly ash-kaolin composite ceramic membrane as described in claim 1, characterized in that, Spray the coating on the support surface for 20-80 seconds for every 314-490 square millimeters, with a spray flow rate of 0.6-1.5 mL / min.

4. The application of the high-alumina fly ash-kaolin composite ceramic membrane prepared by the method described in claim 1, characterized in that, Includes the following steps: Industrial wastewater with a particle concentration of 3~5 g / L was filtered using a composite ceramic membrane at a pressure of 0.1~0.2 MPa. The particle size range is 44~500nm.

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