Separation membrane layer slurry preparation process, ceramic membrane preparation process and ceramic membrane
By using powder self-assembly technology to form particle aggregates, the problems of uneven pore size distribution and high cost in ceramic membrane preparation are solved, realizing the preparation of high-precision, high-stability and high-throughput ceramic membranes, forming a mirror-smooth separation membrane layer.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-04-07
AI Technical Summary
In existing ceramic membrane preparation processes, the pore size distribution of the separation membrane layer is uneven, resulting in an inability to simultaneously achieve high flux and filtration accuracy. Furthermore, the main raw materials have strict requirements, are costly, and are prone to defects during the coating process.
By employing powder self-assembly technology, the ratio of main raw materials, suspending agent and sodium tripolyphosphate is adjusted through ball milling to form particle aggregates, control particle size distribution, reduce the requirements for main raw materials, and balance high precision, high stability and high throughput.
This achieves uniform pore size distribution in the separation membrane layer, reduces costs, improves product stability and filtration accuracy, and forms a mirror-smooth separation membrane layer.
Smart Images
Figure CN121797113A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ceramic membrane technology, and in particular to a process for preparing a separation membrane slurry, a process for preparing a ceramic membrane, and a ceramic membrane. Background Technology
[0002] Currently, most commercially available flat-plate ceramic membranes are obtained using solid-state sintering processes. The pore size and morphology of the separation membrane layer in flat-plate ceramic membranes are primarily controlled by the main raw materials constituting the separation membrane layer (such as alumina, zirconium oxide, silicon carbide, etc.). That is, to obtain a separation membrane layer with high throughput and uniform pore size distribution, it is necessary to use raw materials with large particle size, small particle size distribution range, and good powder morphology. However, this also leads to defects: (1) The main raw materials have strict requirements, resulting in high costs. Furthermore, any fluctuation in the main raw materials may cause changes in the performance of the separation membrane, making it difficult to standardize the process parameters during production and to stabilize the product performance. (2) Based on the existing ceramic membrane preparation process, to obtain a large flux, the pore size of the separation membrane layer must be increased. However, increasing the pore size of the separation membrane layer means a decrease in filtration accuracy. Therefore, flux and filtration accuracy cannot be achieved simultaneously. (3) In the existing ceramic film preparation process, after the separation film slurry is coated, the drying speed is too fast due to the capillary effect, which can easily lead to the amplification of defects during the coating process, the retention of defects on the substrate surface, and the unevenness of the film surface. Summary of the Invention
[0003] To address the problems existing in the prior art, this invention provides a process for preparing a separation membrane slurry, a process for preparing a ceramic membrane, and a ceramic membrane. This reduces the requirements and cost of the main raw materials for the separation membrane, while taking into account the advantages of high precision, high stability, small pore size, and large throughput. The sintered separation membrane has a near-mirror-smooth finish.
[0004] The technical solution adopted in this invention is: A process for preparing a separation membrane slurry based on powder self-assembly technology involves weighing the main raw materials, suspending agent, sodium tripolyphosphate, and water according to a specified ratio, or weighing the main raw materials, sintering aid, suspending agent, sodium tripolyphosphate, and water according to a specified ratio, and then ball milling the mixture while maintaining the ball milling temperature at 40~60℃. During the ball milling process, the main raw materials are first dispersed and then self-assembled and polymerized into particle aggregates. After the ball milling is completed, the separation membrane slurry is obtained.
[0005] Furthermore, the amount of sintering aid is 14-18 wt% of the weight of the main raw material, the amount of suspending agent is 0.4-2.5 wt% of the weight of the main raw material, the amount of sodium tripolyphosphate is 0.4-2.5 wt% of the weight of the main raw material, and the amount of water is 100-400 wt% of the weight of the main raw material.
[0006] Furthermore, the suspending agent is one or more of the following: polyvinyl alcohol, methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, sodium polyacrylate, and polyacrylamide; And / or, the main raw materials are alumina, zirconium oxide or silicon carbide; And / or, the sintering aid is silica sol, alumina sol, or water glass.
[0007] Furthermore, the weight ratio of the main raw material to the grinding balls during ball milling is 1:4~5.
[0008] Furthermore, the grinding balls used in ball milling are one or more of alumina grinding balls, zirconia grinding balls, silicon carbide grinding balls, and silicon nitride grinding balls, including grinding balls with a diameter of 8-10 mm at 37.5-62.5 wt%, grinding balls with a diameter of 4-6 mm at 6.25-31.25 wt%, and grinding balls with a diameter of 1-3 mm at 37.5-62.5 wt%.
[0009] Furthermore, the ball milling time is >10~20 min; And / or, the ball mill speed is 300~700 rpm.
[0010] Based on the same inventive concept, the present invention also provides a ceramic membrane preparation process, comprising the following steps: Step S1: Prepare the separation membrane slurry using the separation membrane slurry preparation process based on powder self-assembly technology as described above; Step S2: The separation membrane slurry is applied to the ceramic membrane support by spraying, brushing, coating or immersion, dried and sintered to obtain the ceramic membrane.
[0011] Furthermore, in step S2, the drying temperature is 90~120℃ and the drying time is 0.5~2h.
[0012] Furthermore, in step S2, during sintering, the temperature is increased to 1100-1500℃ at a rate of 1-10℃ / min and held for 1-5 hours.
[0013] Based on the same inventive concept, the present invention also provides a ceramic membrane, prepared by the ceramic membrane preparation process described above. The beneficial effects of this invention are: This invention provides a process for preparing a separation membrane slurry, a ceramic membrane preparation process, and a ceramic membrane. In the separation membrane slurry preparation process, sodium tripolyphosphate, a suspending agent, and the main raw material, or sodium tripolyphosphate, a suspending agent, a sintering aid, and the main raw material, work together. During ball milling, the main raw material is first dispersed, reducing its particle size. Then, it spontaneously and orderly assembles and polymerizes, with larger particles as the core, and other smaller particles forming uniformly sized aggregates with similar internal structures. The particle size of these aggregates increases with ball milling time. Ball milling is stopped when the preset size requirement is reached. The resulting separation membrane slurry is stable and does not easily settle. In this invention, the particle size and micromorphology of the main raw material particles are modified to a certain extent after ball milling, for example, changing from angular to near-spherical, with smaller particle size and a more uniform particle size distribution. Therefore, the requirements for the main raw material are greatly reduced, significantly lowering costs. Meanwhile, in this invention, only the size of the particle aggregates formed by the self-assembly technology of powder needs to be controlled. Even if there is a large difference in the initial particle size of the main raw material used as the separation membrane layer (i.e., the initial particle size distribution range of the powder is wide), the pore size of the separation membrane layer can still be kept within a very small error range, which helps to reduce the stringency of the preparation process. Furthermore, when using the same main raw material, compared with the traditional ceramic membrane preparation process, using particle aggregates formed by the self-assembly technology of powder as the final composition of the separation membrane slurry can reduce the pore size of the separation membrane layer by one-third, resulting in a smaller pore size distribution range and a very small bubble point pore size, thus achieving higher filtration accuracy. However, it can still maintain the high flux of the separation membrane layer with large pore size under the traditional ceramic membrane preparation process, that is, it takes into account the advantages of high precision, high stability, small pore size, and high flux. Finally, under this ceramic membrane preparation process system, the formula structure is simple, the process flow is stable, and the product can maintain high stability. After the separation membrane slurry is coated, a self-leveling phenomenon will occur on the surface of the ceramic membrane support in a semi-liquid state (lasting for 1~2 seconds). After sintering, a smooth glaze layer with a thickness of about 1μm will be formed on the surface, and the sintered separation membrane layer approaches a mirror smooth effect. Attached Figure Description
[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0015] Figure 1 The curve shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 1.
[0016] Figure 2 This is an initial microscopic photograph of the alumina powder in Example 1.
[0017] Figure 3 This is a photograph of the slurry separated from the membrane layer after ball milling in Example 1, after which it has been left to stand for 24 hours.
[0018] Figure 4 The curve shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 2.
[0019] Figure 5 The curve shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 3.
[0020] Figure 6 This is a microscopic diagram of the slurry separated from the film layer after grinding in Example 3.
[0021] Figure 7 This is a photograph of the separated film slurry after grinding in Example 3, after which it was left to stand for 24 hours.
[0022] Figure 8 The curve shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 4.
[0023] Figure 9 This is a photograph of the slurry separated from the membrane layer after ball milling in Example 4, after which it has been left to stand for 24 hours.
[0024] Figure 10 This is a microscopic photograph of the slurry separated from the membrane layer after ball milling in Example 4.
[0025] Figure 11 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 5 is shown.
[0026] Figure 12 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 6 is shown.
[0027] Figure 13 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 7 is shown.
[0028] Figure 14 This is an initial microscopic photograph of alumina powder.
[0029] Figure 15 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 8 is shown.
[0030] Figure 16The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 9 is shown.
[0031] Figure 17 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 10 is shown.
[0032] Figure 18 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 11 is shown.
[0033] Figure 19 This is an initial microscopic photograph of the zirconium oxide powder in Example 11.
[0034] Figure 20 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 1 is shown.
[0035] Figure 21 This is a photograph of the slurry separated from the ball mill in Example 1 after standing for 24 hours.
[0036] Figure 22 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 2 is shown.
[0037] Figure 23 This is a photograph of the slurry separated from the ball mill in Comparative Example 2 after standing for 24 hours.
[0038] Figure 24 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 3 is shown.
[0039] Figure 25 This is a photograph of the slurry separated from the ball mill in Comparative Example 3 after standing for 24 hours.
[0040] Figure 26 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 4 is shown.
[0041] Figure 27 This is a photograph of the slurry separated from the ball mill in Example 4 after standing for 24 hours.
[0042] Figure 28 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 5 is shown.
[0043] Figure 29 This is a cross-sectional SEM image of the ceramic membrane prepared in Example 14. Detailed Implementation
[0044] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.
[0045] Preparation of separation membrane slurry
[0046] Example 1
[0047] Weigh out 25 kg of alumina powder, 0.1 kg of sodium carboxymethyl cellulose, 0.1 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 1.
[0048] Table 1 Particle size of the separation membrane slurry
[0049] Figure 1 The curve shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 1. Figure 2 These are initial microscopic photographs of the alumina powder in Example 1. See Table 1 and... Figures 1-2 As shown, the initial D50 particle size of the alumina powder was 1.75 μm, and there was obvious powder agglomeration. As the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.36 μm at about 120 min. Then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 2.47 μm at 180 min. The rate of increase in the particle size (D50 particle size) of the separation membrane slurry decreased thereafter. This indicates that during the grinding process, alumina powder is first dispersed, and the particle size (D50 particle size) of the separation film slurry gradually decreases. Then, spontaneously and orderly, with the larger particles in the alumina powder as the core, other smaller particles are orderly combined and self-assembled to form particle aggregates with uniform size and similar internal structure, and the particle size (D50 particle size) of the separation film slurry gradually increases.
[0050] Figure 3 This is a photograph of the slurry from the separated membrane layer after ball milling in Example 1, after standing for 24 hours. As can be seen from the image, the slurry from the separated membrane layer is stable and shows no obvious stratification.
[0051] Example 2
[0052] Weigh out 25 kg of alumina powder, 0.625 kg of sodium carboxymethyl cellulose, 0.625 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 2.
[0053] Table 2 Particle size of the separation membrane slurry
[0054] Figure 4 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 2. See Table 2 and... Figure 4 As shown, the initial D50 particle size of the alumina powder was 1.75 μm. As the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.25 μm at around 140 min. Then, the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 1.68 μm at 180 min. The rate of increase in the particle size (D50 particle size) of the separation membrane slurry subsequently decreased.
[0055] Example 3
[0056] Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 3.
[0057] Table 3 Particle size of the separation membrane slurry
[0058] Figure 5 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 3. See Table 3 and... Figure 5As shown, the initial D50 particle size of the alumina powder was 1.75 μm. As the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.31 μm at around 120 min. Then, the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 2.12 μm at 180 min. The rate of increase in the particle size (D50 particle size) of the separation membrane slurry subsequently decreased.
[0059] Figure 6 This is a microscopic image of the separated membrane slurry after grinding in Example 3. As can be seen from the image, the separated membrane slurry clearly contains uniformly sized aggregated particle clusters. Figure 7 This is a photograph of the separation membrane slurry after grinding in Example 3, taken after standing for 24 hours. The image shows that the separation membrane slurry is stable and shows no obvious stratification.
[0060] Meanwhile, based on the particle size measurement results in Examples 1-3, it can be seen that by changing the amount of alumina powder, suspending agent and tripolyphosphoric acid, particle aggregates of different sizes can be obtained.
[0061] Example 4
[0062] Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 100 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 4.
[0063] Table 4. Particle size of the separation membrane slurry
[0064] Figure 8 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 4. See Table 4 and... Figure 8 As shown, the initial D50 particle size of the alumina powder was 1.75 μm; as the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.68 μm after about 10 min; then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 3.13 μm after 140 min.
[0065] Figure 9This is a photograph of the slurry from the separated membrane layer after ball milling in Example 4, after standing for 24 hours. As can be seen from the figure, the slurry from the separated membrane layer is stable and shows no obvious stratification. Figure 10 This is a microscopic photograph of the separation membrane slurry after ball milling in Example 4. It is clearly visible from the image that uniformly sized particle aggregates are evenly dispersed within the separation membrane slurry.
[0066] Example 5
[0067] Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 25 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 5.
[0068] Table 5 Particle size of the separation membrane slurry
[0069] Figure 11 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 5. See Table 5 and... Figure 11 As shown, the initial D50 particle size of the alumina powder was 1.75 μm; as the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.68 μm at about 20 min; then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 8.62 μm at 140 min.
[0070] Meanwhile, based on the particle size measurement results of Examples 3-5, it can be seen that reducing the water content significantly shortens the grinding and dispersion time of alumina powder, and also significantly increases the size of the self-assembled polymer particles. That is, with the same amounts of alumina powder, suspending agent, and sodium tripolyphosphate, different sizes of polymer particles can be obtained by adjusting the water content.
[0071] Example 6
[0072] Weigh out 25 kg of alumina powder, 0.375 kg of polyvinyl alcohol, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 6.
[0073] Table 6. Particle size of the separation membrane slurry
[0074] Figure 12 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 6. See Table 6 and... Figure 12 As shown, the initial D50 particle size of the alumina powder was 1.75 μm; as the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.32 μm at around 140 min; then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 2.08 μm at 200 min.
[0075] Meanwhile, based on the particle size measurement results in Examples 3 and 6, it can be seen that changing the type of suspending agent has no effect on the formation process of particle aggregates when the amount of sodium tripolyphosphate remains unchanged.
[0076] Example 7
[0077] Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 7.
[0078] Table 7 Particle size of the separation membrane slurry
[0079] Figure 13 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 7 is shown. Figure 14 These are initial microscopic photographs of alumina powder. See Table 7 and... Figures 13-14As shown, initially, the D50 particle size of the alumina powder was 0.96 μm and there was obvious powder agglomeration. As the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 0.89 μm at around 80 min. Then, the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 1.68 μm at 200 min.
[0080] Meanwhile, based on the particle size measurement results in Examples 3 and 7, it can be seen that even if there are differences in the initial size of alumina powder, particle aggregates with similar sizes can be obtained by changing the ball milling time, thereby reducing the stringency of the separation membrane layer on the main raw material.
[0081] Example 8
[0082] Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 40°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 8.
[0083] Table 8. Particle size of the separation membrane slurry
[0084] Figure 15 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 8. See Table 8 and... Figure 15 As shown, the initial D50 particle size of the alumina powder was 1.75 μm; as the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.32 μm at around 120 min; then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 2.67 μm at 280 min.
[0085] Example 9
[0086] Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 60°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 9.
[0087] Table 9. Particle size of the separation membrane slurry
[0088] Figure 16 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 9. See Table 9 and... Figure 16 As shown, the initial D50 particle size of the alumina powder was 1.75 μm; as the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.35 μm at about 60 min; then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 2.76 μm at 200 min.
[0089] Meanwhile, based on the particle size measurement results in Examples 3 and 8-9, it can be seen that the size of particle aggregates can be controlled by changing the ball milling temperature.
[0090] Example 10
[0091] Weigh out 25 kg of alumina powder, 3.75 kg of silica sol, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 10.
[0092] Table 10 Particle size of the separation membrane slurry
[0093] Figure 17 The graph shows the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 10. See Table 10 and... Figure 17As shown, the initial D50 particle size of the alumina powder was 1.75 μm; as the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 1.29 μm at around 140 min; then the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 1.82 μm at 400 min.
[0094] Based on common knowledge in the art, adding silica sol to the raw materials of the separation membrane can lower the sintering temperature and further improve the alkali resistance of the separation membrane. Combining the particle size measurement results in Examples 3 and 10, adding silica sol to the separation membrane slurry increases the viscosity of the slurry, prolongs the dispersion time of the alumina powder, and slows the increase in particle size. Larger particle aggregates can be obtained by further extending the ball milling time.
[0095] Example 11
[0096] Weigh out 25 kg of zirconium oxide powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 11.
[0097] Table 11 Particle size of the separation membrane slurry
[0098] Figure 18 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Example 11 is shown. Figure 19 These are initial microscopic photographs of the zirconia powder in Example 11. See Table 11 and... Figures 18-19 As shown, the initial D50 particle size of the zirconia powder was 1.06 μm, and there was obvious powder agglomeration. As the ball milling time increased, the particle size (D50 particle size) of the separation membrane slurry gradually decreased until it reached a minimum of 0.9 μm at about 100 min. Then, the particle size (D50 particle size) of the separation membrane slurry gradually increased, reaching 1.89 μm at 200 min.
[0099] Meanwhile, based on the particle size measurement results in Examples 3 and 11, it can be seen that the preparation method of the separation membrane slurry is applicable to a variety of inorganic powders, such as alumina, zirconium oxide, and silicon carbide.
[0100] Compare with Example 1 Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 12.
[0101] Table 12 Particle size of the separation membrane slurry
[0102] Figure 20 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 1 is shown. Figure 21 The photographs are of the slurry from the separated membrane layer after ball milling in Comparative Example 1, after standing for 24 hours. See Table 12 and... Figures 20-21 As shown, although the slurry of the separated membrane layer did not separate into layers after ball milling, the particle size of the separated membrane layer slurry continued to increase during the ball milling process, without a significant particle size reduction process. That is to say, although there was particle aggregation and the particle size increased rapidly during the ball milling process, there was no self-assembly process and no uniformly dispersed particle agglomerates were formed.
[0103] Compare with Example 2 Weigh out 25 kg of alumina powder, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 13.
[0104] Table 13 Particle size of the separation membrane slurry
[0105] Figure 22 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 2 is shown. Figure 23 The photograph shows the slurry from the separated membrane layer after ball milling in Comparative Example 2, after standing for 24 hours. See Table 13 and... Figures 22-23 As shown, as the ball milling time increases, the slurry particle size continues to decrease, with no significant increase in particle size, which means there is no self-assembly process. Furthermore, the slurry in the separation membrane layer is clearly stratified after the ball milling is completed (the red line in the figure indicates the approximate location of the stratification boundary).
[0106] Compare with Example 3 Weigh 25 kg of alumina powder and 50 kg of water and add them to the ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 14.
[0107] Table 14 Particle size of the separation membrane slurry
[0108] Figure 24 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 3 is shown. Figure 25 The photographs are of the slurry from the separated membrane layer in Comparative Example 3 after ball milling and allowing it to stand for 24 hours. See Table 14 and... Figures 24-25 As shown in the figure, as the ball milling time increases, the particle size of the slurry fluctuates, that is, there is an obvious phenomenon of dispersion-agglomeration alternation, and the slurry of the separation membrane layer is obviously stratified after the ball milling is completed (the red line in the figure is the approximate location of the stratification boundary).
[0109] Compare with Example 4 Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium hexametaphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm and a temperature of 50°C. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 15.
[0110] Table 15 Particle size of the separation membrane slurry
[0111] Figure 26 The curve showing the change in particle size (D50 particle size) of the separation membrane slurry over time during the grinding process in Comparative Example 4 is shown. Figure 27 This is a photograph of the slurry from the separated membrane layer after ball milling in Comparative Example 4, taken after 24 hours of settling. See Table 15 and... Figures 26-27 As shown, as the ball milling time increases, the slurry particle size continues to decrease without a significant increasing trend, meaning there is no self-assembly process, and the slurry of the separated membrane layer is clearly stratified after the ball milling is completed (the red line in the figure is the approximate location of the stratification boundary).
[0112] Compare with Example 5 Weigh out 25 kg of alumina powder, 0.375 kg of sodium carboxymethyl cellulose, 0.375 kg of sodium tripolyphosphate, and 50 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8–10 mm, 20 kg of alumina grinding balls with a diameter of 4–6 mm, and 40 kg of alumina grinding balls with a diameter of 1–3 mm. Start the ball mill at a speed of 500 rpm. During the ball milling process, take samples periodically and measure the particle size of the slurry using a particle size analyzer. The measurement results are shown in Table 16.
[0113] Table 16 Particle size of the separation membrane slurry
[0114] Figure 28 The curve showing the change in particle size (D50 particle size) of the separated membrane slurry over time during the grinding process in Comparative Example 5 is shown in Table 16. Figure 28 As shown, the slurry particle size continuously decreases with increasing ball milling time, and then gradually increases, but the point at which the slurry particle size begins to increase significantly is delayed, approximately 200 minutes. Furthermore, the viscosities (at 20°C) of the separated membrane slurry after ball milling in Example 3 (260 minutes) and the separated membrane slurry after ball milling in Comparative Example 5 (260 minutes) are 97 mPa·s and 521 mPa·s, respectively. The higher viscosity of the separated membrane slurry in Comparative Example 5 is detrimental to subsequent membrane coating.
[0115] Based on the particle size measurement results in Example 3 and Comparative Examples 1-5, this invention utilizes the synergistic effect of alumina powder, suspending agent, and sodium tripolyphosphate. At the appropriate ball milling temperature, alumina powder can first disperse, reducing its particle size. Then, it spontaneously and orderly assembles with larger particles in the main raw material as the core, combining with other smaller particles to form uniformly sized particle aggregates with similar internal structures. The particle size of these aggregates increases with ball milling time. Once the preset size requirement is met, ball milling can be stopped. The resulting separation membrane slurry is stable, does not easily settle, and has low viscosity, which facilitates coating the separation membrane slurry onto the ceramic membrane support. It undergoes self-leveling in a semi-liquid state (lasting 1-2 seconds), potentially yielding a separation membrane with a near-mirror-smooth finish.
[0116] Ceramic membrane preparation Example 12
[0117] A ceramic membrane preparation process includes the following steps: (1) Weigh 35 kg of alumina powder, 5 kg of silica sol, 0.2 kg of sodium carboxymethyl cellulose, 0.2 kg of sodium tripolyphosphate, and 59.6 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8-10 mm, 20 kg of alumina grinding balls with a diameter of 4-6 mm, and 40 kg of alumina grinding balls with a diameter of 1-3 mm. Start the ball mill, with a grinding speed of 500 rpm, a grinding temperature of 50℃, and a grinding time of 12 h to obtain a separation membrane slurry; (2) The separation membrane slurry was applied to the pre-prepared ceramic membrane support by spraying and dried at 110℃ for 1 hour; then the temperature was increased to 1250℃ at 5℃ / min and held for 3 hours to obtain a flat ceramic membrane. The performance test results of the separation membrane layer of the flat ceramic membrane are shown in Table 17.
[0118] The preparation of the ceramic membrane support involves mixing α-alumina A1 (average particle size 30 μm, dosage 70 kg), α-alumina A2 (average particle size 5 μm, dosage 25 kg), and calcined kaolin (average particle size 5000 mesh, dosage 5 kg). Then, starch (dosage 2 kg), tung oil (2.5 kg), gum arabic (dosage 2.5 kg), and clay (dosage 3 kg) are added and mixed evenly using a high-speed mixer. The mixture is then placed in a kneader, and an appropriate amount of PVA aqueous solution with a solid content of 5% is added for kneading. The kneaded mud... Clay was prepared using a vacuum clay mixer; after preparation, it was placed in a sealed container and aged for 48 hours under constant temperature and humidity conditions (temperature 25℃, humidity 80%). After aging, the support blank was prepared by extrusion molding at 25℃ and 8 MPa. After molding, it was dried in a 110℃ oven for 4 hours. After drying, the ceramic membrane blank was sintered at 1500℃ for 3 hours at a heating rate of 5℃ / min, resulting in a flat ceramic membrane support with an average pore size of 3.5 μm and a porosity of 37%. The three-point flexural strength of the ceramic membrane support was >50 MPa. The ceramic membrane support process in subsequent examples and comparative examples was the same as in Example 12.
[0119] Table 17 Test results of the separation membrane layer of the flat ceramic membrane.
[0120] Example 13
[0121] A ceramic membrane preparation process includes the following steps: (1) Weigh 45 kg of alumina powder, 8 kg of silica sol, 1 kg of sodium carboxymethyl cellulose, 1 kg of sodium tripolyphosphate, and 45 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8-10 mm, 20 kg of alumina grinding balls with a diameter of 4-6 mm, and 40 kg of alumina grinding balls with a diameter of 1-3 mm. Start the ball mill, set the ball milling speed to 500 rpm, the ball milling temperature to 50℃, and the ball milling time to 12 h to obtain the separation membrane slurry; (2) The separation membrane slurry was applied to the pre-prepared ceramic membrane support by spraying and dried at 110℃ for 1 hour; then the temperature was increased to 1250℃ at 5℃ / min and held for 3 hours to obtain a flat ceramic membrane. The performance test results of the separation membrane layer of the flat ceramic membrane are shown in Table 18.
[0122] Table 18 Results of Separation Membrane Performance Testing for Flat Plate Ceramic Membranes
[0123] Example 14
[0124] A ceramic membrane preparation process includes the following steps: (1) Weigh 39 kg of alumina powder, 6 kg of silica sol, 0.5 kg of sodium carboxymethyl cellulose, 0.5 kg of sodium tripolyphosphate, and 54 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8-10 mm, 20 kg of alumina grinding balls with a diameter of 4-6 mm, and 40 kg of alumina grinding balls with a diameter of 1-3 mm. Start the ball mill, with a grinding speed of 500 rpm, a grinding temperature of 50℃, and a grinding time of 12 h to obtain a separation membrane slurry; (2) The separation membrane slurry was applied to the pre-prepared ceramic membrane support by spraying and dried at 110℃ for 1 hour; then the temperature was increased to 1250℃ at 5℃ / min and held for 3 hours to obtain a flat ceramic membrane. The performance test results of the separation membrane layer of the flat ceramic membrane are shown in Table 19.
[0125] Table 19 Test results of the separation membrane layer of the flat ceramic membrane.
[0126] Figure 29 This is a cross-sectional SEM image of the ceramic membrane prepared in Example 14. The image shows that the pore size of the separated membrane layer is relatively uniform.
[0127] Example 15
[0128] A ceramic membrane preparation process includes the following steps: (1) Weigh 40 kg of alumina powder, 0.8 kg of sodium carboxymethyl cellulose, 0.8 kg of sodium tripolyphosphate, and 58.4 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8-10 mm, 20 kg of alumina grinding balls with a diameter of 4-6 mm, and 40 kg of alumina grinding balls with a diameter of 1-3 mm. Start the ball mill, with a grinding speed of 500 rpm, a grinding temperature of 50℃, and a grinding time of 12 h to obtain a separation membrane slurry; (2) The separation membrane slurry was applied to the pre-prepared ceramic membrane support by spraying and dried at 110℃ for 1 hour; then the temperature was increased to 1300℃ at 5℃ / min and held for 3 hours to obtain a flat ceramic membrane. The performance test results of the separation membrane layer of the flat ceramic membrane are shown in Table 20.
[0129] Table 20 Results of Separation Membrane Performance Testing for Flat Plate Ceramic Membranes
[0130] Compare with Example 6 A ceramic membrane preparation process includes the following steps: (1) Weigh 35 kg of alumina powder, 5 kg of silica sol, 0.2 kg of sodium carboxymethyl cellulose and 59.8 kg of water, and add them to a ball mill. Then add 40 kg of alumina grinding balls with a diameter of 8-10 mm, 20 kg of alumina grinding balls with a diameter of 4-6 mm and 40 kg of alumina grinding balls with a diameter of 1-3 mm. Start the ball mill, set the ball milling speed to 500 rpm, and the ball milling time to 12 h to obtain the separation membrane slurry; (2) The separation membrane slurry was applied to the pre-prepared ceramic membrane support by spraying and dried at 110℃ for 1 hour; then the temperature was increased to 1250℃ at 5℃ / min and held for 3 hours to obtain a flat ceramic membrane. The performance test results of the separation membrane layer of the flat ceramic membrane are shown in Table 21.
[0131] Table 21 Results of Separation Membrane Performance Tests for Flat Plate Ceramic Membranes
[0132] Based on the test data from Examples 12-14 and Comparative Example 6, it can be seen that, using the same main raw materials, compared with the traditional ceramic membrane preparation process, using particle aggregates based on powder self-assembly technology as the final composition of the separation membrane slurry can reduce the pore size of the separation membrane layer by one-third, resulting in a smaller pore size distribution range and a very small bubble point pore size, thus achieving higher filtration accuracy. However, it can still maintain the large flux of the separation membrane layer with a large pore size under the traditional ceramic membrane preparation process, thus taking into account the advantages of high precision, high stability, small pore size, and large flux. At the same time, the sintered separation membrane layer approaches a mirror-like smooth effect.
Claims
1. A process for preparing a separation membrane slurry based on powder self-assembly technology, characterized in that, Weigh the main raw materials, suspending agent, sodium tripolyphosphate and water according to the formula, or weigh the main raw materials, sintering aid, suspending agent, sodium tripolyphosphate and water according to the formula, and then ball mill them, maintaining the ball milling temperature at 40~60℃. During the ball milling process, the main raw materials are first dispersed and then self-assembled and polymerized into particle aggregates. After the ball milling is completed, the separation membrane slurry is obtained.
2. The process for preparing separation membrane slurry based on powder self-assembly technology according to claim 1, characterized in that, The amount of sintering aid is 14-18 wt% of the weight of the main raw materials, the amount of suspending agent is 0.4-2.5 wt% of the weight of the main raw materials, the amount of sodium tripolyphosphate is 0.4-2.5 wt% of the weight of the main raw materials, and the amount of water is 100-400 wt% of the weight of the main raw materials.
3. The process for preparing separation membrane slurry based on powder self-assembly technology according to claim 1 or 2, characterized in that, The suspending agent is one or more of the following: polyvinyl alcohol, methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, sodium polyacrylate, and polyacrylamide; And / or, the main raw materials are alumina, zirconium oxide or silicon carbide; And / or, the sintering aid is silica sol, alumina sol, or water glass.
4. The process for preparing separation membrane slurry based on powder self-assembly technology according to claim 1, characterized in that, During ball milling, the weight ratio of the main raw material to the grinding balls is 1:4~5.
5. The process for preparing separation membrane slurry based on powder self-assembly technology according to claim 1 or 5, characterized in that, The grinding balls used in ball milling are one or more of the following: alumina grinding balls, zirconia grinding balls, silicon carbide grinding balls, and silicon nitride grinding balls. These include grinding balls with a diameter of 8-10 mm at 37.5-62.5 wt%, grinding balls with a diameter of 4-6 mm at 6.25-31.25 wt%, and grinding balls with a diameter of 1-3 mm at 37.5-62.5 wt%.
6. The process for preparing separation membrane slurry based on powder self-assembly technology according to claim 1 or 5, characterized in that, Ball milling time > 10~20 min; And / or, the ball mill speed is 300~700 rpm.
7. A ceramic membrane preparation process, characterized in that, Includes the following steps: Step S1: Prepare the separation membrane slurry using the separation membrane slurry preparation process based on powder self-assembly technology as described in claims 1-6; Step S2: The separation membrane slurry is applied to the ceramic membrane support by spraying, brushing, coating or immersion, dried and sintered to obtain the ceramic membrane.
8. The ceramic membrane preparation process according to claim 7, characterized in that, In step S2, the drying temperature is 90~120℃ and the drying time is 0.5~2h.
9. The ceramic membrane preparation process according to claim 7, characterized in that, In step S2, the temperature is increased to 1100-1500℃ at a rate of 1-10℃ / min during sintering, and held for 1-5 hours.
10. A ceramic membrane, characterized in that, It is prepared by the ceramic membrane preparation process described in any one of claims 7 to 9.