Preparation Method and Product of Flat Ceramic Membrane with High-Hardness Smooth Film Layer

Abstract

The present invention aims to overcome the problems that the film layer of the existing flat ceramic membrane has low hardness, is relatively rough, has poor anti-fouling performance, and affects the qualified rate and stable operation period of the flat ceramic membrane, and provides a preparation method and product of a flat ceramic membrane with a high-hardness and smooth film layer. The preparation method includes the following steps: subjecting silica sol to gelation treatment to obtain jelly-like silica sol; mixing the jelly-like silica sol with alumina powder, water, etc. to prepare a film layer slurry; coating the film layer slurry on the surface of a flat ceramic membrane support, and sintering after drying to obtain a flat ceramic membrane with a high-hardness and smooth film layer. The obtained flat ceramic membrane has a Mohs hardness of 5-6 for the film layer and a surface roughness of 1-3 for the film layer. The present invention improves the packing state of particles on the film layer surface by using gelated silica sol, thereby obtaining a film layer with high hardness and very smoothness, improving the anti-fouling performance of the flat ceramic membrane film layer, and ensuring the qualified rate and stable operation period of the flat ceramic membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membrane products, and particularly to a preparation method and product of a flat ceramic membrane with a high-hardness smooth film layer. Background Art

[0002] Currently, the warranty period of flat ceramic membranes at the product application end is required to exceed 5 years, and even reach 10 years. However, the Mohs hardness of the film layer of flat ceramic membranes on the market is about 2-3. The low hardness of the film layer makes it easy to scratch during the loading and unloading processes in the production of flat ceramic membranes, reducing the qualified rate of flat ceramic membranes. At the same time, scratches and damages are also likely to occur during the transportation and transfer of flat ceramic membranes, resulting in the loss of the filtration function of flat ceramic membranes. Moreover, during the operation of flat ceramic membranes, the film layer with a thickness of 10-50 μm will be worn due to long-term aeration scouring, resulting in leakage and non-compliance with filtration standards.

[0003] On the other hand, the film layers of flat ceramic membranes on the market are relatively rough, and contaminants are easily adsorbed and adhered to the surface of the film layer to form a dense and irreversible contamination, resulting in the inability to be cleaned and restored by simple backwashing means, which also causes the flat ceramic membrane to be unable to operate stably for a long time. Summary of the Invention

[0004] In order to overcome the problems of the existing flat ceramic membrane having a low hardness and roughness of the film layer, poor anti-fouling performance, and affecting the qualified rate and stable operation period of the flat ceramic membrane, the present invention provides a preparation method and product of a flat ceramic membrane with a high-hardness smooth film layer. The present invention improves the packing state of the particles on the surface of the film layer by using gelated silica sol, thereby obtaining a film layer with high hardness and very smoothness, improving the anti-fouling performance of the flat ceramic membrane film layer, and ensuring the qualified rate and stable operation period of the flat ceramic membrane.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A preparation method of a flat ceramic membrane with a high-hardness smooth film layer, the preparation method comprising the following steps:

[0007] Step S1, performing gelation treatment on silica sol to obtain jelly-like silica sol;

[0008] Step S2, mixing the jelly-like silica sol with alumina powder, lubricating oil, dispersant, lubricant, thickening agent, defoaming agent and water to prepare a film layer slurry;

[0009] Step S3, adopting spraying, brushing or dipping methods to coat the film layer slurry on the surface of the flat ceramic membrane support body, drying and then sintering to obtain a flat ceramic membrane with a high-hardness smooth film layer.

[0010] Further, in the step S1, the specific process of subjecting the silica sol to a gelation treatment to obtain a jelly-like silica sol includes:

[0011] Step S11, mixing the silica sol with a phosphate or a nitrate under a stirring state;

[0012] Step S12, maintaining the stirring state, adding or not adding soda ash or water glass to the mixture in the step S11, continuing to stir for a preset duration and then stopping stirring, and the mixture gradually gels to obtain the jelly-like silica sol.

[0013] Further, the solid content of the silica sol is 10-30%;

[0014] And / or, the phosphate is sodium hexametaphosphate or sodium tripolyphosphate;

[0015] And / or, the nitrate is sodium nitrate or potassium nitrate;

[0016] And / or, the weight ratio of the silica sol, the phosphate or the nitrate, and the soda ash or the water glass is 5-15:0.1-1:0-1.

[0017] Further, the preset duration of continuous stirring in the step S12 is 1-30 min.

[0018] Further, in the step S2, taking the weight of the alumina powder as 100%, the proportion of each raw material in the weight of the alumina powder is:

[0019] Alumina powder, 100%;

[0020] Jelly-like silica sol, 5-20%;

[0021] Lubricating oil, 0.1-1%;

[0022] Dispersant, 0.1-1%;

[0023] Lubricant, 0.01-0.1%;

[0024] Thickener, 0.1-1%;

[0025] Defoamer, 0.1-1%;

[0026] Water, 100-200%.

[0027] Further, the D50 particle size of the alumina powder is 0.9-2.6 μm;

[0028] And / or, the lubricating oil is one or more of tung oil, white oil, palm oil, glycerol, oleic acid, sodium stearate;

[0029] And / or, the dispersant is one or more of polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol;

[0030] And / or, the lubricant is one or more of polyethylene oxide, polyvinyl alcohol, and polyethylene glycol;

[0031] And / or, the thickener is one or more of carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methylcellulose;

[0032] And / or, the defoamer is a silane defoamer.

[0033] Further, the specific process of preparing the membrane layer slurry in step S2 includes:

[0034] Step S21, putting alumina powder, jelly-like silica sol, lubricating oil, dispersant, lubricant, thickener, and water into a ball mill for ball milling and dispersion for a preset time;

[0035] Step S22, filtering the slurry after ball milling and dispersion in step S21, adding a defoamer, and then continuously high-speed stirring for a preset time by a high-speed stirrer to obtain the membrane layer slurry.

[0036] Further, the preset time for ball milling and dispersion in step S21 is 1.5 - 7h;

[0037] And / or, the preset time for continuously high-speed stirring by the high-speed stirrer in step S21 is 5 - 30min.

[0038] Further, the sintering temperature in step S3 is 1200 - 1300°C, and the sintering time is 2 - 2.5h.

[0039] Based on the same inventive concept, a flat ceramic membrane product is obtained by the preparation method of the flat ceramic membrane with a high-hardness smooth membrane layer described above;

[0040] The Mohs hardness of the membrane layer of the flat ceramic membrane is 3 - 6, and the surface roughness of the membrane layer is 1 - 3.

[0041] The beneficial effects of the present invention are:

[0042] The present invention aims to overcome the problems that the film layer of existing flat ceramic membranes has low hardness, is relatively rough, has poor fouling resistance, and affects the qualification rate and stable operation period of flat ceramic membranes. It provides a preparation method and product of a flat ceramic membrane with a high-hardness and smooth film layer. In the preparation method of the flat ceramic membrane with a high-hardness and smooth film layer in the present invention, first, the silica sol is subjected to gelation treatment to obtain a jelly-like silica sol, and then the jelly-like silica sol is mixed with raw materials such as alumina powder to prepare a film layer slurry. Finally, after sintering, a flat ceramic membrane with a high-hardness and smooth film layer is obtained. Due to the gelation treatment of the silica sol, the nano-silica particles are transformed into large-particle-sized branched or bead-like silica aggregates. Then, the branched or bead-like silica aggregates are mixed with alumina powder and other materials to support the film layer slurry and coated on the surface of the flat ceramic support. During the drying process to form a film, they overlap with each other to form a dense and uniform film layer. Finally, through high-temperature sintering, a film layer with high hardness and very smoothness is prepared. This preparation method is simple in operation and the raw materials are easy to obtain. At the same time, the film layer of the flat ceramic membrane prepared by the preparation method in the present invention has relatively high hardness. During the production and transportation of the flat ceramic membrane, it can better avoid phenomena such as scratching, ensuring the qualification rate and filtration function of the flat ceramic membrane, and can effectively cope with aeration scouring, ensuring the stable operation state of the flat ceramic membrane and extending its service life. At the same time, the film layer of the flat ceramic membrane supported by the preparation method in the present invention is very smooth, which can delay the adhesion of pollutants and the like to the surface of the flat ceramic membrane, improve the fouling resistance of the flat ceramic membrane, and can be restored by backwashing, ensuring the stable operation state of the flat ceramic membrane and extending its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0044] Figure 1 It is a schematic flow chart for the preparation of a flat ceramic membrane.

[0045] Figure 2a It is a diagram of the appearance state of silica sol without any treatment.

[0046] Figure 2b It is a diagram of the appearance state of the silica sol after gelation in Example 3.

[0047] Figure 3a It is a scanning electron microscope image of silica sol without any treatment.

[0048] Figure 3b It is a scanning electron microscope image of the silica sol after gelation in Example 3.

[0049] Figure 4 Appearance diagram of the membrane layer of the flat ceramic membrane in Example 12.

[0050] Figure 5a and Figure 5b and Figure 5c and Figure 5d are respectively the scanning electron microscope images of four position points on the surface of the membrane layer of the flat ceramic membrane in Example 12.

[0051] Figure 5e and Figure 5f and Figure 5g and Figure 5h are respectively the scanning electron microscope images of four position points on the surface of the membrane layer of the flat ceramic membrane in Comparative Example 5.

[0052] Figure 6a is the scanning electron microscope image of the cross-section of the flat ceramic membrane at a magnification of 1000 times in Example 12.

[0053] Figure 6b is the scanning electron microscope image of the cross-section of the flat ceramic membrane at a magnification of 5000 times in Example 12. Detailed implementation manners

[0054] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0055] The following disclosure provides many different implementation manners or examples for implementing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention.

[0056] The embodiments of the invention will be described in detail below with reference to the figures.

[0057] A preparation method of a flat ceramic membrane with a high-hardness smooth membrane layer, the process of which is as shown in Figure 1 and the preparation method includes the following steps:

[0058] Step S1: Gelatinize the silica sol to obtain a jelly-like silica sol. Specifically: Under stirring, mix the silica sol with phosphate or nitrate; maintain the stirring state, add or not add soda ash or water glass to the mixture, continue stirring for a preset time (such as 1 - 30 min), and then stop stirring. The mixture gradually gels to obtain a jelly-like silica sol.

[0059] Step S2: Mix the jelly-like silica sol with alumina powder, lubricating oil, dispersant, lubricant, thickener, defoamer, and water to prepare a film layer slurry. Specifically: Put the alumina powder, jelly-like silica sol, lubricating oil, dispersant, lubricant, thickener, and water into a ball mill for ball milling and dispersion for a preset time (such as 1.5 - 7 h); filter the slurry after ball milling and dispersion, add a defoamer, and then continue high-speed stirring for a preset time (such as 5 - 30 min) using a high-speed stirrer to obtain a film layer slurry.

[0060] Step S3: Adopt spraying, brushing, or dipping methods to coat the film layer slurry on the surface of the flat ceramic membrane support, dry it, and then sinter it at a sintering temperature of 1200 - 1300 °C for a sintering time of 2 - 2.5 h to obtain a flat ceramic membrane with a high-hardness and smooth film layer.

[0061] Among them, the solid content of the silica sol is 10 - 30%; the phosphate is sodium hexametaphosphate or sodium tripolyphosphate; the nitrate is sodium nitrate or potassium nitrate; the weight ratio of the silica sol, phosphate or nitrate, and soda ash or water glass is 5 - 15:0.1 - 1:0 - 1.

[0062] Based on the weight of the alumina powder being 100%, the proportion of each raw material in the weight of the alumina powder is as follows: alumina powder, 100%; jelly-like silica sol, 5 - 20%; lubricating oil, 0.1 - 1%; dispersant, 0.1 - 1%; lubricant, 0.01 - 0.1%; thickener, 0.1 - 1%; defoamer, 0.1 - 1%; water, 100 - 200%.

[0063] The D50 particle size of the alumina powder is 0.9 - 2.6 μm; the lubricating oil is one or more of tung oil, white oil, palm oil, glycerol, oleic acid, sodium stearate; the dispersant is one or more of polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol; the lubricant is one or more of polyethylene oxide, polyvinyl alcohol, polyethylene glycol; the thickener is one or more of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose; the defoamer is a silane-based defoamer.

[0064] The following is further illustrated through more specific examples.

[0065] (I) Preparation of jelly-like silica sol

[0066] Examples 1-9 describe the preparation of jelly-like silica sols. The process is as follows: silica sol (solid content 20%) is mixed with phosphate or nitrate while stirring; while maintaining the stirring, soda ash or water glass is added to the mixture with or without addition. Stirring is continued for 10 minutes, then stopped. The mixture gradually gels to obtain jelly-like silica sols. The composition and appearance of the jelly-like silica sols in Examples 1-9 are shown in Table 1.

[0067]

[0068] From the observation results of the appearance of the silica sol after gelation in Table 1, it can be seen that after adding phosphate or nitrate to the silica sol, or after adding phosphate or nitrate and soda ash or water glass to the silica sol, the silica sol will gradually flocculate and agglomerate, and finally form a jelly-like gel.

[0069] The appearance of the silica sol after gelation in Example 3 is compared with Figure 2a and Figure 2b As shown in . Among them, Figure 2a It is silica sol without any treatment. Figure 2b The silica sol gel. As can be seen from the figure, the silica sol is a colorless and transparent liquid before any treatment. However, when sodium tripolyphosphate and soda ash are added to the silica sol, the silica sol becomes a milky white jelly.

[0070] The scanning electron microscope images of the silica sol in Example 3 before and after gelation are as follows: Figure 3a and Figure 3b As shown. Among them, Figure 3a It is silica sol without any treatment. Figure 3b This is the silica sol after gelation. As can be seen from the figure, the silica sol is uniformly dispersed in small droplets before gelation. However, after sodium tripolyphosphate and soda ash are added to the silica sol, the small droplets gradually flocculate, forming larger, branched, or beaded aggregates.

[0071] (2) Preparation of flat ceramic membrane

[0072] Examples 10 to 17 are the preparation of flat ceramic membranes, and their preparation processes refer to the aforementioned preparation method. The composition and performance test results of the flat ceramic membranes of Examples 10 to 17 are shown in Table 2.

[0073] Among them, the composition raw materials of the flat ceramic membrane support are as follows: in parts by weight, the raw materials of the support body include 80 parts of ceramic aggregate, 15 parts of activated carbon (D50 particle size is 2μm), 10 parts of polyvinyl alcohol, 5 parts of polyethylene glycol, and 20 parts of water. The ceramic aggregate includes 90 parts of spherical alumina for the support body (D50 particle size is 20μm), 5 parts of magnesium oxide, and 5 parts of kaolin.

[0074] The D50 particle size of the alumina powder in the membrane layer slurry is 1.1μm. The ball milling and dispersion time is 4.5h. The stirring time of the high-speed mixer is 5min. Spraying, the number of times is 1 time. The sintering temperature is 1250°C, and the sintering time is 2h.

[0075] Comparative Examples 4 to 6 were prepared into flat ceramic membranes with reference to the foregoing method, the difference being:

[0076] Comparative Example 4: Silica sol, sodium tripolyphosphate and soda ash were directly ball-milled and dispersed with alumina powder, etc. to prepare a membrane layer slurry, and the composition and dosage were the same as those in Example 12.

[0077] Comparative Example 5: The jelly-like silica sol was replaced with silica sol without any treatment, and the remaining composition and dosage were the same as those in Example 12.

[0078] Comparative Example 6: After the membrane layer slurry was ball-milled and dispersed, it was not stirred at high speed by a high-speed mixer and was directly sprayed, and the composition and dosage were the same as those in Example 12.

[0079] The performance test results of the flat ceramic membranes in Comparative Examples 4 to 6 are shown in Table 3.

[0080]

[0081] It can be seen from the data in Table 3 that the Mohs hardness of the membrane layer of the flat ceramic membrane prepared in this example is between 3 and 6, and the membrane layer is smooth. After analysis, the reason is that due to the gelation treatment of the silica sol, the nano-silica particles are transformed into large-particle-sized branched or beaded silica aggregates, and then the branched or beaded silica aggregates are mixed with alumina powder, etc. to support the membrane layer slurry and coated on the surface of the flat ceramic support. During the drying and film-forming process, they overlap with each other to form a dense and uniform membrane layer, and finally a membrane layer with high hardness and very smoothness is prepared through high-temperature sintering.

[0082] Due to the high hardness of the flat ceramic membrane layer, during the production and transportation of the flat ceramic membrane, scratches and other phenomena can be better avoided, ensuring the qualification rate and filtration function of the flat ceramic membrane, and effectively coping with aeration scouring, ensuring the stable operation state of the flat ceramic membrane and extending its service life. At the same time, the flat ceramic membrane layer supported by the preparation method in the present invention is very smooth, which can delay the adhesion of pollution and the like to the surface of the flat ceramic membrane, improve the anti-pollution performance of the flat ceramic membrane, and can be restored by backwashing, ensuring the stable operation state of the flat ceramic membrane and extending its service life.

[0083] Comparing the data in Table 3 and Table 4, it can be seen that by subjecting the silica sol to gelation treatment, it is beneficial to improve the hardness and smoothness characteristics of the flat ceramic membrane layer. At the same time, compared with the simultaneous gelation of silica sol, sodium tripolyphosphate, etc. with alumina powder during the ball milling and dispersion process, the process of the silica sol first undergoing gelation alone during the ball milling and dispersion is more conducive to improving the hardness and smoothness characteristics of the flat ceramic membrane layer. After analysis, the reason is that when the silica sol and alumina powder undergo gelation simultaneously during the ball milling and dispersion process, the small droplets of the silica sol are violently impacted and are not easy to aggregate, which is not conducive to the transformation of nano-silica particles into large-particle branched or bead-like silica aggregates.

[0084] On the other hand, continuing to supplement high-speed stirring for a certain period of time after the membrane layer slurry is ball milled can further improve the dispersion effect of each raw material in the membrane layer slurry, which is beneficial to further enhancing the hardness and smoothness characteristics of the flat ceramic membrane layer.

[0085] The appearance photo of the membrane layer of the flat ceramic membrane in Example 12 is as Figure 4 shown. It can be seen from the figure that the surface of the membrane layer of the flat ceramic membrane is smooth, without obvious protrusions and cracks.

[0086] The comparison of the scanning electron microscope images of the membrane layer surface of the flat ceramic membrane in Example 12 and the flat ceramic membrane in Comparative Example 5 is as Figure 5a 、 Figure 5b 、 Figure 5c and Figure 5d ,as well as Figure 5e 、 Figure 5f 、 Figure 5g and Figure 5h shown. Among them, Figure 5a 、 Figure 5b 、 Figure 5c and Figure 5d are the scanning electron microscope images of multiple position points on the membrane layer surface of the flat ceramic membrane in Example 12 respectively. Figure 5e 、 Figure 5f 、 Figure 5g and Figure 5hThey are SEM images of multiple position points on the surface of the membrane layer of the flat ceramic membrane in Comparative Example 5. It can be seen from the figure that the surface of the membrane layer of the flat ceramic membrane sintered after adding jelly-like silica sol is relatively flat at the microscopic state. However, there are still protrusions, pits, etc. on the surface of the membrane layer of the flat ceramic membrane sintered after adding silica sol at the microscopic state. And these protrusions, pits, etc. can serve as the anchoring points for pollutants, etc. on the surface of the membrane layer of the flat ceramic membrane, that is, it increases the difficulty of backwashing recovery of the flat ceramic membrane.

[0087] The SEM image of the cross-section of the flat ceramic membrane in Example 12 is as Figure 6a and Figure 6b shown. Among them, Figure 6a the magnification is 1000 times, Figure 6b and the magnification of

[0088] is 5000 times. It can be seen from the figure that at the cross-section of the flat ceramic membrane, the thickness of the membrane layer is about 20μm. At the same time, the pore diameter of the membrane layer is smaller than that of the support of the flat ceramic membrane.

[0089]

[0090] From the detection data in Table 4, it can be known that with the increase of the ball milling and dispersion time, the spraying state of the membrane layer slurry remains unchanged, and the smoothness of the membrane layer surface increases slightly until after ball milling and dispersing for 3h, the spraying state and surface smoothness change suddenly, showing obvious differences. Therefore, ensuring a certain ball milling and dispersion time for the membrane layer slurry is beneficial to ensuring the improvement of the hardness and smoothness characteristics of the membrane layer of the flat ceramic membrane. And with the increase of the ball milling and dispersion time, the bubble point pore diameter of the membrane layer decreases and then tends to a stable value, the pore diameter concentration of the prepared membrane layer increases, and the filtration accuracy and anti-pollution performance of the product are also improved.

[0091] Taking the flat ceramic membrane in Example 12, the flat ceramic membrane in Comparative Example 4, and the commercially available flat ceramic membrane as examples, a roughness measuring instrument using the stylus measurement method is used to detect the surface roughness of the membrane layer of the flat ceramic membrane. The detection results are shown in Table 5.

[0092]

[0093] From the detection data in Table 5, it can be known that the membrane layer of the flat ceramic membrane prepared in this example is very smooth.

[0094] Taking the flat ceramic membrane in Example 12, the flat ceramic membrane in Comparative Example 4, and the commercially available flat ceramic membrane as examples, first operate under the same concentration of sewage conditions for the same time (such as 3 days), and then start the backwashing operation and continue to operate for the same time (such as 3 hours). Calculate the ratio of the transmembrane pressure difference after backwashing to the initial transmembrane pressure difference under the same flux, and this ratio is defined as the initial pressure difference recovery rate. After measurement, the initial pressure difference recovery rate of the flat ceramic membrane in Example 12 is calculated to be 98%, the initial pressure difference recovery rate of the flat ceramic membrane in Comparative Example 4 is 93%, and the initial pressure difference recovery rate of the commercially available flat ceramic membrane is 88%. The flat ceramic membrane prepared in this example shows a more excellent initial pressure difference recovery rate under the same backwashing method, which also verifies from the side that the membrane layer of the flat ceramic membrane prepared in this example is very smooth and not conducive to the attachment of impurities, etc.

Claims

1. A preparation method of a flat ceramic membrane with a high-hardness smooth film layer, characterized in that, The preparation method includes the following steps: Step S1: Gelatinize the silica sol to obtain a jelly-like silica sol, and the nano-silica particles are transformed into branched or beaded silica aggregates; Step S2: Mix the jelly-like silica sol with alumina powder, lubricating oil, dispersant, lubricant, thickener, defoamer and water to prepare a film layer slurry; Step S3: Apply the film layer slurry on the surface of the flat ceramic membrane support by spraying, brushing or dipping, and dry. During the drying and film-forming process, the silica aggregates and the alumina powder overlap with each other to form a dense and uniform film layer, and then sinter to obtain a flat ceramic membrane with a high-hardness and smooth film layer; the Mohs hardness of the film layer of the flat ceramic membrane is 3-6, and the surface roughness of the film layer is 1-3; Among them, in the step S2, based on the weight of the alumina powder being 100%, the proportion of each raw material in the weight of the alumina powder is as follows: Alumina powder, 100%; Jelly-like silica sol, 5-20%; Lubricating oil, 0.1-1%; Dispersant, 0.1-1%; Lubricant, 0.01-0.1%; Thickener, 0.1-1%; Defoamer, 0.1-1%; Water, 100-200%; In the step S3, the sintering temperature is 1200-1300 °C, and the sintering duration is 2-2.5 h.

2. The preparation method of the flat ceramic membrane with a high-hardness smooth film layer according to claim 1, characterized in that, In the step S1, the specific process of gelatinizing the silica sol to obtain a jelly-like silica sol includes: Step S11: Mix the silica sol with phosphate or nitrate under stirring; Step S12: Maintain the stirring state, add or not add soda ash or water glass to the mixture in the step S11, continue stirring for a preset time and then stop stirring, and the mixture gradually gels to obtain the jelly-like silica sol.

3. The preparation method of the flat ceramic membrane with a high-hardness smooth film layer according to claim 2, characterized in that, The solid content of the silica sol is 10-30%; And / or, the phosphate is sodium hexametaphosphate or sodium tripolyphosphate; And / or, the nitrate is sodium nitrate or potassium nitrate; And / or, the weight ratio of the silica sol, the phosphate or the nitrate, and the soda ash or the water glass is 5-15:0.1-1:0-1.

4. The preparation method of the flat ceramic membrane with a high-hardness smooth film layer according to claim 2 or 3, characterized in that, The preset time for continuous stirring in the step S12 is 1-30 min.

5. The preparation method of the flat ceramic membrane with a high-hardness smooth film layer according to any one of claims 1 to 3, characterized in that, The D50 particle size of the alumina powder is 0.9-2.6 μm; And / or, the lubricating oil is one or more of tung oil, white oil, palm oil, glycerol, oleic acid, sodium stearate; And / or, the dispersant is one or more of polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol; And / or, the lubricant is one or more of polyethylene oxide, polyvinyl alcohol, polyethylene glycol; And / or, the thickener is one or more of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose; And / or, the defoamer is a silane defoamer.

6. The preparation method of the flat ceramic membrane with a high-hardness smooth film layer according to any one of claims 1, characterized in that, The specific process of preparing the film layer slurry in the step S2 includes: Step S21: Put the alumina powder, jelly-like silica sol, lubricating oil, dispersant, lubricant, thickener and water into a ball mill for ball milling and dispersion for a preset time; Step S22: Filter the slurry after ball milling and dispersion in step S21, add an antifoaming agent, and then continue to stir at high speed for a preset time using a high-speed mixer to obtain a film layer slurry.

7. The preparation method of the flat ceramic membrane with a high-hardness smooth film layer according to any one of claims 1, characterized in that, In step S21, the preset time for ball milling and dispersion is 1.5 - 7 h; And / or, in step S21, the preset time for continuous high-speed stirring using a high-speed mixer is 5 - 30 min.

8. A flat ceramic membrane product, characterized in that, Prepared by the method for preparing a flat ceramic membrane with a high-hardness smooth film layer according to any one of claims 1 - 7.

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