Asymmetric iron oxide ceramic composite membrane as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of an asymmetric ferric oxide ceramic composite membrane, which comprises the following steps: step 1, carrying out high-temperature hydrolysis reaction on a ferric chloride aqueous solution to obtain ferric hydroxide sol, cooling, and adding a polyvinyl alcohol aqueous solution into the ferric hydroxide sol to obtain a ferric hydroxide sol membrane preparation solution; and 2, dipping a ceramic microfiltration membrane in the iron oxide sol membrane preparation solution obtained in the step 1, taking out, drying at room temperature, and carrying out microwave sintering. According to the invention, a new iron oxide film layer is formed on the surface of the ceramic microfiltration membrane by regulating and controlling the iron oxide sol membrane preparation liquid and the microwave sintering power and time. The steps and time required by sintering are greatly reduced, the energy required by sintering is saved, the membrane preparation cost is reduced, and the obtained asymmetric iron oxide ceramic composite membrane has the advantages of high membrane flux and strong pollution resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic membranes, and in particular to an asymmetric iron oxide ceramic composite membrane and a preparation method and application thereof. Background Art

[0002] Desizing wastewater is wastewater generated in the pre-treatment stage of printing and dyeing. It contains a large amount of organic matter, with a chemical oxygen demand (COD) of more than 20g / L. The total amount of organic matter it contains accounts for more than 50% of the printing and dyeing wastewater, making it difficult to treat. Ceramic membranes are widely used in harsh environments with high temperature and strong alkalinity due to their good chemical stability, high mechanical strength, acid and alkali resistance, and high temperature resistance. However, desizing wastewater contains polymer slurry (such as PVA, carboxymethyl cellulose), starch, oil, etc., which can easily form a gel layer on the membrane surface or clog the membrane pores, resulting in a sharp drop in the permeation flux. After the pollutants are adsorbed on the membrane surface, they are difficult to remove by conventional backwashing and require frequent chemical cleaning (such as strong acid, strong alkali or oxidant), which increases the cost of equipment operation and maintenance.

[0003] Fe2O3 is considered to be a natural hydrophilic material, and it is abundant in source and inexpensive. Due to the high hydrophilicity of nano-iron oxide particles, the Fe2O3 nanoparticles deposited on the membrane surface have the least tendency to scale. The existing technology mainly modifies Fe2O3 nanoparticles on the surface of ceramic membranes to enhance the hydrophilicity and oleophobicity of the membrane surface. In the treatment of desizing wastewater, this kind of ceramic membrane with surface modified iron oxide still has the problem of rapid decline in permeation flux and the need for frequent cleaning. The composite ceramic membrane with a complete iron oxide film layer has better anti-pollution performance when treating desizing wastewater. The core lies in its continuous and uniform surface characteristics. The complete film layer forms a dense coverage, giving the entire membrane surface a high hydrophilicity, effectively blocking the direct adhesion of hydrophobic organic matter. In contrast, the surface of the ceramic membrane modified only with iron oxide has increased gaps and roughness between particles, and pollutants are easily adhered, forming a dense and difficult-to-remove dirt layer.Patent CN 113926321A modifies Fe2O3 on the surface of ceramic microfiltration membrane to obtain anti-pollution ceramic membrane, but the patent clearly indicates that Fe2O3 is modified only on the surface of ceramic microfiltration membrane, and the iron hydroxide sol particle size obtained in Example 2 of the patent is only 40-50nm. Under this condition, it is impossible to form a complete iron oxide film on the surface of a ceramic support with a pore size of 100nm, so the patent has no corresponding data support such as the pore size of the iron oxide film. Similarly, Barati N et al. (Barati N, Husein MM, Azaiez J. Modifying ceramic membranes with in situ grown iron oxide nanoparticles and their use for oily water treatment [J]. Journal of Membrane Science, 2020, 617: 118641.) and Karnik BS et al. (Karnik BS, Baumann MJ, Masten SJ, et al. AFM and SEM characterization of iron oxide coated ceramic membranes [J]. Journal of Materials Science, 2006, 41(20): 6861-6870.) also modified the surface of the ceramic membrane with iron oxide nanoparticles, but no complete iron oxide film layer was formed on the surface of the ceramic membrane disclosed in these documents (Barati N et al. directly stated in the 8th and 9th lines of the 4th paragraph of Section 3.1.2 of their document that no additional layer consisting only of nano-iron oxide was observed; Karnik BS et al. showed in their document the EDS spectrum of the iron oxide-coated ceramic membrane prepared according to the method in the document (Fig. 9b). It can be clearly seen from the figure that the surface of the modified ceramic membrane is mixed with chemical substances (titanium dioxide, zirconium oxide, iron oxide and aluminum oxide) of different sizes and shapes, and the signal response of the EDS spectrum of the Fe element is uneven, indicating that the ceramic membrane is only modified with iron oxide. If a complete film layer is formed, the surface of the modified ceramic membrane should be composed of chemical substances of uniform size and similar shape, and the signal response of the Fe element in the EDS spectrum of the Fe element should be uniform).

[0004] Microwave sintering has many advantages such as fast and uniform heating, high efficiency and energy saving, and no heat source pollution, which has attracted great attention from scientific and technological personnel in the field of materials. Since 1998, the American Materials Research Society (MRS) has discussed microwave sintering technology as a special topic. At present, microwave sintering is mainly used in the field of material preparation. The microwave sintering method pursues densification and macro-performance control in the field of materials, overcoming the difficulties of size effect and temperature uniformity. In the field of membranes, it focuses more on the fine control of membrane microstructure, balancing porosity, separation efficiency and mechanical stability. Fe is considered to be an absorbing material with significant absorbing properties, especially in the high-frequency band, and is a good microwave sintering material. How to apply microwave sintering to the preparation of ceramic membranes to produce composite ceramic membranes with a complete iron oxide membrane layer, higher permeability and stronger resistance to membrane pollution is a problem that needs to be solved urgently. Summary of the Invention

[0005] The present invention aims to address the rapid decline in permeate flux and poor anti-fouling capabilities of existing iron oxide-modified ceramic membranes when treating desizing wastewater. By providing a method for preparing an asymmetric iron oxide ceramic membrane, the present invention rapidly prepares an iron oxide film layer on the surface of a ceramic microfiltration membrane using microwave sintering. The resulting asymmetric iron oxide ceramic membrane exhibits high permeate flux and superior anti-fouling properties during desizing wastewater treatment.

[0006] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0007] A method for preparing an asymmetric iron oxide ceramic composite membrane comprises the following steps:

[0008] Step 1: hydrolyzing an aqueous ferric chloride solution at high temperature to obtain a ferric hydroxide sol, cooling the solution, and adding a polyvinyl alcohol aqueous solution to the solution to obtain a ferric hydroxide sol film-forming solution;

[0009] Step 2: immersing the ceramic microfiltration membrane in the iron oxide sol membrane-forming solution obtained in step 1, taking it out, drying it, and microwave sintering it to obtain the membrane.

[0010] In step 1, the high-temperature hydrolysis is: adding the ferric chloride aqueous solution dropwise into boiling water, and reacting at a temperature of 90-100° C. for 0.1-12 hours; the cooling is cooling to 70-90° C.

[0011] In step 1, after adding the polyvinyl alcohol aqueous solution to the ferric hydroxide sol, stirring and reacting at a temperature of 70 to 90° C. for 10 to 30 minutes, the ferric hydroxide sol film-forming solution is obtained.

[0012] In step 1, the solid content of ferric hydroxide in the ferric hydroxide sol film-forming solution is 0.1-0.6 wt %.

[0013] When the content C of polyvinyl alcohol in the ferric hydroxide sol film-forming solution in step 1 is in the range of 0.25wt%≤C<0.5wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 400~600W, and the microwave sintering time is 3~5min; or, during the microwave sintering process, the microwave power is first linearly increased from 0 to the target power within 2~3min, and then sintered at a constant target power for 1~2min, and the target power is 400~600W.

[0014] When in step 1, the content C of polyvinyl alcohol in the ferric hydroxide sol film-forming solution is in the range of 0.5wt%≤C≤0.75wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600-800W, and the microwave sintering time is 3-5min; or, during the microwave sintering process, the microwave power is first linearly increased from 0 to the target power within 2-3min, and then sintered at a constant target power for 2-3min, and the target power is 600-800W.

[0015] When in step 1, the content C of polyvinyl alcohol in the ferric hydroxide sol film-forming solution is in the range of 0.75wt%<C≤1wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600-800W, and the microwave sintering time is 4-5min, or, during the microwave sintering process, the microwave power is first linearly increased from 0 to the target power within 2-3min, and then sintered at a constant target power for 3-4min, and the target power is 600-800W.

[0016] Wherein, the polyvinyl alcohol is polyvinyl alcohol 124 type.

[0017] In step 1, the particle size of the ferric hydroxide colloid in the ferric hydroxide sol film-forming solution is 100 to 200 nm.

[0018] In step 2, the room temperature drying is drying at room temperature for 6 to 24 hours.

[0019] In step 2, the material of the ceramic microfiltration membrane is any one or a combination of aluminum oxide, titanium oxide, zirconium oxide and silicon oxide.

[0020] The ceramic microfiltration membrane is a common microporous ceramic membrane available on the market.

[0021] In step 2, before immersing the ceramic microfiltration membrane in the ferric hydroxide sol membrane-forming solution, the ceramic membrane is cleaned; the cleaning method is preferably: immersing the ceramic microfiltration membrane in water and heating it to boiling for 60 minutes to remove impurities on its surface and in its pores.

[0022] In step 2, before immersing the ceramic microfiltration membrane in the ferric hydroxide sol membrane-forming liquid, the ferric hydroxide sol membrane-forming liquid is degassed; the degassed method is preferably as follows: the ferric hydroxide sol membrane-forming liquid is stirred in a degassing mixer at 2000 r / min for 3 minutes, and then degassed at 2200 r / min for 5 minutes.

[0023] The asymmetric iron oxide ceramic composite membrane prepared by the above preparation method is also within the protection scope of the present invention.

[0024] The present invention also claims to protect the use of the asymmetric iron oxide ceramic composite membrane prepared by the above preparation method in treating desizing wastewater in the printing and dyeing industry.

[0025] Preferably, when the asymmetric iron oxide ceramic composite membrane is used to treat desizing wastewater in the printing and dyeing industry, the filtration method is cross-flow filtration, the transmembrane pressure difference is 1-2 bar, and the membrane surface flow rate is 1-1.5 m·s -1 , the operating temperature is 50~70℃.

[0026] Beneficial effects:

[0027] (1) The present invention prepares an asymmetric iron oxide ceramic composite membrane by microwave sintering. Microwave sintering can achieve bulk heating through the dielectric loss inside the material, and the heating rate is fast (up to 1000°C / min). Compared with conventional sintering, the membrane preparation time of microwave sintering is shortened by 50-90%, and the energy consumption is reduced by 30-70%. It greatly reduces the membrane preparation steps and time, reduces energy consumption, and thus effectively reduces the membrane preparation cost.

[0028] (2) The present invention forms a new iron oxide film layer on the surface of the ceramic microfiltration membrane by regulating the composition of the iron hydroxide sol membrane-forming liquid, the microwave sintering frequency and time, and reduces the degree of membrane scaling and improves the membrane permeation flux during the desizing wastewater treatment process. Moreover, the rapid sintering of microwave sintering inhibits excessive grain growth, makes the membrane pore size distribution more uniform, optimizes the membrane microstructure, and avoids the organic volatilization pollution caused by long-term high temperature in traditional sintering. Due to the uniformity of microwave heating, the obtained iron oxide nanoparticles are more uniform, which improves the porosity of the obtained iron oxide film layer and reduces the isoelectric point of the membrane surface. At the same time, due to the existence of electrostatic repulsion, the scaling degree of the iron oxide membrane in the desizing wastewater treatment process is further reduced, and the permeation flux is further improved.

[0029] (3) Microwave sintering has a significant effect on the uniform sintering of porous structures or composite membranes, avoiding delamination between membrane layers. The present invention uses microwave sintering to calcine the ceramic membrane coated with iron hydroxide sol, which greatly improves the bonding strength of iron oxide nanoparticles on the ceramic membrane surface, and the operational stability of the resulting iron oxide ceramic membrane is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0031] Figure 1 These are scanning electron microscope images of the surface and cross-section of the original alumina ceramic membrane and the ceramic membranes obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2; wherein, Figure a is a scanning electron microscope image of the surface (left picture) and cross-section (right picture) of the original alumina ceramic membrane; Figure b is a scanning electron microscope image of the surface (left picture) and cross-section (right picture) of the asymmetric iron oxide ceramic composite membrane obtained in Example 1; Figure c is a scanning electron microscope image of the surface (left picture) and cross-section (right picture) of the asymmetric iron oxide ceramic composite membrane obtained in Example 2; Figure d is a scanning electron microscope image of the surface (left picture) and cross-section (right picture) of the ceramic membrane obtained in Comparative Example 1; Figure e is a scanning electron microscope image of the surface (left picture) and cross-section (right picture) of the ceramic membrane obtained in Comparative Example 2.

[0032] Figure 2 The element distribution map and EDS spectrum obtained by EDS scanning on the surface of the asymmetric iron oxide ceramic composite membrane prepared in Example 1; wherein, Figure a is the EDS spectrum obtained by energy spectrum scanning on the surface of the asymmetric iron oxide ceramic composite membrane; Figure b is the surface morphology map of the asymmetric iron oxide ceramic composite membrane; Figure c is the Al element distribution map on the surface of the asymmetric iron oxide ceramic composite membrane; Figure d is the O element distribution map on the surface of the asymmetric iron oxide ceramic composite membrane; Figure e is the Fe element distribution map on the surface of the asymmetric iron oxide ceramic composite membrane.

[0033] Figure 3 The pressure-flow curve (Figure a) and pore size distribution diagram (Figure b) obtained by measuring the pore size distribution of the original alumina ceramic membrane and the asymmetric iron oxide ceramic composite membrane prepared in Example 1 by the bubble pressure method.

[0034] Figure 4 Graph showing pure water flux of the original alumina ceramic membrane in Example 3, the ceramic membranes obtained in Comparative Example 2 and Example 1.

[0035] Figure 5 This is a graph showing the flux changes during the treatment of desizing wastewater by the original alumina ceramic membrane in Example 4, the ceramic membrane modified only with iron oxide on the surface, and the asymmetric iron oxide ceramic composite membrane prepared in Example 1.

[0036] Figure 6 This is a comparison chart of the membrane flux recovery rates of the original alumina ceramic membrane in Example 4, the ceramic membrane modified only with iron oxide on the surface, and the asymmetric iron oxide ceramic composite membrane prepared in Example 1 after treating desizing wastewater. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the following examples. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0038] Example 1

[0039] 1.29 g of FeCl3·6H2O compound was accurately weighed and added to 50 mL of deionized water under ultrasonication for 5 minutes to fully dissolve the mixture. The mixture was then added dropwise to 40 mL of pre-boiled deionized water and heated in an oil bath to 100° C. The reaction was continued for 3 hours and then cooled to 80° C. to obtain a ferric hydroxide sol. 10 mL of a 10 wt% PVA aqueous solution was then added dropwise to the ferric hydroxide sol, stirred and reacted at 80° C. for 20 minutes, and finally naturally cooled to room temperature to obtain a ferric hydroxide sol film-forming solution having a ferric hydroxide solid content of 0.5% and a PVA content of 1 wt%. The solution was stirred and mixed at 2000 r / min for 3 minutes in a mixing-degassing machine, degassed at 2200 r / min for 5 minutes, and the mixing and degashing were repeated 3 times. The ferric hydroxide colloidal particle size was measured to be 100 to 200 nm. A sheet-type alumina ceramic membrane with an average pore size of 100 nm (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., 3 cm in diameter, 2 mm thick) was cleaned with deionized water and dried at 110°C for 4 hours. The cleaned alumina ceramic membrane was immersed in a ferric hydroxide sol membrane-forming solution for 1 minute, then removed at a speed of 10 mm / s. After air-drying for 12 hours, the membrane was placed in a microwave sintering furnace and sintered at a constant power of 800 W for 4 minutes to obtain the asymmetric ferric oxide ceramic composite membrane of the present invention.

[0040] The microstructure of the original alumina ceramic membrane and the asymmetric iron oxide ceramic composite membrane prepared in this example was analyzed using a scanning electron microscope (SEM). Figure 1 As shown in Figure a (sheet alumina ceramic membrane) and Figure b (asymmetric iron oxide ceramic composite membrane), by comparing the microscopic morphology of the ceramic membrane surface before and after coating with the membrane-making liquid, it was found that compared with the original alumina ceramic membrane, a new iron oxide film layer with a thickness of 0.5 μm was formed on the surface of the asymmetric iron oxide ceramic composite membrane. The surface nanoparticles are smaller and the surface is smoother.

[0041] The surface EDS spectrum of the original aluminum oxide ceramic membrane and the asymmetric iron oxide ceramic composite membrane prepared in this embodiment was analyzed. Figure 2 As shown, by comparing the elements on the surface of the original alumina ceramic membrane and the asymmetric iron oxide ceramic composite membrane prepared in this embodiment, it was found that since the surface of the asymmetric iron oxide ceramic composite membrane is a new iron oxide film layer, there is an obvious Fe element signal response on its surface, and the Fe element accounts for 20.4wt%.

[0042] The pore size of the asymmetric iron oxide ceramic composite membrane prepared in this example was measured by bubble pressure method. Figure 3 As shown in FIG, it is found that the pore size of the asymmetric iron oxide ceramic composite membrane prepared by this method is between 100 and 120 nm, which is consistent with the Figure 1 The results are consistent with those of the SEM image shown in Figure b, with a porosity of 35-41%.

[0043] Example 2

[0044] 1.29 g of FeCl3·6H2O compound was accurately weighed and added to 50 mL of deionized water under ultrasonication for 5 minutes to fully dissolve the mixture. The mixture was then added dropwise to 40 mL of pre-boiled deionized water and heated in an oil bath to 100° C. The reaction was continued for 3 hours and then cooled to 80° C. to obtain a ferric hydroxide sol. 10 mL of a 10 wt% PVA aqueous solution was then added dropwise to the ferric hydroxide sol, stirred and reacted at 80° C. for 20 minutes, and finally naturally cooled to room temperature to obtain a ferric hydroxide sol film-forming solution having a ferric hydroxide solid content of 0.5% and a PVA content of 1 wt%. The solution was stirred and mixed at 2000 r / min for 3 minutes in a mixing-degassing machine, degassed at 2200 r / min for 5 minutes, and the mixing and degashing were repeated 3 times. The ferric hydroxide colloidal particle size was measured to be 100 to 200 nm. A 100nm average pore size alumina ceramic membrane (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., 3cm diameter, 2mm thickness) was cleaned with deionized water and dried at 110°C for 4 hours. The cleaned alumina ceramic membrane was immersed in a ferric hydroxide sol membrane-forming solution for 1 minute, removed at a speed of 10mm / s, and air-dried for 12 hours. The membrane was then placed in a microwave sintering furnace with the power linearly increased from 0 to 800W over 2 minutes. The membrane was then sintered at 800W for 3 minutes to produce an asymmetric ferric oxide ceramic composite membrane.

[0045] The micromorphology of the asymmetric iron oxide ceramic membrane prepared in this embodiment was analyzed by scanning electron microscopy (SEM). Figure 1 As shown in Figure c, the microscopic morphology of the ceramic membrane surface before and after coating the membrane solution is compared. It is found that compared with the original alumina ceramic membrane ( Figure 1 a) A new iron oxide film layer with a thickness of about 0.6 μm is also formed on the surface of the asymmetric iron oxide ceramic membrane. The pore size of the membrane is between 105 and 124 nm, and the porosity is 35 to 41%.

[0046] Comparative Example 1

[0047] 1.29 g of FeCl3·6H2O compound was accurately weighed and added to 50 mL of deionized water under ultrasonication for 5 minutes to fully dissolve the mixture. The mixture was then dropwise added to 40 mL of pre-boiled deionized water and heated in an oil bath to 100°C. The reaction was continued for 3 hours and then cooled to 80°C to obtain a ferric hydroxide sol. 10 mL of a 10 wt% PVA aqueous solution was then added dropwise to the ferric hydroxide sol, stirred at 80°C for 20 minutes, and then naturally cooled to room temperature to obtain a ferric hydroxide sol film-forming solution with a solid content of 0.5%. The solution was stirred in a mixer-degasser at 2000 rpm for 3 minutes, degassed at 2200 rpm for 5 minutes, and the mixing and degassing were repeated 3 times. The particle size of the ferric hydroxide sol was measured to be 100 to 200 nm. A sheet-type alumina ceramic membrane with an average pore size of 100 nm (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., diameter 3 cm, membrane thickness 2 mm) was cleaned with deionized water and dried at 110°C for 4 hours. The cleaned alumina ceramic membrane was immersed in the iron hydroxide sol membrane-forming solution for 1 minute, taken out at a speed of 10 mm / s, and naturally dried for 12 hours. The membrane was placed in a microwave sintering furnace and the power was linearly increased from 0 to 600 W within 3 minutes. The membrane was then sintered at 600 W for 4 minutes to obtain an asymmetric iron oxide ceramic membrane.

[0048] The micromorphology of the asymmetric iron oxide ceramic membrane prepared in this comparative example was analyzed by scanning electron microscopy (SEM). Figure 1 As shown in Figure d, the microscopic morphology of the ceramic membrane surface before and after coating the membrane solution is compared. It is found that compared with the original alumina ceramic membrane ( Figure 1 a) A new iron oxide film layer with a thickness of 2 μm was formed on the surface of the asymmetric iron oxide ceramic membrane. The surface nanoparticles were smaller and the surface was smoother. However, due to its long overall sintering time, the surface of the iron oxide film layer was densified and the pores were not obvious, indicating the formation of a dense layer. The pure water flux test showed a pure water flux of 0, which also indicated the formation of a dense layer and could not be used.

[0049] Comparative Example 2

[0050] 1.29 g of FeCl3·6H2O compound was accurately weighed and added to 50 mL of deionized water under ultrasonication for 5 minutes to fully dissolve the mixture. The mixture was then dropwise added to 40 mL of pre-boiled deionized water and heated in an oil bath to 100°C. The reaction was continued for 3 hours and then cooled to 80°C to obtain a ferric hydroxide sol. 10 mL of a 10 wt% PVA aqueous solution was then added dropwise to the ferric hydroxide sol, stirred at 80°C for 20 minutes, and then naturally cooled to room temperature to obtain a ferric hydroxide sol film-forming solution with a solid content of 0.5%. The solution was stirred in a mixer-degasser at 2000 rpm for 3 minutes, degassed at 2200 rpm for 5 minutes, and the mixing and degassing were repeated 3 times. The particle size of the ferric hydroxide sol was measured to be 100 to 200 nm. A sheet-type alumina ceramic membrane with an average pore size of 100 nm (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., diameter 3 cm, membrane thickness 2 mm) was cleaned with deionized water and dried at 110°C for 4 hours. The cleaned alumina ceramic membrane was immersed in the iron hydroxide sol membrane-forming solution for 1 minute, taken out at a speed of 10 mm / s, and naturally dried for 12 hours. Then, it was placed in a microwave sintering furnace and sintered at a constant 600 W for 4 minutes to obtain an asymmetric iron oxide ceramic membrane.

[0051] The micromorphology of the asymmetric iron oxide ceramic membrane prepared in this comparative example was analyzed by scanning electron microscopy (SEM). Figure 1 As shown in Figure e, the microscopic morphology of the ceramic membrane surface before and after coating the membrane solution is compared. It is found that compared with the original alumina ceramic membrane ( Figure 1 a) A complete iron oxide film layer is not formed on the surface of the asymmetric iron oxide ceramic membrane, and the membrane surface is still very rough. This is because the sintering microwave power is low, and the incomplete sintering causes PVA to remain on the membrane surface, and a complete iron oxide film layer cannot be formed. The cross section also shows that no obvious iron oxide layer is formed ( Figure 1 e right). However, the incomplete iron oxide layer on the surface of the ceramic membrane will gradually fall off, making it unusable.

[0052] Example 3

[0053] Pure water flux test experiments were conducted using the original alumina ceramic membrane, the asymmetric iron oxide ceramic membrane prepared in Example 1 and Comparative Example 2. During the experiment, the transmembrane pressure difference was 0.5 bar, the membrane surface flow rate was 1 m / s, and the operating temperature was 20°C. The experimental results are as follows: Figure 4 As shown in the figure, the results show that the stable flux of the original alumina ceramic membrane is 262 L·m -2 ·h -1 , while the asymmetric iron oxide ceramic membrane prepared in Example 1 has a stable flux of 213 L·m -2 ·h -1, the flux of the original ceramic membrane is reduced by 20%, which is because the load of the new iron oxide layer increases the total membrane resistance. Similarly, the asymmetric iron oxide ceramic membrane prepared in Comparative Example 2 has a stable flux of 230 L·m -2 ·h -1 , the flux of the original ceramic membrane was reduced by 12%. Because a complete iron oxide membrane layer was not formed, the flux drop was not as obvious as in Example 1.

[0054] Example 4

[0055] Continuous concentration and separation experiments were conducted on desizing wastewater (from a company in Quanzhou) using the original alumina ceramic membrane, the asymmetric iron oxide ceramic composite membrane prepared in Example 1 of the present invention, and the ceramic membrane prepared in Example 2 of patent CN 113926321A with iron oxide modified only on the ceramic membrane surface. The desizing wastewater had a COD of 10,000 to 18,000 mg / L, a pH of 12 to 14, and main components of 3 to 10 g / L of starch and 1 to 3 g / L of polyvinyl alcohol. During the membrane separation process, the transmembrane pressure difference was 1 bar, the membrane surface flow rate was 1.5 m / s, and the operating temperature was 70°C. The membrane flux was detected during the membrane separation process. The experimental results are as follows: Figure 5 As shown in the figure, the results show that after 210 min of operation, the permeation flux of the original alumina ceramic membrane is 60 L·m -2 ·h -1 The permeation flux of the ceramic membrane modified with iron oxide alone is 69 L·m -2 ·h -1 , while the permeation flux of the asymmetric iron oxide ceramic membrane prepared in Example 1 was 85 L·m -2 ·h -1 , which is 41.6% higher than the original ceramic membrane flux and 23.2% higher than the ceramic membrane modified with iron oxide alone. At this point, the feed solution is concentrated by 2 times or more, indicating that the asymmetric iron oxide ceramic composite membrane has better anti-fouling performance.

[0056] After 210 minutes of continuous concentration experiment, the membrane surface was rinsed with pure water for 60 minutes and backwashed for 5 minutes, and the membrane flux was tested again to calculate the membrane flux recovery rate. The experimental results are as follows: Figure 6As shown, the results show that the flux recovery rate of the original alumina ceramic membrane under pure water flushing is 42%, and the flux recovery rate under backwashing is 67%. The flux recovery rate of the ceramic membrane modified only with iron oxide is 49% under pure water flushing, and the flux recovery rate under backwashing is 76%. The flux recovery rate of the asymmetric iron oxide ceramic membrane prepared in Example 1 increased to 57% under pure water flushing, and the flux recovery rate under backwashing increased to 82%, which are 36% and 22% higher than the flux recovery rate of the original ceramic membrane, and 16.3% and 8% higher than the flux recovery rate of the ceramic membrane modified with iron oxide, respectively. The flux recovery performance of the asymmetric iron oxide ceramic composite membrane prepared by the present invention is improved.

[0057] The present invention provides an asymmetric iron oxide ceramic composite membrane and its preparation and application. Numerous methods and approaches exist for implementing this technical solution. The foregoing description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for preparing an asymmetric iron oxide ceramic composite membrane, characterized in that: The steps include: Step 1: hydrolyzing an aqueous ferric chloride solution at high temperature to obtain a ferric hydroxide sol, cooling the solution, and adding a polyvinyl alcohol aqueous solution to the solution to obtain a ferric hydroxide sol film-forming solution; Step 2: immerse the ceramic microfiltration membrane in the iron oxide sol membrane-forming solution obtained in step 1, take it out, dry it at room temperature, and sinter it with a microwave to obtain the membrane.

2. The preparation method according to claim 1, characterized in that In step 1, the high-temperature hydrolysis is: adding the ferric chloride aqueous solution dropwise into boiling water, and reacting at a temperature of 90-100° C. for 0.1-12 hours; the cooling is cooling to 70-90° C.

3. The preparation method according to claim 1, characterized in that In step 1, after adding the polyvinyl alcohol aqueous solution to the ferric hydroxide sol, stirring and reacting at a temperature of 70 to 90° C. for 10 to 30 minutes, the ferric hydroxide sol film-forming solution is obtained.

4. The preparation method according to claim 1, characterized in that In step 1, the solid content of ferric hydroxide in the ferric hydroxide sol film-forming solution is 0.1-0.6 wt %.

5. The preparation method according to claim 1, characterized in that When the content C of polyvinyl alcohol in the ferric hydroxide sol film-forming solution in step 1 is in the range of 0.25wt%≤C<0.5wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 400~600W, and the microwave sintering time is 3~5min; or, during the microwave sintering process, the microwave power is first linearly increased from 0 to the target power within 2~3min, and then sintered at a constant target power for 1~2min, and the target power is 400~600W.

6. The preparation method according to claim 1, characterized in that When in step 1, the content C of polyvinyl alcohol in the ferric hydroxide sol film-forming solution is in the range of 0.5wt%≤C≤0.75wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600-800W, and the microwave sintering time is 3-5min; or, during the microwave sintering process, the microwave power is first linearly increased from 0 to the target power within 2-3min, and then sintered at a constant target power for 2-3min, and the target power is 600-800W.

7. The preparation method according to claim 1, characterized in that When in step 1, the content C of polyvinyl alcohol in the ferric hydroxide sol film-forming solution is in the range of 0.75wt%<C≤1wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600-800W, and the microwave sintering time is 4-5min, or, during the microwave sintering process, the microwave power is first linearly increased from 0 to the target power within 2-3min, and then sintered at a constant target power for 3-4min, and the target power is 600-800W.

8. The preparation method according to claim 1, characterized in that In step 1, the polyvinyl alcohol is polyvinyl alcohol 124 type.

9. An asymmetric iron oxide ceramic composite membrane obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the asymmetric iron oxide ceramic composite membrane according to claim 9 in treating desizing wastewater in the printing and dyeing industry.

11. The use according to claim 10, characterized in that When the asymmetric iron oxide ceramic composite membrane is used to treat desizing wastewater in the printing and dyeing industry, the filtration method is cross-flow filtration, the transmembrane pressure difference is 1 to 2 bar, and the membrane surface flow rate is 1 to 1.5 m·s -1 , the operating temperature is 50~70℃.

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