Study On The Controlling Of Membrane Defect Of α-Al₂O₃ Microfiltration Membrane

Inorganic membrane has good mechanical strength, acid and alkali resistance and solvent resistance, can be repeated washing recycling advantages, make it widely used in chemical industry, metallurgy, food, environment and other fields. Separation of function depends on the microstructure of inorganic membrane, such as pore size, porosity, pore size distribution, curvature of pore channel and so on. The inorganic membrane used asymmetric structure, namely making smaller aperture transition layer and the smallest aperture separation layer on the surface of the support with big aperture, this structure helps to reduce the penetration resistance, but also make the preparation process very complex, in order to obtain the membrane with narrow distribution of pore size, every layer is required to process control system preparation of the right. At present, The main problem of the inorganic membrane preparation technology system in our country is the membrane defect lead to the pore size distribution is too wide, affecting the separation performance of inorganic membrane. Therefore, we must reduce the defect of inorganic membrane from the perspective of producing technology, membrane defect control including support, transition layer, the separation layer.In this paper, taking α-Al2O3 as the main raw material, by means of testing SEM, pore size analyzer, laser particle size analyzer, study on effects of the alumina raw materials performance of porous ceramic support, transition layer, separation layer membrane defect and suspension stability of alumina coating slurry, the particle size distribution control of membrane defect, powder surface modification in order to help obtain the stability suspension coating slurry, resulting in alumina microfiltration membrane with narrow distribution of pore size distribution and controllable pore size. The main research results are as follows:(1) In order to reduce the defects of the support, using α-Al2O3 that average particle size is 40μm as the main raw material, adding α-Al2O3 that average particle size is 1μm and 70μm respectively obtained certain particle size distribution mixed powder, through the analysis of the influence of the maximum and smallest particle on the support pore size distribution, porosity and flexural strength, we can find that small particles are filled with macroporous support, reduce the maximum hole of the support, reduce membrane defects. At the same time, small particle size powder also plays the role of sintering additives, help to improve the support strength, but it will reduce the support pore size and porosity. Maximum particle of powder can obtain a large aperture and high porosity, but also the main source of defects of large aperture, we need to control it.(2) In order to improve the suspension stability of large particle size powder, using aluminum isopropoxide as the precursor, on the surface of 5μm, 10μm irregular and spherical α-Al2O3 particles prepared by a layer of nano alumina by solvothermal method respectively, increasing specific surface area of the particle size of powder then then reinforcing the function of particles and dispersing agent, adjust the content of dispersing agent and stabilizer to improve the stability of the slurry. The results show this method makes the suspension of the large particle size were significantly improved, helps to reduce membrane defects.(3) In order to control membrane defect of the transition layer, three kinds of α-Al2O3 powder with average particle size of 1μm 3μm and 5μm were mixed and prepared into the stable suspension, study on the influence of the particle size distribution of the change of membrane pore size distribution of the membrane. The results show that the pore size of membrane depends on the particle size distribution of the raw material, the most probable pore depends on the peak of particle size distribution. The particle size distribution is wide, the pore size distribution of the obtained membrane is wide, and vice versa. The number of large particles in the mixed powder increased, the maximum pore and the most probable pore of pore size distributionl increased too, the big hole defects increased. The number of small particles in the mixed powder increased, the maximum hole and the most probable pore decrescent, the big hole defects reduced. In addition, with the thickness of the membrane growth, the maximum pore and average pore size of the membrane reduced in a certain extent.(4) Slurry particles at the bottom of the rapid accumulation of membrane, contribute to the formation of continuous wet membrane, to prevent defect underlying the membrane transfer to the upper. Coating thickness can be controlled by coating time. In the condition of the same membrane layer thickness, The large hole defects of the membrane were rapidly filled with the slurry particles by the pressure leaching slurry coating process, helps to reduce the defects of the membrane. The membrane thickness using 3μm spherical alumina coating the 30s in 0.2MPa is 22μm,the most probable pore was 0.33μm, while the maximum pore is 0.6μm, which shows that the technology can reduce the membrane defect effectively, obtained a narrow pore size distribution and good permeability flux microfiltration membrane.