Preparation, characterization and permeation property of Al2O3, Al2O3–SiO2 and Al2O3–kaolin hollow fiber membranes

Al2O3, Al2O3–SiO2 and Al2O3–kaolin hollow fiber precursors were prepared by a wet-spinning method using polyethersulfone (PES), Al2O3, SiO2 and kaolin. The hollow fiber membranes were obtained after a preheating and sintering combining process. These inorganic hollow fiber membranes had been characterized by SEM, XRD, porosity, density, mechanical property, permeation property and the mean/maximum pore size as well as pore size distribution, to investigate the effects of SiO2 and kaolin on α-Al2O3 hollow fiber membranes. The morphology of precursors depended on the particle contents and PES concentrations in the dispersion, and the final structure of sintered membranes were controlled by the precursors. XRD results showed that Al2O3 remained as α-Al2O3 before and after being sintered while SiO2 changed from tridymite to cristobalite from ambient temperature to 1450 °C, and at higher temperature it would react with Al2O3 to produce the stoichiometric 3:2 mullite (3Al2O3·2SiO2, or Al6Si2O13) by solid state reaction. The effect of SiO2 and kaolin on the membrane properties depended on both the ratio of Al2O3:SiO2/kaolin and the sintering temperature. Moreover, when sintering temperature was 1600 °C, Al2O3–kaolin-5 (Al2O3:kaolin = 1:1) achieved a mean pore size of about 0.5 μm.