Application of mullite-zeolite-alumina microfiltration membranes coated by SiO2 nanoparticles for separation of oil-in-water emulsions

The main objective of this work is the manipulation of hydrophilic materials in support, intermediate and selective layer to synthesize a novel nano-tubular ceramic membrane for treatment of oily wastewater. First, porous mullite-alumina-zeolite composite membranes were prepared by an extrusion method. Changes in porosity, pore size, shrinkage, and mechanical strength of the support membranes were investigated as function of percentage composition and sintering temperature in order to obtain the optimal conditions. According to the results, the most favorable condition set was determined to be a support membrane with a weight percent of 50, 30, and 20 for mullite, alumina, and zeolite, respectively, and a porosity of 38%, a pore size of 0.39 µm, and a shrinkage of 10.2% sintered at 1250 °C and with good mechanical properties at 24.6 MPa. The cross-flow filtration technique was employed to coat the natural zeolite on the inner surface of the support membrane to achieve a narrower pore size distribution. Finally, a thick layer of nano-SiO₂ was coated on the membrane by utilizing the dip-coating method to develop a hydrophilic membrane while avoiding defects. Moreover, scanning electron microscopic (SEM) analysis of the SiO₂ membranes showed that the natural zeolite and nano-SiO₂ layer is homogeneous and demonstrates high adhesion to the support membrane. Besides, the result of COD rejection showed that the SiO₂ membranes have an undeniable capability in rejection of oil droplets with a reasonable permeation flux. Therefore, the obtained membranes are highly promising for practical applications and environmental remediation in sensitive Persian Gulf zone.