Comparison of various membrane distillation methods for desalination using hydrophobic ceramic membranes

Membrane distillation (MD) is an emerging separation process suitable for desalination of brackish or seawater. In this technique, hydrophobic membranes are required to allow only water vapour permeation through the porous barrier. In this work, zirconia and titania ceramic membranes with pore diameters of 50 nm (Zr50) and 5 nm (Ti5), respectively, were chemically modified to change their hydrophilic feature into hydrophobic one by grafting of the C8F17(CH2)2Si(OC2H5)3 perfluoroalkylsilane molecule (C8). Water contact angles around 160° were measured, indicative of highly hydrophobic membranes. Desalination of NaCl solutions of 0.5 and 1 M was performed using three MD configurations, AGMD, DCMD and VMD methods, with the aim to compare their efficiency. High salt rejection rates higher than 99% were obtained in all investigated configurations.