Evaluation of the cleaning of a new hydrophobic membrane for osmotic evaporation

Osmotic evaporation (OE) is a membrane contactor process which can be used to concentrate aqueous solutions with minimal thermal or mechanical damage. Generally OE is carried out with hydrophobic polymeric membranes, but these membranes can be easily deformed under operating conditions causing the wetting of the pores. In this study we modify the surface of tubular ceramic membranes in order to be used in OE process. Flat and tubular ceramic macroporous alumina membranes with 2 × 10−7 m of mean pore size were modified by grafting with fluoroalkylsilane. Scanning electron microscopy, mercury porosimetry, contact angle measurements and water penetration pressure (WPP) were used to characterize the porous structure and the hydrophobicity of grafted membranes. The resistance of the hydrophobic layer to cleaning agents (1% NaOH, 1% HNO3, 1% Ultrasil-10, 200 ppm Cl−1 and vapour sterilization) was evaluated by WPP and the performance in OE process was measured after each cycle of cleaning. The cleaning with 1% NaOH and 1% Ultrasil-10 produced a reduction of 15 and 21% of the WPP, respectively. Indeed, the membranes can be used in the OE process while the WPP is higher than the transmembrane pressure applied.