Air gap membrane distillation of aqueous alcohol solutions

Aqueous solutions of alcohol (ethanol, methanol or isopropanol) have been experimentally investigated in air gap membrane distillation (AGMD), for a wide range of operating conditions. The effects of the relevant process parameters on the permeate flux have been studied. On the basis of a temperature polarisation model - which takes into account the mass and heat transfers across the hydrophobic membrane - the equivalent film heat transfer coefficient and the overall membrane mass transfer coefficient can be obtained from the experimental data. Also the alcohol and water membrane transfer coefficients have been obtained assuming the validity of Graham's diffusion law for multicomponent mixtures. From these coefficients the temperature and composition in the liquid-vapour interfaces are evaluated, taking into account the temperature polarisation acid concentration polarisation models. Finally, the effect of the Reynolds number on the permeate flux has been discussed using the temperature polarisation model and the heat transfer correlation given by Sieder and Tate. (C) 2000 Elsevier Science B.V. All rights reserved.