Temperature polarization in pervaporation

The incidence of temperature polarization has received considerable attention in membrane processes such as membrane distillation and thermoosmosis but has been much less investigated in pervaporation. Based on a theoretical computation on a case study (pervaporation of water through a dense cellulose acetate membrane), it has been confirmed that this phenomenon is likely to occur frequently, as soon as a thin and permeable membrane is used, with the temperature drop being located essentially in the liquid boundary layer. Experimental investigations on the importance of temperature polarization and its influence on pervaporation flux have been further performed with pure liquids (water and organic compounds) by changing the impeller agitation rate in a batch stirred cell. Different membrane materials (cellulose acetate, Cuprophan, PDMS, PEBA) and various liquids (water, ethanol, butanol, pentanol, ethyl propionate) were investigated in order to point out the influence of either liquid or membrane material physico-chemical properties on the temperature polarization effect. A simplified data treatment of the observed results, derived from theoretical computations, is proposed and discussed.