Pervaporation is one of the most active areas in membrane research, and the pervaporation
process has been shown to be an indispensable component for chemical separations. In this
paper, the recent development in pervaporation membranes and pervaporation processes is
reviewed, and some outstanding questions involved in membrane pervaporation are discussed
with emphasis on the following issues: mass transport in the membrane, membrane material
selection, concentration polarization in the boundary layer, pressure buildup in hollow fiber
membranes, asymmetric and composite membranes, and the activation energy for permeation.
We attempt to provide insight into this dynamic field and to highlight some of the outstanding
problems yet to be solved or clarified.