The advantages of a liquid−vapor feed in a pervaporation unit are presented in comparison to a single-phase
feed pervaporation unit that uses interstage heating. The comparison is based on calculations for the dehydration
of isopropyl alcohol (IPA) from 13 to 1 wt % in a transverse system with hollow-fiber membranes. Because
of the presence of the vapor phase, high mass- and heat-transfer coefficients in combination with low pressure
drops are achieved. Vapor also supplies the heat for the evaporation and expansion of the permeating
components through the membrane. Mass-transfer coefficients from the liquid to the membrane surface were
measured using an electrochemical method. At low liquid superficial velocities, mass transfer increases up to
4-fold as compared to single-phase flow. Both the enhancement in mass and heat transfer to the membrane
and the energy supply to the liquid result in a reduction of the required membrane area of 45%. This reduction
in membrane area combined with the avoidance of interstage heat exchangers results in a marked reduction
of capital costs, thus significantly expanding the application window of pervaporation.