Separation of Organic-Water Mixtures by Co-current Vapor-Liquid Pervaporation with Transverse Hollow-Fiber Membranes

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.