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

The advantages of a liq.-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 calcns. for the dehydration of iso-Pr alc. (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 coeffs. in combination with low pressure drops are achieved. Vapor also supplies the heat for the evapn. and expansion of the permeating components through the membrane. Mass-transfer coeffs. from the liq. to the membrane surface were measured using an electrochem. method. At low liq. 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 liq. result in a redn. of the required membrane area of 45%. This redn. in membrane area combined with the avoidance of interstage heat exchangers results in a marked redn. of capital costs, thus significantly expanding the application window of pervaporation. [on SciFinder (R)]