Heat supply and reduction of polarization effects in pervaporation by two-phase feed

Gas– and vapor–liquid two-phase pervaporation have been experimentally studied using a lab scale and a bench scale pervaporation setup. Pervaporation experiments with low liquid flow rates in internally coated tubes have been carried out for dewatering of 1,4-dioxane and isopropyl alcohol. Relatively small amounts of gas or vapor are sufficient to reduce concentration and temperature polarization and to increase the total flux and selectivity more than two-fold compared with single-phase experiments. The beneficial effects of a two-phase feed are also demonstrated by calculations. Additionally, by condensation the vapor effectively supplies the heat required for the selective evaporation through the membrane. As a consequence, this eliminates the liquid temperature drop that reduces the performance of pervaporation modules. The values of the total flux achieved using vapor–liquid two-phase pervaporation at laminar flow conditions are close to those for turbulent conditions.