CONCENTRATION POLARIZATION IN PERVAPORATION SEPARATION PROCESSES

Concentration polarization is a phenomenon inherent to membrane separation processes. Starting from the basic equations for mass transport, a theoretical approach is pursued to describe the concentration polarization in pervaporation processes. A parametric analysis shows that the significance of concentration polarization is determined not only by the membrane permeability and the system hydrodynamics but also by the membrane selectivity. The effect of concentration polarization is intensified with an increase in membrane permselectivity and/or a decrease in the mass transfer coefficient in the liquid boundary layer. The concentration polarization may be, but is not necessarily, more severe in the pervaporation of dilute solutions at lower concentration levels where the minor component permeates through the membrane preferentially; however, when the feed concentration is considerably high, the concentration polarization is unlikely to pose a severe problem to the separation performance. The validity of the approach is verified by testing the agreement between the experimental data in the literature and the theoretical calculations.