Pervaporation and vacuum membrane distillation processes: Modeling and experiments

Two separation processes, pervaporation (PV) and vacuum membrane distillation (VMD), were studied using polyvinylidene fluoride (PVDF) flat-sheet membranes for the separation of chloroform-water mixtures. Both PV and VMD membranes were prepared using the phase-inversion method and the same polymer material. VMD membranes with different pore sizes were prepared using pure water as a pore forming additive in the PVDF/dimethylacetamide casting solution, whereas PV membranes were obtained with higher polymer concentration, without nonsolvent additives and with solvent evaporation before gelation. The mean pore size, porosity, and pore size distributions of the VMD membranes were determined. Water and formamide advancing and receding contact angles of PV membranes were measured. The swelling degree, the solubility parameter of PV membranes, and the interaction of the permeants with the PVDF polymer were calculated. In the VMD process, a more general theoretical model that considers the pore size distribution, the solution-diffusion contribution through nonporous membrane portion, and the gas transport mechanisms through membrane pores was developed based on the kinetic theory of gases. The contribution of each mechanism was analyzed. A comparative study was made between both membrane separation technologies. (C) 2004 American Institute of Chemical Engineers.