PERVAPORATION AND VAPOR PERMEATION BEHAVIOR OF WATER AND 2-PROPANOL IN WATER-SELECTIVE MEMBRANES

The pervaporation (PV) behavior of water and 2-propanol mixtures is co mpared with vapor permeation (VP) behavior using three types of water- selective composite or asymmetric membranes with different materials i n their skin layers, Le., membranes of polyion complex with polyacryli c acid (PIG-PAAc), polyion complex with partially hydrolyzed polyacryl onitrile (PIG-PAN), and polyparabanic acid (PPAc). From solubility mea surements of water-2-propanol mixtures in dense membranes at 356 K, it is found that in liquid phase experiments PIG-PAAc and PIG-PAN membra nes show higher solubility of water than PPAc membrane, although no si gnificant difference in solubilities of water vapor among the three me mbranes is observed in vapor phase experiments. In permeation experime nts at 356 K, the PV water fluxes through the three membranes are high er than those for VP if the mole fractions of 2-propanol in the feed s olution (x(1p)) are below 0.90. Using PIG-PAAc and PIG-PAN membranes, higher fluxes of 2-propanol are obtained for PV at less than x(1p)=0.6 as compared with those for VP. However, remarkable differences in 2-p ropanol fluxes are not observed between PV and VP using a PPAc membran e. Based on the solution-diffusion theory and taking account of water solubility in the membranes, the fluxes of water and 2-propanol for bo th PV and VP are analyzed for PIG-PAAc, PIG-PAN and PPAc membranes. Ap proximate coincidence in the estimated values of diffusion coefficient s without swelling and the swelling parameters for water and 2-propano l, which indicated their diffusivities in the membranes, are obtained for PV and VP using the respective membranes.