Pervaporation and vaper permeation behavior of water and 2-propanol in water-selective membranes

The pervaporation (PV) behavior of water and 2-propanol mixtures is compared with vapor permeation (VP) behavior using three types of water-selective composite or asymmetric membranes with different materials in their skin layers, i.e., membranes of polyion complex with polyacrylic acid (PIC-PAAc), polyion complex with partially hydrolyzed polyacrylonitrile (PIC-PAN), and polyparabanic acid (PPAc). From solubility measurements of water-2-propanol mixtures in dense membranes at 356 K, it is found that in liquid phase experiments PIC-PAAc and PIC-PAN membranes show higher solubility of water than PPAc membrane, although no significant difference in solubilities of water vapor among the three membranes is observed in vapor phase experiments. In permeation experiments at 356 K, the PV water fluxes through the three membranes are higher than those for VP if the mole fractions of 2-propanol in the feed solution (x1p) are below 0.90. Using PIC-PAAc and PIC-PAN membranes, higher fluxes of 2-propanol are obtained for PV at less than x1p = 0.6 as compared with those for VP. However, remarkable differences in 2-propanol fluxes are not observed between PV and VP using a PPAc membrane.Based on the solution-diffusion theory and taking account of water solubility in the membranes, the fluxes of water and 2-propanol for both PV and VP are analyzed for PIC-PAAc, PIC-PAN and PPAc membranes. Approximate coincidence in the estimated values of diffusion coefficients without swelling and the swelling parameters for water and 2-propanol, which indicated their diffusivities in the membranes, are obtained for PV and VP using the respective membranes.