Sweeping gas pervaporation with hollow-fiber ion-exchange membranes

Selective and transport properties of an anion-exchange hollow-fiber membrane (Pervasiv Ltd., Israel) were determined in the sweeping gas pervaporation process used for the dehydration of different organic solvents. C2– C4 alcohols (i.e. ethanol — EtOH, propanol — nPrOH, isopropanol — iPrOH, n-butanol — nBuOH and isobutanol —iBuOH) and two esters (i.e. methyl acetate — MeAc and ethyl acetate — EtAc) were chosen for investigations. The water content in the feed mixture was in the range 1–8 wt.%. Pervasiv membrane possessed the hydrophilic properties in contact with water–organic mixtures investigated. The separation factor α of Pervasiv membrane was correlated with the dielectric constant of the organic solvent. It was found that α increased exponentially with the decrease of the dielectric constant of organic solvent. Such behaviour was caused not only by the decrease of the flux of the less polar organic component through the membrane but also by the substantial increase of the water flux. The concentration dependence of the permeate fluxes showed that the total flux increased when the amount of water in the feed increased. The molar partial fluxes of organic solvents were much higher for polar solvents (ethanol) when comparing with solvents of lower polarity (e.g. isobutanol, methyl acetate).

Selectivity and transport results obtained for the Pervasiv ion-exchange membrane in contact with different water–organic mixtures are in a good accordance with other results on pervapora tion with the ionomeric membranes [6–11,16]. Fig. 9 [17] presents the comparison of the selec tivity of the PESS-1/Li+ ion-exchange membrane in contact with different water–alcohol mixtures. It can be seen that selectivity of PESS ion- exchange membrane increases with decreasing polarity of a given alcohol [17]. It was already found that the supermolecular structure of ion-exchange membranes consists of Fig. 8. Comparison of the permeate molar fluxes of the different organic solvents. System: water–organic solvent mixtures.