Pervaporation of water/ethanol mixtures through microporous silica membranes

Several microporous silica membranes prepared by sol–gel processing were studied for separation of water–ethanol mixtures by pervaporation (PV). The permeate flux and separation factor of the prepared silica membranes decreased gradually at the beginning of the pervaporation-based separation of the water–ethanol mixture (ethanol concentration: 94 wt%); after 6–10 h, the PV performance characteristics reached a steady state. The water flux of the silica membranes ranged from 0.3 to 0.8 kg/(m2 h), while the separation factor ranged from 10 to 500. Repeated PV experiments revealed that water and ethanol flux were high during the initial stages of the experiments and then declined; this pattern was observed more clearly at higher temperatures. A possible explanation for this phenomenon is that gradual physical and physicochemical adsorption subsequently plugged the membrane pores and prevented permeation. The relationship between PV performance and temperature was examined in the context of the adsorption–diffusion model for determination of the appropriate PV temperature.