Pervaporative separation of n-butanol from dilute aqueous solutions using silicalite-filled poly(dimethyl siloxane) membranes

Pervaporative separation of n-butanol from dilute aqueous solutions (<0.5 wt%) using a silicalite-filled poly(dimethyl siloxane) composite membrane was investigated. The effects of operating conditions (e.g., feed composition, temperature) on the permeation flux, separation factor and pervaporation separation index were evaluated. It was shown that at a given temperature, water flux increased almost linearly with an increase in feed butanol concentration, whereas the butanol flux increased in a concave fashion due to silicalite fillers that have a strong affinity to butanol molecules. Consequently, the permeate butanol concentration initially increased and then gradually leveled off when the feed butanol concentration was high enough, and the leveling off started to occur at a lower butanol concentration at a higher temperature. The temperature dependence of permeation flux followed a typical Arrhenius relation, and a variation in temperature would increase or decrease the membrane selectivity, depending on feed butanol concentration. These results are especially important for potential use of the membrane for in situ butanol extraction from fermentation where butanol becomes inhibitory at a low concentration of 4–6 g/L.