Selective separation of n-butanol from aqueous solutions by pervaporation using silicone rubber-coated silicalite membranes

BACKGROUND: To use butanol as a liquid fuel and feedstock, it is necessary to establish processes for refining low-concentration butanol solutions. Pervaporation (PV) employing hydrophobic silicalite membranes for selective recovery of butanol is a promising approach. In this study, the adsorption behavior of components present in clostridia fermentation broths on membrane material (silicalite powder) was investigated. The potential of PV using silicone rubber-coated silicalite membranes for the selective separation of butanol from model acetone-butanol-ethanol (ABE) solutions was investigated. RESULTS: The equilibrium adsorbed amounts of ABE per gram of silicalite from aqueous solutions of binary mixtures at 30 degrees C increased as follows: ethanol (95 mg) < acetone (100 mg) < n-butanol (120 mg). The amount of butanol adsorbed is decreased by the adsorption of acetone and butyric acid. In the separation of ternary butanol/water/acetone mixtures, the enrichment factor for acetone decreased, compared with that in binary acetone/water mixtures. In the separation of a model acetone-butanol-ethanol (ABE) fermentation broth containing butyric acid by PV using a silicone rubber-coated silicalite membrane, the permeate butanol concentration was comparable with that obtained in the separation of a model ABE broth without butyric acid. The total flux decreased with decreasing feed solution pH. CONCLUSION: A silicone rubber-coated silicalite membrane exhibited highly selective PV performance in the separation of a model ABE solution. It is very important to demonstrate the effectiveness of PV in the separation of actual clostridia fermentation broths, and to identify the factors affecting PV performance. (C) 2011 Society of Chemical Industry