Pervaporative butanol removal from PBE fermentation broths for the bioconversion of glycerol by Clostridium pasteurianum

Abstract

Batch-wise butanol removal using vacuum pervaporation (VPV) was investigated to assess its technical feasibility for future integration with a continuous PBE (1,3-propanediol-butanol-ethanol) fermentation process using glycerol as feedstock. Two commercial polydimethylsiloxane (PDMS) membrane configurations were characterized using binary model solutions and authentic fermentation broths, while varying feed temperature, butanol concentration and flow rate. The Sulzer Chemtech flat sheet membrane (Pervap 4060) showed superior selective removal of butanol, presumably due to the thinner membrane and the turbulent flow regime which minimizes concentration polarization. Most important, butanol had the highest removal rate of all fermentation products and intermediates measured, while glycerol (substrate), acetic acid and 1,3-propanediol (1,3-PDO) did not cross the membrane in measurable quantities. Great improvements can be made by operating pervaporation at higher temperature (50 versus 35 °C) and higher feed butanol concentration. The performances using fermentation broths mimicked that of binary model solutions in repeated trials, indicating little interference from media components. Under the best operating conditions, 8.8 g h−1 (517.3 g m−2 h −1) butanol was removed when the feed concentration of butanol was 11 g L−1 (1.1% w/w). The potential of using pervaporation for in-situ butanol removal in PBE fermentation was successfully demonstrated.