Block copolymer pervaporation membrane for in situ product removal during acetone-butanol-ethanol fermentation

We address two major challenges facing commercialization of acetone-butanol-ethanol (ABE) fermentation: product inhibition and low productivity. We studied a polystyrene-b-polydimethylsiloxane-b-polystyrene (SDS) triblock copolymer membrane for selective removal of butanol from aqueous solutions by pervaporation. The SDS membrane exhibited higher permeabilities than a commercially available cross-linked polydimethylsiloxane (PDMS) membrane. Both types of pervaporation membrane were also used for in situ product removal of ABE biofuels in Clostridium acetobutylicum fermentations operated in a semi-continuous mode. Membrane performance and its effect on the fermentation process were assessed by measuring flux, OD₆₀₀ and concentrations of different components in the fermenter as a function of time. Volumetric ABE productivity increased from 0.45g/(Lh) in simple batch fermentation to 0.66g/(Lh) in the case of pervaporative-fermentation with the PDMS membrane. A further increase in productivity to 0.94g/(Lh) was obtained in the case of pervaporative-fermentation with the SDS membrane. Overall, total ABE production improved by a factor of three, viable fermentation time increased by a factor of two, and cell density increased by a factor of 2.5 upon applying SDS membrane pervaporation, relative to the batch process.