Bioseparation 9: 145–154, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 145 Pervaporative stripping of acetone, butanol and ethanol to improve ABE fermentation Kawedia Jitesh D., Vishwas G. Pangarkar 1 & K. Niranjan 2 1 Department of Chemical Technology, University of Mumbai, Matunga, Mumbai 400 018, India; 2 Department of Food Science and Technology, University of Reading, Whitenights PO Box 226, Reading RG6 2AP, UK Key words: acetone, butanol, ethylene-propylene-diene-rubber, pervaporation, polydimethyl-siloxane, styrene- butadiene-rubber Abstract Acetone-butanol-ethanol fermentation by anaerobic bacterium C. acetobutylicum is a potential source for feedstock chemicals. The problem of product induced inhibition makes this fermentation economically infeasible. Pervapor- ation is studied as an effective separation technique to remove the toxic inhibitory products. Various membranes like Styrene Butadiene Rubber (SBR), Ethylene Propylene Diene Rubber (EPDM), plain Poly Dimethyl Siloxane (PDMS) and silicalite filled PDMS were studied for the removal of acetone, butanol and ethanol, from binary aqueous mixtures and from a quaternary mixture. It was found that the overall performance of PDMS filled with 15% w/w of silicalite was the best for removal of butanol in binary mixture study. SBR performance was best for the quaternary mixture studied. Introduction The acetone-butanol-ethanol (ABE) fermentation, us- ing anaerobic bacterium Clostridiunm acetobutylicum, continues to attract attention as a potential source of feedstock chemicals and liquid fuels (Maddox et. al., 1992). Considerable work has been carried out to improve the productivity of this process as the acetone–butanol-ethanol fermentation suffers from severe product induced inhibition. Product-induced inhibition is one of the major reasons that the production of acetone and butanol via fermentation is economically infeasible compared with the synthetic method based on petroleum feed- stock. The drawbacks of the inhibition are two fold: (1) The slow metabolic rate due to the inhibition res- ults in the requirement of a large reactor size and/or a long time to process a given quantity of substrate; (2) The inhibition also causes a dilute final product, which raises the energy cost for product separation and re- covery (Tsao and Yang, 1994). Thus, this route will be successful only if it is coupled to an effective product recovery technique to remove the inhibitory products. Extractive fermentation is a process that removes inhibitory products directly from the fermenter. Ex- tractive butanol fermentation improves butanol pro- ductivity by removing the toxicity. Separation techniques such as gas stripping (En- nis et al., 1986), liquid–liquid extraction (Eckert et al., 1987; Maddox et al., 1992), adsorption (Groot and Luyben, 1986; Neilson et al., 1988), ultrafiltra- tion (Ferras et al., 1986), reverse osmosis (Garcia et al., 1986), perstraction (Shukla et al., 1989) and pervaporation (Bengtson et al., 1991; Friedl et al., 1991; Groot and Luyben 1987; Larrayoz and Puig- janer 1987; Park and Qinghuang 1993) have been applied to ABE fermentation. In most cases, the separation of organic com- pounds is carried out at the industrial level using distillation, which is very expensive in terms of energy consumption. On the other hand, membrane separa- tion proccesses are more promising due to their low energy requirement and due to the fact that they have been widely developed in several industrial areas, such as salt water desalination, oxygen rich air production, etc. Membrane based processes such as pervaporation and perstraction have attracted recent attention, be- cause they can be more selective than non-membrane based processes. Pervaporation received more atten-