PROCESS IMPROVEMENT IN ACETONE-BUTANOL PRODUCTION FROM HARDWOOD BY SIMULTANEOUS SACCHARIFICATION AND EXTRACTIVE FERMENTATION

The acetone-butanol production by simultaneous saccharification and ex tractive fermentation (SSEF) was investigated. In the SSEF employing c ellulase enzymes and Clostridium acetobutylicum, both glucan and xylan fractions of pretreated aspen are concurrently converted into acetone and butanol. Continuous removal of the fermentation products from the bioreactor by extraction was an important factor that allowed long-te rm fed-batch operation. The use of membrane extraction prevented the p roblems of phase separation and extractant loss. Increase in substrate feeding as well as reduction of nutrient supply was found to be benef icial in suppressing the acid production, thereby improving the solven t yield. Because of prolonged low growth conditions prevalent in the f ed-batch operation, the butanol-to-acetone ratio in the product was si gnificantly higher at 2.6-2.8 compared to the typical value of two.