| An integrated bioprocess called simultaneous saccharification and extractive fermentation (SSEF) was developed for conversion of cellulose and hemicellulose fractions of hardwood into acetone and butanol.; For pretreatment of hardwood, two novel methods, monoethanolamine (MEA) and supercritical CO{dollar}sb2{dollar}-SO{dollar}sb2{dollar} (SCS), were investigated. The cellulose and hemicellulose fractions were retained in the wood, while lignin and potential inhibitors were selectively removed from the wood. Especially, the retention of hemicellulose in wood was an important accomplishment. Overall carbohydrate yield of 83% was achieved in both pretreatments.; Cellulase and Clostridium acetobutylicum were employed in the simultaneous saccharification and fermentation (SSF) to convert pretreated hardwood into acetone-butanol. Near complete utilization of both cellulose and hemicellulose was achieved in a single bioreactor. Further investigation of batch SSF indicated that low cellulase loading and high substrate concentration were effective. Inhibition of the microorganism by butanol was the main factor limiting the total amount of substrate that can be processed in a batch reactor.; To alleviate the butanol inhibition, membrane assisted extraction was incorporated into SSF; thus, a fed-batch operation became feasible. This process was termed SSEF. In the SSEF, substrate and enzyme were fed to the bioreactor at regular intervals while the products were continuously extracted by oleyl alcohol. Due to product removal, C. acetobutylicum cells remained viable for an extended period of time. An increased substrate feeding rate increased the solvent production. The decreased nutrient supply was beneficial in minimizing biomass and acid production and thus enhancing the yield of solvents. Glucan and xylan utilization as high as 95 and 80%, respectively could be achieved in the SSEF. Due to glucose-limited condition prevalent in the SSEF process, both glucose and xylose were concurrently consumed by C. acetobutylicum.; An economic analysis showed that the SSEF process has potential to be commercialized. Cost of pretreatment equipment was 15 to 25% of the total cost. Therefore, its impact on overall economies was relatively small. |
