(226d) Two-Stage Gas Stripping Recovery Process for Enhanced Butanol Production in Acetone-Butanol-Ethanol Fermentation by Clostridium Beijerinckii

Butanol is an important chemical and a potential biofuel that can be produced from biomass feedstock in acetone-butanol-ethanol (ABE) fermentation by solventogenic Clostridia. However, conventional ABE fermentation is limited by the low butanol product titer (<15 g/L), yield (~0.2 g/g glucose), and productivity (~0.3 g/L/h) due to strong butanol toxicity. In this work, a two-stage gas stripping recovery process was developed for online butanol recovery from ABE fermentation by a butanol-tolerant mutant strain of Clostridium beijerinckii immobilized in a fibrous bed bioreactor operated under repeated batch mode. In the successive batch fermentations with online gas stripping, total glucose utilization was 474.9 g/L and ABE production and productivity were 172.1 g/L and 0.53 g/L/h, respectively. In contrast, conventional batch fermentation without online gas stripping consumed 81.0 g/L glucose with ABE production and productivity of 25.5 g/L and 0.48 g/L/h, respectively. Overall, online gas stripping increased ABE productivity and yield 10.4% and 12.5%, respectively. Butanol, acetone and ethanol concentrations were 150.5, 36.9 and 8.6 g/L, respectively, in the condensate from the first-stage gas stripping and reached 434.2 g/L, 107.9 g/L and 19.2 g/L in the final product from the two-stage gas stripping. Acetic and butyric acids were not found in the condensate from the two-stage gas stripping process. The high butanol concentration obtained in the two-stage gas stripping process makes it highly energy efficient in recovering and purifying butanol from dilute ABE fermentation broth.