RESUMO
The Isopropanol-Butanol-Ethanol productivity by solventogenic clostridia can increase when cells are immobilized on low-cost, renewable fibrous materials; however, butanol inhibition imposes the need for dilute sugar solutions (less than40 g/L). To alleviate this problem, the in-situ vacuum product recovery technique was applied to recover IBE in repeated-batch cultivation of Clostridium beijerinckii DSM 6423 immobilized on sugarcane bagasse. Five repeated batch cycles were conducted in a 7-L bioreactor containing P2 medium (â¼60 g/L glucose) and bagasse packed in 3D-printed concentric annular baskets. In three cycles, glucose was consumed by 86% on average, the IBE productivity was 0.35 g/Lâh or 30% and 17% higher relative to free- and immobilized (without vacuum)-cell cultures. Notably, the product stream contained 45 g/L IBE. However, the fermentation was unsatisfactory in two cycles. Finally, by inserting a fibrous bed with hollow annuli in a vacuum fermentation, this work introduces the concept of an internal-loop boiling-driven fibrous-bed bioreactor.
Assuntos
2-Propanol , Butanóis , Reatores Biológicos , Etanol , Fermentação , VácuoRESUMO
Production of butanol for fuel via the conventional Acetone-Butanol-Ethanol fermentation has been considered economically risky because of a potential oversupply of acetone. Alternatively, acetone is converted into isopropanol by specific solventogenic Clostridium species in the Isopropanol-Butanol-Ethanol (IBE) fermentation. This route, although less efficient, has been gaining attention because IBE mixtures are a potential fuel. The present work is dedicated to reviewing past and recent advances in microorganisms, feedstock, and fermentation equipment for IBE production. In our analysis we demonstrate the importance of novel engineered IBE-producing Clostridium strains and cell retention systems to decrease the staggering number of fermentation tanks required by IBE plants equipped with conventional technology. We also summarize the recent progress on recovery techniques integrated with fermentation, especially gas stripping. In addition, we assessed ongoing pilot-plant efforts that have been enabling IBE production from woody feedstock.