Current challenges and advances in butanol production
Abstract The fluctuating and overall average high market prices of fossil fuels have impacted the geopolitical scenario in the past few decades. In the majority of the United States this has resulted in policy shifts toward developing technologies for the use of renewable resources as feedstock for the production of biofuel and other valuable products. The biofuel butanol is mostly produced commercially by the acetone–butanol–ethanol (ABE) fermentation pathway using the Clostridium species. This strain consumes diverse sources of substrate via its anaerobic metabolic pathway. The biological production of butanol was one of the largest industrial fermentation processes during the early 20th century, but it lost its competitiveness by the 1960s due to the cost of substrates and with the advent of more efficient petrochemical processes. Other challenges in ABE fermentation have also restricted its growth in commercial production through fermentation. Advances in the fields of biotechnology, systems biology, metabolic engineering, and innovative process development have renewed the interest in the ABE fermentative process from its conventional roots. This chapter reviews the conventional butanol production process and addresses the problems and challenges that must be overcome in butanol production. Moreover, this chapter expands on current research trends in the development of production processes in areas like pretreatment, anaerobic and aerobic fermentation pathways, genetic modification of strains to enhance solvent production, and downstream processes for solvent extraction. The chapter also provides an analysis of the overall butanol fermentation process with a focus on improving the efficiency of the fermentation stage by altering the upstream (pretreatment of the raw material) and downstream (product recovery and purification) processes as a major possibility for development.