ABSTRACT
The process of producing butanol by fermentation was first discovered by Pasteur in 1861 (1). Butanol fermentation, also called acetone butanol ethanol (ABE) or solvent fermentation, is one of the oldest fermentation processes, second only to ethanol (1). The typical ratio of acetone to butanol to ethanol in the final product is usually 3:6:1 with maximum concentration of total solvents being 20 g L1 when using traditional strains and traditional batch fermentation processes. The low concentration of solvents is caused by end product inhibition and results in a high cost for solvent recovery using distillation. During the early part of the twentieth century this fermentation was commercially viable. However, in the 1950s and 1960s butanol and acetone produced by fermentation were unable to compete economically with petrochemically produced solvents.
