IBE production (isopropanol, butanol, and ethanol) from the fermentation of sugarcane bagasse lignocellulosic sugars mixed with molasses

Abstract

Regarding the second-generation ethanol production from sugarcane bagasse integrated into existing mills, the yeast Saccharomyces cerevisiae, commonly used in the industries for first generation ethanol production, cannot metabolize an important fraction of hemicellulose sugars (mostly composed by pentoses). Among several possibilities of using pentose sugars (C5), the conversion to n-butanol is attracting commercial interesting due to its use as chemical and biofuel. Nowadays, this solvent is industrially produced through acetone/butanol/ethanol (ABE) fermentation. However, this process has been considered less economical when compared to ethanol fermentation process due to the presence of acetone, an undesirable co-product because of its corrosiveness and poor fuel properties. Acetone can be easily converted to isopropanol in a single biochemical step by some Clostridium beijerinckii strains, which produce the IBE (isopropanol/butanol/ethanol) mixture at the end of the fermentation. For fuel application, the IBE mixture seems to be more attractive than the ABE due to advantageous isopropanol properties over acetone, such as higher energy density (23.9 ML/L vs 22.6 MJ/L). Furthermore, it is expected an energy gain since IBE mixture separation is not necessary. However, technical limitations in the fermentation process persist. The use of low-cost lignocellulosic materials readily available in the ethanol producing plants, such as sugarcane bagasse hydrolysates and molasses allows for a flexible process in response to market demands. Furthermore, the utilization of in situ product removal techniques would alleviate product inhibition (especially butanol) leading to increased yields and productivities. Therefore, the aim of this work is to evaluate the IBE fermentation process by the strain Clostridium beijerinckii DSM 6423 in media composed by different mixes of molasses and sugarcane bagasse hydrolysate (C5 and C6 fractions), as well as determine potential performance gains (productivities, product final concentration) using the vacuum fermentation technology. (AU)