Opportunities and barriers for n-butanol production in integrated first and second generation sugarcane biorefineries in Brazil

Oil prices instability and concerns about fossil fuel diminishing reserves and impacts on the environment have motivated the use of renewable feedstocks for production of fuels and chemicals. Ethanol is already produced in large scale, whereas n-butanol has received increasing attention due to its properties that make it a suitable alternative fuel for gasoline engines, in addition to a highly employed precursor in industrial processes.

Second generation biofuels have been envisioned as a more sustainable alternative than first generation, due to the larger availability of lignocellulosic feedstocks and presumably non-competitiveness with food production. The ABE (acetone – butanol – ethanol) fermentation route has been implemented in industrial processes despite its drawbacks (low n-butanol yield and productivity). Alternatively, n-butanol could be produced from the catalysis of ethanol in existing production facilities.

In this study, ABE fermentation and ethanol catalytic conversion to n-butanol and co-products have been evaluated in an integrated first and second generation sugarcane biorefinery. Process simulation and Monte Carlo-based analysis were used to identify critical techno-economic parameters for the financial model. Life cycle assessment was carried out to evaluate the environmental benefits of n-butanol use as liquid vehicle fuel.

Promising figures were obtained for the economic feasibility of both ABE fermentation and ethanol catalytic process. Environmental impact analysis showed reduction of over 60 % for greenhouse gas emissions associated with n-butanol use in comparison with gasoline, which is in compliance with EPA’s Renewable Fuel Standard advanced biofuel classification rule.