Techno‐economic analysis and life‐cycle assessment of cellulosic isobutanol and comparison with cellulosic ethanol and n‐butanol

Abstract

AbstractThis work presents a detailed analysis of the production design and economics of the cellulosic isobutanol conversion processes and compares cellulosic isobutanol with cellulosic ethanol and n‐butanol in the areas of fuel properties and engine compatibility, fermentation technology, product purification process design and energy consumption, overall process economics, and life cycle assessment. Techno‐economic analysis is used to understand the current stage of isobutanol process development and the impact of key parameters on the overall process economics in a consistent way (i.e. using the same financial assumptions, plant scale, and cost basis). The calculated minimum isobutanol selling price is $3.62/gasoline gallon equivalent ($/GGE) – similar to $3.66/GGE from the n‐butanol process and higher than $3.26/GGE from the cellulosic ethanol conversion process. At the conversion stage, the n‐butanol process emits the most direct CO2, at 26.42 kg CO2/GGE. Isobutanol and ethanol plants have relatively similar CO2 emissions, at 21.91 kg CO2/GGE and 21.01 kg CO2/GGE, respectively. The consumptive water use of the biorefineries increases in the following order: ethanol (8.19 gal/GGE) < isobutanol (8.98 gal/GGE) < n‐butanol (10.84 gal/GGE). Field‐to‐wheel life cycle greenhouse gas (GHG) emissions for the ethanol and n‐butanol conversion processes are similar at 4.3 and 4.5 kg CO2‐eq/GGE, respectively. The life cycle GHG emissions result for the isobutanol conversion process is 5.0 kg CO2‐eq/GGE, approximately 17% higher than that of ethanol. The life cycle fossil fuel consumption is 39 MJ/GGE for n‐butanol, 43 MJ/GGE for ethanol and 51 MJ/GGE for isobutanol. The energy return on investment for each biofuel is also determined and compared: isobutanol (2.2:1) < ethanol (2.7:1) < n‐butanol (2.8:1). © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd