Techno-Economic Analysis and Life-Cycle Assessment of Cellulosic Isobutanol and Comparison with Cellulosic Ethanol and n-Butanol

This 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). published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.