Greenhouse Gas Footprint, Water-Intensity, and Production Cost of Bio-Based Isopentenol as a Renewable Transportation Fuel

Although ethanol remains the dominant liquid biofuel in the global market, there is a strong interest in high-energy density and low-hygroscopicity compounds that can be incorporated into gasoline at levels beyond the current ethanol blend wall. Isopentenol (3-methyl-3-buten-1-ol) is one of these promising advanced biofuels that is also an important precursor for isoprene (the main component of natural rubber). In this study, we model the production cost, greenhouse gas (GHG) emissions, and water footprint of biologically produced isopentenol, including the current state of the technology and the impact of potential improvements. We find that the minimum selling price of biobased isopentenol, given the current state of technology demonstrated at bench-scale, is $5.14/L-gasoline equivalent, and the GHG footprint exceeds that of gasoline. However, biobased isopentenol could reach a $0.62/L-gasoline equivalent [$2.4/gal-gasoline equivalent (gge), just 5% above the 10-year average gasoline price] in an optimized future case where yield and other process parameters are pushed to near their theoretical limits. In this future case, isopentenol could achieve a GHG reduction of 90% relative to gasoline and a carbon abatement cost of $9.3/metric ton CO2e. Reaching these goals will require dramatic improvements in isopentenol yield, near-100% recovery of ionic liquid used in pretreatment, and low-lignin and high-cellulose and -hemicellulose biomass feedstocks.