On the synthesis of biorefineries for high-yield isobutanol production: from biomass-to-alcohol experiments to system level analysis

The production of isobutanol from lignocellulose has gained attention due to its favorable physical and chemical properties. The use of lignocellulosic biomass as a feedstock to produce isobutanol has substantial sustainability benefits, but the biological conversion to isobutanol faces challenges, such as low yields and by-product formation. In this work, we demonstrate the high-yield production of isobutanol through microbial fermentation of pulp hydrolysates. Three hydrolysates are produced from poplar, sorghum, and switchgrass using pretreatment based on gamma-valerolactone. Furthermore, we synthesize a biomass-to-isobutanol biorefinery and perform technoeconomic analysis of three resulting processes using experimental results obtained from an engineered yeast strain which consumes most of the glucose available in the hydrolysate and produces isobutanol at 89-94% theoretical yields. The corresponding minimum fuel selling price (MFSP) is $14.40-$16.01 per gasoline gallon equivalent, with the sorghum-based biorefinery resulting in the lowest price. We identify that solvent/biomass ratio during pretreatment and enzyme loading during hydrolysis have the greatest impact on the MFSP; improvements in these parameters can reduce the MFSP by 46%. High yield isobutanol production is experimentally demonstrated. The solvent-to-biomass ratio during pretreatment and enzyme production during hydrolysis are identified as the major economic drivers of the biorefinery.