(454d) Progress Toward Sustainable Biofuels ― Pilot-Scale Demonstration of Integrated Cellulosic Ethanol Production

In 2007, the U.S. Department of Energy’s (DOE) Office of the Biomass Program, in collaboration with the National Renewable Energy Laboratory (NREL), established the goal of achieving cost competitive cellulosic ethanol production from corn stover by 2012. The baseline conversion process to be improved consisted of dilute sulfuric acid pretreatment followed by enzymatic cellulose hydrolysis and cofermentation of biomass sugars to ethanol using a metabolically-engineered fermentation strain. The technology improvement strategy was based on achieving yearly increases in overall process conversion yields, along with associated reductions in modeled ethanol production costs, from 2007 to 2012. Progress toward this goal was measured using n^th-plant technoeconomic models to estimate ethanol production cost based on conversion yields obtained in integrated pilot and bench-scale experiments. The final objective was to demonstrate at pilot scale integrated process conversion yields commensurate with the 2012 cost target.

This presentation will briefly review the history of this technology development effort and highlight results achieved by the DOE Biomass Program at NREL from 2000 to the present. Much of the progress was facilitated by DOE-supported, industry-led research to develop improved hydrolytic enzymes for cellulose conversion and more robust microorganisms for ethanol production from a broader range of biomass sugars. Specifically, improved cellulases increased cellulose-to-glucose yields during enzymatic hydrolysis of pretreated biomass in the presence of high levels of biomass-derived sugars, and improved cofermenting microorganisms were able to convert more of the available biomass-derived sugars to ethanol in the presence of inhibitory compounds. Work at Idaho National Laboratory to improve the efficiency of the corn stover collection and supply chain also lowered the cost of delivered feedstock.

The presentation will highlight work that led to improved process understanding, higher sugar and ethanol titers, and ultimately increased conversion yields and associated cost reductions culminating in pilot scale demonstration runs. Preliminary results from bench-scale experiments are achieving yields above 75 gal ethanol/ton feedstock, ethanol titers above 68 g/L and a modeled cost below $2.20/gal ethanol.  Pilot scale results will be presented along with bench-scale testing results performed in parallel characterizing integrated conversion performance over a wider range of operating conditions than could be demonstrated at pilot scale.