3-06: Integrated Cellulosic Ethanol Production - Historical Progress and Recent Pilot Scale Demonstrations

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. Progress toward the goal was measured using n^th-plant technoeconomic models to estimate ethanol production cost based on conversion yields and other performance data obtained during integrated bench and pilot scale experiments. The final objective was to demonstrate at pilot scale integrated process performance commensurate with the 2012 cost target. The effort culminated with integrated pilot scale demonstration runs in 2012 achieving ethanol yields above 70 gal ethanol/ton feedstock, ethanol titers above 70 g/L and a modeled ethanol cost below $2.20/gal ethanol.

This presentation will also review progress achieved by the DOE Biomass Program at NREL from 2005 to 2012 and will highlight work that led to improved process understanding that was ultimately employed in the integrated pilot scale runs. 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. 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.