Benchmarking Sustainability for Lignocellulosic Conversion

Biofuels derived from both starch and lignocellulosic feedstocks are expected to contribute 36 billion gallons per year by 2022 according to the Energy Independence and Security Act (EISA) of 2007. Questions regarding the overall sustainability of such an unprecedented increase in bioethanol and biofuels production have focused, to a large extent on the feedstock production side of the bioethanol supply chain because of issues of direct and indirect land use changes. Tools for their assessments are still evolving. Other issues include food versus fuels, hunger and poverty issues, among others, which make it imperative to explore lignocellulosic biomass. Recent studies have illustrated the importance of the biorefinery to the overall life cycle greenhouse gas emissions and fossil energy demand. It is imperative for each component of the ethanol supply chain to be optimized with regard to key metrics of sustainability as well as the overall system. The National Renewable Energy Laboratory is currently using process engineering and life cycle assessment coupled to analyses of other parameters to establish benchmarks for sustainability within the biorefinery. These metrics will be used to spur novel process and system improvements and to ultimately establish sustainability targets. These targets will complement traditional technoeconomic analyses that have so far guided selection of key technical barriers for cost optimization. Key areas under investigation include greenhouse gas (GHG) emissions (includes energy sources and energy efficiency), water consumption, and refinery waste treatment needed in both the biochemical conversion of corn stover to ethanol and the thermochemical gasification of mixed woods to ethanol and mixed alcohols. Examples of sustainability benchmarks for a few biorefinery processes and potential improvements will be presented.

*This work is funded entirely by the United States Department of Energy's Office of Energy Efficiency and Renewable Energy's Biomass Program.