Life Cycle Assessment of Ethanol Via Five Feedstocks.

Widespread deployment of renewable liquid transportation fuel is viewed as a key component of a multifaceted strategy to strengthen national security, reduce fossil fuel consumption, moderate greenhouse gas (GHG) emissions, and stimulate rural economies. The Energy Independence and Security Act of 2007 (EISA) mandates explicit renewable energy market goals for the year 2022. Under the EISA liquid transportation fuel mandate, biofuels are targeted to reach 36 billion gallons per year (bgy), of which 21 bgy must come from feedstocks other than corn starch such as agricultural residues and herbaceous energy crops. The objective of this study is to use life cycle assessment to evaluate the overall sustainability of the ethanol production volumes needed to meet the EISA mandate of 36 bgy.  Ethanol production was modeled to include all product stages from feedstock production to vehicle end-use. Modules were developed in SimaPro v.7.1.8 database for materials and processes that were not user-generated. Five ethanol feedstocks were evaluated: corn grain, corn stover, wheat straw, switchgrass, and forest residue. Feedstock production included all activities and infrastructure required to establish, grow, and harvest the biomass. Cconversion was modeled using corn dry mill (corn grain), biochemical conversion (corn stover, wheat straw, switchgrass), and thermochemical conversion (forest residue). Conversion processes included preprocessing, storage, and conversion to ethanol. Feedstock and ethanol transportation were modeled from projected distances and modes. Vehicle end-use included only vehicle operation. Vehicle operation impacts were developed from the GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation) 1.8b (Argonne National Laboratory, Argonne, Illinois, USA) model. Infrastructure required for each stage was included in the scope of this study. Results from this study, including sensitivity analysis around key input parameters, will be presented.