Life cycle assessment of drop-in biofuels from prairie cordgrass

Abstract. This study uses the life cycle assessment framework to compare the effects on human health and the environment of drop-in biofuels produced from switchgrass and prairie cordgrass using a variety of low-input farming methods. Biofuel scenarios were developed using experimental data from South Dakota State University's Felt Farm, pretreatment and biomass conversion testing through South Dakota State University, and process models of biomass catalytic fast pyrolysis to biogasoline and biodiesel from the National Renewable Energy Laboratory. In particular, we examined the influence of low-input cropping systems, biomass densification and pretreatment (such as pelleting and AFEX) at regional biomass preprocessing depots, and transportation distance on net greenhouse gas emissions, human health, and ecotoxicity. Results show that greenhouse gas emissions from biogasoline from catalytic fast pyrolysis of prairie grasses provide emissions reductions of up to 80% compared to fossil fuels, though the extent of emissions reductions vary greatly by scenario. Biomass pretreatment and preprocessing steps, particularly drying biomass prior to catalytic fast pyrolysis, can have large contributions to net greenhouse gas emissions. Notably, differences in biomass composition between crop species could play a large role in the energy requirements, fuel yield, and carbon balance of catalytic fast pyrolysis. We conclude that biogasoline from both prairie cordgrass and switchgrass has potential to provide substantial emissions reductions. Catalytic fast pyrolysis is the primary contributor to human health and ecotoxicity metrics. This conversion process, for which little data is available, should be a key target for improved modeling of environmental outcomes from drop-in biofuels.