Life-Cycle Assessment of Bioethanol from Pine Residues via Indirect Biomass Gasification to Mixed Alcohols*

Abstract

Abstract The goal of this study was to estimate the greenhouse gas (GHG) emissions and fossil energy requirements from the production and use (cradle-to-grave) of bioethanol produced from the indirect gasification thermochemical conversion of loblolly pine (Pinus taeda) residues. Additional impact categories (acidification and eutrophication) were also analyzed. Of the life-cycle stages, the thermochemical fuel production and biomass growth stages resulted in the greatest environmental impact for the bioethanol product life cycle. The GHG emissions from fuel transportation and process chemicals used in the thermochemical conversion process were minor (less than 1 percent of conversion emissions). The net GHG emissions over the bioethanol life cycle, cradle-to-grave, was 74 percent less than gasoline of an equal energy content, meeting the 60 percent minimum reduction requirement of the Renewable Fuels Standard to qualify as an advanced (second generation) biofuel. Also, bioethanol had a 72 percent lower acidification impact and a 59 percent lower eutrophication impact relative to gasoline. The fossil fuel usage for bioethanol was 96 percent less than gasoline, mainly because crude oil is used as the primary feedstock for gasoline production. The total GHG emissions for the bioethanol life cycle analyzed in this study were determined to be similar to the comparable scenario from the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation model. A sensitivity analysis determined that mass allocation of forest establishment burdens to the residues was not significant for GHG emissions but had significant effects on the acidification and eutrophication impact categories.