Life cycle assessment of renewable diesel production via anaerobic digestion and Fischer-Tropsch synthesis from miscanthus grown in strip-mined soils

Abstract

Climate change induced by greenhouse gas emissions from the extraction and use of fossil fuels has raised global concerns and needs to develop alternative and environmentally friendly transportation fuels from biomass and other organic carbon sources. In this study, a cradle to grave attributional life cycle assessment (LCA) was conducted to produce drop-in renewable diesel from biogas (via solid-state anaerobic digestion) derived from energy crop, i.e. miscanthus cultivated in strip-mined lands. The analysis included miscanthus cultivation, harvesting, and transportation to the biorefinery, conversion of the biomass to Fischer-Tropsch diesel, and combustion of the drop-in renewable diesel for a passenger vehicle. Results showed that the miscanthus derived drop-in renewable diesel could reduce greenhouse gas emissions by up to 73% when compared with that of the conventional fossil-derived diesel. Similarly, the proposed design consumes 4.91 MJ/GGE of fossil fuel compared to the conventional diesel with fossil fuel depletion of 18.98 MJ/GGE. Although the respiratory effects, smog formation, acidification, and eutrophication potentials of the miscanthus to drop-in renewable diesel process are relatively higher than the conventional process, the proposed technology still represents a sustainable liquid fuels pathway that is less dependent on fossil fuel, can substantially reduce greenhouse gas emissions, and help attain the renewable transportation fuels standard.