Renewable diesel production from lignocellulosic feedstock: life cycle environmental and cost analysis

Computer simulations are used to study the production of renewable diesel through the biological transformation of lignocellulosic material (specifically biomass sorghum) to free fatty acids using a genetically modified strain of Escherichia Coli.  We evaluate select environmental and economic metrics using life cycle assessment (LCA) and techno-economic analysis (TEA). The biofuel supply chain we analyze includes feedstock production, handling, pretreatment and hydrolysis, fermentation to free fatty acids, saponification of the free fatty acids, wax production on an electrochemical synthesis reactor, and hydrocracking to convert the wax to  renewable diesel. To develop this model we modify the National Renewable Energy Laboratories (NREL) techno-economic model developed using AspenPlus® for corn stover based bioethanol production process design and apply experimental and public data. The AspenPlus®-TEA model is combined with the LCA tool, SimaPro to estimate life cycle greenhouse gas and non-renewable energy consumption. The minimum selling price for diesel ranges from $39 to $12 U.S. per gallon depending on the yields considered for the different stages, higher than the current price of diesel. The biggest contributions to the selling price of the fuel are the capital recovery charge and raw materials; therefore, working with woody residues and improving the process to reduce capital costs are good strategies to reduce the minimum selling price of the renewable diesel in order to reach a competitive price. Life cycle findings show a need to reduce feedstock harvesting energy and chemical and nutrient inputs to meet U.S. policy objectives, which is consistent with previous research.