2013 NREL Design Report: Biochemical Conversion of Biomass-to-Hydrocarbons, Process Design and

Economics

Ryan Davis, Ling Tao, Eric C.D. Tan, Mary Biddy, Chris Scarlata

National Renewable Energy Laboratory, Golden, CO
While economics and process understanding for commercial-scale cellulosic ethanol production have been thoroughly investigated, documented, and refined in recent years as the industry has grown,
similar considerations for biologically-derived hydrocarbon biofuels moving beyond ethanol have not yet been established publicly to such an extent. In support of an expanded focus to begin considering the technical and economic potential for such a route, this work presents a detailed techno-economic analysis focused on biochemical hydrocarbon production via deconstruction of cellulosic biomass to sugars and subsequent biological conversion (â??fermentationâ?) of the hydrolysate sugars to
hydrocarbons. This â??design reportâ? leverages earlier analyses widely circulated for biochemical ethanol
processes (Wooley et al. 1999, Aden et al. 2002, Humbird et al. 2011) with key differences and new challenges highlighted relative to ethanol production. The overarching process design utilizes dilute alkaline and acid pretreatment of biomass followed by enzymatic hydrolysis, hydrolysate conditioning, and aerobic bioconversion to long-chain hydrocarbon intermediates. The intermediate product is purified and upgraded via hydrotreating to a renewable diesel blendstock and residual solids are combusted to produce heat and power. Material and energy balances are rigorously computed using an Aspen Plus model, which enables cost estimates and cash flow calculations to be run to set the
minimum fuel selling price (MFSP, $/gallon). The outcome of this work demonstrates one plausible path forward towards achieving a cost goal near $5/gallon gasoline equivalent (GGE) for the pathway, and also discusses the potential to further reduce costs towards an ultimate goal of $3/GGE by increasing carbon efficiencies beyond the fermentable fraction of the biomass, i.e. by utilizing lignin components
for conversion to value-added chemical coproducts, with several optional products considered. The
work also presents a cost sensitivity analysis to quantify impacts of uncertainties and identify key areas for research focus moving forward. Finally, key sustainability metrics including greenhouse gas, fossil energy, and water use profiles associated with the modeled biorefinery are also presented.