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Systems-Level Analysis of Energy and Greenhouse Gas Emissions for Coproducing Biobased Fuels and Chemicals: Implications for Sustainability

Beck, Andrew W., O’Brien, Anthony J., Zaimes, George G., Resasco, Daniel E., Crossley, Steven P., Khanna, Vikas
ACS sustainable chemistry & engineering 2018 v.6 no.5 pp. 5826-5834
biochar, biofuels, biorefining, carbon, coproducts, credit, electricity, energy, environmental performance, fossil fuels, greenhouse gas emissions, greenhouse gases, hydrogen, liquids, markets, models, prices, torrefaction, wastes
In light of advances in the simultaneous production of biobased fuels and chemicals, a prospective well-to-wheel lifecycle assessment (LCA) model of a two-step multistage torrefaction biorefinery is constructed to quantify both lifecycle greenhouse gas (GHG) emissions and energy return on primary fossil energy investment (EROIfₒₛₛᵢₗ) for a transportation-range biofuel product. Coproducts—including cyclopentanone (CPO), biochar, and a potential net electricity export—are handled via six coproduct scenarios, evaluated across both market-based allocation and displacement methods. Process-scale performance metrics and product distributions are compared across cases to evaluate trade-offs between process and environmental performance; carbon flows are visualized to better explain patterns of carbon yield and waste. LCA results include median GHG values spanning from −30.8 to +36.1 g CO₂e/MJ-fuel and median EROIfₒₛₛᵢₗ values ranging from 1.6 to 12.8 MJ-fuel/MJ-PEfₒₛₛᵢₗ. Sensitivity results for the Market CPO case under market-based allocation display a large dependence on CPO yield, hydrogen consumption and fuel and CPO prices, while exhibiting minimal dependence on liquid fuel yield. Unrealistically low lifecycle GHG and high EROIfₒₛₛᵢₗ values are obtained under displacement for the maximum level of CPO production, prompting a discussion of methodological limitations, especially as they relate to the assignment of system expansion coproduct credit within existing EROI formulations.