(35d) Optimizing Land Use Change and Life Cycle Greenhouse Gas Emissions of Biofuels
In this work, we develop a first-ever LUC life cycle optimization (LCO) model that incorporates cutting-edge characterization and calculation methods for bioethanol LUC GHG emissions within an optimization framework. This modeling framework identifies an optimal bioethanol production and biomass sourcing strategy that minimizes LUC GHG emissions by selecting any combination and size of 14 bioethanol production pathways and 5 biomass feedstocks. We choose bioethanol production pathways that are either already commercialized or are commercialization-ready, using data from technoeconomic analyses/reports from the U.S. DOE or the peer-reviewed scientific community.3-6 LUC and direct processing GHG emissions are considered as well as excess electricity production credits from processing. We calculate LUC GHG emissions from exhaustive data bases for soil organic carbon (SOC), carbonaceous biomass cover, foregone CO2 sequestration by forested land, and the net primary productivity (NPP) of each land type in each region around the world.7-10 The CGE is integrated into the LCO modeling framework with the land carbon data to determine LUC GHG emissions around the world due to economic forces arising from increased bioethanol production in the US. Thus, for the first time, cutting-edge LUC characterization and calculation methods are integrated into an LCO modeling framework. Furthermore, this study presents the first time an integrated CGE-LCO model has been developed and utilized.
We consider a case study of US bioethanol production levels ranging from 10 â?? 100 Bgal/year. We find that minimized LUC GHG emissions from our results are lower than previous estimates, indicating that these previous estimates are at least possible. Corn stover is always preferred, as LUC due to its utilization is negligible. Switchgrass is then selected when the sustainably harvestable corn stover resource base is exhausted. Two-stage dilute acid pretreatment followed by distillation or dilute acid pretreatment followed by pervaporation are preferred technologies for corn stover conversion. Dilute acid pretreatment followed by distillation is always the selected bioethanol production pathway for switchgrass.Â Forested land is largely preserved around the world whenever possible, and pastureland is by far preferred for conversion to cropland. However, some of the recent LUC GHG emissions estimates for biofuels are close to our minimized value, indicating that some might be optimistic. Nonetheless, if the optimal bioethanol production and biomass sourcing strategies produced by our work are followed, then life cycle GHG emissions including LUC GHG emissions of bioethanol can be managed.
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