Aviation industry’s quest for a sustainable fuel: considerations of scale and modal opportunity carbon benefit

Aviation biofuels require higher processing energy inputs than fuels derived from the same feedstocks used for land-based transport. This article investigates the tradeoffs in the decisions of feedstock and processing by introducing the opportunity carbon benefit metric for the resulting transportation service across modes. We evaluated combinations of feedstocks, processing methods, and transport system use between aviation and surface modes (i.e., pathways) for fuel yields, as well as the process energy and greenhouse gas emissions of several feedstocks to determine their opportunity carbon benefit. In the current conditions, gasification for electricity generation to power electric vehicles would lead to the highest transportation services. Taking into account process energy and the limited number of electric vehicles, diesel and ethanol pathways maintain a lead. Contrary to their relatively high transportation service yields, biomass-to-electricity conversion pathways fail to generate the opportunity carbon benefits of biomass-to-liquid pathways. Biomass-to-liquid pathways vary little, with the jet pathway having a slight disadvantage over the diesel option owing to its higher process energy needs. On the feedstock side, the marginal land feedstocks, such as salicornia and switchgrass, have the advantage over the process energy and cultivation energy inputs, despite their relatively lower per hectare yields.