15-01: The potential and challenges of "drop-in" biofuels

Fossil-based transportation fuels are finite and are becoming more costly to source and process. At the same time the oil refining sector is increasing parts of its processing capacity to be able to process “heavier and sourer” crude oil. Although biofuels have been advocated as a renewable alternative, current biofuels such as ethanol and biodiesel are too oxidized to be readily “dropped into” the existing transportation fuel infrastructure (refineries, gas stations, automobile engines, etc.). Less oxygenated and more fungible biofuels have been termed as “drop-in”. These biofuels can be made from various intermediates such as sugars, lipids and “bio/syngas” but they need further processing in order to remove oxygen and yield a hydrocarbon-like biofuel. Most “drop-in” biofuel technologies remove oxygen from biomass by using large amounts of hydrogen gas as an input. The US would need to double its current 10 million t/y hydrogen production capacity to meet the advanced biofuel RFS mandate with pyrolysis-type drop-in biofuels. At the same time an equal amount of additional hydrogen will be needed to meet the projected US oil industry hydrogen requirements for heavier crude processing. Lipid-based “drop-in” biofuels are already commercial at scale while fermentation-based “drop-in” biofuels appear more problematic (low productivities of 0.1-0.7 g/L/h). Although thermochemical processes show promise (once selectivity and catalyst life issues are resolved) they will require significant hydrogen inputs. The competing technologies, pathways for insertion to oil refineries and potential challenges for “drop in” biofuels, such as the availability of cheap and plentiful hydrogen, will be discussed.