Oilseed feedstock and conversion technology co-optimization for sustainable aviation fuel

Abstract: Commercial aviation accounts for ~2% of global carbon dioxide emissions. The US Department of Energy Sustainable Aviation Fuel (SAF) Grand Challenge aims to reduce the carbon footprint of the aviation industry by reaching the goals of three billion gallons of SAF production by 2030, resulting in >50% reduction in life cycle greenhouse gas emissions relative to petroleum-derived fuel, and complete replacement of petroleum jet fuel with SAF (35 billion gallons annual production) by 2050. Our research addresses the top two priorities of this initiative: feedstock innovation and conversion technology innovation. Conventional SAF production involves the conversion of triacylglycerol (TAG) and fatty acid feedstocks to kerosene-type alkanes through the two-stage Hydroprocessed Esters and Fatty Acids (HEFA) process. HEFA requires high energy inputs (300-430^oC) and high capital expenditures (CAPEX) to deoxygenate fatty acids and crack carbon chains into shorter alkanes. As an alternative approach, we are currently optimizing a one-pot biphasic tandem catalytic process (biTCP) to produce SAFs under relatively mild conditions that deoxygenate fatty acids to alkanes in a single step and involves lower energy inputs and CAPEX and operational expenditure. In parallel, we are also developing germplasm of the oilseed crop camelina with seed TAG that contains fatty acids of a range of carbon chain-lengths and reduced unsaturation that can be readily converted by biTCP to alkanes with composition similar to Jet A fuel. We have engineered camelina for seed-specific expression of thioesterases and specialized acyltransferases to generate TAGs with fatty acids ranging from C8 to C18. A portion of this camelina germplasm has been used for field-based production. We have shown that oil pressed from seeds of these plants can be converted by biTCP at high efficiency to C7-C19 hydrocarbons. Ongoing metabolic engineering efforts to further optimize camelina seed TAGs for biTCP SAF production will be described.