The potential and technology challenges of producing renewable aviation fuels

The presentation will describe the strengths and weaknesses of the various technologies that have been advocated to produce jet-biofuels. Renewable aviation fuels (or biojet) have to be “drop-in fuels” that are functionally equivalent to current petroleum-derived jet fuels. Four main technological approaches for producing drop-in fuels, namely oleochemical, thermochemical, biochemical and hybrid technology pathways or platforms were reviewed. Oleochemical processes involving the hydroprocessing of lipid feedstocks are the only pathways that are currently producing significant volumes of drop-in biofuels. Thermochemical processes, such as pyrolysis and gasification, involving the thermal conversion of biomass to intermediates (gas or oil) that can be catalytically upgraded and hydroprocessed into drop-in biofuels have several challenges. Biochemical processes that utilize biological conversion of sugars into hydrocarbon products such as farnesene which can be further upgraded and processed to produce drop-in fuels have more valuable intermediates, limiting likely production via this route. Hybrid technologies including processes such as alcohol-to-jet (ATJ) also has challenges. A major concern for all of the drop-in biofuel technologies is the requirement for hydrogen (H₂) or other chemical reduction processes to upgrade oxygen-rich feedstocks to hydrogen-rich hydrocarbon fuels. The presentation will show that it is likely that initial supply chains will be established using oleochemical derived drop-in biofuels as lipid feedstocks have the lowest oxygen content and require the least hydroprocessing. In the long-term, processes that use cheaper and more abundant feedstocks such as lignocellulosic biomass will be required to supply large volumes of drop-in fuels.