Which processes to making biojet/Sustainable Aviation Fuel (SAF) are likely to supplement the predominant,...

Currently, the Hydroprocessed Esters and Fatty Acids (HEFA) or lipid-to-biojet route is the only commercial way to make biojet or Sustainable Aviation Fuel (SAF). Although the lipid-to-biojet pathway is likely to continue to predominate, other routes need to be commercialised if the aviation sector is to meet its 2030/2050 decarbonisation targets. Although the Power-to-Liquid (PtL) pathway appears attractive from a carbon reduction perspective, its high cost, low Technology Readiness Level (TRL), and the demand for "green" electricity from other sectors will limit its commercialization. Europe's reluctance to use any food/feed feedstock has partially influenced their interest in the biomass Gasification Fischer-Tropsch (G/FT) route to SAF. However, Shell's natural Gas-to-Liquid (GTL) process in Qatar has indicated the high cost, needed economies of scale, and gas clean-up challenges of this process. The Americas are already major producers of alcohols, with the Alcohol-to-Jet (AtJ) route being developed by companies such as Lanzajet and Gevo. However, ongoing challenges include the Carbon Intensity (CI) of the sugar and starch feedstocks, capturing and using the CO₂ produced via fermentation, and the need for "green" hydrogen when making SAF. While SAF is predominantly produced via the lipid-to-biojet route in stand-alone biorefineries, coprocessing of lipids or biocrudes provides a way of decarbonising both oil refineries and the fuels they produce. Rather than blending the SAF produced from stand-alone biorefineries with fossil-derived jet fuel at airports, coprocessing allows the blending at the refinery and the production of Low Carbon-Intensity Jet Fuel (LCJF) at a lower cost and shorter timeframe.