The aviation industry is looking to sustainable aviation fuel (SAF) to reduce its carbon footprint, but there are a variety of methods for producing it, each with their own advantages and disadvantages. Currently, the most popular method is hydroprocessed esters and fatty acids (HEFA), which involves refining vegetable oils, animal fats or used cooking oil into hydrocarbons that can be blended with traditional jet fuel, but the process has issues with consuming large amounts of hydrogen and energy. Fischer-Tropsch (FT) — which converts biomass or waste materials into natural gas and then liquid hydrocarbons — is complex, expensive and energy intensive, while alcohol to jet (ATJ) processes bio-based alcohols and catalytic hydrothermolysis jet (CHJ) uses waste materials heated in the presence of water and a catalyst. Power-to-liquid and algae-based biofuel are among the horizon technologies being explored, though scaling up production poses challenges.
SAF must conform to the same safety standards as jet fuel and must also be certified to ASTM D7566 as a synthetic fuel. The certification process takes into account the fuel’s carbon intensity and takes into consideration any potential loss of biodiversity, deforestation, global hunger, or water pollution from the fuel feedstock. SAF is expected to become incorporated into the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), but operators have to comply with the International Civil Aviation Organization’s sustainability requirements. The International Sustainability and Carbon Certification and Roundtable for Sustainable Biomaterials are currently the two accredited pathways to certify fuels as CORSIA eligible.