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Annex 16 Vol IV defines a conversion process as "a type of technology used to convert a feedstock into aviation fuel".
SAF conversion processes are evaluated and approved by organizations such as ASTM International. As of April 2023, 9 conversion processes for SAF production have been approved and 8 other conversion processes are currently under evaluation.
In order to be eligible for use within the ICAO Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), SAF must also meet a set of sustainability criteria. More information on CORSIA eligible fuels is available on the dedicated CORSIA Eligible Fuels webpage. Specific details on the conversion processes that already have CORSIA default Life Cycle Emission values (FT, HEFA, SIP and ATJ) are available in the CORSIA supporting document "LCA methodologies"
Fischer-Tropsch hydroprocessed synthesized paraffinic kerosene
Coal, natural gas, biomass
Synthesized paraffinic kerosene from hydroprocessed esters and fatty acids
Bio-oils, animal fat, recycled oils
Synthesized iso-paraffins from hydroprocessed fermented sugars
Biomass used for sugar production
Synthesized kerosene with aromatics derived by alkylation of light aromatics from non-petroleum sources
Alcohol to jet synthetic paraffinic kerosene
Biomass from ethanol or isobutanol production
Catalytic hydrothermolysis jet fuel
Triglycerides such as soybean oil, jatropha oil, camelina oil, carinata oil, and tung oil
Synthesized paraffinic kerosene from hydrocarbon - hydroprocessed esters and fatty acids
co-hydroprocessing of esters and fatty acids in a conventional petroleum refinery
Fats, oils, and greases (FOG) co-processed with petroleum
co-hydroprocessing of Fischer-Tropsch hydrocarbons in a conventional petroleum refinery
Fischer-Tropsch hydrocarbons co-processed with petroleum
Various conversion processes are currently under evaluation by ASTM. More information is available on the article "New Sustainable Aviation Fuels (SAF) technology pathways under development", published on the ICAO Environmental Report 2022. Work is also ongoing to allow the use of 100% SAF in aircraft, as well as to increase the
maximum blending for co-processing (from 5% to 30%).
A detailed description of the ASTM qualification process is provided in the ACT-SAF Training Session #3.