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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"
Approved Conversion Processes
ASTM reference
| Conversion process
| Abbreviation
| Possible Feedstocks
| Maximum Blend Ratio |
ASTM D7566 Annex 1
| Fischer-Tropsch hydroprocessed synthesized paraffinic kerosene
| FT | Coal, natural gas, biomass
| 50% |
ASTM D7566 Annex 2
| Synthesized paraffinic kerosene from hydroprocessed esters and fatty acids | HEFA
| Bio-oils, animal fat, recycled oils | 50%
|
ASTM D7566 Annex 3
| Synthesized iso-paraffins from hydroprocessed fermented sugars
| SIP | Biomass used for sugar production | 10% |
ASTM D7566 Annex 4
| Synthesized kerosene with aromatics derived by alkylation of light aromatics from non-petroleum sources
| FT-SKA | Coal, natural gas, biomass
| 50%
|
ASTM D7566 Annex 5
| Alcohol to jet synthetic paraffinic kerosene
| ATJ-SPK | Biomass from ethanol or isobutanol production | 50% |
ASTM D7566 Annex 6
| Catalytic hydrothermolysis jet fuel
| CHJ
| Triglycerides such as soybean oil, jatropha oil, camelina oil, carinata oil, and tung oil
| 50%
|
ASTM D7566 Annex 7
| Synthesized paraffinic kerosene from hydrocarbon - hydroprocessed esters and fatty acids
| HC-HEFA-SPK | Algae
| 10%
|
ASTM D1655
Annex A1 | co-hydroprocessing of esters and fatty acids in a conventional petroleum refinery
| co-processed HEFA
| Fats, oils, and greases (FOG) co-processed with petroleum
| 5%
|
ASTM D1655 Annex A1 | co-hydroprocessing of Fischer-Tropsch hydrocarbons in a conventional petroleum refinery | co-processed FT
| Fischer-Tropsch hydrocarbons co-processed with petroleum
| 5%
|
Conversion processes under evaluation
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.
