Take-off for cleaner skies starts now with SAF
Sustainable aviation fuel is the most promising pathway to decarbonisation, but which routes are the most commercially advanced?
Milica Folic Topsoe
G lobally, 137 countries have pledged to achieve carbon neutrality by, for the most part, 2050. Governments and states worldwide are taking measures to lower GHG emissions through subsidies and legislation, including the transportation sector, which accounts for 14% of the world’s GHG emissions. With aviation responsible for 8% of the transport sector’s emissions, there is no way the industry can fly under the radar. Change is coming, and that means sustainable aviation fuel (SAF) will be under the spotlight, with projected demand of around 15 Mt in 2030 and 200 Mt in 2050. Eventually, and as is our
collective aim, both renewable jet and e-Jet fuels are expected to overtake fossil jet fuel. Change has been coming for some time. Indeed, since 2008, airlines have been exploring the potential of SAF. However, so far, uptake has been slow, and by 2019 SAF accounted for just 0.1% of all fuel consumed by the aviation industry. In terms of ambition and tangible action, it has only been the last year or so since we have started seeing real change. In 2022 airlines bought every drop of SAF available worldwide, test flights are being run partially or fully powered by SAF, and regulations reducing barriers to entry are
Pathway
ASTM Annex
Year of approval
Feedstock options
Current blending limits
Fischer-Tropsch Synthetic Paraffinic Kerosene
A1
2009
Coal, natural gas, biomass (syngas)
50%
(FT-SPK)
Hydroprocessed Esters and Fatty Acids Synthetic
A2
2011
Vegetable oils and fats, animal fat, recycled oils
50%
Paraffinic Kerosene (HEFA-SPK)
Hydroprocessed Fermented Sugars to Synthetic
A3
2014
Biomass used for sugar production Coal, natural gas,
10%
lsoparaffins (HFS-SlP)
Fischer-Tropsch Synthetic Paraffinic Kerosene
D7556
A4
2015
50%
with Aromatics (FT-SPK/A)
biomass
Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK) Catalytic Hydrothermolysis Synthesized Kerosene
A5 A6
2016 2020
Ethanol or isobutanol Triglyceride-based
50% 50%
(CH-SK, or CHJ)
feedstocks
Hydroprocessed Hydrocarbons, Esters and Fatty Acids Synthetic Paraffinic Kerosene (HHC-SPK
A7
2020
Triterpenes produced by the Botryococcus braunii species of algae
10%
or HC-HEFA-SPK)
Table 1
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