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What is SAF?

Courtesy of Southwest Airlines

SAF is a biofuel used to power aircraft that has similar properties to conventional jet fuel but with a smaller carbon footprint. Depending on the feedstock and technologies used to produce it, SAF can reduce life cycle GHG emissions dramatically compared to conventional jet fuel. Some emerging SAF pathways even have a net-negative GHG footprint.

SAFs lower carbon intensity makes it an important solution for reducing aviation GHGs, which make up 9%–12% of U.S. transportation GHG emissions, according to the U.S. Environmental Protection Agency.

Feedstock is Collected

There are different types of feedstocks, including:

  • Fats, oils, and greases (FOGs), which can come from used cooking oil and tallow, energy or cover crops like willow wood and switchgrass, and edible oil crops like corn.

  • Biomass, such as forestry and agricultural residues and municipal solid waste. Examples include waste woody biomass and corn stover.

  • Carbon captured directly from the atmosphere, also known as direct air capture (DAC), which is non-biomass based. Fuel made through a process involving renewable energy, carbon from DAC, and green hydrogen is generally referred to as power-to-liquid (PtL), synthetic fuel (synfuel), and/ or e-fuel.

Feedstock is converted to SAF

There are several approved pathways to convert feedstocks into SAF, including:

  • Hydroprocessed fatty acid esters and fatty acids (HEFA) converts FOGs into jet fuel.

  • Alcohol-to-jet (ATJ) converts ethanol or isobutanol made from biomass into jet fuel.

  • Gasification/Fischer-Tropsch (FT) converts biomass into jet fuel. FT can also be used to convert carbon from DAC into jet fuel (PtL, synfuel, or e-fuel).

SAF is blended with conventional jet fuel

The blended SAF must be certified to American Society for Testing and Materials standards (ASTM Standard D1655), which the Federal Aviation Administration (FAA) has deemed acceptable for use on aircraft and is the same standard for conventional jet fuel.

Blended SAF is delivered to the airport: The blended SAF goes into the fuel supply at the airport, meaning it could be used by any aircraft uplifting fuel from the airport. Because of this, it’s not possible to tie SAF to a specific flight.

Learn more about sustainable aviation fuel.

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