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Sustainable aviation fuel (SAF) describes a replacement for conventional or fossil-based fuel used to power aircraft that has similar properties to conventional jet fuel (such as Jet A). This non-conventional fuel is derived from sustainable sources or feedstocks and produces less carbon emissions when in flight.
With the potential to lower carbon emissions up to 80% over the fuel’s life cycle, sustainable aviation fuel, or SAF offers the largest potential to reduce those emissions over the next 30 years.
Today, sustainable aviation fuels are mixed directly with conventional jet fuel up to a 50/50 blend — the maximum allowed under current fuel specifications.
A wide variety of sustainable sources — or feedstocks — can be used to make sustainable aviation fuel: non-edible plant oils, purpose-grown crops such as sugarcane, agricultural waste, forestry trimmings, non-recyclable household waste, industrial off-gassing and others.
These feedstocks are processed into sustainable aviation fuel using a range of technologies, some of which are still in development. Boeing and our partners work together to identify feedstocks that are appropriate for regional climates and supply chain needs, and meet sustainability and other criteria.
A variety of feedstock sources give power to SAF
Seven types of sustainable aviation fuels using different processing methods — or pathways — have been approved for commercial use:
Made from forestry trimmings, grasses, municipal solid waste. Approved in 2009 for up to a 50% blend. This fuel has not yet been commercially produced from sustainable feedstocks.
Made from plant oils and waste agriculture greases from agriculture. Approved in 2011 for up to a 50% blend. The vast majority of biofuel flights have used this type of fuel.
Made from sugarcane. Approved in 2014 for up to a 10% blend. It has been used by several airlines.
Similar to the original Fischer-Tropsch fuel. It can be produced from a wide range of feedstocks, but includes a class of molecules called aromatics. Approved in 2015 for up to a 50% blend.
Sustainable feedstocks can be fermented to produce alcohols such as iso-butanol, which can then be chemically converted to jet fuel. Approved in 2016 for up to a 30% blend, but ASTM revised its alcohol-to-jet specification in 2018, allowing ethanol to be used as a feedstock and increasing the blending ratio for both varieties to 50%. Ethanol can be produced from industrial off-gases, municipal solid waste and biomass wastes — significantly increasing the availability of an economical and sustainable fuel feedstock.
Essentially the same feedstocks as HEFA — plant oils and waste agriculture greases. Approved in 2020 for up to a 50% blend.
Variation to HEFA production that creates a synthesized paraffinic kerosene from hydrocarbon-hydroprocessed esters and fatty acids. Approved in 2020 for up to a 10% blend.
There is an increasing spectrum for innovation occurring in “drop-in” (meaning aircraft and airport compatible) qualified pathways that can make existing SAF pathways cleaner over time and potentially even make power to liquid (PtL) or synthetic fuels viable in the longer term.
There are several SAF technologies in development, including: waste- and biomass-based SAF, power-and-biomass-to-liquid (PBtL), and power-to-liquid (PtL).
Power to liquid fuels are a subset of sustainable aviation fuels that use hydrogen produced through carbon-free sources and CO2 captured from waste streams or the atmosphere as feedstock to produce synthetic hydrocarbon fuels.
To avoid the emissions related to shipping or trucking SAF to airports, SAF is typically transported to its nearest fuel farm. To allow airlines to utilize SAF even when the fuel isn’t available at the airport where a particular plane requires fuel, the book and claim process was developed.
The book and claim process allows a company to purchase SAF, enter it into a nearby fueling system and, in return, claim the emissions reduction benefits no matter where the purchaser is located.
The aviation industry will need a many-fold increase in the amount of SAF if it is to meet the civil aviation’s commitment to net zero by 2050. In simple terms, we have an industry to build. Building a commercial SAF market will require a concerted, symbiotic effort from aviation, finance, energy and policy.
Keys to accelerating sustainable aviation fuel supply growth
Boeing has been a pioneer in making sustainable aviation fuels a reality, partnering globally with airlines, industry, governments and research institutions to enable use, expand limited supplies and reduce fuel costs.
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