Aviation biofuel
File:Refuel EC-KNM Iberia.jpg|thumb|upright=1.2|Refueling an Airbus A320 with biofuel in 2011
An aviation biofuel, or bio-aviation fuel ) is a biofuel used to power aircraft. The International Air Transport Association considers it a key element in reducing the environmental impact of aviation. Aviation biofuel is used to decarbonize medium and long-haul air travel. These types of travel generate the most emissions. Synthetic paraffinic kerosene refers to any non-petroleum-based fuel designed to replace kerosene jet fuel, which is often, but not always, made from biomass.
Biofuels are biomass-derived fuels from plants, animals, or waste; depending on which type of biomass is used, they could lower emissions by 20–98% compared to conventional jet fuel.
The first test flight using blended biofuel was in 2008, and in 2011, blended fuels with 50% biofuels were allowed on commercial flights. In 2023 SAF production was 600 million liters, representing 0.2% of global jet fuel use. By 2024, SAF production was to increase to 1.3 billion liters, representing 0.3% of global jet fuel consumption and 11% of global renewable fuel production. This increase came as major US production facilities delayed their ramp-up until 2025, having initially been expected to reach 1.9 billion liters.
Aviation biofuel can be produced from plant or animal sources such as Jatropha, algae, tallows, waste oils, palm oil, Babassu, and Camelina ; from solid biomass using pyrolysis processed with a Fischer–Tropsch process ; with an alcohol-to-jet process from waste fermentation; or from synthetic biology through a solar reactor. Small piston engines can be modified to burn ethanol.
Sustainable biofuels are an alternative to electrofuels. Sustainable aviation fuel is certified as being sustainable by a third-party organisation.
SAF technology faces significant challenges due to feedstock constraints. The oils and fats known as hydrotreated esters and fatty acids, crucial for SAF production, are in limited supply as demand increases. Although advanced e-fuels technology, which combines waste with clean hydrogen, presents a promising solution, it is still under development and comes with high costs. To overcome these issues, SAF developers are exploring more readily available feedstocks such as woody biomass and agricultural and municipal waste, aiming to produce lower-carbon jet fuel more sustainably and efficiently.
History
The first flight using blended biofuel took place in 2008. Virgin Atlantic used it to fly a commercial airliner, using feedstocks such as algae. Airlines representing more than 15% of the industry formed the Sustainable Aviation Fuel Users Group, with support from NGOs such as Natural Resources Defense Council and The Roundtable For Sustainable Biofuels by 2008. They pledged to develop sustainable biofuels for aviation. That year, Boeing was co-chair of the Algal Biomass Organization, joined by air carriers and biofuel technology developer UOP LLC.In 2009, the IATA committed to achieving carbon-neutral growth by 2020, and to halve carbon emissions by 2050.
In 2010, Boeing announced a target 1% of global aviation fuels by 2015.
By June 2011, the revised Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons allowed commercial airlines to blend up to 50% biofuels with conventional jet fuel. The safety and performance of jet fuel used in passenger flights is certified by ASTM International. Biofuels were approved for commercial use after a multi-year technical review from aircraft makers, engine manufacturers and oil companies. Thereafter some airlines experimented with biofuels on commercial flights. As of July 2020, seven annexes to D7566 were published, including various biofuel types:
- Fischer-Tropsch Synthetic Paraffinic Kerosene
- Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene
- usHydroprocessed Fermented Sugars to Synthetic Isoparaffins
- Fischer-Tropsch Synthetic Paraffinic Kerosene with Aromatics
- Alcohol to Jet Synthetic Paraffinic Kerosene
- Catalytic Hydrothermolysis Synthesized Kerosene.
Biofuel provider Solena filed for bankruptcy in 2015.
By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, Isochrysis, was under research.
By 2016, Thomas Brueck of Munich TU was forecasting that algaculture could provide 3–5% of jet fuel needs by 2050.
In fall 2016, the International Civil Aviation Organization announced plans for multiple measures including the development and deployment of sustainable aviation fuels.
Dozens of companies received hundreds of millions in venture capital from 2005 to 2012 to extract fuel oil from algae, some promising competitively-priced fuel by 2012 and production of by 2012-2014. By 2017 most companies had disappeared or changed their business plans to focus on other markets.
In 2019, 0.1% of fuel was SAF: The International Air Transport Association supported the adoption of Sustainable Aviation fuel, aiming in 2019 for 2% share by 2025:.
File:United Airlines - N851UA -Airbus A319 - San Francisco International Airport-0383.jpg|thumb|In 2019, United Airlines purchased up to of SAF from World Energy over two years.
In early 2021, Boeing's CEO Dave Calhoun said drop-in sustainable aviation fuels are "the only answer between now and 2050" to reduce carbon emissions. In May 2021, the International Air Transport Association set a goal for the aviation industry to achieve net-zero carbon emissions by 2050 with SAF as the key component.
The 2022 Inflation Reduction Act introduced the Fueling Aviation's Sustainable Transition Grant Program. The program provides $244.5 million in grants for SAF-related "production, transportation, blending, and storage." In November, 2022, sustainable aviation fuels were a topic at COP26.
As of 2023, 90% of biofuel was made from oilseed and sugarcane which are grown for this purpose only.
Regarding future biofuel use, the European Union requires 6% of all aviation fuel sales to be biofuel by 2035, and 70% of sales to be biofuel by 2050.
Production
is a mixture of various hydrocarbons. The mixture is restricted by product requirements, for example, freezing point and smoke point. Jet fuels are sometimes classified as kerosene or naphtha-type. Kerosene-type fuels include Jet A, Jet A-1, JP-5 and JP-8. Naphtha-type jet fuels, sometimes referred to as "wide-cut" jet fuel, include Jet B and JP-4."Drop-in" biofuels are biofuels that are interchangeable with conventional fuels. Deriving "drop-in" jet fuel from bio-based sources is ASTM approved via two routes. ASTM has found it safe to blend in 50% SPK into regular jet fuels. Tests have been done with blending synthetic paraffinic kerosene in considerably higher concentrations.
; HEFA-SPK
; Bio-SPK
; FT-SPK
; ATJ-SPK
Alternative production routes
Several research initiatives and companies have reported work on technologies intended to produce synthetic hydrocarbons and sustainable aviation fuels.The SUN-to-LIQUID project was a European Union Horizon 2020-funded research initiative that demonstrated the production of sustainable aviation fuel directly from sunlight, water, and carbon dioxide. The project utilised a solar thermochemical process involving a high-temperature solar reactor to produce synthesis gas, which was then converted into jet fuel through Fischer-Tropsch synthesis. On June 13, 2019, researchers at the IMDEA Energy Institute in Móstoles, Spain successfully demonstrated the complete production chain, marking a significant milestone in solar fuel technology. The project consortium included partners from seven European countries and Switzerland, led by Bauhaus Luftfahrt, and received support from the Swiss State Secretariat for Education, Research and Innovation. While the demonstration proved the technical feasibility of producing drop-in aviation fuel from renewable sources without competing for agricultural land, the technology remained at an early stage with challenges related to scaling and economic viability requiring further development.
Alder Fuels developed a technology to convert lignocellulosic biomass, including forestry and agricultural residues, into a hydrocarbon-rich intermediate product called "greencrude" through pyrolysis. This greencrude can subsequently be processed in conventional petroleum refineries using existing infrastructure to produce drop-in aviation and transportation fuels. The company's process utilises waste biomass feedstocks that do not compete with food production, addressing one of the sustainability concerns associated with first-generation biofuels.
Universal Fuel Technologies developed Flexiforming technology, a catalytic process designed to convert various feedstocks, including byproducts from existing renewable fuel production, into sustainable aviation fuel. The technology has feedstock flexibility, allowing for the processing of multiple biomass-derived inputs through a single conversion pathway.
Arcadia eFuels developed a power-to-liquid facility at the port of Vordingborg, Denmark, utilising a process that combines water electrolysis powered by renewable electricity with carbon dioxide capture to produce synthetic aviation fuel. The process involves generating green hydrogen through electrolysis, which is then combined with captured CO2 to create synthesis gas, subsequently converted to jet fuel via Fischer-Tropsch or similar gas-to-liquid processes.