Aviation biofuel

{{Short description|Sustainable fuel used to power aircraft}} <section begin="summary" /> [[File:Refuel EC-KNM Iberia (6218464950).jpg|thumb|upright=1.2|Refueling an Airbus A320 with biofuel in 2011]]

An '''aviation biofuel''' (also known as '''bio-jet fuel''',<ref name=IU4dec2020>{{Cite web |date= 2020-12-04 |access-date= 2022-12-12|title= Sustainable aviation fuel market demand drives new product launches. |url=https://investableuniverse.com/2020/12/04/sustainable-aviation-fuel-argus-price-gunvor-group/ |website= Investable Universe}} Note: ''[https://investableuniverse.com/home/about/ Investable Universe>About]''</ref> '''sustainable aviation fuel''' (SAF), or '''bio-aviation fuel''' (BAF)<ref name="Doliente2020">{{Cite journal |last= Doliente |first= Stephen S. |display-authors=etal |date= 10 July 2020 |title= Bio-aviation Fuel: A Comprehensive Review and Analysis of the Supply Chain Components |journal= Frontiers in Energy Research |volume= 8 |article-number= 110 |doi= 10.3389/fenrg.2020.00110 |language= English |doi-access= free |bibcode= 2020FrER....8..110D |url= https://purehost.bath.ac.uk/ws/files/205375761/Doliente_et_al_2020_Accepted_Manuscript_Frontiers_in_Energy_Research.pdf }}</ref>) is a biofuel used to power aircraft. The International Air Transport Association (IATA) considers it a key element in reducing the environmental impact of aviation.<ref>{{cite web |url= https://www.iata.org/en/programs/environment/sustainable-aviation-fuels/ |title= Developing Sustainable Aviation Fuel (SAF) |publisher= IATA}}</ref> Aviation biofuel is used to decarbonize medium and long-haul air travel. These types of travel generate the most emissions. '''Synthetic paraffinic kerosene''' (SPK) refers to any non-petroleum-based fuel designed to replace kerosene jet fuel, which is often, but not always, made from biomass.

<!--Environmental impact--> Biofuels are biomass-derived fuels from plants, animals, or waste; depending on which type of biomass is used, they could lower {{chem2|CO2}} emissions by 20–98% compared to conventional jet fuel.<ref name="Bauen2009">{{cite CiteSeerX |last1=Bauen |first1=Ausilio |first2=Jo |last2=Howes |first3=Luca |last3=Bertuccioli |first4=Claire |last4=Chudziak |title=Review of the potential for biofuels in aviation |date= August 2009|citeseerx=10.1.1.170.8750 }}</ref> <!--Timeline-->The first test flight using blended biofuel was in 2008,<!--ref name=IEA18mar2019/--> 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.<ref>{{Cite web |last=IATA |date=December 2023 |title=Net zero 2050: sustainable aviation fuels – December 2023 |url=https://www.iata.org/en/iata-repository/pressroom/fact-sheets/fact-sheet---alternative-fuels/#:~:text=Aviation%20fuel%20suppliers%20will%20have,rising%20to%2070%25%20in%202050. |archive-url=https://web.archive.org/web/20240224104907/https://www.iata.org/en/iata-repository/pressroom/fact-sheets/fact-sheet---alternative-fuels/ |archive-date=24 February 2024 |website=www.iata.org/flynetzero}}</ref> By 2024, SAF production was to increase to 1.3 billion liters (1 million tonnes), representing 0.3% of global jet fuel consumption and 11% of global renewable fuel production.<ref>{{Cite web |title=Disappointingly Slow Growth in SAF Production |url=https://www.iata.org/en/pressroom/2024-releases/2024-12-10-03/ |access-date=2025-03-31 |website=www.iata.org |language=en}}</ref> This increase came as major US production facilities delayed their ramp-up until 2025, having initially been expected to reach 1.9 billion liters.<!--ref name=ASTMsep2011--><!--ref name=IATAmay2019-->

<!--Production--> Aviation biofuel can be produced from plant or animal sources such as ''Jatropha'', algae, tallows, waste oils, palm oil, Babassu, and ''Camelina'' (bio-SPK); from solid biomass using pyrolysis processed with a Fischer–Tropsch process (FT-SPK); with an alcohol-to-jet (ATJ) process from waste fermentation; or from synthetic biology through a solar reactor. Small piston engines can be modified to burn ethanol.<!--ref name=SDSU2016-->

<!--Sustainable fuels--> Sustainable biofuels are an alternative to electrofuels.<ref>{{Cite web|author=Mark Pilling|title=How sustainable fuel will help power aviation's green revolution|url=https://www.flightglobal.com/flight-international/how-sustainable-fuel-will-help-power-aviations-green-revolution/143044.article|date=2021-03-25|website=FlightGlobal}}</ref> Sustainable aviation fuel is certified as being sustainable by a third-party organisation.<section end="summary" />

{{anchor|Hefa}} {{TOCLimit}}SAF technology faces significant challenges due to feedstock constraints. The oils and fats known as hydrotreated esters and fatty acids (Hefa), crucial for SAF production, are in limited supply as demand increases. Although advanced e-fuels technology, which combines waste {{Chem2|CO2}} 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.<ref>{{Cite web |date=2024-05-10 |title=New Technology Helps Advance Non-Hefa SAF Projects |url=https://www.energyintel.com/0000018f-5ac5-d00d-a7df-7ff56da40000 |access-date=2024-05-14 |website=Energy Intelligence |language=en}}</ref><ref>{{Cite web |date=2024-08-14 |title=New SAF Process Could Transform Industry |url=https://www.ainonline.com/aviation-news/aerospace/2024-08-14/new-saf-process-could-transform-industry |access-date=2024-08-14 |website=Aviation Industry News |language=en}}</ref>

==History== {{see also|Aviation biofuel demonstrations}}{{Update section|date=March 2024|reason=Lots of plans announced years ago. No info on whether the plans were carried out.}} The first flight using blended biofuel took place in 2008.<ref name="IEA18mar2019" /> Virgin Atlantic used it to fly a commercial airliner, using feedstocks such as algae.<ref>{{cite news |url= https://news.bbc.co.uk/2/hi/7261214.stm |work=BBC News|title= First biofuel flight touches down |date= 24 February 2008}}</ref> 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.<ref>{{cite news |title=Our Commitment to Sustainable Options |url=https://www.boeing.com/aboutus/environment/environmental_report_09/_inc/3.4.3-Sustainable-Aviation-Fuel-Users-group.pdf |archive-url=https://web.archive.org/web/20210710123836/https://www.boeing.com/aboutus/environment/environmental_report_09/_inc/3.4.3-Sustainable-Aviation-Fuel-Users-group.pdf |archive-date=July 10, 2021 |publisher=Sustainable Aviation Fuel Users Group}}</ref> That year, Boeing was co-chair of the Algal Biomass Organization, joined by air carriers and biofuel technology developer UOP LLC (Honeywell).<ref>{{cite news |url= http://www.greencarcongress.com/2008/06/first-airlines.html |title= First Airlines and UOP Join Algal Biomass Organization |work= Green Car Congress |date= 19 June 2008}}</ref>

In 2009, the IATA committed to achieving carbon-neutral growth by 2020, and to halve carbon emissions by 2050.<ref>{{cite press release |url= https://www.iata.org/en/pressroom/pr/2009-06-08-03/ |title= Carbon-Neutral Growth By 2020 |publisher= IATA |date= 8 June 2009 |access-date= 2020-12-06 |archive-date= 2021-04-14 |archive-url= https://web.archive.org/web/20210414025050/https://www.iata.org/en/pressroom/pr/2009-06-08-03/ }}</ref>

In 2010, Boeing announced a target 1% of global aviation fuels by 2015.<ref>{{cite news |url= https://www.bloomberg.com/news/2010-07-22/commercial-airlines-may-get-1-of-fuel-from-biofuels-by-2015-boeing-says.html |title= Airlines May Get 1% of Fuel From Biofuels By 2015, Boeing Says |date=22 July 2010 |agency= Bloomberg}}</ref>

[[File:US Navy 110921-N-ZZ999-002 An AV-8B Harrier assigned to Air Test and Evaluation Squadron (VX) 31 conducts the first test flight of a mix of 50-50 j.jpg|thumb|upright|US Marine Corps AV-8B Harrier II test flight using a 50–50 biofuel blend in 2011]]

By June 2011, the revised ''Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons'' (ASTM D7566) allowed commercial airlines to blend up to 50% biofuels with conventional jet fuel.<ref>{{cite news |url=http://www.renewableenergyworld.com/rea/news/article/2011/07/50-percent-biofuels-now-allowed-in-jet-fuel |title=50 Percent Biofuels Now Allowed in Jet Fuel |date=1 July 2011 |work=Renewable Energy World |access-date=6 December 2020 |archive-date=8 June 2020 |archive-url=https://web.archive.org/web/20200608062153/https://www.renewableenergyworld.com/2011/07/01/50-percent-biofuels-now-allowed-in-jet-fuel/ }}</ref> The safety and performance of jet fuel used in passenger flights is certified by ASTM International.<ref name=ASTMsep2011>{{cite web |url= http://www.astm.org/SNEWS/SO_2011/enright_so11.html |title= Aviation Fuel Standard Takes Flight |quote= D7566 Revision Adds Bioderived Components |publisher= ASTM |date= September–October 2011}}</ref> Biofuels were approved for commercial use after a multi-year technical review from aircraft makers, engine manufacturers and oil companies.<ref>{{cite news |url= https://www.bloomberg.com/news/2011-07-01/airlines-win-approval-to-use-plant-based-biofuels-on-commercial-flights.html |title= Airlines Win Approval to Use Biofuels for Commercial Flights |date= 1 July 2011 |agency= Bloomberg}}</ref> Thereafter some airlines experimented with biofuels on commercial flights.<ref>{{cite news |url= https://www.nytimes.com/2011/10/10/business/global/10iht-green10.html?_r=1 |title= Airlines Weigh the Advantages of Biofuels |newspaper= NY Times |date= 9 Oct 2011 |author= Bettina Wassener}}</ref> As of July 2020, seven annexes to D7566 were published, including various biofuel types:<ref>{{cite news|url=https://www.greencarcongress.com/2020/05/20200514-ihi.html|title=ASTM approves 7th annex to D7566 sustainable jet fuel specification: HC-HEFA|date=May 14, 2020|journal=Green Car Congress|access-date=August 8, 2021}}</ref> * Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK, 2009) * Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene (HEFA-SPK, 2011) * usHydroprocessed Fermented Sugars to Synthetic Isoparaffins (HFS-SIP, 2014) * Fischer-Tropsch Synthetic Paraffinic Kerosene with Aromatics (FT-SPK/A, 2015) * Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK, 2016) * Catalytic Hydrothermolysis Synthesized Kerosene (CH-SK, or CHJ; 2020).

In December 2011, the FAA awarded US$7.7 million to eight companies to develop drop-in sustainable fuels, especially from alcohols, sugars, biomass, and organic matter such as pyrolysis oils, within its {{abbr|CAAFI|Commercial Aviation Alternative Fuel Initiative}} and {{abbr|CLEEN|Continuous Lower Emissions, Energy and Noise}} programs.<ref>{{cite news |url=http://www.renewableenergyworld.com/rea/news/article/2011/12/faa-awards-7-7-million-for-advancement-of-aviation-biofuels |title=FAA Awards $7.7 Million for Advancement of Aviation Biofuels |author=Meg Cichon |date=2 December 2011 |work=Renewable Energy World |access-date=6 December 2020 |archive-date=28 March 2014 |archive-url=https://web.archive.org/web/20140328195458/http://www.renewableenergyworld.com/rea/news/article/2011/12/faa-awards-7-7-million-for-advancement-of-aviation-biofuels }}</ref>

Biofuel provider Solena filed for bankruptcy in 2015.<ref>{{Cite web|title=AirportWatch {{!}} Solena, the company meant to be producing jet fuel from London waste for BA, goes bankrupt|url=https://www.airportwatch.org.uk/2015/10/solena-the-company-meant-to-be-producing-jet-fuel-from-london-waste-for-ba-goes-bankrupt/|access-date=2021-08-30|website=www.airportwatch.org.uk}}</ref>

By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, ''Isochrysis'', was under research.<ref>{{cite web|author1=Chris Reddy|author2=Greg O'Neil|title=Jet Fuel from Algae? Scientists probe fuel potential in common ocean plant |url= https://www.whoi.edu/oceanus/feature/jet-fuel-from-algae |date=28 January 2015 |work= Oceanus magazine |publisher= Woods Hole Oceanographic Institution}}</ref>

By 2016, Thomas Brueck of Munich TU was forecasting that algaculture could provide 3–5% of jet fuel needs by 2050.<ref>{{cite news|title=From green slime to jet fuel: algae offers airlines a cleaner future |url= https://reuters.com/article/idUSKCN0Z117F |work= Reuters |date= 15 June 2016}}</ref>

In fall 2016, the International Civil Aviation Organization announced plans for multiple measures including the development and deployment of sustainable aviation fuels.<ref name=ICAOdec2018>{{Cite web |url= https://www.icao.int/environmental-protection/Documents/Sustainable%20Aviation%20Fuels%20Guide_100519.pdf |title= Sustainable Aviation Fuels Guide |publisher= ICAO |date= Dec 2018}}</ref>

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 {{convert|1|e9USgal|e6m3|abbr=unit}} by 2012-2014.<ref name=Greentech19april2017/> By 2017 most companies had disappeared or changed their business plans to focus on other markets.<ref name=Greentech19april2017>{{cite web|last1=Wessof|first1=Eric|title=Hard Lessons From the Great Algae Biofuel Bubble|url=https://www.greentechmedia.com/articles/read/lessons-from-the-great-algae-biofuel-bubble#gs.5jG2khs|publisher=Greentech Media|date=19 April 2017}}</ref>

In 2019, 0.1% of fuel was SAF:<ref>{{cite web|last= |date=2021-03-25 |title=How sustainable fuel will help power aviation's green revolution|url=https://www.flightglobal.com/flight-international/how-sustainable-fuel-will-help-power-aviations-green-revolution/143044.article|access-date=2021-03-28|website=FlightGlobal }}</ref> The International Air Transport Association (IATA) supported the adoption of Sustainable Aviation fuel, aiming in 2019 for 2% share by 2025: {{convert|7|e6m3|e9USgal|abbr=unit}}.<ref name=IATAmay2019>{{cite web |url= https://www.iata.org/contentassets/ed476ad1a80f4ec7949204e0d9e34a7f/fact-sheet-alternative-fuels.pdf |title= Sustainable Aviation Fuels Fact sheet |publisher= IATA |date= May 2019}}</ref><ref name=IEA18mar2019>{{cite news |url= https://www.iea.org/commentaries/are-aviation-biofuels-ready-for-take-off |title= Are aviation biofuels ready for take off? |author= Pharoah Le Feuvre |date= 18 March 2019 |publisher= International Energy Agency}}</ref>

[[File:United Airlines - N851UA -Airbus A319 - San Francisco International Airport-0383.jpg|thumb|In 2019, United Airlines purchased up to {{convert|10|e6USgal|m3}} of SAF from World Energy over two years.<ref>{{cite press release |url= https://hub.united.com/united-biofuel-commitment-world-energy-2635867299.html |title= Expanding our commitment to powering more flights with biofuel |publisher= United Airlines |date= May 22, 2019}}</ref>]]

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.<ref name=AvWeek4feb2021>{{cite news |url= https://aviationweek.com/aerospace/manufacturing-supply-chain/boeing-moves-forward-airbus-a321xlr-competitor-plan |title= Boeing Moves Forward With Airbus A321XLR-Competitor Plan |author= Guy Norris |date= February 4, 2021 |work= Aviation Week}}</ref> In May 2021, the International Air Transport Association (IATA) set a goal for the aviation industry to achieve net-zero carbon emissions by 2050 with SAF as the key component.<ref>{{Cite web |title=Net Zero Roadmaps |url=https://www.iata.org/en/programs/environment/roadmaps/ |access-date=2023-11-17 |website=www.iata.org |language=en}}</ref>

The 2022 Inflation Reduction Act introduced the Fueling Aviation's Sustainable Transition (FAST) Grant Program. The program provides $244.5 million in grants for SAF-related "production, transportation, blending, and storage."<ref>{{Cite web |date=November 16, 2023 |title=Fueling Aviation's Sustainable Transition (FAST) Grants |url=https://www.faa.gov/general/fueling-aviations-sustainable-transition-fast-grants |access-date=November 16, 2023 |website=Federal Aviation Administration}}</ref> In November, 2022, sustainable aviation fuels were a topic at COP26.<ref>{{Cite web |author=United Nations |title=COP26: Together for our planet |url=https://www.un.org/en/climatechange/cop26 |access-date=2023-11-17 |website=United Nations |language=en}}</ref>

As of 2023, 90% of biofuel was made from oilseed and sugarcane which are grown for this purpose only.<ref>{{Cite web |title=Biodiesel Market Size, Share & Trends Analysis Report, 2030 |url=https://www.grandviewresearch.com/industry-analysis/biodiesel-market |access-date=2023-11-17 |website=www.grandviewresearch.com |language=en}}</ref>

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.{{Citation needed|date=February 2023}}

==Production== Jet fuel 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.<ref>{{Cite web|url=https://www.astm.org/d7566-11.html|title=Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons|website=www.astm.org}}</ref><ref name=ASTMsep2011/> Tests have been done with blending synthetic paraffinic kerosene (SPK) in considerably higher concentrations.<ref>{{Cite journal|url=https://repository.tudelft.nl/islandora/object/uuid%3Aca415372-6ac0-4e7a-ab66-6e6dbf564e22|title=Evaluation of safety, performance and emissions of synthetic fuel blends in a Cessna Citation II|first1=T. A.|last1=Snijders|first2=J. A.|last2=Melkert|date=December 22, 2011|journal=Conference Proceedings of the 3AF/AIAA Aircraft Noise and Emissions Reduction Symposium, 25–27 October 2011, Marseille, France|via=repository.tudelft.nl}}</ref>

; HEFA-SPK : Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosine (HEFA-SPK) is a specific type of hydrotreated vegetable oil fuel.<ref name="Doliente2020" /> {{As of|2020|}} this was the only mature technology<ref name="IEA18mar2019" /><ref name="Doliente2020" /><ref>{{cite journal |last1=Starck |first1=Laurie |last2=Pidol |first2=Ludivine |last3=Jeuland |first3=Nicolas |last4=Chapus |first4=Thierry |last5=Bogers |first5=Paul |last6=Bauldreay |first6=Joanna |title=Production of Hydroprocessed Esters and Fatty Acids (HEFA) – Optimisation of Process Yield |journal=Oil & Gas Science and Technology – Revue d'IFP Energies nouvelles |date=January 2016 |volume=71 |issue=1 |page=10 |doi=10.2516/ogst/2014007 |s2cid=45086444 |url=https://ogst.ifpenergiesnouvelles.fr/articles/ogst/pdf/2016/01/ogst120241.pdf |access-date=3 November 2022 |language=en}}</ref> (but by 2024 FT-SPK was commercialized as well<ref>{{Cite web |title=The feedstocks of the future has landed |url=https://www.topsoe.com/saf-feedstocks |access-date=2024-10-15 |website=www.topsoe.com |language=en}}</ref>). HEFA-SPK was approved by Altair Engineering for use in 2011.<ref>{{cite web |title=Biofuel Factsheet - Aviation Biofuels |url=https://www.etipbioenergy.eu/images/ETIP_Bioenergy_Factsheet_Aviation_Biofuels.pdf |website=European Technology Innovation Platform - Bioenergy |access-date=3 November 2022 |archive-url=https://web.archive.org/web/20220629124155/https://www.etipbioenergy.eu/images/ETIP_Bioenergy_Factsheet_Aviation_Biofuels.pdf |archive-date=29 June 2022 |language=en |date=2017 |url-status=live}}</ref> HEFA-SPK is produced by the deoxygenation and hydroprocessing of the feedstock fatty acids of algae, jatropha, and camelina.<ref>{{Cite web|url=https://aviationbenefits.org/environmental-efficiency/climate-action/sustainable-aviation-fuel/producing-sustainable-aviation-fuel/|title = Producing sustainable aviation fuel}}</ref> : The Diamond Green Diesel facility in Port Arthur, Texas, operated by Valero Energy, began producing SAF in late 2024, using the HEFA-SPK process.<ref name=":0" /><ref>{{Cite web |title=Denver terminal joins Avfuel's growing SAF supply chain {{!}} Biodiesel Magazine |url=https://biodieselmagazine.com//articles/denver-terminal-joins-avfuels-growing-saf-supply-chain |access-date=2025-08-05 |website=biodieselmagazine.com}}</ref> ; Bio-SPK : This fuel uses oil extracted from plant or animal sources such as ''jatropha'', algae, tallows, waste oils, babassu, and ''Camelina'' to produce synthetic paraffinic kerosene (bio-SPK) by cracking and hydroprocessing. Using algae to make jet fuel remains an emerging technology. Companies working on algae jet fuel include Solazyme, Honeywell UOP, Solena, Sapphire Energy, Imperium Renewables, and Aquaflow Bionomic Corporation. Universities working on algae jet fuel are Arizona State University and Cranfield University. Major investors for algae-based SPK research are Boeing, Honeywell/UOP, Air New Zealand, Continental Airlines, Japan Airlines, and General Electric.{{Citation needed|date=February 2023}} ; FT-SPK : Processing solid biomass using pyrolysis can produce oil or gasification to produce a syngas that is processed into FT SPK (Fischer–Tropsch Synthetic Paraffinic Kerosene).{{Citation needed|date=February 2023}} ; ATJ-SPK : The alcohol-to-jet (ATJ) pathway takes alcohols such as ethanol or butanol and de-oxygenates and processes them into jet fuels.<ref>{{Cite web|url=https://advancedbiofuelsusa.info/tag/atj-spk-alcohol-to-jet-synthetic-paraffinic-kerosene/|title=Advanced BioFuels USA – Truly Sustainable Renewable Future|website=advancedbiofuelsusa.info}}</ref> Companies such as LanzaTech have created ATJ-SPK from {{chem2|CO2}} in flue gases.<ref>{{Cite web|url=https://www.lanzatech.com/2018/04/03/jet-fuel-derived-ethanol-now-eligible-commercial-flights/|title=Jet Fuel Derived from Ethanol Now Eligible for Commercial Flights|access-date=2020-12-22|archive-date=2022-01-25|archive-url=https://web.archive.org/web/20220125161620/https://www.lanzatech.com/2018/04/03/jet-fuel-derived-ethanol-now-eligible-commercial-flights/}}</ref> The ethanol is produced from CO in the flue gases using microbes such as ''Clostridium autoethanogenum''. In 2016 LanzaTech demonstrated its technology at Pilot scale in NZ – using Industrial waste gases from the steel industry as a feedstock.<ref>Voegele, E. November 2009. "Waste to ethanol projects move forward", Ethanol Producer Magazine</ref><ref>{{Cite web|url=https://www.triplepundit.com/story/2013/interview-lanzatech-ceo-jennifer-holmgren/52196|title=Interview: LanzaTech CEO Jennifer Holmgren|website=www.triplepundit.com}}</ref><ref>{{Cite journal|url= |title=Genome editing of Clostridium autoethanogenum using CRISPR/Cas9|first1=Shilpa|last1=Nagaraju|first2=Naomi Kathleen|last2=Davies|first3=David Jeffrey Fraser|last3=Walker|first4=Michael|last4=Köpke|first5=Séan Dennis|last5=Simpson|date=October 18, 2016|journal=Biotechnology for Biofuels|volume=9|issue=1|page=219|doi=10.1186/s13068-016-0638-3|pmid=27777621|pmc=5069954 |doi-access=free |bibcode=2016BB......9..219N }}</ref> Gevo developed technology to retrofit existing ethanol plants to produce isobutanol.<ref>{{Cite web |url=https://gevo.com/wp-content/uploads/2020/05/Gevo-Whitepaper-Sustainable-Aviation-Fuel.pdf |title=Gevo |access-date=2021-11-23 |archive-date=2021-06-23 |archive-url=https://web.archive.org/web/20210623212715/https://gevo.com/wp-content/uploads/2020/05/Gevo-Whitepaper-Sustainable-Aviation-Fuel.pdf }}</ref> Alcohol-to-Jet Synthetic Paraffinic Kerosene (ATJ-SPK) is a proven pathway to deliver bio-based, low-carbon fuel.{{Citation needed|date=February 2023}}

===Alternative production routes===

Several research initiatives and companies have reported work on technologies intended to produce synthetic hydrocarbons and sustainable aviation fuels (SAF).

The SUN-to-LIQUID project (2016-2019) 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 (syngas), 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.<ref>{{cite web |title=The Future Is Bright for Turning Sunlight Into Sustainable Jet Fuel |url=https://www.solarpaces.org/the-future-is-bright-for-turning-sunlight-into-sustainable-jet-fuel/ |publisher=SolarPACES |date=2023-12-30 |access-date=2025-10-05}}</ref><ref>{{cite web |title=Sustainable Aviation Fuel From Solar Energy: Not A Dream Any More |url=https://cleantechnica.com/2022/07/20/sustainable-aviation-fuel-from-solar-energy-not-a-dream-any-more/ |publisher=CleanTechnica |date=2022-07-20 |access-date=2025-10-05}}</ref><ref>{{cite web |title=Solar fuel by SUN-to-LIQUID: Demonstration Event |url=https://cordis.europa.eu/event/id/147038-solar-fuel-by-suntoliquid-demonstration-event |publisher=CORDIS (Community Research and Development Information Service) |access-date=2025-10-05}}</ref><ref>{{cite web |title=Aviation liquid fuels from sunlight and air |date=3 July 2020 |url=https://www.iea.org/articles/aviation-liquid-fuels-from-sunlight-and-air |publisher=International Energy Agency |access-date=2025-10-05}}</ref> 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.<ref>{{Cite news |date=August 17, 2022 |title=Ways to make aviation fuel green |newspaper=The Economist |url=https://www.economist.com/science-and-technology/2022/08/17/ways-to-make-aviation-fuel-green |access-date=2023-02-23 |issn=0013-0613}}</ref>

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.<ref>{{Cite news |date=August 14, 2024 |title=New SAF Process Could Transform Industry |newspaper=Aviation Industry News |url=https://www.ainonline.com/aviation-news/aerospace/2024-08-14/new-saf-process-could-transform-industry}}</ref>

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 (syngas), subsequently converted to jet fuel via Fischer-Tropsch or similar gas-to-liquid processes.<ref>{{Cite web |last=Brelsford |first=Robert |date=2023-02-20 |title=Denmark-based operator lets contract for first-of-a-kind electrofuels plant |url=https://www.ogj.com/energy-transition/article/14290070/denmark-based-operator-lets-contract-for-first-of-a-kind-electrofuels-plant |access-date=2025-01-20 |website=Oil & Gas Journal|language=en}}</ref><ref>{{Cite web |date=2024-10-02 |title=Arcadia hit by delay: Won't be able to deliver green aviation fuels until 2028 |url=https://energywatch.com/EnergyNews/Cleantech/article17501728.ece |access-date=2025-01-20 |website=energywatch.com |language=en}}</ref>

=== Piston engines === Small piston engines can be modified to burn ethanol.<ref name="SDSU2016">{{cite web |url= http://www.age85.org/index.htm |archive-url= https://web.archive.org/web/20080515192245/http://www.age85.org/index.htm |archive-date= 2008-05-15 |title= AGE-85 (Aviation Grade Ethanol) |publisher= South Dakota State University |year = 2006 }}</ref> Swift Fuel, a biofuel alternative to avgas, was approved as a test fuel by ASTM International in December 2009.<ref>{{cite press release |title=Indiana Airline Fuel Developer Moves Ahead With Testing |publisher=Purdue Research Park |date= December 14, 2009 |url= https://www.purdue.edu/uns/x/2009b/091214SwiftASTM.html }}</ref><ref>{{cite news |url= https://www.avweb.com/news/efforts-move-forward-to-produce-alternative-aviation-fuels/ |title= Efforts Move Forward To Produce Alternative Aviation Fuels |last= Grady |first= Mary |date= December 15, 2009}}</ref>

=== Technical challenges === Nitrile-based rubber materials expand in the presence of aromatic compounds found in conventional petroleum fuel. Pure biofuels without petroleum and paraffin-based additives may cause rubber seals and hoses to shrink.<ref>{{cite web | title =Technical Report: Near-Term Feasibility of Alternative Jet Fuels | publisher =Sponsored by the FAA. Authored by MIT staff. Published by RAND Corporation| url =http://web.mit.edu/aeroastro/partner/reports/proj17/altfuelfeasrpt.pdf | access-date =August 22, 2012 }}</ref> Synthetic rubber substitutes that are not adversely affected by biofuels, such as Viton, for seals and hoses are available.<ref>{{cite web | title =Biodiesel FAQ | publisher =University of Kentucky College of Agriculture, Food, and Environment | year =2006 | url =http://www.ca.uky.edu/agc/pubs/aen/aen90/aen90.pdf | access-date =August 22, 2012 }}</ref>

The United States Air Force found harmful bacteria and fungi in their biofueled aircraft, and use pasteurization to disinfect them.<ref>{{Cite web|url=https://www.af.mil/News/Article-Display/Article/939659/afrl-discovering-whats-bugging-military-aircraft/|title=AFRL discovering what's "bugging" military aircraft|website=U.S. Air Force|date=11 September 2016 }}</ref>

====Aromatics and cycloalkanes==== {{As of|2025|05}} SAF is generally required to be blended with fossil fuel—because jet fuel needs cycloalkanes and aromatics, which are generally deficient in SAF; as well as the more prevalent in SAF n-alkanes and isoalkanes.<ref name="NREL-MIT-Comstock">{{cite web | title=With a Technology License From MIT and NREL in Hand, Comstock Fuels Aims To Produce Jet Fuel From Lignin | website=NREL | date=2025-04-22 | url=https://www.nrel.gov/news/program/2025/with-a-technology-license-from-mit-and-nrel-in-hand-comstock-fuels-aims-to-produce-jet-fuel-from-lignin.html | access-date=2025-05-04}}</ref>

==Economics== In 2019 the International Energy Agency forecast SAF production should grow from 18 to 75 billion litres between 2025 and 2040, representing a 5% to 19% share of aviation fuel.<ref name=IEA18mar2019/> By 2019, fossil jet fuel production cost was $0.3-0.6 per L given a $50–100 crude oil barrel, while aviation biofuel production cost was $0.7-1.6, needing a $110–260 crude oil barrel to break-even.<ref name=IEA18mar2019/> As of 2024, SAF represents just 0.3% of global aviation fuel.<ref name="IATA25_web">{{cite web |url=https://www.iata.org/en/pressroom/2024-releases/2024-12-10-03/ |website=IATA |title=Disappointingly Slow Growth in SAF Production|access-date=25 September 2025}}</ref>

{{As of|2020|}} aviation biofuel was more expensive than fossil jet kerosene,<ref name=IU4dec2020/> considering aviation taxation and subsidies at that time.<ref>{{Cite web |title= Sustainable Aviation Fuel: Review of Technical Pathways |url= https://www.energy.gov/sites/prod/files/2020/09/f78/beto-sust-aviation-fuel-sep-2020.pdf |date= Sep 2020 |publisher= United States Department of Energy}}</ref>

As of a 2021 analysis, VFA-SAF break-even cost was {{Convert|2.50|$/gal|$/l|abbr=on}}.<ref name="Huq-2021"/> This number was generated considering credits and incentives at the time, such as California's LCFS (Low Carbon Fuel Standard) credits and the US Environmental Protection Agency (EPA) Renewable Fuel Standard incentives.

==Sustainable aviation fuels== [[File:Oslo Airport terminal night view.jpg|thumb|In 2016, Oslo Airport became the first international airport to offer sustainable aviation fuel as part of the fuel mix.]]

Sustainable biofuels do not use food crops, prime agricultural land or fresh water. '''Sustainable aviation fuel''' (SAF) is certified by a third-party such as the Roundtable For Sustainable Biofuels.<ref>{{cite news |url= http://aviationweek.com/commercial-aviation/glacial-pace-advancements-biofuel-threatens-emissions-targets |title= Glacial Pace Of Advancements In Biofuel Threatens Emissions Targets |date= Oct 10, 2017 |author= Kerry Reals |work=Aviation Week & Space Technology}}</ref>

As of 2022, some 450,000 flights had used sustainable fuels as part of the fuel mix, although such fuels were ~3x more expensive than the traditional fossil jet fuel or kerosene.<ref name=Economist18aug2022>{{Cite news |title=Ways to make aviation fuel green |newspaper=The Economist |url=https://www.economist.com/science-and-technology/2022/08/17/ways-to-make-aviation-fuel-green |date=2022-08-17 |issn=0013-0613}}</ref> In 2023, SAFs account for less than 0.1% of all aviation fuels consumed.<ref>{{Cite book |url=https://www.wipo.int/web-publications/wipo-technology-trends-future-of-transportation/en/5-emerging-technologies-in-transportation.html#h2-air-sustainable-aviation-fuel |title=WIPO Technology Trends: Future of Transportation - 5 Emerging technologies in transportation |language=en}}</ref> Throughout 2024, Alaska Airlines was the leader among U.S. airlines in SAF implementation, accounting for 0.68% of its fuel usage. Other major airlines including United, Delta and JetBlue used SAF in roughly .3% of fuel.<ref name=":0">{{Cite web |last=Elgin |first=Ben |date=2025-07-22 |title=Airlines face climate reality check with green jet fuel |url=https://www.latimes.com/environment/story/2025-07-22/airlines-face-climate-reality-check-with-green-jet-fuel |access-date=2025-07-25 |website=Los Angeles Times |language=en-US}}</ref>

===Certification=== A SAF sustainability certification ensures that the product satisfies criteria focused on environmental, social, and economic "triple-bottom-line" considerations. Under many emission regulation schemes, such as the European Union Emissions Trading Scheme (EUTS), a certified SAF product may be exempted from carbon compliance liability costs.<ref>{{cite web|url=http://ec.europa.eu/energy/renewables/biofuels/sustainability_schemes_en.htm|title=Sustainability schemes for biofuels|work=European Commission/Energy/Renewable energy/Biofuels|access-date=1 April 2012}}</ref> This marginally improves SAF's economic competitiveness versus fossil-based fuel.<ref>{{cite web|url=http://www.qantas.com.au/travel/airlines/sustainable-aviation-fuel/global/en#jump4 |title=Sustainable Aviation Fuel |publisher=Qantas|access-date=2013-10-24}}</ref>

The first reputable body to launch a sustainable biofuel certification system was the European-based Roundtable on Sustainable Biomaterials (RSB) NGO.<ref>{{cite web |url=http://rsb.epfl.ch/files/content/sites/rsb2/files/Biofuels/Documents%20and%20Resources/11-10-07_RSB_Fact_Sheet_EN.pdf |title=RSB Roundtable on Sustainable Biomaterials &#124; Roundtable on Sustainable Biomaterials |website=Rsb.epfl.ch |date=2013-10-17 |access-date=2013-10-24 |archive-date=2011-12-22 |archive-url=https://web.archive.org/web/20111222050201/http://rsb.epfl.ch/files/content/sites/rsb2/files/Biofuels/Documents%20and%20Resources/11-10-07_RSB_Fact_Sheet_EN.pdf }}</ref> Leading airlines and other signatories to the Sustainable Aviation Fuel Users Group (SAFUG) pledged to support RSB as their preferred certification provider.<ref>{{cite web|url=http://www.safug.org/information/pledge/ |access-date=March 29, 2012 |archive-url=https://web.archive.org/web/20120425051329/http://www.safug.org/information/pledge/ |archive-date=April 25, 2012 |title=Our Commitment to Sustainable Options}}</ref><ref>{{cite web|url=http://www.safug.org/ |title=Sustainable Aviation Fuel Users Group – SAFUG |website=Safug.org |access-date=2013-10-24}}</ref>

Some SAF pathways procured RIN pathways under the United States's renewable fuel standard which can serve as an implicit certification if the RIN is a Q-RIN. ; EU RED II Recast (2018) : Greenhouse gas emissions from sustainable fuels must be lower than those from the fuels they replace: at least 50% for production built before 5 October 2015, 60% after that date and 65% after 2021.<ref>{{Cite web |title=Renewable Energy – Recast to 2030 (RED II) - European Commission |url=https://joint-research-centre.ec.europa.eu/welcome-jec-website/reference-regulatory-framework/renewable-energy-recast-2030-red-ii_en |access-date=2025-03-31 |website=joint-research-centre.ec.europa.eu |language=en}}</ref> Raw materials cannot be sourced from land with high biodiversity or high carbon stocks (i.e. primary and protected forests, biodiversity-rich grasslands, wetlands and peatlands). Other sustainability issues are set out in the Governance Regulation and may be covered voluntarily.

; ICAO 'CORSIA' : GHG Reduction - Criterion 1: lifecycle reductions of at least 10% compared to fossil fuel. Carbon Stock - Criterion 1: not produced from biomass obtained from land whose uses changed after 1 January 2008 from primeval forests, wetlands or peatlands, as all these lands have high carbon stocks. Criterion 2: For land use changes after 1 January 2008, (using IPCC land categories), if emissions from direct land use change (DLUC) exceed the default value of the induced land use change (ILUC), the value of the DLUC replaces the default (ILUC) value.{{cn|date =February 2026}}

===Global impact=== As emissions trading schemes and other carbon compliance regimes emerge, certain biofuels are likely to be exempted ("zero-rated") by governments from compliance due to their closed-loop nature, if they can demonstrate appropriate credentials. For example, in the EUTS, SAFUG's proposal was accepted<ref>{{cite web |title=Revision of the EU Energy Tax Directive - technical press briefing |url=http://ec.europa.eu/taxation_customs/resources/documents/taxation/review_of_regulation_en.pdf |access-date=2013-10-24 |website=Ec.europa.eu}}</ref> that only fuels certified as sustainable by the RSB or similar body would be zero-rated.<ref>{{cite web|url=http://www.safug.org/assets/docs/SAFUG_Brochure.pdf |title=Sustainable Aviation Fuel Users Group: European Section |website=Safug.org |access-date=2013-10-24}}</ref> SAFUG was formed by a group of interested airlines in 2008 under the auspices of Boeing Commercial Airplanes. Member airlines represented more than 15% of the industry, and signed a pledge to work towards SAF.<ref>{{cite web|url=http://www.boeing.com/newairplane/environment/#/SustainableAviationBiofuel/UsersGroup |title=Environment and Biofuels &#124; Boeing Commercial Airplanes |website=Boeing|access-date=2013-10-24}}</ref><ref>{{cite web|url=http://www.safug.org/safug-pledge/ |title= SAFUG Pledge; Boeing Commercial Airplanes |website=Safug.org |access-date=2015-07-10}}</ref>

In addition to SAF certification, the integrity of aviation biofuel producers and their products could be assessed by means such as Richard Branson's Carbon War Room,<ref>{{cite web |url=http://www.carbonwarroom.com/sectors/transport/aviation/operation-renewablejetfuels#mission |title=Renewable Jet Fuels |work=Carbon War Room |date=9 December 2011 |access-date=2013-10-24 |archive-date=2013-10-30 |archive-url=https://web.archive.org/web/20131030013036/http://www.carbonwarroom.com/sectors/transport/aviation/operation-renewablejetfuels#mission }}</ref> or the Renewable Jet Fuels initiative.<ref>{{cite web |url=http://renewablejetfuels.org/ |title=Welcome |publisher=Renewable Jet Fuels |access-date=2013-10-24 |archive-date=2013-10-29 |archive-url=https://web.archive.org/web/20131029205231/http://renewablejetfuels.org/ }}</ref> The latter works with companies such as LanzaTech, SG Biofuels, AltAir, Solazyme, and Sapphire.<ref>{{cite web|url=http://www.sustainablesky.com |title=Sustainable Sky Institute |publisher=Sustainable Sky Institute |access-date=2016-04-26}}</ref>{{verify source|date=February 2023}}

Along with her co-authors, Candelaria Bergero of the University of California's Earth System Science Department stated that "main challenges to scaling up such sustainable fuel production include technology costs and process efficiencies", and widespread production would undermine food security and land use.<ref>{{cite journal |last1=Bergero |first1=Candelaria |display-authors= etal |title=Pathways to net-zero emissions from aviation |journal= Nature Sustainability |date=30 January 2023 |volume=6 |issue=4 |pages=404–414 |doi=10.1038/s41893-022-01046-9 |s2cid=256449498 |doi-access=free |bibcode=2023NatSu...6..404B |url=https://www.researchsquare.com/article/rs-1871023/latest.pdf }}</ref>

=== Market implementation === By 2019, Virgin Australia had fueled more than 700 flights and flown more than one million kilometers, domestic and international, using Gevo's alcohol-to-jet fuel.<ref>{{Cite press release |title=Virgin Australia's sustainable aviation fuel flies one million kilometres |date=17 June 2019 |publisher=Virgin Australia |url=https://newsroom.virginaustralia.com/release/virgin-australia%E2%80%99s-sustainable-aviation-fuel-flies-one-million-kilometres}}</ref> Virgin Atlantic was working to regularly use fuel derived from the waste gases of steel mills, with LanzaTech.<ref name="AvWeek26apr2019">{{cite news |author=Kerry Reals |date=Apr 26, 2019 |title=Biofuel Market Is Nearing A Tipping Point |url=https://aviationweek.com/commercial-aviation/biofuel-market-nearing-tipping-point |work=Aviation Week & Space Technology}}</ref> British Airways wanted to convert household waste into jet fuel with Velocys.<ref name="AvWeek26apr2019" /> United Airlines committed to {{convert|900|e6USgal|m3|abbr=unit}} of sustainable aviation fuel for 10 years from Fulcrum BioEnergy (of its {{convert|4.1|e9USgal|m3|abbr=unit}} fuel consumption in 2018), after a $30 million investment in 2015.<ref name="AvWeek26apr2019" />

From 2020, Qantas planned to use a 50/50 blend of SG Preston's biofuel on its Los Angeles-Australia flights. SG Preston also planned to provide fuel to JetBlue over 10 years.<ref name="AvWeek26apr2019" /> At its sites in Singapore, Rotterdam and Porvoo, Finland's Neste expected to improve its renewable fuel production capacity from {{convert|2.7 to 3.0|e6t|e9lb|abbr=unit}} a year by 2020, and to increase its Singapore capacity by {{convert|1.3|e6t|e9lb|abbr=unit}} to reach {{convert|4.5|e6t|e9lb|abbr=unit}} in 2022 by investing €1.4 billion ($1.6 billion).<ref name="AvWeek26apr2019" />

By 2020, International Airlines Group had invested $400 million to convert waste into sustainable aviation fuel with Velocys.<ref name="Flight3jan2020">{{cite news |date=3 January 2020 |title=BA begins offsetting domestic flight emissions |url=https://www.flightglobal.com/ba-begins-offsetting-domestic-flight-emissions/135987.article |work=FlightGlobal}}</ref>

United Airlines has expanded SAF use across multiple airports worldwide, including Amsterdam in 2022,<ref>{{Cite web |title=United Becomes First U.S. Airline to Sign Agreement to Purchase Sustainable Aviation Fuel Overseas |url=https://united.mediaroom.com/2022-05-10-United-Becomes-First-U-S-Airline-to-Sign-Agreement-to-Purchase-Sustainable-Aviation-Fuel-Overseas |access-date=2025-04-19 |website=United - Newsroom}}</ref> San Francisco and London in 2023,<ref>{{Cite news |last=Kelly |first=Stephanie |date=May 4, 2023 |title=United Airlines will use lower-carbon fuels in San Francisco, London |url=https://www.reuters.com/business/sustainable-business/united-airlines-will-use-lower-carbon-fuels-san-francisco-london-2023-05-04/ |access-date=April 19, 2025 |work=Reuters}}</ref> and Chicago O'Hare and Los Angeles in 2024.<ref>{{Cite web |title=United Airlines sign 8m gallon SAF offtake deal with Phillips 66 |url=https://www.safinvestor.com/news/146568/united-airlines/ |access-date=2025-04-19 |website=SAF Investor |language=en-US}}</ref>

In March 2024, regular use of SAF began in the Northeastern United States at John F. Kennedy International Airport, as part of a new effort by JetBlue.<ref>{{Cite web |last=Rivera |first=Valeria |date=2025-03-17 |title=JetBlue celebrates first regular supply of SAF at JFK |url=https://www.aviationbusinessnews.com/low-cost/jetblue-celebrates-first-regular-supply-of-saf-at-jfk/ |access-date=2025-04-19 |website=Aviation Business News |language=en-GB}}</ref> Southwest Airlines began using sustainable jet fuel at Chicago Midway International Airport in October 2024.<ref>{{Cite web |title=Southwest signs 3.6m gallons SAF offtake deal with Valero |url=https://www.safinvestor.com/news/146181/southwest/ |access-date=2025-04-19 |website=SAF Investor |language=en-US}}</ref>

Fuel supplier Avfuel expanded its SAF offerings in Texas in November 2025 through its fixed-base operator (FBO) partner Million Air at Austin-Bergstrom International Airport (AUS). The companies had already partnered earlier in the year to provide SAF at an FBO at the Albany International Airport (ALB) in New York.<ref>{{Cite web |date=2025-12-09 |title=Million Air and Avfuel add sustainable aviation fuel to Austin airport |url=https://www.globalair.com/articles/million-air-and-avfuel-add-sustainable-aviation-fuel-to-austin-airport?id=11649 |access-date=2025-12-24 |website=Globalair.com |language=en}}</ref>

=== Certified processes === {| class="wikitable" |- ! Abbreviation !! Conversion Process !! Possible Feedstocks !! Blending Ratio !! Commercialization Proposals / Projects |- | HEFA-SPK || Synthesized paraffinic kerosene produced from hydroprocessed esters and fatty acids || Bio-Oils, Animal Fat, Recycled Oils || 50% || World Energy, Universal Oil Products, Neste, Dynamic Fuels, EERC |- | FT-SPK || Fischer-Tropsch hydroprocessed synthesized paraffinic kerosene || Coal, Natural Gas, Biomass || 50% || Fulcrum Bioenergy, Red Rock Biofuels, SG Preston, Kaidi Finland, Sasol, Shell Oil Company, Syntroleum |- | SIP-HFS || Synthesized kerosene isoparaffins produced from hydroprocessed fermented sugars || Biomass-derived sugar|| 10% || Amyris (company), TotalEnergies |- | SPK/A || Synthesized kerosene with aromatics derived by alkylation of light aromatics from non-petroleum sources || Coal, Natural Gas, Biomass || 50% || Sasol |- | ATJ-SPK || Alcohol-to-jet synthetic paraffinic kerosene || Biomass-derived ethanol or isobutanol || 50% || Gevo, Cobalt, Universal Oil Products, Lanzatech, Swedish Biofuels, Byogy |}

==Environmental impact== {{further|Environmental impact of aviation|Biofuel#Greenhouse gas emissions}}

Plants absorb carbon dioxide as they grow, therefore plant-based biofuels emit only the same amount of greenhouse gases as they had previously absorbed. Biofuel production, processing, and transport, however, emit greenhouse gases, reducing the emissions savings.<ref name="Doliente2020" /> Biofuels with the most emission savings are those derived from photosynthetic algae (98% savings) although the technology is not developed, and those from non-food crops and forest residues (91–95% savings).<ref name="Doliente2020" />

Jatropha oil, a non-food oil used as a biofuel, lowers {{chem2|CO2}} emissions by 50–80% compared to Jet-A1, a kerosene-based fuel.<ref name=AImar2009>{{cite magazine |title= A Greener Future? |magazine= Aircraft Illustrated |date= March 2009}}</ref> Jatropha, used for biodiesel, can thrive on marginal land where most plants produce low yields.<ref>{{cite news |author= Ron Oxburgh |url= https://www.theguardian.com/commentisfree/2008/feb/28/alternativeenergy.biofuels |title= Through biofuels we can reap the fruits of our labours |newspaper= The Guardian |date= 28 February 2008}}</ref><ref>{{cite news |author= Patrick Barta |title= As Biofuels Catch On, Next Task Is to Deal With Environmental, Economic Impact |url= https://www.wsj.com/articles/SB120631198956758087 |newspaper= Wall Street Journal |date= 24 March 2008 |url-access= subscription}}</ref> A life cycle assessment on jatropha estimated that biofuels could reduce greenhouse gas emissions by up to 85% if former agro-pastoral land is used, or increase emissions by up to 60% if natural woodland is converted.<ref>{{Cite journal | last1 = Bailis | first1 = R. E. | last2 = Baka | first2 = J. E. | doi = 10.1021/es1019178 | title = Greenhouse Gas Emissions and Land Use Change from Jatropha Curcas-Based Jet Fuel in Brazil | journal =Environmental Science & Technology| volume = 44 | issue = 22 | pages = 8684–91 | year = 2010 | pmid = 20977266| bibcode = 2010EnST...44.8684B }}</ref>

Palm oil cultivation is constrained by scarce land resources and its expansion to forestland causes biodiversity loss, along with direct and indirect emissions due to land-use change.<ref name="Doliente2020" /> Neste Corporation's renewable products include a refining residue of food-grade palm oil, the oily waste skimmed from the palm oil mill's wastewater. Other Neste sources are used cooking oil from deep fryers and animal fats.<ref>{{Cite web|url=https://www.neste.com/products/all-products/raw-materials/waste-and-residues|title=Waste and residues as raw materials |date=15 May 2020 |publisher=Neste Corporation website}}</ref> [https://www.neste.com/en-us/products-and-innovation/sustainable-aviation/sustainable-aviation-fuel Neste's sustainable aviation fuel] is used by Lufthansa;<ref>{{Cite press release|url=https://www.neste.com/releases-and-news/aviation/neste-and-lufthansa-collaborate-and-aim-more-sustainable-aviation|title=Neste and Lufthansa collaborate and aim for a more sustainable aviation|date=October 2, 2019|publisher=Neste Corporation website}}</ref> Air France and KLM announced 2030 SAF targets in 2022<ref>{{Cite press release|url=https://news.klm.com/klm-groups-co2-emission-reduction-targets-for-2030-approved-by-sbti/|title=KLM Group's CO2 emission reduction targets for 2030 approved by SBTi|date=16 December 2022 |publisher=KLM website |access-date=2023-01-02}}</ref> including multi-year purchase contracts totaling over 2.4 million tonnes of SAF from Neste, TotalEnergies, and DG Fuels.<ref>{{Cite news| url=https://www.reuters.com/business/energy/totalenergies-air-france-klm-agree-sustainable-jet-fuel-deal-2022-12-05/|title=TotalEnergies and Air France KLM agree sustainable jet fuel deal|date=5 December 2022 |publisher=Reuters |access-date=2023-01-02}}</ref>

Aviation fuel from wet waste-derived feedstock ("VFA-SAF") provides an additional environmental benefit. Wet waste consists of waste from landfills, sludge from wastewater treatment plants, agricultural waste, greases, and fats. Wet waste can be converted to volatile fatty acids (VFA's), which then can be catalytically upgraded to SAF. Wet waste is a low-cost and plentiful feedstock, with the potential to replace 20% of US fossil jet fuel.<ref name="Huq-2021">{{Cite journal |last1=Huq |first1=Nabila A. |last2=Hafenstine |first2=Glenn R. |last3=Huo |first3=Xiangchen |last4=Nguyen |first4=Hannah |last5=Tifft |first5=Stephen M. |last6=Conklin |first6=Davis R. |last7=Stück |first7=Daniela |last8=Stunkel |first8=Jim |last9=Yang |first9=Zhibin |last10=Heyne |first10=Joshua S. |last11=Wiatrowski |first11=Matthew R. |last12=Zhang |first12=Yimin |last13=Tao |first13=Ling |last14=Zhu |first14=Junqing |last15=McEnally |first15=Charles S. |date=2021-03-30 |title=Toward net-zero sustainable aviation fuel with wet waste-derived volatile fatty acids |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=118 |issue=13 |article-number=e2023008118 |doi=10.1073/pnas.2023008118 |issn=1091-6490 |pmc=8020759 |pmid=33723013 |doi-access=free |bibcode=2021PNAS..11823008H }}</ref> This lessens the need to grow crops specifically for fuel, which in itself is energy intensive and increases {{chem2|CO2}} emissions throughout its life cycle. Wet waste feedstocks for SAF divert waste from landfills. Diversion has the potential to eliminate 17% of US methane emissions across all sectors. VFA-SAF's carbon footprint is 165% lower than fossil aviation fuel.<ref name="Huq-2021"/> This technology is in its infancy; although start-ups are working to make this a viable solution. Alder Renewables, BioVeritas, and ChainCraft are a few organizations committed to this.

NASA has determined that 50% aviation biofuel mixture can cut particulate emissions caused by air traffic by 50–70%.<ref>{{cite news |url= http://www.flyingmag.com/nasa-confirms-biofuels-reduce-jet-emissions |work= Flying magazine |title= NASA confirms biofuels reduce jet emissions |date= March 23, 2017}} Note: Firefox 'does not trust' the weblink 2022-12-22.</ref> Biofuels do not contain sulfur compounds and thus do not emit sulfur dioxide.{{Citation needed|date=December 2022}} While, it may be true that the burning of biofuels do not emit sulfur compounds, some forms of production, such as pyrolysis, can in fact produce sulfur compounds and other pollutants. Some potential pollutants that could be released are hydrogen sulfide and different nitrogen compounds like hydrogen cyanide, ammonia, and nitrogen dioxide.<ref>{{Cite journal |last=Li |first=Simeng |date=2024-01-30 |title=Reviewing Air Pollutants Generated during the Pyrolysis of Solid Waste for Biofuel and Biochar Production: Toward Cleaner Production Practices |journal=Sustainability |language=en |volume=16 |issue=3 |pages=1169 |doi=10.3390/su16031169 |bibcode=2024Sust...16.1169L |doi-access=free |issn=2071-1050}}</ref> There are other forms of biofuel production that may not have the same emissions.{{citation needed|date=October 2025}}

Because of the scaling required to make aviation biofuel mainstream, the impact of land usage is a current hindrance to the growth of the biofuel industry. Potential solutions to this issue have begun to surface. For example, algae farms can produce a lot more biofuel per unit of area than crops.<ref>{{Cite journal |last1=Shurin |first1=Jonathan B. |last2=Abbott |first2=Rachel L. |last3=Deal |first3=Michael S. |last4=Kwan |first4=Garfield T. |last5=Litchman |first5=Elena |last6=McBride |first6=Robert C. |last7=Mandal |first7=Shovon |last8=Smith |first8=Val H. |date=November 2013 |editor-last=Grover |editor-first=James |title=Industrial-strength ecology: trade-offs and opportunities in algal biofuel production |url=https://escholarship.org/content/qt6zp2t2xf/qt6zp2t2xf.pdf?t=nwkg0j |journal=Ecology Letters |language=en |volume=16 |issue=11 |pages=1393–1404 |doi=10.1111/ele.12176 |pmid=24015819 |bibcode=2013EcolL..16.1393S |issn=1461-023X|url-access= }}</ref> Trials of using algae as biofuel were carried out by Lufthansa and Virgin Atlantic as early as 2008, although there is little evidence that using algae is a reasonable source for jet biofuels.<ref>{{cite news |url= http://news.bbc.co.uk/1/hi/uk/7261214.stm |work= BBC News |title= First biofuel flight touches down |access-date=24 February 2008 | date=24 February 2008| archive-url= https://web.archive.org/web/20080229004604/http://news.bbc.co.uk/1/hi/uk/7261214.stm| archive-date= 29 February 2008 | url-status= live}}</ref> By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, ''Isochrysis'', was under research as a possible jet biofuel feedstock.<ref>{{cite web|last1=Reddy|first1=Chris|last2=O'Neil|first2=Greg|title=Jet Fuel from Algae? Scientists probe fuel potential in common ocean plant|url=https://www.whoi.edu/oceanus/feature/jet-fuel-from-algae|access-date=26 March 2018|date=28 January 2015}}</ref>

== Technological pathways and economic challenges == To meet international greenhouse gas (GHG) reduction targets, the aviation industry is prioritizing Sustainable Aviation Fuels (SAF). In countries with high biomass availability like Brazil, the primary pathways identified for decarbonization are Hydroprocessed Esters and Fatty Acids (HEFA) and Alcohol-to-Jet (AtJ).<ref name="Ambrosio2025">{{cite arXiv |last1=Ambrosio |first1=Wesley Bonicontro |last2=de Sousa |first2=Bruna Araújo |last3=Kanieski |first3=João Marcos |last4=Marchiori |first4=Priscila |last5=Mockaitis |first5=Gustavo |title=Sustainable Aviation Fuels: Opportunities, Alternatives and Challenges for Decarbonizing the Aviation Industry and Foster the Renewable Chemicals |date=2025 |class=econ.GN |eprint=2504.03880 }}</ref>

The use of vegetable oils as a feedstock for aviation fuel has been studied for decades. Dunn (2001) highlighted the potential of these oils as alternative jet fuel sources, which fundamentally underpins the modern HEFA pathway.<ref>{{cite journal |last1=Dunn |first1=R.O. |title=Alternative Jet Fuels from Vegetable Oils |journal=Transactions of the ASAE |volume=44 |issue=6 |year=2001 |url=https://elibrary.asabe.org/abstract.asp??JID=3&AID=6988&CID=t2001&v=44&i=6&T=1 |doi=10.13031/2013.6988|url-access=subscription }}</ref> However, economic viability has historically been a major barrier; early assessments by Lander and Reif (1986) noted that producing jet fuel from alternative sources would require significant capital investment compared to conventional petroleum refining.<ref>{{cite journal |last1=Lander |first1=H.R. Jr. |last2=Reif |first2=H.E. |title=The Production of Jet Fuel From Alternative Sources |journal=Journal of Energy Resources Technology |volume=108 |issue=1 |pages=3–11 |year=1986 |doi=10.1115/1.3239959}}</ref>

Current perspectives suggest that to overcome these economic challenges, SAF production should be integrated into biorefineries that also foster the production of renewable chemicals, thereby diversifying revenue streams.<ref name="Ambrosio2025" />

Less than 1% of global liquid biofuels are currently used for aviation purposes, with biojet fuel fueling less than 0.5% of all flights; most is used for road transport, but even if the entire biofuel production was allocated to aviation, this would provide, at most, one-third of demand.<ref>{{Cite journal |last=Ritchie |first=Hannah |last2=Rosado |first2=Pablo |date=2026-01-26 |title=Could biofuels meet demand for global aviation? |url=https://ourworldindata.org/biofuels-demand-global-aviation |journal=Our World in Data |language=en}}</ref>

== See also ==

* {{Annotated link |Biodiesel}} * {{Annotated link |Fossil fuel phase-out}} * {{Annotated link |List of emerging technologies}} * {{Annotated link |Vegetable oil fuel}}

==References== {{Reflist}}

==Further reading== {{refbegin|30em}} * {{cite news |url= http://aviationweek.com/technology/opinion-biofuels-sustainable-essential-aviation-s-future |title= Opinion: Biofuels Sustainable, Essential To Aviation's Future |date= Oct 23, 2017 |author=Adam Klauber (Rocky Mountain Institute) |author2=Isaac Toussie (Rocky Mountain Institute) |author3=Steve Csonka (Commercial Aviation Alternative Fuels Initiative) |author4=Barbara Bramble (National Wildlife Federation) |work=Aviation Week & Space Technology}} * {{cite web |url= https://aim-builds.s3.amazonaws.com/gevo/Gevo+WP_aviation+fuel.pdf |title= Sustainable Aviation Fuel |quote= Alcohol-to-Jet Synthetic Paraffinic Kerosene Is a Proven Pathway to Deliver a Bio-Based, Low-Carbon Option to Travelers |publisher= Gevo |date= December 2019 }} * {{cite report |url= https://www3.weforum.org/docs/WEF_Clean_Skies_Tomorrow_SAF_Analytics_2020.pdf |title= Clean Skies for Tomorrow |quote= Sustainable Aviation Fuels as a Pathway to Net-Zero Aviation |date= Nov 2020 |publisher= World Economic Forum |author= McKinsey & Company}} {{refend}}

==External links== * {{cite web |url= https://www.sustainablesky.com/ |title= Sustainable Sky Institute |quote= non-profit think tank/do tank focused on [...] the market transformation of the world's air transport system towards a [...] sustainable long-term future}} * {{cite web |url= https://aviationbenefits.org/environmental-efficiency/climate-action |publisher= Air Transport Action Group |work= Aviation: Benefits Beyond Borders |title= Aviation industry reducing its environmental footprint}} * {{cite web |url= http://www.cleancluster.dk/NISA |title= Nordic Initiative for Sustainable Aviation |work= Clean Cluster |quote= Nordic association working to promote and develop a more sustainable aviation industry, with a specific focus on alternative sustainable fuels |access-date= 2015-03-27 |archive-date= 2015-04-02 |archive-url= https://web.archive.org/web/20150402212013/http://cleancluster.dk/NISA }} * {{cite web |url= https://rsb.org/ |title= Roundtable on Sustainable Biofuels |quote= The RSB is supporting the development of a sustainable bioeconomy}} * {{cite web |url= http://www.inderscience.com/jhome.php?jcode=ijsa |title= International Journal of Sustainable Aviation |publisher= Inderscience Publishers}} * {{cite web |url= https://ec.europa.eu/energy/topics/renewable-energy/biofuels/biofuels-aviation_en |title= Biofuels for aviation |date= 5 September 2023 |publisher= European Commission}} * {{cite news |url= https://www.flightglobal.com/flight-international-opinion/why-industry-needs-global-standards-for-sustainable-fuel-use/143384.article |title= Why industry needs global standards for sustainable fuel use |date= 22 April 2021 |author= Geoff Hunt |work= Flightglobal}}

{{subject bar|auto=y|d=y}} {{Authority control}}

Category:Algae fuel Category:Aviation and the environment Category:Aviation fuels Category:Biofuels