Aviation biofuel

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: blending and co-processing. ASTM has found it safe to blend in 50% SPK into regular jet fuels. Tests have been done with blending synthetic paraffinic kerosene (SPK) in considerably higher concentrations.

HEFA-SPK

Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosine (HEFA-SPK) is a specific type of hydrotreated vegetable oil fuel. As of 2020 this was the only mature technology (but by 2024 FT-SPK was commercialized as well). HEFA-SPK was approved by Altair Engineering for use in 2011. HEFA-SPK is produced by the deoxygenation and hydroprocessing of the feedstock fatty acids of vegetable oils such as jatropha, and camelina, algae, or animal fats such as tallow.

The Diamond Green Diesel facility in Port Arthur, Texas, operated by Valero Energy, began producing SAF in late 2024, using the HEFA-SPK process.

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).

ATJ-SPK

The alcohol-to-jet (ATJ) pathway takes alcohols such as ethanol or butanol and de-oxygenates and processes them into jet fuels. Companies such as LanzaTech have created ATJ-SPK from CO₂ in flue gases. 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. Gevo developed technology to retrofit existing ethanol plants to produce isobutanol. Alcohol-to-Jet Synthetic Paraffinic Kerosene (ATJ-SPK) is a proven pathway to deliver bio-based, low-carbon fuel.

Certified processes

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.

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.

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 (syngas), subsequently converted to jet fuel via Fischer-Tropsch or similar gas-to-liquid processes.

Piston engines

Small piston engines can be modified to burn ethanol. Swift Fuel, a biofuel alternative to avgas, was approved as a test fuel by ASTM International in December 2009.

Technical challenges

A number of technical challenges and additional requirements exist for manufacturing, distribution, and use of SAF.

Aromatics and cycloalkanes

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. Synthetic rubber substitutes that are not adversely affected by biofuels, such as Viton, for seals and hoses are available.

As of May 2025 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.

Anti-Oxidant

ASTM D7566 mandates addition of anti-oxidant additives for SAF derived via certain pathways such as HEFA.

Low Temperature Viscosity

Due to the higher viscosity of some types of SPK, ASTM D7566 includes an additional kinematic viscosity limit of 12mm²/s at -40°C for certification of SAF.

Microbiological Growth

The United States Air Force found harmful bacteria and fungi in their biofueled aircraft, and used pasteurization to disinfect them.

Economics

Economic viability has historically been a major barrier to SAF adoption. 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.

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. 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. As of 2024, SAF represents just 0.3% of global aviation fuel.

As of 2020 aviation biofuel was more expensive than fossil jet kerosene, considering aviation taxation and subsidies at that time.

As of a 2021 analysis, VFA-SAF break-even cost was $2.50/US gal ($0.66/L). 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.

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).

Market implementation

Based on Renewable Identification Number volumes reported to the U.S. Environmental Protection Agency, the United States Department of Energy estimated U.S. sustainable aviation fuel consumption at 1.9 million US gallons in 2016 and 111.86 million US gallons in 2024.

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. Virgin Atlantic was working to regularly use fuel derived from the waste gases of steel mills, with LanzaTech. British Airways wanted to convert household waste into jet fuel with Velocys. United Airlines committed to 900 million US gal (3,400,000 m³) of sustainable aviation fuel for 10 years from Fulcrum BioEnergy (of its 4.1 billion US gal (16,000,000 m³) fuel consumption in 2018), after a $30 million investment in 2015.

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. At its sites in Singapore, Rotterdam and Porvoo, Finland's Neste expected to improve its renewable fuel production capacity from 2.7 to 3.0 million t (6.0 to 6.6 billion lb) a year by 2020, and to increase its Singapore capacity by 1.3 million t (2.9 billion lb) to reach 4.5 million t (9.9 billion lb) in 2022 by investing €1.4 billion ($1.6 billion).

By 2020, International Airlines Group had invested $400 million to convert waste into sustainable aviation fuel with Velocys.

United Airlines has expanded SAF use across multiple airports worldwide, including Amsterdam in 2022, San Francisco and London in 2023, and Chicago O'Hare and Los Angeles in 2024.

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. Southwest Airlines began using sustainable jet fuel at Chicago Midway International Airport in October 2024.

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.

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.

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. In 2023, SAFs account for less than 0.1% of all aviation fuels consumed. 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.

Sustainability Certification

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.

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. This marginally improves SAF's economic competitiveness versus fossil-based fuel.

The first reputable body to launch a sustainable biofuel certification system was the European-based Roundtable on Sustainable Biomaterials (RSB) NGO. Leading airlines and other signatories to the Sustainable Aviation Fuel Users Group (SAFUG) pledged to support RSB as their preferred certification provider.

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. 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.

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 that only fuels certified as sustainable by the RSB or similar body would be zero-rated. 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.

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, or the Renewable Jet Fuels initiative. The latter works with companies such as LanzaTech, SG Biofuels, AltAir, Solazyme, and Sapphire.

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.

Environmental impact

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. 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).

Jatropha oil, a non-food oil used as a biofuel, lowers CO₂ emissions by 50–80% compared to Jet-A1, a kerosene-based fuel. Jatropha, used for biodiesel, can thrive on marginal land where most plants produce low yields. 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.

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. 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. Neste's sustainable aviation fuel is used by Lufthansa; Air France and KLM announced 2030 SAF targets in 2022 including multi-year purchase contracts totaling over 2.4 million tonnes of SAF from Neste, TotalEnergies, and DG Fuels.

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. This lessens the need to grow crops specifically for fuel, which in itself is energy intensive and increases 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. 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%. Biofuels do not contain sulfur compounds and thus do not emit sulfur dioxide. 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. There are other forms of biofuel production that may not have the same emissions.

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. 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. By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, Isochrysis, was under research as a possible jet biofuel feedstock.