// Technology
eSAF is synthetic kerosene made from renewable electricity, water, and captured CO₂. Several proven industrial processes are combined into one production chain. The result is a fuel that is chemically equivalent to fossil jet fuel, works on existing aircraft and engines, and produces a fraction of the lifecycle emissions.
Click any step in the process below to read what happens at that stage.
Feed water must be treated to the purity required by the electrolyser. Contaminants that would degrade electrolyser membranes or catalysts are removed before the water enters the process.
Renewable electricity splits purified water into hydrogen and oxygen. This is the most energy-intensive step in the chain and the primary determinant of production cost. Both alkaline and PEM electrolysers are commercially deployed at gigawatt scale globally.
Carbon dioxide is sourced from industrial point sources, biogenic processes such as fermentation or biomass combustion, or directly from the air. The raw CO₂ must be purified, compressed, and stored before it enters synthesis. The carbon source has a direct effect on the final fuel's lifecycle emissions: biogenic and air-captured CO₂ yield the lowest carbon intensity.
Hydrogen and CO₂ react over a catalyst to produce e-methanol. This is one of the most mature processes in the chain, with over 40 commercial methanol plants operating worldwide and the first commercial CO₂-to-methanol plant running since 2012.
Methanol is dehydrated to dimethyl ether and then converted to a distribution of light olefins (C3-C6). Water is produced as a byproduct and must be removed before the next stage.
The light olefins are combined over a catalyst into longer-chain hydrocarbons in the jet fuel range.
The hydrocarbon stream is hydrogenated and refined to meet the ASTM D7566 jet fuel specification, producing synthetic paraffinic kerosene (SPK).
The finished SPK is blended with conventional Jet A-1 at up to 50% under current ASTM specifications and tested to confirm the blend meets all fuel quality requirements. Pathways for 100% drop-in eSAF are under active development.
// Production process
Producing eSAF via the methanol-to-jet pathway (MtJ), which makes kerosene by way of methanol, requires a series of distinct industrial processes, each commercially proven in its own right. What makes a commercial eSAF facility challenging is not any single step, but integrating them into one continuous production chain and operating that chain reliably at scale.
The chain begins with purified water and renewable electricity. Electrolysis splits the water into hydrogen and oxygen; it is the most energy-intensive step and the primary determinant of production cost. The hydrogen is combined with captured CO₂ to synthesise e-methanol, one of the most mature processes in the chain. The methanol is then converted to light olefins, the olefins are joined into longer jet-range hydrocarbons, and that stream is hydroprocessed into synthetic paraffinic kerosene meeting the ASTM D7566 specification.1 Finally the kerosene is blended with conventional Jet A-1, at up to 50% under current specifications, and tested for quality. The diagram above breaks the chain into its individual steps.
The process also yields co-products: naphtha, green diesel, light hydrocarbons, and aromatics. SAF yield exceeds 70% on a carbon basis, with the balance distributed across these co-products.2
The alternative to the methanol route is Fischer-Tropsch synthesis (FT-SPK), the older route that builds liquid hydrocarbons directly from synthesis gas, where hydrogen and CO₂ are converted to syngas and then directly to liquid hydrocarbons, bypassing the methanol and olefin stages. FT-SPK is ASTM-certified and operational at demonstration scale, including Haru Oni in Chile (approximately 100 t/yr) and ERA ONE in Germany (2,500 t/yr).3 The MtJ pathway was recently approved under ASTM D7566, making it a certified route to jet fuel alongside FT-SPK.4 MtJ is the pathway used by the Iceland eSAF Project.
// History
Almost nothing about eSAF is new chemistry. What is new is the electricity.
Fischer-Tropsch synthesis, one of the two routes to synthetic kerosene, was invented in the 1920s and ran at national scale for decades to turn coal and gas into liquid fuel. Methanol synthesis, the first step of the route this project uses, is a century-old industrial process running today in more than forty commercial plants worldwide.3 Converting methanol to hydrocarbons, joining short molecules into jet-range chains, refining them to specification: each is a standard refinery or petrochemical operation with a long operating record. Aviation has burned synthetic kerosene made this way, and certified it, for years.1
What has changed is the front of the chain. Historically the hydrogen and the carbon came from fossil sources, which is why synthetic fuel was never clean. eSAF keeps the proven chemistry and swaps the inputs: renewable electricity and water in place of coal or gas for the hydrogen, captured CO₂ in place of fossil carbon. The result is the same fuel the chemistry has always produced, made from inputs that make it count as renewable.
This is why the engineering risk in eSAF is not invention. It is integration: operating these long-proven steps as one continuous chain, at commercial throughput, on renewable power. The section below sets out exactly how mature each step is, and where the real frontier lies.8
// Technology readiness
Each stage of eSAF production is individually proven at commercial or near-commercial scale. The integration challenge, operating all stages in a continuous chain at the throughput required for commercial production, is where the industry is now focused.89 Technology Readiness Level (TRL) is a 1 to 9 scale for how proven a technology is: levels 5 to 6 cover pilot and demonstration scale, 7 a full pre-commercial system, and 8 to 9 a technology already proven in commercial operation.
// Readiness by process step, hover a step for detail
// Reduction logic
The lifecycle carbon reduction achieved by an eSAF facility depends on three factors:
Hydrogen production is the largest energy input. Electricity from fully renewable sources (hydro, wind, solar, geothermal) yields the lowest carbon intensity. Grids with high fossil shares produce hydrogen with higher embedded emissions, reducing the lifecycle benefit.
Biogenic CO₂ and CO₂ captured directly from the atmosphere are counted as carbon-neutral at combustion. CO₂ captured from fossil industrial sources carries a higher lifecycle penalty.
How heat is recovered, how unreacted gases are recycled, and how the synthesis chain is optimised all affect the energy used per tonne of fuel produced.
Published lifecycle figures for eSAF place the technology at approximately 70-95% reduction versus fossil kerosene, with individual projects varying meaningfully depending on the inputs above. The EU RED III framework requires a minimum 70% lifecycle reduction for a fuel to qualify as an RFNBO.5 Producers on fully renewable grids using biogenic or atmospheric CO₂ achieve the highest reductions. Every eSAF project should publish its specific figure, verified under EU RED III or ICAO CORSIA methodology.67
// Standards
Aviation fuel is among the most tightly regulated products in the world. A synthetic fuel cannot reach an aircraft until it has passed strict safety and quality testing, and its emissions reductions have been independently verified and monitored against published methodology. The frameworks below are the gates an eSAF facility must clear, covering both fuel performance and lifecycle carbon.
ASTM D7566: The international jet fuel specification that synthetic aviation fuels must meet to be approved for use in commercial aircraft.1
RED III (Renewable Energy Directive III): Defines the criteria under which a fuel qualifies as a Renewable Fuel of Non-Biological Origin (RFNBO) in the EU. Producers on grids exceeding 90% renewable electricity are exempt from the additionality, temporal correlation, and geographic correlation requirements (the rules that otherwise require the electricity to come from new, time-matched, and locally-sited renewable generation) under Article 4(1) of Delegated Regulation 2023/1184.512
ReFuelEU Aviation (EU 2023/2405): Sets binding SAF and synthetic sub-mandate targets at EU and EEA airports, rising from 2% in 2025 to 70% by 2050.13
ICAO CORSIA: The international framework under which eligible SAF, including eSAF, can be used to reduce international aviation offset obligations.7
ISCC EU and ISCC CORSIA: Voluntary sustainability certification schemes recognised under both EU and ICAO frameworks.14
For project-specific certifications, see For Airlines.
