Synthetic Fuels: Can SAF Decarbonize Aviation?

Aviation accounts for approximately 2.5% of global CO₂ emissions — a number that understates its total climate impact, since contrail formation and high-altitude NOₓ emissions roughly triple the effective radiative forcing. Unlike road transport, aviation cannot currently be electrified at scale for long-haul routes: batteries carry too little energy per kilogram, and hydrogen requires either cryogenic storage or fuel cells that are far from commercial maturity for large aircraft. Sustainable Aviation Fuel is, at the moment, the only credible bridge between today's aviation and a net-zero future.

## What SAF Actually Is

Sustainable Aviation Fuel is a drop-in replacement for conventional Jet-A fuel — it can be blended with fossil jet fuel and used in existing engines and infrastructure without modification. Current certification standards allow blends up to 50% SAF, with 100% SAF approval still working through the certification process.

SAF is not a single fuel: it is a family of fuels produced through different feedstock and processing pathways, each with different economics, lifecycle emissions, and scalability constraints.

## Production Pathways: The Three Main Routes

**HEFA (Hydroprocessed Esters and Fatty Acids)** is the most commercially mature SAF pathway today. Vegetable oils, waste cooking oils, and animal fats are hydroprocessed — reacted with hydrogen at elevated temperature and pressure — to remove oxygen and produce hydrocarbon fuel chains nearly identical to conventional jet fuel. HEFA SAF can achieve lifecycle CO₂ reductions of 50–85% compared to fossil Jet-A, depending on the feedstock.

The constraint is feedstock: the global supply of waste cooking oil and non-food lipid feedstocks is limited. If HEFA is scaled to meet even a fraction of global aviation demand, it would require dedicating significant agricultural land to fuel crops — which undermines the lifecycle carbon benefits. HEFA is best understood as a near-term solution using genuinely waste-derived feedstocks, with inherent supply limits.

**Fischer-Tropsch (FT) synthesis** gasifies solid carbonaceous feedstocks — municipal solid waste, agricultural residues, forestry waste, coal — into syngas (CO + H₂), then catalytically converts the syngas into liquid hydrocarbons. The process was developed in Germany in the 1920s and was used industrially by South Africa during the apartheid era to produce synthetic fuels from coal.

FT from waste biomass can achieve high lifecycle CO₂ reductions. The challenge is capital intensity: FT plants are large, expensive, and complex. The minimum economic scale for an FT plant is substantial, making investment difficult without long-term offtake agreements and policy support.

**Power-to-Liquid (PtL)** — also called electrofuels or e-fuels — is the pathway with the highest potential and the furthest from cost competitiveness. PtL uses renewable electricity to electrolyse water into hydrogen and oxygen. The hydrogen is then reacted with CO₂ captured from the atmosphere (direct air capture, DAC) or from industrial point sources to produce syngas via the reverse water-gas shift reaction, followed by FT synthesis to produce jet fuel.

The lifecycle CO₂ emissions of PtL, when powered by truly renewable electricity and using atmospheric CO₂, approach net-zero. The fundamental problem is energy efficiency: converting electricity → hydrogen → syngas → liquid fuel involves multiple conversion losses, resulting in an overall energy efficiency of roughly 10–15%. That means producing 1 GJ of PtL jet fuel requires 7–10 GJ of renewable electricity input. At current renewable electricity costs, this translates to jet fuel prices of $4–8 per litre — versus $0.4–0.6 per litre for fossil Jet-A.

## Energy Density vs Hydrogen

A persistent misconception is that liquid hydrogen could simply replace Jet-A in existing aircraft. The energy density comparison is instructive: hydrogen has a gravimetric energy density of roughly 120 MJ/kg (three times Jet-A's 43 MJ/kg), but its volumetric energy density as liquid is only about 8.5 MJ/L versus Jet-A's 34 MJ/L. An aircraft storing the same energy in liquid hydrogen would require fuel tanks four times the volume. New aircraft designs with cryogenic tank integration are technically feasible — Airbus has prototype designs — but represent a complete reimagining of aircraft architecture. SAF requires no such redesign.

## CORSIA Mandates and the Policy Driver

The **Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)**, administered by the International Civil Aviation Organization (ICAO), is the primary international policy mechanism pushing SAF adoption. From 2027, international airlines must offset or reduce emissions above 2019 baseline levels. SAF use is one of the primary compliance mechanisms.

Individual nations are going further: the EU's ReFuelEU Aviation regulation mandates 2% SAF blending from 2025, rising to 6% by 2030 and 70% by 2050. The UK has a similar trajectory. These mandates are the critical demand signal that is beginning to unlock investment in SAF production infrastructure.

## Real-World Airline Adoption in 2026

**Lufthansa Group** has been among the most active SAF purchasers in Europe, running SAF-blended flights on high-frequency routes and offering customers the option to pay a surcharge for higher SAF content. The actual volumes consumed remain a fraction of total fuel use — less than 1% — reflecting supply constraints rather than demand hesitancy.

**Delta Air Lines** has signed long-term offtake agreements with multiple SAF producers, including deals with Gevo (an isobutanol-to-jet pathway) and with Neste (HEFA). Delta's strategy acknowledges that SAF at 2026 prices is materially more expensive than conventional jet fuel, making the economic case dependent on anticipated carbon pricing and regulatory mandates.

## The 2050 Net-Zero Gap

The math of getting aviation to net-zero by 2050 is sobering. Global aviation consumes roughly 300 million tonnes of jet fuel annually. Current global SAF production capacity is approximately 300,000 tonnes — less than 0.1% of demand. IRENA and IEA projections suggest that even with ambitious policy support and capital deployment, SAF could reach 10–15% of aviation fuel demand by 2035.

The remaining gap will require some combination of operational efficiency improvements (better routing, load factors), demand management, next-generation aircraft efficiency, and — for the hardest-to-abate long-haul segment — direct air capture and offsetting. SAF is essential but not, on its own, sufficient. The engineering is tractable. The economic and political mobilisation required is the harder problem.

Synthetic Fuels: Can SAF Decarbonize Aviation?

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