Defossilising European aviation requires millions of tonnes of sustainable aviation fuels – VTT solves bottlenecks in eSAF production

The current total consumption of aviation fuels in Europe is about 70 million tonnes (Mt) per year. Under the EU’s ReFuelEU Aviation regulation, the aviation sector must gradually increase the share of sustainable aviation fuel in jet fuel blends. Particular attention must be paid on eSAF production. By 2030, at least 6% (~4 Mt) of the aviation fuel blend must be renewable, and the share of synthetic eSAF must be 1.2% (~1 Mt).

Currently,  renewable aviation fuels are produced almost exclusively via the biomass-based HEFA route (hydroprocessed esters and fatty acids), with a production capacity of approximately 1 Mt/a. Synthetic eSAF is still in the testing and piloting stage. Considering the plants under construction, an estimated ~4 Mt EU target will be reached by 2030 according to EASA, but the production capacity will still be based almost entirely on HEFA. By 2050, the renewable share increases to 70%, with 35% synthetic e-fuels. This means that by mid-century, the EU aviation sector’s annual demand for eSAF exceeds 20 million tonnes.

Sustainable biobased aviation fuel such as HEFA-based SAF is already produced commercially, but large-scale use is limited by the availability of vegetable oil and waste animal fat feedstocks. Therefore, synthetic eSAF, produced from carbon dioxide and renewable hydrogen, will be essential for achieving high SAF blending ratios in the future. Today, eSAF is not yet produced at an industrial scale. Significant technological challenges and the associated high production costs (6–10 times those of fossil jet fuel) must be addressed before large-scale investments can proceed. 

In synthetic e-fuel production, carbon dioxide is combined with renewable hydrogen. Hydrocarbons are produced via routes such as the reverse water-gas shift followed by Fischer–Tropsch synthesis or methanol-to-jet pathways.

Using biogenic carbon dioxide is particularly important: Current EU regulations favour biogenic CO₂ over fossil CO₂ in fuel accounting, and it is obligatory for classifying the resulting fuel as eSAF. This has a direct positive impact on production economics by avoiding fossil carbon penalties and reducing regulatory costs.

The forest industry plays a key role in supplying biogenic CO₂ as a feedstock. In Finland, large-scale emitters (over 100 kt of CO₂ per year) are concentrated mainly in the forest industry and other bioenergy production. Annually, they emit about 30 million tonnes of biogenic carbon dioxide, which could be captured and converted into eSAF. Moreover, there are over 10 point sources in Finland that produce more than 1 million tons per year. No other European industrial sector offer such a concentrated, stable, and scalable source of biogenic carbon dioxide for eSAF production.

Figure 1 presents a simplified process scheme for converting CO2 into eSAF. Most renewable energy is needed for the water electrolysis to produce green hydrogen (120–170 TWh/a) and CO2 capture & purification (15–30 TWh/a). If all 30 million tonnes of CO2 captured annually were used to produce eSAF, output could reach around 7 Mt/a. Additionally, the process generates significant amount of heat (60–85 TWh/a). 

Figure 1, CO2 to eSAF estimates for mass and energy inputs and outputs.

For fossil CO₂ emitters, eSAF production is still technically possible using captured carbon dioxide. However, the fuels produced cannot be classified as eSAF (renewable fuels of non-biological origin, RFNBO) beyond 2035/2040, and they won’t benefit from the same regulatory incentives. This underlines the strategic importance of biogenic sources for early eSAF markets such as pulp mills in Nordic countries and, e.g., biogas and bioenergy production in other parts of Europe. 

The central barrier to eSAF deployment is the cost. Currently, synthetic eSAF costs approximately €5,000–8,000 per tonne, compared to around €800 per tonne for fossil jet fuel. Commercial SAF, such as HEFA, typically falls between these price levels, although generally closer to the price of fossil jet fuel, while also facing feedstock constraints.

Over 70% of eSAF production costs stem from green hydrogen production, including the cost of renewable electricity sourcing. Other significant cost components include:

• carbon dioxide capture, purification, and logistics
• production scale and plant utilisation rates
• integration and optimisation of process steps

Therefore, reducing hydrogen demand, improving process efficiency, scaling production, and optimising CO₂ sourcing are essential to lowering overall costs. 

Figure 2, An example pathway for reducing the eSAF production cost (€/tonne) 

VTT’s research projects aim at reducing eSAF production costs by up to 70% compared to today’s levels. Rather than focusing on a single process step, VTT addresses cost drivers across the entire value chain:

• development of electrolysis technologies to produce green hydrogen
• development and testing of carbon dioxide capture and utilisation (CCU) technologies
• experimental research on synthesis routes and catalyst development and testing
• analysis of CO₂ quality requirements for different fuel pathways
• process integration, optimisation, and techno‑economic analysis (TEA)
• piloting and validation together with industrial partners

These activities support investment decisions by reducing technical uncertainty and clarifying where the largest cost reductions can be achieved. 

Impurities are a key cost component in eSAF production. Industrial carbon dioxide, especially captured from biomass-based processes, can contain sulphur compounds and other trace impurities. This is problematic since many catalytic fuel synthesis processes are highly sensitive to sulphur and other contaminants.

Thus, impurities must be removed, increasing both capital and operating costs. In addition, impurity levels vary by source, and there is no universal purification solution. Acceptable impurity threshold values for different synthesis routes are still being defined, which slows down investment and standardisation.

VTT addresses this challenge by:

• analysing impurity profiles from different CO₂ sources
• experimentally testing catalyst tolerance and purification needs
• developing tailored cleaning and conditioning concepts
• linking impurity management directly to process design and cost optimisation

The aim is to identify fit‑for‑purpose solutions rather than over‑engineering purification systems. 

At VTT Bioruukki Pilot Centre, companies can test and optimise key steps of the eSAF production chain, including carbon dioxide capture and purification, green hydrogen production, synthesis, intermediate upgrading and process integration. The advantage of VTT’s offering lies in systematic testing, modelling-based optimisation, and validation of integrated process concepts in collaboration with industry.

VTT’s research infrastructure supports multiple pathways to renewable aviation fuels. In addition to laboratory-scale equipment and analytical capabilities, VTT enables different process units to be integrated and the entire production chain to be tested at pre-industrial scale. Figure 3 illustrates an example configuration of a modular pilot plant that can be reconfigured to match the selected production pathway.

One example of an aviation fuel production route is the combination of reverse water-gas shift (RWGS) and Fischer–Tropsch (FT) synthesis. The RWGS and FT synthesis unit can be deployed in different environments and tailored to the objectives of each test campaign. The plant in figure 3 was successfully delivered from VTT Bioruukki to Germany, Höchsts industrial zone, where aviation fuel components were produced from carbon dioxide emissions from a biomethane plant. 

Figure 3, VTT Bioruukki’s modular pilot plant, including a gas compression container and a hydrocarbon synthesis container, among others. The gas compression unit can be adapted to different gas compositions as required. The hydrocarbon synthesis container can be equipped with key process units for CO₂ utilisation, such as a reverse water-gas shift (RWGS) reactor and a hydrocarbon synthesis reactor (e.g. Fischer–Tropsch, methanol synthesis, or methanation).

Whether the route is based on Fischer–Tropsch synthesis or methanol-to-jet, downstream upgrading steps are practically always required. VTT Bioruukki has the equipment and expertise needed to test a range of upgrading processes. The reactor system shown in Figure 4 can be used, for example, for hydrocracking, hydroisomerisation, and hydrotreatment, which are essential post-treatment processes for several aviation fuel production pathways. 

Figure 4, Aviation fuel intermediate post-treatment reactor system at VTT Bioruukki.

Hydrogen production, CO₂ utilisation, and synthesis steps can be studied together as an integrated process to balance electricity demand and improve overall efficiency before scaling up. 

Large-scale eSAF production requires major investments in electricity and hydrogen infrastructure, carbon dioxide capture systems, and fuel synthesis facilities.

VTT supports companies and investors by reducing technical and economic risk, providing data-backed analyses, and supporting technology choices from early pilots to near-commercial designs. VTT works with energy companies, oil refiners and fuel producers, technology providers, start-ups, forest industry actors, the aviation sector, and investors to develop viable eSAF value chains.

Synthetic aviation fuels are crucial to defossilising aviation, but large-scale deployment will require costs, quality requirements, and integration challenges to be addressed together.