Sustainable Aviation Fuels (SAF)

Sustainable aviation fuels are liquid aviation fuels produced from biomass, waste, or using renewable electricity and CO₂. SAFs have the potential to replace fossil kerosene.

SAFs can be classified according to their production pathway, as they each have different chemical properties. There are basically two groups: biogenic SAFs, which are based on renewable feedstock (e.g., sugar, starch, vegetable oils, and wood residues), and synthetic SAFs, in which kerosene is produced from hydrogen, CO₂, and electricity. All currently approved SAFs are so-called drop-in fuels – this means that they are compatible with existing aircraft and refueling infrastructure and, depending on their approval, can be used directly without technical modifications (in specified Blending i ratios).

• HEFA i -SPK i : The most widely used SAF production process currently is based on esters and fatty acids derived from biogenic sources such as animal fats, vegetable oils, and used cooking oils.
  
• AtJ-SPK: This process produces aviation fuels from alcohols obtained, for example, through the fermentation of biogenic feedstock or cellulose-containing residual biomass.

• FT-SPK i : In this process, synthetic kerosene – known as E-kerosene i – is produced via Fischer-Tropsch synthesis i from CO₂, green hydrogen, and renewable electricity (power-to-liquid, PtL i ). The CO₂ can come from biogenic or industrial sources
  
  
• MtJ i : The methanol-to-jet process uses methanol as a starting material, which is obtained from CO₂ and green hydrogen.

The sustainability of individual SAF types depends on their production pathways. The feedstock used in these pathways determine the environmental impact, economic efficiency, and technical performance of the respective SAF type.

While the combustion of fossil Kerosene i causes high CO₂ emissions, SAFs based on green electricity and CO₂ – in particular PtL i fuels produced via Fischer-Tropsch synthesis i (FT) – have the lowest CO₂ footprint. Such fuels can reduce emissions by up to 95% compared to fossil kerosene, as the CO₂ emitted has been previously captured.

In addition to the greenhouse gas balance, land use, water requirements, and feedstock availability also play a significant role in ecological evaluation. Biogenic processes, for example, have a significantly higher water footprint due to water-intensive agriculture, but are comparatively sustainable when using waste products such as used cooking oil.

The production costs for SAFs are significantly higher than for fossil Kerosene i . Production costs vary greatly between technologies, depending on the market maturity of the technologies and the availability of suitable feedstock. For example, the HEFA i process has the lowest production costs, while synthetic PtL i SAF currently costs around €7,700 per tonne – about ten times the price of fossil kerosene.

Regardless of ecological or economic aspects, all aviation fuel must be technically safe and reliable. This is ensured by international certification procedures such as ASTM i approval, which guarantees that SAFs meet the necessary requirements in terms of energy density, aromatic content, low-temperature behavior, and combustion characteristics.

SAFs usually have a lower content of Aromatics i , which reduces the formation of soot and Contrails i – an advantage in terms of climate-impacting non-CO₂ effects. At the same time, this can cause technical challenges for seals in engines. For this reason, SAFs are currently only approved for use in commercial aviation up to a content of 50% by volume.

In order for SAFs to be used in commercial aviation, they must meet two key regulatory requirements: they must be both technically and chemically safe. Technical suitability is tested according to ASTM i standards, while chemical safety and environmental compatibility must be demonstrated in accordance with the EU REACH i regulation.

• ASTM i certification (D7566/D1655): Only fuels approved in accordance with ASTM D7566 or D1655 are internationally recognized and may be used worldwide in compliance with the specifications. The prerequisite is that the SAF – after Blending i with fossil kerosene – meets all specifications for Jet A or Jet A-1. This ensures technical compatibility with existing infrastructure, including engines, flight systems, fuel tanks, and logistics. Currently approved fuels include HEFA i -SPK i , FT-SPK, AtJ-SPK, and their aromatic variants. The maximum blending ratio for these processes is currently 50%.
  
• REACH i registration: Every chemical substance must be registered in the EU in accordance with the REACH Regulation. The responsibility for this lies with the manufacturer or importer. Extensive information on substance identity, physical-chemical properties, toxicology, and potential environmental impacts must be submitted for registration. This usually requires complex studies, which represents a high barrier to entry, especially for new market players.

A reliable and sufficient supply of SAF is crucial for effectively reducing emissions in aviation

To increase demand for SAF, the European Union has introduced a mandates for sustainable aviation fuels of 2% since 2025, which will gradually increase to 70% in 2050. This means that aviation fuel suppliers will have to replace a growing proportion of the Kerosene i they supply with sustainable alternatives. In addition, a minimum quota for synthetic SAF (e-SAF) will be introduced from 2030. This will start at 1.2% and rise to 35% by 2050.

In order to meet the targets for 2030, around 3.1 million tonnes of SAF will be needed within the EU – including 620,000 tonnes of synthetic fuel. This contrasts with global SAF production of currently around 2.6 million tonnes (as of 2024). Forecasts predict that annual production volume will rise to around 35 million tonnes by 2030.

Based on the facilities currently planned and already under construction, it seems realistic that the EU SAF quota for 2025 and 2030 will be met. However, the e-SAF sub-quota is not guaranteed: achieving it depends largely on several large-scale projects that are still in the early planning stages or are dependent on pending investment and funding decisions.

In 2023, Air France-KLM, the DHL Group, and IAG were among the largest consumers in Europe, with SAF consumption ranging between 50,000 and 90,000 tonnes. However, SAF accounted for only 0.65–3.27% of these airlines' total kerosene consumption.

While there is still little willingness to pay for SAF in the passenger sector, demand is higher in the B2B segment, especially in air freight. Companies are increasingly using SAF to reduce their indirect greenhouse gas emissions (Scope 3) in the supply chain.