Digital Feature: The evolving role of SAF in aviation’s energy transition
C. TAN, S. ROOSE, A. MARTIN and A. ALEXANDRE, Global Impact Coalition (GIC)
Decarbonizing flight will not happen overnight, but the journey for innovative pathways to create sustainable jet fuel has already taken off. The aviation sector is responsible for about 2.5% of global greenhouse gas (GHG) emissions and in the U.S., approximately 98% of aviation-related emissions result from jet fuel combustion.1,2 This highlights the critical role of fuel decarbonization strategies, with sustainable aviation fuel (SAF) being considered among the more feasible options available for reducing emissions from medium- to long-haul flights.3 Governments in the European Union (EU) and UK are pushing this transformation forward by setting mandates for the progressive use of aviation fuel originating from sustainable materials.4 For example, as of January 1, 2025, commercial flights taking off from EU airports must carry at least 2% of SAF in their tanks. By 2030, the mandate requires a minimum of 6% of SAF, including a 1.2% synthetic aviation fuel (eSAF) blend with conventional jet fuel.5 In addition, many airline members of the International Air Transport Association (IATA) have committed to a 10% reduction by 2030, aiming for net zero by 2050.6
The state of SAF. There are two primary categories of SAF: bio-SAF, derived from biomass and eSAF (also known as synthetic or power-to-liquid SAF), produced by combining green hydrogen (H₂) from water electrolysis with captured carbon dioxide (CO₂). These intermediates can be converted into hydrocarbons through several pathways, including Fischer–Tropsch synthesis, methanol-to-jet (MtJ) and alcohol-to-jet (AtJ) processes. Each route upgrades intermediates into jet-range hydrocarbons through a series of catalytic steps, which may include oligomerization, hydrogenation and hydroprocessing to meet jet fuel specifications.7,8 When produced from waste-based feedstocks, SAF can reduce lifecycle CO₂ emissions by up to 80%–90% compared to conventional jet fuel, depending on the production pathway.9
Today, SAF deployment faces investment barriers. Cost estimates indicate that SAF is 2─10 times more expensive than conventional jet fuel, depending on the feedstock and conversion technology used, largely due to high capital expenditure (CAPEX) for early-stage facilities, limited economies of scale and the expense of green H2 for eSAF pathways.10,11 While SAF is technically mature and scalable, achieving cost competitiveness will require coordinated investment, supportive policy and continued innovation across the value chain.12
Moreover, feedstock availability is limited. The Air Transport Action Group (ATAG) projects global SAF demand could reach 330 MM metric t (MMt)–450 MMt by 2050; however, production is only a fraction of this target.13 For example, Neste (an SAF producer) produces approximately 1.5 MMtpy,14 while Spanish energy company Moeve delivered 14,400 metric t of SAF in 2024 and aims to scale to 800,000 metric tpy by 2030 through a second-generation biofuels plant in Huelva, Spain.15 These figures underscore the scale-up challenge and the need for coordinated policy, investment and technology development to close the gap between capacity and future demand.
While there is a massive SAF market on the rise, the limited availability of waste-based feedstock makes it difficult to meet alternative fuel mandates with bio-based SAF alone. This opens the need for eSAF, made with green H2 and captured biogenic CO2, which is a byproduct of many industrial processes.
Different pathways and types of SAF. The production of SAF can follow many different, and often interconnected, routes. Each pathway has its own feedstocks, conversion processes and advantages, but together they highlight the opportunities and challenges of scaling SAF for global aviation.
Bio-SAF. Bio-based SAF is derived from renewable feedstocks such as used cooking oil, animal fats, forestry byproducts and organic waste. While these feedstocks support multiple conversion pathways, including hydro-processed esters and fatty acids (HEFA), AtJ and gasification-based routes, their global availability is limited. According to ICF (consulting firm) and International Civil Aviation Organization (ICAO) analyses, bio-based feedstocks will only be sufficient to supply approximately 50% of the SAF required by 2050 to meet the aviation sector’s net-zero targets.16 HEFA, the dominant commercial pathway, is projected to contribute less than 10% of total SAF volumes by 2050 due to feedstock constraints.17 Current bio-based SAF costs range from €1,600/t─€2,500/t, compared to approximately €700/t for fossil jet fuel.18 These structural limitations make it clear that bio-based SAF, while essential, must be complemented by synthetic alternatives such as power-to-liquid fuels to achieve net-zero targets.
eSAF. eSAF combines captured CO₂ with green H2 from renewable-powered electrolysis to produce synthetic hydrocarbons via two main routes: MtJ or Fischer-Tropsch synthesis. Unlike bio-SAF, it avoids agricultural feedstocks, reducing land use by 3–30 times and water use by up to 1,000 times, while achieving 85%–95% lifecycle GHG reductions.19,20 This advantage comes with high energy intensity, about 15 megawatt hour (MWh)–20 MWh of renewable electricity per metric t of fuel, making power availability the key scalability constraint.21 Today, costs are €4,000/t–€6,000/t, nearly 6–8 times the cost of fossil jet fuel and 2–3 times the cost of bio-SAF but could fall below €2,000 by 2050 with large-scale deployment and cheaper renewables.22 These characteristics position eSAF as a cornerstone for deep decarbonization, contingent on investments in renewable energy and CO₂ capture infrastructure.
Fischer-Tropsch vs. MtJ pathways. Fischer-Tropsch is an American Society of Testing and Materials (ASTM) approved pathway for SAF, certified for up to 50% blending and recertification. MtJ is not yet approved; it is under evaluation before inclusion in the ATSM standard specification.23,24 Both pathways can enable the production of drop-in SAF using renewable carbon sources.25 Fischer-Tropsch, a commercially mature process, converts synthetic gas (syngas) directly into liquid hydrocarbons, while MtJ first produces methanol, then converts it into light olefins such as ethylene and propylene using zeolite catalysts.
These olefins are oligomerized into longer hydrocarbon chains, which are equivalent to the intermediates from the Fischer-Tropsch process.26 Then these long chains undergo a hydrocracking process to a shorter-chain jet range (C9-C14), and finally these linear paraffins are isomerized to meet the aviation fuel cold properties. Both pathways are critical for scaling SAF beyond bio-feedstock limits.27
Within the MtJ route, a high potential pathway is methanol-to-olefins (MTO), which is particularly relevant for the production of eSAF from eMethanol. This distinction is critical because bio-methanol is generally not suitable for bio-SAF production due to sustainability, purity and economic constraints, making eMethanol the preferred feedstock for this pathway. Additionally, the MTO approach creates synergies with other sectors by enabling the production of sustainable olefins, which are also key intermediates for low-carbon chemicals and materials.
Future outlook for eSAF. SAF remains a critical element in aviation decarbonization strategies. Its production leverages MTO, providing a promising route to jet-range hydrocarbons while maintaining integration with chemical and energy value chains. The Global Impact Coalition (GIC) is actively working on several projects focused on MTO and sustainable methanol, adjacent to emerging technologies for SAF. These initiatives can help accelerate the transition toward a more sustainable and scalable SAF supply, leveraging synergies across energy and chemical sectors. Meeting the target of increasing SAF output to 17 MMt by 2030 will require diversification of pathways. eSAF represents a technically viable option to accelerate capacity expansion, leveraging sustainable synthetic feedstocks to reduce reliance on conventional fossil fuel.
LITERATURE CITED
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