وقود الطيران المستدام (SAF): شرح وافٍ

What Is Sustainable Aviation Fuel?

Sustainable Aviation Fuel (SAF) is a catch-all term for aviation fuel produced from non-fossil feedstocks that generates significantly fewer lifecycle greenhouse gas emissions than conventional Jet A-1 fuel. The term "sustainable" is defined by certification standards rather than a single production method — multiple pathways qualify as SAF if they meet minimum lifecycle emissions reduction thresholds established by ICAO's CORSIA program (at least 10% reduction) or the EU's ReFuelEU Aviation mandate (65% reduction for blended fuels).

SAF is chemically near-identical to conventional jet fuel — it must be, because the same engines, fuel systems, and infrastructure handle both. This "drop-in" compatibility is SAF's most important characteristic: airlines can blend SAF into their existing supply chains without modifying aircraft, ground equipment, or fueling systems. Current certification standards allow blending up to 50% SAF with conventional Jet A-1, though fully synthetic neat SAF (100% SAF) is under active certification effort, with some early flights completed on 100% SAF in 2023.

Global SAF production reached approximately 600 million liters (roughly 500,000 tonnes) in 2023, representing less than 0.2% of the approximately 300 billion liters of conventional jet fuel consumed by the global aviation industry in the same year. This tiny fraction underlines the enormous scale challenge ahead: to meet IATA's industry target of 10% SAF by 2030, production must increase roughly 50-fold from 2023 levels in seven years.

How SAF Is Made

Multiple production pathways can produce SAF, each with distinct feedstocks, conversion chemistry, scalability, and lifecycle emissions profiles. The ASTM International D7566 standard, which governs SAF certification, currently approves eight pathways, with more under development.

HEFA Pathway (Used Cooking Oil)

Hydroprocessed Esters and Fatty Acids (HEFA) is currently the dominant commercial SAF production pathway, accounting for approximately 80–90% of all SAF produced globally. HEFA converts fats, oils, and greases — including used cooking oil (UCO), animal fats, and purpose-grown oilseed crops — into jet fuel through a process of hydrogenation and cracking that strips oxygen from fatty acid chains and restructures the carbon skeleton into kerosene-range hydrocarbons.

HEFA's lifecycle emissions reduction compared to Jet A-1 is typically 60–85% on a well-to-wake basis, depending on the feedstock and energy source used in processing. Used cooking oil, which would otherwise be landfilled or require energy-intensive disposal, achieves the highest reductions — sometimes claimed at over 90%. Purpose-grown crops like palm, soybean, or rapeseed perform much worse when land-use change emissions are included, and many SAF certification schemes exclude or heavily discount these feedstocks.

HEFA's critical limitation is feedstock scarcity. The global supply of waste fats and oils suitable for HEFA is finite — estimates suggest it could sustainably produce 30–40 million tonnes of SAF per year at most, against an industry that currently consumes 250 million tonnes of conventional fuel annually. Even if every drop of global used cooking oil went into SAF production, it would cover only 12–15% of aviation's fuel needs. Scaling HEFA further requires either purpose-grown crops (with serious land-use competition) or breakthrough alternative feedstocks.

Fischer-Tropsch Synthesis

Fischer-Tropsch (FT) synthesis converts a syngas feedstock — a mixture of carbon monoxide and hydrogen — into liquid hydrocarbons through a catalytic reaction developed commercially in Germany in the 1920s. For SAF purposes, the syngas can come from gasification of solid biomass (municipal solid waste, agricultural residues, woody biomass) or from renewable electricity-derived hydrogen combined with captured CO₂ (producing "e-fuels" — covered in the next section).

Biomass-to-liquid (BtL) FT SAF using agricultural waste or forestry residues achieves lifecycle emissions reductions of 90–95% compared to fossil Jet A-1. The feedstocks — wheat straw, corn stover, bagasse, wood chips, municipal solid waste — are abundant but geographically dispersed, require collection and pre-processing, and compete with other uses (soil amendment, animal feed, energy generation). World Energy in California and Fulcrum BioEnergy in Nevada have operated commercial FT SAF facilities using waste feedstocks since the early 2020s, but scaling remains challenging due to the capital intensity of FT plants (a commercial-scale facility costs $500 million to $1 billion).

Power-to-Liquid (e-fuels)

Power-to-Liquid (PtL) SAF, also called electrofuels or e-kerosene, uses renewable electricity to electrolyze water into hydrogen and oxygen, then combines the green hydrogen with CO₂ captured from the atmosphere or concentrated industrial sources via the FT or methanol synthesis route to produce synthetic kerosene. The resulting fuel is chemically identical to conventional jet fuel but, if produced using 100% renewable electricity and direct air capture of CO₂, achieves lifecycle emissions approaching zero or even net-negative.

PtL is the most promising long-term SAF pathway because it decouples production from biological feedstocks entirely — it requires only renewable electricity, water, and CO₂, all of which are in principle unlimited. The EU's ReFuelEU Aviation mandate specifically targets PtL e-fuels for 35% of aviation fuel by 2050. Companies including Norsk e-Fuel (Norway), HIF Global (Chile and Texas), and Synhelion (Switzerland, solar-powered) are building or operating pilot PtL facilities.

The challenge is cost and energy efficiency. Current PtL production costs are approximately $5–$8 per liter of jet fuel equivalent, versus $0.70–$0.90 for conventional Jet A-1. The conversion process from electricity to liquid fuel is only 45–55% efficient, meaning roughly half the renewable electricity input is lost as heat. At scale, with cheap renewable electricity ($20–$30/MWh from solar and wind), PtL costs could fall to $1.50–$2.50 per liter by 2035 — still 2–3× the cost of fossil jet fuel, requiring either a significant carbon price or mandate to close the gap.

How Much Does SAF Reduce Emissions?

SAF's emissions reduction depends critically on the feedstock and production pathway chosen. The most widely cited figure — "up to 80% reduction" — applies to the best-performing HEFA pathways. However, lifecycle analyses vary significantly in methodology, and the actual emission savings depend on what baseline is used, how land-use change is accounted for, and whether non-CO₂ effects (contrails, NOx) are included.

On a well-to-wake CO₂-only basis, typical SAF pathways achieve:

• HEFA (used cooking oil): 65–90% reduction
• HEFA (animal fats): 55–80% reduction
• FT (municipal solid waste): 80–95% reduction
• Alcohol-to-Jet (agricultural waste ethanol): 50–75% reduction
• PtL (100% renewable electricity + DAC): 85–100% reduction
• HEFA (purpose-grown soy, with land-use change): sometimes negative (worse than fossil)

A critical caveat: SAF does not eliminate the non-CO₂ warming effects of aviation. Contrail formation and NOx chemistry occur regardless of whether the fuel is fossil-derived or bio-based, though some research suggests SAF's lower aromatic content may reduce contrail ice crystal formation. The non-CO₂ effects account for roughly half of aviation's total climate forcing, meaning even 100% SAF adoption would still leave significant climate impact to address.

Airlines Leading SAF Adoption

SAF adoption varies enormously across airlines, driven by voluntary commitments, regulatory mandates, and fuel availability. As of 2024, no airline sources more than 2–3% of its fuel from SAF on an annual average basis, but several have made substantial commitments and investments in future supply.

United Airlines has been among the most aggressive SAF investors, committing to purchase 1.5 billion gallons (roughly 5.7 million tonnes) of SAF by 2026 through various off-take agreements. United signed a 15-year deal with Aemetis for 1 billion gallons of HEFA SAF and has invested in multiple SAF producers including Cemvita Factory (synthetic biology-based SAF). The airline claims SAF already accounts for 1–2% of its fuel on key routes, mostly blended at hub airports where SAF is available.

KLM Royal Dutch Airlines has operated regular SAF-blended flights since 2011 and launched its "Fly Responsibly" initiative to fund SAF development. The airline's 2030 target is 10% SAF across its entire fuel uplift, and it operates flights from Amsterdam (AMS) routinely blended at 0.5–1% SAF. KLM was also among the first airlines to offer passengers the option to co-fund SAF purchases on their ticket, though take-up has been modest.

Lufthansa Group — encompassing Lufthansa, SWISS, Austrian, Brussels Airlines, and Eurowings — has set a target of 10% SAF by 2030 and has signed off-take agreements with multiple producers. The group introduced a voluntary "Green Fares" tariff in 2023 that includes SAF and carbon offset surcharges, with a stated SAF blend contribution of approximately 20% for those fares. Scandinavian Airlines (SAS) has arguably the most ambitious relative target: 20% SAF by 2025 on its Scandinavian routes, though supply challenges have complicated delivery.

Challenges and Costs

The primary challenge for SAF is cost. Conventional Jet A-1 in most markets trades at $0.70–$0.95 per liter; SAF from HEFA pathways costs $1.50–$2.50 per liter (a 2–3× premium), while PtL SAF currently costs $5–$8 per liter. For an airline with fuel representing 25–35% of operating costs, switching to 10% SAF at a 2× price premium raises total fuel costs by roughly 10% — a significant competitive disadvantage unless competitors face the same mandates.

Feedstock competition is the second major challenge. Used cooking oil, currently the dominant HEFA feedstock, is already used for biodiesel production in road transport; increased aviation demand competes with that market, potentially bidding up UCO prices and displacing emissions reductions that would otherwise occur in road transport. The EU's RED III directive attempts to manage this by capping HEFA from food and feed crops and prioritizing "advanced" feedstocks for aviation.

Supply chain infrastructure requires development at airports. SAF is currently available in commercial quantities at fewer than 50 airports worldwide. Building blending facilities, adjusting fuel hydrant systems, and establishing supply agreements requires capital investment and regulatory certainty that many airports and fuel suppliers have been reluctant to commit to without clearer demand signals.

Regulatory Mandates Worldwide

Blending mandates are the primary policy mechanism for driving SAF demand. Without mandates or equivalent carbon pricing, most airlines have limited incentive to pay the SAF premium voluntarily. The European Union's ReFuelEU Aviation regulation, in force from 2025, requires jet fuel suppliers at EU airports to blend minimum SAF percentages: 2% in 2025, rising to 6% by 2030, 20% by 2035, 34% by 2040, 42% by 2045, and 70% by 2050. Within these totals, specific sub-targets require increasing shares of PtL e-fuels (0.7% by 2030, rising to 35% of total by 2050).

The United Kingdom has a Sustainable Aviation Fuel mandate requiring 2% SAF by 2025, rising to 10% by 2030 and 22% by 2040. The US Inflation Reduction Act (IRA) introduced blender tax credits for SAF of $1.25–$1.75 per gallon (roughly $0.33–$0.46 per liter) depending on lifecycle emissions reduction, significantly improving the economics of domestic SAF production and driving major investment in US HEFA and emerging pathway facilities. Singapore, Japan, South Korea, and India have announced voluntary or mandatory SAF targets in the 2–10% range by 2030.