DALLAS — The world's aviation sector is under increasing pressure to reduce its carbon footprint. Since air travel accounts for 2% to 3% of total CO2 emissions, air transport is now law- and market-mandated to switch to low-carbon fuels.

While hydrogen power and electrification hold long-term promise, neither technology is currently mature enough to propel long-range aircraft. Therefore, the fastest path is Sustainable Aviation Fuels (SAFs).

The two leading areas of debate in SAFs are biofuels, produced from renewable organic biomass feedstocks, and power-to-liquid (PtL) fuels, which are artificially created using captured carbon dioxide and renewable power.

Both provide significant emissions benefits, are drop-in compatible with existing engines and equipment, and are certified for use in aircraft. They are fundamentally different, however, in terms of cost, technology readiness, and scalability.

What Are Biofuels?

Bio-based SAFs are produced from biological materials, such as waste cooking oil, animal fat, and agricultural waste. HEFA (Hydroprocessed Esters and Fatty Acids) is the most developed process that converts oils and fats into hydrocarbons that are virtually identical to Jet A.

Other nascent pathways include:

• Alcohol-to-Jet (AtJ): Ethanol or isobutanol transformed into synthetic kerosene.
• Gasification + Fischer–Tropsch (FT): Biomass is gasified into syngas, which is then converted into liquid fuel.
• Advanced Generations: Utilizing algae or microbes to produce lipids that can be processed into jet fuel.

HEFA-based fuels have been ASTM-approved since 2011 and are now being used in commercial operations globally. Airlines have commercially operated over 450,000 SAF-fueled flights, nearly all on HEFA blends.

What Is PtL?

Power-to-Liquid (PtL) fuels, also known as synthetic e-fuels, are produced by combining green hydrogen (generated through electrolysis using renewable electricity) with captured CO₂. Through methods such as Fischer–Tropsch synthesis, this provides synthetic kerosene chemically identical to traditional jet fuel.

In contrast to biofuels, PtL is not based on biological feedstocks. Its principal inputs, renewable electricity and CO₂, are theoretically boundless. In theory, PtL could grow to supply global aviation needs without competing with food or agricultural land use.

However, the process is both expensive and energy-intensive. Present pilot plants produce small quantities at prices significantly higher than those of biofuels, not to mention fossil Jet A.

Emissions Reduction Potential

They both have high emissions reduction potential, but in different ways.

• Biofuels: Lifecycle CO₂ savings vary between 60–80% depending on the feedstock. Waste oils have the highest savings; crop-based feedstocks could have reduced savings because of fertilizer and land conversion effects.
• PtL: Provides 90–100% lifecycle savings, as burning releases only the CO₂ fixed during production. This depends on whether 100% of the energy for electrolysis and capture comes from renewable sources.

This renders PtL theoretically climate-neutral, whereas biofuels yield immediate, pragmatic reductions.

Costs, Scalability

Biofuels

• Cost: Currently 2–5 times costlier than Jet A.
• • Scalability: There's a limited supply of feedstock. Even if all available waste oils were used, they could only meet about 2-3% of aviation's fuel needs. 
• • Market Outlook: According to IDTechEx, SAF capacity – primarily based on HEFA – is expected to reach around 57 million tonnes per year by 2035, with HEFA dominating the market in the near future.

PtL

• Cost: Currently USD $8–10 per liter, which is many orders of magnitude above the cost of fossil kerosene.
• Scalability: Theoretically unlimited but limited by renewable electricity supply and CO₂ capture technology.
• Market Outlook: PtL deployment on a large scale is anticipated after 2030, as the cost of renewable energy and electrolyser decreases.

Infrastructure, Compatibility

Both fuels have the major benefit that they are drop-in fuels, with no need for modifications to current aircraft or airport fueling infrastructure.

• Biofuels: Already mixed up to 50% with Jet A to ASTM D7566. Compatible with existing refineries through co-processing.
• PtL: The same as Jet A at the molecular level and thus directly compatible. However, infrastructure for electrolysis and CO₂ capture has not been developed at scale yet.

Industry Example

Biofuels in Operation

In 2011, KLM flew the world's first commercial HEFA-powered flight using used cooking oil, paving the way for the uptake of bio-SAF. Multiple airlines, including United, Delta, and Singapore Airlines, have since entered multi-year offtake agreements with producers. 

Regulatory Drivers

• European Union: With a strong preference for advanced biofuels and synthetic fuels, the ReFuelEU mandate calls for 2% SAF blending by 2025, 1.2% by 2030, and 70% by 2050. 
• United States: With the help of tax incentives in the Inflation Reduction Act, the SAF Grand Challenge seeks to produce 3 billion gallons of SAF annually by 2030. 
• ICAO CORSIA: Biofuels and PtL are recognized as acceptable methods of reducing emissions on international flights.

These measures are propelling investment across both categories, albeit near-term supply is expected to be weighted towards biofuels.

Challenges in Deployment

Biofuels

• Feedstock Competition: Waste oils also serve the road transport and chemical industries.
• Land Use Pressure: Crop-based feedstocks pose a threat to deforestation and food price inflation.
• Supply Limits: Even with optimistic assumptions, biofuels cannot service long-term aviation demand alone.

PtL

• Energy Intensity: To produce one liter of PtL, significant quantities of renewable electricity are required. 
• Cost Barrier: Without subsidization, PtL is economically uncompetitive.
• Technology Scale: Electrolysis and carbon capture are not yet constructed to the scale of aviation demands.

Market Outlook: 2025–2035

IDTechEx predicts that production of SAFbiofuels and PtL together will reach over 57 million tonnes per year by 2035 at a CAGR of 8.5% from 2025.

• 2025–2030: SAF will be dominated by HEFA biofuels based on existing feedstocks and refinery compatibility.
• 2030–2035: PtL projects will expand, particularly in regions with high availability of renewable energy, such as Northern Europe, Chile, and Canada.
• After 2035: As the cost of renewable electricity decreases and carbon capture enhances, PtL may become the dominant SAF source. 

Conclusion

For aviation, the decarbonization problem is pressing and multifaceted. Biofuels provide short-term reductions, backed by mature supply chains and mandatory regulations. However, they have inherent limitations in the availability of feedstocks, so they serve as a bridging solution rather than a long-term solution.

PtL fuels represent a longer-term solution: carbon-neutral, scalable, and infrastructure-ready when renewable energy and CO₂ capture are at an industrial scale. Punitively expensive for now, the momentum picks up as demonstration projects show it can be done.

The SAF future will not be about either-or but about biofuels being today's solution on the ground and PtL tomorrow's scalable foundation. The effective management of that transition will determine whether flying can meet its net-zero by 2050 pledge while remaining safe and efficient enough to keep the world connected.