What to consider when embarking on an eSAF project
Pete Cairns
Senior Licensing Manager
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Topsoe
Choosing the right technology is essential for unlocking value and decreasing the cost of production in the energy-intensive world of electrofuel production, writes Topsoe’s Pete Cairns.
As the aviation sector seeks to decarbonize, interest in power-to-liquid sustainable aviation fuels – or eSAFs – is rapidly gaining momentum. With regulatory pressure increasing and the promise of high greenhouse gas savings, many industry players are exploring how best to initiate an eSAF project. But while the technology is ready, other forces are not: policy uncertainty, offtake commitments, feedstock availability and project costs continue to hold back scale-up. For any project team considering this complex space, the question is no longer if eSAF can be made, but how best to make it economically viable. That begins with choosing the right production method.
Key project drivers: technology, policy and profitability
There are three pillars to consider when assessing eSAF projects: the technology platform, the policy environment in your region, and how you intend to improve financial returns.
From a regulatory perspective, projects are navigating evolving certification rules, lifecycle greenhouse gas (GHG) accounting methods and uneven policy support across jurisdictions. The right time-to-market can significantly affect your exposure to carbon price incentives and funding schemes.
Then there’s offtake. Investors will not back a project without clear product demand. Your choice of technology can influence your offtake success – by determining the fuel mix, emissions profile and operational reliability. Above all, the project must focus on maximizing yield, minimizing energy use and translating as much of your electricity and hydrogen input into certified kerosene as possible.
Why energy efficiency is non-negotiable
At the heart of every eSAF project is a basic truth: you are working against the laws of thermodynamics. Producing liquid hydrocarbons from electricity and carbon dioxide is, by nature, energy intensive. This is especially true for reverse combustion pathways, where energy is consumed to recreate fuels that were originally burned.
Because of this, energy efficiency isn’t just a technical metric – it’s an economic imperative. Hydrogen, produced via electrolysis, represents over half of the total cost of eSAF production[1]. Minimizing hydrogen and electricity consumption across the entire process chain can significantly reduce the cost per tonne of fuel. For any project, the question becomes: how do we get the most certified kerosene out of every electron and every kilogram of hydrogen?
Comparing the three core technology routes
While multiple technologies are under development, three primary pathways are frontrunners:
Fischer-Tropsch with Combustion RWGS (Reverse Water-Gas Shift)
Fischer-Tropsch with eREACT™ (electrified RWGS)
Methanol-to-Jet (MtJ), including methanol synthesis followed by olefin oligomerization
The three dominant e-SAF technology pathways.
All three aim to convert CO₂ and hydrogen into synthetic hydrocarbons. Fischer-Tropsch (FT) processes first create syngas, a mixture of CO and H₂, which is then converted into hydrocarbons. In the FT-Combustion pathway a traditional tubular reformer or autothermal reformer is required to convert H₂ and CO₂ to synthesis gas (CO + H₂) for the Fischer-Tropsch reaction. The heat of reaction must be supplied through combustion of methane (converted from CO₂ and H₂) or by burning pure H₂ (directly or indirectly) – a high energy and cost penalty solution. By contrast, eREACT™ replaces combustion with electric heating, improving hydrogen and electricity efficiency.
MtJ seems deceptively simple, involving direct methanol synthesis from CO₂ and H₂, followed by conversion into jet-range hydrocarbons. However, this route introduces its own complexities, particularly with carbon losses during the methanol-to-olefins (MTO) step, which directly translates to lost hydrogen.
Hydrogen and electricity – the economic heartbeat
The economic success of any eSAF pathway hinges on how efficiently it uses hydrogen and electricity. In the FT-Combustion route, a significant amount of hydrogen is sacrificed to drive the RWGS reaction through combustion, releasing heat but converting hydrogen into water rather than fuel. This makes it the least hydrogen-efficient option, and thus the most expensive in an environment where hydrogen accounts for over 55% of total production cost.
Both FT with eREACT™ and MtJ offer clear improvements in this regard. FT with eREACT™, which uses electrically heated reactors, avoids hydrogen combustion entirely. MtJ appears slightly less efficient than eREACT™ due to carbon deposition losses during the methanol upgrading step, but the two are broadly comparable in once-through analysis. Yet once you look beyond total liquid output and focus specifically on jet fuel yields, critical differences begin to emerge.
Unlocking efficiency with recycle and integration
One of the major advantages of FT with eREACT™ lies in its flexibility to recycle unused hydrocarbons. In a once-through system, lighter products such as naphtha are typically removed and sold separately – reducing overall kerosene yield and potentially complicating offtake strategies. With the G2L™ e-fuels approach - a fully integrated process where the Topsoe technologies are fully integrated with Sasol LTFT® technology - these light ends can be redirected into the front of the process, converted again alongside fresh CO₂ and hydrogen.
By recycling light ends and naphtha, with the G2L™ e-fuels solution, you can maximize SAF yield and reduce overall hydrogen and electricity demand.
This recycling loop not only increases kerosene yield to 100% of product output, while maintaining a higher than 95% CO₂ efficiency but also significantly reduces hydrogen and electricity demand. By eliminating the need to produce non-target products, the system becomes highly selective – and far more efficient. Compared to once-through production, naphtha recycling alone cuts electricity use by around 15%, all while maintaining the same level of certified SAF output.
The case for Fischer-Tropsch with eREACT™
Fischer-Tropsch with eREACT™ becomes even more compelling when deeper system integration is introduced. One key innovation is the use of high-temperature steam – naturally produced by the exothermic FT process – to integrate with a Solid Oxide Electrolyzer Cell (SOEC) plant for hydrogen generation. This creates a tightly integrated loop, where process waste heat is repurposed to lower the electricity required for electrolysis.
Using the steam generated from Fischer-Tropsch in SOEC to generate hydrogen is a further integration benefit with regard to electricity.
The result is striking: electricity demand drops by as much as 33% compared to conventional alkaline electrolysis systems. When combined with naphtha recycle, the FT with eREACT™ system achieves over 95% carbon efficiency, 97% hydrogen efficiency and delivers 100% of its output as ASTM-certified kerosene. These figures are not theoretical – they represent a practical, highly integrated approach that aligns technical performance with economic viability.
Summary comparison and takeaway
When comparing the three major technology routes, FT with combustion RWGS stands out as the least favorable due to high hydrogen wastage. Methanol-to-Jet and FT with eREACT™ appear similar on a once-through basis, but when optimized for 100% SAF production through recycling and heat integration, FT with eREACT™ pulls clearly ahead. It reduces capital burden on electrolyzers, lowers electricity and hydrogen usage and maximizes kerosene yield – simplifying offtake and improving return on investment.
For today’s eSAF projects, the most cost-effective and efficient route is a fully integrated G2l™ eFuels solution including Fischer-Tropsch system with eREACT™, naphtha recycle and SOEC-based hydrogen production. It not only addresses the thermodynamic and economic challenges of reverse combustion but sets a benchmark for how thoughtful technology choice can unlock real project value.
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