A Novel Approach To SAF Development May Offer A New Route To Net Zero

For sustainable aviation fuels (SAF) development, 2050 will arrive in the blink of an eye, and the ambition of achieving net zero aviation sector CO₂ emissions will depend on the availability of billions of gallons of affordable fuel. According to IATA, SAF production reached 1 million tonnes (1.3 billion liters) in 2024, double that produced in 2023, but significantly below the 1.5 million tonnes (1.9 billion liters) projected.

The race to produce enough fuel to meet both mandates and demand is one that, according to some in the industry, including IATA director general Willie Walsh, the industry is already losing. “SAF volumes are increasing, but disappointingly slowly. Governments are sending mixed signals ... and investors in new generation fuel producers seem to be waiting for guarantees of easy money before going full throttle,” Walsh said in December.

To date, the modus operandi of producing SAF is to use inexpensive and abundant feedstocks that require complex facilities with limited scale, driving up costs and making the end product largely unaffordable. However, in an industrial park in metropolitan Chicago, a partnership between technology firm GTI Energy and sustainable fuels developer Aether Fuels is looking to bridge the impasse using a novel method of SAF creation.

Sustainable fuels are primarily made by hydrotreating waste fats and oils, feedstocks where supply is limited and processes that do not account for the much more abundant availability of waste gases. Aether Fuels CEO Conor Madigan saw the opportunity in this void when, in 2022, his company partnered with GTI Energy to begin the scale-up of a three-phase production process.

“In the terms of chemistry, the flexibility [of the process] comes from its ability to convert CO, CO₂, hydrogen and light hydrocarbons,” Madigan told ATW. “Light hydrocarbons are most commonly methane, but also could be ethane, propane, butane—basically any other hydrocarbons that are in gas phase at room temperature—and convert all of those into the syngas that we need” to produce SAF.

Alongside these gaseous sources, biogas (methane and CO₂), gasified biomass from solid agricultural waste, and industrial off-gases from sources like chemical plants and refineries can be used.

“Almost any waste carbon streams you can possibly use are ones that can be efficiently integrated,” Madigan said. “I think of it as a Swiss Army knife technology.”

EARLY BEGINNINGS

In 2016, GTI Energy began early-stage development of a process to create gas-to-liquid (GTL) SAF. Supported by the US Department of Energy, the nonprofit organization created an integrated pilot line capable of producing 1.5 gal of sustainable fuel per day, which came online in 2021. But while R&D development at this level was well within GTI’s wheelhouse, scaling to commercialization required a partner.

“R&D is done typically in idealized conditions. You find exactly the process you want to do, you just provide the pure feeds for that process, and you don’t try to disturb the conditions too much,” Madigan said. “When you move into commercialization, you really focus on ‘how can I disturb every part of the process as much as possible so that I understand how robust it is?’ So, you introduce poisons, you look at the much higher and lower pressures, you look at what upsets it will cause.”

In the intervening years since the first iteration of what Aether now calls the Aurora process proved out, further R&D has been the name of the game, a time-intensive process—“typically, 18 to 24 months,” Madigan noted—that must consider iterative success and longer-term viability. “It’s sort of a natural part of the process that the catalyst you start with turns out not able to handle this, that, or the other disruption,” Madigan said. “And so, you identify that issue, you find the root cause, you reformulate to make it more robust. We’ve really focused primarily on rebuilding the process and reactor design in a progressive fashion to make it a robust process that has a durable process window and is manufacturable, so things aren’t going to break when it’s run in a commercial plant.”

During the first step in Aether’s three-phase SAF production process, gasified feedstock inputs are fed into an electric thermochemical reactor, which the company calls a Tri-Converter, to yield a syngas.

“To date, you needed to have separate reactors for all of these [different] components. You were not able to do all of these reactions in one reactor,” Aether senior director R&D Elie Fayad told ATW, noting that the electric converter also allows renewable electricity to be employed where available and bears a lower carbon footprint than gas-fired reactors, which generally take much longer to reach stable temperatures. “You need to have a very good temperature profile for your reactor, which for us is enabled by the fact that we have an electric reactor. So, we have the capability to control that profile.”

Phases two and three take the syngas produced by the Tri-Converter and run it through a Fischer-Tropsch (FT) synthesis process that converts carbon monoxide and hydrogen into liquid hydrocarbons, and then on to an upgrading process, which includes a recycle loop that directs unconverted reactants and any byproduct gases back to the syngas generation stage for reprocessing.

It is here that the process becomes more painstaking and delicate.

“The FT converter takes the syngas and starts building all of these carbon chains in a very neat and straight form, and if you let the reaction go, you will end up with a product that is more like a Vaseline, like a wax,” Fayad said. “So, what you need to do is bring that mixture into a reactor that breaks down the long chains to the desired range, which is the jet fuel range. Another part of the upgrading is that these straight chains tend to freeze at temperatures that are usually encountered at high altitude, and we do not want that in an airplane. You don’t want jet fuel to freeze. So, to improve that property, we put some branches on [the chains] during hydro-isomerization,” which is a step that improves the cold flow properties of fuels.

The next iteration of the Aurora process is expected to be online by the end of 2025, producing 1 barrel (42 gal) of SAF per day, though Madigan is hedging his bets to some degree: “Its unit capacity will be about 100 gallons per day.”

THE LONG VIEW

The caution being taken in measuring the expectations of what Aurora will ultimately be capable of producing is in line with Aether’s philosophy of sustainable growth. The challenges of getting this technology up to commercial scale are much more than what bears out in the lab.

“Good supply chain verification is key,” Aether director sustainable development Alyssa Norris told ATW. “It is really important that we are verifying the feedstock we’re looking at, whether that’s renewable natural gas, waste, industrial waste gases, agriculture waste, forestry waste—making sure that it’s aggregated and accessible and making sure that we have long-term offtake agreements.”

Transportation logistics also presents challenges, as getting input feedstock gases to the production facilities and the resulting SAF to where it can be processed will be a pivot point in commercial growth, something Norris is presently engaged with: “Most SAF producers—us included—produce neat SAF, so it still has to be blended before it can be used in the actual aircraft.”

AIRLINE PARTNERS

Madigan is eyeing 2028 for Aurora’s first commercial production outpost. Aether signed MoUs with JetBlue Airways (also a stakeholder) last September and Singapore Airlines in February with offtake agreements pending the successful establishment of that first outpost, which will be capable of producing 50 barrels, or more than 2,000 gal, per day. Despite growing concerns within industry about both the 2030 and 2050 benchmarks, the predominant mood at Aether is one of cautious optimism combined with pragmatism.

“There’s a misconception that perfection should always be the goal, and I take the approach that progress should be, especially for this industry,” Norris said, to which Madigan added, “2050 is a really important aspiration. We don’t advocate changing that date, but it will be very challenging to get to net zero in aviation by 2050. Right now, we make less than 1% of jet fuel as SAF and scaling this industry a hundred times over the next 25 years will be difficult, especially because the current technologies that we use are already running out of their feedstocks. If we get [robust guidance], I think that the will and the technology will be there to enable the industry to get to net zero—but can we get it by 2050? It really just depends on how crisp the policy is, because if that’s not there, it will definitely take longer.”