Often made using biological material, including waste and animal fats, SAF production can be held back by limited feedstocks and processing issues. Some firms are developing so-called Power-to-Liquid (PtL) fuels instead, converting carbon dioxide (CO2) and hydrogen into usable fuel.
That process generally involves first converting CO2 to carbon monoxide (CO). But a new demonstration plant, opened this week by Oxford University spin-out OXCCU, reduces the multi-step technique to a single step. That change could cut the cost of PtL SAF, the company claimed – currently a barrier to widescale adoption.
The demonstration plant, opened at Oxford Airport on Monday (12 August), will produce fuel from September. Although it will only make 1kg (1.2 litres) of fuel per day, OXCCU already has plans for a 160kg (200 litres) per day plant, which will operate at Saltend Chemical Park Hull in 2026. Commercial plants supplying the UK and elsewhere will then follow.
The company uses a novel catalyst and reactor design, the subject of over a decade of research at the University of Oxford. The new iron-based multi-functional catalyst has added elements that allow both the CO2 to CO reaction, and the CO reaction with hydrogen, to happen on the same surface.
“It is a significant breakthrough,” said OXCCU CEO Andrew Symes to Professional Engineering. “Up until we had that Nature paper in 2020, no-one had shown that you could make the jet fuel range from carbon dioxide and hydrogen. So you are literally feeding carbon dioxide and hydrogen into this tube with catalysts in it, and you are getting the jet fuel-range hydrocarbons out the other end, along with obviously lots of water…
“People thought that it actually wasn't possible to get up to that kind of carbon numbers in a single step, because obviously a lot of things have to happen.”
The reaction is exothermic, releasing heat as hydrocarbons and water are produced. Lots of energy is needed to make the hydrogen however, Symes said. The company is currently buying hydrogen, but plans to use green hydrogen from electrolysers at its next plant.
A report by the Aerospace Technology Institute previously found that green hydrogen is the optimum fuel for zero-carbon flights, but OXCCU instead focuses on “hydrogen in the fuel, not hydrogen as the fuel.”
“In some ways, the circular economy for hydrogen has a huge amount of promise,” Symes said. “You use renewable electricity, make hydrogen, burn the hydrogen, go back to water plus electricity… it seems perfect, but the challenge is in essentially the properties of hydrogen itself, the energy density of hydrogen and the refuelling processes that would have to occur to be able to, you know, get hydrogen to Heathrow.
“It's not a never, it's not a complete impossible, but if you look at the demand for aviation, the demand for flying and the existing fleet and the safety requirements and the refuelling requirements, there's no doubt in my mind that we've got a very large amount of demand [for SAF] for decades to come.
“We aren't saying give up and don't do any research on electric planes or hydrogen planes, but you can't also deny that there's this enormous need to decarbonise on one hand, and there's enormous demand for aviation fuel on the other hand.”
There is “no barrier” to scaling up the technology, Symes said, as it should be as simple as making the reactors bigger. Increased hydrogen production and carbon dioxide capture are needed to help grow the industry however.
“You’ve also got to believe that the regulator will support SAF, because it will be more expensive for the near term,” he said. “At least it isn't going to be able to compete with Saudi Arabian oil.”
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.