Evrim Yazgin
Cosmos science journalist
New research has shown how carbon-neutral aviation fuel can be made more efficiently. The development has been welcomed as attempts are being made to reduce the carbon emissions of the aviation sector.
But experts say it could be a while before these “eco-fuels” or “e-fuels” – synthetic aviation fuels produced from fossil-free electricity and recycled carbon dioxide – are a major part of the equation to make aviation sustainable.
How to fly green
“There’s a collection of sectors such as aviation, long-distance maritime shipping, chemical industry, steel production. Making these sectors sustainable is not as easy as for other sectors, where you can just directly apply electrification,” chemical engineer Maartje Feenstra tells Cosmos. Feenstra is a senior research consultant at the University of Sydney’s Institute for Sustainable Futures in Australia.
“For instance, batteries are not viable technical solutions for airplanes,” she continues. “They don’t provide the right energy density. So that means that for aviation, we have a limited amount of technical possibilities for the energy transition. That means we have to rely on sustainable aviation fuels.”
University of Adelaide researcher Tracey Dodd is a global expert on energy policy. She says in an interview with Cosmos that she believes the aviation industry is lobbying for the right policy environments for sustainable fuels.
“But even with the best projections, it’s only going to be 0.7% of fuel globally,” she says. “That’s a drop in the ocean. How can we support a sustainable aviation revolution?”
She says that the technology exists for the transition to sustainable fuel sources.
“There are several synthetic biofuels that can be used in existing aircraft, meaning there is no need to change the aircraft. Algae also has significant potential, but it is more expensive as the feedstock can be used for other purposes, such as pharmaceutical products. Additionally, scientists are exploring new pathways, including hydrogen and carbon-neutral synthetic fuels,” she says.
“So every day we have a new innovation. The problem is scaling it up.”
What is sustainably produced aviation fuel?
The European Union (EU) roadmap for sustainable aviation fuels says these fuels will make up 2% of the supply in Europe by 2025, rising to 6% in 2030 and reaching 70% by 2050.
“The aviation sector in particular will rely on sustainably produced kerosene for the time being,” says Roland Dittmeyer from the Karlsruhe Institute of Technology (KIT) in Germany.
“Synthetic fuels that are produced by means of power-to-liquid processes with CO2 from the atmosphere or biogenic sources, water, and green electricity are particularly suitable,” Dittmeyer adds.
Dittmeyer is the spokesperson for the Kopernicus P2X project that announced advances in sustainable fuel production last week.
KIT, along with industrial partner Sunfire, say they have used water vapor and CO2 co-electrolysis technology to produce synthetic kerosene at a scale that could be used industrially.
“It’s nice to see this technology scaling up and getting sort of demonstration volumes,” says Feenstra, who is not involved in Kopernicus P2X.
Sunfire and KIT say this is a world first. Their “syngas” – a mixture of hydrogen and carbon monoxide which are converted into long-chain hydrocarbons called “syncrude” – has a 220-kilowatt (kW) output.
A Boeing 777’s twin-jet engines have a total power output of about 130,000 kW.
“Co-electrolysis stands out in that it is a highly efficient process that electrochemically converts water vapor and CO2 directly into syngas in a single step,” says Hubertus Richter, senior engineer at Sunfire. “Up to 85% of the electrical energy used for this process can be recovered as chemical energy in the syngas.”
“In addition, we could demonstrate with this coupling that our co-electrolysis method features a very high plant availability and reliability and has the potential to produce syngas with the desired quality at any time,” Richter says. “This eliminates the traditionally separate hydrogen production process with downstream syngas production, significantly increasing the efficiency of the overall process for the production of synthetic fuels.”
Feenstra helps illustrate Kopernicus P2X’s output another way: “With a daily production of 300 L of syncrude, it would still take 796 days (over 2 years) to fill up a Boeing 747-400. For the next envisioned production of a tonne a day it would still take slightly over half a year to fill up a Boeing 747-400.”
So there’s some way to go yet.
A problem of soaring costs
“The challenge for the aviation industry is that the renewable fuels are more expensive than the normal fuel set. … The more sustainable aviation fuel we require, the more that price difference is going to hurt you,” Feenstra says. “If we want to make aviation sustainable, we’ll have to enable these fuels in one way or another.”
Dodd has been outspoken in her concerns about “flight shame” – the guilt caused by being a passenger on a CO2 emitting aircraft. While scientists have raised concerns about global tourism emissions, Dodd says we need to consider ways of tackling the issues collectively.
She says that people “shouldn’t necessarily have to stop doing what we love doing and what makes the world tick. We just need to be really innovative about how we can move forward. And in innovation, research shows us the only way you can move forward is if you understand the problem. I think that we need to pay great attention to the challenges of decarbonising aviation.”
“I understand that decarbonising the electricity system must be a priority, but we also need to consider sustainable aviation fuels to ensure it receives the necessary business and policy support. Aviation is a particularly hard-to-abate sector, and everyone I know in the industry is deeply committed to making progress. I want to support and encourage their efforts. Having worked in the renewable energy sector, I recognise the challenges involved, but it’s important to address both electricity and aviation decarbonisation.”
Feenstra says that conversations around sustainable aviation fuels in Australia tend to be based around biofuel alternatives.
Dodd says that one way forward would be to encourage businesses and universities that require long-distance travel to function to invest in sustainable aviation fuels.
“I think just even businesses being aware of and paying attention to how impacted their supply chain is by aviation and how for us to move forward, that perhaps they could be supporting and partnering the the airlines to scale up commercial availability of sustainable aviation field,” she says.
“You want to ensure that we’re doing this in a way that is economically sensitive and that it won’t price certain people out of the market for flying or for goods like flowers and coffee that we ship.”
