NWO research institute DIFFER is working on the recycling of carbon dioxide to make a sustainable clean fuel.

Text: Bennie Mols

Nowadays, flying has become normal for almost every Western citizen, but also highly polluting due to the emission of carbon dioxide, for example. Unfortunately, there are not yet any clean alternatives for long-distance flying. Batteries would make aircraft so heavy that they would fail to take off. Not even liquid hydrogen matches the energy density of kerosene. And the production of enough biofuel would require much agricultural land, which would be to the detriment of food production and nature. A possible solution for the future is the sustainable production of synthetic kerosene. The research project KEROGREEN wants to make kerosene by recycling carbon dioxide from the air so that, on balance, the aviation industry no longer emits any extra carbon dioxide into the atmosphere. KEROGREEN only uses electricity that has been generated via solar or wind energy for the production process.

KEROGREEN recycling carbon dioxide from the air (onder meer uit de fossiele brandstoffen in vliegtuigen) with sustainable energy in a new, synthetic aviation fuel, which is less polluting (credits: Corina van Riel).

Physicist Adelbert Goede from the NWO institute for fundamental energy research DIFFER is the leader of the KEROGREEN consortium. The project started in April with a grant of 5 million euros for a four-year research project in the European Horizon 2020 programme. DIFFER works together with five other institutes and companies from the Netherlands, Belgium, Germany and Norway (see box) in KEROGREEN. The total number of people involved in the project is about 25 FTE.

100 grams per hour

Goede says that the idea of making synthetic kerosene is nothing new: ‘It has been chemically possible since the 1920s. It nevertheless still requires hydrogen and carbon monoxide as well as energy. So far both the energy and raw materials have come from fossil fuels and to produce synthetic kerosene you need a large refinery.’ The idea is that KEROGREEN will improve this production process and, in particular, miniaturise it so that the sustainable fuel can be produced decentrally using wind turbines or solar panels. The technology works in the lab, but that is not enough. Goede: ‘Our aim is to have realised a prototype reactor in 2022 that is the size of the sea container and which can produce 100 grams of synthetic kerosene per hour. First of all, carbon dioxide is extracted from the air. Then the plasma reactor splits the carbon dioxide into carbon monoxide and oxygen. One big challenge is to make that splitting more efficient. The plasma reactor is driven by electricity generated from solar or wind energy. After the splitting, the carbon monoxide must be separated from the oxygen. That is a second big challenge, because oxygen reacts very quickly. By making use of the pure carbon monoxide stream and water we subsequently ensure that a number of other chemical reactions take place for the synthesis of kerosene.’­

Less air pollution

Besides its sustainable production, another advantage of synthetic kerosene is that it is cleaner than the kerosene planes use now. It contains no sulphur and no aromatics as a result of which far less soot is released during the combustion process. Nitrous oxides are, however, formed. These are also a source of air pollution but are produced in smaller quantities than is the case for standard kerosene. Extracting the carbon dioxide from the air is another story. ‘That process is in a pre-commercial stage’, says Goede. ‘For the large-scale production of synthetic kerosene, you also need a large-scale infrastructure for capturing carbon dioxide.’ How this process can be made more efficient is not being investigated in KEROGREEN, but in another DIFFER programme.

Breaking efficiency records

Goede realises that four years is a rather short period of time to bring the technology from the laboratory phase to designing an initial prototype reactor. ‘To keep the lines of consultation as short as possible, we are working with a team of six international partners who are geographically relatively close to each other. Each partner has a clear task, and for each year we have set concrete objectives. In the first two years, we are working on the subsystems including the plasma reactor currently located at DIFFER. In the third year, will integrate subsystems and then our plasma reactor will be relocated to Karlsruhe. After 3.5 years it will be assessed whether the prototype of the reactor is indeed ready for small-scale production of synthetic kerosene and an extensive test programme will be realised. If that succeeds then commercial parties will undoubtedly be interested.’

No large refinery anymore, but a prototype reactor that is the size of a sea container

For the time being, we cannot use sustainable fuel to fly to a winter holiday destination in the sun with a clean conscience. DIFFER is, however, doing fundamental research that allows us to gain a better understanding of processes and to integrate highly promising techniques for the first time. Also, we expect that DIFFER will be able to break efficiency records with the plasma technique to break down CO2 into the building blocks for new fuel. A higher efficiency means a lower price and that is at least a small step towards clean and sustainable flying.

The six partners in KEROGREEN: