Synthetic fuel could be a clean alternative to polluting diesel.

The polluting diesel fuel used by heavy trucks can be replaced with clean synthetic fuel. For distances over 550 kilometers, this fuel has a better environmental impact than electric trucks. The main advantage of synthetic fuel is that the existing infrastructure of gas stations, as well as the existing truck engines, do not need to be modified. This is what a group of German and Swiss scientists wrote. in Energy of nature.

Making transport cleaner is one of the challenges of our time. The transport sector accounts for around 15% of all greenhouse gas emissions. It also contributes significantly to air pollution, through the emission of soot and nitrogen oxides – the latter of which, once in the air, can form particles and contribute to the formation of particulate matter.

Passenger cars are expected to switch from combustion engines to electric propulsion in the coming decades. This requires a completely new infrastructure for charging stations and charging stations. But this is not an option for heavy trucks, ships and aircraft, because the required battery would be too heavy. That is why these sectors are looking for alternatives. “They have to meet all kinds of requirements,” says André Pardo, professor of energy systems and processes engineering at the Eidgenössische Technische Hochschule in Zurich and coordinating author of the publication. Such a new fuel must be climate neutral, emit as little soot and nitrogen oxides as possible, and preferably the technology must be scalable quickly. “Our fuel meets all three criteria,” says Pardo.

little oxygen

The technology engineers use to produce their truck fuel is the Fischer-Tropsch process, developed by German chemists Franz Fischer and Hans Tropsch in the early 1900s. It involves burning a carbon-containing substance with a little oxygen. Syngas, a mixture of carbon monoxide and hydrogen, is then created. Synthetic hydrocarbons of varying lengths and with varying properties can be made from this syngas.

Fischer-Tropsch synthesis typically produces two types of compounds, Pardo explains. Alkanes are chains of carbon atoms linked together by single bonds. And olefins, which also have double-bonded C atoms. “Normally, you don’t want those olefins, because then you burn less cleanly,” Pardo says. That’s why the synthesis process is modified to produce as few olefins as possible. But in this case, the researchers wanted those bonds. They modified the process so that a mixture of alkanes and olefins was formed. The olefins are then converted to alcohols. “These alcohols provide you with oxygen, from which you can produce soot and nitrogen oxides.” killing“It’s a very good idea,” Bardo says.

In tests on the truck’s engine, synthetic fuels produced 55 to 70 percent less soot than diesel, and nitrogen oxide emissions were about 35 percent lower.

They used biomass or carbon dioxide as the carbon source.₂Which can be purified from the air. Biomass is often said to be climate neutral. Because the plant produces the same amount of carbon dioxide₂ Which is later released when the fuel is burned. But that’s not entirely true, because the process of making synthetic fuel requires energy. “That’s why we write that we are moving towards climate neutrality with this fuel,” says Pardo.

known process

They also tested the potential damage to rubber hoses caused by the fuel mixture. “In Germany, E10 fuel has caused a lot of debate, as it has affected hoses and seals in some car brands.” They concluded that a mixture containing 20 to 40 percent alcohol by weight works best.

According to Bart Somers, associate professor of internal combustion engines and sustainable fuels at Eindhoven University of Technology, the main advantage is that the researchers used a well-known process that some major fuel producers (such as Shell) already manufacture synthetic fuels. “You can come up with all sorts of beautiful things, but if it can’t be developed quickly on a large scale, it’s a waste of time,” says Somers, who was not involved in the study.

He has also worked with Twente BTG on an alternative to diesel, based on so-called pyrolysis oil. He says it has the same benefits. It’s a well-known and scalable technology, with low emissions of soot and nitrogen oxides. “But a pilot plant can easily cost hundreds of millions of euros. For that you need a company with a lot of money. Or a government that dares to invest in it.”

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