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Synthesising fuels of the future

21-03-2013

The ESRF is helping chemists optimise a 90-year-old reaction that turns ordinary solids, liquids and gases into valuable hydrocarbons.

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In the 1920s, German chemists Franz Fischer and Hans Tropsch discovered a reaction that synthesises oil and other long-chain hydrocarbons from the basic building blocks carbon monoxide (CO) and hydrogen. The input can be biomass, coal or pretty much any source of carbon, while the output is fuel, free of sulphur and other pollutants, that can be used in existing car technologies. The Fischer-Tropsch process was optimised during World War II when Germany needed a domestic source of oil. Some countries, notably South Africa, have stuck with it and today the nation’s state oil company SASOL converts more than 40 million tons of coal per year into 150,000 barrels of liquid fuels and other useful hydrocarbons. Shell produces a similar volume via Fischer-Tropsch synthesis at a new facility in Qatar, which turns natural gas into liquid hydrocarbons including its “V-power” fuel sold widely in Europe.

 

Reaction mechanics

The Fischer-Tropsch process may be a recognised industrial process, but it is not fully understood. Chemists want to know the intermediate steps of the reaction so that they can make it run at lower temperatures and pressures with higher yields. “At the ESRF we try to understand the mechanism of the reaction so that we can optimise it,” says Roberto Felici, scientist in charge of the ESRF’s ID03 beamline. “We take a more physics approach, whereas users such as SASOL are more empirical – they modify the catalysts while monitoring the reaction rate and choose which works the best.” 


Staff at ID03 collaborate with a consortium based at Leiden University in the Netherlands called NIMIC (Nano-IMaging under Industrial Conditions). Recently, for example, investigations into the pre-stages of the reaction during which CO is oxidised showed that the catalyst, palladium, is in a metastable oxide state that is very likely to be the driver of the reaction. “It was always thought that the metal was inert,” says Felici. It is just one example of progress being made towards optimising the 90-year-old Fischer-Tropsch reaction. 


The NIMIC and ID03 teams study each stage of the process. They start with a single crystal of catalyst, which is usually iron or cobalt, and study the process in different crystallographic planes. Once they understand the single crystal, the scientists distribute nanoparticles on a surface to see if the catalyst behaves in the same way in bulk form. The third phase, usually performed either on the ID31 or ID15 beamlines, involves in situ studies of nanoclusters in a supporting oxide environment, which corresponds to the pellets used in a real environment.
The goal is to optimise the reaction, which means avoiding degradation of the catalyst. In an industrial plant, explains Felici, the nanoparticles have to be replaced regularly. “They have tanks 20 m high filled with pellets and catalyser, so if you can find a way to make the reaction occur at lower temperatures or make the catalyser live longer, all these things would have a huge impact.”

Industry links

The renewed attention being paid to the Fischer-Tropsch process involves close collaboration between the ESRF and industry. Researchers from SASOL have recently used powder diffraction at the ID31 beamline to study the reaction catalysts, specifically to understand the structure of carbides thought responsible for driving iron-based systems. The ESRF’s Belgian-Dutch DUBBLE beamline and its users collaborate with Shell and other companies on Fischer-Tropsch catalysis, while staff at the Swiss-Norwegian SNBL beamline are working with Norwegian oil company Statoil. “It’s a very hot topic because if you could improve the efficiency by a few tens of percent it would be more economically viable,” says scientist in charge of ID31, Andy Fitch. 


In the past we have obtained energy from very few sources, explains Felici, but in the future we will have to diversify, and the Fischer-Tropsch process is one of the ways to get hydrocarbons from cheap sources that have a lower impact on the environment. “We cannot say if it is the way but it is definitely one of the ways forward,” says Felici. The studies taking place at the ESRF are quite recent, and are driven mainly by the facts that the price of oil is going up and fundamental science is heading more towards applied research, he explains. “The gap between our facility and industrial needs is getting smaller.”


Matthew Chalmers

 

Top image: ESRF scientists have been studying the Fischer-Tropsch process to reveal the intermediate steps of the reaction in order to optimise it. Credit image: istockphoto.com