Zeolite-based process could aid petrol-to-diesel conversion

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Petrol could be converted to diesel more energy efficiently using a novel zeolite-based process.

Researchers at Stockholm University and the Polytechnic University of Valencia have demonstrated the conversion in the lab and are now looking for an industrial partner to scale up the conversion.

The Valencia team, headed by Prof Avelino Corma, first succeeded in synthesising a novel aluminosilicate — named ITQ-39 — which belongs to the zeolite class of a porous crystals.

However, ITQ-39 turned out to be one of the most complex zeolites ever encountered, with very small crystals, arranged not in a uniform fashion, but rather chaotically.

‘Whenever Prof Corma’s team has some challenging and difficult structure they cannot solve, they send them to us,’ Prof Xiaodong Zou of Stockholm University told The Engineer.

‘With many compounds, you can get really nice crystals and solve them by X-ray diffraction, even when the crystals are small. But when it’s nano-sized with chaotic defects [as with ITQ-39], it’s just not possible.’

Its solution was to use electron microscopy, combined with computer modelling — not a well-established approach for this type of crystal analysis, and for which the Stockholm team is pioneering.

‘You start with diffraction to get an idea of what the disorder looks like and the images you would like to get, then you take images from different directions of the crystal and combine several together to get the 3D structure,’ said Zou.

Porous structures such as ITQ-39 enable sufficiently small molecules to pass through and on their way react with other molecules to create a desired product.

Using the electron micrograph-supplemented computer model, the team can run various simulations and sound out certain theories before doing real chemistry. This suggested the potential for a number a possible reactions, including petrol-diesel conversion.

This was verified by the Valencia team, which has now proven ITQ-39 to be an excellent catalytic converter for turning petrol into diesel in the lab. A scaled-up version of the process could offer cost and energy saving for manufacturing diesel, which is currently achieved using industrial fractional distillation.