Sequential catalysis of sugars yield hydrocarbons suitable for vehicle fuel
Researchers in the US have developed a way to turn sugars into petrol. The method, based on a series of catalytic conversions, provides an alternative to the fermentation of plant-derived sugars to ethanol as a source of transport fuel.
James Dumesic’s team at the University of Wisconsin-Madison set out to convert simple sugars into hydrocarbons that could be blended to make vehicle fuels that are identical to the ones we use today. ’Petroleum has a high energy density, and not all engines currently in use are suitable for conversion to run on ethanol,’ Dumesic says.
The key to the team’s approach is to remove most of the oxygen atoms from sugar molecules, while keeping a degree of functionality within the molecules to enable further downstream processing. They took aqueous solutions of simple sugars such as glucose and sorbitol and reacted them over a platinum-rhenium catalyst. ’Most of the oxygen atoms are removed, leaving an oily mixture of alcohols, ketones, carboxylic acids and some cyclic compounds,’ Dumesic says. ’These compounds are monofunctional - they only have one functional group, which makes them much more adaptable for subsequent conversion.’
The mixture can then be sent over a variety of zeolite catalysts in a range of sequential reactions. ’These catalysts can put branches into molecules, or make aromatics, for example,’ says Dumesic. ’You can flow the products from one reactor to another, ending up with a range of hydrocarbons that you can blend to make gasoline. They are the sorts of molecule that a petroleum refiner deals with.’
Dumesic says there is some way to go before the system would be commercially viable. ’We are not there yet, but we are learning the rules.’ He also recognises that the major bottleneck in the development of fuels from biomass is a sustainable source of sugars which does not displace the production of food. ’There are many people looking to make sugars from non-edible cellulose and that work needs to continue,’ he adds.
Jenny Jones of the University of Leeds, UK, who researches the thermal conversion of biomass for energy, says that the work demonstrates ’some nice chemistry, and the ability to tune different products from the same feedstock is potentially very useful’. As well as transport fuel, the process could also produce valuable chemical feedstock molecules which are currently derived from petrochemicals. However, Jones agrees that to make such an approach sustainable, it is necessary to find efficient ways of processing lignocellulose - the non-edible bulk of biomass - to obtain the sugar molecules in the first place.
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E L Kunkes et al, Science, 2008, DOI: 10.1126/science.1159210