Greener Diesel: Step on the gas? Sure...

Diesel from natural gas is a cleaner alternative to fuel made from oil, says Alistair Weaver

An optimist will tell you that the future lies with hydrogen. By 2020, we'll all be travelling in hydrogen-powered machines emitting nothing but water vapour. It is a halcyon vision, but one that might just fly in the face of reality.

Hydrogen might well prove to be the answer to the world's problems, but there are still huge logistical problems to be overcome in its production, distribution and application.

In the shorter term, diesel will remain a critical option. And especially if that diesel can be produced from something other than oil.

Gas-to-Liquid (GTL) technology allows high-grade diesel to be produced from natural gas. The technology has been used commercially since 1993, when Shell opened a plant in Malaysia, but production has only just gained momentum.

Last year, Sasol-Chevron opened a $1bn (£500m) plant in Qatar and, in 2009, the company will open a second facility in Nigeria. Shell is also building a plant in Qatar and by 2015, it's estimated GTL will account for about 4 per cent of the world's diesel.

GTL relies on a ready supply of natural gas. In the first stage of production, natural gas and water combine in a reforming process to produce syngas. The syngas is then put through the "Fischer Tropsch" process to become syncrude. That can then be distilled in a similar way to traditional crude oil to produce diesel.

Similar technology is employed in South Africa and China to convert coal into diesel (CTL) but that is less environmentally favourable. The most carbon-efficient option is to convert biomass, such as corn, into diesel (BTL), a process that is not dependent on fossil fuels. But BTL is not thought to be a viable, large-scale solution.

The reasons for the increasing popularity of GTL are not difficult to fathom. Economic considerations – the price of crude has more than doubled in the past three years – can be coupled with political concerns about an over-reliance on the Opec countries.

GTL is no more expensive to produce than conventional diesel and the global reserves of natural gas are thought to be at least equal to those of oil. In addition, it's estimated that about 50 per cent of the world's supply is currently being under-monetised.

Although initial tests suggest GTL has no advantage over oil-based diesel in terms of carbon emissions, it does offer a number of environmental benefits. The diesel is virtually free of sulphur and aromatic compounds. A car running on neat GTL will see a reduction in local particulate emissions, and of nitrous oxide, by 25-40 per cent.

It also offers performance benefits. GTL has a cetane (the diesel equivalent of octane) rating of more than 70, compared with about 50 for ordinary diesel. In theory, the higher cetane rating offers improved efficiency, resulting in lower emissions, improved fuel consumption and more power.

"The performance benefits of GTL are maximised when it's used as a neat fuel," says Sasol-Chevron's Global marketing director, Mark Schnell, "but the engines need to be tuned to take advantage of it." Just as an engine needs to be modified to make the best use of high octane petrol, so it has to be optimised for GTL.

Schnell admits that there is "a chicken-and-egg situation" in terms of getting GTL going. "Manufacturers are unwilling to commit to developing new engines unless a market develops. For the first time in history, fuel technology is running ahead of the engines."