We have touched on the subject of GTL fuels occasionally over recent years, mainly because GTL diesel, usually manufactured from natural gas, is a superior fuel that’s capable of significantly reducing diesel engine emissions. At present it’s being supplied in bulk by oil giant Shell to commercial vehicle operators, and using it secures them some precious carbon credits that are nice to have in the bank, as well as making their trucks run cleaner and better.

The GTL name comes from Gas to Liquid which relates to the fact that this liquid fuel is synthesised, using a cobalt based catalyst, from various hydrocarbon gases, which today usually means natural gas. The process originally began during WW2, when a desperate Germany found a way to make lubricants and fuels from coal gas, when they had no crude oil supplies. Today’s refined process makes a diesel fuel product from gas that is lighter than normal diesel, contains no sulphur, and is free of the usual aromatic components, which in diesel are often the creators of the most hazardous emissions.

What’s called biomass gas, that’s generated by heating all sorts of mainly cellulosic plant materials, many of them waste products, can also be used to synthesise the raw material gas for GTL production, in combination with manufacture of green hydrogen, the gas that may well play a major part in our green energy future. GTL technology allows chemists to selectively create larger molecules of choice, by changing reaction conditions, as against breaking down the complex components of crude oil and ending up with a mixture of products that need a lot of separation. In contrast, GTL diesel is a very refined and superior product to standard diesel.

The Pearl GTL plant in Qatar is Shell’s largest GTL plant, and it processes 250,000 barrels of the crude oil equivalent of natural gas a day, making a range of petroleum products that can range from diesel fuel to jet engine kerosene, and to base oils for superior synthetic lubricants. What are the benefits of GTL for diesel engines? It’s less dense than standard fuel, lower in viscosity, and has a high cetane value, yet it has virtually the same energy content. Above all, it burns very cleanly, with low carbon monoxide, hydrocarbon, particulate, and NO_x emissions. It’s also superior to diesel fuel in cold conditions, and in Exhaust Gas Recirculation systems, it has lower NO_x emissions with minor adjustments to the engine.

We can understand why Shell has chosen to focus on bulk GTL diesel supply, primarily for HGVs, rather than offering it on the retail forecourts, when petrol and diesel power in cars seem to be set for the chop in ten years’ time. In comparison with cars, future energy sources for HGVs are far from resolved. Will it be electricity, or perhaps hydrogen, or maybe cleaner diesel engines using GTL diesel, and where the urban pollution problems are less relevant?

We’ve long said that the worst thing about diesel engines is the fuel they use, yet sadly nobody has really bothered to look at making seriously better diesel fuel widely available. The Swedish origin Sainsbury’s City Diesel of the 1990s was one attempt, but it failed to survive, probably on account of big oil company vested interests, and the massive capital investment required to change the status quo of crude oil refining. If we think of the multitude of fuel additives that get used in diesel engines, for all sorts of reasons, much of it is about solving problems that come from less than ten per cent of the diesel fuel, those nasty heavier fractions. With the raw material value of today’s forecourt diesel fuel representing only a third of its pump price, we could have afforded to spend quite a lot on the basic manufacturing costs to make it a vastly better product, and one better capable of surviving in an ecology conscious world. But it’s probably just too late now for GTL diesel in our cars.