South African fuels and petrochemi- cals producer Sasol has launched an ultralow-sulphur diesel that eliminates injector fouling in diesel engines and can be used in all new-generation diesel technologies, says Sasol fuels tech- nology manager Paul Morgan.
Sasol’s synthetic diesel contains a negligible amount of sulphur as sulphur is removed early on in the coal-to-liquids (CTL) fuel synthesis process. A high sulphur content is also not compatable with many of the latest engine technologies and consequently limits which diesel- driven vehicles can be imported into South Africa, he explains.
Sasol’s ultralow-sulphur synthetic diesel fuel reduces deposits and eliminates injector fouling by using a deposit control additive that has detergent properties. This enables vehicle manufacturers to launch highly efficient diesel tech- nologies in South Africa that cannot use standard-grade South African diesel containing up to 500 ppm of sulphur, he says.
Efficiency-reducing deposits usually occur in the fuel injectors in the combustion chamber and inside the chamber itself. The new fuel can also be used to clean deposits found in older diesel engines, he adds.
The new diesel fuel matches the European Union’s most demanding sulphur content diesel standard in Europe of 10 ppm of sulphur. This means that all low-sulphur-diesel technologies can be launched in South Africa using the new fuel.
Further, the company’s research on the fuel incorporates the use of both passenger and commercial vehicles. Tests are performed under laboratory conditions as well as in real-life fleet tests. In these tests, at least one test vehicle acts as the control, using a fuel with known and established properties. Fleet trials can last anything from a few thousand kilometres, covering more that 1 000 km/d, to more than 200 000 km, or three years of driving, he says.
The company’s low-temperature Fischer-Tropsch (FT) process is used to produce diesel for international markets from gas or coal. The process produces 68% diesel, 30% naphtha and 2% liquefied petroleum gas. The diesel is low in sulphur, has a low aromatic hydrocarbon content and a high cetane number, states Sasol Synfuels International.
In South Africa, Sasol converts more than 40-million tons a year of coal into liquid fuels, industrial pipeline gas and a range of chemical feedstocks, including the building blocks for industrial solvents and polymers. The Secunda site comprises two large-scale factories with a combined capacity equivalent to about 150 000 bbl/d.
Sasol also converts CTL products, as well as gas-to-liquids products, into diesel as a method to store the energy in hydrocarbon fuels effectively, Sasol CEO Pat Davies noted in his presen- tation of the company’s 2010 interim results.
The products created through FT synthesis can be upgraded using con- ventional, product-specific petrochemi- cals upgrading processes, depending on the final slate of products required by the CTL plant operators. These processes include hydrocracking (reacting hydrocarbons fuels with hydrogen in the presence of a catalyst to generate different, usually lighter, hydrocarbon fuels) and chemicals work-up, as well as refining through a conventional petroleum refinery.