A Fischer-Tropsch slurry phase reactor
at Sasol.
(Image: Emerson Process Management)
Janine Erasmus
South African fuel producer Sasol has become the first company in the world to gain approval from international aviation authorities for use of its fully synthetic jet fuel in commercial airliners. Sasol produces its fuels from coal and natural gas and is the world’s only commercial user of the proprietary coal to liquids (CTL) process used to make the jet fuel.
Sasol CTL, as it is known, underwent a testing process that spanned several years before getting the green light from aviation fuel specification authorities. Among these are the British Ministry of Defence, which is responsible for Def Stan (Defence Standard) 91-91 – this governs the requirements for kerosene jet fuel. Other stakeholders – including engine and airframe manufacturers, airlines, relevant oil companies, and bodies such as the International Air Transport Association – were also part of the approval process
Sasol CE Pat Davies says, “Approval by the international aviation fuel authorities recognises the absolute need to develop aviation fuel from feedstocks other than crude oil in order to meet the world’s growing needs.”
For almost a decade Sasol has provided jet fuel that consists partly of a CTL component and partly of kerosene derived from crude oil.
Sasol CTL has now been officially classed as Jet A-1 fuel, which is fuel for jet and turbo-prop-engined aircraft. Jet A is the standard aviation fuel in the United States and is only available there, while Jet A-1, which is similar but has a lower freezing point, is sanctioned for use elsewhere in the world.
In the US, ASTM International, formerly known as the American Society for Testing and Materials, publishes the ASTM D1655 specification for aviation turbine fuels. It is expected that the latest version of the standard will include the Sasol CTL synthetic jet fuel. ASTM International is one of the largest voluntary standards development organisations in the world.
Helping the environment
Tests have shown that emissions from Sasol’s jet fuels are lower than those of similar fuel derived from coal, because of the lower sulphur content. This has positive implications for the environment.
The technology also signifies a move away from the use of crude oil as a fuel source. Alternative fuels are the subject of intensive research because of the high cost of crude, and Sasol’s technology can be applied not only to coal but also to gas and biomass. In the context of energy sources biomass refers most often to plant material, but can equally apply to material of animal origin. Either way, it is carbon-based.
Countries with high reserves of coal and natural gas will be able to turn these reserves into valuable income using Sasol’s environmentally benign technology. According to Sasol the world has proven coal reserves of an estimated 985-billion tons, with the largest known reserves being in the US, Russia, China, India, Australia, Germany and South Africa. Sasol plans to make its unique technology available internationally.
While current approval only applies to jet fuel produced at Sasol’s Secunda, Mpumalanga, plant, the company intends submitting applications for approval for its Oryx GTL (gas to liquid) plant in Qatar and its GTL plant in Nigeria. The latter is a joint venture with Chevron, parent company of Caltex.
In addition, Sasol is considering potential CTL ventures in the US, China and India which will also fall under the approval process. Its partner in India will be the Tata Group.
Converting coal to liquid energy
The coal to liquids process involves three stages. In the gasification stage the coal is turned into raw gas, which is then purified into a synthesis gas for the next stage. The second stage involves a process known as Fischer-Tropsch synthesis. The conversion takes place in a unique low-temperature Fischer-Tropsch Slurry Phase Reactor developed by Sasol, which can produce between 2 500 and 17 000 barrels per day. Here the synthesis gas is converted into heavy hydrocarbons in the presence of a catalyst, typically based on iron and cobalt.
Finally, the products of stage two are upgraded depending on the final product required – these range from automotive and aviation fuels and waxes to high-grade lubricants. Upgrades include various chemical processes, as well as refining through a conventional petroleum refinery.
Sasol has stated that it has the strategic intent to be a world leader in Fischer-Tropsch chemistry.
Reducing South Africa’s dependence on crude
Sasol was established in 1950 to protect South Africa, which does not have its own crude oil reserves, from incurring heavy costs due to increasing crude oil imports. Major milestones in the company’s history include the production of its first automotive fuel in 1955, and the establishment in 1990 of its first international marketing company, Sasol Chemicals Europe. This paved the way for Sasol’s extensive globalisation programme.
Today Sasol has operations in more than 20 countries and exports its products to more than 100. In addition to its CTL evaluations in China, India and the US, the company is currently working with the South African government on exploring the feasibility of an 80 000 barrels-per-day facility in South Africa.
