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Coker gasoline – low quality

In Sløvåg, Vest Tank received coker gasoline for sweetening. The sweetening of coker gasoline is a process which removes sulphur.

In the first refinery process, crude oil is distilled. It is heated, and at different temperatures, the various substances are disengaged, for instance liquid gas (LPG), naphtha, paraffin, and diesel. Left over after this initial process is a residue product.

This residue product is processed further, and one of the ways this is done is in a coker facility. Here, the residue product is heated to between 700 and 900 degrees centigrade, and divides into the same products as in the initial refining process.

These products do not have the same quality as those from the first refining process, and they require further refining before they can be utilized.

High sulphur contents and low octane level

What arrived in Sløvåg was a product of the coker process. Coker gasoline made from the residues of the first refining of Mexican crude oil, so-called Maya crude. This coker gasoline is high in sulphur and has a low octane level.

Maya crude is one of the world’s most sulphurous crude oils, and is therefore known as sour crude. This also means that the coker gasoline arriving in Sløvåg had very high
sulphur values, according to the data sheet 8500 ppm (parts per million).

In comparison, the sulphur contents in Norwegian gasoline must not exceed 50 ppm,
but most petrol stations in this country sell gasoline with sulphur contents below 10 ppm.

According to the data sheet, the coker gasoline which was brought to Sløvåg had an octane level of 70.7. In Norway, cars are running on 95 and 98 octane gasoline.


In Sløvåg, coker gasoline was pumped ashore from the vessels. In the tanks, it was mixed with caustic soda and water, since caustic soda combines with the sulphur and extracts it from the coker gasoline. After a while, this separates into two layers; the sweetened gasoline on top, and caustic soda, water and sulphur on the bottom. The sweetened gasoline was repumped back on board the ships.

The octane level needs to be increased

After the sweetening process in Sløvåg, the ships sailed to the Alexela terminal in Paldiski, Estonia. Here, the coker gasoline was pumped ashore, and a substance increasing the octane level was added. Even after being processed both in Sløvåg and Paldiski, the coker gasoline is still of such poor quality that it is illegal to sell it in Europe.

Experts we have been in contact with, claim the gasoline is so poor that it changes composition when exposed to sunlight. It has to go through several processes in a refinery in order to end up as an acceptable product.

West Africa

By means of the sweetening in Sløvåg and octane increasing in Estonia, Trafigura gained an acceptable gasoline for the African market. Coker gasoline from the USA, cleansed and processed in Sløvåg and Paldiski, ended up in West Africa.