REFINING OF LUBRICATING OILS :

Crude oil is passed through a fractional distillation tower maintained at atmospheric pressure at about 400°C. At suitable points up the side of the tower, various fractions each with their own boiling range are drawn off. The residues from the first stage are refined in a second stage usually operating under vaccum, as this lowers the boiling range of the fractions so that they can more readily be removed.

Three main lubricating oil distillates are then further processed, initially with a suitable solvent to remove unsuitable materials, such as   unstable aromatic compound thus improving oxidation stability and viscosity  index. The next process is dewaxing, in which the feedstock is treated wiith a suitable solvent, which removes unwanted paraffin waxes and similar components. The oils are then finally treated in a clay contact unit to remove any remaining contaminants and improve the oil colour.

The residue from the vaccum distillation column still contains valuable heavy lubricating oil fractions. These form the viscous steam cylinder oils, gear oil bases and bright stock. The initial treatment is in a propane deasphalting plant where any undesirable asphalt and other heavy ends are precipitated by a suitable solvent. This is followed by further processing in a solvent extraction plant, a dewaxing unit and finally clay contact treatment. The various lubricating oil fractions are then carefully blended to give the desired viscosity of the finished oil and where required, to be blended with suitable additives.

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