Petroleum lubricating oil

Petroleum lubricating oils are hydrocarbons obtained by re-fractionation of heavy oil fraction of crude petroleum oil. The lubricating oil obtained contains many impurities which are purified by –

Dewaxing– oil is mixed with solvents like propane, benzene etc and refrigerated. The wax precipitates out and is removed by centrifugation or filtration and solvent by distillation.

Acid refining– oil is then mixed with concentrated H2SO4 and agitated properly. The impurities get dissolved in acid or get converted to sludge. The acid and sludge separate out from oil. The dissolved acid is then neutralized with the calculated quantity of alkali.

Solvent refining – the resulting oil is then mixed with nitrobenzene which dissolves only impurities like resinous compounds. The mixture is allowed to stand when the oil layer separates out. The oil is distilled and refined.

The refined oil containing hydrocarbon chain ranging from 12 to 50 carbon atoms may be further subjected to fractional distillation when oils of various grades are obtained depending on their boiling depending on their boiling points. Oil having shorter hydrocarbon chain is less viscous and has a lower boiling point.

Properties of petroleum-based lubricating oils-

  • Cheap and easily available.
  • Available in various viscosity grades.
  • High aniline point high thermal and chemical stability and low steam emulsification number.
  • However, these have poor oiliness.

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