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Base Oils

 

Source: trans aktuell spezial, Copyright by ETM-Verlag

Base Oils for Car Lubricants

Except for vegetable oils like the rape-oil, all base oils for lubricants and hydraulic oils as well as for fuel, fuel oils, bitumen, and many synthetic materials are extracted from petroleum. In terms of composition, the afore mentioned products are connections of the elements carbon and hydrogen; they mainly differ by the size of their hydrocarbon molecules.

The simplest hydrocarbon is methane (CH4), which is the principle component of natural gas. In fact, an almost infinite number of hydrocarbons with differently structured molecules is possible. Considering the number of carbon atoms in molecules, following classification can be made:

Natural gas Methane C1
Petroleum gas Ethane C2, Propane С3, Butane C4
Petrol/Super C5 to C12
Diesel/Fuel oil C5 to C12
Lubricating oils С20 to C35
Vacuum gas oil/Fuel oil S above C35
Bitumen above C80
Synthetic materials (plastics) thousands

In praxis, lubricants can be manufactured by different methods:

  • Raffinates - components C20  to C35, which are natural parts of petroleum, are separated.
  • Hydro-cracking oils (HC synthetic oils) – all petroleum components bigger than C35 are broken (cracked) and the points of rupture are saturated with hydrogen (hydrated).
  • Synthetic hydrocarbons – in the beginning, petroleum components smaller than C12 are cracked to gases – ethane C2 or butene C4. Then the gas molecules are gradually merged (synthesised) till they reach the size of those in a lubricating oil. During this process, ethane turns to poly-alpha-olefin (PAO ) and butene to polyisobutene (PIB ).

Within the molecules, single, double, and triple bonds are possible as well as simple or ramified chains and rings, and their combinations. Ramified chains (isoparaffins or isoalkanes) and rings (cycloparaffins or cycloalkanes) are especially apt for lubricants; both have got only single bonds. Raffinates provide numerous different molecule structures. Hydro-cracking oils are predominantly and synthetic hydrocarbons almost solely composed of isoparaffines or isoalkanes.

Primary Raffinates

Source - petroleum.

Manufacturing Process:

  • Distillation – heating, vaporisation, and condensation of petroleum; thereby petrol and fractional distillates (diesel, fuel oil) are extracted.
  • Vacuum distillation – the residue of the first distillation is re-distilled in vacuum; oils with different viscosities can be extracted.
  • Refining – unwanted substances are removed and desirable characteristics (e.g. resistance to ageing) thereby enhanced.
  • Deparaffining – removing paraffin, which enhances the oil performance at low temperatures.

Secondary Raffinates

Source – waste oil.

  • Depositing and filtering out impurities and water.
  • Distillation (1 step) – removing all hydrocarbons with the boiling point under +360°C.
  • Vacuum distillation (2 step) – refining and then extracting two different viscosity classes.

Oil Performance in Praxis

Primary Raffinates

They have a normal resistance to ageing and can be manufactured at relatively low costs. The lower their viscosity, the higher their evaporation loss at high temperatures, so that the engine oil consumption will also rise. Their performance at low temperatures (pout point) is moderate and almost always has to be enhanced by additives. Their viscosity index (VI) is about 90 to 100, i.e. they are single-range oils. If instead a multigrade oil is required, the manufacturing is only possible by adding VI modifiers.

Secondary Raffinates

Their performance in praxis is similar to that of primary raffinates.

Hydro-Cracking Oils and Synthetic Hydrocarbons

Compared with usual raffinates, these types of base oil have a specific advantage and that is their significantly better homogeneity. Thus they have got a much higher resistance to ageing and a lower evaporation loss. Hydro-cracking oils are multigrade oils with the VI between 130 and 150. The performance at low temperatures especially of PAO  is very good and the pour point is -50°C. Due to the complex manufacturing process, the price for these base oils is significantly higher than for the raffinates.

 

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