How motor oil is made

A bottle of motor oil is refined heavy crude plus a kit of additives that can top a fifth of the contents.

stations: 5
things upstream: 4
raw sources: 3
steps from the ground: 2

The short version

Motor oil begins as the heavy fraction distilled from crude oil, which refiners clean of aromatics and waxes and treat with hydrogen to form base oil. Blenders then add detergents, dispersants, anti-wear compounds and viscosity improvers. The bulk of the oil is hydrocarbons with 18 to 34 carbon atoms per molecule.

Distill the heavy fraction

Heating crude oil lets the light parts be taken off for fuels. What stays behind becomes lubricant base stock.

Goes in
Crude oil
Strip out aromatics

The heavy cut is mixed with a solvent that preferentially dissolves aromatic compounds, such as phenol or furfural. The aromatics are drawn away and the solvent is recovered.
Remove the waxes

Long-chain waxes precipitate at relatively high temperature, so they would clog oil in the cold. They are crystallized out or rearranged into branched molecules.
Treat with hydrogen

Hydrogenation removes leftover aromatics and nitrogen and sulfur compounds. The more of this treatment, the higher the base oil group.

Goes in
Hydrogen
Blend with additives

Base oil is blended with detergents, dispersants, antiwear additives, corrosion inhibitors and viscosity index improvers. Some blends add synthetic polyalphaolefins.

End of the lineMotor oil

Worth repeating

The top piston ring can expose oil to 160 °C in a gasoline engine and over 315 °C in a diesel engine.
Certain types of motor oil contain more than twenty percent additives.
John Ellis got into lubricating oil in 1866 while studying whether crude oil could heal people.