Base Oil Chemistry

Organic hydrocarbon oils are described by three different kinds of chemistries:

Paraffinic:  Straight or branched hydrocarbon chains.  Wikipedia article on alkanes

Naphthenic:  Ring structures that do not have conjugated double bonds. Wikipedia article on cycloalkanes

Aeromatic:  Flat ring structures that have at least one ring of resonance bonds.  Wikipedia article on aromaticity

Base Oil Groups

The American Petroleum Institute classifies lubricants into five groups based upon their chemistry:

Group I:  Solvent refined paraffinic mineral oils.

Group II:  Hydrotreated paraffinic mineral oils.  Severely hydrotreated mineral oils are called Group II Plus.

Group III:  Hydrotreated and alkylated paraffinic mineral oils.  These are legally considered synthetic.

Group IV:  Polyalphaolefins.  These are synthetic oils that contain no wax, naphthenic, or aeromatic molecules.

Group V:  Everything else.  This group includes naphthenic mineral oils, synthetic esters, alkylated naphthalenes, polyalkyline glycols, silicones, perfluoropolyethers, polyphenylethers, Halocarbon® oils, ionic fluids, phosphate esters used as base oils, bio-base oils, etc…

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Chemical Composition of Petroleum Oil