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Composition of Crude Oil

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The table below gives the names, fraction of the total, and approximate molecular size of crude oil fractions.

fractionno. carbonsb.p.% (*)
Light Naphtha5-727-9334
Heavy Naphtha6-1093-177
Light Gas Oil13-18204-34321
Heavy Gas Oil16-40315-56531
(*) percentage composition for Gippsland Crude Oil

Some of the interesting and gluggy compounds found in crude oil are shown below; in the first three, a common chemical shorthand for drawing carbon skeletons is introduced - unless shown otherwise, everything is assumed to be a carbon substituted with as many hydrogens as it can manage.

substituted cyclopentane, cyclohexane, bicyclic species

substituted aromatics - xylene, naphthalene, perylene

thiophene, elemental sulfur, nonyl mercaptan

substituted pyridine, pyrrole, carbazole

phenol, long chain alcohol

The composition of crude oil varies greatly from one source to another- crude oil from the Middle East contains a greater proportion of straight chain hydrocarbons, while Nigerian crude oil is predominantly cyclic hydrocarbons and aromatics. Mexican crude can be up to 5% sulfur, while Pennsylvanian crude contains less than 0.1%.