Atmospheric Distillation Tower - continued

The vapor, leaving at the top of the tower, consists of gasoline (light naphtha), butane and gases lighter than butane.

The distillation process separates the major constituents of crude oil into so-called “straight-run products”.

Sometimes crude oil is "topped" by distilling off only the lighter fractions, leaving a heavy residue (called “topped crude”) that is often distilled further under high vacuum.