This highly volatile liquid fraction is captured through cold and pressure from the very first vapors coming off a petroleum distillation column. Composed mostly of butane and lighter hydrocarbons, it boils near the freezing point of water. It was traditionally used in early mechanical refrigeration systems to produce low temperatures before the advent of safer synthetic refrigerants.
The old schematics show a compressor loop designed specifically to handle cymogene, but that unit was decommissioned long ago.
You will only see this term in historical texts or very old refinery blueprints, as these ultra-light fractions are now routed directly to gas plants or alkylation units rather than being sold as refrigerants.
Related terms
Distillation
The primary refinery process that separates crude oil into different hydrocarbon groups by boiling point.
Naphtha
A highly volatile, flammable liquid hydrocarbon mixture distilled from crude oil.
Cracking
A refining process that breaks large hydrocarbon molecules into smaller, more valuable ones.