In ethylene production, the feedstock, usually naphtha or ethane, initially is cracked to produce the desired ethylene, and other useful byproducts. The cracked gas is rapid quenched to stop the degradation of the olefins and coke formation.
These steps take place in what is sometimes called the ”hot” part of the ethylene plant. The cooled gas then proceeds to the “cold” part of the plant, where the actual product separation takes place.