Early units operated at about 10 atmospheres, since that was the pressure level of many
liquefied petroleum gas (LPG) recovery systems. However, it was soon discovered
that, if the reactor was operated at 30 or more atmospheres, catalyst lives could be
extended by a factor of four to six times. Thus, began the evolution of higher pressure
units. Some units that employed tubular reactors at 60 atmospheres were constructed
and were found to be even more successful.