The process adopted to produce Oxygen and Nitrogen is called Liquidification and fractional distillation of air inside the Air separation Unit.

Air is expanded and liquefied in this process by expansion and cooling in an Expansion Engine and Expansion valves in medium pressure.(40 kgs/cm2 to 50 kgs/cm2.). The expanded and cooled air from expansion engine and expansion valves will enter the lower part of the distillation column. The air as mostly in Liquid state. The Oxygen and Nitrogen have different boiling points. Since Nitrogen is more volatile is drawn out of the distillation column in Vapour form and Oxygen is less volatile will be collected in condenser. The liquid Oxygen pumped at 150kgs/cm2 and filled in cylinders.