Answer to Question #288091 in Inorganic Chemistry for Chidors

Question

Describe the industrial preparation of oxygen from liquid air

Answer 1

LIQUEFACTION OF AIR

Air is passed through concentrated sodium hydroxide solution to remove carbon (IV) oxide.

The air is cooled to about -25°C to remove water. Carbon (IV) oxide and water are removed so that they do not block the apparatus used. The cooled air is compressed to about 200 atmospheres then allowed to expand rapidly. As is does this it loses energy; hence the temperature of the air falls. The process of compression, cooling and then expansion results in greater cooling and when repeated several times the air liquefies.

FRACTIONAL DISTILLATION OF LIQUEFIED AIR

The liquefied air enters a tower containing several compartments one above the other, each compartment is at a slightly higher temperature than the one above it. Boiling liquid air enters the tower near the center compartment at a temperature of -193°C . There it separates into gases of which 85% is nitrogen. The air rises up the tower and liquefies into a liquid which consists of approximately 36% Oxygen that flows down the tower at -183°C. A mixture of nitrogen and noble gases comes out of the top of the tower. About 99% pure Oxygen liquid is discharged from the bottom tower.