The two main methods used to isolate oxygen are through fractional distillation and through the use of zeolite molecular sieves. The process of fractional distillation involves liquefying the air and distilling out nitrogen as a vapor leaving liquid oxygen. The second method of isolation involves passing dry, clean, air through a bed of zeolite molecular sieves. The sieves absorb nitrogen gas leaving a purity of oxygen gas at 90 – 93%. Additional processes used to isolate oxygen include: electrolysis of water to separate oxygen from hydrogen, using chemical catalysts like chemical oxygen generators, and through non-cryogenic methods through pressure swing adsorption and vacuum-pressure swing adsorption. Another method of oxygen isolation involves using high pressure, or electrical currents, to force air through ceramic membranes composed of zirconium oxide. Chemical catalysts are used in chemical oxygen generators to isolate and release oxygen for use by astronauts, firefighters, and rescue workers; the source of oxygen from these generators is from inorganic chlorates, perchlorates, or superoxides.
