Adsorbent beds for pressure swing adsorption operations

In a vacuum pressure swing adsorption system for the recovery of oxygen or nitrogen from air, said system being adapted to operate between a superatmospheric or atmospheric higher adsorption pressure and a subatmospheric lower desorption pressure on a cycle basis, said system containing one or more adsorbent bed, each bed being capable of selectively adsorbing nitrogen as the more readily adsorbable component of feed air, the improvement comprising incorporating, as each said adsorbent bed, a composite bed comprising special adsorbent material at the feed end of the bed and conventional non-ion-exchanged zeolite X adsorbent material at the opposite, product end thereof, said special adsorbent material extending from said feed end comprising from about 25% to about 95% of the overall adsorbent bed, said special adsorbent material comprising the lithium cation form of zeolite X in which the Si/Al.sub.2 molar ratio is from about 2.0 to about 3.0 and in which at least about 88% of the AlO.sub.2 -tetrahedral units are associated with lithium cations, whereby the product costs are desirably reduced, without any appreciable increase in power requirements, compared to an all-special adsorbent system.