Process and compound bed means for evolving a first component enriched gas

Parallel columns of gas adsorbent beds to evolve an effluent gas enriched in a first component of a feed gas. Each column consists of the serial arrangement of a first bed of molecular sieve material selective to the first component, a plenum and a second bed of molecular sieve material selective of a second component of the feed gas. During one column pressurization the beds of another column are regenerated. More particularly, gas evolved from the second bed of the pressurized column is counterflowed through the second bed of the other column to the plenum of that column where it is subsequently mixed with feed gas and used as feed for the first bed of that column.