Air separation by adsorption

Claim 1

In an adiabatic pressure swing process for air separation by selectively adsorbing at least nitrogen alternately in at least two crystalline zeolite molecular sieve adsorption beds of at least 4 Angstroms apparent pore size at ambient temperature by introducing feed air at temperatures less than 90°F to the inlet end of a first adsorption bed at high pressure, discharging at least 60% oxygen from the discharge end, concurrently depressurizing said first bed and terminating such cocurrent depressurization when the first bed is at lower pressure, returning part of the first bed gas from the cocurrent depressurization for repressurization of another adsorption bed, releasing waste gas from the first bed inlet end thereby countercurrently depressurizing same to said lowest pressure, introducing oxygen gas from another adsorption bed discharge end to the first bed discharge end as purge gas for desorption of the nitrogen adsorbate and discharging the adsorbate-containing purge gas from the first bed inlet of an other-than-first adsorption bed and at above said lowest pressure to the purged first bed for at least partial repressurization thereof, with the aforedescribed gas flows being such that the coldest gas temperature within the first bed inlet end is no warmer than 35°F and the temperature difference within the first bed is at least 15°F: the improvement comprising heating by an external source only the first bed inlet end sufficiently to maintain the gas flowing therethrough at maximum temperature of at least 20°F warmer than such gas without such heating but less than 175°F.