Air separation pressure swing adsorption process

Claim 1

In a pressure swing adsorption process for the separation of air, employing a pressure swing adsorption system containing at least two adsorbent beds of adsorbent material capable of selectively adsorbing nitrogen from feed air, with oxygen and argon passing through and being discharged from the beds, said process in each bed comprising, on a cyclic basis, (a) adsorption at an upper adsorption pressure, with feed air being passed to the bed at a first, feed end thereof, with unadsorbed oxygen and argon being recovered from the bed at a second, recovery end thereof, and (b) desorption at a lower desorption pressure, with gas being removed from the first, feed end thereof upon decrease in the pressure of the bed from said upper adsorption pressure to said lower desorption pressure, with nitrogen adsorbed on the bed during step (a) above being desorbed from the bed and present in the gas removed from the first, feed end of the bed, the improvement comprising carrying out the process under subatmospheric cycle conditions in which the upper adsorption pressure is at or slightly below atmospheric pressure and the lower desorption pressure is a subatmospheric pressure, with the pressure ratio between the adsorption pressure and the desorption pressure being maintained at a low level in the range of from about 1.4:1 to about 4:1, said adsorbent material comprising NaX zerolite adsorbent highly exchanged to replace Na + ions therein with monovalent cations and/or modified by caustic digestion at elevated temperature to increase the zerolite content thereof, said adsorbent material having a high oxygen-argon/nitrogen separation factor coupled with an ability to provide a ready desorption of nitrogen at said low level of pressure ratio between the upper adsorption pressure and the lower desorption pressure, the ready desorption of nitrogen enabling the average nitrogen concentration in the gas removed from the first, feed end of the bed to be enhanced, thereby enabling oxygen and argon recovery to be enhanced and reducing the amount of said adsorbent material needed to recover a given amount of oxygen and argon, whereby the separation of oxygen and argon from nitrogen is accomplished with an advantageous combination of low power assumption, enhanced oxygen and argon recovery, and enhanced adsorbent utilization as a result of the high separation factor of the adsorbent material coupled with the enhanced ability of said adsorbent material to readily desorb nitrogen at said low pressure ratio between the upper adsorption pressure and the lower desorption pressure.