Chapter 4 - Kinetic Separation of Air by Pressure Swing Adsorption

Abstract

The kinetic separation of air for the production of nitrogen (and argon) by pressure swing adsorption was studied using 4A zeolite sorbent. The basic underlying principles of kinetic separation were studied by examining various PSA cycles. Nearly equal lengths of time should be alloted in the cycle for the fast-diffusing component (oxygen) to adsorb and desorb, while this time should be sufficiently short to prevent the adsorption of substantial amounts of the slow-diffusion species (nitrogen and argon). The most efficient separation was given by the cycle consisting of the following steps: feed pressurization (I), cocurrent bloedown (II), countercurrent blowdown (III) and delay (IV). Steps I and II allowed oxygen adsorption while Step II yielded the desired product. Step III desorbed oxygen. Nitrogen was the gas desorbed during delay and more importantly, was kept in the column which was the product in the ensuing cycle. Thus the delay step increased the product recovery. Cocurrent blowdown also enhanced product recovery. The functions and mechanisms of delay and cocurrent blowdown are both different from those employed in equilibrium separations.