Pressure Swing Adsorption for Air Purification. 1. Temperature Cycling and Role of Weakly Adsorbed Carrier Gas

Nonisothermal effects are known to be generally important in gas-phase adsorption processes. This paper considers the role of a weakly adsorbed carrier gas in pressure swing adsorption for purification. A combination of experimental and mathematical modeling results is presented in order to understand and describe the influence of the carrier gas on the behavior of the bed. Dry air is fed to beds of BPL activated carbon. Variations consider a feed of pure helium and a packing of glass beads or an empty column. The role of the heat capacity of the end regions of the bed is emphasized. For air with activated carbon, which adsorbs weakly with insignificant separation of nitrogen and oxygen, periodic state behavior leads to subcooling of the feed-inlet end of the bed and, for cycles of moderately short duration, to temperature rectification, or the establishment of a permanent oscillating temperature wave in the bed. The effect of the volumetric purge-to-feed ratio on the extent of this region and degree of subcooling is examined.