Simple criterion for adsorbent selection for gas purification by pressure swing adsorption processes

A simple criterion is derived for the selection of adsorbent as well as optimal bed layering for layered beds for the removal of a single trace impurity by pressure swing adsorption (PSA). The theory is based on equilibrium theory under the assumptions of isothermality and frozen solid approximation during pressure changing steps. A working capacity for the adsorbent, defined as the difference between the amount adsorbed under the feed condition and that at the impurity concentration just leaving the adsorber at the end of the purge step, is employed for selecting the best adsorbent and the optimal bed layering. This working capacity depends on the adsorption capacity, isotherm nonlinearity, and operating conditions such as the purge-to-feed ratio. Thus, in selecting the best adsorbent and determining the optimal bed layering, all these factors should be accounted for. The sorbent selection criterion is also applicable for more general bulk purification processes such as H₂ PSA. However, care must be taken when weak sorbents are involved because the frozen solid approximation is no longer valid.