Integrated steps in pressure swing adsorption cycles

Abstract

Conventional pressure swing adsorption (PSA) cycles consist of discrete steps in which pressurization, feed, blowdown and purge occur. When certain steps are partially or totally integrated, process logic and equipment may be simplified and/or superior performance may be possible. A preliminary study of combinations of the pressurization and feed steps and the feed and blowdown steps has been performed. A simple equilibrium-based theory has been extended to accomodate such combinations. Results of a few PSA experiments have verified the applicability of the theory. Recovery of the less strongly adsorbed component is predicted by the theory, and effects of pressures, adsorbent-adsorbate interactions, and feed composition have been studied. For difficult separations, i.e. those in which the feed is heavily contaminated with the more strongly adsorbed component or in which the adsorbent is only slightly selective, recovery of the less strongly adsorbed component may be increased dramatically by integrating the feed and blowdown steps. Conversely, for easy separations product recovery is only slightly reduced by combining the pressurization and feed steps, which can be accomplished in a simple PSA process.