EFFECTS OF MAIN AND CROSS TERM DIFFUSIVITIES ON KINETIC SEPARATIONS BY PRESSURE SWING ADSORPTION

A simple solution to the pressure swing adsorption (PSA) cyclic steady state for a kinetically controlled two-step isothermal process is der ived. This solution uses the linear driving force (LDF) model for diff usion rates, non-linear mixed gas isotherms and is general for any num ber of adsorbing components. The solution permits the calculation of t he maximum possible purity for simple PSA cycles. The LDF model is als o modified for binary diffusion by including main and diagonal terms o f the diffusivities. The concentration dependence of diffusivity and c oupling or interference introduced by the addition of these terms affe cts PSA performance predictions of purity, which improves, and recover y, which diminishes. At fixed low pressures, the reduction in recovery and productivity on inclusion of cross terms may be related to a phen omenon of counter-diffusion. (C) 1998 Elsevier Science Ltd. All rights reserved.