Cycling-zone pressure-swing adsorption (CZPSA) and combination PSA−CZPSA cycles have been developed to increase the high-pressure product recovery of the Skarstrom PSA cycle. CZPSA uses a low-pressure feed as purge, whereas the combination PSA−CZPSA cycles use both a low-pressure feed gas and a product gas as purge. Extensive parametric studies were simulated using ADSIM for the model system of dilute benzene in nitrogen on activated carbon to determine how process performance was affected by flow scheme, purge sequence, penetration distance, feed and purge pressures and velocities, and pressurization procedure. For example, a nitrogen product purity of yB,prod/yB,feed = 0.05 and a high-pressure nitrogen recovery of P/F1 = 0.46 were obtained using the Skarstrom cycle, whereas the CZPSA cycle achieved values of yB,prod/yB,feed = 0.18 and P/F1 = 0.58. Air drying with activated alumina and air separation with zeolite 13X were also modeled. The Skarstrom cycle produced dry air with a dew point of −71 °C and P...