A model for the design of a PSA system in which hydrogen is recovered is proposed. It is found that mass transfer between the gas phase and adsorbent phase during blow-down can be omitted, while this is not the case during the repressurization step. The change in interstitial gas velocity during adsorption and desorption also needs to be considered. A basis design for a two-column system is presented and compared to results obtained by using a short-cut method. It is concluded that rigorous models are needed in order to determine exactly the important effects of interactions among the components in the gas mixture and the interactions between the different steps in the cycle.