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A numerical simulation has been developed for a simple two-bed PSA system in which kinetic effects and changes in flow rate due to adsorption are significant. The model is therefore more general than most previous models for the PSA cycle. The model equations are solved by the method of double collocation. When applied to air separation on a carbon molecular sieve, using independently measured kinetic and equilibrium parameters, the predicted performance appears consistent with available performance data for a commercial unit. N. S. RAGHAVAN and D. M. RUTHVEN Department of Chemical EnglneerlngUniversity of New Brunswick Fredericton, N.B., Canada SCOPEIn many PSA separation processes (e.g., air separation on a carbon molecular sieve) kinetic effects are important and the volume of gas adsorbed is significant. Under these circumstances the assumptions which have been traditionally employed in modeling of the PSA cycle (adsorption equilibrium, constant velocity) are no longer valid. In the present analysis a more general mathematical model for simulation of a PSA cycle is developed without recourse to either of these simplifying assumptions. This model, which should be directly applicable to air separation as well as to other bulk PSA separations, is solved numerically by the method of double collocation using parameter values typical of air separation on a carbon molecular sieve. CONCLUSIONS AND SIGNIFICANCEThe model appears to provide a reasonable representation of the behavior of a two-bed PSA adsorption system. Using independently measured kinetic and equilibrium parameters the predicted performance is comparable with the reported performance of the commercial units, suggesting that the basic assumptions as well as the approximations used to represent the blowdown and repressurization steps are reasonable. The method of double collocation is shown to be a useful tool for solving complicated model equations for such systems, and the approach delineated here seems capable of being extended to the simulation of the more complicated PSA cycles commonly used in commercial processes. Although in the present analysis the equilibrium relationships are assumed to be linear, such an assumption is not critical and the same general method may be applied to a nonlinear system without any significant increase in complexity. Although the analysis has been developed in relation to air separation on a carbon molecular sieve, the simulation is in principle applicable to other PSA bulk separations where kinetic effects and volume changes are significant. INTRODUCTIONand purge to feed ratio. The effects of these variables are coupled so that it is difficult to arrive at an optimal design simply by intuition and empiricism; a reliable mathematical simulation of the system is therefore required. Because of the transient nature of the process and the complexity of the equations describing the system dynamics, it has not hitherto been possible to obtain a general mathematical simulation. Various simplifying assump-