Mathematical modeling of the adsorptive separation of multicomponent gaseous mixtures

A general dynamic model describing the adsorptive separation of multicomponent gaseous mixtures is developed in this study. The dusty-gas model and D'Arcy's law are used to describe the diffusive and viscous mass transport in the adsorbing bed, respectively, and the local equilibrium assumption or the linear driving force approximation are used for the uptake rate. The versatility of the developed model is demonstrated by applying it to separation of binary, ternary and quaternary mixtures by pressure swing adsorption (PSA). The relative importance of the diffusive (bulk and Knudsen) and viscous mass transport and the effects of the different uptake rate representations are also investigated. For the PSA process, it is found that viscous transport dominates in the adsorbing bed and the inclusion of other modes of transport in the model equations has practically no effect on the solution. However, for dynamic processes occurring in porous media of smaller pore sizes (macroporous membranes, for instance) both the viscous and the diffusive modes of transport must be included in the overall model to predict the system behavior correctly. The model with only viscous transport in bed and the linear driving force approximation for the uptake rate is the recommended option for modeling PSA operations, provided that the LDF approximation is applicable, since it is easier to handle numerically and reduces to the equilibrium model in the limiting case of large adsorption rate constants. Copyright (C) 1996 Elsevier Science Ltd