Pressure- and vacuum-swing adsorption processes are challenging to model and difficult to solve rapidly because the system response is a nonlinear function of both the axial and temporal domains with periodic boundary conditions. Extensive computing power is required to solve the conservation equations that describe the temperature, composition, and pressure profiles during operation of an adsorption process. Furthermore, the physics of the source/sink terms in the conservation equations of mass and energy, which relates to the ad/desorption of absorbable species, is not always easily described. These rigorous numerical models are useful for furthering our understanding of these complex processes and are the only methods available for the design of industrial units. However, such complicated numerical simulators for model-based control schemes are not feasible at the current level of computing resources. Simplification of the conservation equations is required to derive a practical mechanistic model for predictive control purposes. In a previous study, Beh and Webley (Adsorpt. Sci. Technol. 2003, in press) have demonstrated that much of the complexity of these processes can be captured through the use of a simple model consisting of a series of coupled tanks which approximates the bulk flows and pressures to a satisfactory degree. In this paper, an extension is made to this model to incorporate the time-varying composition variable. The limitations of this method will be discussed in relation to field operation.