In this work, we consider a generic class of process networks that feature large material recycle streams and in which impurities are present, and are removed by a small purge stream. We show that such networks exhibit a dynamic behavior featuring three time scales. Employing a nested application of singular perturbation arguments, we propose a method for deriving non-linear, non-stiff, reduced order models for the dynamics in each time scale. Subsequently, we propose a hierarchical controller design framework that takes advantage of the identified time scale multiplicity. The developed concepts are exemplified through a case study on the dynamics and control of a reactor-single-stage separator network core, and illustrative numerical simulation results are provided. (c) 2006 Elsevier Ltd. All rights reserved.