Control-relevant scheduling of polymer grade transitions

Grade transition is a critical step in the operation of a polymerization reactor. The nonlinear input-output behavior of the reactor can lead to severe differences in the dynamic response of different grade transitions. These differences are analyzed tinder the assumption that the polymerization reactor is regulated by a linear controller. The cost of each transition is calculated based on a linear first-order model of the transition. Robust control theory is employed to propose screening tools and heuristics for the identification of the transitions that are difficult from an operational perspective in the presence of uncertainty. The dependence of the transition cost on the gain and the time constant of various transitions is analyzed to determine the effect of process nonlinearities on the scheduling problem. This approach is demonstrated on the problem of scheduling grade transitions in an isothermal methyl methacrylate polymerization reactor.