Simple Control Scheme for Batch Time Minimization of Exothermic Semibatch Polymerizations

Polymerization processes are typically characterized by strongly exothermic reactions with complicated nonlinear kinetics, and they usually require a very precise temperature control to maintain product uniformity. Polymerization reactors are usually operated with a constant monomer feed, while a cascade of PI controllers manipulates the heating and cooling power to keep the reaction temperature within the tolerance limits. Because a robust operation has to be guaranteed for different products under various disturbing influences, for example, fouling in the reactor, oscillations in the supply of the utilities and feed impurities, the monomers are usually slowly dosed into the reactor, leading to large batch times and limiting the process productivity. In this work, a simple and efficient control scheme for the time optimal operation of exothermic semibatch reactors that can be easily implemented in industry is introduced and evaluated by means of simulations using a well-known industrial benchmark problem. The results show that the new control scheme can shorten the reaction period by more than fifty percent without jeopardizing the quality of the temperature control and performs more robustly than a fully model-based controller that employs a fixed nominal process model.