Extended Two-Step Method for Molecular Weight Control in a Batch Polymerization Reactor

Abstract

This paper presents an extended two-step method for the control of the molecular weight distribution in a batch polymerization reactor. While the conventional two-step method uses a quadratic form for the instantaneous average chain length (IACL), it is proved here that, starting from an arbitrary form for the IACL, one can generate a temperature trajectory that would produce polymer having desired molecular weight averages at a specified level of conversion. Furthermore, the form chosen for the IACL exercises influence not only on the temperature trajectory but also on the reaction time required. These observations are readily incorporated to develop an extended version of the two-step method in such a way that constraints imposed on the reactor temperature may be taken into account and also the reaction time may be reduced. Simulation results for the methyl methacrylate polymerization reactor demonstrate that the extended two-step method is very useful for constructing the reactor temperature trajectories bounded by both upper and lower bounds. It also shows that the reaction time can be reduced effectively by the extended two-step method without changing the desired molecular weight averages and monomer conversion. The trajectory tracking control experiment proves that the polymer product having desired molecular weight averages is indeed obtained with the specified level of monomer conversion at a reduced reaction time.