Extended two-step method for molecular weight control in a batch polymerization reactor

This paper presents an extended two-step method for the control of the mole cular weight distribution in a batch polymerization reactor. While the conv entional two-step method uses a quadratic form for the instantaneous averag e chain length (IACL), it is proved here that, starting from an arbitrary f orm for the IACL, one can generate a temperature trajectory that would prod uce polymer having desired molecular weight averages at a specified level o f conversion. Furthermore, the form chosen for the IACL exercises influence not only on the temperature trajectory but also on the reaction time requi red. These observations are readily incorporated to develop an extended ver sion of the two-step method in such a way that constraints imposed on the r eactor 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 co nstructing the reactor temperature trajectories bounded by both upper and l ower bounds. It also shows that the reaction time can be reduced effectivel y by the extended two-step method without changing the desired molecular we ight averages and monomer conversion. The trajectory tracking control exper iment proves that the polymer product having desired molecular weight avera ges is indeed obtained with the specified level of monomer conversion at a reduced reaction time.