Product quality improvement in a high-temperature free-radical polymerization reactor

In response to the strict environmental regulations on volatile organic solvents in paints and coatings, high-temperature solution polymerization has increasingly been used to manufacture low-molecular-weight, acrylic polymer resins for automotive coatings. Free-radical polymerization of acrylate and methacrylate monomers at high-temperatures (140-200 °C) involves a number of side reactions that have a marked effect on the quality of the polymer product. These reactions are not significant at low temperatures. We have studied kinetics of liquid-phase, high-temperature, free-radical, n-butyl acrylate (nBA), polymerization reactions, leading to the development of a mathematical model for the polymerization. The model is capable of predicting the polymer molecular weight distribution and several functionality indices very accurately. For a semi-batch nBA polymerization reactor, a multi-objective optimization problem is solved to calculate optimal feed (initiator, solvent and monomer) flow-rate and reactor temperature profiles. These profiles minimize total amount of initiator fed to the reactor, polydispersity index of the final product, and batch time (t_f), subject to (a) the reactor dynamics, (b) a monomer conversion of above 0.99 at t_f, and (c) a polymer weight-average molecular weight of 8,000 at t_f. The results show that high-quality polymers can be produced at lower operating costs by minimizing initiator usage and batch time.