Control Strategy and Comparison of Tuning Methods for Continuous Lactide Ring-Opening Polymerization

Polylactic acid is industrially produced by ring-opening polymerization of lactide. This reaction is extremely sensitive to the level of monomer contaminants, thus posing some challenges for the operability of continuous processes. A control strategy was designed and the corresponding controller parameters were determined using gProms simulations by applying the Ziegler-Nichols, Tyreus-Luyben, and Cohen-Coon methods. The simulation results show that the proposed strategy is effective in restoring the targeted process conditions after a sudden change in the level of contaminants, with the Cohen-Coon controller providing the best results. Additionally, the simulations demonstrate that the use of automatic process control significantly reduces the pressure rise along the reactors after a feed disturbance, thus ensuring safer plant operation.