Development of Computer Control Systems for Molecular Weight Distribution Control in Polymerization Reactors

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The recent increase in the use of synthetic polymers in various fields has been accompanied by strict demand for higher and higher quality. The quality of polymer products is closely related with the molecular weigh distribution (MWD). This research focused on the computer control probelm of the molecular weight distribution in a free radical polymerization reactor.We developed a method by which we derive the proper poerating temperature pattern and feeding speed of initiator in order to achieve a desired average chain length and polydispersity. The method consists of two stages. In the first stage, the profiles of instantaneous average chain length and instantaneous polydispersity are obtained so as to produce the desired MWD. In the second stage, temperature pattern and feeding speed of initiator are calculated from the obtained profiles of instantaneous average chain length and instantaneous polydispersity.In order to realize the obtained temperature pattern in practice, a sophisticated computer control system is required. The free radical polymerization process is one of the typical chemical processes with the strong nonlinearities. Furthermore batch polymerization reaction is carried out in non-steady state operation. Such time-varying process characteristics and nonlinearity make it difficult for classical PI control to track the obtained temperature pattern. To deal with the strong nonlinearity and time-dependent properties, two brand-new adaptive control schemes (Adaptive Internal Model Control, Adaptive Inferential Control System) and model predictive control scheme are newly developed. Simulation calculation and experiments were performed to validate these control schemes. *