Otimização da transição de grades na polimerização em massa do propeno

Abstract

Polyolefins are the most produced plastics worldwide. The large demand for these materials is related to the high versatility of use in the modern society. Among these materials, polypropylene deserves special attention, being surpassed only by polyethylene in terms of production volumes. In order to meet consumer demands, large scale plants must frequently perform transitions from one grade to another so as to manufacture polypropylene with pre-specified properties. In the majority of the plants, these grade transitions are performed by plant operators using knowledge-based strategies, which can eventually cause long transition times and large amounts of off-specification product. For this reason, this dissertation formulates and solves a dynamic optimization problem regarding grade transitions in bulk propylene polymerizations, in order to find optimal trajectories of the manipulated variables which lead to minimization of transition time. The results obtained show that the optimal trajectories result in significant reduction of transition times. Furthermore, it is shown that the effects of additives and hydrogen on catalyst activity also affect the shape of the optimal trajectories. Finally, the transitions were investigated in terms of safety of operation, being shown that a compromise between the implemented actions and process safety should be pursued.