The Borstar technology contains a loop reactor and a fluidized bed reactor connecting in series. Aiming at minimizing the grade transition time and the quantity of off-specification product

a grade transition model involving catalyst changeover was presented for this process. Meanwhile

the models of instantaneous and cumulative polyethylene properties

including melt index and polymer density in each reactor

were presented for the tanks-in-series process involving catalyst changeover. The results showed that if grade transition involved catalyst changeover

the recommended optimal strategy was to feed new catalyst step by step. Further more

it is necessary to consider the respective demands for manipulated variable profiles by old and new catalysts and the effect of old catalyst mass fraction on resin properties in each reactor. In this way

the transition time was remarkably reduced

the sharp fluctuation of manipulated variables was restrained and the profiles of polymer properties were smoothed up.