Experiment And Simulation Of Propylene Polymerization In Multizone Circulating Reactor

Innovative polymerization process which can improve the performance of polypropylene and broaden its application range is the focus of industry and academia's attention. Multizone circulating reactor is one of the newest propylene gas phase polymerization reactors that has simple structure, wide operating conditions, lower production costs and superior product performance. But the foreign kept the technology of this process secret and the current open literature about it were rarely reported.In this paper, polymerization in multizone circulating reactor was simulated by multi-stage sequential polymerization experiments and the effect of switching frequency on the catalyst activity, mechanical properties and polymer composition were studied. The experiment results showed that increasing the switching frequency could not only improve polymerization activity, but also enhance the polymer's mechanical properties. Meanwhile, the results from DSC,13C-NMR,GPC showed that switching frequency could control the polymer chain structure and the block copolymer was the most sensitive to it. The ethylene-propylene random copolymer dispersed phase size became smaller and its size distribution became more uniform in the impact sample fracture with the switching frequency increased.Based on this reactor model, parameters sensitivity analysis were performed for the effects of switch frequency, reaction time and hydrogen concentration on polymer properties. The simulation results showed that reaction time ratio and hydrogen concentration could change the polymer average molecular weight and molecular weight distribution obviously, but switching frequency could not. The polymer average molecular weight and molecular weight distribution is the most sensitive to hydrogen concentration.Besides, with propylene homopolymerization kinetics mechanism, the multizone circulating reactor model had been developed based on the assumption that riser model and downer model are plug-flow model, in order to investigate the effect of particle flow characteristics on the polymerization process. Moreover, the effect of operating parameters and reactor parameters on the monomer concentration throughout the reactor and polypropylene average molecular weight were investigated. The results from the proposed process model showed that recycling ratio, catalyst feed rate, reactor height and reactor diameter affected the polymer average molecular weight and molecular weight distribution by changing particles residence time and the active site concentration. Changing operating conditions in downer can influence polymer property more obviously than that in riser.