A Study of the Gas Phase Polymerization of Propylene: The Impact of Catalyst Treatment, Injection Conditions and the Presence of Alkanes on Polymerization and Polymer Properties

Abstract

Propylene is polymerized in the gas phase in a 2.5 L semibatch reactor using a commercially available supported Ziegler–Natta (ZN) catalyst. The mode of injection (wet vs dry), the impact of including a prepolymerization step, and of changing the composition of the gas phase are systematically investigated in terms of their influence on the instantaneous polymerization rate and polymer properties. Prepolymerization is observed to enhance the polymerization activity. This is attributed, at least in part, to the effect of prepolymerization step in decreasing local particle overheating in the initial instants of reaction. Furthermore, a noticeable decrease of the catalyst activity is observed when the catalyst is injected dry as compared to when is first wetted with paraffinic oil before being charged to the reactor. Adding a hydrocarbon to the catalyst can eventually reduce the risk of overheating during the critical initial instants of polymerization since it increases resistance of the diffusion of monomer to the active sites, acting as an “in situ” prepolymerization. Methods that increased the productivity also lead to an improvement of the powder morphology. Finally, it is found that adding vaporized iso‐hexane to the gas phase provokes an increase in the instantaneous polymerization rate, and increases the impact of hydrogen on the rate and molecular weight. image