Performance of post phthalate Ziegler Natta catalysts with activity limiting agents for propylene gas phase polymerization

Abstract

The performance of isopropyl myristate, methyl trimethylacetate, and dibutyl sebacate (IPM, MTMA, and DBS, respectively) as activity limiting agents (ALA) were evaluated using a post phthalate Ziegler Natta catalyst system for the gas phase polymerization of propylene at different ALA ratios to titanium (ALA/Ti) and different temperatures. ALAs are used to limit catalyst activity and prevent formation of agglomerates in the reactor in cases of thermal runaways. All the ALAs were effective at retarding the catalyst activity at temperatures higher than 90 °C when used with n-propyltrimethoxysilane (N-donor) as an external donor, even at the lowest ALA/Ti. The lowest drop in catalyst activity at the lowest reaction temperature was observed with IPM, while the highest drop was observed with MTMA. Moreover, when used without an external donor the ALAs showed a retarding effect on the catalyst at higher temperatures but to a lesser extent than when an external donor was used. Furthermore, none of the ALAs had a significant impact on the molecular weight averages or distributions, bulk density or fine content. On the other hand, the isotacticity, evaluated in terms of the isotactic pentads and the average meso sequence length (MSL), was found to increase slightly with MTMA and DBS. Finally, it was observed that the reaction between the co-catalyst and the ALA is very crucial in determining the retarding effects of the ALA.