Characterization of the nature of chemical species of heterogeneous Ziegler-Natta catalysts for the production of HDPE

Highly active Ziegler-Natta (ZN) catalytic systems are used in slurry polymerization technology for high density polyethylene (HDPE) production. The nature of the active sites presented in the ZN catalyst influences the polyethylene properties. In this work, Ziegler-Natta heterogeneous supported catalysts were synthesized from TiCl4 and magnesium ethylate with MgCl2 in situ generation. It was observed that annealing time and temperature significantly influenced the catalytic activity. The non-annealed catalyst (ZNST) and the annealed catalyst (ZNT) presented the highest and the lowest catalyst activity, respectively. The ZNST and ZNT catalysts are amorphous solids and both have approximately the same surface area and particle size. By the catalyst chemical compositions, determined through different techniques, it was possible to conclude that thermal treatment (annealing) increases the Ti percentage and titanoxane sites in the catalyst. A structure was proposed for the titanoxane site different of that obtained in the MgCl2 chloride addition using TiCl4. ZNT catalyst with titanoxane active sites produces HDPE with high molecular weight while ZNST has different active sites, including titanates, and produces HDPE with low molecular weight.