Comparison of Mg-ethoxide based Ziegler Natta catalysts using different internal donors employed for ethylene polymerization

Abstract

The effect of two types internal electron donors (IDs) on Mg-ethoxide based ZN catalysts employed for ethylene polymerization, was investigated using three similar catalysts with different IDs. P-cat (containing di isobutyl phthalate), S-cat (containing tetra ethoxy silane) at a constant molar ratio ID/Mg = 0.1, and N-cat (with no electron donor) were analyzed by FTIR, XRD, SEM, PSD, and BET. Some of available data of an Industrial catalyst (I-cat) were added to compare. FT-IR spectroscopy in transmission mode confirmed the presence of each electron donor in the catalyst. X-ray patterns of the catalysts showed that the disordered structure of δ-MgCl2 was formed in each catalyst and IDs in this manner do not influence the crystallinity of the support. This study showed that the use of IDs has a great influence on the resulting catalyst morphology (particle size and porosity) so that S-cat has the lower particle size and higher porosity but P-cat has the highest particle size and the lowest porosity. Ethylene polymerization was performed using catalysts under the same set of conditions (time, temperature, and Al/Ti) and in the presence of high pressure hydrogen. Then to better compare, an industrial catalyst (I-cat) was also used in this condition and the result were compared by the synthesized catalysts. The activity of catalysts with various kinds of IDs is in the following order: S-cat > N-cat > I-cat > P-cat. To better comparison, the kinetic polymerization rate of catalysts was fitted by a simple model and showed that the P-cat activated more slowly than others, I-cat has the fasten activation and deactivation rate, and S-cat has the highest propagation rate constant. IDs can change the active site behavior against hydrogen by affecting on the chain lengths measured by MFR value and molecular weight distribution. DSC analysis of the polymers showed the IDs can change the crystalline content of homo polyethylene. So that polymer obtained from P-cat and N-cat have more crystalline ( $$\approx$$ 80%) but polymer from S-cat has lower crystalline content ( $$\approx$$ 65%). Polymers with higher crystallinity also have lower molecular weight value. The polymer Bulk density as an important industrial parameter are presented for the catalysts.