Effects of titanium content in ziegler-natta catalyst on the reducibility of triethylaluminum cocatalyst

Abstract

The Ziegler-Natta catalytic system for olefin polymerization comprises the TiCl4 precursor adsorbed on MgCl2 support and reacted with an alkylating agent to generate active sites. The reduction of TiCl4 valence plays a crucial role in the formation of Ti3+ and Ti2+ active species for ethylene polymerization whereas only Ti3+ active for propylene polymerization. Thus, the reducibility of Ti-based catalyst using AlEt3 cocatalyst was studied during ethylene and propylene polymerization which has not been previously studied yet. For this study, the effect of Ti content on the reducibility was considered through the changing of catalytic activity with the increase of AlEt3 concentration. The results indicated that Adduct High catalyst with high Ti content shows the large-size clustered Ti species and the blockage of the active site on the surface leading to Ti species is hard reduced by low AlEt3 due to the steric hindrance of the formed complex, and then the complete reduction of the buried Ti occurs at the excessive AlEt3 causing the reduction is evidently decreased. Moreover, the weak binding interaction of Ti-Cl stretching in TiCl4 strongly adsorbed on (110) MgCl2 by Grignard and Ethoxide methods affects the easier exchanging of Cl atom and ethyl group results in more sensitive to the reduction of Ti species by AlEt3 cocatalyst. Therefore, the reducibility depends on the Ti cluster and the interaction of TiCl4 on the surface of catalyst.