Deactivation of oxide-supported titanium catalysts in the ethylene polymerization process

Abstract

The kinetics of ethylene polymerization initiated with a titanium-based catalyst supported on alumina was studied. The termination rate constants for both slurry and gas-phase polymerization processes were obtained. The portions of stable and unstable active sites in the titanium catalyst were calculated. High concentrations of an organoaluminium co-catalyst were found to have no effect on the polymerization rate over the supported titanium catalyst. The kinetic results were also correlated with the morphology of the support. A good correlation was found between the polymerization rate and the ratio of pore radius to volume of the catalyst support. The results suggest, that the reduction of the active Ti-species with the Al-alkyl co-catalyst is not the main reason of the deactivation of the supported titanium catalyst, in contrast to its unsupported equivalent. This undesirable process can be attributed to diffusion limitations resulting from encapsulating the active sites located in deep and narrow pores of the support by the polyethylene produced.