On the reactivity of supported zirconium organic catalysts in the polymerization of ethylene

Abstract

The ethylene polymerization with tetrabenzyl zirconium displays a higher concentration of active centres on catalysts obtained by supporting of the organometallic compound on alumina o r silica-alumina carriers than by activation without supporting. The active centres of the supported catalysts possess different polymerization reactivity. At the beginning of the polymerization in the presence of monomer, these active centres are formed from a small amount of the stable surface compounds originated in the carrier impregnation. The maximum polymerization rate depends on the pretreatment, the loading and the porosity of the carrier. The more active these centres, the quicker they lose their activity. A relation was found between a chemical deactivation reaction and the concentration of the hydroxyl groups remaining on the catalyst after impregnation. Addition of hydrogen o r butyllithium can change the polymerization in a different manner. The addition of butyllithium causes an increase in the number and the reactivity of the active centres and a suppression of the chemical deactivation.