Evaluation of catalyst leaching in silica supported zirconocene alumino hydride catalysts

Zirconocene aluminohydride complexes (e.g. nBuCp2ZrH3AlH2) afford higher MW polyethylene at significantly higher activity than their zirconocene dichloride counterparts (nBuCp2ZrCl2) when activated by methylaluminoxane (MAO). In this work, supported catalysts with different Al:Zr ratios on SiO2, modified with MAO were prepared, and evaluated for their tendency towards leaching in ethylene polymerization, using additional MAO or other alkylaluminum compounds. The extent of catalyst leaching was estimated by comparing kinetic data of filtered versus unfiltered catalysts during ethylene polymerization. Polydispersities and molecular weights of the HDPE obtained using filtered versus unfiltered catalysts were also compared under similar polymerization conditions. Polyethylene morphologies obtained in homogeneous and heterogeneous phase were compared by SEM. Bulk densities of the HDPE were evaluated and related to the leaching in the polymerizations. Effect of the zirconocene aluminohydride leaching in the morphology of HDPE obtained in slurry.