Ethylene polymerization in gas phase and slurry phase with metallocene (n-BuCp)2ZrCl2 supported on mesoporous molecular sieves

Abstract

Ethylene homopolymerization and ethylene/a-olefin copolymerization were studied in the gas phase and in slurries using mesoporous molecular sieves impregnated with methylaluminoxane and (n-BuCp)2ZrCl2; the mesoporous molecular sieves had pore diameters of 2.5 to 25 nm. Activities were measured for these catalysts at ethylene pressures of 200 psia and 50 to 100 degree celcius for gas-phase operation and, at total pressures of 115 psia and 50 to 80 ํC for slurry operation. Gas-phase copolymerizations of ethylene/1-hexene at various 1-hexene concentrations were done at 70 ํC and slurry copolymerizations of ethylene and 1-hexene, 1-octene and 1-decene, were done by adding 3.0 mL of the a-olefin to 30 mL of the heptane reaction medium. Polymerization activities and the shape of the activity profiles were a function of the support pore size for both gas-phase and slurry systems. Maximum activities for gas-phase operation occurred for support pore sizes of 2.6 to 5.8nm; the maximum activities for slurry operation occurred for support pore sizes of 2.5 and 2.6 nm. Temperature rising elution fractionation, differential scanning calorimetry, scanning electron microscopy and size exclusion chromatography were used to characterize the products. The results showed that the catalysts contained multiple types of catalytic sites; the types and concentration of these sites were a strong function of the support pore size and reaction time. Ethylene polymerization rates and 1-hexene incorporation rates were strong functions of support pore size, 1-hexene concentration and reaction temperature. Large-pored catalysts had higher 1-hexene incorporation rates than small-pored catalysts for gas-phase polymerization, and the 1-hexene incorporation rate was a function of reaction time. For slurry operation, no clear trends in a-olefin incorporation as a function of pore size was observed.