Continuous Solution Polymerization of Ethylene Using Metallocene Catalyst System, Zirconocene Dichloride/Methylaluminoxane/Trimethylaluminum

A high-pressure, high-temperature continuous stirred-tank reactor (CSTR) system having approximately an ideal residence time distribution (RTD) has been set up for the polymerization of olefins utilizing metallocene catalysts. Preliminary experiments of ethylene polymerized with the metallocene catalyst system zirconocene dichloride (Cp2ZrCl2)/modified-methylaluminoxane (MMAO)/trimethylaluminum (TMA) in toluene at 1500 psig have been carried out. The reactor system showed good control over temperature, pressure, and ethylene feed rate. The steady state was obtained after four mean residence times (4 τ's). With increasing Cp2ZrCl2 concentration, the molecular weight (MW) of polyethylene (PE) decreased and the catalyst activity (kg of PE/([ethylene]·g of catalyst)) increased. With increasing temperature between 140 and 200 °C, the MW of PE decreased and molecular weight distribution (MWD) polydispersity increased. PEs with weight-average molecular weight (M w) 18 000−52 000 were obtained. The catalyst activity decreased with increasing temperature with an apparent activation energy of −93 kJ/mol. The deactivation of the catalyst is first-order with the rate constant k d = 2.1 × 10-3 s-1 at 140 °C. The rate constants of propagation and β-scission at 140 °C are k p = 5 × 103 (M·s)-1 and k tr, β = 3 s-1.