Summary: Ethylene homopolymerizations were executed with a supported Ind2ZrCl2/MAO catalyst using the so‐called Reactive Bed Preparation method. This RBP method combined a slurry polymerization with a gas phase polymerization with the same polymerizing particles, i.e., a reactive bed. Polymerization kinetics were measured with high accuracy and reproducibility. Slurry and gas phase polymerization rates showed the same dependency on monomer bulk concentration. A complexation model has been proposed to describe the non‐first order polymerization rate‐monomer concentration dependence observed. This model also explains the non‐Arrhenius temperature dependence and the observed pressure dependence of the activation energy of the commonly used polymerization rate model: Rp = kp · C* · M.
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The influence of 1‐hexene is examined on the kinetics of ethylene copolymerization with a metallocene catalyst in gas phase. A model is derived, which is able to describe a large reaction rate increase due to a small amount of incorporated comonomer. This complexation model describes the measured reaction rates for ethylene and 1‐hexene, and the co‐monomer incorporation. Polymer properties were analyzed, such as comonomer weight fraction. The density, melting point, and molecular weight of the produced polymer decreased with increase in 1‐hexene gas concentration. The in situ 1‐hexene sorption is estimated and follows Henry's law, but seems much higher than reported in the literature.
Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1‐hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5‐litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1‐hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1‐hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.
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