Fluidized bed reactor for catalytic olefin polymerization

Due to the continuous improvement of catalysts and processes, polyolefins have become one of the most important plastics in the world. Polyolefins can be produced at low costs with a variety of end-use properties. Nowadays, the most important propylene polymerization processes are executed in the liquid or the gas phase or a combination of both. In contrast to propylene polymerizations in slurry phase, only a few studies have been published concerning gas or liquid phase polymerization. Especially experimental investigations of gas phase polymerizations at relevant process conditions, i.e. high pressure and temperature, are rare. The most widely established industrial gas phase technology is the fluidized bed reactor operating at 10 – 30 bar. Conversion per pass is kept low, 1-3%, to diminish concentration and temperature gradients in the reactor, which both affect the polymer properties. In 1 to 3 hours, polymer particles with a broad size distribution are obtained. There are no experimental data available in the open literature about the polymerization in such a reactor. The study reported in this thesis is concerned with a modified small-scale fluidized bed reactor to study aspects of the gas phase polymerization of propylene with a heterogeneous metallocene catalyst at conditions resembling those of industrial units as well as strongly deviating conditions. Controlled thermal gradients are provoked as they may be of interest to broaden the molecular weight distribution. To study the polymerization in such a reactor an experimentally validated kinetic model is required. The kinetic model, obtained from experiments at isothermal and isobaric conditions, is used to describe the polymerization at non-isothermal conditions in the fluid bed reactor with related molecular weight distribution of the polymer. Other important aspects that will be studied are electrostatic charging, particle mixing and elutriation of fines.