Ethylene Polymerization with Supported Metallocene Catalysts: Predictions using a Cube-Cell Model

MARIO CHIOVETTA; DIANA ESTENOZ

Río de Janeiro (Brasil)

Congreso; 2nd Mercosur Congress on Chemical Enginnering/4th Mercosur Congress on Process Systems Engineering – ENPROMER 2005; 2005

In ethylene polymerization, a typical slurry contains support-catalyst-polymer particles composed of millions of microparticles arranged in cells, originally displayed in a cube pattern. Micro-grains usually have silica nuclei covered with a metallocene-MAO layer. These active sites are exposed to varying reaction conditions during polymerization. Changing particle morphology and kinetic-diffusion effects are critical in establishing monomer availability at said active sites. The complex phenomena taking place are studied using a mathematical model employed to generate a set of predictions. The system considered is one with particles polymerizing ethylene in a toluene-slurry CSTR under various operating conditions. The model includes a detailed description of each microparticle cell and of its evolution during particle residence time in the reactor. The simulation data are used to evaluate the micro- and macroparticle behavior and to explore catalyst activities and monomer availabilities under several reactor conditions. Kinetic constants and concentrations range from typical laboratory, reference values up to 10 times these figures. Reactor-slurry temperatures are varied between 323 and 353 K, with particle Reynolds-numbers changing in a 1 to 10 relative scale. Using the model, density profiles inside the support-catalyst-polymer particle are followed along time. Their interaction with transport and reaction phenomena is studied. Increasing catalyst-activity alone is found not to produce proportional raises in yield. High catalyst-activity usually generate monomer depletion at inner cells thus decreasing local polymer-production.