Behavior of Active Sites in a Changing, Supported Metallocene Catalyst Particle: Modeling Monomer Transport and Kinetics
✍ Scribed by Mario G. Chiovetta; Diana A. Estenoz
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 300 KB
- Volume
- 289
- Category
- Article
- ISSN
- 1438-7492
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Summary: Support‐catalyst‐polymer particles composed of millions of microparticles arranged in cells and having silica nuclei covered with metallocene‐methyl alumoxane (MAO) active sites are studied to analyze cell participation during polymerization. Main variables are the changing particle morphology and the kinetic‐diffusion effects determining local monomer availability during residence time. The phenomena were studied by means of a mathematical model used to produce a set of predictions for particles polymerizing ethylene in a toluene slurry continuous stirred tank reactor (CSTR) under various operating conditions. This information is employed to predict the micro‐ and macroparticle behavior in situations designed to explore catalyst activities, monomer availabilities and reactor conditions. Kinetic constants and concentrations range from reference values up to 6 times these figures, with reactor temperatures between 323 and 353 K and particle Reynolds numbers on a 1 to 10 relative scale. Heat transfer and temperature elevation during polymerization are predicted, with no relevant overheating observed. Morphology changes, in the form of density profiles inside the support‐catalyst‐polymer particle, are monitored with time, and their interaction with transport and reaction phenomena analyzed. Increasing catalyst activity alone may not produce proportional raises in yield; it appears more efficient to improve the monomer availability instead. High catalyst activity may produce monomer depletion at inner cells delaying their fragmentation and decreasing local polymer‐production.
Cell density vs. time for cells located at the exterior, at the center and at half the radius of the macroparticle.
magnified imageCell density vs. time for cells located at the exterior, at the center and at half the radius of the macroparticle.