ABSTRACT

Gas phase propylene polymerization using fluidized bed reactor is one of the most widely accepted and commercially used processes for manufacturing of polypropylene (PP). Often small part of reactant propylene is fed to the reactor in liquid form to enhance heat removal rates and capacity. Several fluid dynamic issues like mixing, heat and mass transfer and particle agglomeration and de-fluidization interact with polymerization reactions in this reactor. It is therefore essential to study the fluidization and the reaction engineering aspects simultaneously for proper understanding and optimization of these reactors. A multilevel program was therefore, devised that included studying hydrodynamics of propylene fluidization and developing a comprehensive model for PP fluidized bed reactors. This talk summarizes progress made so far.

Gas phase propylene polymerization using fluidized bed reactor is one of the most widely accepted and commercially used processes for manufacturing of polypropylene (PP). Often small part of reactant propylene is fed to the reactor in liquid form to enhance heat removal rates and capacity. Several fluid dynamic issues like mixing, heat and mass transfer and particle agglomeration and de-fluidization interact with polymerization reactions in this reactor. It is therefore essential to study the fluidization and the reaction engineering aspects simultaneously for proper understanding and optimization of these reactors. A multilevel program was therefore, devised that included studying hydrodynamics of propylene fluidization and developing a comprehensive model for PP fluidized bed reactors. This talk summarizes progress made so far. Experimental and computational study of single jet fluidized bed hydrodynamics is described. The Eulerian-Eulerian CFD model for predicting the hydrodynamics is developed. The results of the model are compared with experimental measurements of bubble size, bubble velocities etc. Since the progress in understanding PP fluidization is still not adequate for incorporating polymerization reactions in CFD model, a separate reaction engineering model for simulating fluidized bed polymerization reactors is developed. The model is capable of simulating the performance of both normal and super-condensed mode of operations. Unlike previously published models, the present model simultaneously predicts both polymer properties as well as particle size distribution. The model was used to understand influence of operating parameters on polymer properties and particle size distribution. Comparison is also made between the two operating modes (normal and super-condensed). The developed framework is useful for simulating multi-monomer, multi-site Ziegler-Natta type olefin fluidized bed polymerization reactors. It is hoped that eventually CFD model and reaction engineering model will communicate with each other to yield a comprehensive tool for optimizing industrial reactors.