A comprehensive model for the micro and meso-scale level olefin polymerization: framework and predictions

A fundamental understanding of the heterogeneous olefin polymerization process is critical for imparting desired properties to the final polymer product. In this work, we have developed a comprehensive model integrating the meso-scale level intraparticle resistances to mass and heat transfer as well as the micro-scale level kinetics. The model formulation is based on the combination of the polymer flow model with the intrinsic kinetic model derived using the method of moments approach. The model is employed to study the effect of varying the mass transfer and kinetic parameters on the monomer concentration and temperature profiles inside the growing polymer macro-particle and the subsequent implications on the catalyst activity, polymer molecular weights and the polydispersity index (PDI). The simulation results showed that the steeper monomer concentration gradients in the polymer macro-particle arose on decrease of the bulk diffusivity (D-b) and increase of the number of active sites. The model also predicted the interdependence between the radial monomer concentration and temperature profiles. Further, with appropriate choice of Db, the number of active catalyst sites, initial catalyst active site concentration and kinetic rate constants, the model predicted the catalyst activity exceeding 100kg/g cat.hr and PDI values higher than 2. We showed that the model is capable of predicting the experimental reported polymer product properties for Ziegler-Natta, hybrid Ziegler-Natta/metallocene and supported metallocene catalyst systems.