A Multi‐Scale Modeling Approach for the Prediction of Molecular and Morphological Properties in Multi‐Site Catalyst, Olefin Polymerization Reactors

Abstract

AbstractSummary: In the present study, a comprehensive, multi‐scale, mathematical model is developed for the calculation of the distributed properties of polymer particles in a gas phase, catalytic, olefin polymerization, fluidized bed reactor (FBR). At the molecular level, a generalized multi‐site, Ziegler‐Natta, kinetic scheme is employed to predict the evolution of the polymer molecular properties. To calculate the particle growth, and the spatial monomer and temperature profiles in a particle, the random pore, polymeric flow model (RPPFM) is utilized. The RPPFM is solved together with a dynamic, discretized, particle population balance model, to predict the particle size distribution (PSD) in the bed. The overall molecular weight distribution (MWD) in the bed is then calculated by the weighted sum of all individual polymer particle MWDs. The effects of hydrogen concentration, the distribution of catalyst active sites, and the polymer crystallinity, on the evolution of the PSD and MWD in an ethylene‐propylene copolymerization FBR are thoroughly analyzed. It is also shown that under certain operating conditions, the proposed multi‐scale model can predict the formation of bimodal MWDs, produced in multi‐stage reactor configurations (e.g., the Borstar® Process, Spheripol, etc.).Schematic representation of the multi‐scale model.magnified imageSchematic representation of the multi‐scale model.