Particle segregation and agglomeration in heterogeneously catalyzed olefin polymerization reactors.

摘要

This dissertation presents the analysis of the behaviors of polyolefin particles in a gas phase fluidized bed olefin polymerization reactor using heterogeneous Ziegler-Natta or metallocene catalyst systems. Although polymer particles in a fluidized bed are assumed to be well mixed and almost isothermal reaction conditions prevail, certain heterogeneity in the polymer properties is often observed depending upon the size of polymer particles. For example, the particle size distribution of polymers withdrawn from the bottom part of the fluidized bed is not always same as that in the upper part of the reactor. It is also possible that polymer particles in the reactor may have different temperatures causing irregular particle growth, particle agglomeration and sheeting. Severe particle agglomeration and segregation may also lead to an unstable fluidization.; In this work, a multi-compartment population balance model is developed to model the particle segregation and agglomeration phenomena in a fluidized bed olefin polymerization reactor. The effects of different fluidization conditions on the particle size distribution in the reactor and polymer properties are investigated through model simulations. It is shown that the empirical size selection factor can be predicted using the model developed in this work. A simple analysis has also been carried out to show that the electrostatic effect can cause the onset of particle agglomeration and sintering in a fluidized bed polymerization reactor.; The effect of catalyst particle size and deactivation on polymer properties and catalytic activity were also discussed using a particle growth model. It is shown that for the catalysts of certain activity characteristics, the overall catalyst productivity can be optimized by controlling the active metal loading and feed catalyst particle size distribution.