(118c) Population Balance Application in Rotating Fluidized Bed Polymerization Reactor

Gas phase olefin polymerizations are now widely achieved in fluidized bed reactors. In fluidized bed poly-olefin reactors, small catalyst particles (20-80 µm) are introduced into the bed, and when exposed to the gas flow (monomer), polymerization occurs. At early stage of polymerization, the catalyst particles fragment into a large number of small particles then the polymer particles grow continuously, reaching a typical size of 1000-3000 µm. A successful analysis of this process not only should account for the kinetics of the polymerization but also should include the particles mixing and particle size distribution in the reactor. Rotating fluidized bed reactors are the promising process to have a better control on the particle size distribution, particle separation and increasing the reactor efficiency. Due to the high rotational acceleration (e.g. 14 ?g?) that can be imposed in these kinds of reactors, our preliminary results showed that the amount of throughput, i.e. monomer flow rate, can be increased without worrying of changing the fluidization regime from well mixed condition to slugging, so the production rate and in consequence the polymerization yield will increase. We used computational fluid dynamics (CFD) approach to predict the reactor hydrodynamics. In addition during polymerization process particles of different size and density will form and change as a function of time. This has to be accounted in the CFD calculation to obtain a realistic flow pattern and to gain a better understanding of theses kinds of processes. In this study the population balance approach is used to describe the evolution and growth of the particle size in gas-solid rotating fluidized bed olefin polymerization reactors along with CFD using Fluent program . The discrete method and QMOM (Quadrature Method of Moments) method are used to solve the population balance equations; these are coupled with the conservation equations of mass and momentum for the gas phase and for the solid phase. Simulations have been performed with a) constant particle growth rate and b) variable particle growth rate that is a function of polymerization reaction rate.

Keywords: Olefin polymerization, Population balance, Rotating fluidized bed, Gas/solid flow