Comprehensive Analysis of Single-Particle Growth in Heterogeneous Olefin Polymerization: The Random-Pore Polymeric Flow Model

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• 作者：Vassileios Kanellopoulos ; Georgios Dompazis ; Bill Gustafsson ; and Costas Kiparissides
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2004
• 出版时间：August 18, 2004
• 年：2004
• 卷：43
• 期：17
• 页码：5166 - 5180
• 全文大小：272K
• 年卷期：v.43,no.17(August 18, 2004)
• ISSN：1520-5045

文摘

In the present study, a comprehensive mathematical model is developed to analyze the effectsof initial catalyst size, active site concentration, catalyst morphology (e.g., porosity, extent ofprepolymerization, etc.), and hydrodynamic conditions on the growth and overheating of highlyactive Ziegler-Natta catalyst particles (e.g., fresh or prepolymerized) in gas-phase olefinpolymerization. The generalized Stefan-Maxwell diffusion equation for porous solids is combinedwith the mass balances on the various molecular species (i.e., monomer and "live" and "dead"polymer chains) and the energy conservation equation to predict the temporal-spatial evolutionof temperature and monomer concentration, as well as the polymerization rate in a singlecatalyst/polymer particle. To calculate the equilibrium monomer concentration in the amorphouspolymer phase, the Sanchez-Lacombe equation of state is employed. It is shown that theevolution of the catalyst/particle morphology greatly affects the internal and external mass-and heat-transfer resistances in the particle and, thus, its growth rate and overheating. Theeffect of the hydrodynamic flow conditions on particle overheating is analyzed in detail. It isshown that, depending on the particle size, the concentration of solids in the bulk gas phase,and the dissipation rate of the turbulence kinetic energy of the flow field, the Ranz-Marshallcorrelation can significantly underestimate the value of the heat-transfer coefficient, resultingin an erroneous overestimation of the particle temperature.