Heat and mass transfer phenomena during the early growth of a catalyst particle in gas-phase olefin polymerization : the effect of prepolymerization temperature and time
| Autor: | Costas Kiparissides, H. Yiannoulakis, V. Dimos, A. Yiagopoulos |
|---|---|
| Rok vydání: | 2001 |
| Předmět: |
chemistry.chemical_classification
Convection Applied Mathematics General Chemical Engineering General Chemistry Polymer Industrial and Manufacturing Engineering Catalysis chemistry.chemical_compound Monomer chemistry Chemical engineering Polymerization Mass transfer Heat transfer Physical chemistry Overheating (electricity) |
| Zdroj: | Chemical Engineering Science. 56:3979-3995 |
| ISSN: | 0009-2509 |
| DOI: | 10.1016/s0009-2509(01)00071-9 |
| Popis: | A comprehensive mathematical particle growth model, accounting for both external and internal mass and heat transfer limitations appearing during the early growth of highly active Ziegler–Natta catalysts in gas-phase ole'n polymerizations, is developed. Based on the well-known “Polymeric Flow Model” approximation for particle growth [see Schmeal and Street (A.I.Ch.E. Journal 17 (1971) 1188) and Galvan and Tirrell (Chemical Engineering Science 41 (1986) 2385)], dynamic mass and energy balances, including both di*usional and convective mass and heat Duxes, are derived to describe the spatial-time evolution of monomer concentration and temperature in a growing polymer particle. To calculate the equilibrium monomer concentration in the amorphous polymer phase, the Sanchez–Lacombe (Macromolecules 11 (1978) 1145) equation of state is employed. The e*ect of e*ective monomer di*usivity, initial catalyst size and catalyst activity on the overall particle growth rate and particle overheating are analyzed in detail. It is shown that, during the early growth of highly active catalyst particles (e.g., polymer production rates ? 15;000 g=gcat h), internal and external mass and heat transfer resistances can become signi'cant, leading to catastrophic particle burn. In an attempt to reduce overheating of highly active catalyst particles, a prepolymerization step is introduced to control catalyst activity and, thus, particle morphology during the early growth of catalyst particles. The e*ect of prepolymerization time and temperature on the overall polymerization rate and particle overheating is investigated. It is demonstrated that by proper selection of prepolymerization temperature and time, particle overheating can signi'cantly be reduced while the polymerization rate is enhanced. ? 2001 Elsevier Science Ltd. All rights reserved. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect