Modelling of a semibatch polypropylene slurry reactor

Abstract

Our previous polymeric multigrain model (PMGM) for the slurry polymerization of propylene is extended to account for the presence of gas-liquid mass transfer resistance and the gradual build-up of the monomer concentration in the liquid medium in an isothermal, semibatch reactor. Results are obtained for the situation where one starts with a pure n-heptane liquid medium. The Soave-Redlich-Kwong (SRK) equation is used for predicting gas-liquid equilibrium, and appropriate correlations are used to estimate mass transfer coefficients and interfacial areas for both the gas-liquid and liquid-solid interfaces. It is found that the initial transient in the monomer concentration leads to important effects on the rate of polymerization, the mean degree of polymerization (D̅P̅) and the mean polydispersity index (Q^-) and one must account for these phenomena. The effects of changing the various parameters are also studied. It is found that products with polydispersities higher than about 2.0 can be formed because of the presence of multiple activity catalyst sites and not because of diffusional limitations, at least for the parameters studied.