“A semi-batch reaction system for the slurry homopolymerization of propylene using metallocene catalysts: Effect of process conditions and a kinetic model.”

摘要

An olefin reaction polymerization facility is described in detail and used to study the performance of metallocene catalysts in propylene homopolymerization. Experiments using racethylenebis( 1-indenyl)zirconium dichloride (Brintzinger’s catalyst, a relatively low activity catalytic species) and rac-Si(CH3)2-(2-CH3-4-Ph-Ind)2 zirconium dichloride (Spaleck’s catalyst, high activity catalytic species) in slurry polymerization were performed. These experiments determined the effects of process conditions on the final characteristics of the polypropylenes produced. A set of experiments using Brintzinger’s catalyst in the semi-batch reaction system demonstrated that rapid agitation is important to avoid mass transfer limitations. A critical agitation speed was calculated to ensure effective dispersion of monomer gas in the liquid phase, and a direct correlation between agitation speed and polypropylene production and molecular weight was found. Using Spaleck’s catalyst and changing the reaction temperature and monomer pressure, it was possible to generate, in a controlled fashion, highly isotactactic polypropylene with 100,000 – 600,000 weight average molecular weight. Using the semi-batch reactor and Britzinger’s catalyst as catalytic species, we measured the rate of propylene reaction in slurry polymerizations at a fixed monomer pressure and different reaction temperatures. A kinetic model for the homopolymerization of propylene by single site catalysts is proposed, and such model is solved by the method of moments. Characterization of the final product by 13C and 1H NMR revealed the nature of the various polymer end-groups. These end-groups assist in determining the modes of chain termination. Measurement of the concentration of the cationic active complexes has been identified as one of the most critical factors in the determination of the kinetic parameters of the model. A method for an estimation of the initial concentration of active site is addressed.