Zirconocene-catalyzed olefin polymerization: Modeling of catalyst stability, nonisothermal mode of operation, and supported catalyst characterization

This paper summarizes (a) an engineering approach to calculation of catalyt ic activity and stability profile, (b) influence of nonisothermal polymeriz ation mode, (c) and characterization of supported zirconocene catalysts by X-ray photoelectron spectroscopy (XPS) and micro-proton induced X-ray spect roscopy (micro-PIXE). The engineering approach is based on modeling the solubility of ethylene in the polymerization diluent as a function of temperature and pressure. Under the nonisothermal mode of polymerization, a change in stirring level from diffusion-controlled regime to nondiffusion-controlled, external gas-l iquid mass transfer resistance-free one, increased the reaction exotherm an d the run time-average catalytic activity. The copolymer composition distri bution and soluble fraction generated by Et(Ind)(2)ZrCl2 was sensitive to m ixing conditions and thermal perturbations. Incorporation of 1-hexene signi ficantly decreased the average molecular weights and density but increased the average catalyst activity, the peak melting temperatures and the weight - and number-average solution crystallization temperatures. Thermal perturb ations broadened the polydispersity index. XPS results showed that heterogenization of Et(Ind)(2)ZrCl2 on silica in th e presence of MAO generated two types of zirconocenium cations (Cations lan d 2), irrespective of the heterogenization procedures. Cation 1 is presumed to be in the form of an ion-pair [SiO](-)[Et(Ind)(2)ZrCl](+) while Cation 2, a trapped multi-coordinated crown complex of MAO. In absence of MAO, onl y Cation 1 is formed. Trace element impurities such as K, Ca, Ti, Fe, Ni, Cu, and Zn detected by micro-PIXE may be the potential sources of poisoning the heterogenized cata lyst.