Particle growth and fragmentation of solid self-supported Ziegler-Natta-type catalysts in propylene polymerization

Particle growth and fragmentation of solid Ziegler-Natta-type catalysts prepared via emulsion technique were studied in propylene polymerization. Before polymerizations the catalyst particles were activated with triethyl aluminum (TEA) and cyclohexyl methyl dimethoxy silane (CMMS). Polymerizations were carried out in gas-phase in a micro-reactor system that allows the particle growth to be observed with a microscope. Several polymerizations were done under a propylene pressure of 2 bar and with polymerization times from 20 s to 2 h. Fragmentation morphology of the catalyst particles and cross-sections of the particles after polymerization were studied by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Fragmentation morphology of the catalysts prepared via emulsion technique was compared with the fragmentation morphology of a conventional MgCl2-supported Ziegler-Nattatype catalyst, which could be described by the multigrain model. Polymer growth appeared to occur throughout the emulsion-based catalyst particle right from the start of the polymerization, even though the surface area and porosity of the catalyst were low. The surface of the catalyst particles broke up at the beginning of the polymerization, and catalyst fragments appeared on the surface as plates between which the polymer was growing. (C) 2009 Elsevier B.V. All rights reserved.