Olefin polymerization over highly active ziegler-natta catalysts

Abstract

Olefin polymerizations were carried out under high pressure and atmospheric pressure slurry reactors using three types of Ziegler-Natta catalysts synthesized by different operational methods. The first type of catalyst to study ethylene polymerization was prepared by anchoring $TiCl_4$/THF/$MgCl_2$ solvate complex onto the inert $SiO_2$. A plausible mechanism for the reaction between the solvate complexes and hydroxyl groups in silica gel was postulated. Ethylene polymerization were then carried out in a semi-batch, constant pressure slurry reactor. The pressure and temperature employed in this study were similar to those employed in industrial practice. Kinetic investigations were carried out on the effect of polymerization conditions and nature of aluminum alkyl cocatalyst on the morphology (size, shape, density, and texture) of nascent polyethylene synthesized with the catalyst. Depending on the nature of cocatalyst, considerably different kinetic profiles were obtained. Fibrillar, globular, cobweb, ribbon-like, worm-like, and lamellar structures were obtained depending upon the catalyst system and polymerization conditions. The effect of polymerization of nascent polyethylene was also investigated. Replication phenomenon was observed depending on the catalyst yield and polymerization time. Generally, the average particle size of polymer particles became larger as the rate of polymerization increased. Polymerization of ethylene and copolymerization of ethylene with 1-hexene were performed by using a second type of catalyst prepared by coprecipitation method. The catalyst system is composed of $TiCl_4$/THF/$MgCl_2$ bimetallic complex. In order to look into the role of magnesium compound in the catalyst, various catalysts with different Mg content (Mg/Ti=0.42-16.5) were characterized by means of elemental analysis, FTIR, x-ray powder diffraction, and SEM techniques. The catalyst activity increased linearly with respect to the Mg/Ti ratio of catalyst t...