A NOVEL LABORATORY SLURRY REACTOR FOR ETHYLENE POLYMERIZATION STUDIES

A novel laboratory slurry reactor useful for studies of polymerization of olefins with solid catalysts such as Cr/silica is described. The o peration of this reactor, in which gaseous impurities are minimized by purification of incoming gases and by in situ activation of the catal yst, has enabled the early stages of the homopolymerization of ethylen e to be studied without interference from catalyst deactivation effect s. By standardizing the conditions for the experimental runs, the reac tor demonstrated its usefulness in isolating and assessing the relativ e physical roles of different silica supports. Four catalysts supporte d on different silica supports were compared, and their differences in promoting the polymerization were interpreted in terms of porosity, a verage particle size, and changes in specific surface area. During ear ly polymerization, the fracturing of catalysts prepared by impregnatio n of the porous silica support ensures access to these original Cr sit es, in the absence of additional concealed sites. At low yields, the p olymerization process is clearly affected by the physical character of the silica support; however, at higher yields, the evidence suggests that other causes such as chemical effects are responsible for the con tinuing acceleration in rate. The porous Cr/silica catalyst tested did not fracture instantaneously; hence, current models of nascent polyme r do not describe this process. The ''hardcore'' model of nascent poly mer seems applicable to polymerization on the nonporous Cr/Cab-O-Sil c atalyst tested.