Fracturing silica‐based catalysts during ethylene polymerization

Publisher Website
Google Scholar
Abstract
The rate and extent to which silica‐based catalysts fracture during the polymerization of ethylene in a slurry process were examined. Reactions were stopped at various times to yield as little as 20 g of polymer per gram of catalyst to more than 20,000 g/g. The catalyst residue was then collected and analyzed. Fragmentation of the catalyst was complete within the first minute or two of polymerization, whereas the rate of reaction continued to increase for more than an hour. Therefore fragmentation cannot be the rate‐controlling step. A comparision of the kinetics of Cr/silica and Ti‐Mg/silica led to the same conclusion. The most active silica gels also tended to be the most porous, which suggests fragility as a necessary requisite. Although 98% of their surface was internal, their activity was comparable to that of nonporous silicas, in which all the surface was external. This suggests that long polymer chains can diffuse out of the pores.