The Effects of Oxygen on the Polymerization of Ethylene in the Presence of Supported Chromium Oxide Catalysis

摘要

The polymerization of ethylene over a supported chromium oxide catalyst was studied first in the complete absence of oxygen and then with controlled amounts of oxygen (60 to 600 micro mole/g catalyst) present. The catalyst was prepared by impregnating a microspheroidal silica-alumina (87 - 13 wt. %) with a dilute solution of chromic acid. This raw compound was then activated by heating it in vacuo at 550C. The data indicated that the inhibitory effect of oxygen involved the chemisorption of some oxygen containing species which could in time be displaced by an excess of ethylene. A comparison of the molecular weight distributions of the products with the rates of polymerization at shutdown suggested that higher rates of reaction cause local heating within the reactor, thereby increasing local rates of chain transfer and broadening the distribution. (Author)