Retardative effect of amine on ethylene oxidation over silver

Abstract

Ethylene oxidation was studied on a silver catalyst by adding small amounts of amines in a stepwise manner in its steady state. Dynamic retardations of the oxidation were followed by gas-chromatographic analysis of the reaction products and by temperature-profile measurements of the catalyst bed. The inlet amine concentration dependence on the retardation of the ethylene oxidation followed an inverse sigmoid shape. The boundary concentration of the amine (Cb) which can maintain the steady state of the retarded oxidation was found to differ from amine to amine. A logarithmic linear relationship was observed between the vapor pressure of the amine andCb. The relationship indicates the existence of a correlation between the gasliquid equilibrium constants of the amines and both adsorption constants of the amines on the catalyst surface during ethylene oxidation and combustion rates of the amines themselves. On the other hand, regardless of the nature of the amines, the boundary space-time conversion of oxygen which can maintain the steady-state retardation of the oxidation showed an intrinsic value for each catalyst. The added amine showed a selective retardation of the formation of carbon dioxide for a catalyst which has relatively high combustion activity even at low temperatures and a nonselective retardation of the formation process of both ethylene oxide and carbon dioxide for a catalyst which has desirable epoxidation activities at higher temperatures.