Sorption of ethylene and propylene oxides on silica gels

Abstract

The adsorption of ethylene oxide from 273·7° to 313·7°K, and propylene oxide at 308°K, has been studied on silica gels. Adsorption–desorption isotherms and calorimetric heats of adsorption were measured for both gases on gels heat-treated at 240° and 500°C. For ethylene oxide, desorption studies were made also with gels impregnated with aluminium (0·274% w/w) and gels heat-treated at 600°, 700°, and 900°C. High heats of adsorption were found at low surface coverages. Thus on 240° gel at θ < 0·02, heats of adsorption around 30 and 40 kcal. mole^–1 were measured respectively for ethylene oxide and propylene oxide. These values decreased, rapidly at first and then more slowly, with increasing surface coverage and tended towards the values of the latent heats of vaporisation at monolayer completion. It is suggested that proton transfer from surface hydroxy-groups to the ether oxygen in propylene oxide may occur at very low θ, while the possibility of hydrogen-bond formation at intermediate surface coverages is also discussed.