Vapor Phase Hydration of Ethylene Catalyzed by Solid Acids

Abstract

The hydration of ethylene over various solid acids such as metal sulfates, phosphates, oxides, solid phosphoric acid and cation exchanged zeolites was investigated in a closed circulation system at 160∼300°C.
Ferric and aluminum sulfates and zeolites Y showed high catalytic activity in comparison with solid phosphoric acid, SiO₂-Al₂O₃, zeolites A and all other catalysts. The selectivity for ethanol formation was extremely high in metal sulfates and zeolites A, but low in SiO₂-Al₂O₃ and zeolites Y. The order of activities of metal sulfates was Fe₂(SO₄)₃>Al₂(SO₄)₃>NiSO₄>Cr₂(SO₄)₃>CuSO₄>MnSO₄>CaSO₄. The catalysts those acid strength in their dried state was as strong as -8.2<H_o_??_-3 were found to be active and selective for ethanol formation. The activities of cation exchanged zeolites A which varied in order of Mg-A>Cd-A>Zn-A>Ca-A>Ag-A>Sr-A>La-A∼Ce-A were shown to correlate with the electronegativities of exchanged cations and the adsorption heats of ethylene.
The rate of ethanol formation increased as the mole ratio of H₂O/C₂H₄ decreased. The experiment on the reaction of ethylene with heavy water showed that deuterium did not transfer into ethylene at all. It was concluded by analyzing the kinetic data that the formation of an adsorbed ethyl carbonium ion from an adsorbed ethylene and a proton on acid sites was the rate-determining step of the hydration.