Over 140 million tonnes of ethylene are produced annually by the cracking of petroleum feedstocks. A greener alternative to ethylene production from petroleum involves the dehydration of biomass-derived ethanol over a solid catalyst. In this work, the kinetics, mechanism, and site requirements of dehydration of ethanol to ethylene and diethyl ether on g-alumina (g‑Al2O3) were investigated at 215 °C. Pyridine titration showed that the active sites for ethylene and diethyl ether formation are acidic and non-equivalent. Kinetic isotope measurements using C2H5OD and C2D5OD revealed that ethylene formation is kinetically limited by the cleavage of a C-H bond in ethanol while diethyl ether formation is kinetically limited by cleavage of the Ca-O bond. Steady state kinetic measurements at various ethanol and water pressures (1.1-7.1 kPa and 0.4-2.3 kPa, respectively) revealed that the surface sites responsible for ethylene formation are populated by ethanol monomers, ethanol-water complexes, ethanol dimers, and water dimers. The surface sites responsible for diethyl ether formation are predominantly populated by ethanol‑water complexes and ethanol dimers. Mechanisms and rate equations consistent with these observations were proposed for ethanol dehydration to ethylene and diethyl ether.
This research was supported by the Undergraduate Research Opportunities Program (UROP); Catalysis Center for Energy Innovation; The Dow Chemical Company.
Kinetics, Mechanism, and Site Requirements of Ethanol Dehydration on γ-Al2O3.
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