Demonstrating on-demand production of bio-ethylene oxide in a two-step dehydration-epoxidation process with chemical looping operations

Abstract

Ethylene oxide (EO) is a key chemical intermediate produced almost exclusively from petrochemically derived ethylene. Currently, EO manufacturing involves epoxidation of ethylene with O2 over Ag/Al2O3 - one of the highest CO2-emitting processes in the chemical sector (Boulamanti and Moya, 2017). The flammability hazards associated with incumbent methods and sluggish process start-ups prevent small-scale, flexible operations or alignment with intermittently available renewable resources. Presented herein is a novel process for on-demand production of bio-EO from bioethanol. Ethanol, laboratory-grade or denatured, was first dehydrated to ethylene over HZSM-5 (at 280 °C) or γ-Al2O3 (at 350 °C) catalysts, producing ethylene and water. The ethylene stream was then selectively oxidised to EO over Ag/SrFeO3 at 270 °C using lattice oxygen from a solid – SrFeO3, employed to drive chemical looping epoxidation (CLE). For a configuration where the dehydration and epoxidation reactions were carried out in separate reactors, the process produced EO with 57 % selectivity at 15 % conversion of ethylene, thus exceeding the incumbent approach with pure Ag/α-Al2O3 and O2. In an alternative configuration, experiments were carried out in one dehydration-epoxidation reactor layered with two catalysts: HZSM-5 and Ag/SrFeO3. The results revealed that water presence at a percentage level enhanced unselective combustion. In-situ removal of water, possible with an additional layer of a drying material between the two catalysts, proved effective in boosting the process performance, reaching selectivity to EO of 50 % at 12 % conversion of ethylene. The catalysts showed no sign of deactivation when using denatured ethanol or when performing experiments intermittently. Hence, our novel process can be kept offline without penalty, allowing for on demand production and complete alignment with renewable resources.