Microwave-assisted ethanol dehydration to ethylene over biochar-based catalyst at low temperature†

Abstract

Modern chemists dream of a low-temperature bioethanol dehydration to ethylene process promoted by biomaterial-based catalysts, which would be without doubt an energy-saving, sustainable achievement in green chemistry. However, limitations on catalytic activity and competition from exothermic side reactions have always been an insurmountable gap. Herein, a microwave-assisted pathway employing biochar-based catalysts was designed to effectively dehydrate ethanol into ethylene at temperatures lower than 100 °C. Either biochar (BC) or phosphoric acid-modified derivate (HBC) was synthesized from bamboo powder through a simple one-step decomposition. ZSM-5/MOR composite zeolite was further introduced to form HBC-2-ZSM-5/MOR hybrid catalysts, which could effectively prevent the formation of diethyl-ether and enhance the production of ethylene. With a microwave input power and reaction temperature as low as 10 W and 82 °C, ethanol (WHSV = 2 h⁻¹) could be completely converted on the HBC-2-ZSM-5/MOR (1.5) catalyst with almost 100% ethylene selectivity. Similar results were obtained in the conversion of bioethanol (model), Chinese liquor and beer, pointing to the wide applicability of this strategy. Investigation of the potential mechanism found that weak acidity, special structure and P-modification characteristics can effectively inhibit the formation of diethyl ether by-products, oligomerization and the coking process, which is conducive to promoting the selective conversion of ethanol to ethylene. This work has blazed another trail for low-temperature ethanol to ethylene by combining the advantage of microwave heating with precise tailoring of biochar-based catalysts, all for a better future life with green chemistry.