One-step synthesis of ethanol from glycerol in a gas phase packed bed reactor over hierarchical alkali-treated zeolite catalyst materials

Abstract

The gas-phase conversion of glycerol into ethanol in a “green” one-step synthesis over a cesium metal-promoted zeolite catalyst has been reported for the first time. To our knowledge, the CsZSM-5 based catalyst presented in this work showed one of the best yields of ethanol in the gas-phase glycerol conversion. The catalyst sample's structure, texture, and acid–base properties were characterized using numerous materials characterization techniques. The catalytic evaluation was carried out in a packed-bed continuous flow reactor. The highest ethanol yield achieved was 99.6 mol% over a 20 wt% CsZSM-5 catalyst with SiO₂/Al₂O₃ = 1500, 10 wt% glycerol feed concentration, 350 °C reaction temperature, and GHSV_total = 625 h⁻¹. It was demonstrated that the best catalytic performance was related to the ample amount of surface basic sites, synergistic interaction between Cs species and the HZSM-5 zeolite and to its smaller crystallite size obtained from XRD analysis. The achieved results exhibit great potential of utilizing the alkali-treated CsZSM-5 catalyst for the gas-phase conversion of glycerol into bio-based ethanol. The possible reaction route from glycerol to renewable ethanol was proposed based on direct glycerol conversion to ethanol via the thermal monodehydration, radical fragmentation, methylation and transfer hydrogenation reactions. Finally, for the first time, methanol was directly converted into ethanol in the gas-phase continuous flow packed-bed reactor over a 20 wt% CsZSM-5 catalyst.