Industrial crude bioethanol dehydration to ethylene: Doping ZSM-5 to enhance selectivity and stability

Abstract

Although the conversion of bioethanol into light olefins is one of the most studied processes in biorefinery schemes, there is a need to develop materials more capable of operating at industrial conditions (WHSV > 20 h-1 crude bioethanol feed). Hence, in this study, we dehydrated crude bioethanol samples derived from sugarcane fermentation to produce ethylene over a series of H-ZSM-5 zeolites. Among them, H-ZSM-5 with different Si/Al ratios (26, 280, and 371) and doped with Ce and Cu were tested on the catalytic activity and stability. Accordingly, a 26 Si/Al ratio showed full conversion and ethylene selectivity at 300 °C with a WHSV of 30.2 h-1. When doping the zeolites, a decrease in relative crystallinity and a higher amount of acid sites were observed, which affected the interaction with reactants. This interaction was deeply analyzed by the in-situ DRIFTS, which showed that ethanol adsorption is lower for doped zeolites, but the desorption rate is higher, showing higher stability over longer reaction times. Therefore, the H-ZSM-5 with a Si/Al ratio of 26 and doped with Ce maintained its activity and improved its selectivity over 140 h under more drastic conditions of WHSV (42.3 h-1). These results elucidate that Ce-doped H-ZSM-5 zeolites can improve stability and represent a starting point for large-scale crude bioethanol conversion.