Propylene and aromatics from ethylene conversion over ZSM-5: Effect of zeolite composition

Abstract

Bioethanol is a green alternative to supply the demand for light olefins (ethylene and propylene) and aromatics (benzene, toluene, and xylenes) that can have a green label. ZSM-5 zeolite is largely used to produce light olefins and aromatics from ethanol or ethylene. The addition of metal species to ZSM-5 can tune the activity and selectivity of the zeolite to specific compounds. The influence of the incorporation of tungsten, iron, and lanthanum species on ZSM-5 was studied. The presence of tungsten species favored the formation of aromatics, while lanthanum promoted the production of light olefins. The density of acid sites and the presence of sites with intermediate strength influenced the ethylene conversion and the product distribution of the metal impregnated zeolites. Moreover, the presence of Lewis acid sites promoted the production of aromatics. However, the role played by the acid properties is dependent on the experimental conditions employed. The reaction routes were elucidated, that is, the aromatics are mainly formed through dehydrocyclization on WHZSM-5, while the olefins are produced from the reaction of ethylene and carbene species (propylene) and the dimerization of ethylene (butenes) on LaHZSM-5.