Inter-conversion of light olefins on ZSM-5 in catalytic naphtha cracking condition

• P modification and steaming effects of HZSM-5 were studied by NH3-TPD and NMR, etc.
• Interconversion of ethylene and propylene cannot be ignored under cracking condition.
• Reaction mechanism of light olefin over ZSM-5 based catalysts was proposed.

The inter-conversion of light olefins over four types of HZSM-5 based catalysts under cracking conditions was investigated systematically and various methods including XRD, Ar adsorption–desorption, NH3-TPD, 27Al and 31P MAS–NMR were used to characterize the effects of P modification and steaming on ZSM-5. Regardless the types of catalyst, the same behaviors of light olefin inter-conversion were observed only depending on conversion of light olefins. Also, the conversion and selectivity were not influenced by the presence of hydrogen, suggesting that light paraffins were mainly produced from hydrogen transfer during cracking rather than hydrogenation of light olefins. It can be suggested that the inter-conversion of light olefins occurs through oligomerization of light olefins and then re-cracking of the oligomerized products. To guarantee high light olefin yield in catalytic naphtha cracking, it is strongly required to suppress oligomerization of light olefins during catalytic cracking.

The inter-conversion of ethylene and propylene over P-modified HZSM5 catalysts in catalytic naphtha cracking conditions are prevailing and the following reaction mechanism is proposed.Figure optionsDownload high-quality image (182 K)Download as PowerPoint slide