Conversion of Light Naphtha into Aromatic Hydrocarbons (Part 1) Kinetic Studies on Hexane Conversion on Zn/H-ZSM-5.

Conversion of light naphtha into aromatic compounds was studied on series of ZSM-5 catalysts loaded with various metal species. Among the catalysts, Zn-, Cd- and Ga-loaded ZSM-5 exhibited. high performances for aromatization of n-hexane. The mechanism of conversion of n-hexane into aromatic compounds over Zn/H-ZSM-5 catalyst was investigated. It is found that aromatization of n-hexane involves dehydrocracking of n-hexane into lower olefins, oligomerization of lower olefins, and dehydrogenation of higher olefins to aromatic compounds. In order to investigate the reaction pathway for aromatization of higher olefins, a series of conversion of n-hexane, 1-hexene, hexadiene, hexatriene, and cyclohexane over Zn/H-ZSM-5, H-ZSM-5, and Pt/H-ZSM-5 were conducted. It is suggested that aromatization proceeds in successive dehydrogenation of higher olefins, and that Zn species play a role to promote formation of hydrogen molecule. On the basis of experimental results, a general reaction model in transformation of light naphtha over Zn/H-ZSM-5 was developed. From results of the kinetic analysis, it is found that promoting the activities for dehydrocracking of n-hexane, dehydrogenation of lower paraffins, and formation of hydrogen molecules may make the catalyst more selective in aromatization of light naphtha.