Catalytic cracking of heavy naphtha-range hydrocarbons over different zeolites structures

Abstract

The effects of textural, structural, morpholgical, and acidic properties of HZSM-5, H-mordenite and (MFI/MOR) composite zeolite on the catalytic cracking of heavy naphtha-range hydrocarbons (dodecane, iso-octane, and ethylbenzene) as well as heavy naphtha were studied. XRD and SEM results revealed the presence of (MFI/MOR) overgrowth composite zeolite upon recrystallization of H-mordenite in the presence of tetrapropylammonium bromide. Significant cracking of dodecane occurred over different zeolites, however, very low cracking of iso-octane was observed over HZSM-5. The conversion of ethylbenzene, iso-octane and dodecane at 400°C was 69.6, 74.5 and 86.4wt.%, respectively, over H-mordenite, compared with 69.8, 11.2 and 83.8wt.%, respectively, over HZSM-5. (MFI/MOR) overgrowth zeolite exhibited an intermediate level of cracking. Catalytic cracking of hydrocarbon mixtures followed similar trends as those for pure model compounds. Catalytic cracking of heavy naphtha was higher over HZSM-5, compared to H-mordenite (94.4wt.% vs. 76.5wt.%). The kinetic modeling studies indicated that the rate of hydrocarbon cracking varies with the nature of model compounds and zeolite structure. The apparent activation energies (Ea) for the three model compounds increased in the following order; HZSM-5>(MFI/MOR)>H-mordenite, whereas the difference in Ea over various zeolites was much larger for iso-octane and ethylbenzene.