Selective Formation of Light Olefins by Catalytic Cracking of Naphtha Components over ZSM-5 Zeolite Catalysts

Kubo Kohei, Iida Hajime, Namba Seitaro, Igarashi Akira

doi:10.1627/jpi.61.10

<p>Catalytic cracking of C6-8 hydrocarbons as model naphtha components was evaluated over H-ZSM-5 catalysts with various Si/Al ratios at 723-923 K to selectively form light olefins. The highest ethylene + propylene yield was 59.7 C-% with a propylene/ethylene ratio of ca. 0.72 at 99.6 % conversion in the cracking of n-heptane over H-ZSM-5 (Si/Al = 31) at 923 K. The selectivities and activation energies indicated that monomolecular cracking was predominant at temperatures higher than 923 K. Next, cracking of various C6-8 hydrocarbons on H-ZSM-5 at high temperatures in the presence of another hydrocarbon was also investigated. Coexistent 1-hexene did not affect the cracking rate of n-heptane, cyclohexane, or methylcyclohexane, also indicating that monomolecular cracking was predominant at temperatures as high as 923 K. In contrast, coexistent cyclohexane and methylcyclohexane considerably affected the cracking rate of n-heptane because of their slow diffusion in the pores of H-ZSM-5. Moreover, catalysts with activity equal or higher than that of H-ZSM-5 and steaming stability higher than that of H-ZSM-5 were examined. The 194 %Cu-ZSM-5 and 95 %Ag-ZSM-5 zeolites exhibited high steaming stabilities and higher cracking activities than H-ZSM-5 and P/H-ZSM-5. In particular, 194 %Cu-ZSM-5 exhibited an ultra-high steaming stability under conditions such as 1023 K and 10 h presumably because Cu²⁺ and Cu⁺ cations in the 194 %Cu-ZSM-5 are not reduced to Cu⁰ at a high temperature of 1023 K in the presence of O₂.</p>

Selective Formation of Light Olefins by Catalytic Cracking of Naphtha Components over ZSM-5 Zeolite Catalysts

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