Roles of Molecular Structure in the Catalytic Cracking of n‐Heptane, Methylcyclohexane and Cyclopentene over HZSM‐5 Zeolites

Catalytic cracking technology is an important candidate for the crude-to-chemicals, which is promising to convert oil into chemicals by a clean and efficient way. n-Heptane, methylcyclohexane and cyclopentene catalytic cracking over HZSM-5 zeolites were studied at 320-550 degrees C under atmosphere, and a particular attention was paid to the effects of reaction temperature and time on stream. The cracked gas was analyzed by an online gas chromatograph, and the spent HZSM-5 zeolites were characterized by TG, N-2 physisorption and NH3-TPD. It provided detailed information about the conversion, product distribution, coke formation and catalyst deactivation. Furthermore, the roles of molecular structure in the reaction network were discussed based on the carbenium ion mechanism. It was found that the protolytic cracking and hydride transfer was favored by n-heptane due to the linear structure; the demethylation, protolytic ring-opening and protolytic dehydrogenation was favored by methylcyclohexane due to the methyl group and cyclic structure; the protonation and oligomerization was favored by cyclopentene due to the cyclic and C=C structure. This made a significant difference on the catalytic performance: The activity was in a descending order of n-heptane approximate to cyclopentene>methylcyclohexane. Alkane formation was in a descending order of n-heptane>methylcyclohexane>cyclopentene. Aromatic and coke formation were in a descending order of cyclopentene>methylcyclohexane>n-heptane.