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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 °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, N2 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≈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. [ABSTRACT FROM AUTHOR]

In this work, the effects of ethanol on n-heptane catalytic cracking over HZSM-5 zeolites were explored at 550 °C for 6 h on stream. Particular attention was paid to the measurement of product distribution, especially alkene and aromatic products. Due to the unique structure, ethanol easily interacts with the acid sites over HZSM-5 zeolites. It favored the dehydration to ethene formation and prevented alkene secondary reaction to aromatic formation. Thus, ethanol addition promoted alkene selectivity while reducing aromatic selectivity in n-heptane catalytic cracking. However, ethanol addition accelerated the deactivation of HZSM-5 zeolites. XRD, 27Al MAS NMR, TG-DSC, N2 adsorption–desorption, and NH3-TPD were employed to characterize the fresh and spent HZSM-5 zeolites and elucidate the roles of ethanol in coke formation and HZSM-5 deactivation during n-heptane catalytic cracking. It was found that alkene promotion caused by ethanol addition enhanced coke formation and its migration from the micropores to the external surface of HZSM-5 zeolites. The formation and accumulation of external coke sharply blocked the pore openings and reduced the accessibility of the acidic site, accelerating HZSM-5 deactivation. Moreover, ethanol was more harmful to the framework of HZSM-5 zeolites compared to n-heptane. It accelerated the collapse of HZSM-5 crystallite, which was negative to the catalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of HZSM-5 zeolites on the growth of CNTs from polymer wastes were studied. • HZSM-5 zeolites were added to the middle of the two-stage reaction system. • HZSM-5 zeolites increased the length and yield, and narrowed the diameter of CNTs. • The promotion of HZSM-5 zeolites on CNTs was effective for divrese polymer wastes. • It was due to the upgrade of the pyrolysis gas from polymers by HZSM-5 zeolites. The efficient synthesis of carbon nanotubes from polymer wastes has been considered one promising technology for the effective management of current environment crisis. In the two-stage reaction system, HZSM-5 zeolites were introduced into the two-stage reaction system between the upper and lower stages, which was expected to upgrade the pyrolysis gas from polymer wastes and boost the growth of carbon nanotubes on Fe-Al 2 O 3 catalyst. The physicochemical properties of HZSM-5 zeolites, Fe-Al 2 O 3 catalyst and the as-obtained carbon materials were systematically characterized by XRD, N 2 physisorption, 27Al MAS NMR, NH 3 -TPD, H 2 -TPR, SEM, TEM, TG-DSC and Raman. It was found that the presence of HZSM-5 zeolites increased the length and yield, and narrowed the diameter of carbon nanotubes. In the absence of HZSM-5 zeolites, the yield of carbon nanotubes was 34 mg/g with an average diameter of 19 nm. The introduction of HZSM-5 and meso -HZSM-5 increased the yield of carbon nanotubes to 109 mg/g and 90 mg/g, and recduced the average diameter to 15 nm and 13 nm, respectively. The improvement of HZSM-5 zeolites on the synthesis of carbon nanotubes was observed for divrese polymer wastes inlcluding LDPE, HDPE and PP. It was attributed to the unique acidity and porosity of HZSM-5 zeolites, which enhanced the secondary cracking of the pyrolysis gas and the formation of light hydrocarbons. [ABSTRACT FROM AUTHOR]