Hexane Cracking: Improving Ethylene Yield and Zeolite Stability by Hydrothermal Urea Modification of HZSM-5

Finely regulating the acidity and pore structure of zeolites has a great influence on performance in the cracking hydrocarbon reaction. In this work, HZSM-5 zeolites were modified with a urea solution under hydrothermal conditions. As a comparison, modification with TPAOH and NaOH solutions was respectively used to investigate the different effects on the desilication, generation of hierarchical pores, and acidity of zeolites. After modification, ZSM-5 zeolites can improve the yield of ethylene and the reaction stability in the reaction of the cracking of hexane. Distinctly, hydrothermal urea treatment of the ZSM-5 zeolite modulates the distribution of Al, significantly improves its acid properties and pore structure, as well as heals the defective sites in the zeolite. For the urea treated sample, in the reaction of the cracking of hexane, the conversion, light olefin yield, and ethylene yield increased by 2.8%, 5.1%, and 13.4% compared with those of the HZSM-5 zeolite, respectively. Moreover, the urea treated sample has reduced coke deposition and a lifetime of 107 h, more than three times that of the HZSM-5 zeolite (29 h).