Effect of acidic properties of single-crystalline hierarchical ZSM-5 zeolite on its activity and mass transfer in n-heptane catalytic cracking

Single-crystalline hierarchical ZSM-5 zeolite with intracrystalline mesopore was successfully synthesized by using L-lysine as a mesoporous template, and the Si/Al ratio was changed by adjusting the adding amount of aluminum source (sodium metaaluminate). Then the effect of acidic properties on zeolite's activity and mass transfer in n-heptane catalytic cracking was investigated in detail. The physical structure, acidic properties and micromorphology of single-crystalline hierarchical ZSM-5 zeolite were characterized by using X-ray diffraction (XRD), nitrogen physical adsorption, ammonia temperature-programmed desorption (NH3-TPD), pyridine infrared (Py-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, the zero-length column (ZLC) device was employed to test the apparent diffusivity of n-heptane in single-crystalline hierarchical ZSM-5 zeolite, which was used to characterize its mass transfer performance. The results showed that the physical structure of single-crystalline hierarchical ZSM-5 zeolite kept almost the same with the increase of Si/Al ratio, while the zeolite's mass transfer performance was improved with the decrease of acid amount, but the catalytic cracking performance was enhanced with the increase of acid amount. When the Si/Al ratio of the single-crystalline hierarchical ZSM-5 zeolite increased from 80 to 140, the apparent diffusivity of n-heptane could be improved by more than 87%. When the Si/Al ratio was 80, the conversion rate of n-heptane could reach up to 97.5%, and the selectivity of ethylene and propylene were 24.3% and 35.1%, respectively. © 2024 Chemical Industry Press Co., Ltd.. All rights reserved.