Synthesis of hierarchical Y and ZSM-5 zeolites using post-treatment approach to maximize catalytic cracking performance

Abstract

Hierarchical zeolites have been recently investigated as catalyst by micro-mesoporous framework to improve the physical transport of large reactants molecules by eliminating the diffusion limitations. In this study, controlled mesoporosity was applied to synthesize two types of hierarchical zeolites by acid/base leaching and surfactant templating followed by steaming. The physico-chemical characteristics of the synthesized parent (NaY and ZSM-5) and hierarchical (UHR/Y and HR/ZSM-5) samples were extensively characterized by XRD, FTIR, TGA, SEM, NH3-TPD, ICP, N2-ads/desorption techniques. The ICP results revealed that post-synthesis approaches successfully washed off Al and Si atoms from the zeolites framework and increased the SiO2/Al2O3 ratios from 3.13 to 6.20 and from 65.55 to 86.34 in UHR/Y and HR/ZSM-5 samples, respectively. Also, the BET analysis showed significant increase in the average pore diameter (DP) size for UHR/Y (31%) and HR/ZSM-5 (153%) compared to their parent ones. Similarly, mesoporous pore volume (Vmeso) exhibited notable surge of 100% and 700% for UHR/Y and HR/ZSM-5, respectively in comparison with their parent forms. The synthesized parent and hierarchical zeolites were used in preparation of fluid catalytic cracking (FCC) catalyst. Catalyst performance was examined in vacuum gas oil (VGO) cracking through a micro-activity test (MAT) unit. Products of interest including gasoline, propylene, and total olefins exhibited significant yield increase from 29.80 to 50.87, 3.93 to 16.41, and 7.36 to 24.98wt%, respectively over the FCC-4 catalysts which prepared by hierarchical (UHR/Y and HR/ZSM-5) zeolites. The enhanced catalytic activity can be attributed to the absence of diffusion problems and more accessibility of the acid sites in the hierarchical zeolite structure.