Using response surface method to analyze the effect of hydrothermal post-treatment on the performance of extrudates HZSM-5 catalyst in the methanol to propylene reaction

In this study, ZSM-5 was synthesized via the hydrothermal method and then extruded using aluminophosphate as a binder. Before using it as a catalyst in methanol to propylene reaction, it was tried to eliminate the undesired contributions of the used binder by hydrothermal post- treatment. The experimental design and the analysis of the results, especially the relation of characterization results and reactor performance, are performed by optimal response surface method in Design Expert Software. The effects of the exposing time and the temperature during the steaming procedure on the catalytic characteristics and the performance of this system were investigated for two different average particle sizes (75 and 150 mu m) of this catalyst. The results of the post-treatment represent the main dependency on the catalyst particle size, where the catalyst with smaller particle size showed lower methanol conversion and selectivity towards light olefins. It was concluded that an increase in the particle size of the catalyst intensifies the transport restrictions within the zeolite structure, which consequently increases the intra-particle residence time for production of higher hydrocarbons and then facilitates their cracking in order to produce more light olefins. This needs to be taken into consideration while synthesizing the catalyst for large-scale application.