Alkaline–acid modification of HZSM‐5 zeolites: Catalytic conversion of methanol in synergy with raffinate oil to light olefins

AbstractHZSM‐5 zeolites were treated by alkaline and alkaline–acid composite modification via the hydrothermal method. A comprehensive series of characterization techniques, including X‐ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption–desorption, temperature‐programmed desorption of ammonia (NH3‐TPD), and pyridine adsorption infrared spectroscopy (Py‐IR), were employed to investigate the physicochemical properties of the ZSM‐5 zeolites before and after modification. The results demonstrated that the relative crystallinity of the modified zeolites remained nearly intact, with the MFI structure being well‐preserved. Nevertheless, the total acid content of both modified samples decreased, accompanied by an increase in specific surface area and pore size. Notably, the zeolites treated with alkaline–acid composite modification showed a slight elevation in the total L‐acid content. When applied to the reaction of coupling methanol with raffinate oil for the production of light olefins, compared with the unmodified ZSM‐5 zeolite, the modified ZSM‐5 zeolites showed a significant increase in the selectivity and yield of triene. In particular, the ZSM‐5 zeolite A2 modified by the alkali–acid composite method exhibited remarkable enhancements in catalytic activity and stability. Its methanol conversion rate exceeded 99%, and when the selectivity for triene reached 60.26%, the yield reached a high value of 36.8%.