Improved para-Xylene Selectivity in meta-Xylene Isomerization Over ZSM-5 Crystals with Relatively Long b-Axis Length

Graphical Join the chain gang: Chain-like ZSM-5 crystals that are synthesized in the presence of starch show higher p -xylene selectivity in m -xylene isomerization than normal, mesoporous, and sheet-like ZSM-5 crystals. ZSM-5 zeolite crystals with controllable b- axis length (sheet-like, S-ZSM-5; chain-like, C-ZSM-5) have been synthesized by using urea and starch as additives in the starting aluminosilicate gels. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images show that these zeolite samples have good crystallinity. Transmission electron microscopy (TEM) images show that there is a strong chemical interaction between the stacked crystals in C-ZSM-5 samples. N 2 sorption isotherms indicate that C-ZSM-5 crystals are mesoporous. Catalytic tests for the formation of p -xylene from m- xylene isomerization show that, compared with other zeolite catalysts, C-ZSM-5 catalysts give both high conversion and improved p -xylene selectivity, which are attributed to the combination of relatively long b -axis length and the present mesoporosity in the crystals. The improvement of p -xylene selectivity in catalytic m- xylene isomerisation is of great importance for selective industrial production of p -xylene in the future.