Intensified Alkylation Reaction to Improve the p‑Xylene Yield in Coaromatization of n‑Hexane and Methanol

The coaromatization of light alkane and methanol is an attractive nonpetroleum pathway balancing the heat to produce high-value aromatics, but achieving high p-xylene (pX) selectivity is a challenging topic. Here, we present a two-stage tandem catalysis for alkylation intensification. [Zn,Ga]/ZSM-5 was used in the first-stage reactor for the coaromatization to provide sufficient aromatics. The HZSM-5@SiO2 catalysts were prepared for alkylation reaction and characterized by means of X-ray diffraction, N2 adsorption/desorption, transmission electron microscopy, and Fourier transform infrared with pyridine. The feasibility to enhance xylene and pX was verified by introducing methanol in the second stage to intensify the alkylation of aromatics. Higher SiO2/Al2O3 ratio benefits for xylene and the elimination of external acid sites benefits for pX were found. The pX selectivity and yield and the alkylation efficiency of methanol were significantly increased over HZSM-5@SiO2 in the coaromatization system of n-hexane and methanol. The pX selectivity and yield were increased to 57.41% and 13.12 wt % over Z50@20P. Moreover, the deactivation of HZSM-5@SiO2 was investigated in detail.