The selective and stable synthesis of aromatics from methanol via two-step route using light alkenes as intermediates

Abstract

As a potential non-petroleum route for the synthesis of aromatics, it is still difficult to obtain high catalytic stability and aromatic selectivity in traditional one-step methanol conversion over traditional low Si/Al ratio ZSM-5. In this work, high Si/Al ratio (220) ZSM-5 was packed above Zn doped low Si/Al ratio (30) ZSM-5 and the obtained catalyst bed was used to convert methanol into aromatics. Based on series of comparative experiments on catalyst packing modes, it was found that over upstream high Si/Al ratio ZSM-5, methanol was mainly converted into light alkenes, especially propene and butene. Then, these light alkenes were further converted into aromatics over downstream Zn doped low Si/Al ratio ZSM-5. The catalytic lifetime was tenfold longer than that of one-step conversion for the native long lifetime of upstream catalyst and the facilitated alkene-based cycle over downstream catalyst, which suppressed the coke formation. The decreased reaction depth of aromatic-based cycle promoted the BTX (benzene, toluene and xylene) formation and BTX selectivity in aromatics reached 71.7% for this two-step conversions using light alkenes as intermediates, much higher than 51.2% of one-step conversion. Regulating the packing ratio of above two catalysts optimized the coupling efficiency of two corresponding reactions, and aromatic selectivity in total hydrocarbons increased from 26.7% to 48.2%. Given the unchanged BTX selectivity in aromatics, BTX selectivity in total hydrocarbons increased from 19.1% to 34.8% and was much higher than that of one-step conversion (15.5%). This work offers a prospective route for the selective and stable synthesis of aromatics from methanol.