Finely regulating methanol concentration to control the alkylation depth in methanol aromatization for optimizing product distribution

Uncontrollable alkylation in methanol to aromatics severely restricts the light aromatic selectivity and catalytic stability. Herein, we proposed a new strategy to control the alkylation depth by precisely regulating methanol concentration in alkylation environment. Firstly, the high Si/Al ratio ZSM-5 (HZ) was packed over Zn doped low Si/Al ratio ZSM-5 (Zn/LZ) to form dual bed to inhibit deep alkylation for high catalytic stability and BTX selectivity. Secondly, part of methanol was introduced into lower Zn/LZ bed to promote methyl-cyclopentene alkylation for aromatic production and product optimization. After such regulation, toluene selectivity in aromatics decreased from 27.9% to 20.8% accompanied by an increase in xylene selectivity from 37.1% to 44.0%. BTX selectivity in aromatics also improved to 66.7% with 97.5 h of catalyst lifetime, much higher than 50.0% and 20 h of the single Zn/LZ bed. This work realized stable light aromatic production from methanol by controlling the microscopic reaction routes. [Display omitted] •The alkylation was precisely controlled by adjusting methanol concentration in MTA.•Intense alkylation in single bed caused poor stability and BTX selectivity.•Pre-conversion of methanol in dual bed weakened alkylation and improved lifetime.•Stratified methanol feed promoted alkylation of MCP for efficient aromatization.