Simulation of catalytic toluene alkylation with methanol in fixed-bed reactors

Toluene alkylation with methanol could serve as a green "molecular engineering" to produce para-xylene (PX). However, the conversion and para-selectivity are the key index to the application of this technology. Based on the reaction network and kinetics, the fixed-bed models were introduced to analyze and optimize the para-selectivity at reactor level. After the validation with the experimental results, the analysis of reaction kinetics showed that increasing temperature not only improves the main reaction rate, toluene conversion, and para-selectivity, but also inhibits the competitiveness of methanol autocatalytic reaction, while higher feed molar ratio of toluene to methanol will suppress the olefins formation but reduce the conversion and promote the polymethylation process with a sharper temperature rise. Then, the one- and three-dimensional model demonstrated that the conditions of 500-520 degrees C, feed molar ratio of 2-3 would be favorable to the para-selectivity, and keeping the wall 20-30 degrees C above the inlet temperature is beneficial for conversion, selectivity, and temperature control. These results have certain guiding value for the choice of reactor condition and further reactor design.