Insight into the side reactions in methanol-to-olefin process over HZSM-5: A kinetic study

The industrial methanol to olefin process over HZSM-5 zeolite is currently faced with a low propylene yield with one third of the products being paraffin and aromatic, implying the side reactions play an evident role. This work focused on the kinetic modeling of the side reactions in the methanol to propylene process over HZSM-5 (Si/Al = 200) following our previous works on the main reactions: methanol and olefin co-conversion and olefin interconversion. The experimental results show that C2-C5 paraffins are mainly produced from the hydrogenation of corresponding olefins and aromatics from C3-C5 olefins through oligomerization, cyclization and dehydrogenation in accordance with the hydride transfer mechanism. Methane comes from the cracking of both higher alkanes and methanol. A comprehensive kinetic model was then established by integrating the alkane and aromatic generation steps into our previous developed model for methanol and olefin conversion, and the calculated results agree well with the experimental data under the investigated feed composition and reaction temperature conditions. The further parameter studies show that the total yields of both paraffins and aromatics decrease with temperature but increase with the methanol concentration.