Methylation of toluene with methanol using synthesized HZSM-5 catalysts : effects of hydrothermal synthesis and operating conditions

Abstract

p-Xylene is an important raw material utilized for producing chemical additives, agricultural chemicals and polymeric materials. At present, there are several processes of p-xylene production based on toluene disproportionation and xylene isomerization, e.g. Tatoray ᵀᴹ and XyMaxˢᴹ. However, these processes produce a large quantity of the undesired co-product benzene. The alkylation of toluene with methanol is a promising route of producing of p-xylene in the absence of undesired by-products if a suitable catalyst can be developed and employed accordingly. In this work, HZSM-5 catalysts with SiO₂/Al₂O₃ ratios of 90 and 185 were synthesized under different hydrothermal conditions. The catalytic activity and selectivity of catalysts were tested using a continuous flow packed-bed reactor at atmospheric pressure. The effects of operating parameters such as reaction temperature (300°C to 500°C), WHSV (12 h⁻¹ to 40 h⁻¹), and toluene-to-methanol (T/M) ratio (1:1 to 4:1) were investigated. The results indicate that a temperature of 400 °C, a WHSV of 24 h⁻¹, and a T/M molar ratio of 4:1 would be the optimal parameters for alkylation of toluene with methanol to p-xylene by using the synthesized HZSM-5 catalyst with SiO₂/Al₂O₃ ratio of 185.