Single site MIL-101 for novel low-temperature liquid-phase toluene methylation

P-xylene is one of petrochemical products eagerly in demand. Until recently, the process for preparing of p-xylene was done via gas-phase toluene methylation reaction at high temperature using a strong acid catalyst. In this work, high surface area, shape-selective and single-site MIL-101(Cr) was used as a catalyst to perform toluene methylation reaction in a liquid phase at low reaction temperature (60-120 °C). Toluene conversion and p-xylene selectivity are up to 50% and 90%, respectively. Under the optimum operating conditions; 1:1 toluene: methanol molar ratio, the reaction temperature is 120 °C. The catalyst was synthesized via the hydrothermal method and the MIL-101 structure was confirmed by different analytical techniques: TGA, XRD, FTIR and BET surface area. The remarkably high toluene conversion and xylene selectivity at a low reaction temperature, in comparison to previous research, was attributed to the suppression of side reactions that could convert methanol to linear hydrocarbons, and to the inhibition of p-xylene isomerization. This suppression can be attributed to the single site properties and to the uniform pore size distribution of the prepared MIL 101 catalyst.

Graphic abstract

Synthesis and characterization of single-site MIL-101(Cr) were used as a catalyst for toluene methylation reaction in a liquid phase at low reaction temperature (60–120 °C). The results suggest that toluene conversion and p-xylene selectivity are up to 50% and 90%, respectively, under the optimum operating conditions; 1:1 toluene: methanol molar ratio, the reaction temperature is 120 °C.