A new catalytic process for high-efficiency synthesis of p-xylene by methylation of toluene with CH₃Br

A new catalytic process for p-xylene synthesis from the methylation of toluene with CH₃Br was proposed. CH₃Br was prepared from the catalytic bromination of natural gas (CH₄), by using H₂O + HBr + O₂ as mediator over supported Rh catalyst. The methylation conditions were investigated using HZSM-5 or modified HZSM-5 catalyst. Under optimal reaction conditions, p-xylene selectivity is up to 93%, and p-xylene yield is more than 21% at 673 k over the Si-P modified HZSM-5 catalyst. Compared to the processes using MeOH or dimethyl carbonate (DMC) as methylation agent, this new process is very attractive in an economic standpoint since CH₄ is much cheaper than MeOH and DMC. In addition, the process has other advantages, such as mild reaction conditions, simple operation, high-product yield, and so on. It is predicted that the process has good industrial potential for para-xylene production.