Selective alkylation of toluene with methanol to produce para-Xylene

Toluene has been alkylated with methanol over ZSM-5-class zeolite catalysts to produce xylenes and water. A near equilibrium mixture containing 24% of the para isomer was usually observed. Production of over 90% para isomer in the xylene product was achieved when the catalyst was modified by impregnation with phosphorus and with boron compounds. para-Xylene selectivity was also enhanced by coking and coating the catalyst surface with heat-stable polymers. A controlled reduction in the effective dimensions of the catalyst pore openings, and/or channels, along with deactivation of acidic surface sites, has been proposed as a mechanism for the selective production of p-xylene.