Transalkylation of toluene with C9 aromatic hydrocarbons over ZSM5 zeolites

The transalkylation reactions of a mixture of toluene and C₉⁺ aromatics were studied over HZSM5 catalysts of varying SiO₂:Al₂O₃ ratios (30–800) as well as over a NiHZSM5 catalyst. As the SiO₂: Al₂O₃ ratio is increased, the rate of transalkylation is decreased. Among the C₉ aromatics that were present in the feed, the ethyl toluenes were extensively de-ethylated to toluene. The shape-selective characteristics of the ZSM5 zeolite were revealed through the relative order of reactivity of the three trimethyl benzene isomers 1.2.4>1.2.3>1.3.5. The stable life of the catalyst can be prolonged by the incorporation of nickel. The influences of process parameters such as temperature, pressure, space velocity and H₂: hydrocarbon ratio are also presented. It was observed that the transalkylation of C₉ aromatics with toluene to yield xylenes occurs mainly on the external surface of the ZSM5 crystals. The disproportionation of toluene to yield benzene and xylene, however, takes place predominantly in the pore system.