Catalytic transformation of 1,3,5-trimethylbenzene over a USY zeolite catalyst

Catalytic transformation of 1,3,5-trimethylbenzene (TMB) has been investigated over a USY zeolite catalyst in a novel riser simulator at different operating conditions. The effect of reaction conditions on the variation of isomerization to disproportionation products ratio, distribution of TMB isomers, xylene/tetramethylbenzenes ratio, and values of p-xylene/o-xylene ratios are reported. Comparisons are made between the results of the 1,3,5-TMB and the earlier reported values of 1,2,4-TMB under similar conditions. Diffusion limitations were observed for the 1,3,5-TMB transformation reactions, while very mild transport effects were seen for the 1,2,4-TMB molecule. This is as a consequence of the kinetic diameters of the reacting molecules (8.6 Å for 1,3,5-TMB and 7.6 Å for 1,2,4-TMB), which are nearly the size of the passageway of the USY zeolite (7.4 Å). Surprisingly, 1,3,5-TMB was found to be more reactive than 1,2,4-TMB at temperatures above 450 °C and reaction times more than 5 s. The experimental results have been modeled using quasi-steady state approximations. Kinetic parameters for 1,2,4- and 1,3,5-TMB conversions into isomerization and disproportionation products were calculated using the catalyst activity decay function based on time on stream. The apparent activation energies were found to decrease as follows: E_{1,3,5-TMB,disproportionation} > E_{1,3,5-TMB,isomerization} ≈ E_{1,2,4-TMB,isomerization} > E_{1,2,4-TMB,disproportionation}.