Kinetics of toluene methylation over ZSM-5 catalyst in a riser simulator

Toluene methylation has been studied over fresh and precoked ZSM-5 based catalyst in a riser simulator, which closely mimics the operation of commercial fluidized-bed reactors. The study was carried out at 375, 400, 425, and 450°C for reaction times of 3, 5, 7, 10, 13, and 15 s. Toluene conversion was found to increase with reaction temperature and time for both forms of the catalyst. Maximum toluene conversion of 16.81% was obtained over the fresh catalyst at 450 °C. The ratio of para-/ortho-xylene (P/O) in the reaction products was much higher than the equilibrium value for all reaction conditions with P/O ratios as high as 3.5-6 times the equilibrium value achieved. For the fresh catalyst, a maximum P/O ratio of 5.6 was attained at 400°C, while the minimum value of 3.17 was observed at 450°C. Partial deactivation of the fresh catalyst with coke deposit from 1,3,5-triisopropyl benzene (TIBP) was found to have a significant effect on the product distribution, as reflected by increased P/O and xylene yield/TMB yield ratios. For the same toluene conversion, P/O ratios for the precoked catalyst were found to be 25-30% higher than those of the fresh catalyst. Similarly, the xylene yield/TMB yield ratios for the precoked catalyst were found to be 25-36% higher than those of the fresh catalyst. The experimental results were modeled over the fresh catalyst using the time-on-stream model, and the activation energy of toluene methylation was found to be ∼67.79 kJ/mol.