Abstract: To monitor and optimize the operation and to predict the concentration profiles of the components in commercial units for toluene disproportionation and transalkylation with C₉-aromatics, a kinetics-based mathematical model was developed and solved by the widely used Runge-Kutta algorithm.Based on several sets of operation data obtained from a commercial unit at steady state, the reaction kinetic parameters involved were estimated by the Broyden-Fletcher-Goldfarb-Shanno (BFGS) method.The kinetic model was also validated by the data from the commercial-scale unit operated with different feedstock compositions and operation variables.The results showed good agreement between the model predictions and plant observations, signifying that the proposed model could be applied to both offline simulation and online soft sensors.