TDP kinetics model was derived as the reversible second order kinetics on toluene with activation energy of 25 I kcal/mol. The kinetics model is applicable for coked mordenite with coke content up to ca. 24.6% and for the estimation of relative activity of the coked at various TOS and thus cycle length. Two stages of deactivation mechanism were devised. Pore plugging and deactivation by coke predominates the initial coking period at ca. 7% coke content, during that period the strong Bronsted acid site diminishes and also the pore voidage shrinks. Upon extending TOS, coke laydown on the external surface of zeolite with pore voidage unaffected and the deactivation is caused by the acid site coverage. Soft coke content was found remaining fairly constant ca. 1.7 wt.% and hard coke increases with extending TOS. As a result, total coke builds up to 24.6 wt.% at TOS of 340 days. (C) 2004 Elsevier B.V. All rights reserved.