A PERCOLATION APPROACH FOR THE MODELING OF DEACTIVATION OF ZEOLITE CATALYSTS BY COKE FORMATION - DIFFUSIONAL LIMITATIONS AND FINITE RATE OF COKE GROWTH

Deactivation of a ZSM-5 catalyst by coke formation is modeled in the presence of diffusional limitations. Coke formation starts with the deposition of a coke precursor, proceeds through growth reactions and stops under the influence of termination reactions. Parallel and consecutive coking mechanisms are considered. The influence of the composition of the reaction mixture is investigated. The concentrations of reactants and reaction products and the coke content are obtained as a function of the position inside the catalyst. The overall rate of the main reaction decreases monotonically with increasing coke content of the catalyst. This is not necessarily so for the coking reaction, when the rate of coke growth is large with respect to the rate of deposition of coke precursor.