COKE DEPOSITION OF H-ZSM-20 AND USHY ZEOLITES

The cracking activity, selectivity and coking rate of H-ZSM-20 and USHY zeolites are compared during the transformation-of n-heptane at 723 K. H-ZSM-20 presents higher initial values for the cracking and coking activities, and for the ramification Of C4 and C5 cracking products. The composition of coke and its deactivating effect are also compared for the same transformation. There is no significant difference in the nature of the coke, although the observed ramification for the compounds deposited on H-ZSM-20 is slightly higher. Nevertheless the observable toxicity of the coke for the cracking process was lower on H-ZSM-20 than on USHY. Coke formation is more strongly deactivated than cracking during n-heptane transformation on both zeolites. A simplified model for the reaction kinetics network is proposed. Both experimental results for the coke deposition level versus time-on-stream and for the cracking activity versus coke level, are very well reproduced by this model. The model parameters clearly express the different cracking and coking abilities, and coke toxicity, between both zeolites.