Kinetic Studies of Xylene Transformation Reactions Over ZSM-5 Zeolite

A systematic study on the influence of reaction time and temperature during transformation reaction of m-, o- and p-xylene has been carried out over HZSM-5 catalyst using a riser simulator reactor system. The product selectivities have revealed that isomerization and disproportionation are the primary reactions. A higher conversion was observed for p-X as compared to that of m-X and o-X at all temperatures and all concentrations of ZSM-5. The highest selectivity of isomerization (100 %) was observed for p-X and o-X at 200 °C over 20 % ZSM-5, whereas the highest disproportionation selectivity (25 %) was observed for m-X at 400 °C over 10 % ZSM-5. The order of reactivity was observed to be dependent upon the concentration of ZSM-5. When ZSM-5 concentration was 10 % the order of reactivity was p-X > m-X > o-X, whereas at a higher concentration of ZSM-5 the order of reactivity was p-X > o-X > m-X. The experimental results have been modeled also using quasi-steady-state approximation. Kinetic parameters for o-X, m-X and p-X conversions into isomerization and disproportionation products were calculated using the catalyst activity decay function based on the time on stream. The apparent activation energies for disproportion as well as for the combined isomerization reactions over 10 % ZSM-5 catalyst were found to decrease as follows: E_p-X > E_m-X > E_o-X. It was also noted that when concentration of ZSM-5 was increased from 10 to 20 % the activation energies were increased for isomerization reactions but decreased for disproportionation reactions.