REACTION PATHWAYS FOR THE AROMATIZATION OF PARAFFINS IN THE PRESENCE OF H-ZSM-5 AND ZN H-ZSM-5/

The effect of the dehydrogenating component of H-ZSM-5 and Zn/H-ZSM-5 catalysts on n-heptane aromatization reaction was studied. An increase in the yield of aromatics observed over Zn/H-ZSM-5 is explained by th e enhanced production of olefins, facilitating the aromatization react ion by the effective dehydrogenating action of zinc on paraffins. A si gnificant change in the selectivities of toluene and C-9+ aromatics wa s observed after addition of zinc. The increase in the yield of toluen e observed over Zn/H-ZSM-5 from both n-heptane and Bombay High (BH) li ght naphtha indicates the possible occurrence of direct dehydrocycliza tion of paraffins in the presence of zinc. Zinc also facilitates the e ffective conversion of C-6-C-8 oligomers to the corresponding aromatic s, an in that way suppresses the further oligomerization of C-6-C-8 ol igomers on one hand, and cracking of C-6-C-8 oligomers on the other; w hich is reflected in the decreased yields of fuel gas and C-9+ aromati cs in the product. The product pattern of the BH light naphtha aromati zation suggests that the presence of zinc also suppresses the acid cat alyzed alkyl transfer reactions which generally take place over H-ZSM- 5. Reaction pathways have been established to explain the selectivity changes that occurred in presence of zinc.