CRACKING OF H-HEPTANE ON METAL-FREE H-ZSM-5 ZEOLITE AT HIGH HYDROGEN PRESSURE

The cracking of n-heptane in the presence of hydrogen on metal-free H-ZSM-5 was investigated. Under certain conditions it was possible to combine the processes of cracking and hydrogenation. The product distribution was attributed to the bimolecular cracking mechanism whether hydrogen was present or not. However, the relative amount of saturated reaction products depended on the hydrogen partial pressure. This was interpreted by hydrogen transfer reactions and direct hydrogenation. 'rhe hydrogenation of alkenes counteracts the coke formation and/or controls the number of vacant acid sites. The rate of cracking increases with increasing hydrogen partial pressure according to be apparent first order kinetics. The apparent activation energy (70 +/- 2 kJ/mol) of n-heptane cracking was found to be independent of hydrogen partial pressure. (C) 1994 Academic Press, Inc.