ON THE LIMITATIONS TO ESTABLISH THE CONTRIBUTION OF THE DIFFERENT REACTION-MECHANISMS FROM SELECTIVITY DATA, DURING CRACKING OF LONG-CHAIN LINEAR PARAFFINS

n-Decane, n-dodecane, and n-tetradecane have been cracked at very shor t time on stream on ZSM-5, BETA; and USY zeolites. It is shown that di fferent reaction schemes can be used to explain the initial selectivit y values obtained for the different products. In all cases an ''uncert ainty band'' was found which makes it impossible to determine with acc uracy the separated contribution of the mono- and bimolecular cracking to the overall cracking. Nevertheless, it has been possible to establ ish the selectivities for the hydrogen transfer reactions. Finally, th e influence of the zeolite structure, chain length, time on stream, an d level of conversion, on the product distribution and the extent of t he reactions involved has been studied.