Cracking of n-heptane on a CrHNaY zeolite catalyst. The network of the reaction

Abstract

The cracking of n-heptane has been studied at 400, 450, and 470 °C over a CrHNaY zeolite catalyst using a tubular packed-bed reactor. The concept of “Optimum Performance Envelope” was used in order to identify which of the observed reaction products are primary and which are secondary. In this way the initial selectivity values for all primary products have been calculated and from such values we have seen that primary reactions other than cracking occur in this process. These reactions include isomerization and disproportionation of n-heptane. All the primary reactions which appear in the cracking of n-heptane can be explained as occurring on acid centers and consequently no direct catalysis by chromium ions in the first steps needs to be invoked to rationalize our results. Finally, a network for the “cracking” of n-heptane on the CrHNaY zeolite catalyst has been constructed on the basis of the observed behaviour of the selectivity curves.