The catalytic cracking of cumene over silica-alumina. A study with stable and radioactive tracer compounds
Azuaje-Fernandez, Alejandro J.
Hightower, Joe W.
Master of Arts
The catalytic cracking of cumene (iso-propyl benzene) over a silica-alumina catalyst (Houdry M-46) has been studied using the pulse technique in a microcatalytic reactor. The initial deactivation of the catalyst was found to follow an empirical first order equation with respect to the initial activity towards the formation of products. Cumene is given as the precursor of the coke formed at the surface of the catalyst. As in (18) the deactivation is thought to proceed by a Hinshelwood mechanism in which two sites are lost in every deactivating event or adsorption of the poison on two sites. The rate of the cracking reaction is described by a first order equation in reactant cumene and is proposed to follow a Langmuir-Hinshelwood mechanism in the range of 25° to 4°C and 1.67 atm. The true activation energy of the reaction was found to be 21.4 kcal mole. Experiments with H-D exchange over this catalyst showed that deuterium distribution in either benzene and cumene occurred to statistical scrambling at equilibrium, indicating the lability of the C-H bonds in the hydrocarbons. D-H exchange measurements gave as result 1.8 x 1 sites/nr and is set as an upper limit for the active sites on the catalyst surface if Br^nsted centers are thought to be the active centers for the dealkylation. Results of experiments with radioactive tracer compounds indicated that the reaction proceeded to almost equilibrium without influence of the back reaction. Values, based on a reaction model of a first order reversible process occurring near equilibrium, obtained for thermodynamic functions for the cracking reaction are reported. These values are in good agreement with the theoretical values obtained from the standard functions of formation of the reaction participant compounds.