Single-Event Rate Parameters for the Hydrocracking of Cycloalkanes on Pt/US-Y Zeolites

Abstract

A single-event kinetic model is applied to the hydrocracking of cycloalkane model components on two bifunctional Pt/US-Y zeolites over a wide range of experimental conditions (T = 493−573 K, P = 10−50 bar, molar H2-to-hydrocarbon ratio = 50−300). Values for the standard activation entropies of the elementary steps were obtained from transition state theory, while independently determined Henry coefficients were used to describe the physisorption. Values for the composite activation energies, i.e., the sums of the protonation enthalpies of the alkene intermediates and the activation energies of the elementary carbenium ion transformations, were obtained from a regression of the experimental data. The composite activation energies for intra-ring alkyl shifts vary from 21 to 25 kJ/mol, which is higher than those for the corresponding acyclic alkyl shifts, which vary from 10 to 16 kJ/mol. The composite activation energies for cyclic protonated cyclopropane branching reactions range between 27 and 40 kJ/mol and are comparable to those of the corresponding acyclic reactions. The same holds for exo- and acyclic β-scission, with values from 22 to 76 kJ/mol. Endocyclic β-scissions, in general, have lower composite activation energies, varying from 31 to 56 kJ/mol, than acyclic β-scissions. However, because of a much lower preexponential factor, they proceed at a lower rate than acyclic β-scissions.