A Fundamental Kinetic Model for Hydrocracking of C8 to C12 Alkanes on Pt/US–Y Zeolites

Abstract

Hydrocracking of n-alkanes in the range n-C8–n-C12 was performed on two commercial Pt/US–Y zeolite catalysts at temperatures of 493–533 K, pressures of 0.5–5 MPa, and molar hydrogen-to-hydrocarbon ratios of 30–300. The experimental data were quantitatively described with a model based on independently determined physisorption parameters, quasi-equilibrated hydrogenation–dehydrogenation and protonation–deprotonation reactions, and a network of elementary reactions of alkylcarbenium ions as rate-determining steps. The preexponential factors of the rate coefficients for skeletal isomerization and carbon–carbon β-scission steps were calculated using the transition-state theory, leaving the composite activation energies of the rate-determining steps, i.e., the sum of the activation energy and the corresponding protonation enthalpy, to be obtained by regression of the data. No statistically significant dependence on the hydrocarbon feed of the estimates for the composite activation energies was found over the investigated range of carbon numbers. Introduction of a single catalyst-dependent adjustable parameter accounting for the difference in protonation enthalpy allows us to use the set of composite activation energies obtained by regression of the data on one zeolite to describe hydrocracking on a Pt/US–Y zeolite with different acid strength.