A fundamental kinetic model for hydrocracking of C-8 to C-12 alkanes on Pt/US-Y zeolites

Hydrocracking of n-alkanes in the range n-Cs-n-C-12 was performed on two co mmercial 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 exper imental data were quantitatively described with a model based on independen tly determined physisorption parameters, quasi-equilibrated hydrogenation-d ehydrogenation and protonation-deprotonation reactions, and a network of el ementary reactions of alkylcarbenium ions as rate-determining steps. The pr eexponential factors of the rate coefficients for skeletal isomerization an d carbon-carbon B-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 protona tion enthalpy, to be obtained by regression of the data. No statistically s ignificant dependence on the hydrocarbon feed of the estimates for the comp osite activation energies was found over the investigated range of carbon n umbers, Introduction of a single catalyst-dependent adjustable parameter ac counting for the difference in protonation enthalpy allows us to use the se t of composite activation energies obtained by regression of the data on on e zeolite to describe hydrocracking on a Pt/US-Y zeolite with different aci d strength. (C) 2000 Academic Press.