Kinetic Models for Hydrogenolysis of Thiophene on Co-Mo/γ-Alumina Catalyst

Abstract

A feasible, comprehensive, and rigorous mechanistic kinetic model was developed for hydrogenolysis of thiophene on a commercial hydrodesulphurization Co-Mo/γ-Al2O3 catalyst. The kinetics were modeled with 24 rate expressions based on three modes of adsorption: molecular and atomic adsorption of hydrogen, and Eley Rideal mechanism. The experimental data were obtained in a bench-scale tubular reactor with plug flow, and the conditions varied over the following range: total pressure, P t = 2–30 bar, temperature = 533–625 K, and molar hydrogen to hydrocarbon ratios 4–9. The experimental rate data were described by a set of Lagmuir-Hinshelwood-Hougen-Watson rate equations for both the hydrogenolysis of thiophene to butene and the hydrogenation of butene to butane on two different sites, σ and τ. The kinetic rate constants and adsorption equilibrium constants were estimated for each model using the optimization routine of Nelder-Mead simplex algorithm. Discrimination among rival models was based upon physicochemical criteria, analysis of the residuals, and statistical tests. The surface reaction between adsorbed thiophene and adsorbed hydrogen on σ sites in the hydrogenolysis, and the surface reaction between adsorbed butene and adsorbed hydrogen on τ sites in the hydrogenation when hydrogen is adsorbed molecularly are found to be the rate-determining steps. The predicted activation energies, enthalpies of adsorption, Gibbs free energies, and adsorption entropies compare exceedingly well with previously reported values in the literature.