Modeling and Simulation of the Isomerization of n-Heptane over a Molybdenum Oxycarbide Catalyst for Elucidation of the Bifunctional Mechanism

Abstract

In this work, the rates of reaction in the hydroisomerization of n-heptane over a molybdenum oxycarbide catalyst were formulated in terms of the transition state theory by applying the single-event kinetic modeling approach. The isomerization reaction was carried out between 603 and 643 K at 18.5 bar on a feedstock of n-heptane (8.3 mol %) and hydrogen (91.7 mol %). A bifunctional mechanism was shown to predominate at the rather high reaction temperature, and the reaction network was described by a bifunctional mechanism using 16 independent kinetic parameters, obtaining a good reproduction of the experimental data. On the acid sites, elementary steps such as (de)protonation, PCP isomerization, β-scission, methyl shift, and hydride shift were taken into account. On the metal sites, (de)hydrogenation and hydrogenolysis were accounted for. By applying the model to the simulation of a fixed bed reactor, an optimum volumetric yield of 95.43 vol % with an RON increase of 36.7 was obtained at 643.15 K. The low cracking selectivity of molybdenum oxycarbide makes it a potential catalyst for the isomerization of n-heptane and heavier paraffins.