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 nheptane 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 nheptane and heavier paraffins.

Study on the preparation and n-heptane isomerization performance of MoOx-Pd/Ce-MCM-48 catalyst

“…3,4 The ideal mature technology for isomerization of n -C7+ ( n -alkanes with C7 and above) has not yet been achieved. 5,6 Therefore, the isomerization of long-chain alkanes, represented by n -heptane, has attracted great attention.…”

“…They believed that the low cracking selectivity of molybdenum carbide makes it a potential catalyst for n -heptane and heavy paraffin isomerization. 6 Molybdenum is prone to form a layered structure and also an electronic additive that can synergistically catalyze with composite catalysts prepared by metal doping. 15 Harmel et al 16 reported the possibility of MoO x catalyst combined with mesoporous solid acid to replace Pt for n -heptane hydroisomerization, which has been proven that an optimized non precious metal MoO x catalyst, when used in combination with mesoporous solid acids, can be similar to the corresponding platinum catalyst in the n -heptane conversion process.…”