Modeling and Bifurcation Analysis of Oxidative Coupling of Methane

In the first part, we present a detailed ignition-extinction analysis of Oxidative Coupling of Methane (OCM) in the gas phase using a global kinetic model for the various oxidation, reforming and dehydrogenation reactions. The kinetic model satisfies the thermodynamic constraints and is validated with literature data as well as new data obtained under near isothermal conditions. It is shown that the type of reactor used has profound influence on the width of the region of multiplicity. Further, the best C₂ yield may be obtained on the ignited branch close to the extinction point where exothermic chemistry dominates or at higher space times or feed temperatures where endothermic chemistry dominates. The extinction locus, which forms the boundary of the region of autothermal operation, is determined as a function of various design and operating variables. In the second part, ignition-extinction analysis of laboratory scale catalytic reactors with heat exchange with the furnace is provided. It is shown that the same volume or mass of catalyst packed in tubes of different diameter and/or with different lengths of inert sections could lead to different types of ignition-extinction behavior as well as product distribution. The impact of tube diameter, heat exchange time, length of inert sections and catalyst dilution on the ignition-extinction behavior is analyzed. Simulations on the impact of heat loss, kinetics and heat/mass dispersion on the region of autothermal operation of lab-scale reactors are also presented. In the third part, ignition-extinction behavior of catalytic OCM with La₂O₃/CaO catalyst in large scale adiabatic reactors is analyzed using a global kinetic model. It is shown that in the homogeneous limit (small particles), the best selectivity of the C₂ products is obtained in the limit of very thin bed (with effective heat and mass Peclet numbers approaching zero). When inter and intra-phase heat and mass transfer gradients are significant (larger particles) so that particle level ignition could occur, selectivity to C₂ product can be enhanced. The impact of catalyst particle properties, inter and intra-particle gradients on conversion and C₂ product selectivity on the ignited branch is analyzed. Finally, some potential autothermal reactor designs for OCM with catalysts of different activity are proposed.Chemical and Biomolecular Engineering, Department o