Kinetic-transport Models of Bimodal Reaction Sequences-l Homogeneous and H@terogeneous Pathways in 0xidative Coupling of Methane

AWract-A reaction-transport model that combines gas-phase reactions mcurting within interstitial and intrapellet voids with surface reactions occurring on catalytic sites was used to descritm the oxidative coupling or methane in packed-bed reactors, a typical example or bimodal (h~ogeneous-heterogeneous) reactjon systcma. A kinetic model for gas-phase reactions was a-bled from available literature data; it describes well experimental results in empty reactors. Simtilationa suggest rhat C, yields greater than B-9% are unattainable with CH,/02 mixtures in homogeneous reactors. Staging the introduction of the oxygen reactant along the reactor length minimi= secondary oxidation reactions by lowering the local O1 pressures, and leads to a &ht increase in maximum yield (12% for 200 injection points) but also to much larger required reactor volumes. The introduction of an ideal catalytic function (methyl arid ethyl radical formation without full oxidation) al= increa&es maximum C, yields by ituzeasing rhe coneenlrdtion of methyl radicals involved in bimolecular coupling step. However, C, yields greater than 30% require seleaivc catalysts with very hi@ turnova rates ( > 100 s ’ ); higher rates bewme ultimately limited by intrapellet diffusion rates. Again, ,staging oxygen by mulriple injmion schemes increases attainable yields but requires larger reactor volumes and catalytic sites with low reaction order 4 < 1) in oxygen. For optimum conditions, staged oxygen injection taEhniques lead to C, yIelda as high BS 50%.