(128a) Manipulating Homogeneous Chemistry in Catalytic Microreactors: Operation Strategies and Design Principles

Combined catalytic and homogeneous chemistry of light hydrocarbons is a key issue in the design and thermal management of several microchemical (sub-millimeter scale) devices, used either for energy production, e.g., heat, or the production of chemicals, e.g., oxidative dehydrogenation of ethane to ethene [1]. Depending on the application, homogeneous chemistry in these devices should either be purposely avoided or promoted. The aim of this work is to study how the interplay between homogeneous and catalytic chemistry is affected by different operating conditions, such as the inlet composition and inlet velocity and by different reactor design parameters, such as the channel gap size (characteristic dimension) and the wall material. To this end, fuel lean propane/air combustion in a microburner is simulated in 2D using Computational Fluid Dynamics. Single-step homogeneous and catalytic chemistry is employed [2,3]. The results show that if only catalytic chemistry is desired, the microburner should either be operated at very low inlet velocities, near the extinction limit, or at high inlet velocities beyond the flame blow-out limit. Within the coupled catalytic/homogeneous chemistry regime, the extent of homogeneous chemistry and consequently the desirable temperature level can be maintained through adjustment of the inlet composition. Our results also show that although external heat losses increase decreasing gap size, homogeneous chemistry is sustained for channel gap sizes as low as 200 microns. The latter finding is attributed to the enhanced gas-to-solid mass transport that assists catalytic chemistry followed by enhanced solid-to-gas heat transfer that sustains homogeneous chemistry as the gap size decreases. Finally, we find that catalytic chemistry without gas reactions is sustained over a substantially wider inlet velocity range when employing high-conductivity wall materials.

References

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