Impact of 2-D bubble dynamics on the selectivity of fast gas–liquid reactions

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Abstract

The impact of mass transfer and bubble-wake dynamics on the selectivity of fast gas–liquid reactions was studied for a parallel-consecutive reaction network using numerical simulations. Depending on bubble size and shape, the bubble wake can be closed or open. Spherical bubbles have only closed wakes without recirculation, while all other bubble types can exhibit recirculation or vortex shedding depending on their shape and the Reynolds number. Although the importance of local mixing on the selectivity of complex reactions was studied by many research groups, there exist no studies addressing the effect of local mixing patterns (bubble-wake dynamics) close to single bubbles on fast gas–liquid reactions, that is, reactions that occur close to the gas–liquid interface. To study this class of reactions, a 2-D bubble model was developed, which accounts for liquid flow around the bubble, mass transfer, and reactions. It was found that different residence times in the bubble wake and at the bubble roof can lead to the formation of different products; recirculation in the bubble wake acts as a transport barrier for the liquid-phase reactants; and vortex shedding causes a qualitatively different mixing pattern than that of a closed wake, leading to a different product distribution in the case of mixing-sensitive reactions. Since bubble shapes and sizes can be controlled by changing operating conditions or design parameters, this analysis can be applied to actual reaction systems to enable a rational design, control, scale-up, and optimization of existing and new processes.

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