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

The impact of mass transfer and bubble-wake dynamics on the selectivity of fast gas-liquid reactions was studied for a parallel-consecutive reaction n etwork using numerical simulations. Depending on bubble size and shape, the bubble wake can be closed or open. Spherical bubbles have only closed wake s without recirculation, while all other bubble types can exhibit recircula tion or vortex shedding depending on their shape and the Reynolds number. A lthough the importance of local mixing on the selectivity of complex reacti ons 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 t o 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 th e 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 dif ferent mixing pattern than that of a closed wake, leading to a different pr oduct distribution in the case of mixing-sensitive reactions. Since bubble shapes and sizes can be controlled by changing operating conditions or desi gn parameters, this analysis can be applied to actual reaction systems to e nable a rational design, control, scale-up, and optimization of existing an d new processes.