Gas-liquid reactions in well-mixed reactors—A fresh perspective

Abstract

Classification of gas-liquid reactions in the past has been based on comparison of characteristic times for diffusional mass transfer and chemical reaction in liquid film near the gas-liquid interface. The fast chemical reactions occur almost entirely in liquid film and the very slow reactions are confined to bulk liquid. Gas-liquid reactions that do not belong to either class have received less attention and have been in general assumed to be confined to either liquid film or bulk liquid for simplification of modeling and design of reactors. A unified approach for modeling of gas-liquid reactors is provided here considering a single reaction occurring over the entire liquid phase, with at least the reactant or the product being volatile. The two-way linkages between liquid film and bulk liquid, largely ignored previously, are properly accounted for in the present approach. The dispositions of concentration profiles for reactant and product in the liquid film are presented and discussed. A first-order reaction is considered as a specific example. Numerical illustrations for a perfectly mixed reactor demonstrate that an unwarranted confinement of liquid-phase reaction to either liquid film or bulk liquid can lead to incorrect design of and erroneous prediction of performance of gas-liquid reactors. Variation in relative importance of reaction in liquid film with respect to reaction in bulk liquid with variations in process parameters is investigated. The effectiveness of the liquid-phase reaction in the presence of mass transfer resistances is examined.