The effect of Marangoni convection on mass transfer in a rising droplet with surface reaction

Abstract

Dispersing of the medium from which the desired component is extracted is still one of the main approaches to liquid extraction. However, despite its high efficiency, this approach is still of empirical nature, since the choice of the main parameters - the average drop diameter and the residence time of the drop in the surrounding liquid (the extractant) - is determined by experiment in relation to the initial concentration of the extracted substance (reagent). The main difficulty with a full-scale theoretical treatment and numerical simulation is a three-dimensional shape of the droplet and, accordingly, the lack of experimental data on the structure of convective flows and the dynamics of reagent concentration fields in the moving droplet. The situation can get worse when the extracted component is a surfactant or reactive against the extractant. The paper presents the results of an experimental study of the structure and evolution of flows and distribution of a reagent (acetic acid) diffusing from a rising cylindrical droplet with an insoluble base component into a chemically active medium (aqueous sodium hydroxide solution). The motion of the droplet is accompanied by the development of Marangoni convection and neutralization reaction on the droplet surface.