Modelling the Mixing and Dissolution Kinetics of Partially Miscible Liquids

The problems of liquid–liquid extraction and solids dissolution in stirred tanks are classic mass transfer problems which have been studied extensively in the literature. An analogous problem, that of dissolution of pure drops close to their solubility limit, has been almost completely neglected. This problem has practical application in the dissolution and dispersion of small amounts of surface active additives, particularly in the water treatment industry and in oil field applications where the cost of the chemical additive is one of the major process costs. The question is also of interest for some chemical reactions, such as the third Bourne reaction (diethylmalonate in water) and the hydrolysis of acetic anhydride to acetic acid. In this paper, the drop size distribution and solute concentration in the bulk are measured throughout the dissolution period and the dissolution process is successfully modelled using an Eulerian–Lagrangian approach. The validated model is used to identify the key variables driving the dissolution rate. The approach to saturation, the impeller rotational speed, and the continuous phase viscosity all play an important role. When the solute is injected close to the impeller, the role played by surface tension is surprisingly small.