Chapter 21 - Influence of impeller type and agitation conditions on the drop size of immiscible liquid dispersions

Abstract

A common need in industrial liquid–liquid dispersion processes is to scale-up a drop size distribution from a small scale to the plant scale. For low-viscosity dispersions the correlations reported in the literature most commonly relate the Sauter mean diameter to impeller diameter ratio (d32/D) to We-0.6 with additional groups to account for effects of dispersed phase concentration and dispersed phase viscosity. However until very recently almost all the work had been limited to Rushton disc turbines. Further, recent research and industrial experience indicate that the We-0.6 correlations do not adequately describe the drop breakage mechanisms. This chapter describes a study which was carried out between 1990 and 1996 as part of a larger research FMP program on liquid–liquid dispersions. The drop size distributions of immiscible liquid dispersions were measured in 0.17 and 0.29m diameter tanks for a variety of impeller types: hydrofoils, Rushton turbines, and pitched blade turbines. Silicone oil, chlorobenzene, xylene, cyclohexane and tri-butyl phosphate at a phase volume fraction of 0.13% were used as the dispersed phases, with distilled water as the continuous phase. The drop size distributions were measured using macro-photography and subsequent manual sizing to generate drop size distributions and Sauter mean diameters (d32) which correlated with the impeller geometry, operating conditions and continuous and dispersed phase physical properties.