Continuous, Recycle and Batch Emulsification Kinetics using a High-Shear Mixer

In-line rotor-stator mixers are widely used to emulsify immiscible liquids, but there is little understanding on the size reduction kinetics and on their performance if used in a continuous or in a recycle arrangement. In this study, a systematic series of experiments were performed to study the droplet size reduction of a 10 cSt silicon oil coarse emulsion using different flow rates and number of passes for a continuous and a recycle configuration using a L5M-A Silverson Laboratory mixer.
The droplets size distributions obtained were bimodal. It was found that the mode of the larger daughter droplets is a better parameter to follow the emulsification kinetics than the Sauter mean diameter; the volume fraction of the small daughter droplets was estimated to be 6% using two generalized gamma functions. For the continuous arrangement it was found that impeller speed and mean residence time inside the rotor-stator correlated with an average error of 3.2%. It was also found that a Poisson chain can link the results of both operation arrangements. This stochastic model allowed following the disappearance rate of the coarse droplets and the evolution of the daughter droplets' mode with an average error of 2.3 %. The model developed allowed the comparison of both arrangements using an in-line rotor-stator.
A simplification of the Poisson chain model for long times was used to analyse batch emulsification kinetics. The droplet size reduction rate and batch volume could be explained in terms of the in-line results.