Drop Coalescence during Emulsion Formation in a High-Pressure Homogenizer for Tetradecane-in-Water Emulsion Stabilized by Sodium Dodecyl Sulfate

Abstract

The present study investigates the effects of homogenizer pressure, surfactant concentration, ionic strength, and dispersed phase fraction on the coalescence rate of tetradecane-in-water emulsions during their formation in a high-pressure homogenizer. Experiments were conducted in a recirculating system consisting of a Rannie laboratory-scale single-stage homogenizer and a stirred vessel for tetradecane-in-water emulsions stabilized by sodium dodecyl sulfate (SDS). The initial evolution of the number concentration of droplets in the stirred tank was measured when subjected to a negative stepchange in the homogenizer pressure. The average drop coalescence rate constant in the homogenizer was inferred by fitting the experimental evolution of the number concentration of drops to a simple model accounting for the coalescence in the homogenizer under the assumption of a quasi steady state in the homogenizer. The residence time of the emulsion in the homogenizer was evaluated from the analysis of radial turbulent flow between disks. The step down homogenizer pressure was varied in the range 20.7–48.3 MPa, the drop size in the range 174–209 nm, the dispersed phase fraction in the range 5%–15%, SDS concentration in the range 0.0033–0.25 wt%, and ionic strength in the range 0.01–0.1 M. The coalescence rate constants were found to be in the range from 3.34×10−17 to 2.43×10−16 m3 s−1. The coalescence rate constant was found to be higher for higher homogenizer pressures, smaller drop sizes, lower dispersed phase fractions, and lower SDS concentrations and was insensitive to variations in ionic strength.