Stability Analysis of Pure Oil-Water Emulsion in Gravity-Based Separators¹

The purpose of this work is to investigate the stability of pure (emulsifier-free) oil-water emulsion in a gravity-based separator as a function of various parameters such as mixing speed, water volume concentration, temperature, and appearance. Only simple fluids (Exxsol^TMD110 and distilled water) were used to form the dispersion in a separator of operational volume 200 ml and internal diameter of 60 mm. Data were gathered from a portable dispersion characterization rig where videos of liquid phase separation can be saved and scanned. The study considered a wide range of mixing speeds between 600 rpm and 2500 rpm, with elevated temperatures of 60 °C and 80 °C. Both types (oil-in-water (O/W) and water-in-oil (W/O)) of pure emulsion were studied. In addition, two volumetric water concentrations (WCs) were considered for each type to investigate its stability under the parameters tested (i.e., 25% and 50% WC for W/O emulsion and 75% and 90% WC for O/W emulsion). The stability of the emulsion was examined in terms of the separation profiles of the water and oil phase, oil/water mixture volume, initiation time of free phase separation and/or the final time of separation. Mixing speed was shown to drastically impact the stability of O/W emulsion, from a few minutes to over 4 h. Conversely, insignificant effects of mixing speed were seen for W/O emulsion as the emulsions overall separated in a few seconds. Although temperature accelerated the oil separation rates of 75% WC emulsions, it delayed the initiation time of water separation.