(107e) Dispersion of Water in Viscous Oils in a High Shear Mixer

The dispersion of two immiscible fluids and the resulting drop size distribution has been a subject of study for quite some time. For emulsions and fine dispersions, it has been found that using rotor-stator mixers for this purpose is superior to the employment of conventional stirred tanks because of the high energy dissipation density near and within the rotor-stator mill head. Most of the studies performed in this area have been done with a low viscosity continuous phase and a viscous drop phase. This is problematic because there is little information available for the dispersion of low viscosity liquids into high-viscosity continuous phase systems. As a result, it has not been possible to correlate the dispersed drop size distribution (DSD) with the disruptive and cohesive forces acting on the drops in these systems. Such information finds application in the scale-up of numerous dispersion processes with a high viscosity phase such as the formation of water droplets in crude oil. This study investigates the effect on the DSD of a water-in-oil dispersion in a Silverson L4R batch mixer with changing agitation rate, wettability of high-shear mixer surfaces, dispersed phase fraction, presence of salt in the dispersed phase, and continuous phase viscosity. The interfacial tension between the oil ? Crystal Oil 500FG ? and water is also modified by the addition of an oil-soluble surfactant, Tergitol NP-4. The wettability of the surfaces of the mixer that cause high shear rates ? the ones that may influence the resulting drop size ? is modified by treatment with dimethyldichlorosilane to make these stainless steel surfaces more hydrophobic. The continuous phase viscosity is controlled with temperature since the oil's viscosity is a strong function of temperature. The results of these experiments are used to postulate correlations for drop-size with the pertinent dimensionless number(s). Furthermore, they are used to investigate the relative importance of the drop size changing mechanisms of drop breakup and coalescence as a result of phase fraction and the other parameters.