Effect of dispersed phase viscosity on solid-stabilized emulsions

The time required to efficiently stabilize viscous oil droplets with finely powdered material during agitation has been investigated. The experimental work relied on silicone oils of varying viscosities (50-5000 cSt) dispersed in distilled water with a Rushton turbine (D = 6.5 cm) under controlled conditions (volume = 0.6 L, 0-17 kW/m(3), and constant agitation time). The emulsion-stabilizing solid particles were made of spherical iron in the 20-50 mu m size range. Each experiment consisted in wetting the powder with water, dispersing the oil/water phases for a given time and conditions, and to record the amount of oil stabilized after stopping agitation. In order to accurately determine the wettability of the powder, a new experimental method was developed. The comparison of the measured contact angle from the proposed technique with the available literature results shows an excellent agreement while being much simpler to use than current published methods. Emulsification in controlled conditions shows that the viscosity of the dispersed phase acted as a damping factor for particle anchoring at the o/w interface and plays an important role during the emulsification process, a role that has never been demonstrated and that must be considered in the design of processes involving solid-stabilized emulsions. Furthermore, the emulsification results at constant mixing intensity indicate the existence of a dispersed phase viscosity limit for a given agitation time beyond which emulsification becomes impossible. A relation between the emulsified oil volume, the o/w viscosity ratio, mixing power density, and agitation time was also proposed for the studied systems. The results from this investigation will support the design of processes for the generation of solid-stabilized emulsions involving extra-heavy oils. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.