Ultrasonic demulsification of water-in-crude oil emulsions: Influence of rheological properties

In this work, we have studied the rheological properties of commercial water-in-crude oil emulsions of different compositions and the effect of their properties on ultrasonic demulsification. Shear rheological measurements in the temperature range of 10 to 30 °C showed that the emulsion with an aqueous phase concentration of 9.7 wt% behaved as a Newtonian fluid. The emulsion with a water content of 15.0 wt% changed from non-Newtonian to Newtonian flow with an increase in temperature. The more concentrated emulsions with water contents of 37.5 and 54.0 wt% behaved as non-Newtonian pseudoplastic fluids. The Ostwald-Weil model best described the rheological properties of all the non-Newtonian emulsions studied. Ultrasonic treatment of Newtonian emulsions at the power and exposure time parameters studied had a slight effect on water separation and resulted in an increase in viscosity, indicating the ineffectiveness of ultrasonic demulsification of these emulsions. In the case of non-Newtonian emulsions, an intensification of the demulsification process reached 46–61 %. The most effective water separation from all emulsions was observed with the ultrasonic treatment at a power of 0.2 kW after 2 min. However, the demulsification and emulsification processes occur simultaneously in emulsions treated with ultrasound. For this reason, the power and the exposure time are the parameters that need to be optimised for each specific type of crude oil emulsion depending on the concentrations of the aqueous phase, natural emulsifiers and solid impurities.