Acoustically aided separation of oil droplets from aqueous emulsions

摘要

A novel method for recovering the oil phase from aqueous emulsions has been developed. The method applies a low-intensity, resonant ultrasonic field within a rectangular chamber, which is optionally filled with a highly porous medium. Oil droplets dispersed in water have negative acoustic contrast factor and thus are driven to the pressure antinodes of the standing wave field under the influence of acoustic radiation forces. Subsequent coalescence and/or wetting onto the internal surfaces of the chamber occur. Three types of porous media (an unconsolidated bed of 3-mm glass beads, aluminum mesh or reticulated polyester mesh) having pore sizes two to three orders of magnitude larger than droplets being collected were used. The oil collection was found to be sensitive to the natural affinity between the oil and the porous medium as well as its porosity. Of the three media studied, the polyester mesh was found to be the best in terms of the percentage oil collection while the bed of glass beads performed the poorest. The oil collection was found to be highly sensitive to the residence time of the emulsion in both the porous medium and acoustic field. Oil collection also showed expected trends with applied electrical power, but it was not found to be strongly dependent on the internal surface area of the mesh for the range of feed concentration tested. These experiments enable a preliminary understanding about the mechanisms underlying the separation process. (C) 2004 Elsevier Ltd. All rights reserved.