Ultrasonic splitting of oil-in-water emulsions

Standing resonant ultrasonic wave fields can be utilized for liquid–liquid separation of the dispersed particles and the fluid caused by the acoustic radiation pressure and the induced particle agglomeration or coagulation/coalescence process. For the splitting of oil-in-water emulsions, the available piezoelectric composite transducer technology was improved and a dedicated resonator with crossed plane wave sonication geometry has been developed. The resonator chamber is entirely made of aluminium or tempax glass and the PZT piezoceramic transducer delivers an acoustic energy flow density of up to 24 W/cm2 into the sonication volume. The chosen resonance frequency is kept stable by automatic frequency control utilizing the maximum true power criterion. Physically and chemically well-defined low and high density pure laboratory and also industrially used cooling-lubricating oil-in-water emulsion samples have been investigated. The quality of the ultrasonic-induced particle separation/coagulation process is characterized by physical–chemical analysis of the separated oil- and water phase and by determining the change of the particle size distribution of the initial emulsion due to the ultrasonic treatment. [Work supported by the European Commission, Contract Nos. ERBFMBICT960916 and ERBFMRXCT970156.]