Ultrasound treated asphaltene laden W/O Interface: Insights into emulsion destabilization mechanism using a Microrheology approach

Abstract

In this study, the effect of different levels of ultrasonic fields on the microrheology of an asphaltene laden flat interface and on the behavior of asphaltene-stabilized emulsions was evaluated. Experiments were performed at frequencies of 20, 40, 50, 80, 120, and 150 kHz, and voltages of 20, 30, 40, and 50 V. In the flat interface experiments, four distinct microrheology regimes were observed: I. no movement, II. slow streaming, III. strong streaming and interfacial cavitation, IV. bulk cavitation and mixing. The regime encountered depended on the inertial effect of ultrasound on the subphase (Reynolds number) as well as the thermodynamic impact of ultrasonic fields. Treating the emulsions with the same ultrasonic fields resulted in three categories of behavior: I. no coalescence, II. coalescence, III. emulsification. There was a strong correlation between emulsion behavior with the microrheology regime. Below the threshold of interfacial cavitation (Microrheology Regimes I and II), no change in the emulsions was detected. When interfacial cavitation occurred (Microrheology Regime II), the emulsions coalesced significantly. This behavior was attributed to the ability of the cavitation process in breaking the asphaltene barrier between the droplets. However, increasing the frequency and the voltage of the field increased the mechanical effects of the ultrasonic field (Microrheology Regime IV) and caused secondary emulsification in the system.