Advanced Ultrasonic Techniques for Monitoring and Detection of Crude Oil Concentration in Water

Abstract This study utilized an extensive array of experimental methods including optical microscopy, UV-visible spectrophotometry, dynamic light scattering, zeta potential analysis, fluorescence spectroscopy, and advanced ultrasonic testing to investigate the properties of oil–water emulsions with crude oil concentrations spanning from 50 to 500 ppm. The ultrasonic techniques encompassed several specific approaches: analysis of higher harmonics (quantified by the nonlinearity parameter γ), spectral dissipation index (SDI), sideband peak count index (SPC-I), and time-of-flight (TOF) measurements processed via the S-transform. The findings revealed that ultrasonic methods were particularly effective in detecting changes in emulsion characteristics across the tested concentration range. Notably, the nonlinearity parameter γ and SDI demonstrated high sensitivity to crude oil concentrations up to 200 ppm, with SDI effectively capturing shifts in spectral energy distribution as oil content increased. In contrast, SPC-I proved especially valuable at higher concentrations (300–500 ppm), showing a robust correlation with particle size distribution, where droplet coalescence led to larger, more heterogeneous droplet sizes. Meanwhile, TOF measurements using the S-transform detected subtle variations in ultrasonic wave propagation. At lower concentrations (50–200 ppm), TOF consistently decreased with the increase of oil concentrations, reflecting faster wave travel through smaller, uniform droplets. However, at higher concentrations (300–500 ppm), TOF increased, likely due to larger droplet sizes slowing wave propagation. These results underscore the distinct yet complementary strengths of different ultrasonic techniques: SDI excels at tracking broad concentration trends, while SPC-I provides insights into particle size dynamics and emulsion saturation effects. Together, these methods offer a comprehensive framework for characterizing oil–water emulsions across a wide range of conditions.