(215l) Kinetics Analysis for Development of a Rate Constant Estimation Model of Ultrasonic Degradation Reaction

Ultrasound is used in various applications such as medical imaging, non-destructive testing of materials, underwater ranging, welding of thermoplastics, and chemical reactions. Especially, ultrasound has been found to be an attractive advanced technology for the degradation of hazardous organic compounds in water. The ultrasonic degradation of dyes has been investigated by many researches. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effects of ultrasonic frequency on degradation rate were not investigated quantitatively. In our previous study, we proposed a simple model for estimating the apparent degradation rate constant of methylene blue based on ultrasonic power and the SE_KI value in the range of frequency between 20 kHz and 500 kHz. However, we have not investigated the ultrasonic degradation of methylene blue in high frequency region around 1 MHz. The effects of initial concentration of methylene blue and volume of sample solution have not been investigated yet, either. In this study, the degradation process using methylene blue as model hazardous organic compounds by ultrasonic irradiation was investigated. The ultrasonic frequency was operated in the range from 20 kHz to 1.6 MHz, the initial concentration of methylene blue was in the range from 0.005 to 0.04 mM, and the sample solution volume was in the range from 0.1 to 0.3 L. Our proposed model can apply to this study which extended the frequency range. The effects of initial concentration and sample solution volume can also be estimated using this model in the range from 0.01 to 0.04 mM and from 0.1 to 0.3 L, respectively. It is also postulated that threshold power is required for degradation to progress, and frequency has less influence on threshold power during degradation. In addition, this model can apply to ultrasonic degradation of other organic hazardous compounds such as phenol.