Degradation of MTBE and Related Gasoline Oxygenates in Aqueous Media by Ultrasound Irradiation

Gasoline oxygenates [methyl tert-butyl ether (MTBE), di-isopropyl ether, ethyl tert-butyl ether, and tert-amyl methyl ether] in aqueous media are readily decomposed upon ultrasonic irradiation (665 kHz). The optimal instrumental settings for the production of reactive radical species employing a specific reactor were determined using dosimetry. Since hydroxyl radical is generally believed to be the predominant reactive species leading to the ultrasonically induced degradation of organic substrates in aqueous media, a terephthalate dosimeter was employed to selectively determine the yields of hydroxyl radicals. The decomposition of the gasoline oxygenates and the primary decomposition products of MTBE were compared in the presence of different saturating gases (O2, N2, and Ar). The observed decomposition rates for the oxygenates were similar under Ar and O2 saturated conditions, but significantly slower under nitrogen saturated conditions. The observed decomposition rates for a number of the primary decomposition products of MTBE are significantly slower under N2 and O2 saturation relative to Ar saturation. All the gasoline oxygenates in this study were degraded by more than 98% within 3 h of ultrasonic irradiation under O2 saturation with half-lives of 21–25 min.