Mechanism of Degradation of Ethyl t-Butyl Ether by Sodium Persulfate

Abstract

Ethyl t-butyl ether (ETBE) is a widely used gasoline additive known to be a persistent chemical substance. In this research, the mechanism of the degradation of ETBE by sodium persulfate was investigated. The sodium persulfate treatment of ETBE revealed that 100% ETBE in aqueous phase was degraded within 79 h. The degradation of ETBE followed a pseudo-first-order reaction and its degradation rate constant was 0.054 h^-1. The identification of byproducts in both aqueous and gas phases by GC-FID and GC-TCD revealed that acetaldehyde, ethanol, acetone, t-butyl alcohol (TBA), acetic acid, t-butyl acetate, CO₂ and CH₄ were generated during the reaction. 95% of the carbon in the degraded ETBE was recovered in the form of these byproducts. The degradation of each byproduct was carried out to determine the degradation pathways of ETBE by sodium persulfate. Consequently, the degradation pathways are proposed as follows: the main pathway in the initial stage is (i) ETBE → TBA + ethanol, and the subpathway is (ii) ETBE → t-butyl acetate. Further degradation pathways are proposed as follows: ethanol → acetaldehyde → acetic acid, TBA → acetone → acetic acid, t-butyl acetate → TBA + acetic acid and acetic acid → CO₂.