Free Radical Mechanisms for the Treatment of Methyl tert-Butyl Ether (MTBE) via Advanced Oxidation/Reductive Processes in Aqueous Solutions

Cooper, W. J.; Cramer, C. J.; Martin, N. H.; Mezyk, S. P.; O'Shea, K. E.; von Sonntag, C.
Chem. Rev. 2009, 109, 1302.

Methyl tert-butyl ether (MTBE), used almost exclusively as a gasoline additive, has emerged as one of the most common environmental contaminants. It is found in the troposphere and also in surface and ground water, and snow. There have been numerous reports of its fate in both air and water, and it appears that it reacts primarily via free radical pathways. Because of its increasing presence in waters intended for drinking, there have been numerous studies investigating treatment processes for MTBE removal from waters. Of all available treatment processes, free radical based destruction using hydroxyl radicals, i.e., Advanced Oxidation Processes (AOPs) have been studied in some detail. Although several studies have proposed mechanisms for MTBE destruction, most of these appear to be incomplete and do not account for all of the reaction by-products. We have comprehensively reviewed the free radical-initiated reactions of MTBE and have proposed an overall mechanism that accounts for all of the reaction by-products that have been reported, and have proposed the likely occurrence of others not yet reported from empirical studies. This mechanism has been linearized in a form that will be used for developing a kinetic model to describe both MTBE destruction and the formation and destruction of its reaction by-products, and can be used in water treatment or remediation. This mechanism will also establish a foundation for condensed phase (heterogeneous) atmospheric chemistry of MTBE and may assist in better understanding the fate and transport of MTBE in the atmosphere. We conclude by identifying additional research required to complete a full MTBE degradation mechanism.