Air-Water Transfer of MTBE, Its Degradation Products, and Alternative Fuel Oxygenates: The Role of Temperature.
The gasoline oxygenate Me tert-Bu ether (MTBE) has become one of the world's most widespread groundwater and surface water contaminants. As a result, there has been increasing interest in the environmental behavior of MTBE and its degrdn. products, mainly tert-Bu formate (TBF) and tert-Bu alc. (TBA). In contrast, the environmental behaviors of the proposed alternatives to MTBE, namely Et tert-Bu ether (ETBE), tert-amyl Me ether (TAME), and diisopropyl ether (DIPE) have hardly been studied yet, although some of them are already in substantial use in various countries. A key parameter for the assessment of the fate, transport, and possible remediation of these contaminants is the air-water partitioning const. (KiH). The KiH is highly temp. dependent, and it is therefore necessary to obtain reliable exptl. values at relevant temps. Hence, the KiH of MTBE, ETBE, TAME, and DIPE, along with the degrdn. products, TBF and Me acetate, were detd. from 5 Deg-40 Deg. The alternatives to MTBE generally had a higher KiH, which implies that, upon emission into the environment, the alternatives partition more readily into the air phase than MTBE. This may favor their use, as it is in the air phase where diln. and degrdn. are the most effective. The degrdn. products of MTBE, with the exception of TBF, have much lower KiH values at all temps. Hence, the degrdn. products will have a stronger affinity for the water phase. The temp. dependency of the kinetics of air-water transfer is discussed using a boundary layer model. A significant effect of temp. was found for TBA but not for the ethers.
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