Chemical kinetics of the oxidation of methyl tert-butyl ether (MTBE)

Abstract

An experimental investigation in a conventional static apparatus of the oxidation of equimolecular methyl tert-butyl ether (MTBE)-oxygen mixtures has shown that MTBE oxidizes far less readily than alkanes like neopentane or 2,2-dimethylbutane. In the investigated pressure (up to 1000 Torr) and temperature ranges (300–500°C) we have not observed any cool flame formation; the mixtures either react slowly or ignite. Such behaviour is in line with the well-known antiknock effect of MTBE since this ether is already largely used as an octane booster in commercial gasolines, especially in Germany and in the United States. An evaluation of the rate constants of the possible elementary steps by the methods of thermochemical kinetics has allowed us to propose a reaction scheme which is in satisfactory agreement with our experimental results. It is shown that the reaction of MTBE-oxygen mixtures around 450°C does not really present the characteristics of a genuine oxidation reaction and appears more as a thermal degradation. This reaction chiefly gives formaldehyde and rather unreactive t-C 4H 9·radicals which react with oxygen to give i-C 4H 8 and HO 2·. The HO 2·radicals cannot be efficient propagating radicals in oxidation reactions. In the presence of 2% added HBr, the ignition limits of equimolecular mixtures of MTBE and O 2 are considerably lowered (∼50°C), and with 10% added HBr, the usual cool flame behavior of hydrocarbon oxidations are similarly observed for MTBE/O 2 mixtures.