COMBINED OXIDATION OF GASEOUS AND LIQUID ALKANES IN THE BARRIER DISCHARGE PLASMA

Abstract

The combined oxidation of gaseous (propane, butane) and liquid (heptane, octane, nonane and decane) alkanes in a barrier discharge plasma in oxygen has been studied. Oxidation process involves simultaneous conversion of gaseous and liquid hydrocarbons. Various C1-C4 hydrocarbon gases and mainly oxygenated compounds corresponding to hydroxyl and carbonyl compounds with the same number of carbon atoms in molecules as in the initial alkanes were detected among reaction products. At the stage of chemical reaction initiation in a barrier discharge, the electrons in the discharge interact with all the molecules of the initial mixture to form atomic oxygen and various hydrocarbon radicals. Their subsequent transformation leads to the formation of peroxide radicals of the corresponding alkanes, and their disproportionation leads to the formation of hydroxyl and carbonyl compounds. The mechanism of gaseous alkane oxidation is generally comparable to the mechanism of liquid hydrocarbon oxidation in a barrier discharge, and the key role in the mechanism of alkane co-oxidation is played by the interaction of atomic oxygen with a gaseous or liquid alkane. A probable mechanism for the combined oxidation of gaseous and liquid alkanes in a barrier discharge is proposed on the basis of experimental and literature data, and a simple equation is deduced, linking the rates of atomic oxygen interaction with alkane molecules to hydrocarbon concentrations in the gas phase of the discharge gas in the reactor. Applying the obtained equation, it is possible to estimate the direction of the oxidation of gaseous and liquid alkane mixtures and to involve the experimental data in calculating yet unknown rate constants of atomic oxygen interaction with alkane molecules. The results obtained make it possible to optimise the experimental conditions for the oxidation of gaseous and liquid alkane mixtures with the predominant oxidation of a gaseous alkane. These data will be useful in developing effective methods for the direct processing of a broad fraction of light hydrocarbons.