Hydrocarbon and lipid oxidation in micro heterogeneous systems formed by surfactants or nanodispersed Al2O3, SiO2 and TiO2

The effect of surfactants and micro dispersed solid oxides on the kinetics and mechanism of hydrocarbon (ethylbenzene, limonene, beta-carotene) and lipid (sunflower oil triacylglycerols) liquid phase oxidation by molecular oxygen have been studied. Ionic surfactants sodium dodecylsulphate (SDS) and cetyltrimetyl ammonium bromide (CTAB) were found to affect the rate and mechanism of hydroperoxide decay and consequently the rate of the ethylbenzene and limonene oxidation. In the case of beta-carotene, which does not form hydroperoxides in the course of oxidation; the surfactants do not affect the beta-carotene consumption rate. Anionic surfactant SDS is found to be a catalyst for the heterolytic decay of hydroperoxides. In the case of alpha-phenyl ethyl hydroperoxide, the decay reaction catalyzed by SDS yields phenol that is an acceptor of free radicals. So the ethylbenzene oxidation is completely inhibited in the presence of SDS. The same effect on the ethylbenzene oxidation and its hydroperoxide decay was found to be caused by nanodispersed Al2O3. Cationic surfactant CTAB as a catalyst causes the decomposition of ethylbenzene and limonene hydroperoxides via free radical formation that results in acceleration of hydrocarbon oxidation. Solid oxides SiO2, TiO2 non-ionic ethoxylated hydrocarbons, and sodium bis (2-ethylhexyl) sulfosuccinate (AOT) show a slight effect on the hydroperoxide decay and hydrocarbon oxidation rates. The effect of surfactants and cosurfactants on the inhibited oxidation of lipid and hydrocarbons is strongly dependent on the nature of antioxidant and surfactant used. (C) 1999 Elsevier Science B.V. All rights reserved.