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 li pid (sunflower oil triacylglycerols) liquid phase oxidation by molecular ox ygen have been studied. Ionic surfactants sodium dodecylsulphate (SDS) and cetyltrimetyl ammonium bromide (CTAB) were found to affect the rate and mec hanism 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 th e beta-carotene consumption rate. Anionic surfactant SDS is found to be a c atalyst for the heterolytic decay of hydroperoxides. In the case of alpha-p henyl ethyl hydroperoxide, the decay reaction catalyzed by SDS yields pheno l that is an acceptor of free radicals. So the ethylbenzene oxidation is co mpletely inhibited in the presence of SDS. The same effect on the ethylbenz ene oxidation and its hydroperoxide decay was found to be caused by nanodis persed Al2O3. Cationic surfactant CTAB as a catalyst causes the decompositi on of ethylbenzene and limonene hydroperoxides via free radical formation t hat results in acceleration of hydrocarbon oxidation. Solid oxides SiO2, Ti O2 non-ionic ethoxylated hydrocarbons, and sodium bis (2-ethylhexyl) sulfos uccinate (AOT) show a slight effect on the hydroperoxide decay and hydrocar bon oxidation rates. The effect of surfactants and cosurfactants on the inh ibited oxidation of lipid and hydrocarbons is strongly dependent on the nat ure of antioxidant and surfactant used. (C) 1999 Elsevier Science B.V. All rights reserved.