Effect of MoО2(VI), Zn(II), Cu (II) and Mg(II) complexes with N-methyldecanohydroxamic acid on the thermal oxidation stability of biodiesel

Abstract

General climate changes and catastrophic environmental pollution cause the steadily increasing interest in the world to bio-based technical oils, including lubricants. In order that they bully comply with current environmental requirements, the additives added to them must not contain environmentally harmful components and provide the maximum thermal oxidation stability of the base oil. A significant disadvantage of zinc dialkyl dithiocarbamates and dialkyl dithiophosphates, which are widely used today as highly efficient polyfunctional additives, is that they contain ecotoxic organosulfur and organophosphorus components. In view of this, complexes of biometals with hydroxamic acids are promising. The paper presents the results of a study of the influence of MoO2L2, ZnL2, CuL2, MgL2 coordination compounds with N-methyldecanohydroxamic acid (HL) and mixtures of MoO2L2 with tert-butylcatechol and 2,6-di-tert-butyl-4-methylphenol (ionol) on the oxidation of distilled sunflower fatty acid methyl esters (one of the variants of biodiesel). Procedures for the synthesis of novel homoleptic Mg(II) and Zn(II) bis-hydroxamate complexes and their spectral characteristics are presented. The antioxidation properties of the complexes contained in the model solutions were determined by the method of oxygen absorption in a hermetically sealed system at 110 C. It has been found that the magnesium complex has no effect on the oxidation of the substrate, and that the copper complex decomposes, under experimental conditions, to metallic copper, which is an oxidation promoter. Zinc and molybdenum complexes exhibit antioxidation properties. It has been shown that ionol is an efficient co-component for MoO2L2, but no synergistic effect was detected. In view of the high tribological characteristics, the MoO2L2 complex is a promising prototype for the development of a polyfunctional eco-friendly additive to commercial biodisel-based lubricating compositions.