Study on the mechanism of auto-oxidation of Jatropha biodiesel and the oxidative cleavage of C[sbnd]C bond

Abstract

Jatropha biodiesel was obtained according to the continuous preparation process which included vapor esterification - transesterification - methanol steam distillation. Accelerated oxidation of small Jatropha biodiesel was obtained by the Rancimat method. GC–MS and liquid phase micro-extraction were used to study and analyze the components in the oxidation process of Jatropha curcas biodiesel. The electronic effects of the related reactants and products were calculated by density functional theory, followed by the deduction of the related chemical reaction paths. Experimental investigation shows that methyl linoleate is the main factor affecting the oxidation stability of the Jatropha biodiesel. The main volatile products at the initial stages of the oxidation of methyl linoleate are hexanal, methyl octanoate, styrene, and 2-heptenal. The cis/trans-3-octyl-oxiranyl octanoic acid methyl ester (18.03% yield) is produced by the reaction of peroxy acid and methyl oleate during the oxidation of methyl oleate. The hydrogen extraction reaction is difficult to occur, and the oxidation reaction energy barrier is relatively high due to the relatively large bond energy of the CH bond in the methyl stearate molecule. In this manuscript, the auto-oxidation mechanism of the biodiesel fatty acid methyl esters at the initial stage of oxidation, the path of oxidative cleavage of the CC bond of Jatropha biodiesel and the formation process of ethylene oxide structure are obtained through DFT calculation and analysis of the oxidation products.