Evaluation of the oxidation stability of jatropha biodiesel/diesel blends

Abstract

One of the major technical issues facing biodiesel is its susceptibility to oxidation which is due to its content of unsaturated fatty acid chains, especially those with bis–allylic methylene moieties. In addition to the presence of air, various other factors influence the oxidation process of biodiesel including presence of light, elevated temperature, as well as extraneous materials such as metals which may be even present in the container material. The overall goal of this work is to evaluate the oxidation stability of Jatropha biodiesel/diesel blends. To achieve this goal, an acid–catalyzed pretreatment followed by a standard transesterification procedure with methanol and potassium methoxide catalyst was untaken to produce Jatropha methyl ester (JME) from Jatropha curcas L. oil (JO) with high acid value of 16.25 mg KOH/g. Analysis of the physicochemical properties has shown JME demonstrated potential as a good candidate for feedstock in biodiesel production because the studied physicochemical properties of JME adequately satisfied the relevant standards for biodiesel quality, with the exception of the kinematic viscosity at 40oC. Also, gas chromatography–mass spectrometry (GC–MS) analytical result showed that fatty acid composition of JO was quite similar to that of conventional oils. Especially, the evaluation of oxidation stability of Jatropha biodiesel/diesel blends was accomplished with respect to the change in the quality after oxidation by bubbling oxygen at elevated temperature as well as oxidation of blend fuels in contact with copper plate. The results demonstrated a strong correlation between biodiesel concentration and blend stability; i.e., the increase in biodiesel concentration results in the lower stability in both cases of the copper strip corrosion test and the accelerated oxidation.