Thermooxidative Properties of Biodiesels and Other Biological Fuels

The aim of this chapter is to show how thermooxidative properties of biological fuels can be evaluated by pressure differential scanning calorimetry (PDSC) and used to correctly classify the fuels studied. The onset oxidation temperature (OOT) is an important parameter for estimating the oxidation stability that can be evaluated by the ASTM method. Nevertheless, in addition to the OOT, other meaningful information can be extracted from the PDSC tests. That additional information provides a better understanding of the thermooxidative process, allowing for identifying subtle differences between similar fuels. In fact, the following lines show that the features extracted from heat flow curves obtained by PDSC allow to characterize and to differentiate each type of fuel respect to the other ones if the adequate statistical tools are applied. Thus, the proposed statistical analysis of the PDSC curves allows to classify the different fuels types chosen for this study: two types of biodiesel, seven different classes of edible oils and two wood species. The statistical study consisted of the application of Analysis of Variance (ANOVA) procedures and the implementation of a simulation study, using parametric bootstrap and methods of multivariate supervised classification as Linear Discriminant Analysis (LDA), Logistic Regression and Naïve Bayes classifier. Studying the thermooxidative properties of a fuel is important attending to various reasons. For example, vegetable oils are protected against oxidation thanks to antioxidants that precisely removed during the production process of biodiesel. For this reason, biodiesel is not stable, being susceptible to oxidation to a greater or lesser extent due to several factors including the presence of air, temperature, light, presence of hydroperoxides and antioxidants (Dunn, 2005; Knothe & Dunn, 2003; Knothe, 2007). The products resulting from the oxidation of biodiesel can damage internal combustion engines, it is therefore essential to study the oxidation stability of biodiesels. In the case of vegetable oils, they can produce significant changes in the salubriousness of food when the same oil is used repeatedly to fry due to the possible oxidation processes produced at the relatively high temperatures (Vorria et al., 2004). For this reason, the thermal stability to oxidation is an important parameter for oils. The study of thermooxidative characteristics of the species of wood is not as common as