Evaluation of Oxidative Stability and Kinetic Parameters of the Cottonseed and Soybean Biodiesels by Rancimat and Differential Scanning Calorimetry Techniques

Abstract

In this study, the oxidative stability of the cottonseed oil biodiesel (CB) and soybean oil biodiesel (SB) was investigated by two methodologies, Rancimat and Differential Scanning Calorimetry (DSC), using samples fresh and aged (mid-term storage condition (100 days)). The biodiesel samples were synthesized by transesterification and characterized by specific mass, kinematic viscosity, acidity value, ester content, viscosity index, and peroxide value. The activation energy (<em>E<sub>a</sub></em>), Arrhenius pre-exponential factor (<em>Z</em>), reaction order (<em>n</em>), and reaction rate at constant temperature (<em>k</em>(T)) were calculated by Borchardt and Daniels method. The results showed that oxidation affected the physicochemical properties of the biodiesel samples, especially, acidity (mg KOH/g), peroxide value (meq/1000 g), and induction period, with a decrease of around 55% for CB and 29% for SB. For kinetic parameters, the k(T) of both aged samples presented the highest values, with an increase of around 314% for SB. It was also observed that the rate constants increased with decreasing values of the induction period, in agreement with the current literature. According to the evaluation, the Borchardt and Daniels method can be recommended for a quick assessment of the biodiesel oxidation kinetic parameters.