Influence of antioxidants in biodiesel degradation: Electronic paramagnetic resonance tracking of free radicals

Abstract

Biodiesel is considered a renewable fuel that has been replacing diesel. However, its degradation, caused by a radical reaction, is one of the biggest concerns about this fuel. Spin trapping is a useful resource to evaluate the radical formation in a sample. In the present work, the biodiesel degradation from canola, corn and soybean oils, with synthetic antioxidants (BHA -butylated hydroxyanisole; BHT- butylated hydroxytoluene; TBHQ- tert-butylhydroquinone) and extracts (rosemary; oregano; basil), were measured by Electron Paramagnetic Resonance (EPR). The measurements were performed at room temperature, applying the spin trapping technique, using the α-phenyl-N-tert-butylnitrone (PBN) as the spin trap. The analyzed data allowed evaluating the degradation of the samples and their stability. Besides, the presence of the hydroxyl radical in all samples in the degradation process was identified. The biodiesel from soybean oil presented the greatest stability compared to the others, with all antioxidants tested. The oregano extract proved to be the most efficient natural antioxidant in the canola and soybean biodiesel, with more than 300 days of free radical detection, while the rosemary extract was more efficient in the corn biodiesel, achieving free radical signals until the 209th day of analysis.