Evaluation of antioxidant additives for biodiesel by EPR and UV-Vis spectroscopies, and the rancimat method (EN 14112)

Abstract

The aim of this study was to identify substances added to biodiesel capable of minimizing oxidation reactions, preventing the onset or anticipating the end of oxidation reactions, without affecting the other characteristics of biofuel. Electronic paramagnetic resonance spectroscopy (EPR) was used to qualitatively identify and characterize these possible antioxidant compounds. To compare and confirm the data obtained by EPR, the UV-VIS method was used, based on the extinction of the free radical DPPH• (2,2-diphenyl-1-picril-hydrazil) by antioxidants, which produces a decrease in absorbance at 515 nm. By the EPR method, all substances were efficient in the consumption DPPH•, but with variations in time and efficiency in consumption. The samples with greater efficiency in the consumption of DPPH• via the EPR method corroborated with substances that presented higher efficiency in antioxidant behavior via UV-VIS, confirming the efficiency of the method. The Rancimat Method (EN 14112), which determines the stability to fuel oxidation, was used to attest to the efficacy of antioxidants added to biodiesel. The sample that presented the best performance in increasing the oxidative stability time of the biodiesel sample was redoxoma 17 (R17), presenting as efficient as the known tempol (redoxoma R01 - 4-Hydroxi-2,2,6,6-tetramethylpiperidine-1-oxil), already patented as an antioxidant of biodiesel.