Effect of additives on the oxidative stability and corrosivity of biodiesel samples derived from babassu oil and residual frying oil: An experimental and theoretical assessment

[Display omitted] •Phenolic compounds and PDA were used as antioxidants and corrosion inhibitors in biodiesel samples.•A theoretical study was carried out based on the formalism of the functional density theory.•PDA showed the highest anti-corrosion potential among the studied additives.•500 mg/kg of additive improved the stability of biodiesel samples. The objective of this work is to evaluate the effect of the addition of N,N′-di-sec-butyl-p-phenylenediamine (PDA), IONOL, and hydrogenated cardanol (HC) (500 mg/kg, each) on the oxidative stability and corrosivity of biodiesel obtained from babassu oil (BB) and from residual frying oil (BRFO). Oxidative stability was assessed by induction period (IP) using the Rancimat method (EN 14112), while the corrosivity was assessed by the mass losses of copper coupons immersed in the biodiesel samples (ASTM TM0169/G31-12a (2010)). The most severe corrosion was observed for the fresh biodiesel samples without any additives (4.85 mpy for BB, and 5.00 mpy for BRFO). Using PDA, IONOL, and HC as additives inhibited the copper corrosion in both biodiesel samples (between 0.61 and 3.09 mpy for BB, and between 2.19 and 4.69 mpy for BRFO). The use of IONOL and PDA as additives, besides showing a decrease in corrosion rates, also improved the oxidative stability (IP values) for both biodiesel samples (by 66 and >100 h, for BB; and by 3.31 and 7.23 h, for BRFO, respectively), demonstrating that these additives have bi-functionality in these biodiesel samples. Conversely, the use of HC increased the oxidative stability for BB (by 10.82 h) but also presented a pro-oxidant effect on biodiesel obtained from residual frying oil, decreasing its IP value by ca.18%. Finally, theoretical studies were carried out based on the formalism of the functional density theory, which confirmed that PDA has indeed the highest anti-corrosion potential among the studied additives.