Stabilizing sunflower biodiesel with synthetic antioxidant blends

Abstract

Biodiesel was prepared using base catalyzed methanolysis of sunflower oil. The oxidative stability of the neat biodiesel, as well as samples spiked with 0.15 wt% antioxidant was quantified by induction periods (IP) obtained with the Rancimat method according to the tangent method. The neat stabilizers, binary blends and a ternary mixture of poly(1,2-dihydro-2,2,4-trimethylquinoline) (Orox PK), tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane (Anox 20), and tris(nonylphenyl)phoshite (Naugard P) were tested. Of these, Anox 20 was the most effective stabilizer while Naugard P proved ineffective for the sunflower biodiesel. Synergistic improvement of oxidative stability was observed on partial substitution of this phenolic-based compound with the Orox PK. Combinations of the latter amine-based stabilizer with other phenolic antioxidants did not show any synergy, with perhaps the exception of DTBHQ. At a dosage of 0.15 wt%, only TBHQ, propyl gallate and pyrogallol, as well as their 2:1 blends with Orox PK, provided IP values that exceeded 8 h as required by the European Standard EN 14,214 for biodiesel.