The effect of synthetic antioxidants on the oxidative stability of biodiesel

Biodiesels were prepared using base catalyzed methanolysis of sunflower, soybean and canola oils. Rancimat oxidative stability measurements showed that the induction period (IP) for neat canola biodiesel conformed to EN 14214, the European specification for biodiesel (IP > 6 h). Stability was enhanced when 0.5 wt.% of the synthetic antioxidants di-tert-butylhydroquinone (DTBHQ) or poly(1,2-dihydro-2,2,4-trimethylquinoline) (Orox PK) was added. Soybean-based biodiesel spiked with 0.5 wt.% DTBHQ also reached this specification. Orox PK improved the stability of sunflower biodiesel but the 3 h induction period specified by ASTM D-6751 could not be reached. Curiously, canola biodiesel was destabilized on adding the antioxidant Naugard P (tris(nonylphenyl) phosphite).