Effect of Metal Contaminants and Antioxidants on the Oxidation Stability of Argemone mexicana Biodiesel: Experimental and Statistical Study

Abstract

Biodiesel’s auto-oxidation by metal catalyzed decomposition of hydroxides (ROOH) is a major hurdle restricting the commercial viability of biodiesel. This paper investigates the oxidation stability of argemone biodiesel contaminated with transition metals such as: Fe, Ni, Mn, Cu, and Co. Pure argemone oil biodiesel (ABD) has a rancimat induction period of 2.5 h which does not satisfy the ASTM-D6751 and EN-14214 standard limits of 3 and 8 h respectively. The results show that the presence of a metal in argemone oil results in accelerating the free radical oxidation reaction. To meet the desired standards, present work experimentally investigates the effect of various antioxidants like BHT, BHA, TBHQ, PY, and PG in the range of 100–500 ppm on argemone oil biodiesel. Effectiveness order of antioxidants in pure biodiesel was observed as: PY > PG > BHA > BHT > TBHQ. The 500 ppm of most effective antioxidant pyrogallol (PY) has the potential to enhance the induction period of argemone biodiesel above 8 h which is vital by EN-14214 standard. Based on the results of most effective antioxidant PY and varying concentration of metals (Fe, Ni, Mn, Cu, and Co), several correlations have been developed to calculate the induction period of argemone oil biodiesel, as a function of antioxidant and metal concentration.