Evaluation of synthetic and bio-based additives on the oxidation stability of palm biodiesel: Parametric, kinetics and thermodynamics studies

This study evaluated the effects of additives on the oxidation stability of palm biodiesel (PBD) and appraised their oxidation kinetics cum thermodynamics. The results of Rancimat induction period (IP) and effectiveness factor, as well as acid value (AV) and iodine value (IV) indicated that tert-butylhydroquinone (TBHQ) was the most effective antioxidant. Notably, the reverse IP ranking of TBHQ under PetroOXY was likely caused by its degradation. Pyrogallol (PY), propyl gallate (PG), butylated hydroxytoluene (BHT), butylated hydroxyanisol (BHA) and quercetin demonstrated mid-range to high effectiveness in terms of IP. Nevertheless, PY, quercetin and curcumin had partial solubility in PBD. While α-tocopherol (α-T) had the least effects on IP and effectiveness factor, it still met the EN14214:2012 limit. The IP, AV, IV and kinematic viscosity except AV for 1000 ppm of PG met the limits. Correlations between the Rancimat and PetroOXY IP values were developed. The oxidation kinetics adhered to the first order kinetic model. By appraising the k values, TBHQ and BHA were clearly the most effective and this concurred with the IP values. The oxidation reactions were endothermic, non-spontaneous and endergonic in nature. Overall, TBHQ and BHA were the most effective synthetic antioxidants while α-T was the best bio-based additive.