Kinetic Modeling of the Effect of Antioxidant Additives on Biodiesel Oxidation Stability

Biodiesel oxidation stability is a major concern for this product. Antioxidants are added to the biofuel to prevent its degradation that can cause filters to clog, pumps to stick, and injection systems to fail. In this study, antioxidant additives were employed to determine biodiesel induction period (IP) behavior along an aging procedure at 43 °C for 13 weeks (ASTM D4625). Treatment rates of 25, 50, and 75 mg/kg of tert-butyl hydroquinone (TBHQ) and 1000 mg/kg of butylated hydroxytoluene (BHT) were used to improve oxidation stability, and IP measurements via EN 14112 were conducted weekly. IP increased with the treatment rate; the highest IP was achieved with 75 mg/kg of TBHQ initially, but the biofuel with 1000 mg/kg of BHT kept higher IP at the end. Kinetic models (R2 > 0.95) for IP change during aging were developed, with IP decrease as a linear function of time being reduction rate characteristic of the type of additive. IP prediction models from TBHQ treatment rates were also constructed and used to estimate the treatment rate to keep the biofuel adequate until consumption. Biodiesel oxidation stability may be adjusted through antioxidant addition, a mandatory procedure in Brazil. Prediction models may be applied to optimize the treatment rate and ensure the proper performance of biofuel in the field. Aware of the kinetic process of degradation of biodiesel over time and the effect of antioxidants in enhancing oxidation stability and keeping it higher for a longer time, the addition of antioxidants leads to a better performance. Comparing different antioxidant molecules results could support the best economical choice for producers.