Biodiesel from Rapeseed and Sunflower Oil: Effect of the Transesterification Conditions and Oxidation Stability

In this study, we produced biodiesel fuel from two vegetal sources, rapeseed oil and sunflower oil, by transesterification reaction. The study aims to evaluate the impact of type of alcohol, its concentration and the reaction time, while keeping constant the temperature and the catalyst on the yield and quality of the biodiesel. For alcohol, methanol and ethanol were used at a molar ratio with the oil from 3 to 24. Transesterification was performed at various reaction times; 20, 40, 60 and 90 min for each oil and defined alcohol:oil molar ratio. The influence of these parameters on the biodiesel yield and properties were investigated in terms of density, viscosity, heating value, flash point, elemental content, density and oxidative stability of the final product. The benefit of oxidation stabilizers, catechol and 4-allyl-2,6-dimethoxyphenol was investigated. Results demonstrate that for rapeseed oil, the optimum reaction conditions to obtain a higher yield and quality of biodiesel were an alcohol:oil molar ratio of 15:1, with 60-min reaction time at 50 °C; while in the case of sunflower oil, the best yield and biodiesel quality were at an 18:1 molar ratio, with a 40-min reaction time and at 50 °C. In both cases, methanol provides the highest yields of biodiesel, and the obtained products satisfy the required standards and present a similarity with mineral diesel tested in same conditions.