The increase of biodiesel B20 oxidation stability using antioxidant obtained from soursop leaves extraction through microwave assisted extraction technique

The purpose of this research is to study the performance of soursop leaves extract as an antioxidant to inhibit biodiesel B20 oxidation. The antioxidant extraction was conducted with ethanol as the solvent (1:13 v/v) using microwave assisted extraction at powers of 300, 450, and 600 W for 2-10 min. In addition, the biodiesel oxidation was performed with air (2.3 L/min) at temperatures of 100, 110, and 120 °C for 0-70 min. The extraction results show that microwave power and extraction time strongly influence the extraction yield. The highest total phenolic concentrations of soursop leaves extract antioxidant obtained at 600 W and 8 min is about 0.608 mg/mL. From the oxidation results, it can also be seen that temperature and time influence the acid numbers of biodiesel B20. In 10 min, at 100, 110, and 120 °C, the acid numbers of biodiesel B20 are 0.09, 0.12, and 0.13 g NaOH/g. The mixture acid numbers of biodiesel B20 and soursop leaf extract are 0.126, 0.13, and 0.15 g NaOH/g. The optimization result shows that the activation energy of biodiesel B20 oxidation is 37.7 kJ/mol and the mixture of biodiesel B20 and soursop leaf extract is 41 kJ/mol. Therefore, it can be concluded that antioxidant additional is proven to inhibit the oxidation of biodiesel B20, as much as 47%.