The Effect of Biodiesel Oxidation Stability on The Removal of Polyunsaturated Fatty Acids

Abstract

Biodiesel has developed as a plant-based fuel alternative over the last 20 years and is now a substitute for fossil diesel oil. Compared to fossil diesel, palm oil biodiesel offers advantages in terms of emissions, toxicity, biodegradability, engine lubrication, and contribution to national energy security. Although palm biodiesel has good quality, its oxidative stability is still lower than that of fossil diesel. This is due to the content of polyunsaturated fatty acids, which ranges from 9-12%, significantly affecting oxidative stability. To improve this stability, methyl esters of polyunsaturated fatty acids need to be removed through a liquid-liquid extraction process using a silver nitrate (AgNO3) solution. The extraction process is carried out with various concentrations of AgNO3 (1 M and 5 M), methanol content in the solution (10%-v, 25%-v, and 50%-v), and the biodiesel to AgNO3 ratio (1:1 and 1:2) at a temperature of 25- 35°C for 3 hours, followed by the separation of extract and raffinate for 45 minutes. The research results show that the induction period for all variations experienced a decrease compared to biodiesel before extraction. However, GC-MS analysis and iodine number indicated a reduction in polyunsaturated fatty acid methyl esters after the extraction process. The best results in the extraction process were obtained with the variation of 1 M, 10%-v methanol, and a 1:1 ratio, with an induction period of 15.26 hours, polyunsaturated fatty acid methyl ester composition of 0.08%, and iodine number of 49.76 g iodine/100g.