Effects of oxidation inducers on palm, jatropha, and sunflower biodiesel properties during 22-week storage and improvements with antioxidants

Oxidative stability is essential for biodiesel quality. This study examines the effects of copper and water as oxidative inducers on biodiesel derived from palm, jatropha, and sunflower oils. Key properties, including fatty acid methyl ester (FAME) content, iodine number, kinematic viscosity, and total acid number, were tracked over 22 weeks. The FAME content declined progressively, with palm biodiesel decreasing from 100% to 98.56% after 2 weeks and 95.76% after 22 weeks. Similarly, jatropha biodiesel dropped from 98.44% to 98.40% and 93.87%, and sunflower biodiesel declined from 96.55% to 96.42% and 91.84% over the same periods. The iodine number, kinematic viscosity, and total acid number also showed slight reductions over time and remained within commercial biodiesel standards. Copper had a more significant impact on oxidative degradation than water, with sunflower biodiesel being most affected due to its higher unsaturated fatty acid content. Three quadratic equations were developed to model quality changes over time. Adding 1000 ppm of tert-butylhydroquinone (TBHQ) effectively maintained the quality of palm and jatropha biodiesel for up to 18 weeks.