THERMAL DEGRADATION MONITORING OF BIODIESEL IN THE PRESENCE AND ABSENCE OF ALCOHOLIC EXTRACT OF JAMBOLAN (Syzygium cumini Lamarck) AND Cu2+ IONS BY 1H NMR SPECTROSCOPY

Biodiesel can be obtained from the transesterification reaction of triglycerides with short-chain alcohols in the presence of a catalyst. Some of the methyl esters present in biodiesel are unsaturated, which favors the oxidation process and can be slowed or suppressed with the addition of antioxidants. There are many options and varieties of synthetic antioxidants, such as tert butylhydroquinone (TBHQ) and butylhydroxytoluene (BHT). However, plant extracts, containing substances such as anthocyanins and flavonoids, with antioxidant properties can be used because they are effective in protecting biodiesel from oxidation. In this study, we evaluated the antioxidant behavior of jambolan pulp extract (Syzygium cumini Lamarck) in biodiesel, in the presence and absence of Cu2+, at different exposure times at a temperature of 110 °C with a flow rate of 10.00 L h-1 of air using proton nuclear magnetic resonance (1H NMR) spectroscopy. The high-intensity signals obtained by 1H NMR spectroscopy showed that the biodiesel used was composed of 98.14% esters, with 35.35% saturated and 62.79% unsaturated esters. The low-intensity resonance signals showed that the main thermal degradation products were epoxides, aldehydes and hydroperoxides. The jambolan pulp extract reduced the oxidation reaction rate of biodiesel even in the presence of Cu2+ ions, demonstrating its potential use as an antioxidant.