Keywords: Esterification; oxidative stability; palm oil fatty acids; trimethylolpropane

Abstract

Refined, bleached, and deodorized palm oil become one of the potential renewable resources in biolubricant application. However, palm oil cannot be used directly as biolubricant because of its low oxidative stability. It is due to the presence of oxidation active site β-hydrogen in a glycerol backbone structure. This drawback can be overcome by molecule structural redesign through chemical modification process such as esterification with polyhydric alcohol. The synthesis of biolubricant was carried out via esterification of palm oil fatty acids with trimethylolpropane in a mole ratio of 3.5:1, 1.34% sulphuric acid as the catalyst at 154°C for 5.97 h. Gas chromatography equipped with a flame ionization detector was used to determine the percentage of ester composition in palm oil trimethylolpropane (POTMP) ester. The structure of POTMP ester was confirmed by Fourier transformation infra-red (FTIR), proton and carbon Nuclear magnetic resonance (1H-NMR and 13C-NMR) spectroscopy. The result showed that POTMP ester had successfully synthesized with 92% yield, 100% composition of triesters and POTMP existed in liquid form at room temperature. The existence of the ester functional group evidenced by FTIR at 1740 cm-1, the chemical shift of 1H NMR at 2.29-2.36 ppm and 13C NMR at 173.53-173.57 ppm. Physicochemical properties analysis showed that POTMP ester had oxidative stability at 183°C, pour point at 8°C, the flash point at 290°C and 158 of viscosity index which made POTMP plausible to be used in many industrial lubrication applications.