Synthesized biolubricants from naturally derived oleic acid: Oxidative stability and cold flow performance

Bio-lubricants are receiving increased interest due to their environmental advantages over petroleum-based analogues. This research demonstrates the evaluation and comparison of thermal and kinetic properties of bio-lubricants synthesized from naturally derived fatty acids. The oxidative stability of the vegetable oil-based bio-lubricants affects their storage stability and reusability. Five different types of bio-lubricants were previously synthesized from oleic acid, iso-oleic acid, and iso-stearic acid. Thermogravimetric analysis was conducted in the presence of air and nitrogen. Comparative studies of the kinetic parameters under thermal decomposition of each synthesized product show that these bio-lubricants are thermally stable. The calculated activation energy showed that trimethylolpropane iso-oleic acid triester (TMP-IOA) was thermally stable with an average activation energy Ea = 188.4 kJ/mol in an inert environment (Under N2). In the oxidative environment (under air), trimethylolpropane iso-stearic acid triester (TMP-ISA) was found as the most stable bio-lubricant with an Ea= 109.8 kJ/mol. The glyceride-iso-oleic acid triester (GLY-IOA) showed a high range frequency factor indicating complex behavior in an air environment. Among these lubricants, the GLY-IOA exhibited superior cold flow properties as measured using cryogenic differential scanning calorimetry. Overall, these comparative studies confirm that the lubricant-based oils produced using saturated or monounsaturated fatty acid provide a good combination of thermal and oxidative stability along with cold flow properties.