Synthesis and characterization of trimethylolpropane based esters as green biolubricant basestock

Abstract

Bio-based lubricant is crucial to be developed considering the toxicity risk, climate change, energy security, and green-environmental approach. In this work, trioleate trimethylolpropane (TOTMP) (1) was synthesized through the esterification between trimethylolpropane (TMP) and oleic acid (OA) using a sulfuric acid catalyst. TOTMP was chemically modified to produce hyperbranched nonaoleate trimethylolpropane (NOTMP) (4). TOTMP was first epoxidized to epoxidized trioleate trimethylolpropane (ETOTMP) (2) followed by ring-opening reaction to produce trihydroxyhexaoleate trimethylolpropane (THHOTMP) (3). Lastly, THHOTMP was further esterified with OA to produce hyperbranched biolubricant NOTMP. Chemical structure confirmation of each product was performed by using Fourier transformation infrared (FTIR), proton, and carbon nuclear magnetic resonance (1H and13C NMR). The physicochemical analysis showed that the oxidative stability of NOTMP was at 172°C, pour point at-34°C, flash point at 320°C, and viscosity index at 237. The tribology analysis showed good wear protection with a minimal decrease in the friction coefficient (µ). Furthermore, rheology analysis showed that all synthesized compounds had been classified as Newtonian fluids. Therefore all the branched esters' bio lubricant products were successfully produced with improved lubricity properties, which are plausible for bio lubricants for both tropical and temperate countries.