Improved thermo-oxidative stability of structurally modified waste cooking oil methyl esters for bio-lubricant application

Abstract

This communication bridges the gap between conventional and alternative (renewable) lubricant basestocks in the lubricant industry. Waste cooking oil methyl esters (WCOME) originated from soybean oil was prepared by aiming at the maximum esters conversion. Esters conversion were confirmed and supported by thin layer chromatography and nuclear magnetic resonance spectral techniques (1H, 13C). WCOME bio-lubricant basestock was synthesized via In-situ epoxidation using acidic ion-exchange resin as a heterogeneous catalyst. A statistical experimental design, response surface methodology (RSM) was implemented to optimize the experimental conditions and to understand the interactions among the process variables. The optimum conditions inferred from the RSM were: temperature, 53.71 °C; catalyst loading, 28.17 wt%; time, 7.51 h; and H2O2, 1.72 mol. Products was confirmed and characterized by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and oxirane analysis by HBr titration method. At this optimum condition maximum epoxide content was found to be 5.8 mass%. Physico-chemical properties of WCOME and its epoxide were determined by standard methods and compared. Characterization results revealed that the structurally modified WCOME epoxide had improved viscosity and thermo-oxidative stability compared with unmodified WCOME. Overall, outcomes of the physico-chemical characterization data indicated that prepared epoxide can act as an alternative lubricant basestock for various industrial applications.