Performance evaluation studies of PEG esters as biolubricant base stocks derived from non-edible oil sources via enzymatic esterification

Abstract

Polyethylene glycol esters (PEGEs) as, environment-friendly biolubricants were produced from different fatty acids derived from plant oils by enzymatic esterification reaction in a solvent-free system using commercially available immobilized Candida antarctica Lipase B (NS 435) biocatalyst. The raw materials used were a 1:1 ratio of oleic acid: linseed oil fatty acid, linseed oil fatty acid: ricinoleic acid, and oleic acid: ricinoleic acid as mixed fatty acids. Enzymatic esterification exhibited around 98.1%, 97.8%, and 98.5% maximum yield for three different PEGEs under the following optimum reaction conditions under vacuum: the molar ratio of mixed fatty acids to polyethylene glycol 200–2:1, reaction time - 4 h, catalyst loading - 10% (w/w), and reaction temperature - 60 °C. This study aimed to improve the thermo-oxidative stability and cold flow behavior of the esterified products. The synthesized esters were confirmed and characterized by acid value, Nuclear Magnetic Resonance Spectroscopy (NMR), and Fourier Transform Infrared Spectroscopy (FTIR). The fatty acid composition of PEGEs was determined by GC-FID (Gas Chromatography). Physicochemical properties, thermo-oxidative stability, and friction-reducing properties of the PEGEs were studied thoroughly and compared against conventional petroleum-based lubricants. Results revealed that the plant oil-based biolubricants had good lubricating properties like high flash point, low pour point, high viscosity index, high thermo-oxidative stability, and improved friction-reducing properties compared with petroleum-based hydraulic lube oil. Overall, the data indicated that enzymatically esterified biolubricants have significant potential as ISO VG-32, VG-46, and VG-68 grade biolubricant base stocks for various commercialized industrial applications.