Synthesis and Physicochemical Properties of Estolide Esters Made From Mixtures of Palm Fatty Acid Distillate and Oleic Acid as Bio-Lubricant Base Oil

Palm fatty acid distillate (PFAD) is an economical, non-edible by-product of palm oil refining, making it a valuable feedstock for bio-lubricants. However, its high saturated fatty acid content typically leads to suboptimal cold flow properties in the resulting bio-lubricants. This study presents a method to improve both the cold flow characteristics and oxidation stability of PFAD-derived bio-lubricants. Neat PFAD and PFAD–oleic acid (PFAD–OA) mixtures were reacted with hydrogen peroxide and acetic acid to produce an estolide mixture containing both hydroxyl and carboxylic acid functionalities. The hydroxyl groups were esterified with fatty acids, whereas the carboxylic acid groups were converted to ester groups using 2-ethylhexanol, forming estolide esters. Analysis of the lubricant properties revealed that estolide esters produced from neat PFAD and PFAD–OA mixtures exhibited performance comparable to commercial products. Specifically, the kinematic viscosity at 40°C ranged from 44 to 121 cSt, increasing with higher OA content in the PFAD–OA mixture. Additionally, the inclusion of more OA significantly enhanced the cold flow properties, achieving temperatures between −12°C and −33°C. Other lubricant characteristics, such as oxidation stability and anti-wear properties, were comparable with a commercial bio-lubricant sample. This study demonstrates that PFAD–OA mixtures can effectively yield bio-lubricants with desirable attributes.

Practical Applications: The estolide esters derived from palm fatty acid distillate and oleic acid have demonstrated significant potential as lubricant base oils for environmentally friendly lubricants due to their natural biodegradability and outstanding lubricant properties.