Catalytic Valorization of Palm-Based Fatty Acids into High-Performance Estolide Ester Lubricants

Abstract

Lubricants derived from petroleum, a nonrenewable resource, raise increasing concerns regarding environmental impact and long-term sustainability, driving demand for renewable alternatives. Vegetable oils are promising candidates; however, their direct use is limited by poor oxidative stability and inadequate low-temperature performance. Herein, palm-derived oleic acid and lauric acid were catalytically valorized into estolide esters via a one-pot process using Amberlyst-15 as a heterogeneous sulfonic acid catalyst. Estolide formation followed by esterification with 2-ethylhexanol proceeded efficiently under vacuum, with the catalyst retaining its ion-exchange capacity and chemical composition after consecutive steps. The effects of reaction temperature, mole ratio, and catalyst amount on estolide synthesis were examined. The resulting oleic–lauric estolide esters (OL-EST-EH) exhibited favorable lubricant-relevant properties, including a high viscosity index (158–169), excellent cloud point below −25 °C, pour point below −27 °C, and oxidative stability of up to 20.3 h under accelerated testing at 140 °C. These results highlight OL-EST-EH as a promising biobased base oil candidate for formulating high-performance, environmentally sustainable lubricants.