Isopropyl‐Branched Fatty Acid Ester From Waste Cooking Oils: Potential Lubricant Base Oils

ABSTRACT Biobased lubricants offer a renewable and biodegradable option. Despite this potential, their commercial adoption is limited by elevated costs and performance issues. The high expense of biobased lubricant production mainly arises from raw materials; therefore, it is crucial to source low‐cost and accessible feedstocks like animal fats, waste or used cooking oil (WCO) and non‐edible oils. However, unmodified oils have drawbacks, especially subpar cold flow characteristics and diminished oxidative stability. In this research, fatty acids sourced from WCO were chemically modified to incorporate isopropyl branches into their chains. Both branched and unbranched free fatty acids were esterified separately with methanol and isopropanol, yielding two types of monoesters. The modifications resulted in a total of four monoesters: WCO‐derived fatty acid methyl ester (WCFAME), isopropyl‐branched fatty acid methyl ester (iPr‐WCFAME), fatty acid isopropyl ester (WCFAiPrE), and isopropyl‐branched fatty acid isopropyl ester (iPr‐WCFAiPrE). Structural integrity across all samples was verified using 1 H / 13 C NMR, GC–MS, and CMS analysis. Compared to polyalphaolefin (PAO‐6), a widely utilized lubricant base oil, most synthesized monoesters exhibited significantly lower viscosity, making them suitable for lubricant formulations in electric vehicles (EVs). All four monoesters demonstrated a higher viscosity index (VI) than PAO‐6, indicating their VIs are acceptable for various applications. The iPr‐branched esters showed better oxidative stability than their unbranched counterparts. The pour point values for the four synthesized products were recorded below freezing, enhancing their potential as biolubricants in cold environments. Furthermore, all esters displayed superior antiwear properties compared to PAO‐6.