Esterification of Composition-modified Coconut Fatty Acid Distillate for the Synthesis of Insulating Esters

The increasing emphasis on environmental sustainability and efficient resource use drives strong demand for ester-based insulating oils. However, their high production cost limits large-scale application. Low-cost coconut fatty acid distillate (CFAD) is used to synthesize coconut-based trimethylolpropane ester (CTE₀). The optimal conditions are 1.2 wt% p-toluenesulfonic acid (TSOH) as the catalyst and a CFAD-to-Trimethylolpropane (TMP) molar ratio of 3.2:1 at 130 °C. CTE₀ exhibits a relatively high pour point (–3 °C) and a low fire point (275 °C). To improve its properties, the influence of molecular structures such as branching, carbon–carbon double bonds (C=C), and the odd–even carbon number effect in fatty acid chains on insulating oil properties is investigated. Simulation results indicate that the incorporation of odd-numbered carbon chains and C=C double bonds significantly lowers the pour point due to higher degree of molecular disorder and greater difficulty in forming static packing, while higher molecular weight (MW) enhances the fire point. Therefore, different ratios of nonanoic acid (C₉) and oleic acid (C_18:1) are added into CFAD to synthesize a high-performance ester insulating oil (CTE₃) with pour and fire points of –15 °C and 301 °C, respectively. This study presents a cost-effective synthesis strategy for ester-based insulating oils that reduces production costs by 50–60% compared with commercial natural esters, while also providing key insights into their structure–property relationships.