Synthesis and physicochemical characterization of fatty acid diethanolamides based on vegetable oils: process kinetics and analytical control

Abstract

The paper presents the results of a comprehensive study of fatty acid diethanolamides (FADEA) synthesis from three types of vegetable raw materials: coconut, palm kernel, and sunflower oils of RBD grade. The fatty acid composition of the starting oils and the resulting amidation products were determined by gas chromatography on a Chromatek‑Crystal 5000.2 analytical system. The coconut and palm kernel oils are characterized by a high content of lauric (47.8–50.8%) and myristic (15.8–18.0%) acids. It ensures the high foaming properties of the corresponding FADEA. Sunflower oil contains predominantly oleic and linoleic acids (88.4%), providing thickening and emulsifying characteristics. The synthesis of FADEA was conducted at a temperature of 100–125 °C under a nitrogen atmosphere using NaOH catalyst (0.1–0.5 wt.%). Kinetic studies showed 3–4 hours as an optimal reaction time. Further the concentration of free diethanolamine (DEA) stabilizes. We determine the free DEA content by two methods: potentiometric titration and gas‑liquid chromatography (GC). The GC method for monitoring the DEA content is the most effective one. The obtained FADEA samples meet consumer requirements: free DEA content 4.6–5.5%, acid value 1.50–2.82 mg KOH/g, Gardner color scale 3–4. The values of the apparent activation energy of the amidation reactions for the studied oils (64–71 kJ/mol) and the selectivity of formation of the target diethanolamides (93.8–96.1% at 100 °C) were calculated.