Solid-liquid equilibrium of binary mixtures of triacylglycerols and fatty acids/alcohols

Abstract

Vegetable oils and fats are complex mixtures primarily composed of large quantities of triacylglycerols (TAGs) and small quantities of other chemicals, such as diacylglycerols, monoacylglycerols, fatty acids, and fatty alcohols. The individual components of these lipidic systems find several applications in lipid-based matrices, particularly in the food, cosmetic, and pharmaceutical industries. Understanding the solid-liquid equilibrium (SLE) data of (TAG)–fatty compound mixtures is essential for designing separation and purification processes to obtain the pure components from the natural complex mixtures.

In the present work, the solid-liquid phase diagrams of trilaurin and four fatty compounds (1-decanol, 1-dodecanol, capric acid, and lauric acid), as well as trilinolein and four other fatty compounds (1-hexanedecanol, 1-octadecanol, palmitic acid, and stearic acid), were determined using differential scanning calorimetry (DSC). Additionally, polarized optical microscopy was applied to complement the calorimetric studies. The trilaurin-based systems exhibit eutectic-type behavior, with eutectic points at $x_{\text{TLA}}$∼ 0.1 (trilaurin + capric acid) and $x_{\text{TLA}}$∼ 0.3 (trilaurin + lauric acid), whereas trilaurin + fatty alcohol mixtures showed eutectic transitions close to the composition of pure alcohol. In the case of the trilinolein mixtures, no eutectic transitions were detected, only the melting of the solid phase. To model the liquidus lines, Margules 2-suffix, Margules 3-suffix, and the UNIFAC models were applied and compared against the ideal approach. Among these, the Margules 3-suffix model provided the best fit (RMSD = 0.5 K), followed by the Margules 2-suffix (RMSD = 0.9 K), demonstrating their suitability for describing the SLE behavior of these systems.