In the present work the phase diagrams of seven fatty acid binary mixtures were obtained by differential scanning calorimetry (DSC). These mixtures were formed by capric acid (C 10:0 ) with lauric acid (C 12:0 ), myristic acid (C 14:0 ), palmitic acid (C 16:0 ), or stearic acid (C 18:0 ) and by lauric acid (C 12:0 ) with myristic acid (C 14:0 ), palmitic acid (C 16:0 ), or stearic acid (C 18:0 ). The spline technique was used to compare the results of this work with prior results available in the literature for some of the investigated systems. The occurrence of the eutectic point in all systems and of the peritectic point in some of the systems was observed. The occurrence of the peritectic point can be associated with the difference in the number of carbon atoms of the fatty acid chains used in the mixture. The approach suggested by Slaughter and Doherty (Chem. Eng. Sci. 1995Sci. , 50, 1679Sci. -1694 was used to model the solid phase, and the liquid phase was modeled using the Margules-2-suffix, Margules-3-suffix, UNIFAC Dortmund, and NRTL models. The best modeling results were obtained using the Margules-3-suffix with an average deviation between experimental and calculated values of 0.14 %.

For the first time, the solid-liquid phase diagrams of five binary mixtures of saturated fatty acids are here presented. These mixtures are formed of caprylic acid (C(8:0))+capric acid (C(10:0)), capric acid (C(10:0))+lauric acid (C(12:0)), lauric acid (C(12:0))+myristic acid (C(14:0)), myristic acid (C(14:0))+palmitic acid (C(16:0)) and palmitic acid (C(16:0))+stearic acid (C(18:0)). The information used in these phase diagrams was obtained by differential scanning calorimetry (DSC), X-ray diffraction (XRD), FT-Raman spectrometry and polarized light microscopy, aiming at a complete understanding of the phase diagrams of the fatty acid mixtures. All of the phase diagrams reported here presented the same global behavior and it was shown that this was far more complex than previously imagined. They presented not only peritectic and eutectic reactions, but also metatectic reactions, due to solid-solid phase transitions common in fatty acids and regions of solid solution not previously reported. This work contributes to the elucidation of the phase behavior of these important biochemical molecules, with implications in various industrial applications.

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