Currently, knowledge on the solid-liquid equilibrium of fatty acids is of great importance for the food and chemical industries. Due to the increase interest of industries in the separation processes to obtain pure fatty acids or a vegetable oil with low acidity, for example to produce biodiesel, the knowledge of equilibrium properties is an important tool that can make it easier to develop new methods to separate such compounds. The purpose of this study was to investigate the influence of the molecule structure and/or size on the phase diagrams of binary mixtures of saturated and unsaturated fatty acids with oleic acid. Differential Scanning Calorimetry was used to measure the following binary mixtures: oleic acid + capric acid, oleic acid + stearic acid, oleic acid + elaidic acid and oleic acid + linoleic acid. Based of the experimental runs, the uncertainty of the equilibrium data is estimated to not be higher than 0.3 K. Moreover, this study presents a better characterization of the solidus lines of such systems and shows that the Margules-3-suffix and NRTL models can be used to accurately describe the liquidus line.
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