Low-Temperature Behavior of Biodiesel: Solid–Liquid Phase Diagrams of Binary Mixtures Composed of Fatty Acid Methyl Esters

Abstract

Although biodiesel is being widely used in blends with conventional diesel (Bx) as an automotive fuel, information on its low-temperature behavior is still scarce, in particular concerning the solid–liquid phase behavior of the biodiesel components at temperatures below the cloud point. Although methyl oleate or methyl linoleate are typically components with the highest concentration in the biodiesel, its cloud point is much more influenced by saturated fatty esters because of their higher melting temperatures. The objective of this study is to present a detailed description of the solid–liquid phase diagrams of selected binary mixtures containing the main saturated methyl fatty esters found in biodiesel. The liquidus lines and phase behavior below this transition were determined for the following binary mixtures: methyl myristate + methyl palmitate, methyl myristate + methyl stearate, and methyl palmitate + methyl stearate. It will be shown that these systems are not eutectic as previously admitted but, instead, have a complex phase behavior that may have unexpected impacts on the behavior of biodiesel at low temperatures.