Determination of cloud point in binary and ternary mixtures containing biodiesel and diesel constituents. Part I - Ethyl palmitate, ethyl stearate and n-hexadecane

Diesel fuel is being substituted by biodiesel in many countries. But, this gradual addition of biodiesel to diesel is causing problems such as the formation of sludge in storage tanks, poor engine performance, transportation difficulties and others. There is strong concern about the use of biodiesel-diesel blends at low temperatures. This study evaluated the cloud point of mixtures containing biodiesel and diesel constituents by preparing solid-liquid equilibrium (SLE) curves obtained by differential scanning calorimetry (DSC). T-x phase diagrams were prepared of solid-liquid equilibrium of binary and ternary systems involving the use of the main saturated esters found in biodiesel; ethyl palmitate (P), ethyl stearate (S) and the representative alkane of diesel, n-hexadecane (H). The diagrams of pseudo-binary systems were also determined, as an alternative way to represent the same data. These phase diagrams studied present eutectic points at 0.2 M fraction of ethyl esters. The experimental results showed no statistically significant difference in cloud point if the mixture has a mass of n-hexadecane equal or greater than 80% according to a T-test. In general, for lower amounts of n-hexadecane, the presence of ethyl palmitate resulted in lower cloud points than when ethyl stearate was used. This work clearly contributed to a better understanding of the behavior of cloud point in biodiesel-diesel blends.