Thermodynamic Properties of Biodiesel and Petrodiesel Blends at High Pressure and High Temperature and a New Model for Density Prediction

This paper presents a new model to predict the density of biodiesel + petrodiesel mixtures at high pressure and high temperature (HPHT) based on the Murnaghan equation of state, as a function of temperature, pressure, volumetric composition, and petrodiesel and biodiesel densities. This model was validated by using experimental data from the literature, along with a new experimental data set for biodiesel (grape seed, corn, and linseed) + petrodiesel, at high pressure (0.10-100.00 MPa) and high temperature (293.15-413.15 K) in a composition range of 0, 20, 40, 60, 80, and 100%vol. These experimental data were correlated by using the Tammann-Tait equation. From these data, the following derivative properties were determined: isothermal compressibility (kappa(T)), isobaric thermal expansibility (alpha(P)), internal pressure (p(int)), and the difference between pressure and volume heat capacities (c(p) - c(v)). Deviations obtained from the model proposed in this work (%AARD) were less than 0.50% for biodiesel + petrodiesel density data.