Biodiesel density and derived thermodynamic properties at high pressures and moderate temperatures

Abstract

Knowledge of the basic thermodynamic properties of biodiesel under different conditions is necessary because of its wide use as a substitute for fossil fuels. The viscosities and refractive indices of the methyl and ethyl esters of the fatty acids from sunflower oil were measured at atmospheric pressure and at temperatures 288.15-373.15 K and 288.15-343.15 K, respectively. The same properties were measured also for the methyl esters of the fatty acids from lard at atmospheric pressure and at temperatures 298.15-373.15 K and 298.15-343.15 K, respectively. The densities of the mentioned biodiesel samples were measured at temperatures up to 413.15 K and at pressures 0.1-60 MPa. The experimental density values were correlated using the modified Tammann-Tait equation. Based on the obtained results, thermodynamic behavior, such as the isothermal compressibility, the isobaric thermal expansivity, the internal pressure and the difference between the specific heat capacity at constant pressure and at constant volume, were calculated. The absolute average deviations between measured densities and those calculated using the modified Tammann-Tait equation of about 0.006% for all of the three examined samples confirm the accuracy of the modeling and reliability of the calculated derived properties.