General models for prediction densities and viscosities of saturated and unsaturated fatty acid esters

Biodiesel is a very promising renewable energy, whose properties are determined by fatty acid esters in it. The work aims to develop prediction models based on their molecular structure to estimate the density and viscosity of saturated and unsaturated fatty acid esters in a wide range of temperature and pressure. Densities and viscosities of ethyl hexanoate and ethyl nonanoate were measured from 313.15 K to 363.15 K and at pressures up to 15 MPa to get more experimental data. The effect of temperature, pressure and molecular structure on density and viscosity based on the experimental data in this work and collected from literature found an interesting phenomenon that densities decrease with the increasing carbon atoms number in the chain of the saturated fatty acid esters at low temperature, but there is an opposite trend at high temperature. Two models derived from the Tait equation were proposed for densities with the average absolute relative deviation of 0.15% for saturated fatty acid methyl esters (FAMEs), 0.13% for saturates fatty acid ethyl esters (FAEEs), 0.17% for unsaturated FAMEs, 0.06% for unsaturated FAEEs, respectively. For viscosity, two models based on the Andrade-Tait model were proposed with the average absolute relative deviation of 1.49% for saturated FAMEs, 0.92% for saturated FAEEs, 4.54% for unsaturated FAMEs and 2.15% for unsaturated FAEEs, respectively.