Comparison of Methods for Estimating Critical Properties of Alkyl Esters and Its Mixtures

Biodiesel is a renewable fuel which can be described chemically as a mixture of different alkyl esters. To predict its different thermophysical properties, critical properties (P-c, T-c, V-c) must be known or estimated. In this work, the use of group contribution and group interaction methods is compared regarding its goodness in the prediction of a widely measured property such as biodiesel density, as there is a lack of data of normal boiling point or densities of pure alkyl esters. The results show that a group interaction method, with the available data of 20 different biodiesels published, can predict better biodiesel density when methanol was used for the transesterification reaction. Data available for biodiesel produced with ethanol are scarcer; only six sets of biodiesel composition and density could be found, and in this case, both group interaction and group contribution methods predict density with a similar error, although more data are needed.