Critical Volumes of Biodiesel-Related Esters: An Indirect Approach to Evaluating Estimation Models

Knowledge of critical properties of biodiesel components
is essential for designing processes involving biodiesel and its mixtures.
In a previous work (Ind. Eng. Chem. Res. 2018, 57, 8552–8565),
we evaluated group contribution methods for estimating critical temperatures
and pressures of fatty acid alkyl esters (FAAEs) and recommended feasible
values of these properties for engineering applications. In this study,
we analyze models for estimating critical molar volumes (Vc) of FAAEs and identify reliable methods for future use. Because
experimental Vc data are not available for FAAEs, we propose
an indirect evaluation in which the model accuracy is inferred from
comparisons of calculated and experimental liquid densities. The results
demonstrate that the critical volumes recommended in this work lead
to highly accurate density estimates, with an average absolute relative
deviation of 0.68% for a database containing 2158 experimental density
values for 47 FAAEs, supporting their use in future studies involving
biodiesel.