Component distribution between light and heavy phases in biodiesel processes

Knowledge of the component distribution in the biodiesel production process is fundamental both during the transesterification reaction, where reactants are partially miscible, and during the recovery of the final products, which exist in two separate phases, a heavy one containing nearly all of the glycerol and a light one containing nearly all of the biodiesel. In this article, a simple methodology able to predict the product distribution at equilibrium between the heavy and light phases is suggested. Experimental equilibrium data for mixtures of two (biodiesel and glycerol), three (biodiesel, glycerol, and methanol), and four (biodiesel, glycerol, methanol, and water) components are collected and correlated with the Wilson activity coefficient model. The approach is based on thermodynamic data already available in the literature, without the addition of any empirical fitting parameter. A small effect brought about by the presence of water at low concentrations on methanol distribution between the two phases is pointed out and qualitatively supported by the model predictions. The influence of the addition of electrolyte contaminants (soap or catalysts) is also considered.