Component distribution between light and heavy phases in biodiesel processes

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