(185b) Double Envelope Reverse-Phase Ternary Phase Diagram for Biodiesel - Glycerol - Methanol

Transesterification reactions for biodiesel production often result in the formation of two separate liquid phases: a polar phase rich in glycerol and methanol, and a nonpolar phase consisting mostly of biodiesel. Understanding how the components partition between the two liquid phases can greatly facilitate the design of efficient separation processes. In the present work, the liquid-liquid phase equilibrium data for biodiesel ? glycerol ? methanol mixtures was determined. At low methanol concentrations, it was found that the lower phase consisted of glycerol and most of the methanol while biodiesel and trace methanol formed the top phase. Interestingly, as the methanol concentration was increased, there existed a small region where the phases reversed and the biodiesel was found at the bottom while the glycerol and methanol formed the top phase. This ?phase flip? is a consequence of the strong hydrogen bonding that exists between glycerol and methanol, which are almost always found to exist in the same phase. The density of this polar phase can be approximated by a weighted average of the two species. As the concentration of methanol increases, the density of the phase decreases and eventually becomes less than that of the biodiesel. This results in the flipping of the top and bottom phases. Further addition of methanol resulted the formation of a complete single phase. The liquid-liquid equilibrium data generated was used to create a ternary phase diagram for the biodiesel ? glycerol ? methanol system. The diagram contains two distinct phase envelopes.