Experimental investigation and modeling of liquid–liquid equilibria in two systems of concern in biodiesel production

• Water solubilities in corn oil biodiesel and frying oil biodiesel were measured.
• Liquid–liquid equilibria of methanol + glycerol + corn oil biodiesel were measured.
• Liquid–liquid equilibria of methanol + glycerol + frying oil biodiesel were measured.
• Results of all four measured systems were successfully correlated with UNIQUAC.
• Othmer–Tobias correlations are presented to predict phase equilibria for each system.

The binary systems of water + biodiesel and ternary systems of methanol + glycerol + biodiesel, which are involved in the biodiesel production process, were investigated in order to find the corresponding equilibrium data. In the case of binary systems, water solubilities in two biodiesels from either corn or frying oil were determined within a temperature range of 297.2–333.2 K. For the ternary mixtures of methanol + glycerol + either corn or frying oil biodiesel, the binodal curves and tie lines were determined at the three temperatures of 293.2, 303.2, and 313.2 K. Results showed that the solubilities in both binary and ternary systems increased with increasing temperature. The Othmer–Tobias correlation was applied to each ternary system to ascertain the reliability of the experimental tie line data obtained, and to provide phase equilibrium correlations at conditions where data are not available. All of the investigated systems were also modeled using the UNIQUAC model. The satisfactory results obtained indicate the suitability of this model for such systems.