Application of UNIFAC models for prediction of vapor–liquid and liquid–liquid equilibria relevant to separation and purification processes of crude biodiesel fuel

Vapor–liquid equilibrium (VLE) of the methanol–biodiesel (BDF)/glycerin binary system and liquid–liquid equilibrium (LLE) of the water–BDF binary system and the methanol–BDF–glycerin and methanol–water–BDF ternary systems were predicted using several UNIFAC models: the latest original UNIFAC model, Kikic’s model, Fornari’s model, Dortmund-UNIFAC model, and LLE-UNIFAC model. The former VLE and latter LLE are used to design methanol recovery processes and separation and purification processes of crude BDF, respectively. Unfortunately, LLE data on the water–BDF binary system was not available. Instead, solubility of water in fatty acid methyl ester (one of the BDF constituents) was measured. By examining the deviation between predicted and experimental results, we determined which of the UNIFAC models was more useful for the design of those processes as follows: either the original UNIFAC model or Dortmund-UNIFAC model should be used for the methanol recovery process. The LLE-UNIFAC model and Dortmund-UNIFAC model were more useful for the recovery and water-washing processes of crude BDF and purification process of water-washed BDF, respectively.