Liquid-Liquid Equilibrium for Ternary Systems Containing Biodiesel + Glycerol + Alcohol (Ethanol or Methanol): Thermodynamic Modeling

Biodiesel is a substitute for fossil fuels which is produced through a transesterification reaction between vegetable oils or animal fats and light alcohols such as methanol or ethanol. In this reaction, along with the production of biodiesel, glycerol as a byproduct and non-reacted alcohol that reduces biodiesel quality is produced. Hence, many studies have been carried out on liquid-liquid equilibrium (LLE) for ternary systems containing biodiesel + glycerol + alcohol. Two phases are formed as 1-rich in biodiesel and 2-rich in glycerol; moreover, alcohol is distributed between these two phases. In this work, based on previous experimental data, the UNIQUAC and NRTL thermodynamic models were used to forecast the composition of the phases. The intermolecular interaction term for each of the models was considered as a linear function of the reverse temperature. In both models, there was no difference between the amount of biodiesel produced from different oils and obtained from the general interaction parameters. Based on the results, the percentage of absolute average deviation for NRTL and UNIQUAC models for biodiesel + glycerol + ethanol system were 1.24% and 2.13%, respectively, and for biodiesel + glycerol + methanol system was 1.13% and 1.71%, respectively.