Application of quasi-chemical models to liquid–liquid equilibrium calculations for ternary systems containing water, propionic acid and organic solvents

Two different models based on Guggenheimʹs renormalized canonical partition function proposed by Wang and Vera, the generalized quasi-chemical model (GEM-QC) and the generalized regular solution model (GEM-RS), have been used in molecular form to correlate the liquid–liquid equilibrium (LLE) of experimental data for ternary systems containing water, propionic acid (PA) and organic solvents. Both the GEM-QC and the GEM-RS models have nine adjustable parameters for a ternary system, which are obtained from a least square fit of the models to the LLE experimental data. In this work the same assumptions made to develop the simplified GEM-RS model (GEM-RS2) by Wang and Vera, have been applied to the GEM-QC model (GEM-QC2), in order to reduce the number of adjustable parameters from 9 to 6. The GEM-RS2 and the GEM-QC2 models have also been used for correlating the LLE experimental data for ternary systems. The results obtained from the studied models were compared to those of the NRTL and UNIQUAC models. The comparison shows that the GEM-QC model can correlate the LLE experimental data of ternary systems more accurately than the other studied models. Finally, the selectivity of five different organic solvents that are used to recover PA from its aqueous solution has been compared.