The Effect of NaCl Aqueous Solutions with Different Concentrations on the Liquid–Liquid Equilibrium of the Water + Pyridine + 2-Ethyl-1-hexanol Ternary System

This study investigates the influence of different mass concentrations of NaCl (0, 1, 5, and 10 wt %) on the liquid–liquid equilibrium of the ternary system {water + pyridine + 2-ethyl-1-hexanol} at 298.2 K temperature and 101.3 kPa atmospheric pressure. Experimental results show that the distribution coefficient and separation factor of pyridine increase continuously with increasing salt concentration. This indicates that the addition of inorganic salt reduces the mutual solubility between water, pyridine, and 2-ethyl-1-hexanol, thereby promoting phase separation and facilitating the selective extraction of pyridine from the aqueous phase by 2-ethyl-1-hexanol. Optimal extraction performance was achieved at a NaCl mass fraction of 10%. Compared to the salt-free system, the pyridine distribution coefficient increased by (11.19–115.43)%, and the separation coefficient improved by (55.46–169.99)%. The NRTL and UNIQUAC thermodynamic models are used to correlate the LLE data, and their model parameters are regressed. Statistical analysis indicates that both models can well predict the phase equilibrium behavior. Verification with the GMcal_TieLinesLL tool shows that the regressed parameters meet the Gibbs stability criterion, confirming the reliability of the models.