Liquid-Liquid Equilibrium and Mechanism of Pyridine Extraction from n -Hexane Using an Alcoholamine-Based Deep Eutectic Solvent

The separation of n -hexane and pyridine is challenging using conventional methods due to the formation of an azeotrope. To address this issue, four alcoholamine-based deep eutectic solvents (DESs) with a molar ratio of 1:1 were synthesized for the extraction of pyridine from n -hexane. Liquid–liquid equilibrium (LLE) experimental data for the ternary systems of n -hexane + pyridine + alcoholamine-based DESs (MEA/TBAC, MAE/TBAC, BAE/TBAC, DEA/TBAC) were measured at 101.325 kPa and 298.15 K. According to Treybal’s classification, all four systems exhibited Type I phase behavior in their triangular diagrams. The distribution coefficients and selectivity factors for pyridine extraction were calculated to evaluate the performance of the DESs. Furthermore, the nonrandom-two-liquid (NRTL) activity coefficient model was applied to correlate the newly measured LLE data, and the corresponding binary interaction parameters were regressed and evaluated via Gibbs energy topology analysis. Moreover, the extraction capability and mechanism were also explored to gain microscopic insight. Overall, this work not only provides new experimental LLE data for the above-mentioned systems but also provides theoretical guidance for selecting DESs to separate pyridine.