Separation of quinoline from quinoline/2-methylnaphthalene using deep eutectic solvents: Experimental and COSMO-RS prediction

The high-temperature coal tar wash oil contains two valuable components, namely, quinoline and 2-methylnaphthalene. These two components are challenging to separate during the deep processing. To address this issue, the COSMO-RS (Conductor-like Screening Mode for Real Solvent) model was utilized to identify them as a potential deep eutectic solvents (DESs) extractant. Based on the calculated infinite dilution activity coefficient, the performance indexes of DESs, including selectivity, solubility, and performance index were determined and utilized to identify high-performance extractants for the quinoline/2-methylnaphthalene system. Finally five DESs were selected based on these indexes, they are DES1 formed by Choline chloride: propionic acid with the molar ratio of 1:1, similarly, DES2 is Choline chloride:oxalic acid of 1:1, DES3 Tetraethylammonium chloride:propionic acid of 1:1, DES4 Tetraethylammonium bromide:itaconic acid of 1:2 and DES5 Tetraethylammonium bromide:propionic acid of 1:2. The liquid-liquid phase equilibrium experiments of the aforementioned five DESs at different temperatures (30 degrees C, 40 degrees C, and 50 degrees C) under atmospheric pressure were conducted. The results showed that five kinds of DESs had good extraction effect on quinoline. The DESs formed by choline chloride and anhydrous oxalic acid had the best extraction effect. The quantum chemical single-molecule optimization of different HBDs and HBAs in DESs, intermolecular interaction energy analysis and independent gradient modeling shows that it is mainly induced by the formation of shared electron pairs by providing empty orbitals from DESs and lone pair of electrons from the quinoline molecule, and the main force is the weak hydrogen bonding force.