Phase behavior and extraction mechanism of methanol-n-hexane separation using choline-based deep eutectic solvent

Deep eutectic solvents (DESs) have attracted increasing attention as green solvents in recent years owing to their potential for use in azeotropic separation and their advantages, such as low vapor pressure, non-toxicity, and low cost. To separate methanol (MeOH)-n-hexane (NHA) azeotrope, three choline-based DESs were prepared using glycerol, ethylene glycol (EG), and urea as the hydrogen bond receptors. The liquid–liquid equilibrium (LLE) data of DES-MeOH-NHA were measured at 298.15 K and 1 atm. The distribution coefficient and selectivity were obtained to compare the extraction efficiencies of different DESs. To further explore the extraction mechanism of LLE, the molecular dynamics (MD) method was used to study the internal mechanism of MeOH extraction by DESs. In addition, the experimental and MD simulation data were compared. Based on the MD simulation, the interaction energies between DES and MeOH/NHA, radial distribution function, and spatial distribution function between DES and MeOH were obtained. In addition, the experimental results were in good agreement with the simulation results, and both the results established that choline chloride (ChCl)/EG(1:2) had the highest extraction efficiency for methanol among the three DESs. Additionally, MD simulation results showed that Cl- plays a vital role in the LLE, and the interaction force between Cl- and MeOH was primarily provided by the electrostatic force.