Separation of Methanol and MTBE Azeotrope via Choline-Based Deep Eutectic Solvents: Liquid–Liquid Equilibrium and Molecular Mechanism

Methyl tert-butyl ether (MTBE) is an excellent additive for gasoline. Because of the formation of an azeotropic mixture by MTBE and methanol during its production, it is a challenge to separate the azeotrope. To investigate the effect of hydrogen bond donor (HBD) functional groups on extraction performance, three choline chloride-based deep eutectic solvents (DESs) were prepared using ethylene glycol, ethanolamine and glycolic acid, which contain –OH, –NH₂, and –COOH, respectively. For separating the azeotropic mixture MTBE and methanol by an extraction process, liquid–liquid equilibrium (LLE) data for the pseudoternary mixtures MTBE + methanol + DESs were ascertained at 298.15 K. Distribution coefficient (D) and selectivity (S) were derived and compared among the different systems. The optimal DES ChCl:MEA attained a distribution coefficient of 8.85 and a selectivity of 436.21. The NRTL model was employed to regress the LLE data. The reliability of the binary parameters of the thermodynamic model was validated through Gibbs energy topology analysis. In addition, quantum chemical calculations and molecular dynamics simulations were applied to investigate the interactions underlying the differences in extractant performance. This multiscale analysis revealed hydrogen bonding Cl···OH plays a crucial function, while van der Waals interactions serve as a secondary contributing factor.