Molecular Dynamic Insights into the Distinct Solvation Structures of Aromatic and Aliphatic Compounds in Monoethanolamine-Based Deep Eutectic Solvents.

Abstract

Deep eutectic solvents (DESs) are developing as an alternate medium for aromatic extraction, especially benzene and thiophene from aliphatic hydrocarbon mixtures. In this work, molecular dynamics (MD) simulations were first used to investigate the solvation structure of benzene, thiophene, and n-hexane in monoethanolamine-based DESs. It reveals the liquid structures in the adjacent neighbor shells, which is a function of electron-withdrawing sulfur attached to thiophene and the π-electron cloud of benzene. The intermolecular forces between aromatic, aliphatic, and DES components are analyzed in van der Waals and hydrogen bond interactions. The chloride ions serve as a charge carrier bridge between choline and monoethanolamine precursors. The solvation of benzene, thiophene, and n-hexane in the DESs depends on volume expansion and minor solvent structural changes. Density functional theory results provided information on the mechanism of short-range interactions between organic solutes and studied DES. It aids in understanding the structural orientations of a DES with the addition of solutes, essential to the formation of DES. The solvation shell structure and characteristics were investigated in tandem with the possibility of benzene and thiophene clustering. The 1H NMR and 2D 1H-1H-NOESY were used to investigate the intermolecular interactions between benzene, thiophene, and n-hexane with monoethanolamine-based solvents. It concludes that high-ordered DES1 is more inclined to higher solubility than lower-ordered ones with a higher molar ratio of monoethanolamine. The solvation was reduced because the entropy gain was not maximized in the lower ordered DESs.