Theoretical Study of Oil Desulfuration by Ammonium-Based Deep Eutectic Solvents

A theoretical study using quantum chemistry and molecular dynamics methods is reported on the properties of deep eutectic solvent prepared by tetrabutylammonium bromide and formic acid regarding oil desulfurization. The objective of the work is to obtain molecular level insights into the mechanisms of extractive desulfuration by deep eutectic solvents for designing suitable processes for deep desulfuration purposes. The intermolecular interactions of solvent molecules and relevant organosulfur compounds (thiophene, benzothiophene, and dibenzothiophene) are analyzed together with the liquid structure of solvent + sulfur compounds as a function of organosulfur content. Interfacial properties between the solvent and model oil (n-octane) with different contents of organosulfur compounds are also studied to analyze the molecular level mechanism of liquid–liquid equilibria. Likewise, free energies of solvation in the solvent and in n-octane are calculated to justify the partition of organosulfur compounds between the solvent and oils. The reported results provide for the first time a nanoscopic analysis of deep eutectic solvents for oil desulfuration purposes, confirming their suitability for designing better desulfuration processes according to the stringent environmental regulations.