Molecular dynamics simulations on extractive desulfurization of fuels by tetrabutylammonium chloride based Deep Eutectic Solvents

In the last five years, several new applications of Deep Eutectic Solvents (DESs) have been developed, including extractive desulfurization of fuels. Among several DESs that have been proposed for extraction of sulfur-compounds from liquid fuels, a combination of tetrabutylammonium chloride (TBAC), polyethylene glycol (PEG-200), and ferric chloride (FeCl₃) at molar ratio of 4:1:0.05, as the DES, has shown the highest efficiency. We herein implement molecular dynamics simulations to analyze the intermolecular interactions within the DES. The simulations present the role of strong interactions between PEG and chloride ion to explain the sharp decrease in the melting point as observed in the DES. Further next, simulations of the DES with model oil and thiophenic compounds were performed to mimic the desulfurization process of liquid fuel. Results indicate a strong interaction between the TBA ion with the thiophenic compounds. Moreover, effect of several process parameters including temperature, concentration, and the type of the thiophenic compounds was analyzed to understand their effect on the extraction efficiency. In addition, composition of DES was varied by selectively removing either PEG or FeCl₃ from the DES to evaluate the influence of each compound on the efficiency of desulfurization process. The results taken together explain the mechanism of desulfurization by the DES and provide insights to development of novel solvents for the process.