Cosolvent effects on organosulfur compound dissolution and coal-cosolvent interfacial interactions: A molecular dynamics study

Cosolvent-assisted supercritical CO 2 (SC-CO 2 ) extraction provides a promising strategy for the clean removal of organosulfur compound from coal. However, different cosolvents lead to different desulfurization performances, and the underlying molecular mechanisms remain insufficiently understood. In this work, molecular dynamics simulations were performed to investigate organosulfur dissolution behavior in SC-CO 2 -cosolvent mixed solvents and coal-cosolvent interfacial interactions using nine representative cosolvents. The results show that dibenzothiophene (DBT) exhibits the highest dissolution extent in the SC-CO 2 -hexane solvent, but complete dissolution is not achieved in any of the investigated systems. DBT dissolution in SC-CO 2 -cosolvent systems is influenced by multiple factors, including solvent-solute polarity matching, molecular structure, and cosolvent molecular size. Analysis of coal-cosolvent interfacial interaction energies shows that van der Waals interactions dominate interfacial stabilization in all systems. Among the investigated cosolvents, methanol exhibits the strongest interaction with coal, with a relatively large electrostatic contribution. These results indicate that enhancing coal-cosolvent interfacial affinity, rather than solely increasing organosulfur dissolution ability, is important for improving SC-CO 2 -based coal desulfurization. This work provides molecular-level guidance for the rational screening and design of cosolvents for clean coal utilization.