Effect of water on extractive desulfurization of fuel oils using ionic liquids: A COSMO-RS and experimental study

When evaluating ionic liquids (ILs) for extractive desulfurization (EDS) of fuel oils, the inevitable presence of water in the system may have a significant and in many cases strongly negative effect. However, few studies have considered this particular issue and a promoted water effect on EDS is scarcely reported. In this work, COSMO-RS was firstly employed to calculate the capacity and selectivity for EDS of various IL/H2O mixtures, which cover different IL characters and a wide water concentration range. Experiments were then conducted with a representative IL [C4MIM][H2PO4], whose stable and even promoted extraction performance with a small amount of water was suggested by COSMO-RS. Through analyses of the desulfurization ratio, the cross-solubility and the water content in the desulfurized fuel, the promoted effect of water within a certain range (< 10 wt%) was experimentally demonstrated. Moreover, such effect of water was explained combining the viscosity, the solvent-solute interactions and the COSMO-RS based analysis.