Solubility of elemental sulfur in pure organic solvents and organic solvent–ionic liquid mixtures from 293.15 to 353.15 K

The solubility of elemental sulfur in pure aromatic and aliphatic hydrocarbons was measured by cloud-point measurements using the laser beam scattering method under atmospheric pressure and temperature ranging from 293.15 to 353.15 K. It was found that the solubility of elemental sulfur in the examined solvents increases with an increase in temperature. Among the solvents tested, sulfur had the highest solubility in toluene. The individual effect of four different imidazolium ionic liquids – 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]), and 1-hexyl-3-methylimidazolium tetrafluoroborate ([C6mim][BF4]) on the solubility of sulfur in toluene was also studied. The results show that both the structures of the cations and concentrations of ionic liquids used to play important roles in the solubility of elemental sulfur. The experimental solubility data of elemental sulfur can be well correlated by the modified Apelblat equation. Finally, the free energies of transfer, ΔtrG, entropies of transfer, ΔtrS, and enthalpies of transfer, ΔtrH, of elemental sulfur from toluene to toluene + [C6mim][PF6] mixture were determined based on the solubility measurements.