Liquid–liquid extraction of caprolactam from water using room temperature ionic liquids

In this paper, investigations have been carried out to determine the suitability of imidazolium-based ionic liquids (ILs), 1-alky-3-methylimidazolium hexafluorophosphate [Cnmim][PF6] (n = 4, 6, 8), 1-hexyl-3-methylimidazolium tetrafluoroborate [C6mim][BF4] and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4mim][NTf2], in replacing toxic organic solvents for liquid–liquid extraction of caprolactam from aqueous solution. The results show that distribution ratio of caprolactam is influenced significantly by the chemical structures of the ILs. The anion/cation effects are the main structural factors ruling the distribution ratio. The results also show that the distribution ratios are much higher for caprolactam into selected ILs than into benzene or toluene. New experimental data for the partitioning of caprolactam between water and the ionic liquid at 303.05 K, 313.05 K, 322.95 K, 332.95 K, 342.95 K, 352.95 K, and 362.95 K have been reported, respectively. It is expected that these ILs are promising for caprolactam recovery from aqueous media. The NRTL model has been employed to correlate the experimental data.