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The liquid-liquid equilibria of ionic liquid-based systems with water and/or acetic acid have been studied at 293.15 K and atmospheric pressure. One hydrophilic ionic liquid and a series of hydrophobic ionic liquids were investigated in order to examine their effect on the separation of water and acetic acid mixtures. The ionic liquids studied were [P666,14]Cl, [P666,14][NTf2], [C4mmim][NTf2], [Cnmim][NTf2] (n = 2, 4, 6, 8, or 10), [C4mpyrr][NTf2], [N1114][NTf2], and [C2mim][EtSO4]. [C2mim][EtSO4] is totally miscible with water and acetic acid in all compositions. Comparing [P666,14]Cl with [P666,14][NTf2], the former showed higher extraction selectivities; however, due to the larger viscosity of [P666,14]Cl, the [NTf2]- based ionic liquids offer a better solvent choice for the liquid extraction processes. As expected, as the solubility of water decreases with increasing the chain length of ionic liquids, this in turn leads to [C10mim][NTf2] showing greater acetic efficiency than [C2mim][NTf2] for the separation of water and acetic acid. The experimental data obtained for ternary systems containing the [C4mmim][NTf2] demonstrated that the modification of the C(2) position on the imidazolium ring does not significantly affect the selectivity compared with [C4mim][NTf2]. Tetraalkyl ammonium and N-alkyl pyrrolidinium based ionic liquids were also studied with the [NTf2]- anion with the results for the system containing the [C4mpyrr][NTf2] demonstrating a higher selectivity for the separation of water and acetic acid than the other [NTf2]- based systems studied. All experimental data were then correlated using the UNIQUAC model within an accuracy close to 1.6%. Finally, the ionic liquids were also compared with standard molecular extraction solvent, for example, methyl tert-butyl ether and methyl isobutyl ketone. The organic solvents showed an advantage over the [Cnmim][NTf2]-based ionic liquids but only over a narrow composition range. In all ionic liquid systems, the selectivity remains high at low acetic acid concentration compared with that found in the organic solvents, which is important for practical operation and demonstrates the advantages of using an ionic liquid for the extraction. [ABSTRACT FROM AUTHOR]