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The study of aqueous two-phase systems (ATPSs) formed by ionic liquids based on the choline cation and nonionic surfactants has received attention in recent years because of the biodegradability and nontoxicity of their components. In this work, liquid–liquid equilibrium data were obtained for ATPSs composed of Triton X (Triton X-100, Triton X-165, and Triton X-305), choline chloride, and water, at 298.15, 313.15, and 328.15 K. In general, these systems presented a top phase rich in choline chloride and a bottom phase rich in surfactant, although the phenomenon of phase inversion was observed for a specific thermodynamic condition of the system formed by Triton X-165. It was observed that increase of the temperature led to an increase of the biphasic region, indicating an endothermic phase separation process. In addition, higher hydrophobicity of the surfactant increased its ability to promote phase segregation (the biphasic region increased in the following order: Triton X-100 > Triton X-165 > Triton X-305). The reliability of the equilibrium data was confirmed using the Othmer–Tobias and Bancroft correlations.

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