Modulation of Miscibility and Phase Behavior of the Phenol‐Water System Using Protic Ionic Liquids and Their Mixtures With Sodium Dodecyl Sulfate

ABSTRACT

The study of phase behavior of phenol‐water systems by adding additives is essential for advancing extraction and separation techniques, optimizing industrial processes, and improving chemical formulations. In this study, ammonium carboxylate‐based protic ionic liquids (PILs) were synthesized and used as additives to phenol‐water mixtures. The miscibility temperatures were recorded with varying mole fractions of phenol, water, and PIL concentrations to construct phase diagrams. The results reveal that the size and shape of the phase diagram vary according to the nature of ions in PILs and their concentration. Notably, ammonium carboxylate PILs lowered the upper critical solution temperature (CST) of the phenol‐water system, and the decrease in CST becoming less pronounced as PIL anion hydrophobicity increased in the sequence formate < acetate < propionate < butyrate. Overall, triethanolammonium (TEA) based PILs produced lower CST values than the corresponding diethylammonium (DEA) based PILs. The combined effect of PILs and sodium dodecyl sulfate (SDS) on the phenol‐water system showed that SDS altered the characteristic phase‐diagram shape in DEA‐based PIL systems, whereas it remained preserved in TEA‐based PIL systems. The observed phase behaviors were analyzed in terms of the effects of PIL anion hydrophobicity, ion‐solvent interactions, hydrophobic interactions, and H‐bonding on phenol‐water miscibility.