Salting-out effect on extraction of phenol from aqueous solutions by [Hmim][NTf2] ionic liquid: Experimental investigations and modeling

Abstract

Abstract This study is concerned on the influence of sodium chloride, sodium sulfate and magnesium sulfate salts on the liquid–liquid equilibrium (LLE) of water + phenol + 1-hexyl-3-methylimidazolium bus(trifluoromethanesulfonyl)imide, [Hmim][NTf2], ionic liquid (IL) system under conditions of T = 298.2 K and ambient pressure of 81.5 kPa. The results showed that salting-out effect was significant and their effectiveness appeared in the order of MgSO4 > Na2SO4 > NaCl, as predicted by the Hofmeister series. Between the used 0.005 and 0.020 salt mass fractions in aqueous phase, the higher concentration was more effective especially at low phenol concentrations. In comparison with salt-free system, enhancements in the separation factor, within (20.55–96.56)% with NaCl, (51.94–154.58)% with Na2SO4 and (73.91–242.57)% with MgSO4 were achieved. The consistency of experimental data was examined with the improved version of Eisen-Joffe equation. Further, the NRTL and UNIQUAC thermodynamic models were satisfactorily used to correlate the phase equilibrium data and the appropriate interaction parameters were determined. Prediction of mass fraction tie-lines gives the maximum root-mean square deviations of only 0.0083 and 0.0367 for NRTL and UNIQUAC models, respectively.