Liquid-liquid and solid-liquid equilibria of several PEG-based ABS with ionic liquid [C4C1im]Br as adjuvant at 298.15 K

Abstract

Liquid-liquid equilibrium (LLE) and liquid–liquid-solid equilibrium (LLSE) data were determined, at T = 298.15 K, for aqueous biphasic systems (ABS) composed of PEG (poly(ethylene glycol)) with a molecular weight 400, different inorganic salts (K2CO3, (NH4)2SO4, or MnSO4), and the ionic liquid (IL) [C4C1im]Br as adjuvant. Binodal curves of two-liquid phases, LLE and LLSE data were determined by the addition of 5 wt% [C4C1im]Br to investigate its effect on the phase diagrams. All binodal curves were determined by the cloud-point titration method and described accurately using the Merchuk equation. The results show that the presence of 5 wt% of [C4C1im]Br produce small effects upon the phase separation. Compositions of LLE and LLSE were determined by gravimetric method, UV-spectroscopy and X-ray diffraction analysis made on the solids. For PEG400/K2CO3 and PEG400/(NH4)2SO4 ABS, the obtained LLE data are in good agreement with those obtained by analytical methods quantifying the concentrations of PEG using refractive index measurements, and of salt by flame photometry or the formaldehyde method, respectively, with the maximum absolute average deviation of 1.94%. The tie-line lengths (TLL) were also addressed. Densities of the coexisting phases were also reported at 298.15 K and correlated satisfactorily using the Othmer rule. Moreover, it was found that [C4C1im]Br has a higher affinity for the PEG-rich phase, which increases with increasing the system composition and the water-structuring effect of the anion of the salt used as the salting-out agent to form ABS. For the sulfate-based ABS, whereas, the tendency of [C4C1im]Br to partition into the PEG-rich phase was observed to decrease with increasing the water-structuring effect of the cations, which may be attributed to the complex forming tendency of Mn2+ with the ether oxygens of PEG. Furthermore, the solid phases in equilibrium with the biphasic regions were K2CO3·1.5H2O, anhydrous (NH4)2SO4, and MnSO4·4H2O. Finally, the experimental LLE data were accurately correlated using the NRTL model.