Liquid-liquid equilibrium of the aqueous two-phase system water plus PEG 4000 plus lithium sulfate at different temperatures.: Experimental determination and correlation

A study was made of the effect of temperature on the liquid-liquid equilibrium (LLE) in the aqueous biphasic system formed by lithium sulfate + polyethylene glycol 4000 + water at 5, 25, and 45 degreesC. The tie lines and binodal curves as well as the densities and refractive indexes were determined on solutions in equilibrium at each temperature. The LLE experimental data obtained were well correlated to the nonrandom two-liquid thermodynamic model for activity coefficients. When using data from seven equilibrium lines for each temperature, a mean deviation of 1.07% was obtained between experimental compositions and compositions calculated using the model.