Effect of Temperature on the Aqueous Two-Phase System Containing Poly(ethylene glycol) Dimethyl Ether 2000 and Dipotassium Oxalate

Liquid-liquid equilibria (LLE) of the poly(ethylene glycol) din ethyl ether 2000 (PEGDME2000) + dipotassium oxalate + H2O system have been determined experimentally at T = (298.15, 303.15, 308.15, and 318.15) K. The effect of temperature on the binodal curves and tie-lines has also been studied. The Graber et al., Merchuk, and empirical equations were used to correlate the binodal data of this system with the temperature dependence expressed in the linear form with (T - T-0) K as a variable. Furthermore, we used the Othmer-Tobias and Bancroft and a temperature-dependent Setschenow-type equation for the correlation and prediction of the liquid-liquid phase behavior of the studied system. The effective excluded volume (EEV) values obtained from the binodal model for this system and other aqueous PEGDME2000-salt systems were determined, and the relation between these values and salting-out ability of different salts was discussed. Also, the effects of type of the polymers PEGDME2000 and PEG2000 on LLE are discussed. Finally, the free energies of cloud points for this system were calculated. According to the results it was concluded that the increase of the entropy is a driving force for the formation of the studied aqueous two-phase system (ATPS).