Liquid−liquid equilibrium data of aqueous two-phase systems composed of PEG 4000 + sodium sulfate, PEG 4000 + lithium sulfate, and PEG 4000 + potassium phosphate were determined from (278.15 to 318.15) K. When the temperature was increased, the slope of the tie line (STL) tended to increase, reducing the quantity of salt necessary for phase splitting. From (308.15 to 318.15) K, for the aqueous systems PEG 4000 + lithium sulfate or potassium phosphate, a small decrease of the STL was verified. In spite of producing a phase diagram with a larger biphasic area, the sodium sulfate showed higher capability for inducing the phase splitting as compared to potassium phosphate and lithium sulfate.

Recebido em 6/10/06; aceito em 24/8/07; publicado na web em 19/12/07The present work analyzed the effect of the temperature and type of salt on the phase equilibrium of aqueous two-phase systems (ATPS) formed by poly (ethylene glycol) (PEG) 1500 + potassium phosphate, from (278.15 to 318.15) K, and PEG 1500 + sodium citrate, from (278.15 to 298.15) K. The rise of the temperature normally increased the slope of the tie line (STL). With respect to the influence of the type of salt, sodium citrate showed better capability to induce phase separation, when compared to potassium phosphate.