The phase behavior of potassium sulfate (K

2

SO

4

) in polyethylene glycol with molecular weight 8000 (PEG8000) and water (H

2

O) mixed solvent at 288.15

298.15

and 308.15 K were determined. According to the results

when the temperature are 288.15 and 298.15 K

there is only a solid-liquid phase equilibrium relationship in the system

and the phase diagrams are both divided into three parts which respectively are the regions of unsaturated homogeneous liquid (L)

one liquid and one solid K

2

SO

4

(L + S) and one liquid and two solids K

2

SO

4

and PEG8000 (L + 2S). The solubility of K

2

SO

4

in PEG8000-H

2

O mixed solvent decreased with the addition of the PEG8000 in the solution. Comparing the diagrams of 288.15 and 298.15 K

the sizes of regions of (L) and (L + S) increased and that of (L + 2S) decreased with the increase of temperature. While at 308.15 K

solid-liquid and liquid-liquid equilibrium coexist

and there are six parts in the complete phase diagram at 308.15 K

adding the areas of one liquid and one solid K

2

SO

4

(L + S)

two liquids (2 L)

two liquids and one solid K

2

SO

4

(2 L + S). The equations developed by Merchuk

Hu

and Jayapal were used to fit the binodal curves data of the system at 308.15 K

meanwhile

the experimental tie-line data of the system at 308.15 K were correlated by Othmer-Tobias equation and Bancroft equation.