CERE Seminar by Kaj Thomsen

Modeling phase equilibria of acetone – water – salt mixtures

Liquid-Liquid, Solid-Liquid, and Vapor-Liquid Equilibria in acetone water solutions with NaCl, Na₂SO₄, KCl, and K₂SO₄ were modeled using the Extended UNIQUAC model. Previous papers on the thermodynamic modeling of phase equilibria in acetone-water-salt solutions were limited to the modeling of vapor-liquid equilibrium.

According to the experimental data available in the open literature, solutions with K₂SO₄ do not split into two liquid phases and the lower consolute temperature of acetone water mixtures with KCl is 40 °C. The corresponding temperature for Na₂SO₄ solutions is reported to be 29.8 °C. For solutions with NaCl, liquid-liquid equilibrium was reported at temperatures down to 4 °C.

Figure 1 shows the experimental and calculated solid-liquid equilibrium curve in the Acetone-water-Na₂SO₄ system at 12 °C. With increasing acetone content, the water activity is lowered, resulting in anhydrous Na₂SO₄ becoming the stable solid phase rather than glauber salt, Na₂SO₄·10H₂O. The acetone concentration required for this transition differs widely between the experimental studies available.

Figure 1: Experimental data and modeling result for solid-liquid equilibrium in the acetone-water-Na₂SO₄ system at 12 °C. The measured and calculated Na₂SO₄·10H₂O/Na₂SO₄ transitions are marked.

The modeling was performed with the Extended UNIQUAC model which combines a Debye-Hückel term with the UNIQUAC local composition model.

Discrepancies between the reported experimental data for the system studied here is probably  a contributing reason why the thermodynamic modeling of this system is more difficult than the modeling of similar systems containing alcohols instead of acetone.

Keyword( italic bold):  Mixed solvent; Acetone; Liquid-Liquid Equilibrium; Solid-Liquid Equilibrium; Vapor – Liquid Equilibrium

References

[1] A. B. Krizhanovskii, E. S. Nenno, R. M. Skripinchenko, Russ. J. Inorg. Chem., 17(1972)1322-1324  [2] H.-H. Emons, H.-U. Triebs, F. Winkler, Z. anorg. allgem. Chemie, 382(1971)1-8