Thermodynamic Study Of System LiCl-LiNO₃-H₂O

Physical and thermodynamic properties of the ternary system LiCl-LiNO3-H2O, including solubility, vapor pressure and viscosity, have been extensively investigated as possible working fluids in absorption refrigeration and heat pump systems. However, the data obtained by experimental technique are not always reliable. Four years ago, when we applied BET model to predict solubility diagram of the ternary system LiCl-LiNO3-H2O, essential differences has been found between predicted and experimental one. Thus, we planed to carry out a series of experiments to identify the reliability of our predicted results and check the correctness of previously published data.Solubility of the binary system LiNO3-H2O from 273.15 K to 333.15 K and solubility isotherms of the ternary system LiCl-LiNO3-H2O were elaborately measured at 273.15 K and 323.15 K. To the binary system, our data are in good agreement with those of Campbell in 1958 and quite different from those reported by Donnan in 1903 and Campbell in 1942. The solubility data of Campbell in 1958 are somewhat scattered and obviously higher than our results at temperatures near 273 K, compared with our results. To the ternary system, the experimental results shows that the solid phases in equilibrium with the solution {x(2.8LiCl+LiNO3)-(1-x)H2O} are LiNO3·3H2O or LiNO3 at 273.15 K and LiNO3 at 323.15 K, which is different from the literature results (Iyoki S, Iwasaki S, Kuriyama Y, et al. J. Chem. Eng. Data., 1993, 38: 396-398.).These solubility data, as well as water activities in the binary systems from literature, were treated by an appropriate empirically modified BET model. And then, by means of solubility determinations in the ternary system and its related binary systems and subsequent correlation of the data with the modified BET model, the isotherms of the ternary system LiCl-LiNO3-H2O were reproduced and a complete phase diagram of the ternary system in the temperature range from 273.15 K to 323.15 K was predicted. Simulated results showed that Iyoki et al.'s experimental results (Iyoki S, Iwasaki S, Kuriyama Y, et al. J. Chem. Eng. Data., 1993, 38: 396-398.) don't represent an equilibrium liquids for LiNO3(s), nor the metastable one for LiCl·H2O(s). Thus, they should be considered as incorrect.