In this paper, the solid–liquid equilibrium of N-methylpyrrolidone (NMP) + MCl (M = Na, K, Rb, and Cs) + H₂O ternary systems was investigated at three temperatures (T = 288.2, 298.2, and 308.2 K). The isothermal solubility, density, and refractive index of the saturated ternary systems were obtained. At the same temperature, as the NMP content in the mixed solvent increases, the solubility of the salt decreases significantly, and the density change trend is consistent with the solubility. However, as the NMP content in the mixed solvent increases, the refractive index increases. As the experimental temperature increases, the solubility and density increase, while the refractive index decreases. Moreover, the semi-empirical four-parameter equation was used to fit the experimental data.

中文翻译：

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的相行为Ñ甲基吡咯烷酮+的MC1（M =钠，钾，铷，铯）+ H ₂输出系统在288.2，298.2，和308.2ķ

本文研究了N-甲基吡咯烷酮（NMP）+ MCl（M = Na，K，Rb和Cs）+ H ₂ O三元体系在三个温度（T= 288.2、298.2和308.2 K）。获得了饱和三元体系的等温溶解度，密度和折射率。在相同温度下，随着混合溶剂中NMP含量的增加，盐的溶解度显着降低，并且密度变化趋势与溶解度一致。然而，随着混合溶剂中NMP含量的增加，折射率增加。随着实验温度的升高，溶解度和密度增加，而折射率降低。此外，使用半经验四参数方程拟合实验数据。