含盐溶液汽液平衡预测(Ⅰ)——Pitzer模型的扩展及其在多元体系中的应用

本文提出一种新的预测含盐溶液汽液平衡的方法.对Pitzer(1980)模型进行扩展后,将其简化成单参数形式,推广至多元电解质溶液;经过适当假定,得到计算含盐挥发性强电解质和水体系及含盐水醇体系的活度系数公式,这些公式仅含二元相互作用参数;由二元溶液的活度关联出该参数后,可用于含盐体系各种温度下汽液平衡的预测.关联了40个二元电解质水溶液及7个电解质甲醇溶液298.15K时的简化Pitzer方程的单参数;用以推算6个水盐体系和2个甲醇盐体系在320-403K的蒸汽压,得到满意的结果,182个数据点的平均偏差小于0.65kPa;用以预测5个不同类型的含盐三元体系的等温、等压汽液平衡,所得的平均偏差对于汽相组成、沸点、压力分别为0.015、1K和1.92kPa.

Prediction of Vapor Liquid Equilibria for Salt Containing Systems ( I ) Extension of Pitzer Model and its Applications to Multicomponent Systems

In this paper a new method for the prediction of salt effects on VLE is proposed. The model of Pitzer(1980)is extended to the aqueous multicompo-nent electrolyte systems and mixed solvent/salt systems. After reasonable simplification, the activity coefficient expressions containing only one parameter for each binary electrolyte-solvent action are derived for the solvent and volatile solute. It is possible to predict the VLE of salt-containing systems by using these parameters which can be correlated with binary solution properties. The solvent activities of binary electrolyte solutions including 40 aqueous systems and 7 methanol solution systems are correlated to get the single-parameter of the simplified Pitzers model. Application of this model to the estimation of the vapor pressure depression in 320-403 K of LiCl, NaCl, KAc, HCl, CaCl2, MgCl2 binary aqueous solutions and LiCl, CaCl2 binary methanol solutions has shown good accuracy. The total mean of absolute deviation of 182 data points is 0.65 kPa. By the extended model and parameters correlated at 298.15K, the VLE of five different type of ternary salt-containing systems, H2O +CaCl2 +MgCl2, H2O+KCl + HCl, H2O+CaCl2 + HCl, H2O+ LiCl + CH3OH, H2O + CaCl2 + CH3OH, are predicted with the total mean of absolute deviation of 0.015 in vapor phase mole fraction, of 1 K in boiling point, of 1.92 kPa in vapor pressure.