Modeling Of Aqueous Electrolyte Solutions Based On Electrolyte Equation Of State For Square-Well Chain Fluids With Variable Range

Equation of state can not only calculate the activity coefficient, fugacity coefficient, osmotic coefficient of electrolyte systems, but also give the information of density, vapor liquid equilibrium. Modeling of thermodynamic properties for aqueous electrolyte solutions based on equation of state plays an important role in the production of chemical industry. Electrolyte equation of state for square-well chain fluids with variable range (eSWCF-VR) was used to model the thermodynamic properties for aqueous electrolyte solutions in this work.The ionic parameters (segment diameter and dispersive energy parameter) for22ions were fitted by experimental data of the mean ionic activity coefficient and osmotic coefficient of more than40strong (1:1type) aqueous electrolyte solutions. The eSWCF-VR was used to calculate the mean ionic activity coefficient and osmotic coefficient of aqueous electrolyte solutions with overall average deviations of6.03%and5.83%, respectively. On this basis, the eSWCF-VR was used to predict the density of aqueous electrolyte solutions and vapor liquid equilibrium of aqueous electrolyte solutions with overall average deviations of0.22%and4.69%, respectively. The results show that the eSWCF-VR can describe the thermodynamic properties for the selected aqueous electrolyte solutions.After considering the contribution from ionic association between cations and anions in the eSWCF-VR, the model can calculate the mean ionic activity coefficient and osmotic coefficient of aqueous electrolyte solutions. At the same time, the information of about the degree of ionic association can be obtained by the eSWCF-VR. The degree of ionic association for the cations increases with increasing the diameter of cations at the same molality. The degree of ionic association for the anions increases with increasing the diameter of anions in the acid solutions which have the same cation. The results show that after considering the contribution from ionic association between cations and anions in the eSWCF-VR, the results of calculation would be improved apparently. For instance, in the aqueous electrolyte solutions LiAc, NaAc and KAc, the eSWCF-VR without considering the contribution from ionic association between cations and anions calculated the mean ionic activity coefficient and osmotic coefficient with the overall average deviations of12.11%,9.93%,10.88%and12.11%,9.93%,10.88%, respectively. With considering the contribution from ionic association between cations and anions, the overall average deviations of calculation the mean ionic activity coefficient and osmotic coefficient is reduced to1.70%,2.04%,2.53%and2.28%,2.33%,2.68%, respectively. It proves that the eSWCF-VR can describe the thermodynamic properties for the weak aqueous electrolyte solutions. Combined with the solubility product, the eSWCF-VR was used to predict the solubility of4aqueous electrolyte solutions at different temperatures. The results of prediction are satisfactory.