Modeling Of Aqueous Electrolyte Solution By Statistical Mechanic Theory

Aqueous electrolyte solution is particularly important in many industrial chemical processes. Much work focus on the empirical equations that were used to correlate the thermodynamic properties of aqueous electrolyte solution. In this work, a new equation of state is constructed based on the statistical mechanic theory.1. An theoretical model based on primitive MSA and FMSA is constructed to describe the single- and multiple- salt solutions. With the universal and transferable ionic parameters derived from mean ionic activity coefficients and solution densities of single-salt solutions, the proposed EOS predicts the correct osmotic coefficients as well as water activities of some practical systems. The predicting result is obviously improved comparing with the SAFT-RPM, which is the latest model in this area. Then the mean activity coefficient of NaCl solution at elevated temperature and pressure is predicted without any additional parameters. The results imply that this model can be used from 1bar to 600bar. However, at elevated temperature, the deviations between the predictions and experiments increase. It can be generally explained that the increasing deviation is due to the fact that the model does not include properly the effects of ion pairing.2. Ion paring is incorporated into the RPM electrolyte to account for the strong attraction between unlike ions. Two methods are investigated: first is the binding mean-spherical approximation (BIMSA) based on the Wertheim Ornstein-Zernike integral equation; and the second is the combination of the BIMSA with a simple interpolation scheme based on the Wertheim thermodynamic perturbation theory. The latter gives a better description compared with molecular simulation result.3. With the consideration of the ion-pair and the revision of the form of coulomb attraction, a new model is used to calculate mean activity coefficients, osmotic coefficients and densities of some single electrolyte solutions. The accuracy of this new model is greatly elevated. The assumption of ion-pair increases with increasing the concentration is approved.