Extension of the electrolyte Trebble–Bishnoi EOS to mixed‐salt systems, and application to vapour liquid and solid (hydrate) vapour liquid equilibrium calculations

Abstract

AbstractThis work examines the use of the electrolyte Trebble–Bishnoi equation of state (eTBEOS) in predicting high‐pressure phase equilibria in the presence of aqueous mixed‐salt solutions. The eTBEOS combines the Trebble–Bishnoi equation of state with a Born energy term, a mean spherical approximation term, and a cation solvation term. Shortcomings in the originally regressed set of eTBEOS parameters are identified and discussed, and a new set of equation of state parameters is subsequently regressed for 58 salts. In order to extend the eTBEOS to mixed‐salt systems, two approaches for computing the EOS parameters of the ionic species are investigated. The first approach uses the originally regressed parameter set plus parameter mixing rules, where appropriate, whereas the second approach uses the newly regressed parameters and no mixing rules. In the prediction of osmotic coefficients in mixed‐salt solutions, the maximum relative difference between the experimental and computed values was 5.70%. For the gas solubility predictions, data were available for the solubility of CO2, CH4, and N2 in a small number of mixed electrolyte solutions; the maximum relative difference was 5.79%. Finally, CH4, C2H6, C3H8, and CO2 gas hydrate formation conditions were predicted in a number of mixed‐salt solutions, with a maximum relative difference of 10.76%. Overall, it was seen that both approaches allowed for comparable accuracy in phase equilibrium calculations. However, in the case of solutions made from salt mixtures with common cations, the second approach consistently resulted in improved accuracy.