Extension and application of the pitzer equation for vapor‐liquid equilibrium of aqueous electrolyte systems with molecular solutes

Abstract

The semi-empirical Pitzer equation for modeling equilibrium in aqueous electrolyte systems has been extended in a thermodynamically consistent manner to allow for.molecular as well as ionic solutes. Under limiting conditions, the extended model reduces to the well-known Setschenow equation for the salting out effect of molecular solutes. To test the validity of the model, correlations of vapor-liquid equilibrium data were carried out for three systems: the hydrochloric acid aqueous solution at 298.15OK and concentrations up to 18 molal; the NH3-C02 aqueous solution studied by Van Krevelen et al. (1949) SCOPEThe use of modern process simulators for analysis and design of processes involving electrolytes has been greatly limited by the lack of adequate correlations for electrolyte thermodynamics. For most systems of industrial importance, empirical correlations are applicable only to one particular system, over a limited range of conditions. The empirical correlations do not provide a framework for treating new systems or for extending the range of existing data, because the nonidealities have not been accounted for in a general and consistent manner.Aqueous electrolyte systems are common in the chemical industry. One example of interest is the potassium carbonate aqueous solution used in the Hot Carbonate Process as the acid gas removal agent in coal conversion plants. The Hot Carbonate Process was developed by the U.S. Bureau of Mines as part of a program on the synthesis of liquid fuel from coal. It provides an economical chemical absorption process for removing large quantities of COz from synthesis gases (Riesenfeld and Kohl 1974).Knowledge of the equilibrium solubility of carbon dioxide in the potassium carbonate aqueous solution is essential to the design of the Hot Carbonate Process. A large amount of comprehensive physical data on the KzCO3-CO2 aqueous solution system is available in the literature. However, due to inability to properly correlate electrolyte thermodynamics, empirical equations or nomographs of the vapor-liquid equilibrium data have been used as basic design tools (Bocard and Mayland 1962, Maddox and Burns 1967, Mapstone 1966, Wen 1971.Recently, there have been a number of significant developments in the modeling of electrolyte behavior. Brornley (1973), Meissner and Tester (1972), Meissner and Kusik (1972), Pitzer and co-workers (1973a, 1973b, 1974, 1976), and Cruz and Renon (1978), presented models for calculating the mean ionic activity coefficients of many types of aqueous electrolytes. In addition, Edwards et al. (1975) proposed a thermodynamic framework to calculate equilibrium vapor-liquid compositions for aqueous solutions of one or more volatile weak electrolytes which involved activity coefficients of ionic species. Most recently, Beutier and Renon (1978) and Edwards et al. (1978) used simplified forms of the Pitzer equation to represent ionic activity coefficients.The purposes of this study are to 1) reformulate the Pitzer equation in a more rigorous way, to obtain a thermodyn...

Fate of ammonia in the atmosphere?a review for applicability to hazardous releases

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