Thermodynamics of high-pressure aqueous systems containing gases and salts

• Published in: AIChE journal 1989-04, Vol.35 (4), p.635-644
• Main Authors: Harvey, Allan H., Prausnitz, John M.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Liquid-liquid equilibria; Liquid-solid equilibria; Liquid-vapor equilibria; Others (including liquid-liquid-vapor equilibria); Phase equilibria
• ISSN: 0001-1541; 1547-5905
• DOI: 10.1002/aic.690350413

This work provides a new method for calculating phase equilibria for systems where conventional activity‐coefficient models are not suitable. A procedure is presented for superimposing ionic effects on a conventional equation of state for nonelectrolytes. A modification of Born's equation is used to describe charging the ions; ion‐ion interactions are described with the Mean Spherical Approximation, coupled with an adjustable salt/solvent parameter that is obtained from osmotic‐coefficient data at room temperature. The equation of state is used to predict gas solubilities in aqueous salt solutions at high pressures. While this method produces qualitative agreement with the experimental solubility data, quantitative agreement requires a salt/ gas parameter obtained from Setchenow‐constant data. When Setchenow constants are used, agreement with experiment is good except at high salt concentrations, where salting‐out is usually underpredicted. Good results are obtained for phase equilibria in a natural‐gas/brine system at high pressures.