MODELING SINGLE AND MIXED ELECTROLYTE-SOLUTIONS AND ITS APPLICATIONS TO GAS HYDRATES

This paper presents a predictive model for phase equilibria calculatio ns in the presence of electrolyte solutions. The model is based on a t hermodynamic approach in which an equation of state is combined with a modified Debye-Huckel electrostatic term, with only one adjustable pa rameter for the water-rich phase. The water-salt parameter has been de termined by using vapour pressure depression data at 373.15 K and free zing point depression data of single salt solutions. NaCl, KCl, CaCl2, Na2SO4, NaF, NaBr, MgCl2, SrCl2, BaCl2 and their mixtures, have been modelled. Although the work is primarily aimed at gas hydrate inhibiti on effect of formation water in subsea gathering networks and transmis sion lines, other properties can also be predicted over a wide range o f temperatures (250-423 K) and salt concentrations (close to saturatio n). These data include vapour pressure and freezing point depressions, hydrate inhibition of pure, and multi-component systems in the presen ce of single and mixed electrolyte solutions. The predictions of the m odel have been compared with experimental data and good agreement has been demonstrated.