Modeling the phase equilibria of CO2 and H2S in aqueous electrolyte systems at elevated pressure

The solubility of carbon dioxide (CO2) and hydrogen sulfide (H2S) in basic aqueous electrolyte solutions is determined by a combined phase and reaction equilibrium. A cubic equation of state is applied to model the vapor-liquid equilibria of these reacting systems. The Peng-Robinson equation of state with Wong-Sandler mixing rules is combined with an extended UNIQUAC model for electrolytes where ion-specific interactions are determined from a Debye-Huckel term. The thermodynamic model is parameterized for aqueous systems containing carbon dioxide and hydrogen sulfide along with water and potassium carbonate solutions at high pressure. The UNIQUAC binary interaction parameters are estimated by minimizing deviations in the liquid phase composition of the model with respect to the experimental data. The data is taken from literature and is supplemented by own experimental work conducted as part of this study. (C) 2008 Elsevier Ltd. All rights reserved.