pH of CO2 saturated water and CO2 saturated brines: Experimental measurements and modelling

Furthermore, a model was developed to predict the changes in the pH due to the solubility of CO2 in the aqueous phase at high pressure and high temperature conditions as well as the effect of NaCl. The pH model was developed by coupling the Cubic-Plus-Association Equation of State (CPA EoS) and the Pitzer equations. The former was used to determine the solubility of acid gases in aqueous solutions while the latter was employed to calculate activity coefficients for each ion species. The predictive capability of the pH model was evaluated against the data gathered from the literature and data measured in this work. The model allowed a prediction of the pH with an overall average absolute deviation (AAD) to measured data of 0.03 and 0.06 pH units in the CO2-H2O system using electrometric and spectroscopic techniques, respectively, and between 0.04 and 0.10 pH units in the CO2-H2O-NaCl systems by employing the spectroscopic technique.