Nitric and Sulfuric Acid Solubility in Dense Phase CO2

Research has shown that strong acids (i.e., sulfuric and nitric acids) may be produced as a result of reactions between impurities during CO2 transport within carbon capture, utilization, and storage (CCUS) systems even when today’s impurity specifications and recommendations are followed. Strong acids are corrosive to carbon steel, which is a very common construction material for CO2 transport pipelines. To establish acceptable impurity limits and to ensure the integrity of pipelines, experimental data are needed as input for modeling possible scenarios and as a foundation for constructing modeling tools. To assess the possibility of formation of concentrated acid-bearing phases in CO2 environments, acid solubility in dense phase CO2 needs to be determined. The nitric and sulfuric acid solubilities in dense phase CO2 were determined by first saturating the CO2 phase with the acids and by subsequently scrubbing the acids using water-filled autoclaves. The water was then analyzed using ion chromatography. The experiments were conducted at two temperatures (25 and 48 °C) with four different pressures (80, 100, 120, and 170 bar). The new solubility measurements have been used in conjunction with available literature data to construct a thermodynamic model for predicting the thermodynamic behavior of acid–CO2 mixtures over wide ranges of temperatures, pressures, and compositions. The model is based on the previously developed Mixed-Solvent Electrolyte (MSE) framework and incorporates speciation and phase equilibria in CO2-rich as well as water-rich environments.