Hydrate Stability of Carbon Dioxide + Oxygen Binary Mixture (CO2 + O2) in Pure Water: Measurements and Modeling

Knowledge of the dissociation conditions of mixed-gas hydrate systems is of great importance for scientific understanding (e.g., clathrate hydrates in the outer solar system) and engineering applications (e.g., flow assurance, refrigeration, and separation processes). In this work, CO2 + O-2 hydrate dissociation points were measured at different O-2 mole fractions (11, 32, and 50%) using the isochoric pressure search method. The consistency of these new data was verified using the Clausius-Clapeyron relationship. The measure-ments performed for pressures up to 19 MPa overcome the lack of data for this system and also allow us to evaluate the model predictions from pure CO2 hydrate to pure O-2 hydrate. To predict gas hydrate stability curves, in this work, the well-established hydrate theory of van der Waals and Platteeuw (vdWP) is combined with an electrolyte CPA-type equation of state (e-PR-CPA EoS), which has been successfully used to represent with high accuracy the fluid phase equilibria (including gas solubility and water content) of complex systems containing gas, water, and salt. The resulting model (e-PR-CPA + vdWP) was applied to the O-2 + H2O and CO2 + H2O + (NaCl) systems by comparing with the literature data. In the studied temperature range (>270 K), the model predicts, as expected, a hydrate structure of type I for O-2, CO2, and their mixtures. An excellent reproduction of the measured data by this complete model was obtained without any additional adjustable parameters.