On the phase behaviour of the (carbon dioxide + water) systems at low temperatures: experimental and modelling

Carbon dioxide coming from capture processes is generally not pure and can contain impurities such as water. In a typical gas sweetening unit, the acid gas stream will be saturated in water. The presence of water in the acid gas stream can result in ice and/or gas hydrate formation and cause blockage. In this communication, new experimental data are reported for the water content of liquid carbon dioxide in equilibrium with hydrates at 13.9 MPa and temperatures range from 253.15 K to 277.15 K. Three different thermodynamic approaches have been employed to investigate the phase behaviour of the (carbon dioxide + water) system: the Valderama–Patel–Teja (VPT) equation of state combined with the NDD mixing rules, the Soave–Redlich–Kwong (SRK) equation of state with the Huron–Vidal mixing rules combined with a modified NRTL local composition model and the Cubic-Plus-Association equation of state. In all cases, the hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. The reliability of the thermodynamic models and approaches were evaluated by using the new data, (vapour + liquid) equilibrium data and phase equilibrium data in the presence of hydrate for both saturated and under-saturated systems.