(456h) Molecular Dynamics Study of the Phase Behaviour of H2O-CO2-NaCl and H2O+NaCl Systems

The vapor-liquid phase behavior for the systems H₂O-CO₂-NaCl and H₂O+NaCl is investigated through interfacial molecular dynamics simulations with GPU acceleration.

While these systems have been studied previously by means of analytical equations of state and molecular simulations, a complete understanding of the phase behaviour near the critical region is still lacking.  Molecular simulation represents the most powerful approach to understand the structure of the fluid mixtures as function of temperature and pressure, and provide the basis for developing thermodynamic models. However its application to the phase behaviour of H₂O-CO₂-NaCl and H₂O-NaCl systems at conditions near the critical points remains limited. In the case of Gibbs ensemble simulations, the molecule-transfer move of NaCl turns out to be the bottleneck of the approach, and the traditional assumption is to neglect the NaCl content in the gas phase. This issue can be overcome by using direct interface simulation since no approximation is made regarding the location of the ions in each phase. Nevertheless, its application remains challenging due to the system size that needs to be considered in order to obtain good statistics for the solubility of NaCl in both vapour and liquid phases. We show that the use of molecular dynamics with GPU acceleration allows the study of the systems while maintaining reasonable computing time.