Molecular dynamics simulation of acid gas mixtures: a comparison between several approximations.

Guillaume Galliero (1, 2) , C. Nieto-Draghi (3) , Christian Boned (1) , J.B. Avalos (4) , A.D. Mackie (4) , Antoine Baylaucq (1) , François Montel (5)

1 TEFC - Thermodynamique et Energétique des fluides complexes
2 LETEM - Laboratoire d'Etudes des Transferts d'Energie et de Matière
3 IFPEN - IFP Energies nouvelles
4 ETSEQ
5 CSTJF - Centre scientifique et Technique Jean Feger

Molecular dynamics simulations of CH4, CO2, H2S and their mixtures, chosen as representative of acid gas mixtures, have been performed. Static properties (pressure or density) and dynamic properties (shear viscosity) have been computed. A comparison has been performed between results from three different models: a simple Lennard-Jones (LJ) model, an isotropic multipolar (IMP) one and the usual Lennard-Jones plus point charge (LJP). For pure fluids, a reasonable agreement is found between all three models and experiments except for CO2, for which the LJ model suffers from its lack of electrostatic contributions. Concerning CH4-H2S mixtures, results obtained using the three molecular models are consistent with each other for static and dynamic properties. In addition, no significant differences between the results obtained using both, Lorentz-Berthelot and Kong combining rules were noticed. For the CH4-H2S-CO2 mixture, the situation is different: a strong dependence of the pressure on the molecular models as well as on the combining rules, in the case of the LJP model, has been noted. Shear viscosity was found to be less dependent on the choice of models and combining rules. Thanks to simulations on H2S-CO2 mixtures, it has been found that the way cross interactions are treated between these two compounds explains the discrepancies for CH4-H2S-CO2 mixtures. For the systems studied, the IMP approximation seems to be the best option for engineering calculations of physical properties since it is quick to compute, ensures accuracy and is weakly dependent on the combining rules employed. In addition, it is shown that a van der Waals one fluid model combined with an accurate LJ Equation of State together with a correlation on viscosity is able to provide results consistent with simulations (on both LJ and IMP models). Such a result makes this correlative scheme a good alternative for industrial applications.

Mots clés: Acid gas mixture; hydrogen sulfide; isotropic multipolar potential; molecular dynamics; one fluid model; viscosity

Domaines: Chimie-Physique [physics.chem-ph]; Milieux fluides et réactifs; Chimie théorique et/ou physique

Guillaume Galliero, C. Nieto-Draghi, Christian Boned, J.B. Avalos, A.D. Mackie, et al.. Molecular dynamics simulation of acid gas mixtures: a comparison between several approximations.. Industrial and engineering chemistry research, 2007, 46 (15), pp.5238-5244. ⟨10.1021/ie061616l⟩. ⟨hal-00322172⟩