(334c) A Predictive Modeling Framework for Structure I Gas Hydrates

Gas clathrate hydrates are non-stoichiometric, crystalline compounds that form under ambient temperatures and high pressures. Modeling their physical and thermodynamic properties is of great interest to the scientific community, yet current methods such as van der Waals-Platteeuuw (vdW-P) theory rely heavily on empirical correlation. In addition, there is some controversy in the open literature regarding the vdWP approach; some studies ( Chialvo et al., 2002) argue that it is flawed because it does not appropriately account for guest-guest interactions while other studies (Wierzchowski and  Monson, 2007) suggest it is only long range forces that are important for accurate modeling.

In this presentation, a new modeling framework for gas hydrate systems is described. Our approach is based on the use of the recently developed multi-scale predictive Gibbs-Helmholtz Constrained (GHC) equation of state (Lucia et al., 2012). The key to the GHC EOS is the novel up-scaling equation that communicates information from the molecular to the bulk phase length scale, and, in the case of hydrates, allows the inclusion of all necessary guest-guest, guest-host, or host-host interactions and structural contributions.  Results for GHC predicted gas hydrate densities and phase equilibria are compared to vdW-P theory and experimental data.