Statistical mechanical theory and computational study on thermodynamic stability of clathrate hydrates

Abstract

Clathrate hydrates are non-stoichiometric inclusion compounds with critical relevance to energy resources and CO2 sequestration, formed by guest molecules encapsulated in water cages. This perspective overviews the synergistic progress achieved through statistical mechanics and molecular simulation with intermolecular potential models in three key areas: thermodynamic stability, structural polymorphism, and dynamic processes. Theoretical estimation of its stability, originated from the van der Waals and Platteeuw theory, has been greatly improved by revisions accounting for constant pressure conditions, multiple occupancy, and host–guest coupling, enabling accurate prediction of multi-phase coexistence. Novel hydrate and ice structures have been synthesized using new strategies. The Frank–Kasper HS-I phase is unstable with small gas molecules, however, it was realized as a semiclathrate hydrate with an alkyl ammonium salt. We also discuss several possible strategies to form metastable ices, such as degassing of gas hydrates. The dynamic aspects have been investigated using molecular dynamics simulations. It was shown that dissociation kinetics are significantly influenced by guest concentration and bubble formation. Molecular dynamics simulations have also provided valuable insights into two types of low dosage hydrate inhibitors.