Methane Hydrate Nucleation Rates from Molecular Dynamics Simulations: Effects of Aqueous Methane Concentration, Interfacial Curvature, and System Size

Abstract

Methane hydrate nucleation rates are reported from over 200 μs of molecular dynamics simulations across a range of thermodynamic conditions and varying degrees of methane–water interfacial curvature. Calculated nucleation rates increase with aqueous phase methane concentration (XCH4), consistent with experimental results. The effect of interfacial curvature on XCH4 is quantified, with dissolved methane concentration increasing with the degree of curvature (i.e., the number of dimensions in which curvature exists). Nucleation rates are reported for system sizes of 3456 and 13 824 molecules (H2O + CH4). Among the smaller simulation systems (which comprise the majority of the data), the calculated hydrate nucleation rates follow the same trend when plotted against XCH4 regardless of whether the predominant contribution to the effective system pressure is the simulation barostat or the methane–water interfacial curvature (Young–Laplace pressure). The incipient hydrate nuclei are destabilized in the immediate vicinity (∼ 1 nm) of the methane–water interface, and the calculated nucleation rates for the larger simulation systems (in which the incipient hydrate solids are less affected by interfacial destabilization) fall above the trend observed in the smaller systems.