Molecular dynamic simulations of methane hydrate formation between solid surfaces: Implications for methane storage

Abstract

Gas hydrates have essential industrial and climate implications in energy exploitation and novel technologies. Hydrate nucleation and growth typically develop under substrate-contact conditions; surface properties affect hydrate formation pathways. Microscopic insights into the effects of solid surfaces on hydrate formation would improve reservoir exploitation and the synthesis and regulation of promoters for hydrate-based methane storage. We thus performed microsecond-scale molecular dynamic simulations to investigate methane hydrate formation in CH4–H2O-substrate systems varying substrate surface hydrophilicity. The evolution of several parameters suggested that the methane storage capacity was controlled by the proportions of surface methyl and hydroxyl groups. The mutually coordinated guest (MCG) was a superior indicator of hydrate nuclei since it recognized all methane separated by water rings in hydrate structures. As surface hydrophilicity decreased, the size of the crystal nucleus shrank, and the amount of captured methane decreased; nevertheless, the nucleation pathways shifted from amorphous to crystalline. Moreover, given the crucial interactions between MCG/four-body order parameters and interaction energy/host-guest local distributions, the underlying mechanisms of hydrate formation were well-represented using two- and three-step microscopic models. Our findings show how solid surface properties influence multi-stage hydrate nucleation and will contribute to developing additives that efficiently promote hydrate formation.