(627i) Quick CH4 Hydrate Nucleation By Ice-Catalytic Effect through Hydrate like Order Propagation: A Molecular Dynamics Study

In the present work, heterogeneous nucleation of methane hydrate in the presence of ice (hexagonal ice-Ih) was studied by molecular dynamics simulations using different initial methane concentrations (from 3 to 10 mole %) at 250 K and 50 MPa. The ice growth rate was observed to decrease with CH₄ concentration. The newly grown ice shows stacking faults with a combination of layers of hexagonal and cubic ice. The growing ice produced an accumulation of methane molecules near the advancing interface and promoted formation of partial hydrate cages at the ice surface. These partial cages have a short lifetime, detached from the ice interface, and migrated into the bulk that works as a seed for methane hydrate nucleation. A growing ice front thus works as a catalyst-promoting agent and initiates a faster rate of hydrate nucleation compared to the homogeneous system. The nucleation time of methane hydrate was significantly reduced in the presence of ice and catalytic effect of ice has been seen in the form of hydrate order fluctuations from the enhanced ice front. The space-time correlation highlights the propagation of hydrate like order parameters and insights the actual mechanism that promotes the hydrate nucleation. The statistical data of nuclei location indicates that sI methane hydrate prefer to nucleate near the ice interface or into the bulk, while surface nucleation was observed only in the case (4/40), where growing front is cubic ice.