Nucleation and Growth of Methane Hydrates under Confinement at Molecular Scale

Abstract

Understanding the microscopic nucleation and growth mechanisms of gas hydrate under confinement is crucial to develop the rapid hydrate nucleation technology for energy utilization and carbon sequestration. In this work, large-scale molecular dynamics simulations are used to explore the effects of confined dimensions, ratios of water to gas, and interfacial hydroxyl contents on methane hydrate nucleation and growth under confinements. Our simulation results demonstrate that hydrate nucleation and growth are strongly associated with the confined dimensions and interfacial interactions. Strong hydrate nucleation and growth occur more readily at low confined dimensions of 57.12 and 59.12 Å, yet weak hydrate growth behavior prefers a high confined dimension of 61.12 Å. Furthermore, at the ratio of water to gas of 3.75, methane hydrates exhibit the most rapid growth among the systems with various ratios of water to gas ranging from 1.75 to 9.75, resulting from sufficient guest molecules and efficient mass transfer. Interestingly, hydrogen-bond hydrate seed structures and hydroxyl groups on graphene oxide can induce water molecules to preferentially arrange at hydrate-solution and solution–substrate interfaces through interfacial interactions, leading to lateral hydrate growth toward the solution phase and longitudinal hydrate growth toward the solid substrate interface. This study not only reveals the microscopic manners of hydrate phase transitions under artificial or natural constrained environments, but also elucidates the regulation mechanism of interfacial interactions on hydrate growth pathways under complex confinements.