Methane hydrate formation in the stacking of kaolinite particles with different surface contacts as nanoreactors: A molecular dynamics simulation study

The heterogeneous nucleation behaviors of methane (CH4) hydrate in the presence of kaolinite (Kaol) were studied, and nucleation was found to be strongly affected by the surface contacts of Kaol particles. Molecular dynamics simulations were performed to investigate CH4 hydrate formation in Kaol particles with different surface contacts, such as silica-alumina face, alumina-alumina face, and silica-silica face. The results revealed two nucleation events, one in the bulk-like solution and the other near the siloxane surface of the Kaol. The crystal growth of CH4 hydrate tended to occur away from the Kaol surface. The silicon-oxygen rings of the siloxane surface served as a plane of the cage, thereby forming a semi-cage arrangement in which the CH4 molecules appeared to have the ability to stabilize the arrangement of water structures. However, strong hydrogen bond interactions made it difficult for CH4 molecules to form clathrate-like structures on the hydroxyl surface. These results indicate that Kaol particles with a siloxane surface promoted CH4 hydrate nucleation and growth but that Kaol particles with a hydroxyl surface were unable to do so. Thus, the surface properties and surface contacts of Kaol particles were found to involve in the formation of aggregates in natural sediments, which shows that they are crucial for nucleation, distribution, and crystallinity of CH4 hydrate.