Molecular insights into gas hydrate formation in the presence of graphene oxide solid surfaces

Abstract

• Molecular dynamics simulations of hydrate homogeneous nucleation and growth influenced by graphene oxide (GO) surfaces are performed. • The methane attraction of hydrates formation competes with the attraction of GO surface which may lead to the hydrate composition. • The increase of oxidation degree increases the instability of the hydrate structure. Different organic or inorganic materials have been used to control the nucleation and growth of hydrate in oil and gas transportation or storage fields and so on. In this study, the molecular dynamics simulations method is used to study the effect of graphene oxide(GO) on nucleation and growth of methane hydrate. The mirror, rotation and random systems for different spatial distributions of oxidized functional groups on GO layers and the different oxidation degree systems are constructed to study the effect on methane hydrate formation. It is found that the spatial distribution has little effect on hydrate formation with the same oxidation degree conditions. Most of the hydrate is normal growth but a few cases produce the hydrate decomposition phenomenon which is caused by the nucleation of randomness and surface adsorption of methane. The GO surfaces compete with the formed cages for solvated methane, which decreases the concentration of solvated methane and is not conducive to hydrate formation. Increasing the degree of oxidation will cause more instability for the hydrate growth state because of the thicker water adsorption layer and more H-bonds formed between GO and water. The adsorption layer of water and methane and their relative positions are displayed clearly for the first time. Our results provide a possible microscopic explanation of the GO influence on methane hydrate formation and provide new insights for using GO surface material as an inhibitor for hydrate formation.