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Understanding and controlling hydrate formation are of vital importance for the storage and transportation of natural gas. In this work, the influence of a solid surface on the stability of a hydrate nucleus is studied by molecular dynamics simulations. The surface with a strong affinity for guest molecules induces the decomposition of the hydrate nucleus because of competitive adsorption on guest molecules. Specifically, the competitive adsorption for guest molecules results in the transformation of interface structures of the hydrate nucleus, and this process can be divided into two steps: transformation from whole cages to semi-cages and aggregation of the isolated semi-cages. While the interaction between the guest molecules and the solid surface decreases to form a weakly affinitive surface, the hydrate nucleus can maintain its structure near the surface. Our research shows that not all surfaces facilitate hydrate nucleation, and the stability of the hydrate nucleus on the surface is closely related to the affinity for guest molecules of the solid surface.

Tetrahydrofuran (THF) is well known as a former and a promoter of clathrate hydrates, but the molecular mechanism for the formation of these compounds is not yet well understood. We performed ab initio calculations and ab initio molecular dynamics simulations to investigate the formation, structure, and stability of THF·(H2O)n=1–10 and its significance to the formation of the THF hydrate. Weak hydrogen bonds were found between THF and water molecules, and THF could promote water molecules from the planar pentagonal or hexagonal ring. As a promoter, THF could increase the binding ability of the CH4, CO2, or H2 molecule onto a water face, but could also enhance the adsorption of other THF molecules, causing an enrichment effect.

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