Recently, clathrate hydrates have attracted a lot of attention as they have exceptional use in climate science, energy recovery, seafloor stability and energy storage affiliated works. Methane hydrate is a non-stoichiometric crystalline inclusion compound which naturally and widely occurs in permafrost and seafloor. The mechanism behind clathrate hydrates formation in the presence of ice is far less comprehended and therefore further investigation is necessary to explicate on what happens on the ice surface. To this quest, molecular dynamics simulations has been proven very helpful in providing molecular-level insights into homogeneous nucleation of clathrate hydrates. Unfortunately, no simulation study has shown that clathrate hydrates nucleate along with the shrinking of ice. To this note, the effects of ice on hydrate nucleation and what happens in the quasi-liquid layer of ice still need to be elucidated.
In a recent paper published in Phys. Chem. Chem. Phys, professor Guang-Jun Guo together with Dr. Zhengcai Zhang proposed a study where they intended to use high-precision constant energy molecular dynamics simulations to evaluate methane hydrate nucleation from vapor–liquid mixtures exposed to the basal, prismatic, and secondary prismatic planes of hexagonal ice. The two researchers from the Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing aimed to shed further insight on the repercussions of ice on methane hydrate nucleation in a microcanonical molecular dynamics study.
They employed an ice-solution-gas metastable system to simulate hydrate formation in the quasi-liquid layer of ice. From the simulation results, the authors of this paper observed that the methane hydrate could nucleate either at the ice–solution interface heterogeneously or in the bulk solution phase homogeneously. It was seen that some factors were responsible for the promotion of the heterogeneous nucleation of methane hydrate on the ice surface, such as the adsorption of methane at interface, hydrogen bonding between hydrate cages and ice, the high heat conductivity of ice, and the high occurrence probability of cages near ice surface, while other factors inhibited the same, including the hydrophilicity of ice and the ice lattice mismatch with hydrates. Additionally, the researchers noted that methane hydrate could directly connect to the ice slab with the 5-/6-membered water rings.
Professor Guang-Jun Guo and Dr. Zhengcai Zhang successfully presented an in-depth analysis of methane hydrate nucleation in the presence of ice. In their work, they have utilized the benefit of ice to absorb heat in the high precision constant energy simulation to mimic the phenomenon of ice shrinking during hydrates form on ice surface for the first time. It has also been seen that the different crystal planes of ice pose no effects on the matter under study. The results observed here are crucial for comprehending the nucleation mechanism of methane hydrate in the presence of ice.
Zhengcai Zhang and Guang-Jun Guo. The effects of ice on methane hydrate nucleation: a microcanonical molecular dynamics study. Phys. Chem. Chem. Phys., 2017, volume 19, pages 19496-19505.
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