Spectroscopic observation of micro-structural transition and crystalline structure analysis of clathrate hydrate

Abstract

Gas hydrates have been applied to many industrial fields such as desalination, food concentration, selective separation of targeted component, CO2 sequestration into the deep ocean and exploitation of natural gas hydrates. The scope of this study can be divided into four fields. The first one is the structure transition and swapping pattern of clathrate hydrates driven by external guest molecules, the second one is storage of He cluster by using clathrate hydrate, the third one is neutron scattering study of hydrogen molecules in the double clathrate hydrates and hydrogen molecular dynamics of binary THF-H2 clathrate hydrate. The fourth is the investigation of heterogeneous methane hydrate formation in marine sediments to gain fundamental insights into the growth of intercalated methane hydrate and to compare the results with those in pure methane hydrate. In this study, thermodynamic and spectroscopic analysis and neutron scattering study of gas hydrate were intensively investigated, especially focused on micro-structural transition observation based on spectroscopic methods and crystalline structure analysis of clathrate hydrate. First, simply judging from the hydrate stability region based on the equilibrium PT behaviour, the sII and sH appear to be more stable than the sI in most of the mixed hydrate systems and thus we might draw such an illusive conclusion that the sII and sH methane hydrates are more abundant than can be discovered at the present level. But, from the actual experiments of guest swapping scenario we confirm that most of the sII and sH methane hydrates ultimately transform to the sI under free methane-rich surroundings sealed by the overlying impermeable hydrate layer, which presumably explain the preponderance of sI among complex structures of naturally-occurring methane hydrates. More importantly, we note that the unique and cage-specific swapping pattern of multi-guests is expected to provide a new insight for better understanding th...