Research of natural gas hydrate sediment layer and thermoydnamics of clathrate hydrate and application to functional icy materials

Abstract

Clathrate hydrates, commonly called gas hydrates, are non-stoichiometric crystalline inclusion compounds that are physically interaction between host-water molecules and relatively small gaseous/liquid guest molecules. In this study, I focused on four scopes; 1) environment and properties of natural gas hydrate in deep ocean sediments, 2) thermodynamics of clathrate hydrate at infinite dilution, 3) simple and general cage occupancy relationship of binary gas hydrate, and 4) clathrate hydrate with metal and radical guests and magnetic properties of clathrate hydrate. First, we focused on the environment and properties of natural gas hydrate in deep ocean sediments. Anomalous chloride concentration enrichment has been detected in marine sediments comprising methane hydrates. In the present work, we designed an electric circuit system linked to the high pressure resistance cell in which the chloride ion concentration can be directly measured withn reliable accuracy under in-situ conditions of the deep-sea floor pressure and temperature. We regulated the methane hydrate formation rate with 4 different interface areas between the sediment and bulk methane gas. We also related the volume of formed methane hydrate and chloride concentration, and assessed whether larger contact area yields a faster formation rate. Chloride concentration increased under a fast methane hydrate formation rate, but no noticeable concentration change was detected under a relatively low rate. Furthermore, we suggested that the methane hydrate formation rate must be maintained at least on the order of $~10^2 mol m^{-2} yr^{-1}$ so as to efficiently enrich chlorides and retain the acquired chloride level. The present experimental system dose not fully reflect the relatively minor effective variables such as vertical advections in real system, but the results seem to be sufficient for revealing chloride enrichment phenomena induced by fast methane hydrate formation rate with free methane gas. T...