Thermodynamic analysis and micro-structural identification of clathrate hydrates

Abstract

Gas hydrates have been applied to many industrial fields such as desalination, food concentration, selective separation of targeted component, $CO_2$ sequestration into the deep ocean and exploitation of natural gas hydrates. In this study, thermodynamic and spectroscopic analysis of double gas hydrates was intensively investigated, especially focused on application to recovery and storage system of gaseous energy. The scope of this study can be divided into three fields. The first one is the recovery of $CH_4$ gas from natural gas hydrate by using replacement technique, the second one is enhancing $CH_4$ storage capacity of sII double hydrate by using tuning phenomenon, and the last one is recovery and storage of $H_2$ cluster by using clathrate hydrate. In this study, thermodynamic and spectroscopic analysis of gas hydrate was intensively investigated, especially focused on application to recovery and storage of gaseous energy system. For thermodynamic analysis, hydrate phase behaviors of multi-guest systems were carefully measured. For spectroscopic analysis, the structure, distribution of guest molecules and cage occupancies of mixed hydrate were determine through XRD, NMR and Raman spectroscopy. First, the primary purpose of this study is to address the guest-guest replacement behavior within host-lattice networks and then examine its potential application to $CO_2$ sequestration at the preliminary phase. We noted the fact that sI hydrate structure was preserved without rearrangement of crystal framework when guest molecules were removed or replaced. The preferable cage occupancy of guest molecules largely depended on their specific molecular details that appear to be so complex for visualization. The present outcome of 85% CH4 replacement rate in $CH_4$ hydrate achieved by the direct use of binary $N_2$ + $CO_2$ guests is quite surprising when compared with 64 % of pure $CO_2$ guest in the previous approach. The higher recovery rate using the $N_2$ + $CO...