Research on the thermodynamic stability and physicochemical property of clathrate hydrate with the host-guest interaction

Abstract

Clathrate hydrates, crystalline host-guest compounds, have received much attention due to their potential applications such as energy resources and carbon dioxide sequestration (CCS). In this dissertation, thermodynamic and electric properties of hydrate phase for gas hydrate production and the effect of the host-guest interaction behavior on hydrate properties were investigated. First, phase equilibria and guest distribution of the $CH_4/N_2/CO_2$ mixed hydrates were investigated for the $CH_4$ - flue gas replacement in natural gas hydrates. The collected phase equilibrium data for the $CH_4/N_2/CO_2$ mixed hydrates could offer insights into potential locations and the expected extent of the replacement when flue gas $(N_2/CO_2)$ is injected for $CH_4$ production. Hydrate Compositions by GC showed the enrichment of $CO_2$ in the hydrate phase, and $^{13}C$ NMR results indicated that the preferential occupation of $N_2$ and $CO_2$ in the small and large cages of sI $CH_4/N_2/CO_2$ hydrates, respectively. Second, the electrical resistance of $CH_4/N_2/CO_2$ mixed hydrates with their compositions and the resistivity change during the replacement process using $N_2/CO_2$ injection were investigated. The electrical specific resistivity of the $CH_4/N_2/CO_2$ mixed hydrates was increased with an increase in $CH_4$ composition. Moreover, the specific resistivity during replacement process for $CH_4$ hydrate by injecting $N_2/CO_2$ gas was also investigated. Finally, the guest-host hydrogen bonding behavior of diazine isomers in the clathrate cage was connected with the hydrate thermodynamic stability. All three diazine are confirmed as new sII hydrate formers with methane as a help gas. The order of the thermodynamic stability of the diazine hydrates as measured by the P-T trajectory of hydrate formation and the dissociation process is pyrazine > pyrimidine > pyridazine hydrates, which is identical to the orders of their probability of hydrogen bonding. The temperature-dependence of the guest-host hydrogen bonding probability was confirmed by measuring the ring-breathing vibration frequencies of the diazine isomers by means of Raman spectroscopy.