Thermodynamic study for sequestrating global warming gases into deep ocean floor using hydrate

Abstract

Hydrates are non-stoichiometric inclusion compounds formed by a lattice of host molecules, strongly hydrogen bonded under certain conditions of pressure and temperature, which encage low molecular weight gases or volatile liquids in different cavities within the lattice. While the guest molecule is enclosed within the lattice, there is no chemical union between the guest and host molecules. Applications of hydrates had been tried to several technologies such as desalination, food concentration, bio-material separation, carbon dioxide deposit in ocean floor, and natural gas production from gas hydrate field. In this study, gases separation and storage, especially global warming gases, were tried and verified through measurements of three-phase equilibria, formation kinetics, and two-phase equilibria excluding gas phase. Three phase equilibrium conditions of hydrate, water and vapor (H-Lw-V) for $CO_2$ and $CH_4$ were measured. For each system, clay and NaCl were added individually or simultaneously. Depending on the concentration of clay mineral, equilibrium pressures were affected. At low concentration of clay mineral, phase condition almost didn``t change. Because of existence of bulk phase water, clay couldn``t play a role to change equilibrium conditions. At high concentration of clay minerals, inhibition phenomena of equilibrium condition occurred. Because water penetrated clay interlayer pore, hydrate formation occurred between the layers. Therefore, due to the capillary effects in case of a system with clay minerals showed higher equilibrium pressure than the system without clay mineral at same temperature condition. Equilibrium line of NaCl solution was shifted to left side of pure hydrate equilibrium line. When NaCl and clay were added together both effect occurred simultaneously. Hydrate formation kinetics of carbon dioxide and sodium chloride solution with and without clay mineral were investigated. It was observed that hydrate formation occurred in t...