高圧水との界面にハイドレート膜を伴う液体CO₂の溶解機構とその熱力学的考察

抄録

Dissolution of liquid CO₂ accompanied by CO₂ clathrate-hydrate film into sea water is observed at CO₂ sequestration in ocean, which is considered to be an effective strategy of CO₂ mitigation. The dissolution mechanism was experimentally investigated by considering the relation between measured CO₂ surface concentration of hydrate-covered CO₂ droplets and CO₂ solubility. It was made clear that, in the temperature range of hydrate formation, the measured surface concentration decreases with the decrease of temperature and it exactly corresponds to CO₂ solubility. This fact indicates that the dissolution rate of a CO₂ droplet with hydrate film is controlled by the mass transfer rate of dissolved CO₂ at the droplet surface into water and the decrease of dissolution rate is caused by the decrease of CO₂ solubility in the hydrate formation region. Further, in order to clarify the decreasing mechanism of CO₂ solubility, a thermodynamic method was employed. CO₂ solubility was estimated from the relationship between the molar Gibbs free energy of water-liquid CO₂ mixture and that of hydrate and it has shown that the present method could predict the decrease of CO₂ solubility in hydrate formation region fairly well.