Thermodynamical explanation of dissolution mechanism of liquid CO2 with clathrate-hydrate film

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. It was made clear that, in the temperature range of hydrate formation, the measured surface concentration of a hydrate-covered CO2 droplet decreases with decreasing temperature and agrees well with the 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 the dissolution rate due to hydrate can be explained 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. The 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 the hydrate formation region fairly well.