THERMODYNAMICAL EXPLANATION OF DISSOLUTION MECHANISM OF LIQUID CO2 WITH CLATHRATE-HYDRATE FILM
Dissolution of liquid C02 accompanied by C02 clathrate-hydrate film into sea water is observed at C02 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 C02 solubility. This fact indicates that the dissolution rate of a C02 droplet with hydrate film is controlled by the mass transfer rate of dissolved C02 at the droplet surface into water and the decrease of the dissolution rate due to hydrate can be explained by the decrease of C02 solubility in the hydrate formation region. Further, in order to clarify the decreasing mechanism of C02 solubility, a thermodynamic method was employed. The C02 solubility was estimated from the relationship between the molar Gibbs free energy of water-liquid C02 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.