Experimental Study of Dissolution Rate of a CO₂ Droplet and CO₂ Solubility in High Pressure and Low Temperature Seawater With Hydrate Free

Against the background of carbon dioxide (CO₂) ocean sequestration technology, we investigated the solubility of CO₂ in seawater at a thermodynamic state similar to that at an ocean depth of 1000 m. The experiment was performed in two steps. In the first step, we reexamined and modified the fundamental relationship between Sherwood (Sh) number and Rayleigh (Ra) number in a natural convective flow over an up-down CO₂ droplet. We derived a new expression of the Grashof number for CO₂ dissolution in water and seawater with the aid of the relation between the density of CO₂ solution and CO₂ concentration. In the second step, this new expression was applied to the estimation of solubility of CO₂ from experiments examining the dissolution of an individual CO₂ droplet in seawater at hydrate-formable pressure and temperature states. We found from our experiments: that (1) at hydrate-formable conditions (step two), no hydrate appeared at interface between liquid CO₂ and seawater throughout the experiments within 5 hours, which suggested that a thermodynamic state (pressure and temperature) is indispensable but not a complete condition for hydrate formation; and (2) associated with this dual nature, the data of CO₂ solubility estimated from this experiment are much larger than those obtained by Kimuro et al [1] from experiments of hydrate coexistence. Our data ranged from 0.052 to 0.062 in mass fraction.