Determination of rate of diffusion of water into liquid carbon dioxide during CO2 storage

Abstract

The disposal of liquid CO2 (LCO2) into the ocean has been recognized as a potential method for mitigating global warming. This approach requires a deep understanding of water solubility and the kinetics of water dissolution into LCO2. Therefore, it is essential to determine both the diffusion rate and the underlying diffusion mechanism of water into LCO2. In this study, the volume change of water dissolved in LCO₂ was visualized using the shadowgraph technique, from which the diffusion rate constant was derived. The diffusion coefficient of water in the LCO₂ system was determined using a steady state dissolution model of a water drop. The diffusion rate of water containing ionic solutes, such as potassium hydroxide (KOH), was further measured at different concentrations. The results showed that the square of the equivalent diameter decreased linearly with time for water without KOH. A linear relationship existed between the diffusion rate constant and water solubility in CO₂. These findings indicate that the diffusion of water is the most important mechanism for the dissolution of water into LCO₂. Increasing the ionic solute concentration decelerates water dissolution due to the discernible precipitation of salts such as bicarbonates or carbonates.