Diffusivity Analysis of Liquid CO₂ and Saltwater under Deep Sea Conditions with the Dynamic Pendant Droplet Volume Analysis Method

Ocean already absorbed almost a third of global CO2 emissions and offers huge CO2 storage potential for widely deployed CCUS projects. Injecting and dispersing CO2 in deep seawater is regarded as a promising method for accelerating the ocean sequestration process. The diffusion coefficient of CO2 into deep seawater is of great value for determining the storage capacity. However, the characteristics of CO2 diffusing into deep seawater are rarely studied. In this study, the diffusion coefficients of liquid CO2 and seawater were measured using the dynamic pendant droplet volume analysis (DPDVA) method under 5–20 °C temperature, 6–20 MPa pressure and 3–4 wt % salinity. The results indicate that the diffusion coefficient increases with temperature and pressure and decreases with salinity. A total of 180 data points were obtained in this study, of which 147 were deemed valid, with an experimental error of less than 6%. The range of diffusion coefficients was found to be 3.53 × 10–10–7.36 × 10–10 m2/s. This study is expected to fill the gap in the field of diffusion coefficient studies between liquid CO2 and brine and support the assessment of CO2 ocean storage capacity.