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

Abstract

Ocean already absorbed almost a third of global CO 2 emissions and offers huge CO 2 storage potential for widely deployed CCUS projects. Injecting and dispersing CO 2 in deep seawater is regarded as a promising method for accelerating the ocean sequestration process. The diffusion coefficient of CO 2 into deep seawater is of great value for determining the storage capacity. However, the characteristics of CO 2 diffusing into deep seawater are rarely studied. In this study, the diffusion coefficients of liquid CO 2 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 m 2 /s. This study is expected to fill the gap in the field of diffusion coefficient studies between liquid CO 2 and brine and support the assessment of CO 2 ocean storage capacity.