Evaluating the Effect of Impurities on the Diffusion Coefficient of CO۲ by Molecular Dynamics Simulation: Application to CO۲ Sequestration Process

At the time, the increase in greenhouse gases is one of the most important environmental problems. Geological CO۲ storage is considered as one of the feasible solutions. A high portion of CO۲ Capture and Storage (CCS) costs are devoted to capturing, purification, and transportation. The injection of CO۲ with impurities can reduce these costs andhelp the development of CO۲ sequestration projects. The diffusion coefficient is an important parameter in CO۲ storage in saline aquifers. In the previous studies, the diffusion coefficient of CO۲ in impure cases assumed to be unchanged. In this study, we considered two of the most important contaminants, N۲ and SO۲, in two levels andcomputed the Fick diffusion matrix by using Molecular Dynamics (MD) simulation. Outcomes of this study indicate the intense effect of impurities on the diffusion coefficient and show the reduction of the CO۲ main diffusion coefficient in all cases. This decrease can be in a range of ۸-۴۲% for CO۲- SO۲-water system and ۷-۴۶% for CO۲-N۲-watersystem. These changes in the diffusion matrix can alter further steps of CO۲ sequestration such as the behavior of dissolution flux, the onset of convection, the motion of convective fingers, and their patterns. These results confirm the necessity to consider the effect of diffusion coefficient alteration in the CO۲ storage process.