Numerical study of the dissolution of carbon dioxide in an ionic liquid

• We model the dissolution of CO2 in ionic liquids.
• The model accounts for the moving phase interface and variable liquid density.
• The initial diffusivity of CO2 in [bmim][BF4] is overestimated with a reduced model.
• The diffusivity increases with the dissolution of CO2 in the ionic liquid.
• The equilibrium diffusivity given by correlations is 28% less than the actual value.

This work investigates the dynamics of the dissolution of carbon dioxide in an ionic liquid using a computational fluid dynamics model. The system is composed of liquid and gas phases separated by a moving boundary. The transport process comprises only one-way mass transfer (from gas phase to liquid phase) since the solubility of ionic liquids in carbon dioxide is immeasurably low in general. The model accounts for the changes in the position of the liquid free-surface and liquid phase molar volume during the dissolution process. Thermodynamic equilibrium condition is valid at the liquid-vapor interface where the discontinuity in the mole fraction of carbon dioxide is formulated using the concept of internal boundary condition. The model is applied to the experimental data obtained for the [bmim][BF4]–CO2 system at 323.15 K and 50 bar. The binary diffusivities are calculated and compared with those obtained from the literature and some correlations.