Publications Details

Molecular simulations of carbon dioxide and water: Cation solvation

Criscenti, Louise; Cygan, Randall T.

Proposed carbon dioxide sequestration scenarios in sedimentary reservoirs require investigation into the interactions between supercritical carbon dioxide, brines, and the mineral phases found in the basin and overlying caprock. Molecular simulations can help to understand the partitioning of metal cations between aqueous solutions and supercritical carbon dioxide where limited experimental data exist. In this effort, we used classical molecular dynamics simulations to compare the solvation of alkali and alkaline-earth metal cations in water and liquid CO2 at 300 K by combining a flexible simple point charge model for water and an accurate flexible force field for CO2. Solvation energies for these cations are larger in water than in carbon dioxide, suggesting that they will partition preferentially into water. In both aqueous and CO2 solutions, the solvation energies decrease with cation size and increase with cation charge. However, changes in solvation energy with ionic radii are smaller in CO2 than in water suggesting that the partitioning of cations into CO2 will increase with ion size. Simulations of the interface between aqueous solution and supercritical CO2 support this suggestion in that some large cations (e.g., Cs + and K+) partition into the CO2 phase, often with a partial solvation sphere of water molecules. © 2012 American Chemical Society.