Effect of Layer Charge on CO₂ and H₂O Intercalations in Swelling Clays

The effect of layer charge on the intercalation of supercritical carbon dioxide (scCO₂)-H₂O mixture in Na-montmorillonite clay interlayers under T = 323 K and P = 90 bar geologic sequestration conditions has been further investigated. This effect includes the charge amount and its location (within either octahedral or tetrahedral layers due to isomorphic substitutions). Two clay models with different layer charges are used in this study. Simulation results show that the increase of charge amount shifts the monolayer-to-bilayer (1W-to-2W) hydration transition toward the lower relative humidity (RH), increasing water sorption at the expense of reducing the overall sorption amount of CO₂ in the clay interlayer. However, the combination of the influence of charge amount and charge location leads to insignificant changes in equilibrium basal spacings of the high- and low-charge clays. Molecular dynamics simulations show that the CO₂ dimers, which are frequently seen in low-charge clay interlayers, vanish in high-charge clay interlayers even at low RH of 30%.