Effect of isomorphic substitution of clay mineral layers on CO2 hydrate formation: Insights from molecular dynamics simulation study

Abstract

Hydrate method for CO₂ sequestration is currently regarded as one of the most promising approaches for carbon capture and storage due to its excellent stability and gas storage density. In this study, molecular dynamics simulations were conducted to investigate the impact of isomorphic substitution in clay minerals layers on CO₂ hydrate formation. The results showed that in pyrophyllite structures without isomorphic substitution, a significant number of CO₂ molecules were adsorbed onto the hydrophobic surfaces, hindering the nucleation of CO₂ hydrates in the bulk solution. However, as the degree of isomorphic substitution increased in montmorillonite, the surface charge also increased, leading to greater adsorption of cations. These cations predominantly accumulated on the montmorillonite surface, while CO₂ hydrate nucleation and growth occurred in the bulk solution, away from the clay mineral surface. Furthermore, among layers with the same degree of substitution, K⁺ cations had a lesser impact on CO₂ hydrate nucleation in the bulk solution compared to Na ⁺ cations. This study highlights the significant role of isomorphic substitution in clay minerals layers in governing CO₂ hydrate nucleation by altering the distribution of CO₂ around the clay mineral surface, thereby influencing CO₂ sequestration in marine sediments.