Nucleation and dissociation of carbon dioxide hydrate in the inter- and intra-particle pores of dioctahedral smectite: Mechanistic insights from molecular dynamics simulations

Abstract The storage of CO2 in the form of gas hydrate is becoming common place in the field of carbon capture and storage. Natural gas hydrate deposits are typically rich in clay minerals, yet their potential effect on CO2 hydrate nucleation and dissociation is rarely elucidated. In the present work, the nucleation and dissociation of CO2 hydrate in the inter- and intra-particle pores of dioctahedral smectite particles were investigated using molecular dynamics simulations. The results show that the hydrate nucleation clearly occurred in the inter-particle pores, whereas clathrate-like structures were formed in the intra-particle pores or on the edge surface of smectite. The properties of smectite, specifically the layer charge distribution and the type of exchangeable cations, are the main factors affecting the nucleation and dissociation of CO2 hydrate by changing the structural ordering of water molecules. The diffusion of CO2 molecules into the intra-particle pores enhances the formation of clathrate-like structures with increasing water content, but it does not increase the structural ordering of water molecules. Increasing the temperature or adding electrolytes in the smectite particles have accelerated the CO2 hydrate dissociation. Overall, the nucleation and dissociation mechanisms of CO2 hydrate in the linked inter- and intra-particle pores of dioctahedral smectite particles not only substantially affects the carbon storage and methane extraction in hydrate reservoirs, but also have potentially important impacts on pore fluids transportation in marine sediments.