Molecular simulation of the potential of methane reoccupation during the replacement of methane hydrate by CO(2).

Molecular dynamics simulations and stabilization energy calculations are performed in this work in order to understand the stability of CH(4) hydrate, CO(2) hydrate, and CH(4)-CO(2) mixed hydrate. The model systems of fully occupied type SI CH(4) hydrate, CO(2) hydrate, and CH(4)-CO(2) mixed hydrate are prepared in a simulation box of 2 x 2 x 2 unit cell with periodic boundary conditions. The MD simulation results reveal that the CH(4)-CO(2) mixed hydrate is the most stable one in above three hydrates. The stabilization energy calculations of small and large cavities occupied by CH(4) and CO(2) show that the CO(2) molecule is less suitable for the small cavity because of its larger size compared with the CH(4) molecule but is more suitable for the large cavity. The results in this work can also explain the possibility of CH(4) molecule in reoccupying the small cavity during the replacement of CH(4) hydrate by CO(2), from the hydrate stability point of view.