CO2 and CH4 Hydrates: Replacement or Cogrowth?

Replacement of CH 4 with CO 2 in gas hydrates is a promising option for producing CH 4 and sequestrating CO 2 simultaneously, but it remains debatable if the CH 4 hydrate dissociates or converts to the CH 4 –CO 2 mixed hydrates during the replacement. To gain insights into the underlying micromechanisms, molecular dynamics simulations were performed in this study at six temperatures (250–275 K) and three pressures (20, 50, and 100 bar) by systematic analysis of the hydrate cages. Results demonstrated that it was possible to destabilize the CH 4 hydrates by decreasing the adsorption of CO 2 on the CH 4 hydrate surface or increasing the interfacial area for the contact between CO 2 and CH 4 hydrates. However, the simultaneous dissociation of CH 4 hydrates and formation of CO 2 hydrates were not observed or only lasted for a very short time, while the released CH 4 would form CH 4 –CO 2 mixed hydrates even though the driving force was suitable for breaking up CH 4 hydrate cages and forming CO 2 hydrate cages. Moreover, this study revealed that the coalescence of CH 4 hydrate particles was mainly contributed by the linkage from 5 12 cages in the region between the two CH 4 hydrate particles, which was further stabilized by the 5 12 6 3 cages.