On the occupancy of carbon dioxide clathrate hydrates: Grandcanonical Monte Carlo simulations

Grandcanonical Monte Carlo simulations are performed in order to examine the cage occupancies of carbon dioxide clathrate hydrate in both the larger and the smaller cages, the latter of which has been controversial issue and is related significantly with its phase behavior. It is found that occupancy of CO₂ in the smaller cage of clathrate structure I is negligible at a pressure of CO₂ below 1 MPa while that in the larger cage increases gradually with increasing the pressure of CO₂ in equilibrium with the clathrate hydrate. It is suggested by the present simulations that CO ₂ clathrate hydrate exhibits a different character in occupancy from ethane, which is a little larger than CO₂ and cannot enter into the smaller cage.