Conversion of CH4-Hydrate to CO2-Hydrate in Liquid CO2.

The recovering rate of CH4 from CH4-hydrate soaked in liquid CO2 was measured at 274–277 K and 4–5 MPa. The fugacity of CH4 in liquid CO2 was kept below its initial hydrate forming fugacity, while that of CO2 was much higher than the initial forming fugacity of CO2-hydrate. The CH4-recovering rate in liquid CO2 was much lower than that in gaseous N2 which dose not make hydrate under the conditions. The composition of the hydrate measured at the end of the experiment indicated that the formation of CO2-hydrate consumed all the H2O molecules which had been encaging the recovered CH4. The observed phenomena was described by a mathematical model based on nonequilibrium thermodynamics for use in feasibility studies.