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 N-2 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.