Methane recovery from methane hydrate using pressurized CO₂

The dynamics of CH₄ replacement in CH₄ hydrate with high-pressure CO₂ was observed with in situ laser Raman spectroscopy at temperatures ranging from 271.2 to 275.2 K and at an initial pressure of 3.25 MPa. The amount of CH₄ hydrate decomposition was found to be almost proportional to that of CO₂ hydrate formation for a series of 150 h experiments at fixed temperatures. This confirmed that the CH ₄-CO₂ replacement mainly occurred in the hydrate phase. Based on the rate data, a kinetic model was developed for CH₄ hydrate decomposition and CO₂ hydrate formation. Under CH ₄-CO₂ replacement in the hydrate, the activation energies were determined to be 14.5 kJ/mol for CH₄ hydrate decomposition and 73.3 kJ/mol for CO₂ hydrate formation after a given initial period (ca. 10 h). It was found that CH₄ hydrate decomposition was probably dominated by re-arrangement of water molecules in the hydrate whereas CO ₂ hydrate formation seemed to be dominated by diffusion in the hydrate phase.