Transformation of methane hydrate to carbon dioxide hydrate: In situ Raman spectroscopic observations

An in situ Raman spectroscopy study on the guest replacement of methane hydrate with carbon dioxide at high pressures is presented. The surface shielding of carbon dioxide hydrate formed in the outer layer plays a key function, retarding dissociation of methane hydrate in the core. A thorough investigation of Raman spectra of the vibration modes of water molecules enables us to understand the phenomena of the coexistence of methane and carbon dioxide hydrates and water phase for guest replacement reactions. These results should aid further efforts in the study of guest stability of clathrate hydrate as well as future technological applications.