Superheating of Structure I Gas Hydrates within the Structure II Cyclopentane Hydrate Shell.

The superheated state of methane (CH) hydrate that exists under the surface ice layer can persist for considerable lengths of time, which showed promise as a method for storing and transporting natural gas. This study extends this further by coating sI CH hydrate with one of several sII hydrates, thus eliminating the need for a defect-free continuous interface between the sI and sII hydrates. Gas hydrate crystals were kept intact above their dissociation temperature by immersing them in liquid cyclopentane (CP), as observed with powder X-ray diffraction and X-ray CT methods. It was observed that placing the CH hydrate in CP converted the outer layer of CH hydrate to a thin layer of CP hydrate at around 270 K under atmospheric pressure, which is ∼80 K higher than the usual dissociation temperature. It was also observed that sI CO hydrate and CH hydrate could be preserved by CP hydrate.