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

The superheated state of methane (CH₄) 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 CH₄ 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 CH₄ hydrate in CP converted the outer layer of CH₄ 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 CO₂ hydrate and C₂H₆ hydrate could be preserved by CP hydrate.