Phase equilibrium and crystallographic structure of clathrate hydrate formed in argon + 2,2-dimethylbutane + water system

•Phase equilibrium for a hydrate formed with argon + 2,2-dimethylbutane.•Range of the equilibrium temperature was from 275.6 K to 284.3 K.•Crystallographic structure of the hydrate was identified as structure H.•Stability of structure H hydrates with noble gases and methane is discussed.

This paper reports the four-phase (Lw–H–V–Lg) equilibrium conditions for the structure H hydrates formed in argon + 2,2-dimethylbutane. The experiments were performed at temperatures between 275.6 and 284.3 K, and at pressures between 2.91 and 9.41 MPa. The crystallographic structure of the hydrate was identified to be structure H by powder X-ray diffraction measurements. At a given temperature, the equilibrium pressure of the structure H hydrate formed with argon + 2,2-dimethylbutane was lower than that of the structure II pure argon hydrate. The difference in the equilibrium pressure is 8.1–20.9 MPa in the temperature range of 275.6–284.3 K. Among the system using methane, argon, krypton and xenon, the system using argon shows the highest reduction ratio of equilibrium pressures.