Crystal Phase Boundaries of Structure-H (sH) Clathrate Hydrates with Rare Gas (Krypton and Xenon) and Bromide Large Molecule Guest Substances

Abstract

Phase equilibrium pressure–temperature (pT) boundaries of structure-H clathrate hydrates (sH hydrates) with rare gas (Kr and Xe)-bromide large molecule guest substances (LMGSs: bromocyclohexane, BrCH and bromocyclopentane, BrCP) were measured. The phase boundaries for the sH hydrates in the Kr–LMGS–water systems shifted to lower pressures than those for the pure Kr hydrate in the temperature range of (273.2 to 279.3) K. In this study, sH hydrate formation was not confirmed in the Xe–BrCP–water system, but sH hydrates were found in the Xe–BrCH–water system. At temperatures below 277 K, equilibrium conditions were observed at lower pressures for the Xe–BrCH–water system than for the pure Xe hydrate. However, the equilibrium pT curve for the Xe–BrCH–water system crossed over the equilibrium pT curve for the Xe hydrate at around 277 K. Intersections between the equilibrium pT curves for the Xe hydrates and the sH hydrates (Xe + LMGS) have also been found in Xe–methylcyclohexane–water systems. Using the Kr–and Xe–bromide LMGS–water systems showed that the sH hydrate phase stabilities are strongly related to the encaptured LMGS.