Disorder of Hydrofluorocarbon Molecules Entrapped in the Water Cages of Structure I Clathrate Hydrate

Abstract

Water versus fluorine: Clathrate hydrates encaging hydrofluorocarbons as guests show both isotropic and anisotropic distributions within host water cages, depending on the number of fluorine atoms in the guest molecule; this is caused by changes in intermolecular interactions to host water molecules in the hydrates.

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

“…The 19 F NMR spectroscopy data show that CH 2 F 2 hydrate formed at 263 K and 0.5 MPa (Figure 3b) occupy 5 12 6 2 cages completely and 5 12 cages partially (the occupancy ratio is approximately 0.24). 46 Our calculation results show that only the CH 2 F 2 hydrate with 5 12 6 2 cages completely occupied can form under this condition. The discrepancy between our results and the experiment may be since the experiment is a statistical rule.…”

“…According to the Thomson−Berthelot 45 where θ L and θ S represent the occupancy rates of large 5 12 6 2 cage and small 5 12 cage, respectively. 46 where θ L and θ S represent the occupancy rates of large 5 12 6 2 cage and small 5 12 1a to determine the relative chemical potential when the lines with minimum ΔG intersect intuitively. The line with m = 8 (black yellow line, corresponding to 8CH 4 @46H 2 O) has the minimum ΔG when Δμ CH 4 (T, p) ≥ −33.82 kJ/mol.…”

“…Phase Diagram of CH 3 F Hydrate. The relationship between ΔG of hydrate and Δμ 46 where θ L and θ S represent the occupancy rates of large 5 12 6 2 cage and small 5 12 cage, respectively. 47 where θ L and θ S represent the occupancy rates of large 5 12 6 2 cage and small 5 12 2b.…”

“…This finding is consistent with the experimental observation that CH 3 F hydrate formed at 263 K and 1.5 MPa (Figure 2b) can almost fully occupy both 5 12 and 5 12 6 2 cages (5 12 cage occupancy of 0.87 and 5 12 6 2 cage occupancy of 1.0). 46 Phase Diagram of CH 2 F 2 Hydrate. The functional relationship between ΔG of hydrate and Δμ CH 2 F 2 (T, p) of CH 2 F 2 molecules at different occupancy rates is shown in Figure 3a.…”

Structure and Density Comparison of Noble Gas Hydrates Encapsulating Xenon, Krypton and Argon

“…The small 5 12 cages are the same in sI and sII hydrates, but the volume of the cage for Xe hydrate is clearly larger than those of Kr and Ar hydrates. The difference could be caused by a difference in crystal structure, but the volume of the 5 12 cage of Xe hydrate is larger than that of the other sI hydrates at the same temperature in the literature such as CH 4 hydrate (164 Å 3 ) . In contrast, the volume of the 5 12 6 2 cage of Xe hydrate is smaller than that of CH 4 hydrate (230 Å 3 ) since their unit‐cell sizes are almost the same.…”