In this study, the kinetics of methane and methane/propane hydrate formation/dissociation were investigated. Simultaneously, microlevel studies, including hydrate structure, preferential cage occupancy, and gas-dissolving behavior studies were also carried out using an in situ Raman spectrometer. In the methane hydrate experiment, the small cages of methane in structure I seemed to be formed preferentially in the initial period of hydrate formation. The results showed that methane collapsed faster in large 51262 cages than in small 512 cages as hydrate dissociation progressed. During kinetic experiments on a binary gas mixture of methane/propane, vapor composition was measured by an in situ Raman spectrometer, and the results were consistent with those obtained by gas chromatography. Small 512 cages of methane in structure II formed quickly during methane/propane hydrate formation and broke down rapidly during hydrate dissociation. The order of cage formation and the dissociation rate was CH4 in 512 ≫ CH4 in 51264 > C3H8 in 51264. The results of the in situ Raman analysis revealed that methane and methane/propane hydrates showed different spectral behaviors for the O–H stretching band, depending on the gas hydrate structure type. Additionally, the mole fractions of dissolved methane were also measured in specific regions, and our results were consistent with those reported in the literature. These findings contribute to a better understanding of the nature of guest–host interactions in clathrate hydrates.

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In this study, the effects of salinity on the equilibrium and kinetics of sulfur hexafluoride (SF6), 1,1,1,2-tetrafluoroethane (HFC134a), and their mixture were evaluated to analyze their potential applications to hydrate-based desalination. The equilibrium pressure of the mixture gas (SF6/HFC134a) was lower than that of pure SF6 gas but higher than that of pure HFC134a gas. The thermodynamic effects of various concentrations (0, 3.5, 5, and 8 wt %) of NaCl on the gas hydrates were evaluated. Experiments were performed on the formation kinetics in the presence of NaCl solution at the same experimental temperature and pressure (274.15 K and 0.70 MPa). The hydrate growth rates decreased with increasing NaCl concentration. The rates also declined with time, associated with the inhibition of mass transfer between the gas and the liquid. During hydrate formation, the vapor compositions of the mixture gas were analyzed by in situ Raman spectroscopy and the results were consistent with those obtained by gas chromatography. Furthermore, an in situ Raman spectroscopic analysis demonstrated that the SF6 and HFC134a molecules occupy only the large cage (51264) of the structure II (sII) hydrate during SF6/HFC134a formation and the addition of salt did not change the structure of the SF6 and HFC134a hydrates. The hydrate phase behavior and kinetic results of this study can serve as foundational data for hydrate-based desalination technology and fluorinated gases separation and recovery processes.