In Situ Raman Study of the Formation and Dissociation Kinetics of Methane and Methane/Propane Hydrates

Abstract

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 5(12)6(2) cages than in small 5(12) 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 5(12) 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 CH(4 )in 5(12) >> CH4 in 5(12)6(4) > C- 3 H- 8 in 5(12)6(4). 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.