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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Poly­(N-vinylcaprolactam) (PVCap) has previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). The inhibition performance of LDHI is known to be influenced by molecular weight (M w) and molecular weight distribution. In this study, PVCaps were synthesized by two different methods. The first method, reversible addition–fragmentation chain transfer (RAFT) polymerization, was used to prepare PVCap with a narrow molecular weight distribution (about M w/M n < 1.5), which is close to theoretical values. The second method, free radical polymerization (FRP), was used to obtain a broad molecular weight distribution (about M w/M n > 1.5). In a semi-batch stirrer reactor, hydrate inhibition performance of PVCap was evaluated. It was found that the inhibition performance was increased when the PVCap molecular weight decreased. PVCap with the narrower molecular weight distribution also showed the better inhibition performance.