Molecular guest exchange and subsequent structural transformation in CH4 – CO2 replacement occurring in sH hydrates as revealed by 13C NMR spectroscopy and molecular dynamic simulations

Enhanced CH4–CO2 Replacement in Structure H Hydrates: Kinetics, Mechanisms, and Implications for CO2 Storage and CH4 Production

“…This finding confirms the preferential replacement of CH 4 by CO 2 in the medium cages of the sH hydrate. A previous study has demonstrated that when forming gas hydrates from (CH 4 + CO 2 + MCP) mixtures, sI is the favored hydrate structure when the CO 2 composition of the injected gas exceeds approximately 20% . Our findings align with this report and provide additional context for the mechanisms underlying the (CH 4 + MCP)–CO 2 replacement process.…”

“…A previous study has demonstrated that when forming gas hydrates from (CH 4 + CO 2 + MCP) mixtures, sI is the favored hydrate structure when the CO 2 composition of the injected gas exceeds approximately 20%. 25 Our findings align with this report and provide additional context for the mechanisms underlying the (CH 4 + MCP)− CO 2 replacement process. Considering the time-dependent PXRD and NMR results obtained in this study, the mechanism of (CH 4 + MCP)−CO 2 replacement can be understood as follows: As shown in Figure 6b, the A L, CHd 4 /A S, CHd 4 ratio obtained for the sI hydrate upon the completion of (CH 4 + MCP)−CO 2 replacement was markedly lower than that following isostructural CH 4 −CO 2 replacement.…”

“…24 Recently, Lee et al investigated guest exchange behaviors in sH (CH 4 + MCP) and sH (CH 4 + NH) hydrates at the molecular level using molecular dynamics simulations. 25 CH 4 −CO 2 replacement in sH NGHs results in enhanced CH 4 production and superior CO 2 storage capacity compared to conventional sI NGHs, thus spurring various research initiatives aimed at optimizing this process. Despite these advancements, there is a lack of research on the replacement kinetics in sH hydrates, particularly in terms of structural transitions.…”

“…experimented with mixed gases of varying CO 2 and N 2 compositions and determined that a mixture of 40% CO 2 + 60% N 2 was the optimal composition for CH 4 production when replacing an sH (CH 4 + MCP) hydrate . Recently, Lee et al investigated guest exchange behaviors in sH (CH 4 + MCP) and sH (CH 4 + NH) hydrates at the molecular level using molecular dynamics simulations …”

Freshwater Recovery and Removal of Cesium and Strontium from Radioactive Wastewater by Methane Hydrate Formation

“…The 13 C NMR resonance peaks appeared at −4.2 and −6.6 ppm, which are attributable to CH 4 molecules captured in the small and large cages, respectively. The additional peak found at −11 ppm is associated with the contribution from CH 4 gas arising from the partial decomposition of CH 4 hydrates. − For the pure CH 4 hydrate, the cage occupancy ratio of CH 4 molecules from the 13 C NMR resonance peaks captured in the large and small cages of the sI hydrate was found to be θ L /θ S = 1.1, in good agreement with that from the Raman spectra (θ L /θ S = 1.15) (Figure S5). Interestingly, the θ L /θ S values from the 13 C NMR resonance peaks of the CH 4 hydrate in the presence of 10 wt % CsCl and 10 wt % SrCl 2 were also found to be 1.09 and 1.03, respectively.…”