Gas hydrate is recognized as an attractive way of storing huge quantities of gases such as natural gas, and hydrogen, but practical concerns such as the trade-off relationship between gas storage capacity and moderate formation conditions still remain. The tuning effect of gas hydrate, which creates additional nanospaces to occupy gaseous guest molecules while maintaining mitigated formation conditions, is a promising strategy to enhance the storage capacity. However, the tuning behavior of sH hydrate which includes the largest potential of storage capacity has not yet been addressed because it has been considered uninducible in experimental conditions. Here, we investigated the tuning effect of sH gas hydrate for efficient natural gas storage. In this study, we report the sH tuning behavior in 1-Methylpiperidine (MPD) + CH4 hydrate system under mild conditions (263.15 K, and 8.0 MPa). The synchrotron high-resolution powder X-ray diffraction (HRPD) was performed to identify the crystallographic structure of 1-MPD + CH4 hydrate in various molar ratio systems. The phase equilibria of 1-MPD + CH4 hydrates were examined to measure the thermodynamic stability. The 13C solid-state HPDEC MAS NMR was acquired to confirm the guest distribution in gas hydrates. The calculation of Density Functional Theory (DFT) was conducted to support the experimental results. The differential scanning calorimetry (DSC) was employed to measure the eutectic point for 1-MPD + water system. The evolution of CH4 encaged in sH large cage which represents the occurrence of tuning effect was firstly confirmed by the spectroscopic investigation and the DFT calculation results supported that. The tuning behavior of 1-MPD + CH4 hydrate was evaluated through investigation of tuning factor and critical guest concentration (CGC) patterns. Relatively higher CGC (2.4 mol%) of sH tuning hydrate was obtained, and it has potential to enhance the gas storage capacity. Furthermore, the distinct tuning pattern is observed at or below the eutectic composition (~2.5 mol%) of 1-MPD + water solution system, suggesting that the supercooled aqueous phase existing on the surface of ice particles plays a significant role in the tuning phenomena. We believe that these findings could open up new strategies for enhancing gas storage capacity for gas storing and transportation areas, and provide useful insight to reveal the fundamental nature of gas hydrate science and inclusion chemistry.

Observation of tuning effect in sH gas hydrate for natural gas storage

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