Observation of Tuning Behavior on Trimethylene Oxide + CH4 hydrate via Thermodynamic and Spectroscopic Analyses

Abstract

Natural gas is a growing energy source due to the less emission of carbon dioxide than other fossil fuels such as coal and oil. Various materials and methods have been investigated so far for effective separation, transportation, and storage. Among the options, gas hydrate has recently been received great attention due to its theoretically promising storage capacity and separation function. To evaluate the potential of gas hydrate as natural gas storage media, however, the fundamental thermodynamic properties should be fully investigated, particularly elucidating its distinct characteristics of cage occupation behavior of natural gas molecules. In this study, we investigated the binary gas hydrate containing trimethylene oxide (TMO) and CH4 molecules focusing on the distinct host-guest interactions between water cages (host) and guests (TMO and CH4). Pressure-temperature phase equilibria were measured. In addition spectroscopies such as synchrotron High Resolution Powder Diffraction (HRPD), Dispersive Raman, and 13C solid-state Nuclear Magnetic Resonance (NMR) were employed. The results indicated that the thermodynamic stability of TMO + CH4 hydrate was higher than that of pure CH4 hydrate. Particularly, structure II type gas hydrate was mainly formed at the concentrations of TMO below 5.56 mol%. When the ratio of water to TMO was 17: 1, abnormal tuning phenomenon was also observed. The cage occupancy of CH4 molecules in TMO + CH4 hydrate was significantly enhanced.