Measurement of micro-structure features of binary CH4-THF clathrate hydrate based on the 13C solid state NMR

Understanding the micro-structural properties of gas hydrate is very important for the study of its formation mechanism and storage and transportation technology. The 13C solid state NMR was used to identify the structure types and guest molecule distribution in different cages of CH4-THF binary clathrate hydrate and pure THF hydrate, the cage occupancy of guests and the hydration index of the binary hydrate were also obtained. The experimental results show that: (1) the chemical shift of the two NMR spectral peaks of pure THF hydrate is δ68.3 and δ26.1 respectively, with THF molecules captured in the large cages of typical II hydrates (51264); (2) The binary clathrate hydrate also belongs to structure II hydrate, and methane molecules occupy only the small cages (512) with a cage occupancy of only about 0.482 5, while THF molecules occupy only the large cages (51264) with a cage occupancy of up to 0.998 4; (3) the hydration index of the binary clathrate hydrate is about 8.67, which is bigger than the stoichiometric value (5.67), suggesting a low gas storage due to the low cage occupancy of CH4 molecules in small cages; (4) the cage occupancy of CH4 molecules in the binary CH4-THF clathrate hydrate is related to formation conditions (temperature, pressure) and preparation method (reaction state, time, etc.). So changing the formation condition of hydrate can regulate the cage occupancy of clathrate hydrate guest molecules, and enhance the gas storage density of gas hydrate. ©, 2015, Natural Gas Industry Journal Agency. All right reserved.