Enclathration of NF3 and c-C4F8 molecules in gas hydrates and their thermodynamic and cage filling characteristics

Abstract

F-gases are man-made gases which are utilized in semiconductor industry and refrigeration systems. Since F-gases have a high potential of global warming effect, various methods to separate F-gases have been widely studied, including gas hydrate-based F-gas separation. However, gas hydrate formation of c-C4F8 and NF3 has not been well-studied, even though they have high global warming potential (c-C4F8: 8,700, NF3: 8,000) and long atmospheric lifetime (c-C4F8: 3,200 years, NF3: 740 years). Therefore, in this study, the fundamental research focusing on the thermodynamic and spectroscopic characteristics of NF3 and c-C4F8 gas hydrates was performed. The three-phase (H – LW – V) equilibria of the pure NF3 and mixed c-C4F8 + CH4 hydrates were measured, and the crystal structures of NF3 and c-C4F8 + CH4 hydrates were identified through PXRD, while the cage-filling characteristics of NF3 and c-C4F8 molecules in each hydrate were analyzed through 13C & 19F NMR, and in-situ Raman spectroscopy. The results obtained in this study are expected to be helpful in future studies about various F-gas hydrates.