13C NMR analysis of C2H6+C2H4+THF mixed hydrate for an application to separation of C2H4 and C2H6

Mixed hydrates (C2H4+5.56mol% THF, and C2H4+C2H6+5.56mol% THF) were analyzed using C-13 MAS NMR spectroscopy. The hydrates were formed using a variety of feed gas compositions (100% C2H4; 20% C2H4+80% C2H6; 40% C2H4+60% C2H6; 60% C2H4+40% C2H6; and 80% C2H4+20% C2H6). According to the peak identification results, C2H4 molecules can occupy both the small and large cavities in the sI and sII hydrate structures, while C2H6 molecules can occupy only the large cavities of sI. Moreover, the mole fraction of C2H4 in the hydrate matrix was found to increase with increasing feed ratio of C2H4. On the basis of the NMR analysis, a hydrate-based process for separating C2H4 and C2H6 by repeated hydrate formation and dissociation was proposed. For cases with a feed-gas mixture with 20% C2H4 and 80% C2H6, a recovery of more than 88% C2H4 in the gas mixture could be achieved after five cycles of hydrate-based separation.