Binary Ethanol−Methane Clathrate Hydrate Formation in the System CH₄-C₂H₅OH-H₂O: Confirmation of Structure II Hydrate Formation

The crystal structure of the binary clathrate hydrate of methane (CH 4 ) and ethanol was identified by powder X-ray diffraction. Raman spectroscopic measurements were also performed. Because hydrogen bonding between the water and ethanol molecules likely affects the hydrate formation and its stability, the role of ethanol for hydrate formation and its stability is important for a further understanding of the guest−host interactions in complex inclusion compounds. In this study, we provide evidence for the occupation of ethanol with CH 4 in a structure II hydrate, whereas the ethanol is one of the inhibitors for hydrate formation. The cage occupancies of CH 4 and ethanol as guest molecules within the hydrate cages was also estimated. It is shown that hexakaidecahedral (5 12 6 4 ) cages were occupied by not only ethanol, but also CH 4, even though a sufficient number of ethanol molecules existed in the current hydrate-forming system.