Self-preservation and structural transition of gas hydrates during dissociation below the ice point: an in situ study using Raman spectroscopy.

ABSTRACT: The hydrate structure type and dissociation behavior for pure methane and methane-ethane hydrates at temperatures below the ice point and atmospheric pressure were investigated using in situ Raman spectroscopic analysis. The self-preservation effect of sI methane hydrate is significant at lower temperatures (268.15 to 270.15?K), as determined by the stable C-H region Raman peaks and A_L/A_S value (Ratio of total peak area corresponding to occupancies of guest molecules in large cavities to small cavities) being around 3.0. However, it was reduced at higher temperatures (271.15?K and 272.15?K), as shown from the dramatic change in Raman spectra and fluctuations in A_L/A_S values. The self-preservation effect for methane-ethane double hydrate is observed at temperatures lower than 271.15?K. The structure transition from sI to sII occurred during the methane-ethane hydrate decomposition process, which was clearly identified by the shift in peak positions and the change in relative peak intensities at temperatures from 269.15?K to 271.15?K. Further investigation shows that the selectivity for self-preservation of methane over ethane leads to the structure transition; this kind of selectivity increases with decreasing temperature. This work provides new insight into the kinetic behavior of hydrate dissociation below the ice point.

SUBMITTER: Zhong JR 

PROVIDER: S-EPMC5150642 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature