title: 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 AL/ASvalue (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 AL/ASvalues. 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.
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Jin-Rong
authors.initials: JR
authors.lastname: Zhong
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Xin-Yang
authors.initials: XY
authors.lastname: Zeng
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Feng-He
authors.initials: FH
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Qi-Dong
authors.initials: QD
authors.lastname: Ran
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Chang-Yu
authors.initials: CY
authors.lastname: Sun
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Rui-Qin
authors.initials: RQ
authors.lastname: Zhong
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Lan-Ying
authors.initials: LY
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China.
authors.forename: Guang-Jin
authors.initials: GJ
authors.lastname: Chen
authors.affiliation: Center for Hydrate Research, Colorado School of Mines, Golden, Colorado 80401, United States.
authors.forename: Carolyn A
authors.initials: CA
authors.lastname: Koh