sII Structural Transitions from Binary Mixtures of Simple sI Formers

Hester, Keith C.; Sloan, E. Dendy

doi:10.1007/s10765-005-2355-1

Cited by 18 publications

(13 citation statements)

References 9 publications

(15 reference statements)

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“…The small cages in sI and sII structures are stabilized by one molecule while the large cages are stabilized by the others. This phenomenon occurs when the lower limit of sI formation is adopted by one molecule from binary guests and the upper limit of sI formation is adopted by the other molecule [78].…”

Section: Resultsmentioning

confidence: 99%

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

Kumari

Khan

Misra³

et al. 2020

Journal of Non-Equilibrium Thermodynamics

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A fugacity-based thermodynamic model for hydrate has been used to determine the equilibrium pressures of hydrate formation. This fugacity-based model uses the PRSV equation of state, which is used to represent the gas phases in the hydrate. The parameters of the model are fitted to the experimental data of binary guest hydrates. The present study is aimed at investigating binary mixtures of CH 4 -H 2 S, C 3 H 8 -N 2 , N 2 -CO 2 , CH 4 -i-butane, C 3 H 8 -i-butane, CH 4 -n-butane, C 3 H 8 -n-butane, i-butane-CO 2 , and n-butane-CO 2 hydrates, which have not been modeled before. Unlike previous studies, the Kihara potential parameters were obtained using the second virial coefficient correlation and the data of viscosity for gases. The fugacity-based model provides reasonably good predictions for most of the binary guest hydrates (CH 4 -C 3 H 8 ). However it does not yield good prediction for hydrates of (CO 2 -C 3 H 8 ). The transitions of hydrate structure from sI to sII and from sII to sI have been also predicted by this model for binary guest hydrates. The AAD % calculated using the experimental data of natural gas hydrates is only 10 %, which is much lower than the AAD % calculated for the equilibrium data predicted by the VdP-w model.

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Section: Resultsmentioning

confidence: 99%

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

Kumari

Khan

Misra³

et al. 2020

Journal of Non-Equilibrium Thermodynamics

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“…The structural transition(s) of hydrates, which can occur by changing composition and temperature/pressure conditions have been previously reported3536373839. For example, methane forms sI hydrate under moderate conditions.…”

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confidence: 88%

“…Otherwise, they form sII hydrate4142. Up to now, most structural transition studies have been performed during the formation process of hydrates374344, while there are limited studies focused on the dissociation process4345. In the latter dissociation studies, the conditions have been mostly outside/not focused on the hydrate self-preservation region.…”

mentioning

confidence: 99%

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

Zhong

Zeng

Zhou

et al. 2016

Sci Rep

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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/AS 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 AL/AS 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.

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“…Crystal structures were drawn using Crystalmaker ® . When multiple guests are present, the concentration of the various guests, as well as size, become important for structural determination of the mixed hydrate (Hester & Sloan 2005, Ripmeester 2000. Whereas methane and ethane form sI as simple hydrates, a mixed methane + ethane hydrate can form either sI or sII depending on their relative concentrations (Subramanian et al 1999).…”

Section: Figurementioning

confidence: 99%

Clathrate Hydrates in Nature

Hester

Brewer

2009

Annu. Rev. Mar. Sci.

179

105

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Scientific knowledge of natural clathrate hydrates has grown enormously over the past decade, with spectacular new findings of large exposures of complex hydrates on the sea floor, the development of new tools for examining the solid phase in situ, significant progress in modeling natural hydrate systems, and the discovery of exotic hydrates associated with sea floor venting of liquid CO2. Major unresolved questions remain about the role of hydrates in response to climate change today, and correlations between the hydrate reservoir of Earth and the stable isotopic evidence of massive hydrate dissociation in the geologic past. The examination of hydrates as a possible energy resource is proceeding apace for the subpermafrost accumulations in the Arctic, but serious questions remain about the viability of marine hydrates as an economic resource. New and energetic explorations by nations such as India and China are quickly uncovering large hydrate findings on their continental shelves.

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sII Structural Transitions from Binary Mixtures of Simple sI Formers

Cited by 18 publications

References 9 publications

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

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

Clathrate Hydrates in Nature

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