Raman study of methane clathrate hydrates under pressure: new evidence for the metastability of structure II

Choukroun, Mathieu; Morizet, Yann; Grasset, O.

doi:10.1002/jrs.1665

Cited by 48 publications

(41 citation statements)

References 42 publications

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“…Propane molecules occupy the 5 12 6 4 cavities in sII, while the smaller cavities are left vacant and, consequently the maximum gas content of pure propane hydrate is less than of hydrates with fully occupied cages. The coexistence of sI and sII for pure methane hydrates has been shown to occur under high pressure conditions [4,5]. Carbon dioxide, normally a sI former, can also form sII hydrates [6][7][8]; mixed hydrates consisting of predominantly sI hydrate formers, like methane and ethane, also can form sII hydrates at certain Mixed hydrates Tetrahydrofuran Methane Structural transformations Laser micro-Raman spectroscopy A B S T R A C T We report laser Raman spectroscopic measurements on mixed hydrates (clathrates), with guest molecules tetrahydrofuran (THF) and methane (CH 4 ), at ambient pressure and at temperatures from 175 to 280 K. Gas hydrates were synthesized with different concentrations of THF ranging from 5.88 to 1.46 mol%.…”

Section: Introductionmentioning

confidence: 99%

Micro-Raman investigations of mixed gas hydrates

Prasad

Sowjanya

Prasad

2009

Vibrational Spectroscopy

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Section: Introductionmentioning

confidence: 99%

Micro-Raman investigations of mixed gas hydrates

Prasad

Sowjanya

Prasad

2009

Vibrational Spectroscopy

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“…For a pure hydrate with only one type of small guest molecule like CH 4 , C 2 H 6 and CO 2 , sI hydrate is usually formed at moderate pressures . sII hydrates were observed to coexist metastably with sI CH 4 ‐ and CO 2 ‐hydrates . For a mixed hydrate with two or more types of guests, like a CH 4 ‐C 2 H 6 mixture, the hydrate structure may vary with the different composition and/or prevailing P‐T conditions .…”

Section: Introductionmentioning

confidence: 99%

Quantitative analysis of gas hydrates using Raman spectroscopy

2013

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A calibration protocol to quantify the compositional information of gas hydrates using Raman spectroscopy is proposed. Structure I pure CH 4 -, CO 2 -and C 2 H 6 -hydrates in their deuterated and hydrogenated forms with known cage occupancies were investigated by Raman spectroscopy. Raman scattering cross sections of CH 4 in the large and small cages were found to be very similar, but not identical. Some C 2 H 6 bands of C 2 H 6 -hydrate were tentatively reassigned or newly reported and assigned. Our results show that the relative cross sections of guest vibrational modes in the deuterated hydrate are in agreement with those in the hydrogenated hydrate, whereas they are considerably different from those in fluid phase. Using our Raman quantification factors, the relative cage occupancies can now be determined more reliably in CH 4 -hydrates. Moreover, with additional assumptions, the absolute cage occupancies, the bulk guest composition and hydration number of pure or mixed gas hydrates become accessible by Raman spectroscopy. m h and m f indicate Raman frequencies of ethane in hydrate lattices and fluid phase, respectively. R is percentage of peak area. a,b and c represent the values given by Helvoort et al. 67 , Fernandez and Montero 71 , and Domingo and Montero 70 , respectively. Dm is the difference between m h and m f .Figure 6. Raman spectra of the deuterated sI CH 4 -CO 2 -C 2 H 6 -hydrate measured at ambient pressure and 113 K.

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“…MH-sI has two peaks, where the first peak and second peak correspond to the medium 5 12 6 2 cages and small 5 12 cages, respectively. 7,10,19 When the MH-sI transitioned to the hexagonal MH-II, one broad Raman band appeared which is the overlapping of the 3 types of cages: the small 5 12 , the small 4 3 5 6 6 3 , and the large 5 12 6 8 in the phase (Figs. 2 and 3).…”

Section: A Raman Spectroscopy Resultsmentioning

confidence: 99%

Elasticity of methane hydrate phases at high pressure

Beam

Yang

Liu

et al. 2016

The Journal of Chemical Physics

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Determination of the full elastic constants (cij) of methane hydrates (MHs) at extreme pressure-temperature environments is essential to our understanding of the elastic, thermodynamic, and mechanical properties of methane in MH reservoirs on Earth and icy satellites in the solar system. Here, we have investigated the elastic properties of singe-crystal cubic MH-sI, hexagonal MH-II, and orthorhombic MH-III phases at high pressures in a diamond anvil cell. Brillouin light scattering measurements, together with complimentary equation of state (pressure-density) results from X-ray diffraction and methane site occupancies in MH from Raman spectroscopy, were used to derive elastic constants of MH-sI, MH-II, and MH-III phases at high pressures. Analysis of the elastic constants for MH-sI and MH-II showed intriguing similarities and differences between the phases' compressional wave velocity anisotropy and shear wave velocity anisotropy. Our results show that these high-pressure MH phases can exhibit distinct elastic, thermodynamic, and mechanical properties at relevant environments of their respective natural reservoirs. These results provide new insight into the determination of how much methane exists in MH reservoirs on Earth and on icy satellites elsewhere in the solar system and put constraints on the pressure and temperature conditions of their environment.

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Raman study of methane clathrate hydrates under pressure: new evidence for the metastability of structure II

Abstract: International audienc

Cited by 48 publications

References 42 publications

Micro-Raman investigations of mixed gas hydrates

Micro-Raman investigations of mixed gas hydrates

Quantitative analysis of gas hydrates using Raman spectroscopy

Elasticity of methane hydrate phases at high pressure

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