Raman spectroscopic determination of hydration number of methane hydrates

Uchida, Tsutomu; Hirano, Takashi; Ebinuma, Takao; Narita, Hideo; Gohara, Kazutoshi; Mae, Shinji; Matsumoto, Ryo

doi:10.1002/aic.690451220

Cited by 179 publications

(240 citation statements)

References 6 publications

(4 reference statements)

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“…Simultaneously, we find CH 4 peaks in the hydrate phase during the dissociation at 2903.8 and 2915.3 cm -1 (Fig. 5a, solid line), which are consistent with previously reported data [25,27].…”

Section: Measurements Of Mnb Solutions Via Raman Spectroscopysupporting

confidence: 81%

“…After the CH 4 hydrate formation was finished, the vessel was cooled below 173.2 K, and then the vessel was opened to recover the solid sample including ice and CH 4 hydrate crystal. The hydrate fraction in the solid sample was about 0.7, which was estimated by measuring the weight and gas volume and assuming a cage occupancy of 0.93 [25].…”

Section: Experimental Methods and Materialsmentioning

confidence: 99%

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Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Uchida

Yamazaki

Gohara

2016

Korean J. Chem. Eng.

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Gas hydrate crystals have a structure in which one molecule is enclathrated in a cage of water molecules.When such a crystal dissociates in water, each enclathrated molecule, generally vapor at standard temperature and pressure, directly dissolves into the water. After the solution is supersaturated, excess gas molecules from further dissociation would start forming small bubbles called micro-and nano-bubbles (MNBs). However, it is difficult to identify such small bubbles dispersed in liquid because they are smaller than a microscope's optical resolution. To confirm the formation of MNBs after gas hydrate dissociation, we used a transmission electron microscope (TEM) to analyze freeze-fracture replicas of CH 4 -hydrate dissociation solution. The TEM images indicate the existence of MNBs in the solution, with a number concentration similar to that from a commercially supplied generator. Raman spectroscopic measurements on the CH 4 -hydrate dissociated solution were then done to confirm that the MNBs contain CH 4 vapor, and to estimate experimentally the inner pressure of the CH 4 MNBs. These results suggest that the dissociation of gas hydrate crystals in water is a simple, effective method to obtain MNB solution. We then discuss how such MNBs may play a key role in the memory effect of gas-hydrate reformation. KeywordsMicrobubble, Nanobubble, gas hydrate dissociation, freeze fracture replica, bubble pressure, memory effect 2

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Section: Measurements Of Mnb Solutions Via Raman Spectroscopysupporting

confidence: 81%

Section: Experimental Methods and Materialsmentioning

confidence: 99%

Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Uchida

Yamazaki

Gohara

2016

Korean J. Chem. Eng.

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“…The hydration number is the number of water molecules per guest molecule. It can be determined experimentally by simultaneously using powder X-ray diffraction and Raman spectroscopy on solid hydrate phase Kumar et al, 2008;Sum et al, 1997;Susilo et al, 2007a;Uchida et al, 1999;Udachin et al, 2007Udachin et al, , 2001 or by solid state NMR spectroscopy (Davidson et al, 1983;Ripmeester and Ratcliffe, 1988). In the presence of THF, the conversion of water to hydrate is determined by the next equation…”

Section: Conversion Of Water To Hydratementioning

confidence: 99%

Capture of carbon dioxide from flue or fuel gas mixtures by clathrate crystallization in a silica gel column

Adeyemo

Kumar

Linga

et al. 2010

International Journal of Greenhouse Gas Control

167

113

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“…[12][13][14][15][16][17][18] Experimentally, Raman, NMR, and other spectroscopic tools are the regular means to study NGHs. Especially, Raman spectroscopy has been used to identify the type of crystal phase, [19][20][21] type of guest molecule, 19 cage occupancy, 21 and hydration number, [21][22] to monitor the nucleation and growth processes in real-time, 23 to study phase transformations, [24][25] and to detect the location of NGH deposits. [26][27] Based on Raman spectroscopy measurements, the characteristics of symmetric C-H and C-C stretching vibration of various guest molecules trapped in water cavities of sI, sII, and sH phase have been mapped out, which can be conveniently used to identify the types of crystal phase and guest molecule.…”

Section: Introductionmentioning

confidence: 99%

C–C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study

Liu

Ojamäe

2014

J. Phys. Chem. A

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Abstract:The presence of specific hydrocarbon gas molecules in various types of water cavities in natural gas hydrates (NGHs) are governed by the relative stabilities of these encapsulated guest molecule ─ water cavity combinations. Using molecular quantum-chemical dispersion-corrected hybrid density functional computations, the interaction energies (ΔEhost-guest) and cohesive energies (ΔEcoh), enthalpies and Gibbs free energies for the complexes of host water cages and hydrocarbon guest molecules are calculated at the ωB97X-D/6-311++G(2d,2p) level of theory. The zero point energy effect of ΔEhost-guest and ΔEcoh is found to be quite substantial. The energetically optimal host-guest combinations for seven hydrocarbon gas molecules (CH4, C2H6, C3H6, C3H8, C4H8, i-C4H10, and n-C4H10) and various water cavities (D, ID, T, P, H and I) in NGHs are found to be CH4@D, C2H6@T, C3H6@T, C3H8@T, C4H8@T/P/H, i-C4H10@H, and n-C4H10@H, as the largest cohesive energy magnitudes will be obtained with these host-guest combinations. The stabilities of various water cavities enclosing hydrocarbon molecules are evaluated from the computed cohesive Gibbs free energies: CH4 prefer to be trapped in a ID cage; C2H6 prefer T cages; C3H6 and C3H8 prefer T and H cages; C4H8 and i-C4H10 prefer H cages; and n-C4H10 prefer I cages. The vibrational frequencies and Raman intensities of the C-C stretching vibrational modes for these seven hydrocarbon molecules enclosed in each water cavity are computed. A blue shift results after the guest molecule is trapped from gas phase into various water cages due to the host-guest interactions between the water cage and hydrocarbon molecule. The frequency shifts to the red as the radius of water cages increases. The model calculations support the view that C-C stretching vibrations of hydrocarbon molecules in the water cavities can be used as a tool to identify the types of crystal phases and guest molecules in NGHs.2

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Raman spectroscopic determination of hydration number of methane hydrates

Cited by 179 publications

References 6 publications

Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Capture of carbon dioxide from flue or fuel gas mixtures by clathrate crystallization in a silica gel column

C–C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study

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