Structure and thermal expansion of natural gas clathrate hydrates

Takeya, Satoshi; Kida, Masato; Minami, Hirotsugu; Sakagami, Hirotoshi; Hachikubo, Akihiro; Takahashi, Naohiko; Hirano, Shoji; Soloviev, V. A.; Wallmann, Klaus; Biebow, Nicole; Obzhirov, A.; Salomatin, A.; Poort, Jeffrey

doi:10.1016/j.ces.2005.11.049

Cited by 91 publications

(69 citation statements)

References 26 publications

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“…Moreover, it has been shown that the size of the clathrate cages depends on their formation temperature. [35][36][37] This also leads us to investigate the influence of the size of cages on the resulting composition of clathrates formed in the low pressure and temperature conditions of the nebula.…”

Section: Introductionmentioning

confidence: 99%

Volatile inventories in clathrate hydrates formed in the primordial nebula

et al. 2010

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Examination of ambient thermodynamic conditions suggest that clathrate hydrates could exist in the martian permafrost, on the surface and in the interior of Titan, as well as in other icy satellites. Clathrate hydrates probably formed in a significant fraction of planetesimals in the solar system. Thus, these crystalline solids may have been accreted in comets, in the forming giant planets and in their surrounding satellite systems. In this work, we use a statistical thermodynamic model to investigate the composition of clathrate hydrates that may have formed in the primordial nebula. In our approach, we consider the formation sequence of the different ices occurring during the cooling of the nebula, a reasonable idealization of the process by which volatiles are trapped in planetesimals. We then determine the fractional occupancies of guests in each clathrate hydrate formed at given temperature. The major ingredient of our model is the description of the guest-clathrate hydrate interaction by a spherically averaged Kihara potential with a nominal set of parameters, most of which being fitted on experimental equilibrium data. Our model allows us to find that Kr, Ar and N 2 can be efficiently encaged in clathrate hydrates formed at temperatures higher than ∼ 48.5 K in the primitive nebula, instead of forming pure condensates below 30 K. However, we find at the same time that the determination of the relative abundances of guest species incorporated in these clathrate hydrates strongly depends on the choice of the parameters of the Kihara potential and also on the adopted size of cages. Indeed, testing different potential parameters, we have noted that even minor dispersions between the different existing sets can lead to non-negligible variations in the determination of the volatiles trapped in clathrate hydrates formed in the primordial nebula. However, these variations are not found to be strong enough to reverse the relative abundances between the different volatiles in the clathrate hydrates themselves. On the other hand, if contraction or expansion of the cages due to temperature variations are imposed in our model, the Ar and Kr mole fractions can be modified up to several orders of magnitude in clathrate hydrates. Moreover, mole fractions of other molecules such as N 2 or CO are also subject to strong changes with the variation of the size of the cages. Our results may affect the predictions of the composition of the planetesimals formed in the outer solar system. In particular, the volatile abundances calculated in the giant planets atmospheres should be altered because these quantities are proportional to the mass of accreted and vaporized icy planetesimals. For similar reasons, the estimates of the volatile budgets accreted by icy satellites and comets may also be altered by our calculations. For instance, under some conditions, our calculations predict that the abundance of argon in the atmosphere of Titan should be higher than the value measured by Huygens. Moreover, the Ar abundance in comets...

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Section: Introductionmentioning

confidence: 99%

Volatile inventories in clathrate hydrates formed in the primordial nebula

et al. 2010

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“…However, Takeya et al (2006) found that gas hydrates encaging 96-98% methane and a small amount of CO 2 are type-Is in the submarine environment of Okhotsk sea. In this work gas hydrates formed from the mixture of methane and CO 2 are assumed as structure-Is.…”

Section: System Of Methane and Hydrogen Sulphide With Pure Watermentioning

confidence: 99%

Empirical expressions for gas hydrate stability law, its volume fraction and mass-density at temperatures 273.15K to 290.15K

Sultan

2008

Geochem. J.

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A series of empirical expressions for predicting gas hydrate stability, its volume fraction out of pore space and gas hydrate mass-density were established in different systems in consideration of gas composition (CH 4 , C 2 H 6 , H 2 S) and salinity (NaCl, seawater), and pore size at temperature between 273.15 and 300 K, based on our gas hydrate thermodynamic model (Sultan et al., 2004b, c). Six of the developed expressions for predicting gas hydrate stability were validated against the available published experimental data and they were also compared with other models. At temperature 273.15 to 290.15 K, the ARDPs (Average Relative Deviation of Pressures between the prediction and the experimental data) have shown that these empirical expressions are in agreement with the experimental data as well as other models, indicating their reliability of predicting gas hydrate stability for these systems. At higher temperatures, the empirical predictions for gas hydrate stability do not well reproduce the experimental data, because they are based on van der Waals model. The empirical expressions for predicting gas hydrate stability in the systems of CH 4 + H 2 S + H 2 O, CH 4 + seawater + poresize, CH 4 + H 2 S + NaCl and CH 4 + CO 2 + NaCl, and for evaluating gas hydrate fraction and its density need further validation due to lack of available published experimental data. However, the empirical expressions for gas hydrate fraction and its density show that the effects of pore size and salinity are negligible; gas hydrate fraction will increase if methane concentration continuously increases relatively in excess of methane solubility and decreases with pressure within gas hydrate stability zone, which is well consistent with data of natural gas hydrates in Cascadia; gas hydrate density tends to increase with ethane percentage and decrease with pressure. Keywords: gas hydrate, stability law, fraction out of pore space, mass-density, empirical expressionsIn recent years, numerous theoretical models are proposed about the gas hydrate stability (Handa, 1990;

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“…Thus, the 13 C NMR technique may be effective for the determination of crystal structure and for the estimation of cage occupancies. However, suitable high quality spectra are difficult to obtain for natural gas hydrate samples because of the low natural abundance of 13 C and the low concentration of natural gas hydrate in the samples recovered from the sea floor 7) . Therefore, the 13 C NMR measurement technique must be improved for the analysis of natural gas hydrate samples.…”

Section: Introductionmentioning

confidence: 99%

“…The cage occupancy is defi ned as the ratio of (number of cages occupied by guest molecules)/(number of total cages), and is also important to estimate the amount of natural gas, since it depends on the conditions of the hydrate formation such as pressure and gas composition. In general, samples of synthesized gas hydrates and natural gas hydrates recovered from sea fl oor contain a certain amount of frozen water 5), 7) . Therefore, the cage occupancy is difficult to estimate from the amounts of water and gas obtained by dissociation of , Hitoshi Shoji 2) , Yasushi Kamata 3), 5) , Takao Ebinuma 3) , Hideo Narita 3) , and Satoshi Takeya CP-MAS 13 C NMR measurements were carried out on mixed gas hydrates containing CH4 _ C2H6.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Gas Composition and Cage Occupancies in CH4-C2H6 Hydrates by CP-MAS 13C NMR Technique

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et al. 2007

J. Jpn. Petrol. Inst.

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13C NMR spectra. The cage occupancies of the small and large cages of the hydrates were estimated from the 13 C NMR spectra on the basis of a statistical thermodynamic model. The large cages were almost fully occupied with guest molecules, whereas small cage occupancy decreased with increasing C2H6 concentration. Therefore, large cages are highly preferentially occupied by C2H6 molecules rather than CH4 molecules.

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Structure and thermal expansion of natural gas clathrate hydrates

Cited by 91 publications

References 26 publications

Volatile inventories in clathrate hydrates formed in the primordial nebula

Volatile inventories in clathrate hydrates formed in the primordial nebula

Empirical expressions for gas hydrate stability law, its volume fraction and mass-density at temperatures 273.15K to 290.15K

Estimation of Gas Composition and Cage Occupancies in CH<sub>4</sub>-C<sub>2</sub>H<sub>6</sub> Hydrates by CP-MAS <sup>13</sup>C NMR Technique

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