Anomalous Energetics in Tetrahydrofuran Clathrate Hydrate Revealed by X-ray Compton Scattering

Lehmkühler, Felix; Sakko, Arto; Sternemann, Christian; Hakala, Mikko; Nygård, Kim; Sahle, Christoph J.; Galambosi, S.; Steinke, Ingo; Tiemeyer, Sebastian; Nyrow, Alexander; Buslaps, T.; Pontoni, Diego; Tolan, Metin; Hämäläinen, K.

doi:10.1021/jz1010362

Cited by 16 publications

(26 citation statements)

References 39 publications

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“…The guest-host hydrogen bonding gradually degrades with increasing of temperature and decreasing activation barrier to motion of THF molecules. [87][88] The water molecules of the framework become more labile and the heat capacity increases rapidly for THF hydrates after the melting temperature (287.15K).…”

Section: Specific Heat Capacity At Constant Pressurementioning

confidence: 99%

Modeling Thermodynamic Properties of Propane or Tetrahydrofuran Mixed with Carbon Dioxide or Methane in Structure-II Clathrate Hydrates

et al. 2017

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A sound knowledge of thermodynamic properties of sII hydrates is of great importance to understand the stability of sII gas hydrates in petroleum pipelines and in natural settings. Here, we report direct molecular dynamics (MD) simulations of the thermal expansion coefficient, the compressibility and the specific heat capacity of C3H8, or tetrahydrofuran (THF), in mixtures of CH4 or CO2, in sII hydrates under a wide, relevant range of pressure-and temperature conditions. The simulations were started with guest molecules positioned at the cage center of the hydrate. Annealing simulations were additionally performed for hydrates with THF. For the isobaric thermal expansion coefficient, an effective correction method was used to modify the lattice parameters, and the corrected lattice parameters were subsequently used to obtain thermal expansion coefficients in good agreement with experimental measurements. The simulations indicated that the isothermal expansion coefficient and the specific heat capacity of C3H8-pure hydrates were comparable, but slightly larger than those of THF-pure hydrates, which could form Bjerrum defects. The considerable variation in the compressibility between the two, appeared to be due to crystallographic defects. However, when a second guest molecule occupied the small cages of the THF hydrate, the deviation was smaller, because the subtle guest-guest interactions can offset an unfavorable configuration of unstable THF hydrates, caused by local defects in free energy. Unlike the methane molecule, the carbon dioxide molecule, when filling the small cage, can increase the expansion coefficient and compressibility as well as decrease the heat capacity of the binary hydrate, similar to the case of sI hydrates. The calculated bulk modulus for C3H8 pure and binary hydrates with CH4 or CO2 molecule varied between 8.7 and 10.6 GPa at 287.15K between 10 and 100MPa. The results for the specific heat capacities varied from 3155 to 3750.0 J kg-1 K-1 for C3H8 pure and binary hydrates with CH4 or CO2 at 287.15K. These results are the first of this kind reported so far. The simulations show that the thermodynamic properties of hydrates largely depend on the enclathrated compounds. This provides a much-needed atomistic characterization of the sII hydrate properties, and gives an essential input for large-scale discoveries of hydrates and processing as a potential energy source.

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Section: Specific Heat Capacity At Constant Pressurementioning

confidence: 99%

Modeling Thermodynamic Properties of Propane or Tetrahydrofuran Mixed with Carbon Dioxide or Methane in Structure-II Clathrate Hydrates

et al. 2017

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“…In Compton scattering the photon scattering cross section is extremely sensitive to any changes in the intra-and intermolecular bond lengths in the subangstrom scale [17,18]. For molecular systems, Compton scattering probes, for example, changes in the hydrogen bond topologies between different thermodynamic conditions [19][20][21][22][23][24] or concentrations [25].…”

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confidence: 99%

Measurement of Two Solvation Regimes in Water-Ethanol Mixtures Using X-Ray Compton Scattering

et al. 2011

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Water-ethanol mixtures exhibit interesting anomalies in their macroscopic properties. Despite a lot of research, the origin of the anomalies and the microscopic structure itself is still far from completely known. We have utilized the synchrotron x-ray Compton scattering technique to elucidate the structure of aqueous ethanol from a new experimental perspective. The technique is uniquely sensitive to the local molecular geometries at the angstrom and subangstrom scales. The experiments reveal two distinct mixing regimes in terms of geometry: the dilute 5 mol % and the concentrated >15 mol % regimes. By comparing with pure liquids, the former regime is characterized by an intramolecular and the latter by an intermolecular change. The findings bring new light to evaluating the hypothesis of formation of clathratelike structures at the dilute concentrations.

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“…A linear change of the intramolecular OH bond length r OH was found to change the Compton profile differences linearly. 37,42,52 This calculated difference fails to model neither the experimental data fully nor the remaining effect after consideration of the temperature effect on the H-bonds. Intra-or intermolecular structural changes which would be expressed in a similar Compton profile difference have been unreported in the literature so far, suggesting the need of improved water models, e.g., taking quantum effects into account.…”

Section: Compton Scatteringmentioning

confidence: 83%

“…Thus, the Compton profile is related to the ground state electron momentum density r(p) and is very sensitive to single particle properties and small changes in the intra-and intermolecular bond geometry in molecular systems, 40 in particular in hydrogen-bonded systems such as liquid, confined and supercritical water, [41][42][43][44][45] structure and energetics of ice [46][47][48][49] and two-component systems. 37,[50][51][52][53] Here, p q denotes a scalar electron momentum variable. Since the electron momentum density is probed, Compton scattering allows accessing the expectation value of the electron kinetic energy hE kin i via 48,52 E kin h i¼ 3 m…”

Section: Methodsmentioning

confidence: 99%

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Intramolecular structure and energetics in supercooled water down to 255 K

Lehmkühler

Forov

Büning

et al. 2016

Phys. Chem. Chem. Phys.

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We studied the structure and energetics of supercooled water by means of X-ray Raman and Compton scattering. Under supercooled conditions down to 255 K, the oxygen K-edge measured by X-ray Raman scattering suggests an increase of tetrahedral order similar to the conventional temperature effect observed in non-supercooled water. Compton profile differences indicate contributions beyond the theoretically predicted temperature effect and provide a deeper insight into local structural changes. These contributions suggest a decrease of the electron mean kinetic energy by 3.3 ± 0.7 kJ (mol K)(-1) that cannot be modeled within established water models. Our surprising results emphasize the need for water models that capture in detail the intramolecular structural changes and quantum effects to explain this complex liquid.

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Anomalous Energetics in Tetrahydrofuran Clathrate Hydrate Revealed by X-ray Compton Scattering

Cited by 16 publications

References 39 publications

Modeling Thermodynamic Properties of Propane or Tetrahydrofuran Mixed with Carbon Dioxide or Methane in Structure-II Clathrate Hydrates

Modeling Thermodynamic Properties of Propane or Tetrahydrofuran Mixed with Carbon Dioxide or Methane in Structure-II Clathrate Hydrates

Measurement of Two Solvation Regimes in Water-Ethanol Mixtures Using X-Ray Compton Scattering

Intramolecular structure and energetics in supercooled water down to 255 K

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