Isotope Effect on Eutectic and Hydrate Melting Temperatures in the Water-THF System

Jones, Camille Y.; Zhang, J. S.; Lee, J. W.

doi:10.1155/2010/583041

Cited by 15 publications

(20 citation statements)

References 16 publications

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“…It means that the THF- d 8 clathrate has a heterogeneous structure in the region between 271.0 and 277.0 K (Figure e). The temperature of the second stage (277.0 K) agrees well with the known apparent equilibrium dissociation point of THF clathrates. − …”

Section: Results and Discussionsupporting

confidence: 77%

“…In the literature, transition I observed in the DSC curve was attributed to the melting of ice as a contaminant in THF clathrate. , However, the onset temperature of transition I is typically below the melting point of pure ice. Some researchers, therefore, attributed this transition to the melting of a eutectic solid solution of THF and water. , Even so, the eutectic composition of THF–water solution is 10 wt % THF, while our DSC experiments indicate that transition I can be measured up to a mixture containing 25 wt % THF- d 8 (Figure S3, Supporting Information). Thus, it is unclear how a eutectic composition of 10 wt % THF- d 8 could form in a solution of 25 wt % THF- d 8 .…”

Section: Results and Discussionmentioning

confidence: 68%

“…Some researchers, therefore, attributed this transition to the melting of a eutectic solid solution of THF and water. 36,39 Even so, the eutectic composition of THF−water solution is 10 wt % THF, 36 3). Moreover, the integrated areas of transition I and transition II in the DSC diagram reflect how much of the sample mass is dissociated in each transition.…”

Section: Resultsmentioning

confidence: 99%

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“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

et al. 2021

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Clathrate structures are sustained by a host lattice formed by hydrogen-bonding water molecules, which encapsulates guest molecules. Up to now, all water molecules in the host lattice are considered ice-like crystallized. Here, we discovered the occurrence of “liquid-like” water molecules and the resulting defects in (polar) tetrahydrofuran clathrates by liquid-state 1H NMR experiments. The liquid-like water molecules start occurring at 271 K, well below the apparent dissociation point (277 K) of the clathrate matrix, via extracting water molecules from the host lattice by host–guest H-bonding. We found an intriguing two-stage dissociation of the clathrate: Partial dissociation at 271 K converting one-third of water molecules into liquid-like followed by complete dissociation at 277 K. The clathrate structure is molecularly heterogeneous in the region between 271 K and 277 K. No liquid-like water exists in (nonpolar) cyclopentane clathrates. This work uncovers the essentiality of host–guest interaction for clathrate structures and the ability to tune their stability using polar molecules.

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Section: Results and Discussionsupporting

confidence: 77%

Section: Results and Discussionmentioning

confidence: 68%

Section: Resultsmentioning

confidence: 99%

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“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

et al. 2021

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“…and clearly show that a mobile fluid phase is present when the sample temperature is around 1°C, which is not visible when the sample is frozen. Given that the freezing point for THF is ‐100°C (Jones, Zhang and Lee ), we determine that the residual fluid is water, and the elevated attenuation in the hydrate phase is due to residual water left in pockets between hydrate crystals. Tittman et al .…”

Section: Discussionmentioning

confidence: 99%

Ultrasonic attenuation of pure tetrahydrofuran hydrate

Pohl

Prasad

Batzle

2018

Geophysical Prospecting

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Improved estimates of the amount of subsurface gas hydrates are needed for natural resource, geohazard, and climate impact assessments. To evaluate gas hydrate saturation from seismic methods, the properties of pure gas hydrates need to be known. Whereas the properties of sediments, specifically sands, and hydrate‐bearing sediments are well studied, the properties of pure hydrates are largely unknown. Hence, we present laboratory ultrasonic P‐wave velocity and attenuation measurements on pure tetrahydrofuran hydrates as they form with reducing temperatures from 25°C to 1°C under atmospheric pressure conditions. Tetrahydrofuran hydrates, with structure II symmetry, are considered as proxies for the structure I methane hydrates because both have similar effects on elastic properties of hydrate‐bearing sediments. We find that although velocity increased, the waveform frequency content and amplitude decreased after the hydrate formation reaction was complete, indicating an increase in P‐wave attenuation after hydrate formation. When the tetrahydrofuran hydrate was cooled below the freezing point of water, velocity and quality factor increased. Nuclear Magnetic Resonance results indicate the presence of water in the “pure hydrate” samples above the water freezing point, but none below. The presence of liquid water between hydrate grains most likely causes heightened attenuation in tetrahydrofuran hydrates above the freezing point of water. In naturally occurring hydrates, a similarly high attenuation might relate to the presence of water.

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“…The modified off-diagonal parameters ( Table 2) increases the attractive interactions between THF and water and thus results in a completely miscible mixture ( Figure S4b) as observed in experiment. 51 The dissociation temperature (T d ) of hydrates is determined by performing several NPT simulations with different temperatures under the same pressure. If the temperature is above T d , the hydrate phase would melt and the potential energy would increase.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study on the Growth Mechanism of Methane plus Tetrahydrofuran Mixed Hydrates

Chen

et al. 2015

J. Phys. Chem. C

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Molecular dynamics (MD) simulations are performed to analyze the dominating factors for the growth of CH 4 + THF mixed hydrates, and the results are compared with the growth of single guest CH 4 and THF hydrates. While CH 4 hydrate has a type I crystalline structure, the presence of THF in the aqueous phase results in the growth the type II structure hydrate. Compared to THF hydrates, the presence of CH 4 in the system enhances the dissociation temperature. The growth rate of CH 4 + THF mixed exhibits a maximum value at about 290 K at 10 MPa. The growth rate is found to be determined by two competing factors: (1) the adsorption of CH 4 at the solid−liquid interface, which is enhanced with decreasing temperature, and (2) the migration of THF to the proper site at the interface, which is enhanced with increasing temperature. Above 290 K, which is about 10 K higher than the dissociation temperature of pure THF hydrate, the growth of cage can proceed only when a sufficient amount of CH 4 is adsorbed at the interface. The growth rate is dominated by the uptake of CH 4 at the interface, as in the case of pure CH 4 hydrate. Below 290 K, the growth is not much affected by the presence of CH 4 . Instead, the growth rate is determined by the rearrangement of THF molecules at the interface, as in the case of pure THF hydrate.

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Isotope Effect on Eutectic and Hydrate Melting Temperatures in the Water-THF System

Cited by 15 publications

References 16 publications

“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

Ultrasonic attenuation of pure tetrahydrofuran hydrate

Molecular Dynamics Study on the Growth Mechanism of Methane plus Tetrahydrofuran Mixed Hydrates

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