On the Role of Ice‐Solution Interface in Heterogeneous Nucleation of Methane Clathrate Hydrates

PaymanPirzadeh,; Kusalik, Peter G.

doi:10.1002/9781118938607.ch22

Cited by 2 publications

(15 citation statements)

References 33 publications

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“…The rest of the contacts between ice and clathrate are mediated by liquid-like water molecules (we refer to these molecules as liquid-like based on their local order, not on their mobility). Our analysis indicates that coupled 5−7 and 5−8 water rings, that previous works 25,26 and this work find to be involved in the anchoring of small clathrate nuclei to the ice surface (and vice versa), represent only a small fraction of water molecules in the interfacial transition layer (ITL) between ice and clathrate. The water molecules in the interfacial transition layer have higher tetrahedral order and lower potential energy than in liquid water, although the difference to liquid water almost vanishes when the clathrate phase is itself disordered (amorphous).…”

Section: Discussionmentioning

confidence: 83%

Structure of the Ice–Clathrate Interface

et al. 2015

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Clathrate hydrates are crystals in which water molecules form hydrogen-bonded cages that enclose small nonpolar molecules, such as methane. In the laboratory, clathrates are customarily synthesized from ice and gas guest under conditions for which homogeneous nucleation of hydrates is not possible. It is not known how ice assists in the nucleation of clathrate hydrates or how ice forms on clathrate hydrate in the case of self-preservation. There is no lattice matching between any plane of ice and clathrate hydrates; therefore, an interfacial transition layer has to form to connect the two crystals. Here, we use molecular dynamic simulations to study the structure of ice−clathrate interfaces produced by alignment and equilibration of the crystals, competitive growth of ice and clathrate from a common solution, nucleation of hydrate in the presence of a growing ice front, and nucleation of ice in the presence of clathrate hydrates. We find that the interfacial transition layer between ice and clathrate is always disordered and has a typical width of two to three water layers. Water in the interfacial transition layer has tetrahedral order lower than either ice or clathrate and higher than liquid water under the same thermodynamic conditions. The potential energy of the water in the interfacial transition layer is between those in liquid water and the crystals. Our results suggest that the disordered interfacial transition layer could assist in the heterogeneous nucleation of clathrates from ice and ice from clathrates by providing a lower surface free energy than the ice−liquid and clathrate−liquid interfaces.

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Section: Discussionmentioning

confidence: 83%

Structure of the Ice–Clathrate Interface

et al. 2015

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“…Above a critical pressure, the concentration of the gas molecules increases in this QLL. Simulations by Pirzadeh and Kusalik have shown that the accumulation of the gas molecules in the QLL leads to induction of defect structures characterized by coupled 5- and 8-membered rings (5–8 rings). , Molinero and co-workers found similar coupled 5–8 and 5–7 rings in the interfacial transition layer (ITL) between ice and clathrate surfaces . Pirzadeh and Kusalik identify the coupled 5–8 rings as the initiation step of their induction-promotion-nucleation (IPN) mechanism for clathrate formation on ice surfaces. , As more gas molecules make it to the ice surface more 5-membered rings and clathrate cages are formed in the promotion phase until eventually a hydrate is nucleated …”

Section: Discussionmentioning

confidence: 99%

“…If the rate-limiting step is determined by surface adsorption, these results imply that propane is adsorbed more strongly onto the ice surface than the fluoromethanes even though the fluoromethanes have higher dipole moments, which seems unlikely to us. The more likely explanation for the negative activation energy lies in the total free energy change as a function of growing cluster sizes as explained by Barrer et al and adapted to the IPN model proposed by Pirzadeh and Kusalik. ,, …”

Section: Discussionmentioning

confidence: 99%

“…45 Pirzadeh and Kusalik identify the coupled 5−8 rings as the initiation step of their induction-promotion-nucleation (IPN) mechanism for clathrate formation on ice surfaces. 43,44 As more gas molecules make it to the ice surface more 5-membered rings and clathrate cages are formed in the promotion phase until eventually a hydrate is nucleated. 44 Because there is no crystal face matching between ice and hydrate crystals, after the nucleation event the ice and clathrate phase separate, leaving behind a disordered water layer between them.…”

Section: Discussionmentioning

confidence: 99%

“…43,44 As more gas molecules make it to the ice surface more 5-membered rings and clathrate cages are formed in the promotion phase until eventually a hydrate is nucleated. 44 Because there is no crystal face matching between ice and hydrate crystals, after the nucleation event the ice and clathrate phase separate, leaving behind a disordered water layer between them. 44 This too has been verified by Molinero and co-workers; in their simulations a thin, disordered, ITL persists on the surface of ice and clathrate crystals even at low temperatures.…”

Section: Discussionmentioning

confidence: 99%

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Kinetics of Trifluoromethane Clathrate Hydrate Formation from CHF₃ Gas and Ice Particles

et al. 2017

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We report the formation kinetics of trifluoromethane clathrate hydrate (CH) from less than 75 μm diameter ice particles and CHF gas. As previously observed for difluoromethane and propane hydrate formation, the initial stages of the reaction exhibit a strong negative correlation of the reaction rate with temperature, consistent with a negative activation energy of formation. The values obtained for trifluoromethane, ca. -6 kJ/mol (HO), are similar to those for difluoromethane, even though the two molecules have different intermolecular interactions and sizes. The activation energy is lesser per mole of HO, but greater per mole of guest molecule, than for propane hydrate, which has a different crystal structure. We propose a possible explanation for the negative activation barrier based on the stabilization of metastable structures at low temperature. A pronounced dependence of the formation kinetics on the gas flow rate into the cell is observed. At 253 K and a flow rate of 15 mmol/h, the stage II enclathration of trifluoromethane proceeds so quickly that the overpressure, the difference between the gas cell pressure and the hydrate vapor pressure, is only 0.06 MPa.

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On the Role of Ice‐Solution Interface in Heterogeneous Nucleation of Methane Clathrate Hydrates

Cited by 2 publications

References 33 publications

Structure of the Ice–Clathrate Interface

Structure of the Ice–Clathrate Interface

Kinetics of Trifluoromethane Clathrate Hydrate Formation from CHF₃ Gas and Ice Particles

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On the Role of Ice‐Solution Interface in Heterogeneous Nucleation of Methane Clathrate Hydrates

Cited by 2 publications

References 33 publications

Structure of the Ice–Clathrate Interface

Structure of the Ice–Clathrate Interface

Kinetics of Trifluoromethane Clathrate Hydrate Formation from CHF3 Gas and Ice Particles

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Kinetics of Trifluoromethane Clathrate Hydrate Formation from CHF₃ Gas and Ice Particles