Direct transition mechanism for molecular diffusion in gas hydrates

Vidal-Vidal, Ángel; Pérez-Rodrı́guez, Martı́n; Piñeiro, Manuel M.

doi:10.1039/c5ra17867c

Cited by 27 publications

(21 citation statements)

References 31 publications

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“…The methane diffusion probed in the present study is much faster than that reported in the literature for the cage-to-cage hopping of CH 4 molecules through clathrate sI. Cage-to-cage hopping is a rare event that requires distortion of the host network 36 and the associated diffusion coefficient is of the order of 10 −11 to 10 −12 cm 2 s −1 at 250 K, as revealed by experimental 21 and computational 24 studies. Similar conclusions have been reported for the cage-to-cage hopping of other guest molecules 37 , 38 , including molecules forming clathrate sII 37 .…”

Section: Discussionsupporting

confidence: 42%

Fast methane diffusion at the interface of two clathrate structures

et al. 2017

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Methane hydrates naturally form on Earth and in the interiors of some icy bodies of the Universe, and are also expected to play a paramount role in future energy and environmental technologies. Here we report experimental observation of an extremely fast methane diffusion at the interface of the two most common clathrate hydrate structures, namely clathrate structures I and II. Methane translational diffusion—measured by quasielastic neutron scattering at 0.8 GPa—is faster than that expected in pure supercritical methane at comparable pressure and temperature. This phenomenon could be an effect of strong confinement or of methane aggregation in the form of micro-nanobubbles at the interface of the two structures. Our results could have implications for understanding the replacement kinetics during sI–sII conversion in gas exchange experiments and for establishing the methane mobility in methane hydrates embedded in the cryosphere of large icy bodies in the Universe.

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Section: Discussionsupporting

confidence: 42%

Fast methane diffusion at the interface of two clathrate structures

et al. 2017

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“…This way, it is possible to retain approximately the shape and volume of the crystal cells and to allow some degree of flexibility in the structure. This type of approximation was successfully applied to a system of two cages in the sI clathrate hydrate for studying the intercage transition of CH 4 and CO 2 in a previous work . Then, one of the central cages of 1L and 2L systems was filled with a single H 2 molecule, with the aim to determine the optimal position of the guest.…”

Section: Resultsmentioning

confidence: 99%

“…This type of approximation was successfully applied to a system of two cages in the sI clathrate hydrate for studying the intercage transition of CH 4 and CO 2 in a previous work. 60 Then, one of the central cages of 1L and 2L systems was filled with a single H 2 molecule, with the aim to determine the optimal position of the guest. The resulting optimal geometry of just one occupied cage is illustrated in Figure 3.…”

Section: Introductionmentioning

confidence: 99%

“…More recently, Trinh et al 52 obtained barriers of 10 kJ/mol (0.1 eV) with occupation θ = 1 and 12 kJ/mol (0.12 eV) with occupation θ = 2, using ab initio MD (BLYP with the local DZPM basis set) at 100 K and values of 22 kJ/mol (0.23 eV) and 29 kJ/mol (0.3 eV), respectively, at 0 K. Our values agree very well with all of those described for both 1L and 2L systems, although using a lower level of theory because of the big size of our systems. If we compare H 2 with larger guest molecules, the barriers obtained for CO 2 or CH 4 in clathrate hydrates 60 were 0.59 and 1.16 eV, respectively, around an order of magnitude higher than the values discussed above.…”

Section: Introductionmentioning

confidence: 99%

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Simulation of Capture and Release Processes of Hydrogen by β-Hydroquinone Clathrate

et al. 2018

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Using molecular simulation techniques, we investigate the storage capabilities of H 2 gas by the clathrate of hydroquinone (HQ). Quantum mechanics calculations have been used to assess structure and interactions at the atomic scale and molecular dynamics to model the HQ clathrate at successive equilibriums during the processes of capture and release of H 2 , as well as the diffusion of H 2 inside the clathrate structure. The thermodynamic conditions of the simulations performed try to reproduce closely the corresponding experimental procedures, with results that are in good agreement with literature observed trends. The results obtained contribute to depict a more complete and better substantiated image of the mechanisms involved in stability and in the processes of capture and release of H 2 by the HQ clathrate.

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“…The transport of guest molecules through the lattice, and their potential for reaction are clearly relevant to applications that involve storage (particularly of hydrogen) and this has motivated several computational investigations. [13][14][15] On the experimental side, the standard tools used for clathrate characterization (X-ray and neutron diffraction, solid-state NMR, and Raman spectroscopy) 16 are not generally suitable for studying guest transport and reactions (although not impossible). 17 A more direct approach is to create isolated reactive species and monitor their behaviour with a specific probe (e.g.…”

Section: Introductionmentioning

confidence: 99%

Characterization of free radicals in clathrate hydrates of pyrrole, thiophene, and isoxazole by muon spin spectroscopy

et al. 2018

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Gas hydrates have long been of interest to the petrochemical industry but there has been growing interest in potential applications for carbon dioxide sequestration and hydrogen storage. This has prompted many fundamental studies of structure and host-guest interactions, but there has been relatively little investigation of chemical reactions of the guest molecules. In previous work we have shown that it is possible to use muon spin spectroscopy to characterize H-atom-like muonium and muoniated free radicals formed in clathrate hydrates. Muonium forms in clathrate hydrates of cyclopentane and tetrahydrofuran, whereas furan and its dihydro-derivatives form radicals. The current work extends studies to clathrates hydrates of other 5-membered heterocycles: thiophene, pyrrole and isoxazole. All form structure II hydrates. In addition to the clathrates, pure liquid samples of the heterocycles were studied to aid in the assignment of radical signals and for comparison with the enclathrated radicals. Similar to furan, two distinct radicals are formed when muonium reacts with thiophene and pyrrole. However, only one muoniated radical was detected from isoxazole. Muon, proton and nitrogen hyperfine constants were determined and compared with values predicted by DFT calculations to aid the structure assignments. The results show that Mu adds preferentially to the carbon adjacent to the heteroatom in thiophene and pyrrole, and to the carbon adjacent to O in isoxazole. The same radicals are formed in clathrates, but the spectra have broader signals, suggesting slower tumbling. Furthermore, additional signals in the avoided levelcrossing spectra indicate anisotropy consistent with restricted motion of the radicals in the clathrate cages.

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Direct transition mechanism for molecular diffusion in gas hydrates

Abstract: In this work, we use dual cage explicit atomic systems to demonstrate theoretically that direct transitions are feasible through hexagonal and pentagonal faces in type I hydrate without compromising the overall structure integrity.

Cited by 27 publications

References 31 publications

Fast methane diffusion at the interface of two clathrate structures

Fast methane diffusion at the interface of two clathrate structures

Simulation of Capture and Release Processes of Hydrogen by β-Hydroquinone Clathrate

Characterization of free radicals in clathrate hydrates of pyrrole, thiophene, and isoxazole by muon spin spectroscopy

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