Coexistence of sI and sII in methane-propane hydrate former systems at high pressures

Menezes, Davi Éber Sánches de; Sum, Amadeu K.; Desmedt, Arnaud; Filho, Pedro de Alcântara Pessôa; Fuentes, María Dolores Robustillo

doi:10.1016/j.ces.2019.08.007

Cited by 23 publications

(16 citation statements)

References 46 publications

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“…For C 3 H 8 /CH 4 systems, a small number of C 3 H 8 molecules can induce the formation of an sII hydrate, but some 5 12 6 2 cages still appear in the CH 4 -rich region (see Figure 4B), suggesting the coexistence of sI and sII motifs in the incipient structure of such a C 3 H 8 /CH 4 mixed hydrate. 4,81 Guest Enrichment. The separation of gas mixtures via gas hydrate formation is another application for gas hydrates.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Molecular Insights into Guest and Composition Dependence of Mixed Hydrate Nucleation

Zhang

Guo

et al. 2020

J. Phys. Chem. C

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Multicomponent crystals, for which natural gas hydrates are important examples, have drawn considerable attention because of their scientific and industrial importance. By performing large-scale molecular dynamics simulations on hydrate nucleation of several common natural gases (CH4, C2H6, C3H8, and H2S) and their mixtures, we aim to elucidate the roles of gas molecules and their compositions on mixed hydrate nucleation. We find that at a fixed temperature and solution composition, the induction time (τ) sequence for pure guest hydrate nucleation is τ(C2H6) < τ(C3H8) < τ(CH4) < τ(H2S). A relatively small number of guest molecules with a shorter induction time for pure guest hydrate nucleation can promote the formation of initial nuclei of a mixed hydrate. Detailed cage analysis shows that small guests such as CH4 can induce the formation of more standard cages for mixture systems with either C2H6 or C3H8 systems, thereby reducing the formation of nonstandard cages and impacting the nucleation kinetics. Enrichment of CH4 in the nucleated cluster of C2H6/CH4 and C3H8/CH4 mixed hydrates was also observed. Four cage type subsets, i.e., 5126 a , 415106 b , 42586 c , and 43566 d (with a ranging from 0, 2, 3, 4; b from 2 to 6; c from 0 to 6; and d from 0 to 6) are identified as dominating the complete-cage populations for the hydrates formed in this study. Moreover, four-membered water rings appear to play an increasingly larger role in nucleated clusters as the size of guest molecules becomes larger.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Molecular Insights into Guest and Composition Dependence of Mixed Hydrate Nucleation

Zhang

Guo

et al. 2020

J. Phys. Chem. C

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“…Hydrates formed from methane-rich methane + propane mixtures have been observed to form sI alongside the expected sII. ,,, Metastable structures formed during growth could be contributors to the partial dissociation on the methane + propane mixtures, but since it was also observed in propane hydrates, a known sII former, it is unlikely that metastability is solely responsible for these events. The y CH 4 = 0.98 gas mixture was reported to exhibit a phase transition from structure II to a mixed sI + sII solid phase, with noticeable changes in the crystal habit before and after the transition .…”

Section: Resultsmentioning

confidence: 99%

“…With greater ratios of water to gas phase, propane is readily depleted in the gas phase, which can lead to secondary growth of methane hydrates . Methane + propane hydrates also have shown formation of metastable phases, specially with propane contents lower than 10% mole fraction in the gas phase. ,, These ”metastable” hydrates have been defined as phases that appear initially as kinetic products and then transform into the thermodynamically stable phase. Hydrates from methane + ethane mixtures have also shown the coexistence of sI and sII structures …”

Section: Introductionmentioning

confidence: 99%

Growth Mechanisms and Phase Equilibria of Propane and Methane + Propane Hydrates

Ovalle

Beltrán

2021

J. Chem. Eng. Data

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Gas hydrates of light hydrocarbons exhibit complex phase behavior, polymorphism, and diverse crystal morphology. We investigated phase equilibria and growth mechanisms of propane and methane + propane gas hydrates in the range of 0.25 to 2.1 MPa and 273.6 to 287.25 K. Clathrates formed from pure propane and the y CH4 = 0.90 methane + propane mixture exhibited similar morphologies at low subcoolings but differed considerably at higher subcoolings. The y CH4 = 0.98 methane + propane mixture formed crystals with radically different morphologies than those of pure propane and the y CH4 = 0.90 mixture. We report a new hydrate growth mechanism that proceeds via partial dissociation of the growing crystal in propane and propane + methane hydrates.

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“…In all clathrate structures, water molecules and hydrogen bonds constitute the vertices and the edges, respectively; however, each structure has its own crystallographic properties and contains geometrically specific water blocks with various cage shapes and sizes. sI structure contains 46 water molecules that form 8 cages per unit cell ( Izquierdo-Ruiz et al, 2016 ): two smaller cages that are made up of 20 water molecules and are arranged in a stretched pentagonal dodecahedron configuration with

faces and six larger hexagonal truncated trapezohedron cages made up of 26 water molecules with

faces ( Figure 4 A), where

represents a cage with m X-sided and n Z-sided faces ( Willow and Xantheas, 2012 ; de Menezes et al, 2019 ). sII hydrates, on the other hand, contain 136 water molecules and are made up of sixteen small

cages and eight larger

cages in a unit cell ( Klapproth et al, 2019 ).…”

Section: Hydrogen Hydratementioning

confidence: 99%

The potential of hydrogen hydrate as a future hydrogen storage medium

2021

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Summary Hydrogen is recognized as the “future fuel” and the most promising alternative of fossil fuels due to its remarkable properties including exceptionally high energy content per unit mass (142 ), low mass density, and massive environmental and economical upsides. A wide spectrum of methods in production, especially carbon-free approaches, purification, and storage have been investigated to bring this energy source closer to the technological deployment. Hydrogen hydrates are among the most intriguing material paradigms for storage due to their appealing properties such as low energy consumption for charge and discharge, safety, cost-effectiveness, and favorable environmental features. Here, we comprehensively discuss the progress in understanding of hydrogen clathrate hydrates with an emphasis on charging/discharging rate of (i.e. hydrate formation and dissociation rates) and the storage capacity. A thorough understanding on phase equilibrium of the hydrates and its variation through different materials is provided. The path toward ambient temperature and pressure hydrogen batteries with high storage capacity is elucidated. We suggest that the charging rate of in this storage medium and long cyclic performance are more immediate challenges than storage capacity for technological translation of this storage medium. This review and provided outlook establish a groundwork for further innovation on hydrogen hydrate systems for promising future of hydrogen fuel.

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Coexistence of sI and sII in methane-propane hydrate former systems at high pressures

Cited by 23 publications

References 46 publications

Molecular Insights into Guest and Composition Dependence of Mixed Hydrate Nucleation

Molecular Insights into Guest and Composition Dependence of Mixed Hydrate Nucleation

Growth Mechanisms and Phase Equilibria of Propane and Methane + Propane Hydrates

The potential of hydrogen hydrate as a future hydrogen storage medium

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