Molecular simulation of non-equilibrium methane hydrate decomposition process

Bagherzadeh, Sharareh; Englezos, Peter; Alavi, Saman; Ripmeester, John A.

doi:10.1016/j.jct.2011.08.021

Cited by 79 publications

(65 citation statements)

References 25 publications

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“…As the released CH 4 molecules are dissolved into water prior to the bubble formation when CH 4 hydrate is dissociating in water, as shown experimentally [29] and theoretically [20][21][22][23], it is reasonable that P g in CH 4 MNB should be less than P d .…”

Section: Measurements Of Mnb Solutions Via Raman Spectroscopymentioning

confidence: 98%

“…3). Thus, the MNB formation can be interpreted not only by the aggregation of CH 4 molecules dissolved in water [20][21][22][23], but also by the shrinkage of larger bubbles formed during the hydrate dissociation.…”

Section: Measurements Of Mnb Solutions Via Raman Spectroscopymentioning

confidence: 99%

“…Molecular dynamic simulations recently predicted the formation of NBs in solution after gas hydrate dissociation [20][21][22][23]. However, it is still difficult to directly confirm the existence of slightly lower than that expected theoretically.…”

Section: Introductionmentioning

confidence: 99%

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Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Uchida

Yamazaki

Gohara

2016

Korean J. Chem. Eng.

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Gas hydrate crystals have a structure in which one molecule is enclathrated in a cage of water molecules.When such a crystal dissociates in water, each enclathrated molecule, generally vapor at standard temperature and pressure, directly dissolves into the water. After the solution is supersaturated, excess gas molecules from further dissociation would start forming small bubbles called micro-and nano-bubbles (MNBs). However, it is difficult to identify such small bubbles dispersed in liquid because they are smaller than a microscope's optical resolution. To confirm the formation of MNBs after gas hydrate dissociation, we used a transmission electron microscope (TEM) to analyze freeze-fracture replicas of CH 4 -hydrate dissociation solution. The TEM images indicate the existence of MNBs in the solution, with a number concentration similar to that from a commercially supplied generator. Raman spectroscopic measurements on the CH 4 -hydrate dissociated solution were then done to confirm that the MNBs contain CH 4 vapor, and to estimate experimentally the inner pressure of the CH 4 MNBs. These results suggest that the dissociation of gas hydrate crystals in water is a simple, effective method to obtain MNB solution. We then discuss how such MNBs may play a key role in the memory effect of gas-hydrate reformation. KeywordsMicrobubble, Nanobubble, gas hydrate dissociation, freeze fracture replica, bubble pressure, memory effect 2

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Section: Measurements Of Mnb Solutions Via Raman Spectroscopymentioning

confidence: 98%

Section: Measurements Of Mnb Solutions Via Raman Spectroscopymentioning

confidence: 99%

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Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Uchida

Yamazaki

Gohara

2016

Korean J. Chem. Eng.

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“…[19][20][21][22][23][24][25][26][27][28] It has been observed that during methane hydrate decomposition, the guest methane molecules are released into the liquid water phase and form methane-rich regions. [29][30][31][32][33][34] It was also recently reported that formation of methane bubbles reduces the dissolved methane concentration in water thus increasing the dissociation rate of the solid hydrate. 35 However, it is expected that methane hydrate dissociation in a finite amount of water should result in phase separation via methane bubble formation due to the liquid phase becoming supersaturated with CH 4 .…”

Section: Introductionmentioning

confidence: 98%

Formation of methane nano-bubbles during hydrate decomposition and their effect on hydrate growth

Bagherzadeh

Alavi

Ripmeester

et al. 2015

The Journal of Chemical Physics

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114

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Molecular dynamic simulations are performed to study the conditions for methane nano-bubble formation during methane hydrate dissociation in the presence of water and a methane gas reservoir. Hydrate dissociation leads to the quick release of methane into the liquid phase which can cause methane supersaturation. If the diffusion of methane molecules out of the liquid phase is not fast enough, the methane molecules agglomerate and form bubbles. Under the conditions of our simulations, the methane-rich quasi-spherical bubbles grow to become cylindrical with a radius of ∼11 Å. The nano-bubbles remain stable for about 35 ns until they are gradually and homogeneously dispersed in the liquid phase and finally enter the gas phase reservoirs initially set up in the simulation box. We determined that the minimum mole fraction for the dissolved methane in water to form nano-bubbles is 0.044, corresponding to about 30% of hydrate phase composition (0.148). The importance of nano-bubble formation to the mechanism of methane hydrate formation, growth, and dissociation is discussed.

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“…An accurate knowledge of the thermodynamic and kinetic properties of methane hydrate is a primary goal for a number of studies. MD studies considering methane hydrates have been reported as early as 1983 with the pioneering work of Tse et al 44 Subsequently, a significant number of MD studies examining methane hydrates have been reported focusing on topics such as hydrate nucleation, [45][46][47][48][49][50] formation and growth, 51,52 dissociation, [53][54][55][56][57][58] inhibition, 59-61 heat transfer effects, 62-64 the effect of hydrate contact with solid surfaces, 65-68 methane replacement by carbon dioxide, [69][70][71][72] and the calculation of transport properties such as thermal conductivity, [73][74][75] or thermodynamic properties such as three-phase equilibrium conditions. [76][77][78][79] In the area of calculation of the three-phase equilibrium conditions for pure methane hydrate which is the main focus of the current study, there is a number of molecular simulation studies that have provided important insights of the mechanisms involved.…”

Section: Introductionmentioning

confidence: 99%

Prediction of the phase equilibria of methane hydrates using the direct phase coexistence methodology

Michalis

Costandy

Tsimpanogiannis

et al. 2015

The Journal of Chemical Physics

122

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The direct phase coexistence method is used for the determination of the three-phase coexistence line of sI methane hydrates. Molecular dynamics (MD) simulations are carried out in the isothermal-isobaric ensemble in order to determine the coexistence temperature (T3) at four different pressures, namely, 40, 100, 400, and 600 bar. Methane bubble formation that results in supersaturation of water with methane is generally avoided. The observed stochasticity of the hydrate growth and dissociation processes, which can be misleading in the determination of T3, is treated with long simulations in the range of 1000-4000 ns and a relatively large number of independent runs. Statistical averaging of 25 runs per pressure results in T3 predictions that are found to deviate systematically by approximately 3.5 K from the experimental values. This is in good agreement with the deviation of 3.15 K between the prediction of TIP4P/Ice water force field used and the experimental melting temperature of ice Ih. The current results offer the most consistent and accurate predictions from MD simulation for the determination of T3 of methane hydrates. Methane solubility values are also calculated at the predicted equilibrium conditions and are found in good agreement with continuum-scale models.

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Molecular simulation of non-equilibrium methane hydrate decomposition process

Cited by 79 publications

References 25 publications

Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

Formation of methane nano-bubbles during hydrate decomposition and their effect on hydrate growth

Prediction of the phase equilibria of methane hydrates using the direct phase coexistence methodology

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