Thermodynamic properties and dissociation characteristics of methane and propane hydrates in 70-.ANG.-radius silica gel pores

Handa, Y. P.; Stupin, D. Yu.

doi:10.1021/j100200a071

Cited by 353 publications

(379 citation statements)

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“…Yousif and Sloan [ 1991] assumed that the presence of a free gas phase within the porous network is needed to form the clathrate, and they ignore the thermodynamic effects of confinement in pores on the hydrate phase itself. Handa and Stupin [1992] considered a water or ice-saturated medium in equilibrium with an external gas pressure. With a 7 nm pore size, capillary pressure on the liquid-water interfaces is so high as to prevent intrusion of free gas into the porous network.…”

Section: Previous Studies Of Gas Hydrate Formation In Porous Mediamentioning

confidence: 99%

Formation of natural gas hydrates in marine sediments: 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

Clennell¹,

Hovland²,

Booth³

et al. 1999

J. Geophys. Res.

607

511

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Abstract. The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within finegrained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a "capillary pressure" in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore-size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This "freezedrying" may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable presence of free gas within the normal zone of hydrate stability.

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Section: Previous Studies Of Gas Hydrate Formation In Porous Mediamentioning

confidence: 99%

Formation of natural gas hydrates in marine sediments: 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

Clennell¹,

Hovland²,

Booth³

et al. 1999

J. Geophys. Res.

607

511

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“…It not only enables the ocean floor to remain stabilized even after recovering the CH 4 gas, because CH 4 hydrate maintains the same crystalline structure directly after its replacement with CO 2 , but also makes the swapping process more viable by enhancing its economical efficiency. Of course, a variety of external variables such as injection depth, salt concentration, and initial droplet size of liquid CO 2 may affect the fundamental dynamics of hydrate formation (6)(7)(8)(9). Accordingly, intense investigations concerning the effect of external factors and the realization of the process have been performed.…”

mentioning

confidence: 99%

Sequestering carbon dioxide into complex structures of naturally occurring gas hydrates

Park

Kim

Lee

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

460

374

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Large amounts of CH4 in the form of solid hydrates are stored on continental margins and in permafrost regions. If these CH4 hydrates could be converted into CO 2 hydrates, they would serve double duty as CH4 sources and CO2 storage sites. We explore here the swapping phenomenon occurring in structure I (sI) and structure II (sII) CH 4 hydrate deposits through spectroscopic analyses and its potential application to CO2 sequestration at the preliminary phase. The present 85% CH4 recovery rate in sI CH4 hydrate achieved by the direct use of binary N 2 ؉ CO2 guests is surprising when compared with the rate of 64% for a pure CO 2 guest attained in the previous approach. The direct use of a mixture of N2 ؉ CO2 eliminates the requirement of a CO2 separation͞purification process. In addition, the simultaneously occurring dual mechanism of CO 2 sequestration and CH4 recovery is expected to provide the physicochemical background required for developing a promising large-scale approach with economic feasibility. In the case of sII CH 4 hydrates, we observe a spontaneous structure transition of sII to sI during the replacement and a cage-specific distribution of guest molecules. A significant change of the lattice dimension caused by structure transformation induces a relative number of small cage sites to reduce, resulting in the considerable increase of CH 4 recovery rate. The mutually interactive pattern of targeted guestcage conjugates possesses important implications for the diverse hydrate-based inclusion phenomena as illustrated in the swapping process between CO2 stream and complex CH4 hydrate structure.clathrate ͉ CO2 sequestration ͉ methane ͉ swapping phenomenon ͉ NMR B ecause the total amount of natural gas hydrate was estimated to be about twice as much as the energy contained in fossil fuel reserves (1, ʈ), many researchers have tried to find a way to exploit CH 4 hydrates deposited worldwide as a new energy source. For recovering them at various conditions in an efficient way, several strategies such as thermal treatment, depressurization, and inhibitor addition into the hydrate layer have been proposed (2). However, all of these methods are based on the decomposition of CH 4 hydrate by external stimulation, which can trigger catastrophic slope failures (3). Furthermore, if CH 4 hydrate decomposes rapidly, it is also possible that the CH 4 released from the hydrate could transfer to the air and significantly accelerate the greenhouse effect (4).Recently, the replacement of CH 4 hydrate with CO 2 has been suggested as an alternative option for recovering CH 4 gas. When CO 2 itself is put under certain pressure, a solid CO 2 hydrate can be formed according to the stability regime (5). In addition, the formation condition of CO 2 hydrate is known to be more stable than that of CH 4 hydrate. Therefore, the swapping process between two gaseous guests is considered to be a favorable approach toward long-term storage of CO 2 . It not only enables the ocean floor to remain stabilized even after recovering the CH 4 ga...

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“…In nature, most natural gas hydrates exist in the form of inclusions within sediment or cemented soils, with only 6% present in bulk form. As the surrounding environment significantly influences natural gas hydrate formation, understanding the thermodynamic mechanism underlying the formation of natural gas hydrates in porous media is instrumental to research on gas hydrate storage [5]. Handa and Stupin [5] pioneered the effort to characterize pore size effects on hydrate equilibrium conditions in porous media, opening the way for many other researchers to refine and expand their work, not only on experiments [6][7][8][9][10][11][12][13][14][15][16], but also from theoretical points of view [17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Methane Hydrate Formation in Artificial and Natural Media

Zhang

Yang

2013

Energies

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Abstract:The formation of methane hydrate in two significantly different media was investigated, using silica gel as an artificial medium and loess as a natural medium. The methane hydrate formation was observed through the depletion of water in the matrix, measured via the matrix potential and the relationship between the matrix potential and the water content was determined using established equations. The velocity of methane hydrate nucleation slowed over the course of the reaction, as it relied on water transfer to the hydrate surfaces with lower Gibbs free energy after nucleation. Significant differences in the reactions in the two types of media arose from differences in the water retention capacity and lithology of media due to the internal surface area and pore size distributions. Compared with methane hydrate formation in silica gel, the reaction in loess was much slower and formed far less methane hydrate. The results of this study will advance the understanding of how the properties of the environment affect the formation of gas hydrates in nature.

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Thermodynamic properties and dissociation characteristics of methane and propane hydrates in 70-.ANG.-radius silica gel pores

Cited by 353 publications

References 1 publication

Formation of natural gas hydrates in marine sediments: 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

Formation of natural gas hydrates in marine sediments: 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

Sequestering carbon dioxide into complex structures of naturally occurring gas hydrates

Characteristics of Methane Hydrate Formation in Artificial and Natural Media

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