An investigation of gas hydrates formation energetics

Avlonitis, Dimitrios

doi:10.1002/aic.10374

Cited by 17 publications

(11 citation statements)

References 39 publications

(64 reference statements)

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“…It is currently impossible to determine the occupancy of the cages in the thermodynamic conditions existing within cometary nuclei and we therefore fix the hydrate number to 6, closer to real values (Handa 1986a,b;Sloan 1998;Sun & Mohanty 2006), as the nominal value of the number of hydration. This assumption is in good agreement with Avlonitis et al (2005) who showed that the hydration number decreases slowly with temperature if both types of cavities are occupied by gas.…”

Section: Modeling Parameters Of Clathratessupporting

confidence: 79%

“…So, the enthalpy of formation/dissociation of single guest clathrates below the ice point is mainly a property of the gas itself: it depends solely on the nature of the enclathrated molecule. The enthalpy of formation of single guest clathrates is then independent of the clathrate structure, the hydration number n hyd , the gas distribution between cavities, the temperature and the pressure (Avlonitis 2005). His model corroborates in every case the experimental data of Handa (1986a,b) and Anderson (2003) as well as the results of Yoon et al (2003), which were derived by application of the ClausiusClapeyron equation (See Eq.…”

Section: Enthalpy Of Formation and Dissociation Of Clathratessupporting

confidence: 75%

“…Experimental measurements of the enthalpy of formation/dissociation are not easily obtained and such data are very scarce (Avlonitis 2005). Only the enthalpy of formation of clathrate hydrates of structure I as Xe, CH 4 , C 2 H 6 (Handa 1986a,b), and clathrate hydrates of structure II as tetrahydrofuran, ethylene oxide (Leaist et al 1982), Kr, C 3 H 8 and iC 4 H 10 (Handa 1986a,b) have been measured, but in a limited temperature range for each molecule, all around or above 200 K. Avlonitis (2005) developed and implemented a method for predicting enthalpies of clathrate formation and demonstrated that a major energetic component in hydrate formation is the heat of enclathration, defined as the residual enthalpy of the enclathrated gas, and that the enthalpy of transformation of crystalline ice into the empty clathrate structure is comparatively small. So, the enthalpy of formation/dissociation of single guest clathrates below the ice point is mainly a property of the gas itself: it depends solely on the nature of the enclathrated molecule.…”

Section: Enthalpy Of Formation and Dissociation Of Clathratesmentioning

confidence: 99%

“…Given, the simplicity of the Clausius-Clapeyron equation and the good correlation with experimental values, we can use this equation to obtain approximate values of the enthalpy of dissociation of single guest clathrate hydrates. Moreover, the model of Avlonitis (2005) showed that the values of enthalpy of all of the seven simple gas hydrates (N 2 , CH 4 , CO 2 , Xe, C 2 H 6 , C 3 H 8 and iC 4 H 10 ) he studied in the range 180−270 K are so slightly decreasing with temperature that they may be considered approximately constant. However, Anderson (2004), by using the Clausius-Clapeyron equation, has shown a decrease of about 10% of the enthalpy of dissociation of the CH 4 clathrate at 150 K compared to its value at 200−220 K. It is also known that H cl x (T ) vary with T as follows (Makogon & Sloan 1994):…”

Section: Enthalpy Of Formation and Dissociation Of Clathratesmentioning

confidence: 99%

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A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

Marboeuf

Schmitt

Petit

et al. 2012

A&A

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Context. Current theories, models of cometary nuclei and of ice formation in the protoplanetary disk, and laboratory studies suggest that cometary materials could be formed of pure crystalline water ice, amorphous water ice, clathrate hydrate, or a mixture of these structures of water ice. However, current models of cometary nuclei consider only two forms of ice during the thermodynamic evolution of comets: amorphous and crystalline water ices. Aims. In this work, we have developed a model of cometary nucleus that takes into account all water ice structures and phase changes in order to predict the outgassing profile of volatile molecules that could be measured by the Rosetta mission and can be used to constrain the structural type of ice existing in the interior of the Comet 67P/Churyumov-Gerasimenko, the target comet of the Rosetta mission, and, hopefully, its initial composition. Methods. We added the physic of formation/dissociation of clathrate hydrates in addition to others physical processes that are taken into account in models without clathrate hydrates. All thermal changes, as well as the release and trapping of gas with water phase changes are taken into account. Results. This model describes heat transmission, latent heat exchanges, all water ices structures and transitions (amorphous-to-pure crystalline, amorphous-to-clathrate hydrates and pure crystalline-to-clathrate hydrates and vise versa), sublimation/recondensation of volatile molecules in the nucleus, gas diffusion, gas released and trapped by crystallization and clathrate formation/dissociation processes, as well as gas and dust release and mantle formation at the surface. Applying this model to the comet 67P/ChuryumovGerasimenko, results show different outgassing profiles of volatiles molecules from the nucleus depending on the water ice structure, the distribution of volatile molecules between the "trapped" and "condensed" states in the nucleus and the thermal inertia of its porous matrix. Conclusions. Given these results, we pretend that this model is able to constrain the water ice structure and chemical composition in comets from outgassing profiles of volatile molecules, and especially those of the target comet of the Rosetta mission.

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Section: Modeling Parameters Of Clathratessupporting

confidence: 79%

Section: Enthalpy Of Formation and Dissociation Of Clathratessupporting

confidence: 75%

Section: Enthalpy Of Formation and Dissociation Of Clathratesmentioning

confidence: 99%

Section: Enthalpy Of Formation and Dissociation Of Clathratesmentioning

confidence: 99%

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A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

Marboeuf

Schmitt

Petit

et al. 2012

A&A

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“…They can also cause the hampering of the operation of heat exchangers and expanders. Thus, modeling the water content is required to determine the extent of drying or the amount of gas hydrate inhibitor necessary to avoid gas hydrate formation [2,3]. On the other hand gas hydrates can be used as an unconventional natural gas energy storage since the gas hydrates can contain more than 150 times as much natural gas than gaseous natural gas at standard temperature and pressure.…”

Section: Introductionmentioning

confidence: 99%

Mutual solubilities of hydrocarbons and water with the CPA EoS

Oliveira

Coutinho

Queimada

2007

Fluid Phase Equilibria

145

103

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The knowledge of hydrocarbon/water phase equilibria is important in the design and operation of equipment for petroleum transport and refining and petrochemical plants. The presence of water in a hydrocarbon mixture can affect the product quality and damage the operation equipment due to corrosion and formation of gas hydrates. Tracing the concentration of hydrocarbons in aqueous media is also important for technical purposes like preventing oil spills and for ecological concerns such as predicting the fate of these organic pollutants in the environment.In spite of its huge interest there was no model able for a qualitative description of the mutual solubility of water and hydrocarbons for a broad range of systems in a wide range of thermodynamic conditions. In this work it is shown that an equation of state incorporating association known as the CPA EoS is able to produce an excellent description of the mutual solubilities of water and several aliphatic and aromatic hydrocarbons in a broad range of pressures and temperatures.

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