Equilibrium Data of Methane, Carbon Dioxide, and Xenon Clathrate Hydrates below the Freezing Point of Water. Applications to Astrophysical Environments

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Methane hydrate exists in huge amounts in certain locations, in sea sediments and the geological structures below them, at low temperature and high pressure. Production methods are in development to produce the methane to a floating platform. There it can be reformed to produce hydrogen and carbon dioxide, in an endothermic process. Some of the methane can be burned to provide heat energy to develop all needed power on the platform and to support the reforming process. After separation, the hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform can be separated from other gases and then sequestered in the sea as carbon dioxide hydrate. In this way, hydrogen is made available without the release of carbon dioxide to the atmosphere, and the hydrogen could be an enabling step toward a world hydrogen economy.

Phase stability conditions of carbon dioxide and methane clathrate hydrates in the presence of KBr, CaBr2, MgCl2, HCOONa, and HCOOK aqueous solutions: Experimental measurements and thermodynamic modelling

This paper reports the three-phase (ice + hydrate + guest-rich vapor) equilibrium pressure−temperature conditions at temperatures (243 to 273) K in the systems of water and each of the following guest gases: methane, ethane, propane, and carbon dioxide. The measurements were also performed for the water-rich liquid + hydrate + guest-rich vapor three-phase equilibrium conditions at temperatures above 273 K. The pressure ranges of the present measurements in the four systems are (0.971 to 2.471) MPa in the methane system, (0.122 to 0.637) MPa in the ethane system, (41.0 to 280.0) kPa in the propane system, and (0.364 to 0.963) MPa in the carbon dioxide system. On the basis of the obtained three-phase equilibrium data, the quadruple points for the ice + water-rich liquid + hydrate + guest-rich vapor were also determined in the respective systems. The measurements were carried out using the batch, isochoric procedure. Fine-grained ice powders with diameters of (1 to 2) mm were used to form the hydrate. The me...

Context. Clathrate hydrates could provide a sink for highly volatile molecules, thus modifying the release and chemical cycling time scales for gases in icy bodies in the solar system (planets, satellites, comets), as well as for interstellar ice mantles. Aims. By providing an infrared spectroscopic identification for the carbon dioxide clathrate hydrate, CO2 being an important constituent of ices in interstellar (ISM) and planetary media, we examine its astrophysical presence or absence. Methods. A carbon dioxide clathrate crystal is produced in an infrared transmitting moderate pressure closed cell. Using FTIR spectroscopy, the stretching modes ( $\rm\nu_3^{12}CO_2$, $\rm ^{13}CO_2$, $\rm ^{18}OCO$) and accidental resonances combinations ( $\rm ^{12}CO_2$, $\rm ^{13}CO_2$ , $\rm ^{18}OCO$ $\rm\nu_1+\nu_3$ Fermi resonance dyad and $\rm 2\nu_1+\nu_3$ Fermi resonance triad) falling in the 5100–2200 cm-1 (1.96–4.43 $\mu$m) range, and their temperature behaviour from 150 K down to 5.6 K are investigated. Results. Combination modes clearly show the two distinct cages expected for type I carbon dioxide clathrate hydrate, and we identify them. The forbidden antisymmetric stretching-mode overtone ($2\nu_3$), activated in the carbon dioxide simple hydrate, is absent in the clathrate hydrate. Combining these distinct spectroscopic profiles will provide a constraint to determine the importance of carbon dioxide clathrate hydrates observationally. Conclusions. We spectroscopically identify the carbon dioxide clathrate hydrate. A direct detection via (near-)infrared probes or telescopic observations is needed to understand whether clathrate formation is ubiquitous, given the widespread occurrence of carbon dioxide and water ice in astrophysics, or whether it is present only very locally in a few objects.

Stability and cell distortion of sI clathrate hydrates of methane and carbon dioxide: A 2D lattice-gas model study

Gas hydrates are crystalline structures formed by water molecules and compounds of low molecular weights, being formed under suitable conditions of pressure and temperature. Although initially considered as inconveniences to the natural gas industries, they are currently considered as promising alternatives for solving some important global issues, such as contributing to the reduction of effects caused by the greenhouse gases. This concern related to the control of emissions of polluting gases has mobilized hundreds of countries that, at the United Nations Climate Change Conference (COP), agreed to reduce emissions of carbon dioxide and other gases by 2100. However, despite several strategies in the reduction of carbon dioxide emissions have been proposed, many rely on political incentives and substantial investments to convert pre-existing technologies to clean technologies, making such applicability and adaptability problematic. Thus, innovative Carbon Capture and Storage (CCS) techniques are being studied, which considers the use of gas hydrates formation to trap these gases, presents perspectives of lower costs and low environmental damages, promising to overcome the above mentioned problem, besides capturing and storing adequately the carbon dioxide and methane emitted. The need for robust evaluation of the thermodynamic equilibrium of hydrate-containing systems arises in order to make the proposal feasible and used on a large scale. The present work extensively solidifies this assessment of hydrate phase equilibria by proposing the isofugacity and Gibbs energy minimization criteria coupled to the nonlinear programming for the calculation of phase equilibria in the formation of methane and carbon dioxide hydrates. The Soave-Redlich-Kong cubic equation (SRK) was used to calculate the liquid and gaseous phases, and the Van der Waals and Platteeuw models were used to describe the solid phase of the hydrate. The procedure was implemented in the General Algebraic Modeling System (GAMS) software and in the CONOPT3 solver, with some numerical procedures performed in Microsoft Office Excel. The comparison between the results obtained from the present study by the isofugacity criterion and experimental data has been carried out, allowing concluding the satisfactory prediction of the phase equilibria behavior of systems containing hydrates.

Clathrate hydrates may represent a sizable fraction of material within the icy shells of Kuiper Belt objects and icy moons. They influence the chemical and thermal evolution of subsurface oceans by locking volatiles into the ice shell and by providing more thermal insulation than pure water ice. We model the formation of these crystalline compounds in conditions relevant to outer solar system objects, using Pluto as an example. Although Pluto may have hosted a thick ocean in its early history, Pluto’s overall heat budget is probably insufficient to preserve liquid today if its outer shell is pure water ice. One previously proposed reconciliation is that Pluto’s ocean has a winter jacket: an insulating layer of methane clathrate hydrates. Unfortunately, assessments of the timing, quantity, and type of clathrate hydrates forming within planetary bodies are lacking. Our work quantifies the abundance of clathrate-forming gases present in Pluto’s ocean from accreted ices and volatiles released during thermal metamorphism throughout Pluto’s history. We find that if Pluto formed with the same relative abundances of ices found in comets, then a buoyant layer of mixed methane and carbon dioxide clathrate hydrates may form above Pluto’s ocean, though we find it insufficient to preserve a thick ocean today. In general, our study provides methodology for predicting clathrate formation in ocean worlds, which is necessary to predict the evolution of the ocean’s composition and whether a liquid layer remains at present.

Phase equilibrium conditions in carbon dioxide + cyclopentane double clathrate hydrate forming system coexisting with sodium chloride aqueous solution

A thermodynamic model for the prediction of pressure–temperature phase diagrams of structures II and H clathrate hydrates of methane, carbon dioxide, or hydrogen sulfide in the presence of “water-insoluble” organic componds is presented. The model is based on the equality of water fugacity in the aqueous and hydrate phases. The solid solution theory of van der Waals–Platteeuw (vdW–P) is used for calculation of the fugacity of water in the hydrate phase. The Peng–Robinson (PR) equation of state (EoS) is employed to calculate the fugacity of the components in the gas phase. It is assumed that the gas phase is water and promoter free and the organic compounds do not have marked effects on water activity in the aqueous phase. The results of this model are compared to existing experimental data from the literature. Acceptable agreement is found between the model predictions and the investigated experimental data.

This paper reports the three-phase (ice + hydrate + guest-rich vapor) equilibrium pressure−temperature conditions at temperatures (243 to 272) K in the systems of water and each of the following two ternary gas mixtures of methane, ethane, and propane: 90:7:3 molar ratio and 99.48:0.5:0.02 molar ratio. The former is a simulated natural gas (natural-gas composition). The latter has a methane-rich composition that is equal to that of the vapor phase in equilibrium with the clathrate hydrate that has the guest composition of 90:7:3 molar ratio. The pressure ranges of the present measurements in the two systems are (0.233 to 0.711) MPa in the natural-gas-composition gas mixture system and (0.939 to 2.070) MPa in the methane-rich-composition gas mixture system. The measurements were carried out using the batch, isochoric procedure. The measured data were compared with the corresponding predictions using phase equilibrium calculation programs.

Kinetic mechanisms of methane hydrate replacement and carbon dioxide hydrate reorganization

Development of dual functional methodology for seawater desalination and salt manufacture by carbon dioxide hydrate formation

It is suggested that halos and other refraction effects caused by crystals of various solids that may occur in their atmospheres might occur on the planets of the solar system and their satellites. The detection of the halos would provide valuable information about the nature and the crystalline form of the solids. The halos caused by the octahedral and cubic crystals of carbon monoxide, carbon dioxide, ice Ic, ammonia, methane, and the structure-I clathrate hydrates of nitrogen, carbon monoxide, carbon dioxide, sulfur dioxide, and methane have been predicted over the range of temperatures that may occur in the atmospheres of the planets.

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal