The direct recovery of methane from massive methane hydrates (MHs), artificial MH-bearing clays, and natural MH-bearing sediments is demonstrated, using either CO(2) or a CO(2)/N(2) gas mixture (20 mol % of CO(2) and 80 mol % of N(2), reproducing flue gas from a power plant) for methane replacement in complex marine systems. Natural gas hydrates (NGHs) can be converted into CO(2) hydrate by a swapping mechanism. The overall process serves a dual purpose: it is a means of sustainable energy-source exploitation and greenhouse-gas sequestration. In particular, scant attention has been paid to the natural sediment clay portion in deep-sea gas hydrates, which is capable of storing a tremendous amount of NGH. The clay interlayer provides a unique chemical-physical environment for gas hydrates. Herein, for the first time, we pull out methane from intercalated methane hydrates in a clay interlayer using CO(2) and a CO(2)/N(2) gas mixture. The results of this study are expected to provide an essential physicochemical background required for large-scale NGH production under the seabed.

This study investigates the effect of gas hydrate formation on the stability of dry water (DW) particles when they are exposed to high pressure methane at low temperatures. The DW particles are prepared by mixing water with hydrophobic silica nanoparticles at high speed to form a water-in-air inverse foam. A high pressure autoclave was used to determine the hydrate equilibrium conditions and formation characteristics including hydrate onset time, subcooling temperature, and initial growth rate. In comparison to bulk water, the equilibrium conditions for methane hydrate are shifted to higher temperatures and low pressures, suggesting that the silica nanoparticles promote the hydrate equilibrium conditions. The surface-to-volume ratio between the gas and the water encapsulated by the silica nanoparticles is increased in comparison to bulk water which enhances the kinetics of methane hydrate formation without the need for vigorous mixing. However, after multiple cycles of hydrate formation and dissociation, the hydrate fraction decreases exponentially and approaches 0.22, which is approximately 20% of the hydrate fraction formed during the first cycle. From the data presented, it was concluded that the hydrates form a shell on the DW particles. Dissociation of this hydrate-shell generates a free water phase that cannot be reabsorbed into the DW particles which causes the exponential reduction in the hydrate fraction. PXRD confirms that structure I methane hydrate is formed with a lattice parameter of 1.1827(1) nm. Raman spectroscopy confirms that the hydrate-shell covers the DW particles as evidenced by the presence of two peaks for methane at 2901 and 2913 cm −1 , which indicates that the methane exists in large and small cages, respectively. These results suggest that the particles are covered with a hydrate-shell when methane hydrates are formed. Therefore, the hydrophobic silica is rearranging during hydrate formation, and after dissociation of the hydrate, free water is expelled. This free water cannot absorb back into the particles due to the hydrophobic surface.

Atomic hydrogen has received recent attention because of its potential role in energy devices, silicon devices, artificial photosynthesis, hydrogen storage, and so forth. Here, we propose a highly efficient route for producing atomic hydrogen using semi-clathrate hydrates. Two major hydrogen radical sources, derived from guest/host materials, are closely examined.

This study investigates the formation characteristics of gas hydrate from bulk water as well as dispersed water in silica gel and dry water particles when they are exposed to natural gas. The inclusion process of methane, ethane, and propane molecules in hydrate cages were observed with in situ Raman spectroscopy, and the resulting cage occupancies were estimated from 13 C NMR spectra. A high-pressure autoclave was used to monitor the formation process to determine hydrate onset time, initial growth rate, and conversion ratio. The obtained data from Raman spectra and gas consumption profiles suggested that hydrate formed within less than 20 min when the temperature is sufficiently lower than the hydrate equilibrium condition at a given pressure. Methane molecules started to occupy the small cages of structure II, but about 6 min later ethane and propane were also included in hydrate cages. 13 C NMR spectroscopy confirms that only 23% of large cages of structure II are occupied by methane molecules when hydrate formed from dispersed water in silica gel, which was much less than 68% from dry water. These results suggest that the dispersion of water in silica gel and dry water would enhance the formation process by increasing gas-to-water ratio, although the composition of hydrate phase may vary depending on the formation condition. However the formation of hydrate in silica gel and dry water still provide an effective option to capture the natural gas without using complex rotating machineries.Résumé : La présente étude a pour but d'étudier les caractéristiques de formation d'hydrates de gaz dans l'eau liquide et à partir d'eau dispersée dans du gel de silice ou de particules sèches contenant de l'eau lorsque ces corps sont exposés au gaz naturel. Nous avons observé le processus d'inclusion des molécules de méthane, d'éthane et de propane dans les cages d'hydrates au moyen de la spectroscopie Raman in situ et nous avons estimé les taux d'occupation des cages à partir des spectres RMN 13 C. Nous avons suivi le processus de formation grâce à un autoclave à haute pression afin de déterminer le délai de formation des hydrates, la vitesse de croissance initiale et le taux de conversion. Les données obtenues à partir des spectres Raman et des profils de consommation de gaz laissent supposer que les hydrates se sont formés en moins de 20 minutes lorsque la température est suffisamment en deçà des conditions d'équilibre des hydrates à une pression donnée. Les molécules de méthane ont d'abord occupé les petites cages de structure II, toutefois, environ 6 minutes plus tard, les molécules d'éthane et de propane étaient aussi incluses dans les cages d'hydrates. La spectroscopie RMN 13 C confirme que seulement 23 % des grandes cages de structure II sont occupées par des molécules de méthane lorsque les hydrates sont formés à partir d'eau dispersée dans du gel de silice, ce qui représente beaucoup moins que les 68 % qui sont occupées dans le cas des particules sèches contenant de l'eau. Ces résultats laissent supposer que la dis...

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