Structural Chemistry of Clathrate Hydrates and Related Compounds

Manakov, Andrey Yu.; Kosyakov, V. I.; Солодовников, С. Ф.

doi:10.1016/b978-0-12-409547-2.13645-5

Cited by 18 publications

(16 citation statements)

References 404 publications

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“…Finally, unit cell of sH hydrates consists of 3 dodecahedron, 2 irregular dodecahedron and one irregular icosahedron cavities; the cell consists of 34 water molecules; sH type hydrates are formed if heavy molecules such as 2,2-dimethylbutane, methylcyclopentane are present in a mixture of hydrocarbons. More information can be found in [2,3].…”

Section: Introductionmentioning

confidence: 99%

Influence of Water Saturation, Grain Size of Quartz Sand and Hydrate-Former on the Gas Hydrate Formation

et al. 2021

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The development of technologies for the accelerated formation or decomposition of gas hydrates is an urgent topic. This will make it possible to utilize a gas, including associated petroleum one, into a hydrate state for its further use or to produce natural gas from hydrate-saturated sediments. In this work, the effect of water content in wide range (0.7–50 mass%) and the size of quartz sand particles (porous medium; <50 μm, 125–160 μm and unsifted sand) on the formation of methane and methane-propane hydrates at close conditions (subcooling value) has been studied. High-pressure differential scanning calorimetry and X-ray computed tomography techniques were employed to analyze the hydrate formation process and pore sizes, respectively. The exponential growth of water to hydrate conversion with a decrease in the water content due to the rise of water–gas surface available for hydrate formation was revealed. Sieving the quartz sand resulted in a significant increase in water to hydrate conversion (59% for original sand compared to more than 90% for sieved sand). It was supposed that water suction due to the capillary forces influences both methane and methane-propane hydrates formation as well with latent hydrate forming up to 60% either without a detectable heat flow or during the ice melting. This emphasizes the importance of being developed for water–gas (ice–gas) interface to effectively transform water into the hydrate state. In any case, the ice melting (presence of thawing water) may allow a higher conversion degree. Varying the water content and the sand grain size allows to control the degree of water to hydrate conversion and subcooling achieved before the hydrate formation. Taking into account experimental error, the equilibrium conditions of hydrates formation do not change in all studied cases. The data obtained can be useful in developing a method for obtaining hydrates under static conditions.

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Section: Introductionmentioning

confidence: 99%

Influence of Water Saturation, Grain Size of Quartz Sand and Hydrate-Former on the Gas Hydrate Formation

et al. 2021

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“…Gas hydrates are inclusion compounds with the crystal framework of water molecules, which are linked to each other by hydrogen bonds. The cavities of this framework can include the molecules of gases so that up to 180 gas volumes may be in the unit volume of hydrate. , Gas hydrates deposits are widespread in nature. The world resources of natural gas in the hydrate state are estimated at 2 × 10 14 –5 × 10 15 m 3 , which exceeds the resources of gas in traditional-type deposits .…”

Section: Introductionmentioning

confidence: 99%

“… a Purple is the outer surface consisting of SiO 2 , and orange is the inner surface of Al 2 O 3 ; unit cell of cubic structure I hydrate was adapted with permission from Elsevier …”

Section: Introductionmentioning

confidence: 99%

Methane Hydrate Formation in Halloysite Clay Nanotubes

Stoporev

Semenov

et al. 2020

ACS Sustainable Chem. Eng.

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Equilibrium conditions of methane hydrate formation in the lumens of natural clay nanotubes were analyzed. The water adsorbed by the pristine nanotubes is capable to form methane hydrate in the confined hydrophilic inner pores of 10–100 nm (surface chemistry of the inner lumens is Al2O3, and external tube’s surface is SiO2). From 17.5 wt % of water adsorbed by the clay, 12 wt % was involved in methane hydrate formation (conversion ≈ 70%). The crystal structure of the hydrate inside the nanoconfined spaces of halloysite did not change as compared with bulk systems. The formation of methane hydrate occurs during cooling at 0–6 °C simultaneously over the whole clay sample, indicating the catalytic activity of halloysite surface. This formulation slows down decomposition of the hydrate confined in the pores at atmospheric pressure at temperatures below 0 °C. The water is retained in the inner clay pores over the formation and decomposition of methane hydrate. We also modified halloysite nanotubes with mesoporous silica MCM-41 (similar silica gel and sand are routinely used for gas hydrate formation) increasing the ratio of SiO2 to Al2O3 to compare methane hydrate formation in these chemically different pores. This allowed us to decrease substantially pore dimensions in the hybrid system (to 2–3 nm). The fraction of methane hydrate stable within the temperature range from −18 to 10 °C in this smaller pore hybrid system was 8 times less as compared to unmodified halloysite. The very small pores of the halloysite/MCM-41 system allowed formation of hydrate only at a temperatures significantly less than −18 °C. Natural halloysite clay nanotubes were suggested as efficient solid containers for methane hydrates encasing. Halloysite is cheap and scalable up to thousands of tons; it is a mesomaterial capable of methane storage in clathrate hydrates with water-based green chemistry processing. Suggested nanoclay-based hydrate technology is also prospective for gas separation.

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“…Samples for PXRD were finely ground at a temperature of 77 K and then kept at 173 K. The X-ray diffraction patterns were recorded at 2θ = 5 − 35° using Cu Kα radiation (λ = 1.5418 Å) and a Bruker D8 Advance diffractometer equipped with a TTK 450 Anton Paar temperature controlling device. The positions of diffraction peaks corresponding to sI and sII hydrates and hexagonal ice (Ih) were calculated with the use of reference data on space group and unit cell parameters of the respective compounds 42 . Hydrate-bound gases were collected using water displacement method and stored in 5 mL glass vials sealed with butyl septum stoppers.…”

Section: Methodsmentioning

confidence: 99%

Characteristics of hydrate-bound gas retrieved at the Kedr mud volcano (southern Lake Baikal)

Hachikubo

Minami

Khabuev

et al. 2020

Sci Rep

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We reported the characteristics of hydrate-bound hydrocarbons in lake-bottom sediments at the Kedr mud volcano in Lake Baikal. Twenty hydrate-bearing sediment cores were retrieved, and methane-stable isotopes of hydrate-bound gases (δ13C and δ2H of − 47.8‰ to − 44.0‰ V-PDB and − 280.5‰ to − 272.8‰ V-SMOW, respectively) indicated their thermogenic origin accompanied with secondary microbial methane. Powder X-ray diffraction patterns of the crystals and molecular composition of the hydrate-bound gases suggested that structure II crystals showed a high concentration of ethane (around 14% of hydrate-bound hydrocarbons), whereas structure I crystals showed a relatively low concentration of ethane (2–5% of hydrate-bound hydrocarbons). These different crystallographic structures comprised complicated layers in the sub-lacustrine sediment, suggesting that the gas hydrates partly dissociate, concentrate ethane and form structure II crystals. We concluded that a high concentration of thermogenic ethane primarily controls the crystallographic structure of gas hydrates and that propane, iso-butane (2-methylpropane) and neopentane (2,2-dimethylpropane) are encaged into crystals in the re-crystallisation process.

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Structural Chemistry of Clathrate Hydrates and Related Compounds

Cited by 18 publications

References 404 publications

Influence of Water Saturation, Grain Size of Quartz Sand and Hydrate-Former on the Gas Hydrate Formation

Influence of Water Saturation, Grain Size of Quartz Sand and Hydrate-Former on the Gas Hydrate Formation

Methane Hydrate Formation in Halloysite Clay Nanotubes

Characteristics of hydrate-bound gas retrieved at the Kedr mud volcano (southern Lake Baikal)

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