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Encyclopedia > Clathrate hydrate

Clathrate hydrates (or alternatively gas clathrates, gas hydrates, clathrates, hydrates etc) are a class of solids in which gas molecules occupy "cages" made up of hydrogen-bonded water molecules. These "cages" are unstable when empty, collapsing into conventional ice crystal structure, but they are stabilized by the inclusion of appropriately sized molecules within them. Most low molecular weight gases (including O2, H2, N2, CO2, CH4, H2S, Ar, Kr, and Xe), as well as some higher hydrocarbons and freons will form hydrate under certain pressure-temperature conditions. Clathrate hydrates are not chemical compounds. The formation and decomposition of clathrate hydrates are first order phase transitions, not chemical reactions. For other uses, see Solid (disambiguation). ... Gas can also refer to gasoline and natural gas and also hydrogen. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... An example of a quadruple hydrogen bond between a self-assembled dimer complex reported by Meijer and coworkers. ... H2O and HOH redirect here. ... For other uses, see Crystal (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Methane is a chemical compound with the molecular formula CH4. ... Hydrogen sulfide (hydrogen sulphide in British English) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs and flatulence. ... Hydrogen sulfide (hydrogen sulphide in British English) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs and flatulence. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... For other uses, see Krypton (disambiguation). ... General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ... Freon is a trade name for a group of chlorofluorocarbons used primarily as a refrigerant. ... Hydrate is a term which means different things in inorganic chemistry and organic chemistry. ... This diagram shows the nomenclature for the different phase transitions. ...


Clathrates are believed to occur in large quantities on some outer planets, moons and trans-Neptunian objects, binding gas at fairly high temperatures. Clathrates have also been discovered in large quantity on Earth, i.e. in giant natural methane clathrate deposits on the deep ocean floor (e.g. in the northern headwall flank of the Storegga Slide, which is a part of the Norwegian continental shelf) and in permafrost regions (e.g. the Mallik gas hydrate field in the Mackenzie Delta of northwestern Canadian Arctic). Hydrocarbon clathrates are a problem for the petroleum industry, since their formation inside gas pipelines frequently leads to plug formation in the latter. Deep sea deposition of carbon dioxide clathrate to remove this greenhouse gas from the atmosphere has also been proposed. This article is about the astronomical term. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... This article is about Earth as a planet. ... Burning ice. Methane, released by heating, burns; water drips (USGS). ... The seabed (also sea floor, seafloor, or ocean floor) is the bottom of the ocean. ... The three Storegga Slides count among the largest recorded landslides. ... The Norwegian continental shelf is the continental shelf over which Norway exercises sovereign rights as defined by the United Nations Convention on the Law of the Sea. ... In geology, permafrost or permafrost soil is soil at or below the freezing point of water (0°C or 32°F) for two or more years. ... Mackenzie Delta is a territorial electoral district for the Legislative Assembly of Northwest Territories, Canada. ... The North, the Canadian Arctic defined politically. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ... Zygmunt Florenty Wróblewski Carbon dioxide hydrate is a Type I gas clathrate (Sloan 1998). ... Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. ...

Contents

Structure

Cages building the different gas hydrate structures.
Cages building the different gas hydrate structures.

Gas hydrates usually form two crystallographic cubic structures – structure (Type) I and structure (Type) II[1] of space groups Pmoverline{3}n and Fdoverline{3}m respectively. Seldom, a third hexagonal structure of space group P6 / mmm maybe observed (Type H).[2] Image File history File links Metadata Size of this preview: 476 × 599 pixelsFull resolution (1800 × 2265 pixels, file size: 891 KB, MIME type: image/jpeg) Author: GGenov, Source: GGenov, I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms... Image File history File links Metadata Size of this preview: 476 × 599 pixelsFull resolution (1800 × 2265 pixels, file size: 891 KB, MIME type: image/jpeg) Author: GGenov, Source: GGenov, I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ...


The unit cell of Type I consists of 46 water molecules, forming two types of cages – small and large. The small cages in the unit cell are two against six large ones. The small cage has the shape of a pentagonal dodecahedron (512) and the large one that of a tetradecahedron, specifically a hexagonal truncated trapezohedron (51262). Typical guests forming Type I hydrates are CO2 in carbon dioxide clathrate and CH4 in methane clathrate. A dodecahedron is any polyhedron with twelve faces, but usually a regular dodecahedron is meant: a Platonic solid composed of twelve regular pentagonal faces, with three meeting at each vertex. ... A tetradecahedron is a polyhedron with 14 faces. ... The hexagonal truncated trapezohedron is the fourth in an infinite series of truncated trapezohedron polyhedra. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Zygmunt Florenty Wróblewski Carbon dioxide hydrate is a Type I gas clathrate (Sloan 1998). ... Methane is a chemical compound with the molecular formula CH4. ... Burning ice. Methane, released by heating, burns; water drips (USGS). ...


The unit cell of Type II consists of 136[citation needed] water molecules, forming also two types of cages – small and large. In this case the small cages in the unit cell are sixteen against eight large ones. The small cage has again the shape of a pentagonal dodecahedron (512) but the large one is a hexadecahedron (51264). Type II hydrates are formed by gases like O2 and N2.


The unit cell of Type H consists of 34 water molecules, forming three types of cages – two small of different type and one huge. In this case, the unit cell consists of three small cages of type 512, twelve small ones of type 435663 and one huge of type 51268. The formation of Type H requires the cooperation of two guest gases (large and small) to be stable. It is the large cavity that allows structure H hydrates to fit in large molecules (e.g. butane, hydrocarbons), given the presence of other smaller help gases to fill and support the remaining cavities. Structure H hydrates were suggested to exist in the Gulf of Mexico. Thermogenically-produced supplies of heavy hydrocarbons are common there. Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH3CH2CH2CH3. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ...


Hydrates in the Universe

Iro et al. [3], trying to interpret the nitrogen deficiency in comets, stated most of the conditions for hydrate formation in the protoplanetary nebulae, surrounding the pre-main and main sequence stars were fulfilled, despite the rapid grain growth to meter scale. The key was to provide enough microscopic ice particles exposed to a gaseous environment. Observations of the radiometric continuum of circumstellar discs around τ-Tauri and Herbig Ae/Be stars suggest massive dust disks consisting of millimeter-sized grains, which disappear after several million years (e.g. [4], [5]). A lot of work on detecting water ices in the Universe was done on the Infrared Space Observatory (ISO). For instance, broad emission bands of water ice at 43 and 60 μm were found in the disk of the isolated Herbig Ae/Be star HD 100546 in Musca. The one at 43 μm is much weaker then the one at 60 μm, which means the water ice, is located in the outer parts of the disk at temperatures below 50 K [6]. There is also another broad ice feature between 87 and 90 μm, which is very similar to the one in NGC 6302 [7] (the Bug or Butterfly nebula in Scorpius). Crystalline ices were also detected in the proto-planetary disks of ε-Eridani and the isolated Fe star HD 142527[8][9] in Lupus. 90 % of the ice in the latter was found crystalline at temperature around 50 K. HST demonstrated that relatively old circumstellar disks, as the one around the 5 million year old B9.5Ve[10] Herbig Ae/Be star HD 141569A, are dusty[11]. Li & Lunine[12] found water ice there. Knowing the ices usually exist at the outer parts of the proto-planetary nebulae, Hersant et al.[13] proposed an interpretation of the volatile enrichment, observed in the four giant planets of the Solar System, with respect to the Solar abundances. They assumed the volatiles had been trapped in the form of hydrates and incorporated in the planetesimals flying in the protoplanets’ feeding zones. General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In telecommunication and physics, radiometry is the science of radiation measurement. ... Continuum theories or models explain variation as involving a gradual quantitative transition without abrupt changes or discontinuities. ... A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... Drawing of a T-Tauri star with a circumstellar accretion disk T Tauri stars are a class of variable stars named after their prototype - T Tauri. ... Herbig Ae/Be stars are pre-main sequence stars - young (<10Myr) stars of spectral types A and B. They are still embedded in the gas-dust envelopes and may be surrounded by circumstellar disks. ... The Infrared Space Observatory (ISO)is a space telescope for infrared light designed and operated by the European Space Agency (ESA). ... Spectral bands are part of optical spectra of polyatomic systems, including condensed materials, large molecules etc. ... Herbig Ae/Be stars are pre-main sequence stars - young (<10Myr) stars of spectral types A and B. They are still embedded in the gas-dust envelopes and may be surrounded by circumstellar disks. ... Musca (Latin for Fly) is one of the minor southern constellations. ... NGC 6302 (also called the Bug Nebula or Butterfly Nebula), is a bipolar planetary nebula in the constellation Scorpius. ... This article is about the constellation. ... Epsilon Eridani (ε Eri / ε Eridani) is a notable main-sequence K2 class star in the constellation of Eridanus. ... Lupus (Latin for Wolf) is a southern constellation. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... Herbig Ae/Be stars are pre-main sequence stars - young (<10Myr) stars of spectral types A and B. They are still embedded in the gas-dust envelopes and may be surrounded by circumstellar disks. ... A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... Volatility in physics is a measure of the speed at which a chemical element or chemical compound evaporates. ... This article does not cite any references or sources. ... This article is about the Solar System. ... The abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. ... Volatility in physics is a measure of the speed at which a chemical element or chemical compound evaporates. ... Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks. ... Protoplanets are moon-sized planet embryos within protoplanetary discs. ...


Kieffer et al. (2006) suggest that the geyser activity in the south polar region of Saturn's moon Enceladus originates from clathrate hydrates, where carbon dioxide, methane, and nitrogen are released when exposed to the vacuum of space by the "Tiger Stripe" fractures found in that area.[14] Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... Atmosphere Surface pressure: trace, significant spatial variability[8][9] Composition: 91% Water vapour 4% Nitrogen 3. ... Cassini view of Enceladus south pole and the tiger stripes Tiger Stripes consist of four, sub-parallel, linear depressions in the south polar region of Saturns moon Enceladus. ...


Carbon dioxide clathrate is believed to play a major role in different processes on Mars. Zygmunt Florenty Wróblewski Carbon dioxide hydrate is a Type I gas clathrate (Sloan 1998). ...


Hydrates on Earth

Natural gas hydrates

Main article: Methane hydrate

Naturally on Earth gas hydrates can be found on the seafloor, in ocean sediments, as well as in the permafrost regions. The amount of methane potentially trapped in natural Methane hydrate deposits may be significant, which makes them of major interest as a potential energy resource for the future. Catastrophic release of methane from the decomposition of such deposits may lead to a global climate change, since CH4 is more efficient greenhouse gas even than CO2(see Methane). On its turn, the fast decomposition of such deposits is considered a geohazard, due to its potential to trigger landslides, earthquakes and tsunamis. However, natural gas hydrates do not contain only methane but also other hydrocarbon gases, as well as H2S and CO2. Air hydrates are frequently observed in polar ice samples. Pingos are common structures in perma frost regions. Simllar structures are found in deep water related to methane leakages. Methane Leakage from Pingo-like Features on the Arctic Shelf, Beaufort Sea, NWT, Canada Authors: Ussler, W.; Paull, C. K.; Lorenson, T.; Dallimore, S.; Medioli, B.; Blasco, S.; McLaughlin, F.; Nixon, F. M. [[1]] Burning ice. Methane released by heating burns, water drips. ... This article is about Earth as a planet. ... The seabed (also sea floor, seafloor, or ocean floor) is the bottom of the ocean. ... In geology, permafrost or permafrost soil is soil at or below the freezing point of water (0°C or 32°F) for two or more years. ... Methane is a chemical compound with the molecular formula CH4. ... Burning ice. Methane released by heating burns, water drips. ... Methane is a chemical compound with the molecular formula CH4. ... This article is about geological phenomenon. ... This article is about the natural seismic phenomenon. ... For other uses, see Tsunami (disambiguation). ... Methane is a chemical compound with the molecular formula CH4. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ... Hydrogen sulfide (hydrogen sulphide in British English) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs and flatulence. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... A pingo is a mound of earth-covered ice found in the Arctic, subarctic, and Antarctica that can reach up to 70 metres in height and up to 600 hundred metres in diameter. ...


Gas hydrates in pipelines

Thermodynamic conditions favouring hydrate formation are often found in pipelines. This is highly undesirable because the clathrate crystals might agglomerate and cause plugging of the flow-line, valves and instrumentation. The results can range from reduction of the flow to physical damages of the equipment.


Hydrate formation prevention and mitigation philosophy

Hydrates have a strong tendency to agglomerate and to adhere to the pipe wall and thereby plug the pipeline. Once formed, they can be decomposed by increasing the temperature and/or decreasing the pressure. Even at these conditions, the clathrate dissociation is a slow process. Agglomerate - Wikipedia /**/ @import /skins-1. ...


Therefore, preventing hydrate formation appears to be the key to the problem. A hydrate prevention philosophy could typically be based on three levels of security, listed in prioritised order:

  1. Avoid operational conditions that might cause formation of hydrates;
  2. Temporarily change operating conditions in order to avoid hydrate formation;
  3. Prevent formation of hydrates by addition of chemicals that (a) shift the hydrate equilibrium conditions towards lower temperatures and higher pressures or (b) increase hydrate formation time (inhibitors)

The actual philosophy would depend on operational circumstances such as pressure, temperature, type of flow (gas, liquid, presences of water etc.) A reaction inhibitor is a substance that prevents or decreases the rate of a chemical reaction. ...


Hydrate inhibitors

When operating within a set of parameters where hydrates could be formed, there are still ways to avoid their formation. Altering the gas composition by adding chemicals can lower the hydrate formation temperature and/or delay their formation. Two options generally exist:

  • Thermodynamic inhibitors
  • Kinetic inhibitors/anti-agglomerants

The most common thermodynamic inhibitors are, methanol, monoethylene glycol (MEG) and di-ethylene glycol (DEG) commonly referred to as glycol. All may be recovered and recirculated, but the economics of methanol recovery will not be favourable in most cases. MEG is preferred over DEG for applications where the temperature is expected to be −10 °C or lower due to high viscosity at low temperatures. TEG has too low vapour pressure to be suited as an inhibitor injected into a gas stream. More methanol will be lost in the gas phase when compared to MEG or DEG. Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). ... Ethylene glycol (monoethylene glycol (MEG), IUPAC name: ethane-1,2-diol) is an alcohol with two -OH groups (a diol), a chemical compound widely used as an automotive antifreeze. ... Diethylene glycol (DEG) is an organic compound described by the structural formula HO-CH2-CH2-O-CH2-CH2-OH. It is a clear, hygroscopic, odorless liquid. ... Ethylene glycol (IUPAC name:ethane-1,2-diol) is a chemical compound widely used as an automotive antifreeze (coolant). ...


The use of kinetic inhibitors and anti-agglomerants in actual field operations is a new and evolving technology. It requires extensive tests and optimisation to the actual system. While kinetic inhibitors work by slowing down the kinetics of the nucleation, anti-agglomerants do not stop the nucleation, they rather stop the agglomeration (sticking together) of gas hydrate crystals. These two kinds of inhibitors are also known as Low-Dosage-Hydrate-Inhibitors because they require much smaller concentrations than the conventional thermodynamic inhibitors. Kinetic inhibitors (which do not require water and hydrocarbon mixture to be effective) are usually polymers or copolymers and anti-agglomerants (requires water and hydrocarbon mixture) are polymers or zwitterionic (usually ammonium and COOH) surfactants being both attracted to hydrates and hydrocarbons.


See also

A clathrate or clathrate compound is a chemical substance consisting of a Greek klethra, meaning bars (in the sense of a lattice). ... This article is about the astronomical object. ...

References

  1. ^ von Stackelberg, M. & Müller, H. M. (1954) Zeitschrift für Elektrochemie 58, 1, 16, 83
  2. ^ Sloan E. D., Jr. (1998) Clathrate hydrates of natural gases. Second edition, Marcel Dekker Inc.:New York.
  3. ^ Iro, N., Gautier, D., Hersant, F., Bockelée-Morvan, D. & Lunine, J. I. (2003) An interpretation of the Nitrogen deficiency in comets. Icarus, 161, p. 513
  4. ^ Beckwith, S. V. W., Henning, T., & Nakagawa, Y. (2000) Dust properties and assembly of large particles in protoplanetary disks. Protostars and Planets IV, p. 533
  5. ^ Natta, A., Grinin, V. & Mannings, V. (2000) Properties and Evolution of Disks around Pre-Main-Sequence Stars of Intermediate Mass. Protostars and Planets IV, p. 559
  6. ^ Malfait, K., Waelkens, C., Waters, L. B. F. M., Vandenbussche, B., Huygen, E. & de Graauw, M. S. (1998) The spectrum of the young star HD 100546 observed with the Infrared Space Observatory. Letter to the Editor Astron. Astrophys. 332, p. L25-L28
  7. ^ Barlow, M.J., In the proceedings of ‘ISO’s view on stellar evolution’, Noordwijkerhout, July, 1-4, 1997
  8. ^ Li, A., Lunine, J. I. & Bendo, G. J. (2003) Modeling the infrared emission from the ε-Eridani disk. Astrophys. J. 598, pp. L51-L54
  9. ^ Malfait, K., Waelkens, C., Bouwman, J., de Koter, A. & Waters, L. B. F. M. (1999) The ISO spectrum of the young star HD 142527. Astron. Astrophys. 345, p. 181
  10. ^ Jaschek, C. & Jaschek, M. (1992) Astron. Astrophys., 95, p. 535
  11. ^ Clampin, M. et al. (2003) Hubble Space Telescope ACS Coronagraphic Imaging of the Circumstellar Disk around HD 141569A. Astron. J. 126, pp. 385-392
  12. ^ Li, A. & Lunine, J. I. (2003) Modeling the infrared emission from the HD 141569A disk. Astrophys. J. 594, pp. 987-1010
  13. ^ Hersant, F., Gautier, D., Lunine, J. I. (2004) Enrichment in volatiles in the giant planets of the Solar System. Planetary and Space Science 52 , p. 623
  14. ^ Kieffer, Susan W.; Xinli Lu, Craig M. Bethke, John R. Spencer, Stephen Marshak, Alexandra Navrotsky (2006). "A Clathrate Reservoir Hypothesis for Enceladus' South Polar Plume". Science 314 (5806): 1764-1766. doi:10.1126/science.1133519. 

  Results from FactBites:
 
MBARI - Ocean Chemistry of Greenhouse Gases (517 words)
Gas hydrates are a solid ice-like phase formed at low temperature and high pressure by van der Waals forces between gas and water molecules, with the "host" water molecules forming a molecular cage which confines the "guest" gas molecules through their mutual electrostatic interaction.
In the ocean, gas hydrates composed dominantly of methane are common constituents of the shallow marine geosphere (Kvenvolden, 1993), and they occur both in deep sedimentary structures (Dickens et al., 1997), and as outcrops on the ocean floor (MacDonald et al., 1994).
Gas hydrate formation in the ocean does not involve shaking, and ice crystals are not part of the natural deep sea environment, and therefore laboratory experiments carried out to date have not been able to simulate natural processes.
Methane clathrate information - Search.com (1365 words)
Methane clathrate, also called methane hydrate or methane ice, is a form of water ice that contains a large amount of methane within its crystal structure (a clathrate hydrate).
Methane hydrates are believed to form by migration of gas from depth along geological faults, followed by precipitation, or crystallization, on contact of the rising gas stream with cold sea water.
Methane clathrates remain stable at temperatures up to 18 °C. The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water, though this is dependent on how many methane molecules "fit" into the various cage structures of the water lattice.
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