Hydrates, clathrate

Clathrate hydrates the other common solid water phase,  

Clathrate Hydrates Clathrate structures in which the framework is composed of polyhedral water cages, capable of encapsulating neutral, non-polar guest species. 

Crystal system Primitive cubic Face-centred cubic Hexagonal 

Cavities are formed by a temptation process around the guest species and therefore smaller guests tend to favour the formation of strucfures in which there is a higher proportion of the smaller 5 cavities. The 5 cages are marginally larger in type-I hydrates due to the surrounding environment and this can sometimes 

Guest species that reside within clathrate hydrates do not participate in strong interactions with the water framework and are most often hydrophobic in nature. Molecules that are good hydrogen bond donors or acceptors (such as carboxylic acids, amines or alcohols) will disrupt the interactions between the water molecules and therefore prevent the hydrate network from forming. The most suitable guests are relatively small, non-polar species, such as halides, noble gases and small hydrocarbons. 

Solid clathrate hydrates are formed under very specific conditions of temperature and pressure. It is one of their most important and remarkable properties that they are often stable solids well above the 0 °C melting point of the most common form of pure ice (symbol Ih, meaning ice-hexagonal). Indeed, some gas hydrates are stable up to 31.5 °C. This property was noted by Davy, who commented on his chlorine (then called oxymuriatic gas) hydrate  

It is generally stated in chemical books, that oxymuriatic gas is capable of being condensed and crystallised at low temperature I have found by several experiments that this is not the case. The solution of oxymuriatic gas in water freezes more readily than pure water, but the pure gas dried by muriate of lime [anhydrous calcium chloride] undergoes no change whatever at a temperature of 40 below 0 of Fahrenheit. 

Alireza Shariati, Sana Raeissi, and CorJ. Peters 

3) moderate synthesis pressure (preferably less than 400 MPa, the pressure that can be reached by a simple compressor) 

4) near ambient pressure and moderate temperature for storage 

The most common vays of storing hydrogen fuel as liquid hydrogen and compressed hydrogen gas have the dra vbacks that the fuel needs to be stored at extremely low temperatures (20 K for liquid hydrogen) or at high pressures (35 MPa for compressed hydrogen) [2]. 

To overcome such issues, much attention is currently being given to storing hydrogen in solid-state materials. Recently emerging materials include doped carbon-based nanostructures [3], metal organic frame vorks [4], metallic hydrides [5], complex hydrides and destabilized hydrides [6, 7]. Ho vever, no material so 

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The history of iaclusion compounds (1,2) dates back to 1823 when Michael Faraday reported the preparation of the clathrate hydrate of chlorine. Other early observations iaclude the preparation of graphite iatercalates ia 1841, the P-hydroquiaone H2S clathrate ia 1849, the choleic acids ia 1885, the cyclodexthn iaclusion compounds ia 1891, and the Hofmann s clathrate ia 1897. Later milestones of the development of iaclusion compounds refer to the tri-(9-thymotide benzene iaclusion compound ia 1914, pheaol clathrates ia 1935, and urea adducts ia 1940. 

Fig. 11. Clathrate hydrates (a) basic structural component (H4QO2Q pentagonal dodecahedron) (b) type I host stmcture (two face-sharing 14-hedra are...

E. D. Sloan, Jr., Clathrate Hydrates of Natural Gases, Marcel Dekker, New York, 1989. 

Clathrate Hydrates of Natural Gases, E. Dendy Sloan, Jr. 

Industrial Gases in Petrochemical Processing, Harold Gunardson Clathrate Hydrates of Natural Gases Second Edition, Revised and Expanded, E. Dendy Sloan, Jr. 

Gaseous SO2 is readily soluble in water (3927 cm SO2 in lOOg H2O at 20°). Numerous species are present in this aqueous. solution of sulfurous acid" (p. 717). At 0° a cubic clathrate hydrate also forms with a composition S02.6H20 it.s dissociation pressure reaches I atm at 7.1°. The ideal composition would be SO2.55H2O (p. 627). 

CIO2 dissolves exothermically in water and the dark-green solutions, containing up to 8g/l, decompose only very slowly in the dark. At low temperatures crystalline clathrate hydrates, C102.nH20, separate (n 6-10). Illumination of neutral aqueous solutions initiates rapid photodecomposition to a mixture of chloric and hydrochloric acids ... 

Davidson, D. W. Clathrate Hydrates, in Water — a Comprehensive Treatise (ed. Franks, F.), Vol. 2, chapter 3, New York, Plenum Press 1973... 

A rather nnexpected solnbilization phenomenon has also been described, i.e., the pressnre-indnced encapsnlation of low-molecnlar-weight gases in the aqneons micellar core, followed by clathrate hydrate formation [144,145],... 

Classifying particles, in filtration, 11 326 Class I hybrids, 13 536, 543, 544 Class II hybrids, 13 536, 543 Clastogenesis, 25 206 Clathrate hydrates, 14 170—171 Clathrate receptor chemistry, 16 797 Clathrates, 12 374 14 159, 170-182 formation of, 10 633-635 26 869 Hofmann- and Werner-type, 14 171-172 phenol-type, 14 180 tri-o-thymotide, 14 179 Claus catalysts... 

Some gases have subsurfece sources that are related to physical phenomena, such as inputs from the introduction of hydrothermal fluids in bottom waters or release from warming sediments. The latter is a source of methane, which can occur in sediments in a solid phase called a clathrate hydrate. Biogeochemical reactions in sediments can also produce gases that diffuse from the pore waters into the deep sea. 

Clathrate hydrates Solid cages of water that form around small gas molecules such as methane, hydrogen, or carbon dioxide under conditions of high pressure and low temperature such as found on the deep sea floor and within the sediments. 

In an oligonucleotide-drug hydrate complex, the appearance of a clathrate hydrate-like water structure prompt a molecular dynamics simulation (40). Again the results were only partially successful, prompting the statement, "The predictive value of simulation for use in analysis and interpretation of crystal hydrates remains to be established." However, recent molecular dynamics calculations have been more successful in simulating the water structure in Ae host lattice of a-cyclodextrin and P-cyclodextrin in the crystal structures of these hydrates (41.42). 

Clathrate Hydrate Crystallization for Clean Energy and Environmental Technologies... 

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