Also known as hydromethane, methane ice, gas hydrate, and methane clathrate.
A large amount of methane that trapped within a crystal structure of water, forming a solid similiar to ice and formed a solid clathrate compound (clathrate hydrate).
Found under sediments on the ocean floors. Carbon that bound in gas hydrates is estimated to total twice the amount of carbon to be all known fossil fuels on earth.
Methane hydrates are believed to form by migration of gas from dept along geological faults, followed by precipitation, or crystallization on contact of the rising gas stream with cold sea water Methane clathrates are also present in
deep Antartic ice cores, and record a history of athmospheric methane concentrations, dating to 800,000 years ago. The ice-core methane clathrate record is a primary source of data for global warming research, along with oxygen and carbon dioxide.
Structure
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. The observed density is around 0.9 g/cm3. One litre of methane clathrate solid would therefore contain, on average, 168 litres of methane gas (at STP).
Methane forms a structure I hydrate with two dodecahedral (12 vertices, thus 12 water molecules) and six tetradecahedral (14 water molecules) water cages per unit cell. This compares with a hydration number of 20 for methane in aqueous solution. A methane clathrate MAS NMR spectrum recorded at 275 K and 3.1 MPa shows a peak for each cage type and a separate peak for gas phase methane. Recently, a clay-methane hydrate intercalate was synthesized in which a methane hydrate complex was introduced at the interlayer of a sodium-rich montmorillonite clay. The upper temperature stability of this phase is similar to that of structure I hydrate.
methane hydrates' structure
ocean floor decreased
methane's release from methane hydrates' crystal
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