What is a methane hydrate or methane clathrate?
Methane hydrate, also known as methane clathrate, hydromethane, fire ice or methane ice, natural gas hydrate, is a solid compound with molecular formula 4CH4.23H2O.
In methane hydrate crystal structure, a large amount of methane accumulates in a solid form like ice.
Methane hydrate crystals also combine with hydrates of other hydrocarbons. These include propane hydrate and ethane hydrate.
Methane hydrates are usually found in areas of the world where temperatures are low and where water ice is prevalent.
In addition, significant deposits of methane hydrate have been found in sediments beneath the Earth’s ocean floor.
Methane hydrate is formed when hydrogen-bonded water molecules and methane gas molecules come in contact with each other at low pressure and low temperature below the ocean.
Methane clathrates are a common component of shallow marine subsoil and they occur in deep sedimentary structures and form extrinsic seabed.
In 2008, studies on the Antarctic Vostok and Epica Dome Sea Ice Core revealed that methane clathrates were present in the deep Antarctic ice core.
The ice-core methane clathrate record is a primary source of information on oxygen and carbon dioxide as well as global warming research.
What is the structure of methane hydrate?
The molecular structure or composition of methane clathrate hydrate is 4CH4.23H2O or (CH4)4(H2O)23. That is, one mole of methane is associated with 5.75 moles of water molecules.
Thus the amount of methane gas in one mole methane clathrate hydrate is 13.4% by mass. Although the actual composition is dependent on how many methane molecules fit into the various cage structures of the water lattice.
The observed density methane hydrate is around 0.9 g/cm3. It has been found by calculation that 1 litre of fully saturated methane clathrate solid contain about 120 grams of methane or around 169 litre of methane gas at 0 °C and 1 atm.
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.
Because of sharing of water molecules between cages, there are only 46 water molecules per unit cell.
Methane hydrate and global warming
As the temperature rises or the pressure decreases, it can easily decompose and release methane and water.
The conversion of this solid sediment methane hydrate into liquids and gases will create a loss of support and shear strength.
These can cause submarine slumping, landslides, or subsidence that can damage production equipment and pipelines.
Methane is a powerful organic greenhouse gas. Methane gas plays an active role in global warming.
Despite its short atmospheric half life of 12 years, methane has a global warming potential of 86 over 20 years and 34 over 100 years.
Methane clathrate or methane hydrate now contains a large amount of methane gas.
The sudden release of large amounts of methane gas trapped in the methane clathrate will cause climate change in the past and probably in the future.
Climate scientists have shown in their research that a large amount of methane gas is released from methane hydrate, increase the concentration of methane in the atmosphere.
Research carried out in 2008 in the Siberian Arctic found millions of tonnes of methane being released with concentrations in some regions reaching up to 100 times above normal.
While investigating the East Siberian Arctic Ocean during the summer, researchers were surprised by the high concentration of methane gas, and theorized that it was being released from pockets of methane clathrates embedded in ice on the sea floor.
Methane hydrate uses
A large amount of methane gas in methane hydrate is associated with water molecules. Of these, large amounts of propane and butane are stored in the form of hydrates.
This huge amount of methane gas is released from methane hydrate when the pressure is reduced or the temperature is increased. The largest source of methane and other hydrocarbons in the world is methane hydrate.
Methane hydrate or methane is the main source of fuel energy. Although methane hydrates deposits are located in difficult environments and present numerous technical challenges.
A variety of technologies could be developed to produce them using pressure reduction, ion exchange, and other processes that take advantage of their unique chemical and physical properties.
The United States, Canada, Japan and other countries around the world, including India, all have strong research programs to discover effective technologies for producing gas hydrates.