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Ice That Burns: Methane Hydrate

© Linda Mamassian

You probably already know about regular ice -- frozen water -- and you may also be familiar with dry ice, frozen carbon dioxide. But have you every heard of ice that burns?

Methane hydrate, or gas hydrate, is an ice-like substance composed of methane (CH₄) -- the main constituent of natural gas -- trapped inside cages of water molecules (H₂O). Such a crystalline combination of a natural gas and water (known technically as a clathrate) looks very similar to ice but burns if it meets a lit match. It is formed at low temperatures and high pressures, with deposits found underneath permafrost in Arctic regions and beneath deep ocean floors.

Gas hydrates were first recognized 70 years ago and were considered a nuisance in the natural gas industry, an icy sludge that fouled natural gas pipelines. The fact that gas hydrates were first noticed in gas pipelines was no accident: pressurized lines contaminated with water happen to be a perfect environment for formation of the icy stuff.

In 1964, naturally occurring gas hydrates were found underground in a gas field in Siberia. Since then, geologists have found huge deposits of gas hydrates in ocean sediments that are at least 500 meters deep, where methane that is produced by decaying organisms or that is seeping up through the Earth's crust is trapped at high pressures (at least 26 times normal atmospheric pressure) and low temperatures (near the freezing point of water).

The U.S. Geological Survey and other studies have estimated that the energy locked up in methane hydrate deposits is equivalent to 250 trillion cubic meters of methane gas, more than twice the global reserves of all conventional gas, oil and coal deposits combined. The existence of this vast global storehouse of methane raises the possibility of using methane hydrate as a source of energy, especially since methane gas burns more efficiently and cleanly than any other fossil fuel, releasing less than half the amount of carbon dioxide when burned that oil and coal do.

CH₄ + 2O₂ CO₂ + 2H₂O (combustion of methane)

When brought to normal atmospheric pressure, methane hydrate will produce more than 160 times its original volume in gaseous methane. (Some have referred to it as a highly pressurized can of natural gas.) However, no method has been developed yet to extract the gas inexpensively, and no one knows how much is actually recoverable. A formidable obstacle to using hydrates as fuel is that when removed from its high-pressure,low-temperature environment the hydrate decomposes and releases the gas contained in it. Currently, there is no way to safely transport large amounts of hydrate to production facilities on land.

The copyright of the article Ice That Burns: Methane Hydrate in Chemistry is owned by Linda Mamassian. Permission to republish Ice That Burns: Methane Hydrate in print or online must be granted by the author in writing.