Clathrates with methane

Sulfurous acid is an equilibrium mixture of two molecules (12a and 12b) in the former, it resembles phosphorous acid, with one of the H atoms attached directly to the S atom. These molecules are also in equilibrium with molecules of S02, each of which is surrounded by a cage of water molecules. The evidence for this equilibrium is that crystals of composition S02-aH20, with x about 7, are obtained when the solution is cooled. Such substances, in which a molecule occupies a cage formed by other molecules, are called clathrates. Methane, carbon dioxide, and the noble gases also form clathrates with water. 

Natural gas (methane) can be obtained from gas hydrates. Gas hydrates are also called clathrates or methane hydrates. Gas hydrates are potentially one of the most important energy resources for the future. Methane gas hydrates are increasingly considered a potential energy resource. Methane gas hydrates are crystalline solids formed by combination of methane and water at low temperatures and high pressures. Gas hydrates have an iee-hke crystalline lattiee of water molecules with methane molecules trapped inside. Enormous reserves of hydrates can be foimd imder eontinental shelves and on land under permafrost. The amount of organic... 

The Sill and Wilkening proposal that clathrates formed in the cold outer parts of the solar system and then transported to the inner solar system (e.g., in comets) might help account for the atmospheres of the terrestrial planets. They contend that infall of 1 ppm of ice-methane clathrate with noble gases dissolved as just described could account for the present inventories of Ar, Kr, and Xe in the terrestrial atmosphere. 

Figure 7 The propeller-shaped host tris(5-acetyl-3-thienyl) methane 31 forms a 3 1 clathrate with cyclohexane. Color code H, light blue host C, green O, red and S, yellow guest C, purple.

Many countries are investing in research into the extraction of methane from these clathrates. An exploration well drilled on land by Imperial Oil in 1971-1972 discovered methane clathrates under the Canadian Arctic permafrost at the edge of the Mackenzie Delta and the Beaufort Sea. This site is known as the Mallik gas hydrate field. It has become a major centre of research into methane clathrates with groups from Canada, the USA, Japan and India working under the umbrella organization known as the International Continental Scientific Drilling Program (ICDP). 

When the above solution is cooled, crystals with a composition of roughly SO2 7H2O form. This substance is an example of a clathrate, in which a molecule sits in a cage of other molecules. Methane, carbon dioxide, and the noble gases also form clathrates with water. 

Thiophens and Benzothiophens.—General. Tris-(5-acetyl-3-thienyI)methane (186) forms 2 1 clathrates with a wide variety of organic compounds. The magnetic circular dichroism of thiophen has been measured. The n.m.r. spectra of thiophen-2-aldehyde and of thiophen-2,5-dialdehyde, partially oriented in anisotropic soap solutions, have been reported. The c.d. spectra of (5)-(-)-a-hydroxy-2-thienylacetic acid (187) and of (/ )-(-)- -hydroxy-3-... 

Gas hydrates are a special form of clathrates. Here water is the host molecule. The first gas hydrate (with chlorine) was described in 1818 by Sir Humphrey Davy. Naturally-occurring gas hydrates in Siberia are methane hydrates. 

Figure 3.49 summarizes the oxygen isotope curve for the last 65 Ma. The most pronounced warming trend is expressed by a 1.5%o decrease in 8 0 and occurred early in the Cenozoic from 59 to 52 Ma, with a peak in Early Eocene. Coinciding with this event is a brief negative carbon isotope excursion, explained as a massive release of methane into the atmosphere (Norris and Rohl 1999). These authors used high resolution analysis of sedimentary cores to show that two thirds of the carbon shift occurred just in a few thousand years, indicating a catastrophic release of carbon from methane clathrates into the ocean and atmosphere. 

Lee, J.D. Song, M. Susilo, R. Englezos, P. (2006b). Dynamics of Methane-Propane Clathrate Hydrate Crystal Growth from Liquid Water with or without the Presence of n-Heptane. Crystal Growth Design, 6 (6), 1428-1439. 

Ohmura, R. Matsuda, S. Itoh, S. Ebinuma, T. Narita, H. (2005d). Clathrate Hydrate Crystal Growth in Liquid Water Saturated with a Guest Substance Observations in a Methane + Water System. Crystal Growth Design, 5(3), 953-957. 

Hydrate clathrates of organic compounds are thought to be responsible for the behavior of ice in the heads of comets and in wet methane under pressure.22 Unless methane is carefully dried, high-pressure lines may become clogged with the ice-like gas hydrate. There may be large deposits of methane hydrates, the ice that burns. beneath the ocean floor. 

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