Geochemistry

Swapping Exhaust for Fuel

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Science  07 Nov 2003:
Vol. 302, Issue 5647, pp. 953
DOI: 10.1126/science.302.5647.953b

Large amounts of methane are stored as hydrates on continental margins and in permafrost regions. If the methane hydrates could be converted into CO2 hydrates, they would serve double duty as methane sources and CO2 storage sites. Lee et al. have investigated the dynamics and thermodynamics of the conversion in a solid-state NMR study.

Methane and CO2 form the same ice-like hydrate structure, with two small and six large cage-like sites per unit cell. When a methane hydrate is exposed to gas mixtures containing CO2, methane is replaced by CO2 in many of the large cages. The authors estimate that at least 64% of the methane could be recovered from methane hydrates in this way. Kinetic data show that the replacement is fast but does not reach the theoretical limit, probably because pockets of pure methane hydrates remain in the converted structure. Whether the process is feasible in natural gas hydrate deposits remains to be shown. — JFU

Angew. Chem. Int. Ed. 42, 5048 (2003).

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