Earth’s Cryosphere, 2011, Vol. XV, No. 4, p. 69-71

METASTABLE STATES OF GAS HYDRATES AT PRESSURES BELOW THE ‘ICE–HYDRATE–GAS’ EQUILIBRIUM

V.P. Melnikov, A.N. Nesterov, L.S. Podenko, A.M. Reshetnikov, V.V. Shalamov

Institute of Earth’s Cryosphere, Siberian Branch of the Russian Academy of Sciences, PO box 1230, Tyumen, 625000, Russia; nesterov@ikz.ru

Reported are experimental results on the behavior of methane, propane, and carbon dioxide hydrates at temperatures below 273 K and pressures below the ‘ice–hydrate–gas’ equilibrium, when ice is the stable phase. The study has furnished evidence for the formation of intermediate supercooled (metastable) water during gas hydrate dissociation. The pressures of hydrate dissociation into supercooled water and gas were measured at the temperature ranges 253–273 K for methane hydrate, 263–273 K for propane hydrate, and 249–273 K for carbon dioxide hydrate. The gas hydrates have been recognized to keep metastable for a long time within the P–T area in the phase diagram bounded by the ‘ice–hydrate–gas’ and ‘supercooled water–hydrate–gas’ metastable equilibrium lines. Contrary to what has been assumed for self-preservation of gas hydrate, their metastability has no relation with ice coating on hydrate particles.

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