Phase Equilibrium for Gas Hydrates Formed from Deuterium Oxide

Abstract

In this study, we measured the hydrate equilibrium conditions for simple methane, ethane, propane, and krypton hydrates formed from liquid/solid deuterium oxide in order to understand the effect of deuterium replacement in the host framework on the gas hydrate equilibrium conditions. We obtained the equilibrium conditions by recording pressure and temperature for gas hydrate formation and dissociation under deuterium oxide-rich conditions in the pressure range of (0.142 to 5.49) MPa and the temperature range of (263.4 to 282.3) K. The hydrate equilibrium pressure for deuterium oxide systems at a fixed temperature decreases in the order of methane, krypton, ethane, and propane. The hydrate equilibrium temperatures for all liquid deuterium oxide systems increase compared with those for its usual liquid water systems at fixed pressure. The deuterium isotopic effect of host water molecules on hydrate equilibrium temperatures for the three phases including liquid water at a fixed pressure becomes greater in the order of methane, ethane, krypton, and propane. The hydrate equilibrium conditions for all solid deuterium oxide systems are approximately consistent with those for its usual liquid water systems. The gas hydrate crystals formed from deuterium oxide were characterized by 13C NMR spectroscopy.