Phase Equilibrium of Hydrogen Clathrate Hydrates with Propylene Oxide and 1,2-Epoxycyclopentane

This study examined the phase behavior of hydrogen hydrates with additives containing oxygen-containing groups. The phase equilibrium of the H2 + propylene oxide (PO) + water hydrate system and the H2 + 1,2-Epoxycyclopentane (ECP) + water hydrate system was measured using the isochoric pressure search method. The mole fractions of PO and ECP were 0.056 and 0.028, respectively. The experimental data were determined in the temperature range of 273.90 to 285.20 K and the pressure range of 3.18 to 18.57 MPa. In the presence of PO and ECP, the hydrate phase equilibrium of the systems moved to a lower pressure and a higher temperature region compared to that of the hydrogen hydrates without additives. The addition of ECP with a mole fraction of 0.056 had the best promotion effect among all reported sII-type thermodynamic additives. The data obtained in this study also showed that the equilibrium was affected by the ether (c-o-c) functional group in epoxy heterocycle compounds, which was the effective functional group in changing the equilibrium conditions of hydrogen hydrates. The results provided a basis for hydrogen storage and transportation based on hydrate technology.