High-Pressure Phase Equilibrium and Raman Spectroscopic Studies on the Nitrous Oxide Hydrate System

摘要

Thermodynamic stability boundaries of nitrous oxide (N2O) hydrate and Raman spectra of the N2O and host water molecules in the N2O hydrate system were investigated in a temperature range of (275.20 to 298.19) K and a pressure range up to 305 MPa. Two three-phase coexisting curves of (hydrate + aqueous + gas) and (hydrate + aqueous + liquid N2O) originate from the quadruple point of (hydrate + aqueous + liquid N2O + gas) located at (285.15 ± 0.05) K and (4.2 ± 0.1) MPa. The phase behavior of the N2O hydrate system is similar to that of the carbon dioxide (CO2) hydrate system up to 100 MPa, while the stability boundaries of the N2O hydrate system are shifted parallel to the (2 to 3) K higher temperature side than that of CO2 hydrate. Raman peak splitting of the intramolecular vibration mode for the nitrous oxide molecule in the hydrate phase indicates the occupancy of the nitrous oxide molecule in both small and large cages of structure-I, and this observation is also corroborated by the pressure-induced Raman shift of the lattice mode.