Effect of Temperature and Pressure on the Hydration Number of Methane Hydrate

Methane hydrates contain a certain number of empty cages that affect their stability and determine the gas-storage capacity of the material. In this study, the effects of temperature and pressure on the hydration number of methane hydrates were investigated in pressure and temperature ranges of 0.53–20.50 MPa and 226–273 K, respectively. Raman spectroscopy measurements showed that the hydration number ranged from 5.88 to 6.12, decreasing with increasing pressure and decreasing temperature. The occupancy of the large cages ranged from 97 to 99%, indicating that most of the cages were occupied. In contrast, small cage occupancy ranged from 82 to 96%, suggesting that small cage occupancy was significantly reduced under high-temperature and low-pressure conditions. The results of this study experimentally demonstrate the change in cage occupancy of methane hydrates as a function of formation temperature and pressure and will help future researchers comprehend not only the cage occupancy of host–guest compounds but also the amount of methane resources on earth.