Investigation on methane hydrate formation in silica gel particles below the freezing point

Herein, methane hydrate formation in silica gel was studied in the temperature and pressure range of 253.1-268.1 K and 4.0-6.0 MPa, respectively. The stability of the hydrate and the morphology of methane hydrate formed in silica gel were analyzed by P-XRD and cryo-SEM technology. An NG_t of 0.150 mol mol^-1 and the conversion of water to hydrate completely were realized at 253.1 K and 6 MPa. But the fastest NR₁₂₀ of 52.96 mol min^-1 m^-3 and shortest T ₉₀ of 160 min were achieved at 263.1 K and 6 MPa. The NG_t of 0.136 and 90.93% water conversion to hydrate were realized at 263.1 K and 6 MPa. The temperature range of 263.1-268.1 K was the optimal temperature for methane hydrate formation and dissolution. From P-XRD patterns and cryo-SEM images, it was confirmed that most of the cubic ice was formed on the silica gel surface and it was metastable. All the silica gel spherical surfaces were covered with intermittent ice particles. Most of the methane hydrate was formed on the interconnection surface between silica gel particles rather than on the single silica gel spherical surface. The methane hydrate formed on the silica gel surface decomposed faster than pure water methane hydrate.