Methane + Propane Structure II Hydrate Formation Kinetics

The growth rates of methane (CH 4 ) + propane (C 3 H 8 ) structure II (sII) hydrates were measured via 13 C NMR in a custom-built nonspinning probe. The CH 4 + C 3 H 8 hydrate surface reaction growth data suggested that the large cages occupied by C 3 H 8 formed twice as fast as small cages filled with CH 4, although there were half as many large 5 12 6 4 cages as small 5 12 cages in a sII unit cell. Growth rates were measured at 269 K as a function of ice particle size ranging between 150 and 1180 μm, and vapor pressure in the range 0.34−0.84 MPa. A hypothesis based on low occupancy of sII small cages was presented to explain faster growth of large cages. A simple surface reaction model, which related growth rate to pressure and particle size, was developed.