Insights into the Kinetics of Methane Hydrate Formation in a Stirred Tank Reactor by In Situ Raman Spectroscopy

We present a new method to observe the kinetics of methane hydrate formation by the simultaneous application of macroscopic and microscopic measurements. In a stirred tank stabilized under two different subcooling conditions, both the consumption rate of methane by water and in situ Raman spectra were measured with time. According to our observations, an abrupt decline in the intensity of the Raman peak of dissolved methane coincided with an increase in the intensity of the Raman peak of methane that occupies the large cages of the hydrate at the beginning of hydrate formation. The occupancy of the small cages only occurred after a considerable delay from the nucleation point, whereas the occupancy of the large cages occurred throughout the growth period. Thus, the early stage of hydrate growth shows a strong preference of the dissolved methane to occupy the large cages.