In situ Raman spectroscopy investigation of the dissociation of methane hydrate at temperatures just below the ice point

Dissociation kinetics of methane hydrates was investigated by using in situ Raman spectroscopy at temperatures just below the melting point of ice. Measurements of decomposition rates were performed using finely powdered hydrate samples with a diameter range of 100-250 mum. It was found that the dissociation rate of methane hydrate at 0.1 MPa is considerably faster than that at 0.25 and 0.5 MPa. A kinetic model using non steady-state approximation and a diffusion-controlled regime is presented for describing the decomposition behavior of methane hydrates. This approach would be effective for modeling the dissociation of methane hydrate in the early stages of dissociation. The diffusion coefficients of methane molecules through the hydrate surface coated with ice are estimated to be 1.7 x 10(-13), 6.7 x 10(-14), and 2.9 x 10(-14) m(2)/s at 272.65, 271.15, and 268.15 K, respectively.