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Methane Hydrate Intrinsic Dissociation Kinetics Measured in a Microfluidic System by Means of in Situ Raman Spectroscopy

Chen, Weiqi, Hartman, Ryan L.
Energy & fuels 2018 v.32 no.11 pp. 11761-11771
Raman spectroscopy, dissociation, energy, fuels, heat transfer, laboratory techniques, methane, microfluidic technology, temperature, theoretical models
The present work investigates the dissociation kinetics of methane (sI) hydrate in a thermoelectrically cooled microfluidic system with in situ Raman spectroscopy. The dissociation profile of methane (sI) hydrate was measured under different Reynolds numbers (0.42–4.16), pressures (60.2 to 80.1 bar), and temperature driving force ([Tₑq – 0.1 K] to [Tₑq + 0.3 K]). A theoretical model was derived from first-principles to describe the contributions of heat transfer and intrinsic kinetics on the dissociation rate of methane hydrate. It was observed that the dimensionless ratio of heat transfer to the intrinsic dissociation rate depended on the initial thickness of methane hydrate, temperature driving force, pressure, and the time. Intrinsic kinetics dominated where the initial thickness of methane hydrate was in the range of 10 μm and the temperature driving force was low. Increasing initial thickness of methane hydrate resulted in a switch to a heat-transfer-limited dissociation. Our results support that the “memory effect” previously reported is the result of dissociation limited by intrinsic kinetics. Furthermore, this work introduces a new laboratory method of unusually sensitive microscale control of the dissociation conditions, while generating molecular-level insight. Our findings support that microfluidics with in situ Raman spectroscopy are excellent laboratory tools to understand methane hydrate dissociation with potentially much broader utility to the field. Methane hydrates play an important role in energy production and storage and the atmospheric and oceanic sciences.