(31a) Methane (sI) Hydrate Crystallization and Dissociation in a Thermoelectrically-Cooled Microreactor

Clathrate hydrates are crystalline materials with hydrogen bonded water clusters entrapping small molecules. They are potential materials for energy, gas storage, and transportation. Even by the most conservative estimate, the amount of the energy in natural gas hydrate is equal to at least twice that of all other hydrocarbon fossil fuels combined. Furthermore, because of its excellent gas absorption capacity, (1 m³ clathrate hydrate could store up to 180 m³ methane under STP) and selectivity, clathrate hydrates could provide a safer and more efficient method of gas purification, storage, and transportation. ^1,2

In the present research, the crystallization and dissociation kinetics of methane (SI) hydrate were investigated in a microfluidic system by utilizing in situ Raman spectroscopy combined with optical microscopy. Rapid and precise control over the microreactor temperature allowed us to acquire reproducible data within minutes, while the nucleation of methane hydrates could take up to 24 hours in a more traditional setup.^3,4 The propagation rates of methane hydrate at the gas/liquid interface were investigated under different Reynolds numbers (0.7 to 68.9), pressures (30.0 bar to 80.9 bar) and sub-cooling temperatures (1.0 K to 4.0 K). While the Reynolds number was observed to have little influence on the propagation rate, higher pressure and sub-cooling temperature would contribute to increase the propagation rates. A theoretical model, derived from first principles, explained the non-linear relationship between the sub-cooling temperature and propagation rate. A transition from heat-transfer limited reaction to a mixed mass-transfer and intrinsic kinetic limited reaction was discovered. ⁵

Microfluidics were also found to serve as an excellent platform to study the dissociation of methane hydrates. The dissociation kinetics were studied in order to better understand its mechanism. Remarkably, a switch from crystallization to dissociation was made possible by control of the isothermal reactor temperature of 0.1 K around the phase boundary. Better understanding of the mechanism of crystallization and dissociation are critical for technology that utilizes gas hydrates.

1 E. D. Sloan and A. C. Koh, Clathrate hydrates of natural gases, 3rd edn., 2007.

2 E. D. Sloan, Nature, 2003, 426, 353–363.

3 P. Skovborg, H. J. Ng, P. Rasmussen and U. Mohn, Chem. Eng. Sci., 1993, 48, 445–453.

4 O. Fandiño and L. Ruffine, Fuel, 2014, 117, 442–449.

5 W. Chen, B. Pinho and R. L. Hartman, Lab Chip, 2017, 17, 2997–3192.