The formation and decomposition kinetics of gas hydrates at sub-zero temperatures

The extended metastability of gas hydrates (clathrate hydrates) forming and residing at temperatures below the ice point has created interest in low-temperature hydrates for convenient gas storage and transport. This study examined the thermodynamic and kinetic behaviour of gas hydrates under such low temperature conditions in order to determine their role in nature and for future technological applications. In particular, it focused on the role of carbon dioxide (CO{sub 2}) hydrates in terra-forming processes on Mars, including the pressure-dependent self-preservation effect. The experimental work was related to the formation and decomposition kinetics of gas hydrates at sub-zero temperatures, with particular focus on CO{sub 2} and methane (CH{sub 4}) hydrates. The stability of neon (Ne) hydrate was also discussed. A general model for hydrate formation and decomposition and the self-preservation effect were established using in-situ neutron diffraction and scanning electron microscopy. The self-preservation effect was explained in terms of an ice-shielding effect and its dependence on the pressure temperature conditions and the microstructural evolution of ice. Preliminary experimental results were presented regarding the cage filling of CO{sub 2} hydrates formed at temperatures below 200 K. It was concluded that these experimental results may contribute to a better understanding of self-preservation phenomena encountered in permafrost regions on Earth, or for chemical engineering efforts towards low-cost solutions for gas storage and transport. 54 refs., 1 tab., 11 figs.