P 01 High - pressure gas hydrates

Many simple gases that do not interact strongly with water form crystalline hydrates in which the gas molecules or atoms occupy ‘cages’ formed by a framework of water molecules. These clathrate hydrates are stabilised by hydrophobic gas-water interactions and are model systems for the study of these interactions. Many gas hydrates also occur in nature and their properties provide a basis for modelling of planetary evolution and processes. For example, a destabilisation of methane hydrate in the Earth’s oceans is thought to have led to catastrophic global-warming events in the Earth’s past. Gas clathrate hydrates are stabilised by modest pressures in the range 0-0.5 GPa, and the dissociation temperature of methane hydrate rises from ~190 to ~320 K in this pressure range. But there was a general expectation, based on modelling studies, that higher pressures, in the 1-2 GPa range, would render all clathrate hydrates unstable with respect to their parent species. However, over the past seven years, a series of experiments has shown that in a large number of gas-water systems this is not the case. Instead, structural transformations occur to new hydrate structures which remain stable to significantly higher pressures. In this poster we will review this work to identify trends in behaviour and structures and to make suggestions for further work.