The clathrate hydrates of natural gases are crystalline compounds in which gas molecules are encaged in a host framework of water molecules. These host-guest materials form under high pressure and low temperature, and occur naturally on the ocean bed and in permafrost. It is estimated that the total amount of hydrated gas on Earth exceeds conventional gas reserves by at least an order of magnitude. This makes natural gas hydrates not only a potential untapped energy resource but also a historic and contemporary source of greenhouse gases. Natural gas hydrates also pose severe problems in oil and gas pipelines: if the mixed phases of water and natural gas are allowed to cool, hydrates may form and block the line, causing production to stall. Although recent progress has been made in understanding bulk methane hydrate formation, the effect of impurity particles, which are always present under conditions relevant to industry and the environment, remains an open question. To understand this problem, we have used neutron scattering in conjunction with hydrogen−deuterium isotopic labeling experiments to investigate methane hydrate formation in the presence of a wide variety of solid nanoparticles. Much to our surprise, we find that the formation of methane hydrate is insensitive to the addition of these impurities. We have also used molecular dynamics (MD) simulations to probe the molecular mechanisms by which methane hydrate forms in the presence of solid surfaces, and find that nucleation happens away from the solid/liquid interface in all the cases studied. Our results therefore suggest that, with regard to designing improved inhibitors, it may be advantageous to focus on understanding the mechanism of methane hydrate formation either in the bulk, or at the gas/liquid interface.

Formation of methane clathrate hydrates at elevated pressures and in the presence of nanoparticles

256th National Meeting (2018)

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