HR: 0830h
AN: OS51B-0846    [PDF]
TI: Gas Hydrate Nucleation Processes
AU: * David, R E
EM: riestenbergd@ornl.gov
AF: Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6036 United States
AU: Zatsepina, O
EM: zatsepinaoy@ornl.gov
AF: Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6036 United States
AU: Phelps, T J
EM: phelpstj@ornl.gov
AF: Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6036 United States
AB: The onset of gas hydrate nucleation is greatly affected by the thermal history of the water that forms its lattice structure. Hydrate formation experiments were performed in a 72 liter pressure vessel by bubbling carbon dioxide through a 1 liter column at hydrate formation pressures (1.4 to 3.7 MPa) and temperatures (275.0 to 278.0 K) to quantify this effect. They show that when even a fraction ( e. g. 20 %) of the water in which hydrate has formed was recently frozen and thawed, the overpressurization for nucleation was reduced by an average of 50 % versus experiments performed in distilled water. In those experiments where a lower overpressure is present when hydrate nucleated, they tended to form on the surface of bubbles, whereas when a higher amount of overpressure was necessary for hydrate to nucleate, they appeared to form abruptly on bubble surfaces as well as from the bulk liquid phase. In approximation of classical nucleation, hydrate formation could be described as occurring by the spontaneous joining together of arising components of the hydrate lattice. In water that was frozen, and kept at a low temperature ($<$ 275 K), molecular simulation models predict the predominance of water molecules organized as penatmeters, a possible subunit of the hydrate lattice. Our results suggest that in nature, initiation of hydrate formation may be strongly influenced by temperature dependant pre-structuring of water molecules prior to their contact with gas.
DE: 4806 Carbon cycling
DE: 4835 Inorganic marine chemistry
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting