HR: 1340h
AN: OS23A-1034    [Abstracts]
TI: Formation of a Structure II Hydrate by 1,4-Thioxane in Sea Water
AU: * Hester, K C
EM: khester@mbari.org
AF: Monterey Bay Aquarium Research Institutue, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Mancillas, O
EM: omancillas@berkeley.edu
AF: Monterey Bay Aquarium Research Institutue, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Walz, P M
EM: wape@mbari.org
AF: Monterey Bay Aquarium Research Institutue, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Peltzer, E T
EM: etp3@mbari.org
AF: Monterey Bay Aquarium Research Institutue, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Brewer, P G
EM: brpe@mbari.org
AF: Monterey Bay Aquarium Research Institutue, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AB: We have show that a sII clathrate hydrate containing 1,4-thioxane (TO) will form under the appropriate pressure and temperature conditions. The molecular size of TO poised it at the boundary between sII hydrate formation either as the sole cage occupant, or where a second help gas molecule is required to stabilize the small hydrate cages. In addition to its size, TO is chemical similar to cyclic ethers, such as tetrahydrofuran, which readily form clathrate hydrates. For the experimental temperatures in this study (all above 273.15 K), a pure TO hydrate was not observed to form. However, binary hydrates of TO and either CH4 and N2 were readily formed under moderate pressure conditions (33-158 bar). Both Raman spectroscopy and visual observations were used to verify that a solid hydrate formed and that TO was trapped in the cages. For TO + CH4, a pressure-temperature phase equilibria diagram was created. This showed that the addition of TO increased hydrate stability versus a pure CH4 system by approximately 10 degC, indicating that should CH4 gas be present a TO hydrate would readily form at shallow depths under typical oceanic temperature regimes. TO is of environmental interest as a breakdown product of mustard gas (1,1'-thiobis[2-chloroethane] as a result of hydrolysis in sea water, and has been shown to occur in seafloor chemical weapon disposal sites. In the years after World War II large quantities of chemical weapons were disposed of in the ocean at sites off the US east and west coasts, off Japan, in the Baltic and Adriatic Seas, and in the Russian Arctic, until the signing of the London Convention in 1972. Mustard gas represents the largest tonnage of weapons materiel and while the general scheme of breakdown by hydrolysis is known there is little information on the actual behavior of these breakdown products in marine sediments. This work illuminates such gaps in knowledge, and formation of a hydrate profoundly alters molecular mobility and diffusion away from a site. Simple calculations show that other help gases, such as H2S, should also form a mixed hydrate with TO with remarkable ease; thus, extending the range of possible hydrate formation with TO in anoxic marine sediments to shallow depths, if a second hydrate former is present.
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 3004 Gas and hydrate systems
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting