HR: 13:55h
AN: B23D-02    [Abstracts]
TI: A new Optical Technique for Raman Spectroscopy of Hydrocarbon-Water Reaction at Elevated Pressures and Temperatures
AU: * Chou, I
EM: imchou@usgs.gov
AF: U.S. Geological Survey, 954 National Center , Reston, VA 20192 United States
AU: Burruss, R C
EM: burruss@usgs.gov
AF: U.S. Geological Survey, 956 National Center, Reston, VA 20192 United States
AB: Our understanding of the reaction pathways and decomposition of organic compounds in the presence of water is limited. We constructed a new hydrothermal-reaction optical cell from square, flexible, fused-silica capillary tubing (300 μm x 300 μm with 50 μm x 50 μm cavity and from 3 to 5 cm long) that allows enclosed fluids to react at temperatures (T) up to 300°C with internal pressures up to 100 MPa. The transparent fused silica allows non-destructive Raman spectroscopy of reaction progress. The sample fluids are loaded cryogenically. For example, to load a mixture of methane and water, one end of the capillary tube (about 10 cm long) was sealed by a hydrogen flame, and water was loaded and centrifuged to the enclosed end and then immersed in liquid nitrogen. The open end of the tube was connected to a vacuum line and then pressurized with methane (at about 0.2 MPa pressure) after evacuation. After sufficient solid methane is precipitated, the tube is evacuated and sealed by a hydrogen flame. We have successfully sealed a water-methane mixture, where solid methane hydrate is stable at room T (22.5°C) and 38 MPa. We heated a methane-water mixture with about 10 MPa methane pressure (at room T) at 206°C for 41 hours, and the Raman spectrum (room T) indicates formation of methanol (CH₄ + H₂O = CH₃OH + H₂). However, no methanol was formed when the same sample was initially heated at 160°C for 41 hours. When ethane and water are reacted at 206°C for 41 hours, the Raman spectrum (room T) shows the formation of both ethanol (C₂H₆ + H₂O = C₂H₅OH + H₂) and acetic acid (C₂H₆ + 2 H₂O = CH₃CO₂H + 3 H₂). Our results are in agreement with the reaction pathways proposed by Seewald (2001, Geochim. Cosmochim. Acta, 65, 1641), except our fluid samples were not in contact with any mineral buffers. Hydrogen diffusion out of the capillary tube promotes the oxidation-hydration reactions. This new method has a great potential for studying chemical reactions of organic materials with water at elevated pressures and temperatures, and also for synthesizing fluid inclusions containing organic compounds.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0452 Instruments and techniques
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1094 Instruments and techniques
SC: Biogeosciences [B]
MN: Fall Meeting 2005