Hydrothermal Organic Chemistry with Cold Seal and other Reactors
We run our experiments at temperatures ranging from 50 up to 250 °C and at pressures from 2-3 MPa up to 400 MPa. Reactions run at the vapor pressure of liquids are run in flame sealed silica tubes. Reactions at high pressure are run using a number of different high pressure devices. The simplest method utilizes cold seal pressure devices affording access to pressures up to 400 MPa. We have run experiments in a gas pressure reactor that provides pressures up to 1 GPa. Work with former post-doc Anurag Sharma using a hydrothermal diamond anvil cell allows for experiments at pressures exceeding 2 Gpa. We also have a high pressure flow reactor designed and assembled by former GL fellow Timothy Filley (now Professor at Purdue) that utilizes a pair of Quizix HP pumps and a titanium back pressure regulator. Currently Dionysis Foustoukos has modified this apparatus to explore hydrogen oxidation kinetics in line with his interests in deep sea hydrothermal systems.
A snapshot of our hydrothermal lab. We currently have 14 cold seal reactors and furnaces under individual pressure and temperature control. We can routinely run reactions up to 350 Mpa.
Analysis of the reaction products is performed in an number of different ways. Welded gold reactors are analyzed post reaction via GC-MS and UV-vis spectroscopy. We have successfully retrieved liquids from the hydrothermal DAC and analyzed the reaction products using GC-MS. Of course the nicest aspects of the DAC is one can utilize Raman spectroscopy to follow reaction progress at T and P; this has been done recently by our former post Doc Anurag Sharma (RPI) following our previous reactions involving citric acid in hot water (see for example Sharma et al. 2004).
A close up view of a cold-seal reactor. Note the water cooled end region. This allows us to do rapid heat up and quench in order to explore reaction kinetics at elevate pressures.
Transition metal sulfide catalysts:
Natural metal sulfides are never compositionally pure, rather extensive cationic substitution is often encountered. Even a minor amount of substitution, e.g. Ni2+ for Fe2+ in FeS or Mn2+ for Zn2+ in ZnS, may affect significant changes in catalytic properties. Perhaps more critical it is now well known that natural sulfides are generally completely contaminated with organic compounds.
Warning to the experimenter: Transition metal sulfides are excellent organosynthetic catalysts, therefore, natural mineral sulfides are likely to be loaded with organic molecules. Only pure-laboratory synthesized minerals can be considered “clean”
In order to avoid the problems associated with natural contamination, therefore, we work with compositionally pure mineral sulfide phases to provide a better base line for the intrinsic catalytic qualities of simple metal sulfides. Our Co-I Nabil Boctor synthesizes all of our sulfides, utilizing dry methods that extend back to those first explored by the pioneers. In our case only puratronic grade metals (99.995-99.998 %) and S (99.9995 %) are used-futher purifying our catalysts. At the termination of the synthesis, a small portion of each charge is mounted in epoxy, polished with diamond abrasive paste, and examined optically in reflected light to ensure that the target phase is the only phase present. The chemical compositions of the synthetic sulfides are determined by electron microprobe analysis with a JEOL Superprobe (JXA-8800). In some cases the crystal structure of the target phase is confirmed with X-ray diffraction (e.g. Cody et al., 2000).
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