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For Reporting Year
[08 August 2014]
University of Colorado (Dr. Tom McCollom, Lead).
Research during the past year focused on the reduction of carbon and generation of abiotic organic compounds during serpentinization of ultramafic rocks. As part of this work, several carbon-rich particles were identified among the products of hydrothermal serpentinization experiments that potentially formed through reduction of dissolved CO2. In the coming year, I will work with DCO colleagues at IPGP and University Claude Bernard in Lyon to characterize these particles and determine their origin. In a related effort, the origin of methane generated during the hydrothermal serpentinization experiments was investigated using isotopic labels. In contrast to several recent reports, we found that the methane came primarily from background sources rather than reduction of CO2 in the experiments. Lastly, hydrothermal fluids from mafic- and ultramafic-hosted deep-sea hydrothermal systems along the Mid-Atlantic Ridge were analyzed for the presence of non-volatile organic compounds. Non-volatile hydrocarbons with an abiotic origin were not found at any of the systems, although a number of carboxylic acids and other compounds of clear biological origin were observed at the moderate-temperature, serpentine-hosted Lost City system.
University of Lyon (Prof. Isabelle Daniel, Lead). We have measured the kinetics of serpentinization of olivine and orthopyroxene in the diamond anvil cell at the European Synchrotron Radiation Facility (high-pressure beamline ID27). This has allowed assessing partly the role of aluminum on the fast kinetics of serpentinization. One aspect is that the nucleation of aluminous serpentine is instantaneous. The role of carbonate and pH was also investigated. This represents hundreds of X-ray patterns that are being subjected to Rietveld refinement by a PhD student (Maria Pens, Venezuela). Complementary SEM and Raman measurements have been done after quenching. The same quenched samples were also investigated by X-ray absorption spectroscopy at the Fe K-edge at the French synchrotron facility SOLEIL (LUCIA beamline) to evaluate the degree of oxidation in mineral phases, which should be correlated to the amount of H2 or C-reduced produced during the experiments. Data are currently being processed.
At this stage, the analysis of mineral phases is almost completed.
In the meantime, long-term serpentinization experiments have been started at 80°C. They will be soon analyzed using the micro GC-MS that was delivered at springtime.
We have also searched for a DCO postdoctoral fellow: Dr. Steve Peuble, who has defended his PhD thesis (University of Montpellier, June 2014) on the experimental characterization of hydration and carbonation of basic and ultrabasic rocks. Steve has already started in the lab, as an assistant during summer 2014 (salary university Lyon1). He will start officially on the DCO grant Sept. 1st 2014 for one year.
Future Work. This second year will be dedicated to the analysis of the gas, fluid phase and carbon phase. We’ll take advantage of the micro GC-MS, which is now operational, and we will use vibrational spectroscopic techniques to analyze the carbon phase. A variety of thermodynamic conditions will be investigated, from 50°C to 350°C under the relevant pressure.
Institut de Physique du Globe de Paris, IPGP (Dr. Benedicte Menez, Lead).
Experimental assessment of reactions and carbon transfers
C. Vacquand started the first round of experiments involving synthetic analogs of oceanic crust and catalysts. She first developed protocols to synthesize fayalite (Fe2SiO4) and olivine (FeMgSiO4) at nanometric scale as well as magnetite and chromite, which are supposed to be good candidates for the catalysis of the Fischer-Tropsch-type reactions. During the last few months, she also developed in our lab the protocol to collect and analyze the gas phase from the capsule by GC. The first set of experiments was performed during June 2014 at 200 bars, 200°C, with 7 gold cells containing the silicate phase and a solution (pure water or water with 30g.l-1 NaHCO3). The analyses of the run products is in progress.
A second set of experiments, involving a catalyst (magnetite and chromite) is being prepared. Using the same protocol and to increase their reactivity, mixtures of silicate and catalysts were ground at a nanometric scale and stored under argon atmosphere.
Associated collaboration and networking: Collaboration has been established with the LRCS for nanosynthesis (N. Recham, Laboratoire de Réactivité et Chimie des Solides, UPJV Amiens). Part of the nano-fayalite was also sintered at the ISTerre (Grenoble, France) to be used as starting material (coll.: F. Brunet). We started a collaboration with Tom McCollom (Boulder, Colorado) invited for one month at IPGP to start the characterization of the high-molecular-weight reaction products of some of his abiotic organic synthesis experiments, using some of the techniques we have been developing at IPGP for natural samples (SEM, TEM, Raman, and IR). Same work could be done also on a suite of samples from drill cores into an active serpentinite in California where we could also look for organic matter. A new collaboration on the abiotic production of hydrocarbons starts with the IFP (French Petroleum Agency) with a PhD thesis now open. This experimental work deals with percolation experiments on oceanic crust samples, in collaboration with Geosciences Montpellier (M. Godard, France).
University College London (Prof. Alberto Striolo, Lead).
We have continued the investigation of mixed fluids under confinement. We have considered methane, propane, octane, CO2, ethanol, and water in narrow slit-shaped pores. Results for the systems containing CO2 are not yet mature for publication. These investigations are based on equilibrium molecular dynamics, with attempts to reproduce experimental observations in collaboration with Cole and coworkers.
DCO funds have been instrumental in establishing a new web of collaborators for Striolo in Europe. Together with Adrian Jones, Striolo is developing a close collaboration with Rob Hull of Halliburton and with Duncan Nicholson of ARUP. The collaboration is focused on shale gas. A large number of academic collaborators have been contacted thanks to DCO.
Future Work. The main goal for the next period is to simulate chemical reactions in pores (the DCO project involves investigating the thermodynamics of the Fischer-Tropsch reaction under confinement). Now that the group is completely moved to our new location (University College London), we can implement the new algorithm. In the meantime, we will continue the investigation of mixed fluids containing alkanes and CO2.
Ohio State University (Prof. Dave Cole, Lead). The overarching objective of this effort, which leverages complementary support from DoE, is to obtain a fundamental atomic- to macro-scale understanding of the sorptivity, structure, and dynamics of simple and complex C-H-O fluids at mineral surfaces or within nanoporous matrices over temperatures, pressures, and compositions encountered in near-surface and shallow crustal environments. To achieve this goal we (a) assess the adsorption-desorption behavior of methane, related hydrocarbons, and CO2 on a variety of mineral substrates and in nanoporous matrices, (b) characterize the microstructure and dynamical behavior of methane and related HC volatiles at mineral surfaces and within nanopores with and without H2O present at relevant P-T-x subsurface conditions, and (c) utilize molecular-level modeling to provide critically important insights into the interfacial properties of these mineral-volatile systems, assist in the interpretation of experimental data, and predict fluid behavior beyond the limits of current experimental capability. A scientifically diverse, multi-institutional team (Ohio State University, University College London (with A. Striolo), Oak Ridge National Lab, Pacific Northwest National Lab, Hunter College) is utilizing novel experimental and analytical techniques in concert with state-of-the-art theory, modeling, and simulation approaches to address these issues. There is a special emphasis on building synergistic links between results obtained from various neutron scattering and NMR studies which are integrated into our research portfolio with molecular dynamics modeling, to provide new phenomenological insights.
Thus far, we have conducted a number of different kinds of experiments focusing on the behavior of propane, ethane, methane, carbon dioxide, or their mixtures with or without water present interacting with different types of mesoporous matrices (e.g., SiO2, Al2O3, TiO2, ZrO2). High temperature-high pressure gravimetric measurements on these fluids have revealed profound fluid densification in nanopores as the density (pressure) approaches that of the bulk critical density followed by a dramatic density decrease (fluid depletion). Densification of propane in model silica pores has been observed in MD simulations, in qualitative agreement with experiments. The CO2 adsorption on TiO2 has been modeled with density functional theory (DFT) that employs a new version of the dispersion correction. Quasielastic neutron scattering (QENS) experiments have been conducted at Oak Ridge National Laboratory on the system propane-mesoporous silica with and without CO2 present. Results from these experiments are interpreted in terms of translational “diffusive” motion of propane, residence times between diffusion jumps, and the jump distances. Interestingly, the presence of CO2 seems to enhance the mobility of propane in the mesopores. Mixed water-methane and water-ethanol systems have also been investigated using MD simulations, suggesting that preferential adsorption might be responsible for the results observed experimentally in mixed systems. We used a recently developed high-pressure Magic Angle Spinning (MAS) NMR system (EMSL) to investigate methane interacting with mesoporous silica having 200 nm particle size and 4 nm pores, a high surface area non-porous silica and montmorillonite. The proton decoupled 13C NMR spectra were acquired with high-pressure MAS probe at 30, 60 and 120 bars. At each pressure, the temperature was varied from 34oC to 73oC. The experiments revealed that pressure induces shifts in the methane peak position: ~0.25 ppm going from 30b to 60b, and ~0.50 ppm shift going from 30b to 120b. The magnitudes of these spectral chemical shifts have been emulated by Amity Andersen at EMSL using DFT. The simulations indicate that the chemical shifts reflect the effects of “molecular crowding” and adsorption on magnetic shielding.