Claudette Moreaux

Structural Evolution of a Sedimentologically Homogeneous Coal Series As a Function of Carbon Content By Solid-state C-13 Nmr

The cross polarization technique combined with magic-angle spinning has been applied to obtain 13C n.m.r. spectra of a sedimentologically homogeneous series of peat, lignite and bituminous coal derived from higher plants. Despite some uncertainties on the quantitative aspects of the method, the structural information obtained was corelated with data from elemental analysis. Structural average parameters were also calculated by using the structural basic unit concept and relating it to the maturation stage of the organic matter.

Analysis of asphaltenes by carbon and proton nuclear magnetic resonance spectroscopy

Abstract Proton and 13 C nuclear magnetic resonance spectroscopy has been used to derive a series of parameters of an ‘average molecule’ which characterize complex multicomponent organic mixtures such as asphaltenes. The method developed here is based on a minimum of assumptions and takes explicitly into account the effects of the oxygen atoms on the chemical shift of the adjacent 13 C atoms. Moreover, the integrated intensities characterizing ring junction or substituted and unsubstituted carbon atoms are no longer determined on a chemical shift basis but are calculated by using parameters extracted from 1 H and 13 C spectra. Factors influencing quantitative 13 C measurements on asphaltenes in the Fourier transform mode are briefly discussed. The variations of parameters such as the aromaticity factor, the degree of substitution, and the number of aromatic and naphthenic cycles per structural unit are studied as functions of depth of burial for rock samples from the Toarcian Paris basin.

Investigation of marine and terrestrial humic substances by 1H and 13C nuclear magnetic resonance and infrared spectroscopy.

Abstract Humic acids were isolated from 5 sediments in which the origin nature of the organic matter are both typical and different. The humic acids were characterized on the basis of elemental compositions, infrared spectra and 1 H and 13 C NMR. This last technique, especially 13 C NMR, provides qualitative and semi-quantitative information regarding aromatic structure. Combined data from the three techniques permits differentiation of marine and terrestrial organic matter as well as identification of mixtures of humic acids from the two sources.

Study of the artificial oxidation of a humic coal by 13C CP/MAS nuclear magnetic resonance

Abstract The cross-polarization/magic-angle spinning technique has been applied to obtain 13 C n.m.r. spectra of samples produced by artificial oxidation of a type III humic coal of southern Utah. The oxygen is mainly incorporated in carboxylic acid and phenol functional groups. Results are confirmed by infra-red spectroscopy.

Kinetics, acid sites and deactivation of H-mordenite during the SCR of NOx with CH4

H-mordenites are active for the SCR reaction but they suffer irreversible partial deactivation after being on stream for one hour at 650°C. The reaction orders and activation energies are not significantly affected by deactivation. This indicates that deactivation originates in a decrease in the number of active sites due to dealumination and possible pore blockage. The NO disappearance rate correlates with TPD NH3 between 300 and 700°C; FTIR confirms these results. 129Xe NMR of adsorbed xenon shows that pore blockage occurs and is due to the presence of aluminum species in the main zeolite channels. The overall deactivation process and the role of acid sites is discussed in terms of the current literature.

A limitation of 13C CP-MAS n.m.r. spectroscopy for the study of treated coals

Abstract Carbon-13 n.m.r. spectroscopy is often considered to be a quantitative method for analysis of coals and treated coals provided the experimental conditions are carefully selected. In some cases, the magnetic impurities strongly affect the spectra leading to non-quantitative measurements and even to the impossibility of observing a spectrum.

Analyses of insoluble residues of altered organic matter by 13C CP/MAS nuclear magnetic resonance

Abstract Alteration phenomena affecting organic matter during diagenesis frequently lead to the formation of residues almost insoluble. Data from 13 C CP/MAS nuclear magnetic resonance analyses (NMR) of these residues have been compared to those obtained by other techniques such as elemental analysis, infrared spectroscopy, Rock-Eval pyrolysis or gas chromatography. Three examples of alteration phenomena have been chosen: the artificial and natural oxidation of coals, the biodegradation of oils and solid bitumens, and the radiolytic degradation of organic matter. NMR results and those obtained by other techniques converge on similar general conclusions. Additional information can be extracted from 13 C NMR data: e.g. definition of the phenol/carbonyl ratio, transformation of the aromatic network and aromatic ring substitution. These comparisons are good evidence for the reliability of non-destructive analysis of the insoluble fraction of altered organic material by 13 C CP/MAS NMR.

2d Spin-echo and 3d Chemical-shift-imaging Techniques for Analysis of Oil-water Replacement in Limestone

NMR imaging for biological studies and medical diagnostics is now a well-established technique and most of the commercially available NMR imaging devices have been developed with this type of application in mind. Efforts to apply NMR imaging to material science are relatively recent: applications to wood, polymers, composites, and ceramics have been reported. Imaging of fluid-filled porous rocks appears to be a scientifically and technically important potential application of MRI. Pioneering work in this field began in 1979, when Gummerson et al. ( 1) and Rothwell et al. (2) reported images which depicted the distribution of fluids within porous samples. Since then several papers on the subject have appeared in the literature and some of them are referenced in this paper (3-l 1). When several fluid phases are present at the same time or when displacement of a fluid by another is studied, it is necessary to have an imaging technique which can distinguish readily between fluids of different chemical compositions. Organic fluids (oil ) and water are very often distinguished by doping one component with paramagnetic ions so that by a shortening of the transverse relaxation time, T2, the corresponding component is eliminated and only one signal is observed. Differences in the longitudinal spin-relaxation time, T, , of the oil and water phases have also been used by Hall et al. (5). In this technique an inversion-recovery step is incorporated in the imaging sequence. Selective images of a particular species can also be obtained either by selective excitation of the fluid under investigation or by suppression of the unwanted species by presaturation (11). These methods are currently used in biomedical application but have not been applied, so far, for the study of fluid-filled porous media. Global methods of chemical-shift imaging( CSI ), producing essentially a chemical-shift spectrum for each localized region or volume element, have been developed for biomedical research.

Chemical shift imaging of fluid filled porous rocks

Three-dimensional chemical shift imaging has been used to map oil and water in porous rock samples. This method does not rely on differences on relaxation times T1 or T2 and works quite well, provided the components of the fluids give reasonably well separated lines. The main limitation is the T2 value which cannot be shorter than the echo time. Reasonably quantitative measurements can be obtained.

23Na microimaging of water phase in porous limestone

Abstract23Na microimaging has been investigated as a method for discriminating multiple fluid phases in porous media. Useful23 Na images from NaCl saturated brine in limestone were obtained in a few-minutes. Good images requires several hours.