2009 Portland GSA Annual Meeting (18-21 October 2009)
Paper No. 215-14
Presentation Time: 5:35 PM-5:50 PM

STRUCTURAL FEATURES OF A BITUMINOUS COAL AND THEIR CHANGES AFTER LOW-TEMPERATURE OXIDATION AND LOSS OF VOLATILES INVESTIGATED BY ADVANCED SOLID-STATE NMR SPECTROSCOPY

MAO, Jingdong1, SCHIMMELMANN, Arndt2, MASTALERZ, Maria3, HATCHER, Patrick1, and LI, Yuan1, (1) Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, jmao@odu.edu, (2) Department of Geological Sciences, Indiana University, Bloomington, IN 47405-1405, (3) Indiana Geological Survey, Indiana University, Bloomington, IN 47405

Quantitative and advanced 13C solid-state NMR techniques were employed to investigate the chemical structure of a high volatile bituminous coal and chemical structural changes of this coal after evacuation of adsorbed gases, during oxidative air exposure at room temperature, and after oxidative heating in air at 75ºC. The solid-state NMR techniques employed in this study included quantitative direct polarization/magic angle spinning at a high spinning speed of 14 kHz, cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CH, CH2, and CHn selection, 13C chemical shift anisotropy (CSA) filter, 2D 1H-13C heteronuclear correlation NMR (HETCOR), and 2D HETCOR with spin diffusion. With spectral editing techniques, we identified methyl CCH3, rigid and mobile CCH2C, CCH, NCH, aromatic CH, aromatics bonded to alkyls, small sizes of condensed aromatics, and aromatic C-O. With direct polarization combined with spectral-editing techniques, we quantified 11 different kinds of functional groups. 1H-13C 2D HETCOR NMR experiments indicated spatial proximity of aromatic and alkyl moieties in cross-linked structures, confirming the macromolecular nature of coal. The proton spin diffusion experiments indicated that the magnetization was not equilibrated at a 1H spin diffusion time of 5 ms. Therefore, the heterogeneity of different functional groups should be above 2 nm. Recoupled C-H long-range dipolar dephasing showed that the fraction of large charcoal-like clusters of polycondensated aromatic rings was relatively small. The exposure of this coal to atmospheric oxygen at room temperature for 6 months did not result in obvious chemical structural changes of the coal but heating at 75ºC in air led to oxidation of coal, generating a small signal of COO. Evacuation removed most volatiles and caused a significant reduction in aliphatic signals in its DP/MAS spectrum. These results demonstrate the applicability of advanced solid-state NMR techniques in characterizing coal.

2009 Portland GSA Annual Meeting (18-21 October 2009)
General Information for this Meeting
Session No. 215
Frontiers in Coal Science: From Basic Research to Applied Technology
Oregon Convention Center: B114/115
1:30 PM-6:00 PM, Tuesday, 20 October 2009

Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 552

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