Characterization of the Argonne premium coals by using NMR of 1H and 13C and FTIR spectroscopy

摘要

Argonne Premium Coal Sample Program (APCSP) coals were analyzed by using a variety of transient techniques in NMR of [superscript]1H (relaxation measurements, spin counting, CRAMPS) and [superscript]13C (CP/MAS) in coals as well as by using FTIR spectroscopy. The quantitative validity of the techniques was evaluated;The true lineshape of the on-resonance [superscript]1H free induction decay (FID) for coals with \u3c2% moisture content was determined by solid echo and described by a superposition of Gaussian and Lorentzian decay functions, corresponding to rigid protons in the macrostructure of coal and to fragments in the coal exhibiting hindered molecular mobility, respectively. For wet coals, an additional slowly decaying Lorentzian fraction must be added to the description of the FID. The species responsible for the longest decay was identified. The NMR quantitation results compared favorably with the results obtained by chemical and thermogravimetric analyses;Hydrogen and carbon aromaticities of the APCSP coals were measured by using [superscript]1H CRAMPS and [superscript]13C CP/MAS NMR, respectively, as well as by using FTIR spectroscopy. Hydrogen aromaticity values of the APCSP coals as measured by NMR are consistently higher than the corresponding values obtained from FTIR. Carbon aromaticity values measured by NMR for the bituminous coals corresponded with the FTIR values. The carbon aromaticity measured for the younger coals (202 and 801) by using NMR are smaller than the values reported from FTIR measurements. The reproducibility of the values of carbon aromaticity of the APCSP coals measured by NMR was better than 95% for most coals. The use of (H/C)[subscript] ar and (H/C)[subscript] al as indicators of coal rank was also evaluated. Hydrogen relaxation time constants reported compared favorably with results from other laboratories.