Evaluation of the aromaticity in French coals by 13C-1H cross polarization, magic angle spinning and dipolar dephasing nuclear magnetic resonance spectroscopy

The aromaticity factor f_a of various French coals, as determined by ¹³C-¹H cross polarization and magic angle spinning, is reported. The f_a, values, which are estimated after a careful examination of the evolution of the ¹³C magnetization as a function of the contact time, are 0.63, 0.74, 0.82 and 0.85, respectively, for the Gardanne, Vouters, Méricourt and Escarpelle coals. The fraction of non-protonated aromatic carbons, fⁿ_a, as determined by dipolar dephasing experiments seems to decrease with increasing rank until a minimum value is reached for the low volatile bituminous coal from Méricourt, followed by an increase for the semi-anthracite coal from Escarpelle.