Influence of carbon type on carbon isotopic composition of coal from the perspective of solid-state 13C NMR

A total of twelve coal samples at bituminous rank from China were studied using a combination of elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) and solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy techniques to determine their carbon isotopic compositions and carbon types. Carbon isotope analysis showed that the delta C-13 values of the studied coals ranged from -22.9% to -25.1% and correlated significantly with the ratios of aromatic carbons to aliphatic carbons. The studied coals were enriched in C-13 due to the fact that the amount of C-13-enriched aromatic carbons is more than that of C-13-depleted aliphatic carbons. The observations suggest that carbon isotopic compositions of whole coal may be controlled by the distribution of carbon types.