Influence of carbon type on carbon isotopic composition of coal from the perspective of solid-state C-13 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 13C nuclear magnetic resonance (NMR) spectroscopy techniques to determine their carbon isotopic compositions and carbon types. Carbon isotope analysis showed that the δ13C 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 13C due to the fact that the amount of 13C-enriched aromatic carbons is more than that of 13C-depleted aliphatic carbons. The observations suggest that carbon isotopic compositions of whole coal may be controlled by the distribution of carbon types