Estimation of the average aromatic cluster size based on solid-state NMR measurement of coal

Measurements of solid-state NMR of eight Argonne Premium Coal Samples were conducted to estimate the average aromatic cluster size in these coals. Firstly, the carbon distribution was obtained from SPE/MAS ¹³C-NMR. Secondary, ¹H-CRAMPS NMR spectra gave the hydrogen aromaticity of coal. Combination use of the hydrogen aromaticity and elemental analysis data could afford the amount of tertiary aromatic carbon. The parameter of χ_b, the mole fraction of aromatic bridgehead carbons in all aromatic carbons, could be derived from above NMR data and elemental analysis of coal. χ_b is directly correlated to the number of aromatic carbon atoms per aromatic cluster, C. In this study, the value of C varied from 10 (corresponding to the size of naphthalene) for Beulah-Zap and Wyodak coals to 23 (corresponding to the size of coronene) for Pocahontas No. 3 coal.