The analysis of three representative premium coals by 13C nuclear magnetic resonance
1993
Abstract The analytical characteristics of the three Argonne premium coals 801, 601 and 501 were examined by magic-angle spinning (MAS) 13 C n.m.r., using large samples (2.5 cm 3 ). Experiments were performed with 13 C magnetization generated by both cross-polarization (CP) and 90 ° pulse, or direct-polarization (DP), approaches. Various 13 C-based relaxation measurements were made. Using the Delrin 13 C signal of the Delrin-zirconia spinner as a built-in intensity reference, spin counting was carried out. The DP-MAS approach appeared to account for ~80%, and the customary CP-MAS technique for only ~50% of the carbon known to be in each sample; however, a CP-MAS approach that incorporated a better T 1 ϱ H determination appeared to account for > 80% of the carbon. It is concluded that, although useful results can be obtained by 13 C CP-MAS experiments (if CP dynamics are properly characterized), the DP-MAS approach with large samples is more straightforward. Dipolar-dephasing 13 C n.m.r. studies provide a measure of the contributions of proton-bearing and non-proton-bearing carbons in the three coals and the fraction of aromatic or aliphatic carbons that are proton-bearing. The attractiveness and utility of large-volume 13 C MAS approaches in the analysis of coal are demonstrated.
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