HIGH-RESOLUTION SOLID-STATE PROTON NMR-SPECTROSCOPY OF DENSITY FRACTIONS FROM CALLIDE COAL

Solid-state high-resolution H-1 spectra of density fractions from Callide coal have been obtained. These spectra reveal that proton aromaticity (H(ar)) changes from 0.06 for the 1.20-1.25 g cm-3 fraction up to 0.76 for the 1.44-1.45 g cm-3 fraction. These values, in conjunction with the atomic H/C ratio, have been used to measure the change in degree of aromatic carbon substitution with density. The fraction of aromatic carbon substitution changes from approximately 0.9 for the lightest fraction to approximately 0.35 for the heaviest fraction, demonstrating that the more dense coal fractions have less aromatic substitution than lighter fractions. Additionally, the NMR measured aliphatic/aromatic proton ratio was compared to the same ratio determined by FTIR spectroscopy. It is shown that the ratio of aromatic to aliphatic protons determined by solid-state NMR compared to the same ratio determined by infrared spectroscopy varies from approximately 6.5 for low-density fractions to a value of approximately 1.5 for high-density fractions.