Structural characterization of Australian coals by FTIR and solid-state \\(^{13}\\)C nmr spectroscopies

The structural characteristics of twenty-nine Australian coals and their hydroliquefaction products have been investigated by Fourier Transform Infrared (FTIR) and solid-state \\(^{13}\\)C nmr spectroscopies. The coal samples were selected to cover a wide range of rank from semianthracite to b~own coals. Chemical compositions of the coals varies from 66.4 to 90.6 wt.% C, 3.8 to 7.2 wt.% Hand 3.1to28.0 wt.% O (by difference). The FTIR techniques were used to measure the structural parameters associated with aliphatic and aromatic structures and oxygen-functional groups, namely, hydroxyl and carbonyl groups. The solid-state \\(^{13}\\)C nmr measuements were carried out at a high-field of 7.05 T by using standard CP/MAS/HPPD techniques in conjunction with a TOSS pulse technique. Modifications of the TOSS sequence have been made for dipolar-dephasing analyses of the samples. Cross-polarization dynamics in the coals. were also studied by means of variable contact time experiments. The structural parameters derived from the FTIR and solid-state \\(^{13}\\)C nmr data were compared and their relationships with the elemental compositions and liquefaction data were examined. It has been demonstrated that the FTIR techniques are more useful in the elucidation of oxygen-containing structures while the solid-state \\(^{13}\\)C nmr methods are more effective in obtaining structural data related to 'the aliphatic and aromatic structures. However, as complementary techniques, both methods have been proved to be very useful in elucidating the structures of coals studied. The results demonstrated the dissimilarity between the general structural features of the brown coals and those of the higher-rank coals. It has been found that the brown coals have uniform aliphatic and aromatic structures with a high variability in the oxygen-functional groups. In contrast, the variations in the aliphatic and aromatic structures of the higher-rank coals are more pronounced with less diverse oxygen-containing groups being observed in these coals.