Structure Characterization and Model Construction of Indonesian Brown Coal

Indonesian brown coal is analyzed using 13C cross-polarization/magic angle spinning nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction (XRD) to obtain the information and parameters of the coal structural unit. A macromolecular structural model of Indonesian brown coal was constructed on the basis of the structural parameters and elemental analysis results. The 13C chemical shift of this model was calculated using the ACD/13C NMR predictor. The results indicate that the aromaticity of Indonesian brown coal is 0.3412, and the structures of aromatic carbon are mainly types of naphthalene and benzene. The ratio of bridge carbon/surrounding carbon is 0.0696. Oxygen in the structural model mainly exists in the form of phenolic hydroxyl oxygen, carboxyl oxygen, and ether oxygen, of which phenolic hydroxyl oxygen and carboxyl oxygen are the most prominent. Nitrogen atom exists in the form of pyridine and pyrrole. The peak of XRD spectra at 20–30° is broad with a strong γ width. The calculated chemical shift spectrogram of the model is highly consistent with that of the experimental results. The structural formula calculated for Indonesian brown coal is C190H170O50N2. This information will be the basis of making use of Indonesian brown coal.