Characterization of high-temperature coal tar and supercritical-water extracts of coal by laser desorption ionization-mass spectrometry

A sample of high-temperature coal tar and the coal liquids derived from supercritical water extraction catalyzed by Ca(OH)2 were examined in their molecular mass distributions, using laser desorption ionization-mass spectrometry. The main peaks observed in both the high-temperature coal tar and the supercritical-water extracts were located at m/z 200–400. Trace signals were observed at the molecular masses up to 15,000 Da for the high-temperature coal tar. Many polycyclic aromatic hydrocarbons (e.g., pyrene, benzofluorene, chrysene and coronene) without lateral groups, were presumably responsible for the intense massed peaks in the high-temperature coal tar. None of these compounds were found in the coal extracts; the components in the coal extracts were found to be rich in hydroxyl and alkyl sides. The results indicated that the hydrolysis of ether bonds is important in the cleavage of the macromolecular structure of low-rank coals to tarry components, under the catalytic effect of Ca(OH)2 in supercritical water. Less nitrogen-containing aromatics were found in the coal extracts.