Micro-FTIR spectroscopy of liptinite macerals in coal

Reflectance FTIR microspectroscopy has been used to investigate the chemical structure of the Liptinite macerals, alginite, bituminite, sporinite, cutinite and resinite in bituminous coals of Carboniferous to Tertiary age. In comparison with the spectra of vitrinite in the same coals, the micro-FTIR spectra of liptinite macerals are characterized by stronger aliphatic CHx absorptions at 3000-2800 and 1460-1450 cm(-1), less intense aromatic C=C ring stretching vibration and aromatic CH out of plane deformation at 1610-1560 and 900-700 cm(-1) respectively and various intense acid C=O group absorptions at 1740-1700 cm(-1). The peaks at 1000-900 cm(-1) due to aliphatic CH2 wagging vibrations in olefins and at 730-720 cm(-1) due to CH2 rocking vibration in long chain aliphatic substances ([CH2](n), n greater than or equal to 4), are characteristic of Liptinite macerals. Collectively the micro-FTIR spectral characteristics indicate that liptinite is composed of greater numbers of long chain aliphatics, fewer aromatics and a broader range of oxygen-containing groups than other macerals. Marked differences exist in micro-FTIR spectra within the liptinite maceral group. Alginite has the strongest aliphatic and least aromatic absorptions followed by bituminite, resinite, cutinite and sporinite. The aliphatic components in alginite are the longest chained and least branched whereas those in sporinite are the shortest chained and most branched. Bituminite, resinite and cutinite are intermediate. Notable differences in micro-FTIR spectra of individual liptinite macerals, such as intensities and peak locations of aromatic C=C in alginite, C=O groups in bituminite and resinite and substituted aromatic CH and C-O-C groups in cutinite and sporinite, also exist, which are attributed to differences in depositional environments or biotaxonomy. (C) 1998 Elsevier Science B.V.