FTIR Study of Pure Vitrains and Associated Coals
Résumé
A semiquantitative analysis of the infrared spectra from 650 to 4000 cm-' of six vitrains and the coals associated with three of them is presented. This analysis supplies information on the concentration of several functionalities in the samples. Relationships between infrared data and several parameters (carbon content, vitrinite reflectance, pyrolysis data) are discussed. The results thus obtained contribute to a better understanding of vitrinite structure. They also help to explain the discrepancies between rank parameters obtained from chemical analyses and those determined by petrographic measurements. The comparison between the infrared data of the Cretacic-Albian vitrain from Teruel (Spain) and its associated coal reveals the unusual chemical composition of this vitrain. The infrared analysis of this vitrain and the vitrian from Asturias (Jurassic-Malm) shows unusual features in comparison with “normal” coals. The intensity of the aliphatic peaks relative to the aromatic (A factor) in these vitrains is characteristic of immature samples, closer to those of type I1 kerogens than type 111. This result agrees with the perhydrous character of these samples and helps to explain volatile matter and pyrolysis data. However, for the vitrain from Asturias, the intensity of the bands due to aromatic hydrogen and the ratio between aromatic and aliphatic hydrogen are consistent with a stage of evolution that is higher than the diagenesislcatagenesis transition in agreement with other chemical and petrographic data. In the vitrains from Asturias and Teruel an absorption band at 1500 cm-l is assigned to aromatic C=C bonds. In these vitrains, the band centered at 815 cm-l is the most prominent in the 900-700 cm-l region. These spectral features are unusual in coal spectra, but they seem to be characteristic of perhydrous coals.