Petrographie and chemical properties of carboniferous resinite from the Herrin No. 6 coal seam

Resinite is a naturally occurring substance found in coal and derived from original plant resins. It is ubiquitous in North American coals and comprises 1 to 4% by volume of most Illinois coals. It has been commercially exploited in the western USA for use in adhesives, varnishes and thermal-setting inks. The major objectives of this study were: (1) to separate resinite macérais from the Herrin No. 6 coal seam and to carefully verify, by pétrographie and fluorescence microspectrophotometric methods, that the separated material was indeed resinite; (2) to characterize the chemical composition of the separated resinite by Py-GC-MS techniques; and (3) to confirm the earlier results that show that this Carboniferous resinite was a much different chemical substance than the Cretaceous and younger resinites. An additional objective was to compare the separated resinite to the resinite being commercially exploited in the western USA. High purity fractions of resinite concentrates were separated from the Herrin No. 6 coal by a combination of density gradient separation and sink-float techniques. The chemical structure of the resinite concentrate indicated by the Py-GC-MS analysis is that of a straight chain aliphatic polymer much like common polyethylene. This result confirms the earlier work of Nip et al. [Nip, M. de Leeuw, J.W., Crelling, J.C., 1992. Chemical structure of bituminous coal and its constituent macérai fractions as revealed by flash pyrolysis, Energy Fuels 6, 125-136.]. The assumption that the resinites in the Illinois basin were similar in nature to the commercial resinites of the younger coals of the western USA appears invalid in the case of the resinite in the Herrin No. 6 coal. Although the botanical function of the Carboniferous resinite is at present unclear, it is clear that the cutinite and resinite precursors had not yet evolved to the point where they had differentiated into significantly different chemical compounds.