Chemical-structural changes during treatment of hydrogen-rich vitrinites caused by the presence of terpene-type resin.
Résumé
Assimilation or impregnation by oil/petroleum-like substances in the vitrinite network and saturation of the botanical tissues by terpene-type resin before peatification are reported as being responsible for the perhydrous character of vitrinites [1,2]. Hydrogen-rich vitrinites show peculiar properties and behaviour. The thermal behaviour of these materials is particularly important because pyrolysis is the basic reaction in the main processes of coal conversion. Moreover, pyrolysis experiments also help clarify the effect of both hydrogen-enrichment and the source of this enrichment on the physico-chemical structure of the vitrinite. In a previous paper [3] the effect of the substances assimilated by the coal network (hydrocarbon/oil-like substances) on its thermal evolution was evaluated. In the present work a similar thermal treatment is developed using a vitrinite whose structure is strongly modified by the presence of terpene-type resin. By comparing the results obtained in this work with those previously reported the effect of the source of hydrogen-enrichment on the vitrinite chemical structure during thermal treatment can be evaluated. The amount of oil and gas released at each pyrolysis stage is analysed. The changes in chemical structure during the increase in pyrolysis temperature were investigated mainly by means of FTIR. A compositional and structural analysis of the oils recovered through GC/MS and NMR was also made. The results obtained show that this type of vitrinite undergoes a more intense degradation at lower temperatures than in the case of other hydrogen-rich vitrinites. Differences in the evolution of aromaticity, aliphatic moieties and phenolic structure with increase in temperature between the two different hydrogen-enriched vitrinites are highlighted. The effect of the changes in the chemical structure of the vitrinite during thermal treatment on the thermoestability and oil potential of the pyrolysates was also evaluated.